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Numerical investigation of a bidirectionally tunable, nanometer-precision, and compact tweezers for screening gold nanoparticles

Mostafa Ghorbanzadeh

DOI: 10.1364/JOSAB.416185 Received 27 Nov 2020; Accepted 24 Feb 2021; Posted 24 Feb 2021  View: PDF

Abstract: Unique optical and chemical properties of gold (Au) nanoparticles (NPs), besides their compatibility with biological entities can made them to emerge as ideal candidates for biomedical applications if size of them can be controlled with nanometer resolution. Taking advantages of (i) enhanced and confined dual wavelength counter-propagating leaky surface plasmons (SPs), (ii) different chemical potential dependencies of graphene’s optical transitions for different incident wavelengths, and (iii) different and intensive size dependencies of extinction efficiency of plasmonic Au NPs for different incident wavelengths, an (i) efficient, (ii) tunable, and (iii) bidirectional tweezers with nanometer-precision has been proposed. At low laser intensities, but at the cost of speed, the proposed setup can be relatively compact due to the realized bidirectional feature that cannot be achieved in conventional unidirectional tweezers. Finite-difference time-domain (FDTD) calculations show that the proposed setup benefits from a dynamical fast-tuning of the screening radius (~1.73 µs/mm2), high bidirectional sorting sensitivity (~14nm/meV), and low tuning voltage (~0.35V). The ability of integrating miniaturized parallel systems with individual operation on a single chip is another potential capability of the proposed system which entitles it as a promising candidate for future lab-on-a-chip devices.

Numerical investigation into the output performance of the silicon Raman laser based on silicon-on-insulator waveguide pumped by 2 μm lasers

Zhenhua Shao, Xuanxi Li, Haotian Wang, Heyuan Zhu, and Deyuan SHEN

DOI: 10.1364/JOSAB.417870 Received 17 Dec 2020; Accepted 24 Feb 2021; Posted 24 Feb 2021  View: PDF

Abstract: We numerically analyze the characteristics of mid-infrared continuous-wave (CW) Raman laser in the silicon-on-insulator (SOI) photonics circuits including the standing-cavity and ring resonator configurations, which are pumped by lasers at 2 μm. The dependence of cascaded Raman laser performance on the cavity length, effective free carrier lifetime and the power transmission are investigated for the optimization of CW Raman silicon standing-cavity lasers. In addition, the mid-infrared Raman laser in the ring resonator are also presented under different parameters, specially, the coupling strengths between the bus waveguide and the ring resonator for both pump and Raman lasers are crucial to the laser performance. The numerical simulation results also reveal that the position of the coupler for extracting the Raman light from the ring resonator plays an important role in optimizing the structures of such Raman lasers.

Numerical study of spatial propagation dynamics and energy delivery of TW square-aperture CO₂ laser pulses in the atmosphere

Paris Panagiotopoulos, Miroslav Kolesik, Victor Hasson, Sergei Tochitsky, and Jerome Moloney

DOI: 10.1364/JOSAB.417071 Received 08 Dec 2020; Accepted 23 Feb 2021; Posted 24 Feb 2021  View: PDF

Abstract: We numerically study the linear and nonlinear spatial propagation dynamics of multi-Joule 10.6 μm square beams in the atmosphere for various square obscuration locations. We show that the spatial reshaping process of these square frame shaped beams, a process normally driven by strong linear diffraction, can be significantly altered in the nonlinear regime. Depending on the input power, linear dynamics can be mostly preserved or overpowered by the optical Kerr effect leading to the formation of single or multi-filament patterns, at propagation distances of a few tens of meters in the atmosphere. Optimal power delivery downstream is dependent on the location of the square obscuration and overall input power. Our results offer significant insight to ongoing efforts of high peak power CO₂ mid-IR lasers generated in unstable resonators for atmospheric applications.

Highly Polarization-Sensitive, Broadband, low darkcurrent, high responsivity graphene-basedphotodetector utilizing metal nano-grating at telecommunication wavelengths

ali farmani, Elham Khosravian, and Hamidreza Mashayekhi

DOI: 10.1364/JOSAB.418804 Received 04 Jan 2021; Accepted 23 Feb 2021; Posted 23 Feb 2021  View: PDF

Abstract: Recent advances in graphene-based photodetectors have demonstrated the feasibility of utilizing graphene as a fantastic material for the development of future high-performance photodetectors. In this paper, a high performance graphene-based photodetector is pro-posed with plasmonic structure by employing a sin-gle graphene layer, periodic metal nano-grating, andSi/SiO2substrate. The plasmonic coupling phenomena between graphene and metal nano-grating can cause absorption enhancement in this structure. The proposed structure has almost perfect absorption at telecommunication wavelength (1.55μm) and its optical response shows polarization sensitive characteristic in the spectral range from 1μm to 2.1μm. Moreover, the electrical characterization and the dynamic response of this structure is obtained. Based on simulation results, the pro-posed structure under 0.5 mW incident optical power and at wavelength of 1.55μm exhibits a low dark cur-rent in the order of about 0.001 mA, a maximum photocurrent of 0.81 mA, and a responsivity of 1650 mA/Wat bias voltage of 3 V. Also, the rise time of the dynamic response is determined to be about 87 ps and the 3 dB bandwidth of the frequency response is obtained to be about 4 GHz.

