Expand this Topic clickable element to expand a topic
OSA Publishing

Early Posting

Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

20 kW-class high-beam-quality CW laser amplifier chain based on Yb:YAG slab at room temperature

wang dan, Du Yinglei, Yingchen Wu, Liu Xu, Xiangchao An, liqiang cao, Mi Li, Juntao Wang, Jianli Shang, Tangjian Zhou, Lixin Tong, Qingsong Gao, Zhang Kai, Chun Tang, and Rihong Zhu

Doc ID: 334631 Received 11 Jun 2018; Accepted 16 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: A continuous-wave-operation laser amplifier chain consisting of three multi-concentration-doped Yb:YAG slab gain modules at room temperature is presented. The output power of 22.3 kW with the beam quality of 3.3 times diffraction limit is achieved from this chain. To the best of our knowledge, this is, based on Yb:YAG slab at room temperature, the highest power while maintaining excellent beam quality laser output. An extraction efficiency of 36% from the single slab gain module is obtained and can be further enhanced to 46% by optimizing the parameters of gain module. These results have confirmed the Yb:YAG slab has an excellent scaling performance and is suitable to the development of high-average-power laser.

Low-noise 750-MHz spaced Yb:fiber frequency combs

Yuxuan Ma, Bo Xu, Hirotaka Ishii, Fei Meng, Yoshiaki Nakajima, Isao Matsushima, Thomas Schibli, Zhigang Zhang, and Kaoru Minoshima

Doc ID: 334691 Received 08 Jun 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: We demonstrate two low-noise 750-MHz ytterbium (Yb) fiber frequency combs that are independently stabilized to a continuous wave (CW) laser. A bulk electro-optic modulator (EOM) and a single-stack piezo-electric transducer (PZT) are employed as fast actuators for stabilizing the respected cavity length to heterodyne beat notes (fbeat). Both combs exhibit in-loop fractional frequency instabilities of ~10^−18 at 1 s. This is the first demonstration of tightly phase-locked (<1 rad RMS phase) fiber frequency combs with 750 MHz fundamental repetition rate.

Statistics of mode area for transverse Anderson localization in disordered optical fibers

Arash Mafi and Behnam Abaie

Doc ID: 333002 Received 30 May 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: We introduce the mode area probability density function (MA-PDF) as a powerful tool to study transverse Anderson localization (TAL), especially for highly disordered optical fibers. The MA-PDF encompasses all the relevant statistical information on TAL; it relies solely on the physics of the disordered system and is independent of the shape of the external excitation. We explore the scaling of MA-PDF with the transverse dimensions of the system and show that it converges to a terminal form for structures considerably smaller than those used in experiments, hence substantially reducing the computational cost to study TAL.

Ultrafast optical imaging at 2.0 µm through second-harmonic-generation-based time-stretch at 1.0 µm

Sisi Tan, Xiaoming Wei, Bowen Li, Tsz Kwan Lai, Kevin Tsia, and Kenneth Kin-Yip Wong

Doc ID: 334139 Received 01 Jun 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: The performance of ultrafast time-stretch imaging at long wavelengths (beyond 1.5 µm) has suffered from the low detection sensitivity due to the increasing loss of optical dispersive fibers. Here, we report an ultrafast optical imaging system with a line scan rate of ~ 19 MHz at the 2.0 µm wavelength window by combining second harmonic generation (SHG) with the highly sensitive time-stretch detection at 1.0 µm. In this imaging system, the sample is illuminated by the pulsed laser source at 2.0 µm in the spectrally encoding manner. After SHG, the encoded spectral signal at 2.0 µm is converted to 1.0 µm and then mapped to the time domain through a highly dispersive fiber at 1.0 µm, which provides a superior dispersion-to-loss ratio of ~53 ps/nm/dB, ~50 times larger than that of the standard fibers at 2.0 μm (typically ~1.1 ps/nm/dB). These efforts make it possible for time-stretch technology not only being translated to longer wavelengths, where unique optical absorption contrast exists, but also benefitting from the high detection sensitivity at shorter wavelengths.

Continous every-single-shot carrier-envelope phasemeasurement and control at 100 kHz

D Hoff, Federico Furch, Tobias Witting, Klaus Rühle, Daniel Adolph, A SAYLER, Mark Vrakking, Gerhard Paulus, and Claus Schulz

Doc ID: 331268 Received 15 May 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: With the emergence of high-repetition-rate few-cyclelaser pulse amplifiers, aimed at investigating ultrafastdynamics in atomic, molecular and solid state science,the need for ever faster carrier-envelope phase (CEP)detection and control has arisen. Here we demonstratea high speed, continuous, every-single-shot measure-ment and fast feedback scheme based on a stereo above-threshold ionization time-of-flight spectrometer capa-ble of detecting the CEP and pulse duration at a rep-etition rate of up to 400 kHz. This scheme is appliedto a 100 kHz optical parametric chirped pulse amplifi-cation (OPCPA) few-cycle laser system, demonstratingimproved CEP stabilization and allowing for CEP tag-ging.

High-Q Fano resonances via Direct Excitation of Antisymmetric Dark Mode

Elena Bochkova, Song Han, André de Lustrac, Ranjan Singh, Shah Nawaz Burokur, and Anatole Lupu

Doc ID: 331768 Received 15 May 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: The engineering of metal-insulator-metal metasurfaces displaying sharp spectral features based on Fano-type interference between symmetric bright mode and antisymmetric dark mode is reported. The proposed mechanism for direct excitation of antisymmetric mode avoids the necessity of mode hybridization through near field coupling. Modeling and experimental results bring evidence that such metasurfaces operating in the microwave or THz domains provides greater flexibility for Fano resonance engineering and provide strong enhancement of the spectral selectivity factor. It is shown that the occurring Fano resonance interference is related to the broken eigenmodes orthogonality in open systems and is independent of hybridization mechanism.

Hollow complementary omega-ring-shaped metamaterial modulators with dual-band tunability

Bin Yang, Hairun Chen, Yan Gui, Jiaqi Niu, and Jingquan Liu

Doc ID: 335044 Received 19 Jun 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: In this letter, we numerically and experimentally report two kinds of metamaterial modulators based on hollow complementary omega-ring-shaped (HCΩ) structures, which are fabricated on parylene-C thin film with high flexibility and can realize dual-band amplitude tunability. The first type of structure (HCΩ-Ⅰ) consists of identical unit cells along similar direction, which achieves different tunability under different compression directions but suffers from polarization dependence. In order to investigate the effect of unit cell direction on polarization direction, the unit cells in HCΩ-Ⅰ device are rotated by 90°in sequence to form a symmetrical type of structure (HCΩ-Ⅱ), which successfully produces reverse dual band variation of transmission with good polarization independence. These two developed flexible modulators with varied tunable ability will have a promising application in THz detection.

Efficient terahertz and infrared Smith-Purcell radiation from metal-slot metasurfaces

Yanan Song, Jiayuan Du, Ningxiao Jiang, Liu Liu, and Xinhua Hu

Doc ID: 335494 Received 18 Jun 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: We demonstrate that when a charged particle moves atop a metal-slot metasurface consisting of metallic slot resonators, strong electromagnetic radiation can be produced at resonant frequency. By adjusting the period of the metasurface, its resonant (or working) frequency can be tuned from GHz to THz and infrared regions. Since the field is localized in the slots rather than in the metal, the metasurfaces are found to exhibit very low absorption loss ratio (<1%) in low working frequencies (<1 THz). Although it becomes larger in high frequencies (>1 THz), the loss ratio remains relatively low (<11%). Our results could benefit the construction of efficient, compact THz and infrared free-electron light sources.

Strain-assisted femtosecond inscription of phase-shifted gratings

Amiel Ishaaya and Aviran Halstuch

Doc ID: 334811 Received 08 Jun 2018; Accepted 12 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: Two slightly shifted gratings are inscribed, one over the other, while exploiting fiber strain in a single mode fiber. The inscription is done with a NIR femtosecond laser, a phase mask, and a cylindrical focusing lens. The first fiber Bragg grating (FBG) is inscribed under normal fiber tension, while the second overlapping FBG is inscribed under higher fiber tension. The transmission spectrum of the complex structure is similar to that of a phase-shifted grating, yet the fabrication process is much faster and simpler compared to other standard methods. A high-quality phase-shifted grating with two −30 dB transmission dips, a 25 dB transmission peak, and <50 pm transmission bandwidth is achieved. We observe polarization dependent transmission in the phase shifted gratings.

Realization of aperiodic fiber Bragg gratings with ultrashort laser pulses and the line-by-line technique

Thorsten A. Goebel, Gayathri Bharathan, Martin Ams, Maximilian Heck, Ria Krämer, Christian Matzdorf, Daniel Richter, Malte Siems, Alex Fuerbach, and Stefan Nolte

Doc ID: 331819 Received 16 May 2018; Accepted 12 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We demonstrate the fabrication of aperiodic fiber Bragg gratings (AFBGs) for their application as filter elements. Direct inscription was performed by focusing ultrashort laser pulses with an oil-immersion objective into the fiber core and utilizing the line-by-line technique for flexible period adaptation. The AFBGs inscribed allow for the suppression of 10 lines in a single grating and are in excellent agreement with simulations based on the specific design. Applications in astronomy for the suppression of OH emission lines are discussed.

Raman-assisted phase sensitive amplifier using fiber Bragg grating based tunable phase shifter

Yinwen Cao, haoqian song, Youichi Akasaka, Peicheng Liao, Ahmed Almaiman, fatemeh alishahi, Ahmad Fallahpour, Changjing Bao, Amirhossein Mohajerin Ariaei, Tadashi Ikeuchi, Dmitry Starodubov, Joseph Touch, Moshe Tur, and Alan Willner

Doc ID: 331891 Received 24 May 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: A low-loss Raman-assisted phase sensitive amplifier (PSA) with >20dB signal net gain is experimentally demonstrated. The amplitude and phase adjustment for PSA is achieved by using non-uniform Raman gain and a tunable fiber Bragg grating (FBG), respectively. The total component loss of the system is measured as low as ~5dB. By tuning the FBG central wavelength, (1) an up-to-5.6dB signal gain improvement is obtained; and (2) a ~4dB receiver sensitivity enhancement is observed for 20 and 25 Gbaud QPSK signals and a 10 Gbaud 16-QAM signal.

Goos-Hänchen effect for Brillouin light scattering by acoustic phonons

Yuliya Dadoenkova, Nataliya Dadoenkova, Maciej krawczyk, and Igor Lyubchanskii

Doc ID: 332197 Received 24 May 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: The lateral shift of an optical beam undergoing a Brillouin light scattering on acoustic wave in the total internal reflection geometry is studied theoretically. It is shown that the lateral shift depends on polarization (longitudinal or transversal) of the acoustic wave, as well as on the type of the scattering process: direct one, when the scattered wave undergoes a lateral shift at reflection from the interface, and cascading one, when fundamental-frequency light beam is laterally shifted at reflection and then is scattered on the acoustic wave.

Simultaneous Excitatory and Inhibitory Dynamics in an Excitable Laser

Philip Ma, Bhavin Shastri, Thomas Ferreira de Lima, Chaoran Huang, Alexander Tait, Mitchell Nahmias, Tsuan-tung Peng, and Paul Prucnal

Doc ID: 335578 Received 19 Jun 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: Neocortical systems encode information in electrochemical spike timings, not just mean firing rates. Learning and memory in networks of spiking neurons is achieved by the precise timing of action potentials that induces synaptic strengthening (with excitation) or weakening (with inhibition). Inhibition should be incorporated into brain-inspired spike processing in the optical domain to enhance its information processing capability. We demonstrate the first simultaneous excitatory and inhibitory dynamics in an excitable (i.e., a pulsed) laser neuron both numerically and experimentally. We investigate the bias strength effect, inhibitory strength effect, and excitatory and inhibitory input timing effect based on the simulation platform of an integrated graphene excitable laser. We further corroborate these analysis with proof-of-principle experiments utilizing a fiber-based graphene excitable laser where we introduce inhibition by directly modulating the gain of the laser. This technology may potentially open novel spike processing functionality for future neuromorphic photonic systems.

