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High-Q, low-mode-volume microsphere-integrated Fabry-Pérot cavity for optofluidic lasing applications

Xiaoqin Wu, Yipei Wang, Qiushu Chen, YU-CHENG CHEN, Xuzhou Li, Limin Tong, and Xudong Fan

Doc ID: 346083 Received 17 Sep 2018; Accepted 14 Nov 2018; Posted 16 Nov 2018  View: PDF

Abstract: We develop a hybrid optofluidic microcavity by placing a microsphere with a diameter ranging in 1-4 μm in a liquid-filled plano-plano Fabry-Pérot (FP) cavities, which can provide an extremely low effective mode volume down to 0.3-5.1 μm^3 while maintaining a high Q-factor up to 1х10^4-5х10^4 and a finesse of ~2000. Compared to the pure plano-plano FP cavities that are known to suffer from the lack of mode confinement, diffraction and geometrical walk-off losses, and being highly susceptible to mirror misalignment, our microsphere-integrated FP (MIFP) cavities show strong optical confinement in the lateral direction with a tight mode radius of only 0.4-0.9 μm, and high tolerance to mirror misalignment as large as 2°. With the microsphere serving as a waveguide, the MIFP is advantageous over a fiber-sandwiched FP cavity due to the open-cavity design for analytes/liquids to interact strongly with the resonant mode, the ease of assembly, and the possibility to replace the microsphere. In this work, the main characteristics of the MIFP, including Q-factor, finesse, effective mode radius and volume, and their dependence on surrounding medium refractive index, mirror spacing, microsphere position inside the FP cavity, and mirror misalignment, are systematically investigated using a finite-element method. Then, by inserting dye-doped polystyrene microspheres of various sizes into the FP cavity filled with water, we experimentally realize single-mode MIFP optofluidic lasers that have a lasing threshold as low as a few μJ/mm2 and a lasing spot radius of only ~0.5 μm. Our results suggest that the MIFP cavities provide a promising technology platform for novel photonic devices and biological/chemical detection with ultra-small detection volumes.

Transmission characteristics of high-order mode in all few-mode fiber laser cavities

Teng Wang, Ao Yang, Fan Shi, Yiping Huang, Jianxiang Wen, and Xianglong Zeng

Doc ID: 346426 Received 20 Sep 2018; Accepted 12 Nov 2018; Posted 13 Nov 2018  View: PDF

Abstract: We experimentally demonstrate two kinds of all few-mode fiber (FMF) ring lasers with high-order mode (HOM) oscillation in the laser cavity to study the HOM transmission characteristics. One is a switchable wavelength all-FMF HOM laser with an output of tunable optical vortex beams (OVBs), the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams (CVBs). The lasers are composed of all-FMF components and few mode erbium-doped fiber. A Sagnac interferometer made of 3-dB FMF coupler functions as the wavelength selector and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube based saturable absorber and nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. To the best of authors’ knowledge, this is the first report on the research of transmission characteristics of HOM in all-FMF laser cavities.

Antenna assisted subwavelength metal-InGaAs-metal structure for sensitive and direct photodetection of millimeter and terahertz waves

Jinchao Tong, Yue Qu, FEI SUO, wei zhou, Zhiming Huang, and Dao Hua ZHANG

Doc ID: 346503 Received 21 Sep 2018; Accepted 11 Nov 2018; Posted 13 Nov 2018  View: PDF

Abstract: Millimeter & terahertz wave photodetectors have a wide range of applications. However, the state of the art techniques lags far behind the urgent demand due to structure and performance limitation. Here, we report sensitive and direct millimeter & terahertz wave photodetection in compact InGaAs-based subwavelength ohmic metal-semiconductor-metal structures. The photoresponse originates from unidirectional transportation of nonequilibrium electrons induced by surface plasmon polaritons under irradiation. The detected quantum energies of electromagnetic waves are far below the bandgap of InGaAs, offering novel direct photoelectric conversion pathway for InGaAs beyond its bandgap limit. The achieved room-temperature rise time and noise equivalent power (NEP) of the detector are 45 µs and 20 pW Hz-1/2, respectively at 0.0375 THz (8 mm) wave. The detected wavelength is tunable by mounting different coupling antennas. Room temperature terahertz imaging of macroscopic samples at around 0.166 THz is also demonstrated. This work opens an avenue for sensitive uncooled millimeter & terahertz focal planar arrays.