Exceptional points in Fabry-Pérot cavities with spatially distributed gain and loss

Yue-De Yang, xiang-hui meng, you-zeng hao, Chun-Guang Ma, Jin-Long Xiao, and Yong-Zhen Huang

DOI: 10.1364/JOSAB.420383 Received 20 Jan 2021; Accepted 23 Feb 2021; Posted 23 Feb 2021  View: PDF

Abstract: We have studied the optical modes in Fabry-Pérot (FP) cavities with spatially distributed gain and loss. Exceptional points (EPs) are observed not only in the parity-time (PT) symmetric FP cavity with but also in these cavities with specially designed gain-loss distributions. Such phenomena result from the interference between the reflected and transmitted waves at the interface of the gain-loss regions, which cannot be explained by the dual-mode coupling theory that is widely used in the description of PT symmetric coupled-cavity system. The optical waves in the FP cavity traveling in forward and backward directions have extremely different intensities at the gain-loss interface, and hence the interference will greatly affect the transmission of the weaker one and lead to unique mode properties such as EPs in the FP cavity. The mode properties are sensitive to the gain-loss distribution, but the split of modal loss is a universal phenomenon and can be used for lasing mode control.

Non-Markovianity as a resource for quantum correlation teleportation

Anahita Motavalibashi, hamidreza mohammadi, and Ahmad Akhound

DOI: 10.1364/JOSAB.418884 Received 10 Jan 2021; Accepted 22 Feb 2021; Posted 23 Feb 2021  View: PDF

Abstract: Quantum teleportation of a correlated state via a noisy channel, is investigated. The noisy channel is realized by a couple of (non-interacting) two level atoms (qubits) embedded in a zero-temperature bosonic bath. The resource of the teleportation is provided by entangled state of the channel provided by information back-flow in the non-Markovian regime of the evolution. More non-Markovianity of the dynamics generates higher amount of induced entanglement and hence enhances the quality of quantum correlation teleportation process. When the degree of non-Markovianity of dynamics is sufficiently high, quantum teleportation superior to classical communication is achievable.

Laser-frequency-comb calibration for the Extremely Large Telescope: an OPO-based infrared astrocomb covering the H- and J-bands

Yuk Shan Cheng, Dong Xiao, Richard McCracken, and Derryck Reid

DOI: 10.1364/JOSAB.421310 Received 01 Feb 2021; Accepted 21 Feb 2021; Posted 24 Feb 2021  View: PDF

Abstract: The Extremely Large Telescope (ELT) will address an unprecedented optical wavelength range from 370 nm to 2400 nm, and its HIRES spectrograph will require a laser frequency comb calibrator of comparable coverage. An architecture based around a Ti:sapphire master comb in principle enables wavelengths across this range to be obtained by a combination of second- and third-order nonlinear effects. In this scheme, near-infrared wavelength coverage can be addressed by down-conversion of the comb to 1600 nm using an optical parametric oscillator (OPO), followed by broadband super-continuum generation in highly nonlinear fiber. Here, we present an example of this approach in the form of a 10-GHz astrocomb comprising a Fabry-Pérot-filtered super-continuum, derived from a degenerate OPO and spanning 1.15–1.80-𝜇m. We characterize the astrocomb using Fourier-transform spectroscopy, enabling the mode orders within the filtered comb to be identified with a precision of 16-MHz.

4 Joule unstable cavity direct-liquid-cooled disk laser

Zhibin Ye, Shu Jiang, Fei Wu, and Xiaolei Deng

DOI: 10.1364/JOSAB.418980 Received 04 Jan 2021; Accepted 21 Feb 2021; Posted 22 Feb 2021  View: PDF

Abstract: A quasi-continuous unstable laser resonator with direct-liquid-cooled method is developed. The refractive index matching liquid and ten pieces of 45 mm × 18 mm × 2 mm Nd:YLF crystals with different doping levels are used as coolant and gain media, respectively. The stepped transmittance convex and concave mirrors are used as the cavity mirror to construct the unstable resonator. Experimentally, the flow rate of the coolant is 5 m/s and the effective amplification rate of the unstable cavity is 1.3. A quasi-continuous output single-pulse energy of 4 J is obtained with the optical-optical efficiency of 20%, the repetition frequency of 250 Hz, the wavelength of 1047 nm and the beam quality factor β of 10 approximately. By introducing an adaptive optical (AO) system into the cavity, a higher power and higher beam quality laser is expected to be achieved.