Spectrally-resolved thermal emission of atmospheric gases measured by laser heterodyne spectrometry

Alex Hoffmann, Marko Huebner, Neil Macleod, and Damien Weidmann

Doc ID: 335850 Received 22 Jun 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: The demonstration of thermal infrared quantum cascade laser heterodyne spectrometry to resolve local thermodynamic equilibrium molecular emission lines from Earth’s atmospheric constituents is presented. The instrument is described, as well as the early steps towards radiometric calibration. Room temperature ethylene emission line measurements carried out in the laboratory are used to validate the instrument. High-resolution (0.02 cm-1) emission lines from atmospheric carbon dioxide and water vapor are then recorded in a zenith looking configuration and compared to radiative transfer model and ideal instrument model expectations.

Ultrafast group-velocity control via cascaded quadratic nonlinearities in optical parametric amplification

Binjie Zhou, Jingui Ma, Jing Wang, Peng Yuan, Guoqiang Xie, and Liejia Qian

Doc ID: 335131 Received 13 Jun 2018; Accepted 10 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: Slow and fast light are ubiquitous in optical amplifiers. In this Letter, we show for the first time that optical parametric amplification (OPA) in chirped quasi-phase-matching structures can act as a platform for group-velocity control in the femtosecond regime. Resonant cascaded nonlinear phase underlies the group-velocity control, which manifests an unusual effect that both slow and fast light can be achieved under the normal condition of signal amplification. As numerically demonstrated in the OPA based on lithium niobate crystal, the signal and idler pulse can be significantly delayed in time comparable to the signal duration, and can also keep high fidelity for durations down to 100 fs until the crystal dispersion begins effective. The broad bandwidth, large group delay, and direct compatibility with integrated optics will make the proposed platform attractive to both the fundamental research and applied science.

Bounding the outcome of a two-photon interference measurement using weak coherent states

Andres Aragones, Nurul Islam, Michael Eggleston, Arturo Lezama, Daniel Gauthier, and Jungsang Kim

Doc ID: 335106 Received 13 Jun 2018; Accepted 10 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: Interference of two photons at a beamsplitter is at the core of many quantum photonic technologies, such as quantum key distribution or linear-optics quantum computing. Observing high-visibility interference is challenging because of the difficulty of realizing indistinguishable single-photon sources. Here, we perform a two-photon interference experiment using phase-randomized weak coherent states with different mean photon numbers. We place a tight upper bound on the expected coincidences for the case when the incident wavepackets contain single photons, allowing us to observe the Hong-Ou-Mandel effect. We find that the interference visibility is at least as large as 0.995$^{+0.005}_{-0.013}$.

Lensfree dynamic super-resolved phase imaging based on active micro-scanning

Jialin Zhang, Qian Chen, Jiaji Li, Jiasong Sun, and Chao Zuo

Doc ID: 327117 Received 29 Mar 2018; Accepted 10 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: In this Letter, we present a new active micro-scanning setup and associated super-resolution (SR) phase reconstruction method in lensfree microscopy to achieve SR dynamic phase imaging. By rotating two orthogonal parallel plates to achieve controllable micro-scanning, a set of low-resolution (LR) intensity images with relative sub-pixel displacements can be acquired. These sequential LR intensity images are then processed to obtain the corresponding super-resolved and quantitative phase images simultaneously. The reconstructed result of Benchmark Quantitative Phase Microscopy Target demonstrates the resolution enhancement quantitatively, which achieves a half-pitch lateral resolution of 775 nm over a large field-of-view (FOV) of ~29.84mm², surpassing 2.15 times of the theoretical Nyquist–Shannon sampling resolution limit imposed by the pixel-size of the sensor (1.67μm). Investigations of unstained Hela cells are then presented, suggesting that the method developed can provide promising application in the dynamic study as well as morphological analysis of the subcellular features for unlabelled biological samples.

External cavity quantum cascade laser using intra-cavity out-coupling

Yohei MATSUOKA, Sven Peters, Mykhaylo Semtsiv, and W. Masselink

Doc ID: 331877 Received 16 May 2018; Accepted 09 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: We describe an external-cavity quantum cascade laser with an intra-cavity out-coupling optical system, tunable from 8.4 μm to 10.8 m. The new optical configuration allows higher output power compared to a conventional Littrow-type external cavity approach, while keeping the broad tunability of wavelength. We achieved 1 W output power at the maximum in pulse-mode operation, which is more than twice the optical power using the Littrow design with the same gain chip.Highlight and novelty

Wavelet analysis on time-frequency plane of optical coherence tomography: simultaneous signal quality improvement in structural and velocity images

Saroch Leedumrongwatthanakun, Panote Thavarungkul, Proespichaya Kanatharana, and Chittanon Buranachai

Doc ID: 334762 Received 08 Jun 2018; Accepted 09 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: In this Letter, one-dimensional wavelet analysis is proposed to improve the quality of both morphology image and velocity profile of Optical Coherence Tomography simultaneously by doing the analysis on the short-time Fourier transform domain of a raw interferogram prior to constructing the images. The results indicate the robust signal improvements of both morphology and velocity images under different flow speeds and various types of samples while preserving the structure of the sample and providing the correct velocity profile.

Few-layer Ti3C2Tx (T = O, OH or F) Saturable Absorber for Femtosecond Bulk Laser

Xiaoli Sun, Baitao Zhang, Bingzheng Yan, guoru li, hongkun nie, Kejian Yang, chengqian zhang, and Jingliang He

Doc ID: 336026 Received 25 Jun 2018; Accepted 09 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: Few-layered titanium carbide (Ti3C2Tx), a novel two-dimensional (2D) Van der Waals material in the MXene family, was fabricated with a liquid-phase method and applied as a saturable absorber for a continuous-wave mode-locked femtosecond bulk laser. Pulses as short as 316 fs with a repetition rate of 64.06 MHz and maximum output power of 0.77 W were achieved at the central wavelength of 1053.2 nm, demonstrating the first known application of MXene in an all-solid-state laser. Considering the flexible band gap for different surface functional groups of Ti3C2Tx, these results may promote the development of ultrafast photonics and further applications of 2D optoelectronic layered materials in the infrared and mid-infrared regions.

Hybrid Diagnostic for Optimazing Domain Size and Resolution of 3D Measurements

Lin Ma and Ning Liu

Doc ID: 336486 Received 02 Jul 2018; Accepted 09 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: This letter reports a hybrid three-dimensional (3D) visualization approach for turbulent flows at kHz range. The approach, named scanning volumetric laser induced fluorescence (SVLIF), combines 3D tomography with scanning to significantly enhance spatial resolution of 3D measurements in a given domain (or equivalently, to enlarge the domain size under a given resolution) compared to past tomographic approaches. The SVLIF technique 1) divides a large measurement domain into smaller sub-domains, 2) performs 3D tomographic measurement in each sub-domain by scanning the excitation laser pulses across them consecutively, and 3) combines the measurements in all sub-domains to form a final measurement. This hybrid approach enables the conversion of temporal resolution into spatial resolution or domain size to optimize 3D measurements in a wider design space. In this work, the SVLIF was demonstrated and validated at a scanning rate of 1.86 kHz, in a volume of 38.4 mm × 26.5 mm × 25.2 mm with 7.1 million voxels, representing a ~5× enhancement in the number of voxels or the domain size, compared to past tomographic techniques.

Observation of micro-scale nonparaxial optical bottle beams

Raluca Penciu, Yujie Qiu, Michael Goutsoulas, Xiaopei Sun, Jingjun Xu, Yi Hu, Zhigang Chen, and Nikolaos Efremidis

Doc ID: 332368 Received 24 May 2018; Accepted 09 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: We predict and experimentally observe three-dimensional micro-scale nonparaxial optical bottle beams based on the generation of a caustic surface under revolution. Such bottle beams exhibit high contrast between the surrounding surface and the effectively void interior. Via caustic engineering we can precisely control the functional form of the high intensity surface to achieve micro-scale bottle beams with longitudinal and transverse dimensions of the same order of magnitude. Although, in general, the phase profile at the input plane can be computed numerically, we find closed form expressions for bottle beams with various type of surfaces both in real and in the Fourier space.

Stable emission and fast optical modulation of quantum emitters in boron nitride nanotubes

JongHoon Ahn, Zhujing Xu, Jaehoon Bang, Andres Allcca, Yong Chen, and Tongcang Li

Doc ID: 335440 Received 15 Jun 2018; Accepted 09 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: Atom-like defects in two-dimensional (2D) hexagonal boron nitride (hBN) have recently emerged as a promising platform for quantum information science. Here we investigate single-photon emissions from atomic defects in boron nitride nanotubes (BNNTs). We demonstrate the first optical modulation of the quantum emission from BNNTs with a near-infrared laser. This one-dimensional system displays bright single-photon emission as well as high stability at room temperature and is an excellent candidate for optomechanics. The fast optical modulation of single-photon emission from BNNTs shows multiple electronic levels of the system and has potential applications in optical signal processing.

A fast analysis method for STORM using multiple measurement vector model sparse Bayesian learning

Jingjing WU, Siwei Li, Saiwen Zhang, Danying Lin, Bin Yu, and Junle Qu

Doc ID: 334362 Received 06 Jun 2018; Accepted 09 Jul 2018; Posted 11 Jul 2018  View: PDF

Abstract: Compressed sensing (CS) can be used in fluorescence microscopy to improve the temporal resolution of stochastic optical reconstruction microscopy (STORM). At present, most algorithms used in CS-STORM belong to single measurement vector (SMV) model, which means each super-resolution image is recovered individually from a raw frame and all super-resolution images are recovered one by one. This mode leads to the long computational time of CS-STORM. In this paper, we apply multiple measurement vector (MMV) model CS algorithm into STORM, namely, all raw images are converted into a matrix and recovered by solving the simultaneous sparse recovery problem. We use MMV model sparse Bayesian learning (SBL) algorithm to reconstitute STORM raw images and compare the imaging resolution and run time of with SMV model CS algorithms. The recovered super-resolution images of simulated and experiment image sequence prove that the resolution of MMV-SBL is comparable with SMV model algorithm, while the run time is far less than SMV model and decrease from several hours to several minutes. The high resolution and shorter reconstitution time make MMV-SBL a promising real time image reconstruction method for CS-STORM.

Near field focusing by edge diffraction

Artem Boriskin, valter drazic, ray keating, Mitra damghanian, Oksana Shramkova, and Laurent Blondé

Doc ID: 328392 Received 22 Apr 2018; Accepted 09 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: Spherical microparticles have the ability for non-resonant focusing of light in the near field zone, forming nanojet (NJ) beams. Arbitrary-shaped microstructures, with wavelength-scale dimensions, may offer similar functionality with lower fabrication complexity. The focusing properties are ruled by the edge diffraction phenomenon. The diffraction of light on the edge of a dielectric microstructure forms a tilted focused beam which deviation angle depends on the index ratio between the structure material and host medium. The beam geometry and field intensity enhancement can be tuned by varying the curvature of the edge line. Interference of edge diffracted waves from different segments of the edge line creates a condensed beam in the structure medium, the photonic nanojet.

Selective photoactivation of neural activity combined with laser speckle imaging of cerebral blood flow

Wen Dong, Li Yangyang, Xuan Zhu, Ming Chen, Jinling Lu, and Pengcheng Li

Doc ID: 331345 Received 10 May 2018; Accepted 09 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: Neural activity leads to alterations in cerebral blood flow, i.e., neurovascular regulation, which is implicated in brain physiology and pathology. Here, a method for simultaneous imaging of cerebral blood flow and spatially selective photoactivation of neural activity is proposed. Cerebral blood flow was obtained by laser speckle contrast imaging, and a liquid-crystal spatial light modulator (LC-SLM) was used to generate photo-activation patterns targeting designated locations in the cortex. Animal experiments stimulating defined cortical regions of VGAT-ChR2 and wild-type mice were conducted, and experiments with low-intensity stimulation were performed to investigate the influence of background light produced by the LC-SLM.