Ultra-compact fiber laser based on highly integrated optical device

Xiaoxiang Han and Xueming Liu

Doc ID: 340462 Received 24 Jul 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: Ultrafast fiber laser has attracted a great deal of research interests due to its low cost, high efficiency, and simple maintaining. Optical passive devices are vital parts of fiber laser. In order to obtain fiber laser with high quality, optical passive devices with high performance are required. Here, we demonstrate a highly integrated optical device with the combination of saturable absorber (SA), coupler, isolator, wavelength division multiplexer (WDM), and erbium-doped fiber (EDF). The built-in SA can withstand high pump power due to the unique structure of proposed device. The proposed device is applied to an ultra-compact fiber laser, which greatly simplify the laser structure and reduce the size of proposed laser. The proposed device has great potential for application in high-power and high-frequency fiber lasers. The proposed ultra-compact fiber laser has important application in optical communication, optical sensing, optical frequency comb, and micromachining.

Complementary transmissive ultra-thin metalenses for broadband polarization-independent refractions

Yueyi Yuan, Kuang Zhang, XUMIN DING, Badreddine Ratni, Shah Nawaz Burokur, and Qun Wu

Doc ID: 341471 Received 03 Aug 2018; Accepted 06 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: Polarization manipulation is a significant issue for artificial modulation of electromagnetic (EM) wave, but general mechanisms are all suffering the restriction of inherent symmetric properties between opposite handedness. Herein, a strategy to independently and arbitrarily manipulate the electromagnetic wave with orthogonal circular polarizations based on metasurface is proposed, which effectually break through traditional symmetrical characteristics between different handedness. By synthesizing propagation and geometric phases, appropriate Jones matrix is calculated to obtain independent wavefront manipulation of EM waves with opposite circular polarizations. Two transmissive ultra-thin metalenses are proposed to demonstrate the asymmetrical refraction of transmitted circularly polarized waves. Simulated transmitted phase front and measured far-field intensity distributions are in excellent agreement, indicating that the transmitted wave with different polarizations can be refracted into arbitrary and independent directions within a wide frequency band (relative bandwidth of 25%). The results presented in this paper provide more freedoms for the manipulation of electromagnetic waves, and motivate the realizations of various polarization-independent properties during all the frequency spectrum.

Wideband tunable passively Q-switched fiber laser in 3 μm region using a broadband carbon nanotube saturable absorber

Chen Wei, Yanjia Lyu, Han Zhang, Zhe Kang, Guanshi Qin, and Yong Liu

Doc ID: 344330 Received 28 Aug 2018; Accepted 02 Nov 2018; Posted 02 Nov 2018  View: PDF

Abstract: We propose and demonstrate a widely tunable passively Q-switched Ho3+/Pr3+-codoped ZBLAN fiber laser operating at ~3 μm mid-infrared (MIR) waveband based on a single-walled carbon nanotube (SWCNT) saturable absorber (SA). The SWCNTs have diameters ranging from 1.4 to 1.7 nm. The modulation depth and saturation intensity of the SWCNT SA measured at 2850 nm are 16.5% and 1.66 MW/cm2, respectively. Stable Q-switched pulses with the shortest pulse duration of 1.46 μs and the maximum pulse energy of 0.43 μJ are achieved at a launched pump power of 445.6 mW. The combined use of a broadband SWCNT SA and a plane ruled grating ensures a broad continuously tuning range of 55.0 nm from 2837.6 to 2892.6 nm. The output powers, emission spectra, repetition rates, and pulse durations at different tuning wavelengths are also characterized and analyzed. Our results indicate that SWCNTs can be excellent broadband SAs in the 3 μm MIR region. To the author’s knowledge, this is the first demonstration of a widely tunable carbon nanotubes enabled passively Q-switched fiber laser operating in the 3 μm MIR spectral range.