A compact green Ti:Sapphire astro-comb with 43-GHz repetition frequency

Eunmi Chae, Eiji Kambe, Kentaro Motohara, Hideyuki Izumiura, Mamoru Doi, and Kosuke Yoshioka

DOI: 10.1364/JOSAB.419078 Received 04 Jan 2021; Accepted 21 Feb 2021; Posted 22 Feb 2021  View: PDF

Abstract: A compact green astro-comb with 43-GHz repetition rate is developed based on a Ti:Sapphire optical frequency comb (OFC) and a mode-selecting cavity. The OFC’s large repetition rate of 1.6 GHz eases the requirements for the mode-selecting cavity. Unnecessary frequency-modes of the OFC are suppressed down to 5×10¯⁴ at 535 nm – 550 nm using a single mode-selecting cavity with 70-MHz linewidth. The radial velocity precision σ ~ 1.4 m/s is achieved at the High Dispersion Echelle Spectrosraph for the Okayama 188-cm telescope of the National Astronomical Observatory of Japan using our astro-comb. With further improvements of the mode-selecting cavity and removal of fiber modal noises, our system will provide a simple, compact, and precise astro-comb setup in visible wavelength region.

Mueller micropolarimeter for colour imaging of aluminium metasurfaces

Mathieu NICOLAS, Ibrahima Soumahoro, Lu Zhang, Géraldine Guida, Willy Daney De Marcillac, Catherine Schwob, Souhir Boujday, and Bruno Gallas

DOI: 10.1364/JOSAB.416833 Received 07 Dec 2020; Accepted 20 Feb 2021; Posted 22 Feb 2021  View: PDF

Abstract: Many anticounterfeiting tags rely on images intricate in different colour and/or different polarization states to create optical effects invisible in conventional observation conditions. We build here an imaging micropolarimeter based on the dual rotating compensator system and using the colour capabilities of cameras to yield the full polarimetric information for any colour coordinates in one acquisition step. After correction for the camera response, the full colour image reconstructed from the polarimetric response is validated by the comparison with images obtained in an optical microscope fitted with polarizers.

Strong-Field Terahertz Control of Plasmon Induced Opacity in Photoexcited Metamaterial

Ali Mousavian, Zachary Thompson, Byounghwak Lee, Alden Bradley, milo sprague, and Yun-Shik Lee

DOI: 10.1364/JOSAB.409224 Received 12 Oct 2020; Accepted 19 Feb 2021; Posted 19 Feb 2021  View: PDF

Abstract: A terahertz metamaterial consisting of radiative slot antennas and subradiant complementary split-ring resonators exhibits plasmon induced opacity in a narrow spectral range due to the destructive interference between the bright and dark modes of the coupled oscillators. Femtosecond optical excitations instantly quench the mode coupling and plasmon oscillations, injecting photocarriers into the metamaterial. The plasmon resonances in the coupled metamaterial are transiently restored by intense terahertz pulses. The strong terahertz fields induce intervalley scattering and interband tunneling of the photocarries, and achieve significant reduction of the photocarrier mobility. The ultrafast dynamics of the nonlinear THz interactions reveals intricate interplay between photocarriers and plasmon oscillations. The high-field THz control of the plasmon oscillations implies potential applications to ultrahigh-speed plasmonics.

Proposal and Proof-of-Principle Demonstration of Fast-Switching Broadband Frequency-Shifting for a Frequency-Multiplexed Quantum Repeater

Gustavo do Amaral, Peng-Cheng Wang, Oriol Pietx-Casas, and Mohsen Falamarzi Askarani

DOI: 10.1364/JOSAB.412517 Received 15 Oct 2020; Accepted 17 Feb 2021; Posted 18 Feb 2021  View: PDF

Abstract: A proposal for fast-switching broadband frequency-shifting technology making use of frequency conversion in a nonlinear crystal is set forth, whereby the shifting is imparted to the converted photons by creating a bank of frequency-displaced pump modes that can be selected by a photonic switch and directed to the nonlinear crystal. Proof-of-principle results show that the expected frequency-shifting operation can be achieved. Even though the dimensions of the currently employed crystal and significant excess loss in the experimental setup prevented conversion of single-photon-level inputs, thorough experimental and theoretical analysis of the noise contribution allowed for the estimation of the system performance in an optimized scenario, where the expected signal-to-noise ratio for single-photon conversion and frequency-shifting can reach up to 25 dB with proper narrow-band filtering and state-of-the-art devices. The proposed frequency-shifting solution figures as a promising candidate for applications in frequency-multiplexed quantum repeater architectures with 25 dB output SNR (with 20\% conversion efficiency) and capacity for 16 channels spread around a 100 GHz spectral region.

A first-principles study of structure, energetics and electrical properties of Ge-N-vacancy complexes in diamond

Xin Tan, Zhixin Liu, Bochen Zhang, Luhua Chen, yuan Wei, Yuan Ren, and Shiyang Sun

DOI: 10.1364/JOSAB.413488 Received 04 Nov 2020; Accepted 17 Feb 2021; Posted 18 Feb 2021  View: PDF

Abstract: Following first principles, according to the special structure of NE8 color center, this article redesigned the known diamond germanium vacancy (GeV) color center by adding nitrogen atoms and increasing the number of vacancies. Results demonstrated that the most stable structure after design is one without vacancy and where germanium atoms are connected with four nitrogen atoms. This work analyzed the new structure of the GeV color center and determined the charge transfer and bonding of the charge density difference. The band and density of the states of the GeV color center with four nitrogen atoms are calculated. By analyzing the electrical properties of each atom, we posit that the nitrogen atom is a transitional modified atom. The new structure of the GeV color center has good prospects in the application of sensors and single-photon sources.