Optical field manipulation by dual magnetic resonances of silicon metasurface

Tianyang Zang, Huiwen Luo, Yong Wang, Liang Wang, Yonghua Lu, and Pei Wang

Doc ID: 334853 Received 11 Jun 2018; Accepted 08 Jul 2018; Posted 11 Jul 2018  View: PDF

Abstract: In this letter, we study the influence of magnetic mode dispersion on the performance of metasurface cylindrical vector beam (CVB) generator. Optical field after metasurface CVB generator can be manipulated by polarization-dependent transmittance arisen from dual magnetic resonance of silicon nanopillars. Perfect CVB is only generated when the transmittances are equal for two orthogonal polarization. Two magnetic resonant wavelengths can be spatially separated because of the coherent superposition between the residual incident light and the generating CVB, which is potentially useful for compact multiplex color router.

Emission of water-window soft x-rays under optically thin conditions using low-density foam targets

Hiroyuki Hara, Hiromu Kawasaki, Toshiki Tamura, Tadashi Hatano, Takeo Ejima, Weihua Jiang, Hayato Ohashi, Shinichi Namba, Atsushi Sunahara, Akira Sasaki, Masaharu Nishikino, Gerard O'Sullivan, and Takeshi Higashiguchi

Doc ID: 334897 Received 19 Jun 2018; Accepted 08 Jul 2018; Posted 11 Jul 2018  View: PDF

Abstract: The effect of optical thickness in a bismuth water-window soft x-ray source, is considered by comparing the emission from laser produced plasmas of a 7.5% atomic density foam target and a solid-density target. The number of photons recorded in the 4-nm region was comparable for both targets at a plasma-initiating laser pulse duration of 6 ns. From experiments at different pulse durations of 150 ps and 6 ns, self-absorption (opacity) effects were found to be relatively small for bismuth plasmas as compared to those of tin, based on the same emission mechanism and which are used in 13.5-nm sources for extreme ultraviolet lithography.

Controllable trapping and releasing of nanoparticles by standing wave on optical waveguide

Ran An, Guanghui Wang, Wenxiang Jiao, Wenbin Ji, min Jiang, Yao Chang, Xiaofu Xu, Ningmu Zou, and Xuping Zhang

Doc ID: 331418 Received 04 Jun 2018; Accepted 08 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: Based on the balance between the scattering force and the trapping force of evanescent wave of standing-wave on silicon waveguides, we propose a structure for controllable trapping and release of nanoparticles, which can act as pause operation for nanoparticles flow control. The design is realized by the cascade of an optical switch with structure of ring-assisted Mach-Zehnder interferometer (RAMZI) and a Sagnac loop reflector which connects to one output of switch. Through thermal tuning, with a tiny refractive index change of 4.30×10^(-4) on ring resonator, the output of RAMZI can switch between two ports. As for the release state for nanoparticles flow, the light is guided to the port without reflector. No standing wave and no traps form on waveguide, and the scattering force dominates, which drives the particle moving forward. Otherwise, for trapping state, the light will be reflected by the Sagnac loop and form a stationary standing wave which provides an array of traps for nanoparticles. Most importantly, the structure can switch its state to trap or sequentially release particle, without losing the control of samples, which has not been realized before. With the statistical description of particle motion, the balance between trapping and releasing is distinguished by trapping time and tuned by reflectance. The feasibility of our design is verified using three-dimensional finite-difference time domain and Maxwell stress tensor methods. Our structure possesses high compactness and time-effectiveness, and thereby, it is highly suitable for on-chip optical manipulation of nanoparticle flow control, which will create infinite possibilities in integrated on-chip optofluidics.

Digitally designed holographic optical element for light field displays

Jackin Boaz Jessie, Lode Jorissen, Ryutaro Oi, Jui Wu, Koki Wakunami, Makoto Okui, Yasuyuki Ichihashi, Philippe Bekaert, Yi-Pai Huang, and Kenji Yamamoto

Doc ID: 328137 Received 11 Apr 2018; Accepted 08 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: Microlens arrays fabricated as holographic optical elements are used in projector based light field displays due to its see-through characteristic. The optical axis of each microlens in the array are usually made parallel to each other, which simplifies the fabrication, integral- image rendering and the calibration process. But this demands the beam from the projector to be collimated and made parallel to the optical axis of each elemental lens. This requires additional collimation optics, which puts a serious limitations on the size of the display. In this letter we propose a solution to the above issue by introducing a new method to fabricate holographic microlens array sheets and explain its working in detail. 3D light field reconstructions are demonstrated upto a maximum of 20 cm × 10 cm in size and 6 cm in depth using a conventional projector without any collimation optics.

Supersymmetry-guided method for mode selection and optimization in coupled systems

Wiktor Walasik, Bikashkali Midya, Liang Feng, and Natalia Litchinitser

Doc ID: 334656 Received 07 Jun 2018; Accepted 08 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: Single-mode operation of coupled systems such as optical-fiber bundles, lattices of photonic waveguides, or laser arrays requires an efficient method to suppress unwanted super-modes. Here, we propose a systematic supersymmetry-based approach to selectively eliminate modes of such systems by decreasing their lifetime relative to the lifetime of the mode of interest. The proposed method allows to explore the opto-geometric parameters of the coupled system and to maximize the relative lifetime of a selected mode.We report a ten-fold increase in the relative lifetime of the fundamental modes of large one-dimensional coupled arrays in comparison to simple 'head-to-tail' coupling geometries. The ability to select multiple supported modes in one- and two-dimensional arrays is also demonstrated.

Proposal of tunable Rydberg exciton maser

David Ziemkiewicz and Sylwia Zielińska-Raczyńska

Doc ID: 334737 Received 07 Jun 2018; Accepted 08 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: We propose a continous mode solid state maser based on Cu2O, where ensemble of highly excited Rydberg exciton states serves as a gain medium. We show that the system is highly tunable with external electric field, allowing for a wide range of emission frequencies within THz range. Numerical simulations of the system dynamics are performed to optimize the conditions for efficient masing and estimate the emission power.

Chirality Dependent Electromagnetically Induced Transparency Based on Double Semi-Periodic Helix Metastructure

Bo Yan, Fan Gao, Hongfeng Ma, Kesong Zhong, Bin Lv, naibo chen, Pinggen Cai, Ziran Ye, Yun Li, Chenghua Sui, Tao Xu, Chenghua Ma, and Qiang Lin

Doc ID: 330321 Received 27 Apr 2018; Accepted 08 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: A chiral metastructure composed of spatial separated double semi-periodic helices is proposed and investigated theoretically and experimentally in this work. Chirality dependent electromagnetically induced transparency (EIT) and slow light effect in microwave region are observed from numerical parameter study, while experimental results from the 3D printing sample yields good agreement with the theoretical findings. The studied EIT phenomenon arises as a result of destructive interference by coupled resonances and the proposed chiral metastructure can be applied in polarization communication, pump-probe characterization and quantum computing areas, etc.

Propagation of surface plasmon modes through discontinuities

Fahimeh Armin, Mahdi Kordi, and Mir Mirsalehi

Doc ID: 332895 Received 29 May 2018; Accepted 08 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: Based on the electromagnetic equations, we have re-investigated the propagation of a surface plasmon mode on a metal-dielectric interface with a discontinuity. Our rigorous study of the boundary conditions illustrates a mismatch between the normal components of the wavevectors of the fundamental plasmon modes which results in the excitation of higher order modes. Furthermore, analytical relations based on the plane wave expansion method reveal the existence of radiation modes above the surface and at the vicinity of discontinuity. If these modes are not included, the boundary conditions are not satisfied. This phenomenon, which has not been considered in the previous works, is also demonstrated by numerical simulations.

Vertically integrated waveguide self-coupled resonator based tunable optical filter

Shan Zhai, Xiaoyu Sun, Jijun Feng, Ryoichi Akimoto, and Heping Zeng

Doc ID: 332988 Received 04 Jun 2018; Accepted 08 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: A vertically integrated waveguide self-coupled resonator based tunable optical filter was demonstrated. Unlike conventional U-bend self-coupled waveguide structure, a top-layer S-bend waveguide was cross-coupled with the racetrack resonator on a bottom layer. Different waveguide coupling effect was compared with the same resonance structure, which can realize the same free spectral range as well as a high quality factor. A heater attached on the top of resonator can be utilized for the resonance wavelength tuning while a heater on the top of cross-coupled waveguide has little influence on the device performance, which can help to improve the stability. Spectrum response can be designed separately by varying the coupling coefficient between waveguide and resonator. The presented device can also be applied as a tunable modulator/switch.

TSAG-based Faraday isolator with depolarization compensation using a counterrotation scheme

Alexey Starobor, Ilya Snetkov, and Oleg Palashov

Doc ID: 334526 Received 08 Jun 2018; Accepted 06 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: A Faraday isolator with depolarization compensation using a counterrotation scheme has been realized in experiment for the first time. It is based on TSAG crystals with negative optical anisotropy parameter. An order of magnitude advantage over the traditional Faraday isolator scheme is achieved in this case. An isolation ratio of 35.7 dB at a radiation power of 1440 W has been obtained. According to the numerical estimates, an isolation ratio of 30dB can be provided up to a power of 5.5 kW.

Light field 3D measurement using unfocused plenoptic cameras

Zewei Cai, Xiaoli Liu, Qijian Tang, Xiang Peng, and Bruce Gao

Doc ID: 332075 Received 17 May 2018; Accepted 06 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: This letter reports a novel method to establish the metric relationship of depth value between object space and image space for unfocused plenoptic cameras. A 3D measurement system was introduced to precisely construct benchmarks and matching features to compute the metric depths in the object space and the corresponding depth values in the image space for metric calibration. Furthermore, via light field ray calibration, not only depth, but also transverse coordinates could be precisely measured to realize light field 3D measurement using unfocused plenoptic cameras. Finally, we experimentally performed accuracy analysis of the proposed method with measurement precision of about 0.5mm, which illuminated potential applications of unfocused plenoptic cameras in the field of 3D measurement.

Validation of the Angular Quasi-Phase-Matching theory for the biaxial optical class using PPRKTP

lu dazhi, Alexandra Pena, Patricia Segonds, Jérôme Debray, Simon Joly, Andrius Zukauskas, Fredrik Laurell, Valdas Pasiskevicius, Haohai Yu, Huaijin Zhang, Jiyang Wang, Carlota Canalias, and Benoit Boulanger

Doc ID: 331307 Received 09 May 2018; Accepted 06 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO4 (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.

Phase-Matched Second-Harmonic Generation in a flux grown KTP crystal ridge optical waveguide

veronique boutou, Augustin Vernay, Corinne Félix, Florent Bassignot, Mathieu Chauvet, Dominique Lupinski, and Benoit Boulanger

Doc ID: 337842 Received 04 Jul 2018; Accepted 05 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: Type II second-harmonic generation was performed in a 15.8-mm-long KTiOPO4 micrometric ridge waveguide with an average transversal section of 38 µm2. Theoretical predictions are compared with experiments. Strong agreements are obtained for both phase-matching wavelengths and second-harmonic intensity. This work opens wide perspectives for integrated parametric optics.

Ultrabroadband microjoule 1.8-μm laser pulse from a single-stage broadband pumped OPA

Zuofei Hong, Seyed Ali Rezvani, Qingbin Zhang, Wei Cao, and Peixiang Lu

Doc ID: 332218 Received 21 May 2018; Accepted 05 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: We propose a broadband pumped optical parametric amplification scheme for the generation of a micojoule few-cycle pulse centered at 1.8 µm. Owing to the opposite chirp of the broadband pump and seed pulses, the idler pulse with a FWHM bandwidth of 434 nm is obtained, which can be effectively compressed to a near-TL duration of 13.1 fs by simply compensating the linear chirp. The pJ-level seed is amplified to μJ-level in a single stage with a pump pulse of 100 μJ, corresponding to an overall conversion efficiency of 9%. The presented scheme is potentially applicable in various nonlinear crystals with different kinds of femtosecond laser systems, which provides not only an efficient approach of down-converting near-infrared laser with moderate energy to the mid-infrared region, but also a suitable seeding source in high-energy OPCPA systems.

Arbitrarily spin-orientated and super-resolved focal spot

Weichao Yan, zhongquan nie, Xiaofei liu, Xueru Zhang, Yuxiao Wang, and Yinglin Song

Doc ID: 332347 Received 22 May 2018; Accepted 05 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: In this letter, we propose an accessible approach for achieving a robust focal spot capable of both super resolution and arbitrary spin orientation. Toward this aim, we meticulously devise a structured incident light consisting of three sorts of beams and detailedly elucidate to produce it by the superposition of a radially polarized beam and an azimuthally polarized beam. Via tightly focusing counter-propagating patterned illuminating beams in a 4π optical microscopic configuration, three polarized components perpendicular to each other are created, enabling to yield a super-resolved focal spot possessing spatial spin axis. By wilfully adjusting the amplitude factors of the containing beams, the spin direction can be freely tunable. Such well-defined electric field behavior is largely ascribed to perfect interference caused by all the polarized components. The demonstrated results may greatly expand the practical applications related to the spin photonics.