Quantum Cheshire Cat: A physically realistic interpretation by invoking entangled correlations.

manzoor fasihi, Muhammad Saeed, Muhammad Imran, Hinna Tariq, and Rameez ul-Islam

DOI: 10.1364/JOSAB.414000 Received 11 Dec 2020; Accepted 17 Feb 2021; Posted 18 Feb 2021  View: PDF

Abstract: The phenomenon of the Quantum Cheshire Cat (QCC) and its interpretation by Aharonov et al [New J. Phys. 15, 113015 (2013)] with the conjecture that any quantum entity can be disembodied from its physical attributes. This has resulted into a heated debate leading to interpretational controversy as well as practical consequences. Here, we propose an experimentally testable and physically more realistic and logically convincing interpretation. We utilize a specifically engineered Mach-Zehnder type interferometeric setup that is quite similar to original QCC setup but with a slight difference that signal-photon of a bipartite entangled state traverses the interferometer such that each path is designated to a photon with different tags. With this specific setup, we demonstrate that the photon's polarization is never physically separated from the photon itself. Rather it becomes dormant and hence inaccessible along the designated interferometric path. We also generalize the schematics and show that any precisely oriented photon's polarization that stands inaccessible or dormant re-emerge along the same, spatially separated and isolated arm as we tune the polarization vector away from the selected angle. Thus our proposal persuasively proves that polarization is never stripped o¤ from the photon itself and instead becomes inaccessible along the interferometeric arm for a certain particularly selected orientation. The schematics further reveal that this inaccessibility of the photon's polarization is not permanent, fixed and universal but rather it is entirely constrained to a specific orientation in the Hilbert space, governed by the particular pre- and post-selected state and Two State Vector Formalism (TSVF)

Brillouin scattering - theory and experiment

Christian Wolff, Michael Smith, Birgit Stiller, and Chris Poulton

DOI: 10.1364/JOSAB.416747 Received 11 Dec 2020; Accepted 17 Feb 2021; Posted 18 Feb 2021  View: PDF

Abstract: Brillouin scattering is an important and interesting nonlinear effect involving the interaction between optical and acoustic fields in optical waveguides. It is increasingly useful in the field of photonics, where it supplies a tunable ultra-narrow linewidth response that can be used for applications including sensing, filtering, and lasing, as well as the acoustic storage of optical pulses. This tutorial gives an overview of the fundamentals of Brillouin scatteringaimed at newcomers to the field, and covers the physics underlying the interaction, the mathematical theory, and setup details of foundational Brillouin experiments.

High Q-value for classical electromagnetically induced transparency based on dipoles overlapping at a spoof localized surface plasmon

siyuan liu, Zhixia Xu, Xiaoxing YIN, and Hongxin Zhao

DOI: 10.1364/JOSAB.417496 Received 17 Dec 2020; Accepted 15 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: This work describes classical electromagnetically induced transparency (EIT) at a spoof localized surface plasmon metasurface (S-LSP), which was realized using only one connected elementary metallic unit cell. The excited electric dipole and magnetic dipole from the S-LSPs almost overlap in an extremely narrow frequency band, which satisfies the condition for classical EIT. This metasurface has increase another possibility to early bright–dark modes produced by classical EIT with separated resonances. Moreover, for the microwave band, our proposed classical EIT has a high Q-value (up to 311) and group index (up to 30.913) compared with recent reports of classical EIT and passive microwave devices with the same working frequency.

An analytical 7-wave model for wave propagation in a degenerate dual-pump fiber phase sensitive amplifier

Fabien Bretenaker, debanuj chatterjee, Fabienne Goldfarb, and Yousra Bouasria

DOI: 10.1364/JOSAB.417542 Received 16 Dec 2020; Accepted 15 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: We develop an analytical model to describe propagation of seven continuous (CW) waves (two strong pumps, a degenerate signal and idler, two high-order idlers (HOIs) and two high-order pumps (HOPs)) through a nonlinear fiber. The model is developed considering the pumps to be much stronger than the other waves. The 7-wave system is analyzed in terms of interactions between its 4-wave subsystems : (a) pumps and degenerate signal and idler, (b) pumps and HOIs, and (c) pumps and HOPs. First we analyze the three 4-wave subsystems, and then we move to the 7-wave system and compare the two analytical models. The analytical 7-wave model reveals that a strong coupling (mediated through four wave mixing processes), between the subsystem with the signal and the subsystem with the HOIs leads to an important role of the HOIs in influencing the signal gain of a degenerate dual-pump fiber phase sensitive amplifier (PSA). We find that the maximum PSA gain of the signal for such an amplifier can be significantly enhanced by launching the HOIs at the fiber input along with the signal. We compare the analytical results with that of a numerical 7-wave model and for the anomalous dispersion regime we find a good agreement between the two when the system nonlinearity is weak, i.e. total nonlinear phase less than 0.6 rad.

What optical fiber modes reveal: Group velocity andeffective index for external perturbations

Swaathi Upendar, Markus Schmidt, and Thomas Weiss

DOI: 10.1364/JOSAB.418272 Received 21 Dec 2020; Accepted 15 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: A precise control of fiber modes and their dispersion is essential particularly for fields such as nonlinearfrequency conversion or biosensing, both of which often requiring extensive and time-consuming simulationsfor design optimization. Here, we develop a first-order perturbation theory for predicting theeffective index of bound and leaky fiber modes that is applicable for arbitrary global perturbations aslong as the perturbations in the external surrounding are constant homogeneous and isotropic deviationsfrom the unperturbed fiber. This includes not only changes in permittivity and permeability, but also inwavelength. Thus, we are able to calculate the group velocity solely from the field distributions of thefiber modes at a single wavelength, which therefore allows for large scale parameter sweeps for accuratelymanaging dispersion. We demonstrate the capabilities of our theory for various trial systems such as stepindex fibers, photonic crystal fibers and light cages.

Frenet-Serret analysis of helical Bloch modes in N-fold rotationally symmetric rings of coupled spiralling optical waveguides

Yang Chen and Philip Russell

DOI: 10.1364/JOSAB.412186 Received 15 Oct 2020; Accepted 15 Feb 2021; Posted 18 Feb 2021  View: PDF

Abstract: The behavior of electromagnetic waves in chirally twisted structures is a topic of enduring interest, dating back at least to the invention in the 1940s of the microwave travelling-wave-tube amplifier and culminating in contemporary studies of chiral metamaterials, metasurfaces, and photonic crystal fibers (PCFs). Optical fibers with chiral microstructures, drawn from a spinning preform, have many useful properties, exhibiting for example circular birefringence and circular dichroism. It has recently been shown that chiral fibers with N-fold rotationally symmetric (symmetry group CN) transverse microstructures support families of helical Bloch modes (HBMs), each of which consists of a superposition of azimuthal Bloch harmonics (or optical vortices). An example is a fiber with N coupled cores arranged in a ring around its central axis (N-core single-ring fiber). Although this type of fiber can be readily modelled using scalar coupled mode theory, a full description of its optical properties requires a vectorial analysis that takes account of the polarization state of the light—particularly important in studies of circular and vortical birefringence. In this paper we develop, using an orthogonal two-dimensional helicoidal coordinate system embedded in a cylindrical surface at constant radius, a rigorous vector coupled mode description of the fields using local Frenet-Serret frames that rotate and twist with each of the N cores. The analysis places on a firm theoretical footing a previous HBM theory in which a heuristic approach was taken, based on physical intuition of the properties of Bloch waves. After a detailed review of the polarization evolution in a single spiralling core, the analysis of the N-core single-ring system is carefully developed step by step. The accuracy limits of the analysis are assessed by comparison with the results of finite element modelling, focusing in particular on the dispersion, polarization states and transverse field profiles of the HBMs. We believe this study provides clarity in what can sometimes be a rather difficult field, and will facilitate further exploration of real-world applications of these fascinating waveguiding systems.

Evaluation and suppression of the magnetic-induced Rabi broadening of magnetic-sensitive Ramsey fringes

Rong Wei, Qingchen Ji, Weijing Zhao, and Yan Wang

DOI: 10.1364/JOSAB.415603 Received 24 Nov 2020; Accepted 12 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: Magnetic-sensitive Ramsey fringes are useful for the magnetic field evaluation of atomic fountain clocks. However, broadening mechanisms affect the visibility of the fringes and limit their application in the measurement of the magnetic field. In this paper, the magnetic-induced Rabi broadening, as a result of magnetic field inhomogeneity in the microwave cavity of fountain clocks, is shown to cause the visibility reduction of the fringes. Furthermore, an improved method for shortening the Rabi interaction time is proposed to suppress the broadening effect. Experiments are conducted on the rubidium 87 atomic fountain clock to test the broadening mechanism as well as demonstrate the effectiveness of the improved method for suppressing the broadening effect. As a result, we obtain magnetic-sensitive Ramsey fringes and evaluate the average magnetic field with different launching heights in the microwave region of the fountain clock. And the second-order Zeeman frequency shift is evaluated with the fractional frequency shift of 1.295×10−¹³, and the frequency uncertainty of 3×10−¹⁶


Yuri Avetisyan

DOI: 10.1364/JOSAB.416305 Received 01 Dec 2020; Accepted 12 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: It is shown that intense multi-cycle THz-pulses can be generated in two-dimensional quasi-phase matching structures formed by placing a binary phase mask in front of the periodically poled lithium niobate crystal. The THz wave is emitted perpendicular to the direction of the pump pulse propagation, which is favorable for their independent control. A THz peak power of 0.6 MW at a frequency of 0.5 THz is predicted for the crystal at 100 K temperature. The efficiency of the pump-to-THz conversation is estimated to be 1.5% with relatively moderate pump pulse energy of 4 mJ. These results could be future improved by resonance enhancement of the pump intensity in an optical cavity or by a proper choice of the pump pulse format.