Energy enhancement of the target surface electron by using a 200 TW sub-picosecond laser

Jingyi Mao, Olga Rosmej, Yong Ma, Minghua Li, Bastian Aurand, Felix Gärtner, Wei-Min Wang, Jurij Urbancic, Andreas Schoenlein, Bernhard Zielbauer, Udo Eisenbarth, Vincent Bagnoud, Florian Wagner, Felix Horst, Marc Syha, Stefan Mattias, Yu Li, Martin Aeschlimann, Li-Ming Chen, and Thomas Kuehl

Doc ID: 332992 Received 01 Jun 2018; Accepted 05 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: One order of magnitude energy enhancement of the target surface electron beams with central energy at 11.5 MeV and total charge of 400±20 pC (E>2.7 MeV) is achieved, by using a 200 TW, 500 fs laser at an incident angle of 72° with a prepulse intensity ratio of 5E-6. The experimental results demonstrate the scalability of the acceleration process to high electron energy with a longer (sub-ps) laser pulse duration and a higher laser energy (120 J). Such a high orientation and mono-energetic electron jet would be a good method to solve the problem of the large beam divergence in the fast ignition scheme and increase the laser energy deposition on the target core.

Magnon-induced high-order sideband generation

zengxing liu, Wang Bao, Hao Xiong, and Ying Wu

Doc ID: 327850 Received 09 Apr 2018; Accepted 05 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: Magnon Kerr nonlinearity plays crucial roles in the study of cavity optomagnonics system and may bring many novel physical phenomena and important applications. In this work, we report the investigation of high-order sideband generation induced by magnon Kerr nonlinearity in a cavity-magnon system. We uncover that the driving field plays a significant rolein controlling the generation and amplification of the higher-order sidebands and the sideband spacing can be adjusted by regulating the beat frequency between the pump laser and the probe laser, which is extremely eventful for the spacing modulation of the sideband spectrum. Based on the recent experimental progress, our results deepen our cognition into optomagnonicsnonlinearity and may find interesting applications in optical frequency metrology and optical communications.

Femtosecond laser damage of germanium from neartomid-IR wavelengths

Drake Austin, Kyle Kafka, yu lai, zhou wang, Cosmin Blaga, and Enam Chowdhury

Doc ID: 331769 Received 06 Jun 2018; Accepted 05 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: Femtosecond laser-induced damage and ablation (fs-LIDA)is a rich field in extreme nonperturbative non-linear optics with wide ranging applications including laser micro- and nanomachining, waveguide writing, and eye surgery. Our understanding of fs-LIDA, however, is mostly limited to visible and near-infrared wavelengths. In this work, we systematically studysingle-shot, fs-laser ablation (fs-LIA) of single crystal germanium from near- to mid-infrared wavelengths, and compare the fs-LIA wavelength scaling with two widely used models. We show that these models are inadequate, particularly at mid-infrared wavelengths. Instead, a hybrid model is proposed involving a constant free-carrier density threshold and multi-bandeffects, which yields good agreement with experimental observations. Aspects of this model may be applied to understanding other strong field non-perturbative phenomena in solids.

Mid-infrared molecular Faraday imaging filter based camera for hot gas visualization

Kuijun Wu, Zhongjie Luo, Yutao Feng, Guangbao Yu, Linmei Liu, Yuanhui Xiong, and Faquan Li

Doc ID: 328957 Received 05 Jun 2018; Accepted 03 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: This work presents recent results of what is to our knowledge the first experimental demonstration of a mid-infrared molecular Faraday imaging filter (MOFIF) based camera for hot gas visualization. Gas-phase nitric oxide (NO) is used as the working material of the MOFIF due to the important role it plays in the chemical and physical process of combustion reaction. The MOFIF transmission with comb-like transmittance spectrum is elaborately designed and matches well with the radiation spectrum of NO gas. Pure NO infrared images have been well captured in combustion environment and shown as a video which demonstrates the imaging capability and gas selectivity of MOFIF.

Recovery of wave-mixing conversion efficiency in weakly scattering nonlinear crystals

Xianfeng Chen, Zhuo Wang, Yanqi Qiao, Shuo Yan, Haoying Wu, and Yuanlin Zheng

Doc ID: 328120 Received 10 Apr 2018; Accepted 03 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: Nonlinear optical wave mixing is a widely used method to produce light with new frequencies, which has a significant impact on laser technology and optical imaging. The most important figure of merit in wave-mixing processes, i.e. high conversion efficiency, is always required in laser applications. We demonstrate a method to recover high conversion efficiency of second harmonic generation in a BaMgF4 single crystal with weakly scattering defects via feedback-based wavefront shaping under birefringent phase matching condition. By optimizing the fundamental wavefront, a typical second harmonic output with an enhancement factor of 1.14 and a corresponding recovery efficiency of 86.3% is displayed. This investigation may modify the wide understanding of scattering in crystals and provide an avenue to recover the nonlinear optical conversion efficiency in crystals which exist various defects without special fabrications.

Design of PANDA-Type Elliptical-Core Multi-Mode Fiber Supporting 24 Fully Lifted Eigenmodes

Shi Chen and Jian Wang

Doc ID: 328385 Received 16 Apr 2018; Accepted 02 Jul 2018; Posted 09 Jul 2018  View: PDF

Abstract: We present a novel PANDA-type elliptical-core multi-mode fiber (e-MMF) featured by the combination of an elliptical core and two symmetrical circular stress-applying parts (SAPs). The characterization results indicate that such a special fiber design is able to support 24 fully separated eigenmodes with minimum effective index difference (min(Δneff)) between adjacent modes larger than 1.35×10-4 over the whole C band. Specifically, all fiber geometric dimension and doping concentration are deviation tolerant and reasonable within the existing fiber manufacture facility restriction, thus would be promising for practical fabrication. The fiber bending effects are also investigated based on conformal mapping. Moreover, ultra-broadband performance is analyzed over the whole C+L band ranging from 1530 to 1625 nm. The designed fiber is targeted at applications in direct fiber vector eigenmode-division multiplexing combined with the mature wavelength-division multiplexing (WDM) technique while eliminating the complex multiple-input multiple-output digital signal processing (MIMO-DSP).

Contour integrals for numerical computation of discrete eigenvalues in Zakharov-Shabat problem

Anastasiia Vasylchenkova, Jaroslaw Prilepsky, and Sergei Turitsyn

Doc ID: 330370 Received 26 Apr 2018; Accepted 02 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: We propose a novel algorithm for the numerical computation of discrete eigenvalues in the Zakharov-Shabat problem. Our approach is based on contour integrals of the nonlinear Fourier spectrum function in the complex plane of spectral parameter. The reliability and performance of the new approach are examined in application to single eigenvalue, multi-eigenvalues and the degenerate breather's multiple eigenvalue. We also study the impact of additive white Gaussian noise on the stability of numerical eigenvalues computation.

Multi-watt sub-30-ns passively Q-switched Yb:LuPO4/WS2 miniature laser operating under high output couplings

Xiaodan Dou, Ma Yanjun, Min Zhu, Honghao Xu, Bing Teng, Degao Zhong, and Junhai Liu

Doc ID: 331392 Received 10 May 2018; Accepted 02 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: We report on a miniature Yb:LuPO4 crystal laser at 1.01 μm that is passively Q-switched with a sapphire-based few-layer WS2 saturable absorber, and that can be operated under very high output couplings (≥ 80%). With 12.6 W of pump power absorbed, an average output power of 4.35 W is generated at repetition rate of 1.33 MHz with a slope efficiency of 47%. The maximum pulse energy and highest peak power achieved are 3.41 µJ and 110 W, respectively; while the shortest pulse duration obtained is 28.6 ns. These results represent the highest output power and shortest pulse duration ever achieved in the 1-μm region from solid-state lasers passively Q-switched by using 2D saturable absorbers.

Carrier Regeneration from a Blockwise Phase Switching Signal for a Frequency Comb Based WDM System

Qiulin Zhang and Chester C.T. Shu

Doc ID: 334061 Received 05 Jun 2018; Accepted 02 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: We demonstrate that an optical carrier can be extracted from a signal based on blockwise phase switching (BPS) technique for locking the frequency combs at the transmitter and the receiver in a wavelength division multiplexing (WDM) system. Two types of carrier regeneration technique, optical injection locking and stimulated Brillouin scattering, are evaluated in the aspects of injection ratio and pump power, respectively, under different carrier to signal power ratios. 7 × 16 Gbaud QPSK data channels with 25 GHz spacing are successfully transmitted over 80-km fiber by direct detection of BPS assisted central channel and coherent detection of the remaining channels.

Plasmonic nano-imprinting by photo-doping

Yi-Ke Sun, Lei Wang, Masaru Kamano, and Saulius Juodkazis

Doc ID: 335200 Received 14 Jun 2018; Accepted 02 Jul 2018; Posted 10 Jul 2018  View: PDF

Abstract: A method to directly explore the effect of electron density on the surface plasmon wave and the corresponding laser induced structures by controllable doping of silver nitrate (AgNO3) into a water-soluble polymer Polyvinyl Alcohol (PVA) is demonstrated. It is shown that periodic nanostructures on PVA appeared only when the electron density was more than 6 × 10^20 cm^−3 and become uniform when doping density corresponded to 1.2 × 10^21 cm^−3. Photo-excitation of electrons in the Ag-doped PVA defined by laser fluence determined the conditions of surface plasmon wave and formation of nanostructures on the surface. The Drude-Lorentz model was used to describe the formation conditions of surface wave and to estimate the period of the structures. The demonstrated photo-electron doping brings required means to control the formation of laser induced patterns with an optical sub-wavelength resolution.

Tandem dual-functioning multiple-quantum-well diodes for self-powered light source

Xumin Gao, zheng shi, Bingcheng Zhu, Fan Wu, Jialei Yuan, Chuan Qin, Yuan Jiang, Wei Cai, and yongjin wang

Doc ID: 324765 Received 26 Feb 2018; Accepted 01 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: Nitride-based semiconductor materials inherently have the intriguing functionalities of emission and photodetection. In particular, InGaN/GaN multiple-quantum-well (MQW) diodes exhibit dual light-harvesting and light-emitting mode of operation. Here, a multifunctional system is proposed to integrate MQW-diodes within a single chip with enhanced functionalities toward diverse applications of Internet of Things (IoT). When we shine light on the MQW-diodes, the absorbed photons can produce electron-hole pairs to charge up an external capacitor. The energy of the ambient light is converted into electrical energy, which in turn powers the same MQW-diode for lighting. The electrical energy within the capacitor is finally converted into the energy of the emitted light. Therefore, InGaN/GaN MQW-diodes can be made to harvest energy from ambient light sources for IoT applications from self-powered light source to intelligent terminal charging system.

Integrated tunable mode filter for mode-division multiplexing system

Sun Chunlei, wenhao wu, Yu Yu, Xinliang Zhang, and Graham Reed

Doc ID: 332719 Received 27 May 2018; Accepted 01 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: Mode-division multiplexing (MDM) using multiple spatial modes as independent signals has been a promising technique to increase the communication capacity in conjunction with wavelength-division multiplexing (WDM). In MDM systems, mode filters are key components to filter out the undesired signals on specific mode. Analogous to a wavelength tunable filter used in a WDM system, here we propose and experimentally demonstrate a fundamental- or high-order-mode pass tunable filter for flexible MDM optical network based on silicon platform. It consists of two switchable mode exchangers and a fundamental-mode pass filter. By controlling the working state of the mode exchangers, dynamic filtering and a tunable output can be achieved. This tunable mode filter exhibits a high extinction ratio of 18 dB and low insertion loss of 3 dB over C-band. For further demonstration, the proposed device is tested using a modulated signal at 20 Gb/s. Eye diagrams and the bit error rates indicate a good filtering performance.