2.7 µm band enhancement induced by energy transfer in Er3+/Tm3+ co-doped tellurite glass

Yu Zhang, LiZhang Xia, Jiale Ding, Chengyan Li, xinjie Shen, Jun Li, and Yaxun Zhou

DOI: 10.1364/JOSAB.416863 Received 07 Dec 2020; Accepted 12 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: In this work, the improved effect on 2.7 µm band fluorescence of Er3+ caused by Tm3+ was investigated. When 0.6 mol% Tm2O3 was incorporated into the tellurite glass doped with 0.5 mol% Er2O3, the 2.7 µm band fluorescence originating from Er3+:4I11/2→4I13/2 transition increased by about 1.4 times under the excitation of 808 nm LD. This significant enhancement was attributed to the energy transfers between Tm3+ and Er3+ ions. The energy transfer mechanism was investigated quantitatively by calculating the micro-parameters. The obtained result indicated that Er3+/Tm3+ co-doped tellurite glass is a promising candidate applied for 2.7 µm band optoelectronic devices.

Thermal and Non-Thermal Intensity Dependent Optical Nonlinearities in Ethanol at 800nm, 1480nm and 1560nm

Jessica Edith Quispe Bautista, Manoel Leonardo, Cecília Veras Campos, Melissa Maldonado Cantillo, Cid Bartolomeu de Araujo, and Anderson S. Gomes

DOI: 10.1364/JOSAB.418635 Received 04 Jan 2021; Accepted 12 Feb 2021; Posted 16 Feb 2021  View: PDF

Abstract: Intensity dependent self-action of a continuous wave (CW) or pulsed optical beam can lead to spatial or spectral effects upon propagation through a nonlinear medium which can be described as an intensity dependence of the refractive index, known as self-phase modulation (SPM). In this work, we revisit the nonlinear optical propagation of a CW and a CW/mode-locked (CW-ML) high repetition rate (~MHz) laser propagating through pure ethanol in regions of very low optical absorption (800nm) or very high absorption (1480nm, 1560nm). Spatial and spectral SPM and Z-scan experiments were performed to clarify the origin of the third order nonlinear optical response in the different optical excitation regimes. From spatial SPM and Z-scan at either CW or CW-ML MHz regime, a thermal nonlinear response was determined to be the origin of the nonlinearity at 800nm or 1480nm, 1560nm region, with nonlinear refractive index response of the order of 10¯⁴-10¯⁹ cm²/W. From the spectral SPM, the non-thermal origin of the nonlinearity, arising from electronic or nuclear processes in the ethanol was determined, and values of the order of 10¯¹³-10¯¹⁶ cm²/W were obtained, depending upon the spectral region. The results were supported by theoretical simulations using the nonlinear Schrodinger equation for the spectral behavior or Fresnel-Kirchhoff integral for the spatial results, and clarify some of the misinterpreted results reported in the literature, besides complementing other nonlinear refraction data available at different wavelengths from 355nm to 1560nm.

Generation of highly pure lower order Laguerre - Gaussian radial beams using an all-fiber Multimode Interference method

Nitin Bhatia

DOI: 10.1364/JOSAB.409000 Received 01 Sep 2020; Accepted 10 Feb 2021; Posted 11 Feb 2021  View: PDF

Abstract: We show that the output beam exiting from the end-facet of a Single mode - Multimode - Few mode (SMFe) device can be designed to be a highly pure LG₀⁰ or LG ₀¹mode. Our investigation provides a method for the generation of the LG beams in free-space using a low cost, all-fiber solution which also shows the potential an integrated device.

Modulation dynamics of atomic Rydberg excitation in strong-field tunneling ionization

P. P. Xin, Qiu Tianhui, LIbo Chen, Hongyang Ma, and H. P. Liu

DOI: 10.1364/JOSAB.415081 Received 16 Nov 2020; Accepted 07 Feb 2021; Posted 08 Feb 2021  View: PDF

Abstract: In this paper, we have theoretically investigated the modulation structure of atomic excitation and ionization probabilities in strong laser fields and shown its feature with diversity of population amplitude as a function of laser peak intensity. Oscillating with opposite phase between the two probabilities are presented and proved to be related with the ac-Stark-shifted of bound-continuum boundary that displayed by the low energy structure of ATI peak near threshold and two-dimensional (2D) electron momentum spectrum, which confirms the multiphoton resonance exists in the tunneling regime. Moreover, the population of Rydberg states belonging to different quantum number during the interaction of the atom with the laser pulse has been simulated by solving the time-dependent Schrodinger equation. It is found that the distribution of bound states with low-lyingprincipal quantum number n tends to be dominant on total excitation probability with the opposite phase of other higher n states accompanied by the angular momentum with well-defined parity that induced by the repopulation of the Rydberg states via two-photon Λ-type Raman transitions.Given the depletion of atomic excited states in the tunneling region comes predominantly from the light pressure of the laser pulse on the electron wave packet in the laser propagation direction, the stabilization mechanisms of the formed excited states in strong laser fields has been analyzed.

Modelling photon pair generation by second-order surface nonlinearity in silica nanofibers

Abderrahim Azzoune, Philippe Delaye, and Gilles Pauliat

DOI: 10.1364/JOSAB.418661 Received 05 Jan 2021; Accepted 07 Feb 2021; Posted 08 Feb 2021  View: PDF

Abstract: In this paper, we present a design of an all-fiber source of correlated photon pairs based on standard telecommunications tapered fibers. We examine the generation of correlated photon pairs using parametric process χ^((2)) in silica tapered optical fibers. This nonlinear process is ensured thanks to surface dipole and bulk multipole nonlinearities. The process of photons creation is modeled by taking into account the vector aspect of the propagation of the optical field in a silica nanofiber. The phase matching is provided by propagating the pump field in one spatial mode, while generating a photon pair in another spatial mode. The generation efficiency of photon pairs depends on diameter uniformity of the nanofiber after the manufacturing process. We size this nanofiber for a good optimization of photon pair generation efficiency, we report that the tolerance in diameter uniformity is Δd=2 nm for a generation rate of photon pairs estimated to N_ph≈22 000 pairs/s, for 1 W power pump and a nanofiber length of 1.1 mm. Deposits on the nanofiber can be used in order to relax the manufacturing constraints on diameter to maximize the generation rate of photon pairs. As an example, the use of Polytetrafluoroethylene (PTFE) on the nanofiber applied as a cladding whose thickness is infinite makes it possible to relax the constraints on the nanofiber diameter. For the same Δd=2 nm, a generation rate of photon pairs estimated to N_ph≈78 000 pairs/s for 1 W power pump and a nanofiber length of 2.4 mm is predicted.

Effect of wavefront rotation on the photoionization process by ultrafast laser spatio-temporal focusing

Yuedong Li, Juan Song, Qinxiao Zhai, Weiyi Yin, Xinlan Tang, and Ye Dai

DOI: 10.1364/JOSAB.416274 Received 29 Nov 2020; Accepted 06 Feb 2021; Posted 08 Feb 2021  View: PDF

Abstract: In this paper we theoretically studied the propagation of the first-order spatio-temporal coupled ultrafast pulse in fused silica glass by using the Cartesian nonlinear Schrödinger equation coupled with the electron density rate equation. We found that wavefront rotation, one parameter of the shaped pulse, may play a vital role to adjust the asymmetrical modification under different initial coupling conditions. During the focusing wavefront rotation mainly influences the evolution of pulse front tilt, which leads directly to the inclination of laser intensity and fluence distributions at the focal plane. Furthermore, it might even reverse the excited electron density distribution, because the inclined direction of the pulse front tilt could flip over in the case that a relatively large value of group delay dispersion has been introduced at the initial state. Based on our numerical simulation, the possible mechanism of nonreciprocally direct-writing phenomena is revisited by taking into account the effect of wavefront rotation.

Measurement of net Goos–Hänchen shift and reshaping shift

Makoto Tomita and HIROZUMI SAITO

DOI: 10.1364/JOSAB.417113 Received 09 Dec 2020; Accepted 03 Feb 2021; Posted 08 Feb 2021  View: PDF

Abstract: We develop the concepts of net Goose Hansen (GH) shift and reshaping shift, and apply these concepts to lateral beam shift arising from (wavenumber) domain dispersion. Specifically, our interest is in cases in which the traditional concept of GH shift loses its meaning. We analyzed the effects of finite beam size, complicated beam profiles, and phase modulations on GH shift. We experimentally examined the GH shift for surface plasmon polaritons and a leaky wave guide mode. The results agreed well with those from analyses based on the net GH shift and reshaping shift, indicating that these concepts are useful for extending the traditional concept of GH shift to complicated reflection systems.

Mode characteristics for gapless-coupled twin circular-side square microcavity lasers

Ke Yang, you-zeng hao, Ji-Liang Wu, zheng-zheng shen, Min Tang, Jin-Long Xiao, Yue-De Yang, and Yong-Zhen Huang

DOI: 10.1364/JOSAB.415209 Received 16 Nov 2020; Accepted 03 Feb 2021; Posted 04 Feb 2021  View: PDF

Abstract: We propose gapless-coupled twin circular-side square microcavities (TCSMs), and experimentally demonstrate the TCSM semiconductor lasers with weak mode coupling. The introduction of circular sides modifies the field distributions of the whispering-gallery modes and enables gapless coupling for the TCSMs without degrading the mode quality factors. Numerical simulation results show crossing and avoided crossing of the modes in the TCSMs with the variation of the wavelength difference and gain-loss contrast between the two cavities. By tuning the injection currents on the laser cavities, mode crossing is observed from the experimental lasing spectra of a TCSM laser. The realization of weak mode coupling in TCSM lasers indicates that the gapless-coupled deformed square microcavities provide a feasible robust coupling scheme for photonic integration.

Full 3D+1 modeling of tilted-pulse-front setups for single-cycle terahertz generation: comment

Michael Bakunov and Sergey Bodrov

DOI: 10.1364/JOSAB.404387 Received 31 Jul 2020; Accepted 01 Feb 2021; Posted 02 Feb 2021  View: PDF

Abstract: Wang et al. [J. Opt. Soc. Am. B 37, 1000 (2020)] simulated terahertz generation by tilted-pulse-front optical excitation of a lithium niobate crystal and made predictions about the optimal generation conditions and spatial distribution of the generated terahertz beam. We point out that formulas used by Wang et al. for the tilted-pulse-front optical pulse and optically induced nonlinear polarization are irrelevant to the conventional tilted-pulse-front configuration. Therefore, the predictions made by Wang et al. are incorrect and cannot be used for optimizing experiments.