Tunable SNAP Microresonators via Internal Ohmic Heating

Dashiell Vitullo, Sajid Zaki, Gabriella Gardosi, Brian Mangan, Robert Windeler, Michael Brodsky, and Misha Sumetsky

Doc ID: 331025 Received 16 May 2018; Accepted 01 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: We demonstrate a thermally tunable Surface Nanoscale Axial Photonics (SNAP) platform. Stable tuning is achieved by heating a SNAP structure fabricated on the surface of a silica capillary with a metal wire positioned inside. Heating a SNAP microresonator with a uniform wire introduces uniform variation of its effective radius which results in constant shift of its resonance wavelengths. Heating with a nonuniform wire allows local nanoscale variation of the capillary effective radius, which enables differential tuning of the spectrum of SNAP structures as well as creation of temporary SNAP microresonators that exist only when current is applied. As an example, we fabricate two bottle microresonators coupled to each other and demonstrate differential tuning of their resonance wavelengths into and out of degeneracy with precision better than 0.2 pm. The developed approach is beneficial for ultraprecise fabrication of tunable ultralow loss parity-time symmetric, optomechanical, and cavity QED devices.

Spatio-spectral dynamics of the pulsating dissipative solitons in a normal-dispersion fiber laser

Xuewen Shu, Du Yueqing, and Xu Zuowei

Doc ID: 332636 Received 25 May 2018; Accepted 01 Jul 2018; Posted 02 Jul 2018  View: PDF

Abstract: For the first time, we observed the pulsating dissipative solitons in a mode-locked fiber laser at normal-dispersion using the dispersive-Fourier transformation technology. The artificial saturable absorber as well as the birefringent filter formed by the nonlinear-polarization-rotation make the polarization controller an effective component to adjust the laser state from stationary to pulsating. The pulsating dissipative solitons are accompanied with the spectrum breathing and oscillating structures due to the nonlinear pulse propagation. Our results can enhance the understanding of the pulsating solitons in the dissipative systems.

An integrated visible light phased array system for autostereoscopic image projection

Manan Raval, Ami Yaacobi, and Michael Watts

Doc ID: 331740 Received 16 May 2018; Accepted 01 Jul 2018; Posted 02 Jul 2018  View: PDF

Abstract: We demonstrate a chip-scale autostereoscopic imageprojection system that utilizes a system of multiple integratedvisible light optical phased arrays to reconstructvirtual light fields. Each phased array in this systemserves as a micro-projector that illuminates the desiredvirtual object from a different angle. This recreatesthe virtual object in space with continuous parallaxobservable by the human visual system. In thiswork, a static virtual image with horizontal parallaxand a viewing angle of 5° was generated with an arrayof 16 integrated silicon nitride phased arrays witha 635 nm operating wavelength. Each phased array iscomprised of 3232 optical antennas with passively encodedrelative phases. The presented device demonstratesthe promise of integrated visible light phasedarray platforms for implementing projection-based autostereoscopicdisplays in compact chip-scale platformssuitable for mobile devices.

Generation of high-quality tunable Airy beams with adaptive deformable mirror

Jianqiang Ma, yan li, Qizhi Yu, ZONGFENG YANG, Yanlei Hu, and Jiaru Chu

Doc ID: 332954 Received 29 May 2018; Accepted 30 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: Self-accelerating Airy beams have emerged to hold great promise in wide applications due to its non-diffraction and self-healing characteristics. Generation of Airy beams with high quality and high efficiency still remains challenging for conventional diffractive or refractive optical elements. In this letter, tunable Airy beams with high quality are realized using a reflective adaptive deformable mirror (DM). Not only the controllable cubic phase, but also the compensatory phase for aberrations of the optical system, is generated simultaneously to ensure high quality of the resultant Airy beam. Continuous cubic phases with different amplitudes and rotation angles can be readily generated, demonstrating exceptional tunability of the generated Airy beams using DM device. The intensity profiles and propagation trajectories of the experimentally generated Airy beams are in good agreement with the theoretical results. Benefited from the intrinsic superiority of DM with high reflectivity and high damage threshold, our proposed method for dynamic generation of Airy beams opens up an avenue to plenty of applications such as ultrahigh power laser shaping, laser fabrication and optical manipulation.

Nonlinear imaging through a golden spiral multicore fiber

Siddharth Sivankutty, Viktor Tsvirkun, Olivier Vanvincq, Geraud Bouwmans, Esben Andresen, and Herve Rigneault

Doc ID: 333058 Received 01 Jun 2018; Accepted 30 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: We report two-photon lensless imaging through a novel golden spiral multicore fiber. This unique layout optimizes the sidelobe levels, field of view, cross-talk, group delay and mode density to achieve a sidelobe contrast of atleast 10.9 dB. We demonstrate experimentally the ability to generate and scan a focal point with a femtosecond pulse and perform two-photon imaging.

Observation of Short Wavelength Infrared (SWIR) Cherenkov emission

Xu Cao, Shudong Jiang, Mengyu Jia, Jason Gunn, Tianshun MIAO, Scott Davis, Petr Brůža, and Brian Pogue

Doc ID: 334803 Received 11 Jun 2018; Accepted 30 Jun 2018; Posted 12 Jul 2018  View: PDF

Abstract: Cherenkov emission induced by external beam radiation from a clinical linear accelerator (LINAC) has been shown in preclinical molecular imaging and clinical imaging. The broad spectrum Cherenkov emission should have short wavelength infrared (SWIR, 1000–1700 nm) component, as predicted theoretically. This report is the first experimental observation of this SWIR Cherenkov emission, induced by external beam radiation. The measured spectrum of SWIR Cherenkov emission matches the theoretical prediction very well, with a fluence rate near 1/3 of the visible and near infrared red emissions (Vis-NIR, 400-900 nm). Imaging in water based phantoms and biological tissues indicate that there is sufficient fluence rate for radiotherapy dosimetry applications. The spatial resolution is improved approximately 2.6 times with SWIR Cherenkov emission detection versus Vis-NIR Cherenkov emission, which provides some improvement in the potential for SWIR Cherenkov emission dosimetry and molecular sensing during clinical radiotherapy.

Hybrid Monte Carlo Simulation with Ray Tracing for Fluorescence Measurements in Turbid Media

Seung Yup Lee and Mary-Ann Mycek

Doc ID: 331491 Received 14 May 2018; Accepted 28 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: We present a hybrid Monte Carlo simulation method with geometrical ray-tracing (hMC-GRT) to model fluorescence excitation and detection in turbid media by optical imaging or spectroscopy systems employing a variety of optical components. hMC-GRT computational verification was achieved via reflectance and fluorescence simulations on epithelial tissue models in comparison with a standard Monte Carlo code. The mean difference between the two simulations was less than 5%. hMC-GRT experimental verification employed depth-sensitive steady-state fluorescence measurements using an aspherical lens on two-layered tissue phantoms. hMC-GRT predictions agreed well with experimental results, achieving less than 3.5% error for measurements at the phantom surface. Verification results demonstrate that the hMC-GRT simulation has the potential to become a useful computational toolbox for designing tissue fluorescence imaging and spectroscopy systems. In addition, the hMC-GRT approach enables a wide variety of applications for computational modeling of fluorescence in turbid media.

Highly-sensitive Quasi-distributed Fiber-optic Acoustic Sensing System Based on Interrogating Weak Reflector Array

Mengshi Wu, Xinyu Fan, Qingwen Liu, and Zuyuan He

Doc ID: 330135 Received 24 Apr 2018; Accepted 28 Jun 2018; Posted 28 Jun 2018  View: PDF

Abstract: In this letter, we demonstrate a highly-sensitive quasidistributed fiber-optic acoustic sensing system. This system interrogates weak reflector array by using phasesensitive optical time domain reflectometry (Φ-OTDR) with coherent detection. A phase noise compensated configuration is proposed to reduce the influence of 1/f noise, which is the main limitation when coherent detectionis used in this high-sensitivity system. In the experiment, a high performance system with a sensitivity of 3.84 pε/√Hz @ 10 - 2500 Hz, a sensing range of 20 km and a spatial resolution of 10 m is demonstrated.

Experimental demonstration on an ultra-broadband subwavelength resolution probe from microwave to terahertz regime

Tie-Jun Huang, Heng-He Tang, Li-Zheng Yin, Jiang-Yu Liu, Yunhua Tan, and Pu-Kun Liu

Doc ID: 327747 Received 11 Apr 2018; Accepted 28 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: An ultra-broadband subwavelength resolution probe that consists of a Teflon rod and six metallic strips is developed for the near-field imaging system. The slit between two metallic strips maintains quasi-TEM mode, avoiding the problem of low coupling efficiency caused by cut-off effect. The numerical calculations visualize the process of energy compression into a 0.047λ-diameter spot with great field enhancement at the taper apex, and the probe holds subwavelength focusing behavior from 10 GHz to 0.25 THz. Although limited by the fabrication, the resolution of 0.16λ and 0.25λ are still experimentally demonstrated at 14 GHz and 0.1 THz. The properties of easy fabrication and no cut-off frequency would lower threshold of high resolution near-field imaging system.

Suppression of spontaneous modulation instability and the phase noise with coherent seed in the interferometric fiber sensing systems

Xiaoyang Hu, wei chen, Yang Lu, Mo Chen, and Zhou Meng

Doc ID: 331165 Received 11 May 2018; Accepted 28 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: A method is proposed to suppress spontaneous modulation instability (MI) and the phase noise with coherent seed in the interferometric fiber sensing systems. By generating coherentseedswith phase modulation,induced modulation instability is excited in optical fiber. The preferential gain of the coherent seeds compared to the ASE noise suppresses spontaneous MI. As a result, the induced MI dominates in optical fiber. The coherence of the output light is enhanced and the phase noise is suppressed significantly. The maximum input power and the sensing range can be increased significantly.

Dual narrow-band absorber based on metal-insulator-metal configuration for refractive index sensing

Kai Zhang, Chen Chen, Guan Wang, and Ziyang Zhang

Doc ID: 332124 Received 18 May 2018; Accepted 28 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: Plasmonic gap mode in metal-insulator-metal (MIM) structure has been proved promising for refractive index sensing due to its near unity absorption. However, the sensing performance of gap mode has been limited by the broad resonance band, which is related to the high plasmonic loss. In this work, we theoretically design a square patch based MIM structure for simultaneous excitation of both surface plasmon polariton and Rayleigh anomaly with large absorptions, and demonstrate their excellent sensing performances. For Rayleigh anomaly, the sensitivity and full width half maximum (FWHM) are 1470nm/RIU and 0. nm, respectively. The corresponding figure of merit (FOM) is calculated to be 6400 in wavelength shift form and 58800 in intensity variation form. It is also observed that the two wood’s anomalies have reverse incident angle dependent properties, which can be explained by the opposite propagating direction of surface waves.

Micro lensing induced lineshapes in a single mode cold-atom hollow-core fiber interface

Mohammad Noaman, Maria Langbecker, and Patrick Windpassinger

Doc ID: 332859 Received 29 May 2018; Accepted 28 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We report on the observation of strong transmission line shape alterations in a cold-atom hollow-core fiber interface. We show that this can lead to a significant overestimation of the assigned resonant optical depth for high atom densities. By modeling light beam propagation in an inhomogeneous dispersive medium, we attribute the observations to micro lensing in the atomic ensemble in combination with the mode selection of the atom-fiber interface. The approach is confirmed by studies of Rydberg EIT line shapes.

Compact and electro-optic tunable interleaver in lithium niobate thin film

Kaixin Chen, Peng Xue Li, and Lingfang Wang

Doc ID: 332249 Received 21 May 2018; Accepted 27 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We propose and experimentally demonstrate a compact and electro-optic tunable interleaver in the X-cut lithium niobate thin film using an asymmetrical Mach-Zehnder interferometer configuration. Our typical fabricated device has an electro-optic interactive length of ~1.35 mm and a total length of ~4.0 mm. Over a wide wavelength range from 1528 nm to 1605 nm, the device exhibits polarization-insensitive center wavelengths and channel spacing of ~49.7 GHz, but slight different extinction ratio of 10-20 dB and 12- dB and electrical wavelength-tuning sensitivity of ~18 pm/V and ~16 pm/V for the transverse electric (TE) and the transverse magnetic (TM) polarized input light, respectively. The proposed interleaver also has the potential to be used as a tunable filter or a wavelength selective switch.

Electrically-driven generation of arbitrary vector vortex beams on the hybrid-order Poincar\'{e} sphere

Ruisi Wang, Shanshan He, Shizhen Chen, Jin Zhang, Weixing Shu, Hailu Luo, and Shuangchun Wen

Doc ID: 334305 Received 04 Jun 2018; Accepted 27 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: We propose a simple, efficient, and fast tunable method to generate arbitrary vector vortex beams on the hybrid-order Poincar\'{e} sphere in an electrically-driven way. The scheme incorporates the tunability and switching capabilities of liquid crystals into dielectric metasurfaces to form an efficient vector vortex beam generator. By applying certain voltages on the liquid crystal phase retarder, the generator converts a linearly polarized Gaussian beam into any desirable vector vortex beams. We demonstrate that the evolution route of the corresponding vector vortex states is just a closed circuit on the hybrid-order Poincar\'{e} sphere when the phase retardation varies from $0$ to $2\pi$. Several special cases are selected to demonstrate our scheme, and the experimental results coincide well with the theoretical predictions.

An on-chip silicon photonic integrated frequency-tunable bandpass microwave photonic filter

Jianping Yao and Weifeng Zhang

Doc ID: 332244 Received 21 May 2018; Accepted 27 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: An on-chip frequency-tunable bandpass microwave photonic filter (MPF) implemented on a silicon photonic platform is reported. The on-chip MPF consists of a high-speed phase modulator (PM), a thermally-tunable high-Q micro-disk resonator (MDR), and a high-speed photodetector (PD). The filtering function of the MPF is realized based on phase modulation and phase-modulation to intensity-modulation (PM-IM) conversion, to translate the spectral response of the MDR in the optical domain to the spectral response of the MPF in the microwave domain. The tunability of the MPF is realized by thermally tuning the MDR. The proposed on-chip bandpass MPF is fabricated and characterized. A passband MPF with a bandwidth of 1.93 GHz with a tunable range from 3 to 10 GHz is demonstrated. The power consumption, the insertion loss and the bandwidth over the entire tunable range are studied. This successful implementation of an MPF marks a significant step forward in full integration of microwave photonic systems on a single chip.

Focusing properties of circle Pearcey beams

Xingyu Chen, Dongmei Deng, Jingli Zhuang, Xi Peng, Dongdong Li, Liping Zhang, Fang Zhao, Xiangbo Yang, Hongzhan Liu, and Guanghui Wang

Doc ID: 332258 Received 22 May 2018; Accepted 27 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: We introduce a new class of (2+1) dimensional circle Pearcey beams (CPBs) with the abruptly autofocusing (AAF) characteristics. Compared with circle Airy beams (CABs), CPBs can increase the peak intensity contrast, shorten the focus distance, and especially eliminate the oscillation after the focal point.Furthermore, we discuss the influence of the optical vortexes (including on-axis, off-axis and vortex pairs) on the light intensity distribution of the CPBs during propagating.

A simple technique for compression of nJ pulses from few-cycle laser oscillator to 1.7-cycles duration via nonlinear spectral broadening in diamond

Martin Kozák, Martin Zukerstein, František Trojánek, and Petr Maly

Doc ID: 332972 Received 30 May 2018; Accepted 27 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We report on a simple approach for compression of few-cycle laser pulses generated in an ultrafast laser oscillator to a duration corresponding to 1.7 cycles of near-infrared light by nonlinear spectral broadening in diamond and subsequent dispersion compensation using chirped mirrors. After the spectral broadening, the pulse spectrum spans over almost an octave (580-1000 nm at the –10 dB level). Pulses are compressed by broadband chirped mirrors and a wedge pair to a duration of 4.5 fs measured by spectral shearing interferometry SPIDER. By comparing the spectral broadening to numerical solution of 1D nonlinear Schrödinger equation we conclude that the main source of spectral broadening is self-phase modulation whereas stimulated Raman scattering does not play a significant role.

Dual-comb interferometry via repetition-rate switching of a single frequency comb

David Carlson, Dan Hickstein, Daniel Cole, Scott Diddams, and Scott Papp

Doc ID: 335008 Received 14 Jun 2018; Accepted 27 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We experimentally demonstrate a versatile technique for performing dual-comb interferometry using a single frequency comb. By rapid switching of the repetition rate, the output pulse train can be delayed and heterodyned with itself to produce interferograms. The full speed and resolution of standard dual-comb interferometry is preserved while simultaneously offering a significant experimental simplification and cost savings. We show that this approach is particularly suited for absolute distance metrology due to an extension of the non-ambiguity range as a result of the continuous repetition-rate switching.

Complex-amplitude single-pixel imaging

Yoshio Hayasaki and Kazuki Ota

Doc ID: 330640 Received 30 Apr 2018; Accepted 27 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: A single-pixel camera can be represented using complex-amplitude. The complex-amplitude representation of input and output signals enables us to perform complex-amplitude imaging of an object, particularly profilometry, with reflectance measurements or quantitative phase imaging with transmittance measurements. The complex-amplitude representation of optical coding masks and the coherent addition that is performed by interference can directly represent Hadamard patterns having positive and negative values. Furthermore, the residual area of the mask can be used for a reference beam with phase shifting. Such a complex-amplitude imaging system with a single-beam line structure is highly stabile against external disturbances.

Self-healing of space-time light sheets

Ayman Abouraddy and Hasan Kondakci

Doc ID: 330503 Received 07 May 2018; Accepted 27 Jun 2018; Posted 12 Jul 2018  View: PDF

Abstract: Space-time wave packets are diffraction-free, dispersion-free pulsed beams whose propagation-invariance stems from correlations introduced into their spatio-temporal spectrum. We demonstrate here experimentally and computationally that space-time light sheets exhibit self-healing properties upon traversing obstacles in the form of opaque obstructions. The unscattered fraction of the wave packet retains the spatio-temporal correlations and thus propagation-invariance is maintained. The scattered component does not satisfy the requisite correlation and thus undergoes diffractive spreading. These results indicate the robustness of ST wave packets and their potential utility for deep illumination and imaging in scattering media such as biological tissues.

Enhancing early-time diffusion through beam collimation in pulse propagation in sparse discrete random media

Elizabeth Bleszynski, Marek Bleszynski, and Thomas Jaroszewicz

Doc ID: 331789 Received 17 May 2018; Accepted 26 Jun 2018; Posted 06 Jul 2018  View: PDF

Abstract: Solutions of the time-dependent radiative transport equation (RTE) are used to describe propagation of a pulsed collimated beam through a random medium consisting of discrete scatterers of sizes large compared to the wavelength, a situation particularly relevant to free-space optical communication throughatmospheric obscurants. The RTE is solved in the spherical-harmonics basis, with no approximations other than a truncation N in the angular momenta; the results confirm convergence of the solution for a fixed beam width and growing N. The obtained time-resolved radiance includes both the usual “late-time diffusion” (LTD), responsible for the well known reduction of “coherence bandwidth” and thus a serious limitation in the transfer rate, and the more recently identified “early-time diffusion” (ETD) component, attenuated at a rate significantly lower than for the coherent (ballistic) signal and character-ized by a very short rise time, allowing a high rate data transfer. The ratio of the ETD to the LTD signal for the considered collimated beams is much (orders of magnitude) higher than in the previously examined problem of an omnidirectional source, increasing its potential usefulness in communication and related imaging applications.

Non-destructive characterization of rare-earth-doped optical fiber preforms

Marilena Vivona, Jae Sun Kim, and Michalis Zervas

Doc ID: 334155 Received 05 Jun 2018; Accepted 26 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: We present a non-destructive optical technique for rare-earth-doped optical fiber preform inspection, which combines luminescence spectroscopy measurements, analyzed through an optical tomography technique, and ray-deflection measurements for calculating the refractive index profile of the sample. We demonstrate the technique on an optical fiber preform sample with an Yb3+-doped aluminosilicate core. The spatial distribution of the photoluminescence signals originating from Yb3+-single ions and from Yb3+-Yb3+ cluster sites were obtained inside the core. By modifying the characterization system, we were able to concurrently evaluate the refractive index profile of the core, and thus establishing with good accuracy the dopant distribution within the core region. This technique will be useful for quality evaluation and optimization of optical fiber preforms.

Synthesis of I0-Bessel-correlated beam via coherentmodes

Xi Chen, Jia Li, Mohammad Hashemi, and Olga Korotkova

Doc ID: 332245 Received 24 May 2018; Accepted 26 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: We present the first experimental realization of a random,wide-sense stationary optical beam as a linear superpositionof its coherent (deterministic) modes. Theindividual coherent modes are generated by passing alaser beam through a phase-only spatial light modulator.A random, stationary beam is obtained by using atemporally randomized sequence of its coherent modeseach contributing, on average, with a weight proportionalto the corresponding mode eigenvalue. As anexample, the new method is applied to a I0-Bessel correlatedbeam which was originally introduced in theoryvia the coherent mode decomposition but could nothave been experimentally generated so far by any othermethod.

Chiral dynamics of exceptional points in weakly absorbing biaxial crystal

Nirmal Viswanathan and Samlan C.T.

Doc ID: 332937 Received 29 May 2018; Accepted 26 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: In this letter we report the chiral dynamics of optical exceptional points (EPs), the singular-axes in weakly absorbing biaxial crystal, arising due to a fine balance between the birefringence and dichroism. Taking advantage of the coincidence of the singular-axes and C-point singularity, the EPs are characterized using conoscopic Stokes polarimetry. We observe that the two optic-axes of the biaxial crystal splits into two pairs of singular-axes upon introducing weak dichroism. Which, upon application of transverse electric field follows helical trajectory to coalesce and disappear. Our results show a fine control on the chiral behavior of EPs due to electrogyration effect, which controls the retardance gradient and the fast-axis orientation in the crystal.

Sum-frequency generation with femtosecond conical-refraction pulses

Jingui Ma, Peng Yuan, Jing Wang, Guoqiang Xie, Heyuan Zhu, and Liejia Qian

Doc ID: 332217 Received 21 May 2018; Accepted 26 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: In this Letter, we study short-wavelength conical refraction (CR) via sum-frequency generation (SFG) in the femtosecond regime, a previously unaddressed topic. Based on biaxial crystal of KGd(WO4)2 whose dispersion of optical-axis orientation is negligible in near-IR, conventional femtosecond lasers at 800 nm and 1054 nm are transformed into CR beams, respectively. Femtosecond CR beams at 454 nm are generated via SFG with the near-IR CR beams. While the generated sum-frequency ring is typically incomplete, a full-ring distribution can be achieved by adopting Type-II SFG with a large phase-mismatch. We find that the femtosecond sum-frequency ring under various phase-matching conditions evolves as typical CR beams.

Multiview fringe matching profilometry in a projector-camera system

Xiao Guo, Hong Zhao, Pingping Jia, and li kejia

Doc ID: 332935 Received 29 May 2018; Accepted 25 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: This letter proposes a novel approach, called multiview fringe matching profilometry (MFMP), for 3D measurement in a projector-camera system. An essential difference from the traditional optical profilometries, in our MFMP test, is that a projector will be regarded as a camera with the reverse lightpath and not just as a coding projection device. Therefore, profit by a maximum utilization of multiview matching relationship, the homonymy points can be directly found with the geometric constraint of the corresponding fringe images between the projector and cameras. Meanwhile, the 3D object reconstruction can be obtained quickly and accurately from a single fringe pattern without phase unwrapping, even the discontinuous surface shape is also easily measurable in our MFMP. Experiment results are provided to verify the effectiveness of our approach.

Orbital angular momentum exchange in a picosecond optical parametric oscillator.