Effects of transmission loss on two-mode squeezed vacuum state quantum lidar

Yuefeng zhao, Hui Li, jing gao, Xu Wang, Yurong Zhang, Mengjun Duan, Yanqi Wang, Jie Pan, Yang Jiancai, Jing Wang, and Jing Fang

DOI: 10.1364/JOSAB.413422 Received 27 Oct 2020; Accepted 01 Feb 2021; Posted 04 Feb 2021  View: PDF

Abstract: The performance of two-mode squeezed vacuum state quantum lidar depending on system transmission losses is studied. The sensitivity and resolution of the system with a certain transmission loss are analyzed by parity detection and maximum transmission model. With a loss coefficient of 0.1 < K < 0.5, the system sensitivity breaks through the standard quantum limit. Taking a single transmission loss into consideration, the maximum transmission losses in the system should be 85% and 94%, corresponding to compression coefficients of ξ = 1.0 and 1.5, respectively. The results show that a high compression degree of the light source method is helpful to enhance the sensitivity of the system, while the system resolution can be further improved by an increasing of average photon number.

Impact of DC bias on Weak Optical-Field-Driven Electron Emission in Nano-Vacuum-Gap Detectors

Marco Turchetti, Mina Bionta, Yujia Yang, Felix Ritzkowsky, Denis Candido, Michael Flatte, Karl Berggren, and Phillip Keathley

DOI: 10.1364/JOSAB.413680 Received 02 Nov 2020; Accepted 01 Feb 2021; Posted 04 Feb 2021  View: PDF

Abstract: In this work, we investigate multiphoton and optical-field tunneling emission from metallic surfaces with nanoscale vacuum gaps. Using time-dependent Schrodinger equation (TDSE) simulations, we find that the properties of the emitted photocurrent in such systems can be greatly altered by the application of only a few-volt DC bias. We find that when coupled with expected plasmonic enhancements within the nanometer-scale metallic gaps, the application of this DC bias significantly reduces the threshold for the transition to optical-field-driven tunneling from the metal surface, and could sufficiently enhance the emitted photocurrents, to make it feasible to electronically tag fJ ultrafast pulses at room temperature. Given the petahertz-scale instantaneous response of the photocurrents, and the low effective capacitance of thin-film nanoantenna devices that enables < 1fs response time, detectors that exploit this bias-enhanced surface emission from nanoscale vacuum gaps could prove to be useful for communication, petahertz electronics, and ultrafast optical-field-resolved metrology.

Spectral normalization in dual-comb spectroscopy of acetylene using a liquid nitrogen trap

Feng-Lei Hong, hideki kato, Yohei Sugiyama, and Kazumichi Yoshii

DOI: 10.1364/JOSAB.418681 Received 04 Jan 2021; Accepted 28 Jan 2021; Posted 29 Jan 2021  View: PDF

Abstract: We demonstrate spectral normalization in dual-comb spectroscopy of acetylene using a sealed gas cell and liquid nitrogen trap. The normalized spectra of the P- and R-branches of the ν₁ + ν₃ vibration band of ¹²C₂H₂ were observed at a comb repetition rate of 19.8 MHz. We also observed instantaneous pressure changes inside the cell during the cooling of the liquid nitrogen trap, with different averaging times.

Focusing cylindrical vector beams with fractional order

Vladislav Zaitsev, Sergey Stafeev, Victor Kotlyar, and Anton Nalimov

DOI: 10.1364/JOSAB.413581 Received 27 Oct 2020; Accepted 12 Jan 2021; Posted 16 Feb 2021  View: PDF

Abstract: By simulating tight focusing of vector beams with azimuthal polarization of fractional order 0 < m <1 (m = 1 is azimuthal polarization, m = 0 is linear polarization), it is shown that the shape of the intensity distribution in the focal spot changes from elliptical (m = 0) to round (m = 0.5) and ends with an annular ring (m = 1). The shape of the distribution of the longitudinal component of the Poynting vector (energy flux) in the focal spot changes in a different way: from circular (m = 0) to elliptical (m = 0.5) and ends in an annular ring (m = 1). The diameter of the focal spot at full width at half maximum for a beam with azimuthal polarization (m = 1) with an optical vortex of the first order for a numerical aperture NA = 0.95 is 0.46 of the wavelength, and the diameter of the axial energy flux for linearly polarized light (m = 0) is 0.45 of the wavelength. Therefore, the answers to the questions: Whether the focal spot is round or elliptical and whether the focal spot is minimal: with azimuthal polarization with a vortex or with linear polarization without a vortex, depend on whether we are considering the intensity at the focus or the energy flow. In the second simulation, the effect of the deviation of the beam order from m = 2 (i.e., the case when the backflow is observed at the center of the focal spot) was investigated. It was shown that for integer values of the beam order, the transverse components of the Poynting vector are equal to zero, but for fractional values, they are not.

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