Varun Sharma, Chaitanya Kumar Suddapalli, Goutam K. Samanta, and Majid Ebrahim-Zadeh

Doc ID: 332270 Received 21 May 2018; Accepted 25 Jun 2018; Posted 28 Jun 2018  View: PDF

Abstract: We report on the orbital angular momentum (OAM) exchange among the interacting beams in an ultrafast optical parametric oscillator (OPO). The singly-resonant OPO is synchronously pumped by a picosecond vortex beam from a frequency-doubled Yb-fiber laser at 532 nm in the green. We demonstrate successful transfer of the pump OAM mode to the non-resonant idler beam tunable across 1109-1209 nm, with OAM as high as lp=3. Controlling the cavity loss and spatial overlap between the resonant signal and the pump beam in the nonlinear crystal, we have generated signal and idler OAM mode combinations, (ls,li) of (0,2), (1,1) and (0,3), (1,2) for pump OAM mode lp=2 and 3, respectively. Using a pump power of 1 W, we have generated idler OAM mode of orders, li=1, 2, and 3, with maximum output powers for of 202, 113, and 57 mW, respectively. To the best of our knowledge, this is the first report on controlled generation of OAM modes from an ultrafast OPO.

Quadratic electro-optic effect in silicon-organic hybrid slot-waveguides

Patrick Steglich, Christian Mai, Claus Villringer, Silvio Pulwer, Mauro Casalboni, Sigurd Schrader, and Andreas Mai

Doc ID: 326353 Received 19 Mar 2018; Accepted 25 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: This work reports on the quadratic electro-optic effect of polymers, observed in a silicon slot-waveguide at low voltages. We demonstrate, that in narrow slots the electro-optic response with respect to refractive index change is strong enough for on-chip wavelength tuning and intensity modulation using voltages as low as 1 V. A silicon slot-waveguide embedded by a nonlinear optical polymer, consisting of the dye Disperse Red 1 in poly(methyl methacrylate), serves as phase-shifter in a racetrack ring resonator. As deduced from the experimental data, the third-order susceptibility of the utilized electro-optic polymer is about 2·10^-19 m²/V². The demonstrated low-voltage operation and inherently thermal stability show the potential for silicon-organic hybrid devices using the quadratic electro-optic effect.

Simultaneous dual-channel stimulated Ramanscattering microscopy demultiplexed at distinctmodulation frequencies.

Sandro Heuke, Barbara Sarri, Xavier Audier, and Herve Rigneault

Doc ID: 331728 Received 15 May 2018; Accepted 25 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: To increase the information per pixel in stimulated Raman scattering microscopy as well as to correct from artifacts, it is valuable to acquire images at two different Raman shifts. We present a 3-color SRS approach acquiring two perfectly registered SRS images where both pump beams are modulated at distinct frequencies while demodulating the Stokes beam. Our implementation uses two optical parametric oscillators (OPO) that can be tuned to almost arbitrary energy difference of Raman shifts allowing to investigate fingerprint resonances simultaneously to CH-stretch vibrations.

Excellent luminous efficiency and high thermal stability of glass-in-LuAG ceramic for LDs pumped green emitting phosphor

Qi Zhang, Ruilin Zheng, Jianyong Ding, and Wei Wei

Doc ID: 334082 Received 01 Jun 2018; Accepted 25 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: A kind of glass-in-LuAG (GIP) ceramic with excellent luminous efficiency and high thermal stability was fabricated by solid-state sintering for LDs pumped green emitting phosphor. The GIP ceramic employing particularly designed borosilicate glass as adhesive exhibits high thermal conductivity (2.8 W/m·K at 80°C) and remarkable improvement in thermal stability (luminous flux only 0.5 % drop after 100 h at 300°C). When the GIP ceramic is pumped by 455 nm blue LDs (14.5 W/mm2), a luminous efficacy of 205 lm/W was achieved. More importantly, the GIP ceramic did not have luminescence saturation even under a higher power density (17.1 W/mm2) excitation. The novel GIP ceramic, possessing good optical and thermal properties, is promising for LDs pumped green emitting phosphor.

Spectral pulse shaping of a 5 Hz, multi-Joule, broadband OPCPA front end for a 10 PW laser system

Frantisek Batysta, Roman Antipenkov, Teddy Borger, April Kissinger, Jonathan Green, Robertas Kananavicius, Gilles Cheriaux, Dave Hidinger, Jonas Kolenda, Erhard Gaul, Bedrich Rus, and Todd Ditmire

Doc ID: 331710 Received 16 May 2018; Accepted 25 Jun 2018; Posted 09 Jul 2018  View: PDF

Abstract: We present a broadband optical parametric chirped pulse amplification (OPCPA) system delivering 4 J pulses at a repetition rate of 5 Hz. It will serve as a front end for the 1.5 kJ, <150 fs, 10 PW laser beamline currently under development by a consortium of National Energetics and Ekspla. The spectrum of the OPCPA system is precisely controlled by arbitrarily generated waveforms of the pump lasers. To fully exploit the high flexibility of the front end, we have developed a 1-D model of the system and an optimization algorithm which predicts suitable pump waveform settings for a desired output spectrum. The OPCPA system is shown to have high efficiency, a high-quality top-hat beam-profile, and an output spectrum demonstrated to be shaped consistently with the theoretical model.

Elastomer thin-film pressure sensor based on embedded photonic tunnel-junction arrays

Jae Woong Yoon, Jin Tae Kim, Bong Je Park, Sungryul Yun, Seongcheol Mun, Seung Koo Park, and Suntak Park

Doc ID: 332018 Received 24 May 2018; Accepted 24 Jun 2018; Posted 06 Jul 2018  View: PDF

Abstract: We propose an elastomer thin-film pressure sensor enabled by pressure-sensitive optical signals through vertical photonic tunnel-junction couplers. We provide the operation principle, design, fabrication, and test results from a 50-μm-thick polydimethylsiloxane (PDMS) sheet accommodating embedded vertical photonic tunnel-junction couplers. The result clearly demonstrates a robust pressure-sensing capability realized in a highly flexible, lightweight, transferrable, optically transparent, and bio-compatible thin-film material. Therefore, the proposed approach potentially enables versatile pressure and touch sensors for many applications in practice.

Ultra-broadband spatiotemporal sweeping device for high-speed optical imaging

Cihang Kong, Xiaoming Wei, Jiqiang Kang, Sisi Tan, Kevin Tsia, and Kenneth Kin-Yip Wong

Doc ID: 332173 Received 21 May 2018; Accepted 24 Jun 2018; Posted 25 Jun 2018  View: PDF

Abstract: In this work, we propose and demonstrate a spatiotemporal sweeping fiber bundle for ultra-fast optical diagnoses over a multioctave wavelength span, ranging from ~400 to ~ 2000 nm. This all-optical spaiotemporal sweeping is realized by precisely controlling the length increment between individual fibers in the fiber bundle. Here, a 200-ps pixel delay increment specifically enables a pixel readout rate of up to 5 GHz. Depending on different configurations of the fiber bundle, either 1-D or 2-D spatiotemporal sweeping can be realized. Moreover, the high peak power of the short pulse in each pixel can facilitate the highly sensitive optical detection. To showcase its ultra-broadband operation capability, we here perform ultra-fast optical microscopy at three distinctive wavelengths, which are 710 nm, 1030 nm, and 1600 nm, and achieve 10’s MHz line-scan rate and few-micron resolution for all three experiments. It is anticipated that this inertia-free spatiotemporal sweeping device with ultra-broad bandwidth, GHz pixel readout rate and high detection sensitivity is promising for ultra-fast optical diagnosis, particularly when hyperspectral characteristics are desired.

Twisted Gaussian Schell-model Array Beams

Daomu Zhao and Lipeng Wan

Doc ID: 332985 Received 30 May 2018; Accepted 24 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: We introduce a new class of twisted partially coherent sources for producing rotating Gaussian array profiles. The general analytical formula for the cross-spectral density function of a beam generated by the novel source propagating in free space is derived and its propagation characteristics are analyzed. It is shown that both the irradiance profile of each element of the array and the degree of coherence rotate during propagation, but in opposite directions. Further, the twist effects of the spectral density and the degree of coherence are quantified. It is shown that the direction of rotation is changeable upon propagation. Our results may provide new insight into the twist phase and may be applied in optical trapping.

Extinction matrix for cirrus clouds in the visible and infrared regions

Zhenzhu Wang, Anatoli Borovoi, Alexander Konoshonkin, Natalia Kustova, Dong Liu, and Chenbo Xie

Doc ID: 331993 Received 18 May 2018; Accepted 24 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: The extinction matrix for cirrus clouds has been calculated for the visible and infrared regions by use of the physical-optics approximation. The cirrus clouds are modeled as a statistical ensemble of the hexagonal ice plates distributed over their size and orientations by the gamma and Gaussian laws, respectively. Then the extinction matrixes as the functions of the incident wavelength, incident direction, crystal size, and crystal orientation are numerically calculated for the first time. It is shown that the off-diagonal elements of the matrix are negligible therefore the extinction in cirrus clouds is described with good accuracy by the scalar exponential law.

Polaron effects on nonlinear optical refractive index changes in semi-exponential quantum wells

Meilin Hu, Kangxian Guo, Qiucheng Yu, Zhihai Zhang, and Dongfeng Liu

Doc ID: 330867 Received 10 May 2018; Accepted 23 Jun 2018; Posted 25 Jun 2018  View: PDF

Abstract: Nonlinear optical refractive index changes (RIC) with polaron effects are studied in this paper. The energy levels and wave functions of the polaron Schrödinger equation are calculated and brought into the nonlinear refractive index changes to analyze the difference between the effects of the presence and absence of polaron, as well as the specific representation of refractive index changes with polaron. By transformation, the coefficient f can be used to characterize polaron effects in different states. It is showed that when we consider polaron, the energy interval E21 decreases as the polaron coefficient f raises, making the energy level regions of refractive index changes reduce that called red shift. The change of f will cause the matrix element M21 to form an oscillation curve, and the monotonicity of the curve determines the changes of the peaks of RIC. At the same time, strong light intensity has a bleaching effect on the refractive index changes with polaron effects.

Second harmonic generation of electrostatic origin from extreme nanosized bi-metal structures

Avi Niv, Shlomo Levi, Rakefet Samueli, and Meenakshi Choudhary

Doc ID: 326073 Received 14 Mar 2018; Accepted 23 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We experimentally studied the second harmonic generation from 5 and 25 nanometer-sized gold nanoparticles positioned 5 to 75 nanometers away from a thick silver layer. While known theories fail to predict the results, a proposed model based on the quasistatic interaction of the particles and silver layer shows good agreement with measured data. This agreement points to the possibility of a yet unexplored nonlinear optic mechanism, one that is based on extreme nano-scaled electromagnetic interactions rather than on the particle’s shape or material.

Experimental demonstration of a tunable transverse electric pass polarizer based on hybrid VO2/silicon technology

Luis Sánchez, Irene Olivares, Jorge Parra, Mariela Menghini, Pia Homm, Jean-Pierre Locquet, and Pablo Sanchis Kilders

Doc ID: 332294 Received 21 May 2018; Accepted 23 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: A tunable transverse electric (TE) pass polarizer is demonstrated based on hybrid VO2/Si (vanadium dioxide/silicon) technology. The 20 µm-long TE pass polarizer exploits the phase transition of the active VO2 material to control the rejection of the unwanted transverse magnetic (TM) polarization. Characterized for the wavelength range from 1540 nm to 1570 nm, the device features insertion losses below 1 dB at static conditions and insertion losses of 5 dB and an attenuation of TM polarization of 19 dB in the active state. To the best of our knowledge, this is the first time that tunable polarizers compatible with silicon photonics are demonstrated.

Experimental observations of breathing Kerr temporal cavity solitons at large detunings

Wei Chen, Bruno Garbin, Alexander Nielsen, Stephane Coen, Stuart Murdoch, and Miro Erkintalo

Doc ID: 326243 Received 16 Mar 2018; Accepted 22 Jun 2018; Posted 22 Jun 2018  View: PDF

Abstract: It was recently predicted that, due to stimulated Raman scattering, temporal Kerr cavity solitons may exhibit oscillatory instabilities at large cavity detunings [Phys. Rev. Lett. 120 , 053902 (2018)]. Here we report direct experimental observations of this behaviour. To access the appropriate oscillatory regime, we construct a macroscopic fiber ring resonator with a high finesse $\mathcal{F} \approx 240$. By synchronously driving the resonator with flat-top nanosecond pulses, we can reach very large intracavity power levels where Raman-induced cavity soliton oscillations can be readily observed. We also surprisingly find that, in the limit of large cavity driving strengths, new soliton instability regimes that are not accounted for in the known bifurcation structure of driven Kerr resonators can emerge even in the absence of Raman effects. Our experimental results are in good agreement with numerical simulations.

Spatial resolution improvement of single-shot digital optical frequency comb-based Brillouin optical time domain analysis utilizing multiple pump pulses

Zihao Liang, JINGSHUN PAN, She Gao, Qi Sui, Yuanhua Feng, Fan Li, Jianping Li, Weiping Liu, and Zhaohui Li

Doc ID: 331621 Received 14 May 2018; Accepted 22 Jun 2018; Posted 22 Jun 2018  View: PDF

Abstract: A spatial resolution improvement scheme for the digital optical frequency comb (DOFC) based single-shot Brillouin optical time domain analysis (BOTDA) by utilizing multiple pump pulses is demonstrated. Assisted by four pump pulses, the spatial resolution can be improved by four times without decreasing detection accuracy. The response time, which is mainly limited by the fiber length, and the spatial resolution of our scheme over 10km fiber is 0.1ms and 12.5m. Distributed temperature and strain measurement are carried out with a detection accuracy of 1.6°C and 44με respectively, and the capability of dynamic measurement of this proposed single-shot BOTDA is also demonstrated by probing a vibration with frequency up to 1.2 kHz.

Radial basis function neural network enabled C-band 4 × 50 Gb/s PAM-4 transmission over 80 km SSMF

Yang Zheng, Gao Fan, Songnian Fu, xiang li, Lei Deng, zhixue he, Ming Tang, and Deming Liu

Doc ID: 327947 Received 09 Apr 2018; Accepted 21 Jun 2018; Posted 22 Jun 2018  View: PDF

Abstract: We propose a novel radial basis function neural network (RBF-NN) based nonlinear equalizer (NLE) for the intensity modulation/direct detection (IM/DD) transmission. After optimizing input characteristics of the RBF-NN, we experimentally demonstrate C-band 4 × 50-Gb/s four-level pulse-amplitude modulation (PAM-4) transmission over 80-km standard single-mode fiber (SSMF), using 18-GHz direct-modulated lasers (DMLs) and dispersion compensation fiber (DCF). We demonstrate that the RBF-NN based NLE outperforms the commonly-used Volterra filter (VF) equalizer and recently proposed multilayer perceptron (MLP) based NLE, by about 4.5-dB and 1.5-dB improvements of receiver sensitivity at the 7% forward error correction (FEC) threshold, respectively. Furthermore, we identify that both the training stability and fitting ability of the RBF-NN based NLE are excellent than that of the MLP based NLE.

Influence of the sampling clock pulse shape mismatch on channel-interleaved photonic analog-to-digital conversion

Guang Yang, Weiwen Zou, Jianping Chen, and Lei Yu

Doc ID: 332182 Received 21 May 2018; Accepted 20 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: We investigate the pulse shape mismatch of the sampling clock in channel-interleaved photonic analog-to-digital converters (PADCs) and its influence on the frequency response of the PADC system. Two schemes to generate sampling clock pulses are experimentally implemented to study the influence of the pulse shape mismatch. The scheme with the well-managed pulse shape in all channels is successful to eliminate the influence. Subsequently, a flat 35-GHz frequency response of a 4-channel 40-GS/s PADC is demonstrated and the effective number of bits (ENOB) reaches 7.7 bits at 11 GHz and 7 bits at 31 GHz.

Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing

John Hadden, Vibhav Bharadwaj, Belen Sotillo, Stefano Rampini, Roberto Osellame, J. Witmer, Harishankar Jayakumar, Toney Fernandez, Andrea Chiappini, Cristina Armellini, Maurizio Ferrari, Roberta Ramponi, Paul Barclay, and Shane Eaton

Doc ID: 325661 Received 10 Apr 2018; Accepted 20 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this work, we fabricate laser written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way towards on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.

High aspect ratio microtubes with variable diameter and uniform wall thickness by compressing Bessel hologram phase depth

Shengyun Ji, Liang Yang, Chenchu Zhang, Ze Cai, Yanlei Hu, Jiawen Li, Dong Wu, and Jiaru Chu

Doc ID: 332751 Received 31 May 2018; Accepted 18 Jun 2018; Posted 25 Jun 2018  View: PDF

Abstract: In this Letter, we present a light field regulation method based on compressing the phase modulation depth of Bessel holograms superimposed with blazed gratings to form ring light field with controllable density distribution. The principles of tuning diffraction efficiency of superimposed holograms by grayscale are theoretically and experimentally investigated. The light filed generated by the superimposed holograms are consistent with simulation results. By designing the phase modulation depth of the superimposed holograms with different parameters, ring light fields with suitable intensity distribution are obtained and the fabrication of ring microstructure with uniform wall thickness is realized. Finally, dynamic holographic processing of high aspect ratio microtubes with variable diameter and uniform wall thickness are demonstrated.

Reduction of absorption losses in MOVPE-grown AlGaAs Bragg mirrors

Markus Weyers, Garrett Cole, Markus Aspelmeyer, Ute Zeimer, and Johannes Pohl

Doc ID: 330996 Received 08 May 2018; Accepted 17 Jun 2018; Posted 18 Jun 2018  View: PDF

Abstract: Residual p-type doping from carbon has been identified as the root cause of excess absorption losses in GaAs/AlGaAs Bragg mirrors for high-finesse optical cavities when grown by metalorganic vapor phase epitaxy (MOVPE). Through optimization of the growth parameters with the aim of realizing low carbon uptake, we have shown a path for decreasing the parasitic background absorption in these mirrors from 100 ppm to the 10 ppm range near 1064 nm. This significant reduction is realized via compensation of the carbon acceptors by intentional doping with the donor silicon in the upper-most layer pairs of 40-period GaAs/AlGaAs Bragg mirrors. Thus, we find that such compensation enables MOVPE-derived multilayer mirrors with the potential for a high cavity finesse (>100,000 in the near infrared) approaching the performance levels found with Bragg mirrors grown by MBE.

Intensity surge and negative polarization of light from compact irregular particles

Yevgen Grynko, Yuriy Shkuratov, and Jens Foerstner

Doc ID: 327331 Received 30 Mar 2018; Accepted 16 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: We study the dependence of the intensity and linear polarization of light scattered by isolated particles with compact irregular shape on their size using the Discontinuous Galerkin Time Domain numerical method. The size parameter of particles varies in the range of X = 20 to 150 and the complex refractive index is m = 1.5 + 0i. Our results show that the backscattering negative polarization branch weakens monotonously but does not disappear at large sizes, up to the geometrical optics regime and can be simulated without accounting for wave effects. The intensity backscattering surge becomes narrower with increasing particle size. For X = 150 the surge width is several degrees.

High photon flux Kα Mo x-ray source driven by a multi-TW femtosecond laser at 100 Hz

Yasmina Azamoum, Raphael Clady, amélie Ferré, Mathieu Gambari, Olivier Uteza, and Marc Sentis

Doc ID: 332500 Received 24 May 2018; Accepted 15 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: We develop a pulsed hard x-ray Kα source at 17.4 keV produced by the interaction of a multi-TW peak power infrared femtosecond laser pulse with a thick molybdenum target at 100 Hz repetition rate. We measure the highest molybdenum Kα photon production reported to date corresponding to a Kα photon flux of 1 × 10^{ 11} ph/(sr.s) and an estimated peak brightness of ~ 2.5 × 10^{17} ph/(s.mm2. mrad2 (0.1 % BW)) at ~ 5 × 10^{ 18} W/cm^{2} driving laser intensity.

Dual-wavelength Fourier ptychography using a single LED

Guk-Jong Choi, JINSANG LIM, Sungbin Jeon, Janghyun Cho, Geon Lim, No-Cheol Park, and Young Pil Park

Doc ID: 332015 Received 24 May 2018; Accepted 11 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: We propose dual-wavelength Fourier ptychography for topographic measurement. To extend the axial measurement range, a single light-emitting diode and two appropriate bandpass filters are employed. This provides a speckle-free phase image, and a low systematic error is possible, which yields a high-quality topographic image. The proposed system can measure the surface topography in the range of nano- to micro-structures. The performance of the system is experimentally verified.

Ultra-sensitive spectroscopy of OH radical in high-temperature transient reactions

Shengkai Wang and Ronald Hanson

Doc ID: 331329 Received 10 May 2018; Accepted 11 Jun 2018; Posted 15 Jun 2018  View: PDF

Abstract: The hydroxyl radical, OH, is arguably the most important transient radical in high-temperature gas-phase combustion reactions, yet it is very difficult to measure because of its high reactivity and thus short lifetime and low concentration. This work reports the development of a novel method for ultra-sensitive, quantitative and μs-resolved detection of OH based on UV Frequency-Modulation Spectroscopy (FMS). To the authors’ knowledge, this is the first FMS demonstration in the near-UV spectral region for detection of short-lived radical species. Shot-noise-limited detection was achieved at an optical power of 25 mW. A proof-of-concept experiment in a tabletop H₂O/He microwave discharge cell has reached a 1-σ Minimum Detectable Absorbance (MDA) of less than 2 × 10^-4 over 1 MHz measurement bandwidth. High-temperature OH measurement was demonstrated in a 15-cm diameter shock tube, where a typical MDA of 3.0 × 10^-4 was achieved at 1330 K, 0.38 atm and 1 MHz. These preliminary results have outperformed the previous best MDA by more than a factor of 3; further improvement by another order of magnitude is anticipated following strategies outlined at the end of this paper. The current method paves the path to ppb-level OH detection capability, and offers prospects to significantly advance fundamental combustion research by enabling direct observation of OH formation and scavenging kinetics during key stages of fuel oxidation that were inaccessible with previous methods.

Optimized random phase encryption

Alejandro Velez, Roberto Torroba, and John Barrera Ramírez

Doc ID: 332951 Received 01 Jun 2018; Accepted 04 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: We propose for the first time the use of optimized random phases (ORAP) in a double random phase encryption scheme (DRPE). In DRPE schemes the convolution between two random phase functions encrypts the information to be secured. However, in actual encryption applications, this convolution of random phases also results in unwanted effects like speckle noise. In this paper we show that under certain conditions this noise can be drastically reduced. These conditions can be easily achieved by using ORAPs. These ORAPs besides containing information about the parameters of the optical system and maintaining all the security properties of a random phase function, ensure that the encrypted data is a phase-only function. This leads to a great increase in system performance, with decryption quality similar to the reconstruction of a phase-only hologram generated with the Gerchberg-Saxton algorithm. We show both numerical and experimental results confirming the validity of our proposal.

Full characterization of spatial coregistration errors and spatial resolution in spectral imagers

Hans Torkildsen and Torbjorn Skauli

Doc ID: 328395 Received 23 Apr 2018; Accepted 29 May 2018; Posted 06 Jul 2018  View: PDF

Abstract: For multi- and hyperspectral imagers, the integrity of the spectral information depends critically on the spatial coregistration between bands. There is at present no commonly accepted way to fully specify coregistration performance. This paper shows how a relatively simple measurement technique can be used to form sharp images of the point spread function in all bands, yielding information about spatial coregistration, as well as spatial resolution. A previously proposed metric is applied to characterize coregistration in terms of PSF similarity between bands. Resolution is characterized by ensquared energy. Two commercial hyperspectral cameras with nominally similar specifications are compared, and turn out to have large differences in their actual performance. The results, and the relative simplicity of the measurement, suggest that the method is suitable as a standardized performance test.

Retrieval of weak x-ray scattering using edge illumination

Charlotte Maughan Jones, Fabio Vittoria, A Olivo, Marco Endrizzi, and Peter Munro

Doc ID: 327895 Received 10 Apr 2018; Accepted 24 May 2018; Posted 05 Jun 2018  View: PDF

Abstract: X-ray phase contrast imaging (XPCi) provides additional modes of image contrast compared to conventional absorption based x-ray imaging, thus providing additional structural and functional information about the sample. The edge illumination (EI) technique has been used to provide absorption, refraction and scattering contrast in both biological and non-biological samples, however the retrieval of low scattering signals remains problematic, principally due to beam hardening by the sample. We present a new retrieval method which successfully overcomes the limitations caused by beam hardening, and provide examples of the retrieval of such signals in highly absorbing, weakly scattering samples.

Select as filters

    Select Topics Cancel
    © Copyright 2018 | The Optical Society. All Rights Reserved