Generation and measurement of arbitrary four-dimensional spatial entanglement between photons in multi-core fibers

Hee Su Park and Hee Jung Lee

Doc ID: 347271 Received 02 Oct 2018; Accepted 01 Nov 2018; Posted 02 Nov 2018  View: PDF

Abstract: High-dimensional entanglement is a valuable resource for secure and efficient quantum information processing. A major challenge for practical use of multi-dimensional quantum systems is the establishment of controls over arbitrary superposition states in realistic conditions. This work demonstrates spatially entangled photon pairs propagating through two separate four-core optical fibers with the amplitudes and phases of the superposition being independently controllable. Using quantum state analyzers that can detect arbitrary multi-core superposition states, Bell-type CGLMP inequalities in two, three, and four dimensions are directly tested. Enhanced violation of the inequality by slight non-maximality of entanglement is also demonstrated.

Plasmonic resonant nonlinearity and synthetic optical properties in gold nanorod suspensions

Huizhong Xu, Pepito Jr. Alvaro, Yinxiao Xiang, Trevor Kelly, Yuxuan Ren, Chensong Zhang, and Zhigang Chen

Doc ID: 344401 Received 28 Aug 2018; Accepted 31 Oct 2018; Posted 02 Nov 2018  View: PDF

Abstract: We experimentally demonstrate self-trapping of light in both aqueous and organic (toluene) suspensions of gold nanorods due to plasmonic resonant optical nonlinearity. The threshold power for soliton formation is greatly reduced in toluene as opposed to aqueous suspensions. Surprisingly, as we tune the wavelength of the optical beam from a CW laser, we find that the threshold power is reduced by more than three-fold at the plasmonic resonance frequency, although the optical gradient forces are optimized at other wavelengths where nanorods exhibit strong positive or negative polarizabilities. By analyzing the optical forces and torque acting on the nanorods and associated rotational potential energy, we show theoretically that it is possible to align the nanorods inside a soliton channel into orthogonal orientations merely using two different wavelengths of the laser. We perform a series of experiments to examine the transmission of the soliton-forming beam itself as well as the polarization transmission spectrum of a low-power probe beam guided along the soliton channel, and find that the expected synthetic anisotropic properties are too subtle to be observed clearly. The ability to achieve tunable nonlinearity and nanorod orientations in colloidal nanosuspensions with low-power CW laser beams may lead to many interesting applications.

Optically induced rotation of Rayleigh particles by arbitrary photonic spin

Guanghao Rui, Ying Li, Sichao zhou, Yusong Wang, Gu Bing, Yiping Cui, and Qiwen Zhan

Doc ID: 341017 Received 06 Aug 2018; Accepted 31 Oct 2018; Posted 02 Nov 2018  View: PDF

Abstract: Optical trapping techniques have been of great interests and advantages that enable the direct handling of nanoparticles. In this work, we study the optical trapping effects of diffraction limited focal field possesses arbitrary photonic spin, and propose a convenient method to manipulate the movement behavior of the trapped nanoparticle. In order to achieve controllable spin axis orientation and ellipticity of the tightly focused beam in three dimensions, an efficient method to analytically calculate and experimentally generate complex optical field at the pupil plane of a high numerical aperture lens is developed. By numerically calculating the optical forces and torques of Rayleigh particle with spherical/ellipsoidal shape, we demonstrate that the interactions between the tunable photonic spin and the nanoparticles lead to not only three-dimensional trapping, but also the precise control of the nanoparticle’s movement in terms of stable orientation, rotational orientation and rotation frequency. This versatile trapping method may open up new avenues for optical trapping and their applications in various scientific fields.

Stimulated Brillouin scattering induced all-optical modulation in graphene microfiber

Jiwen Zhu, xue cheng, Yali Liu, Ruiduo Wang, Man Jiang, Diao Li, Baole Lu, and Zhaoyu Ren

Doc ID: 341537 Received 03 Aug 2018; Accepted 30 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Graphene microfibers are burgeoning modulators with great potential in all-optical communication. One of the critical issues remains to be understood is the dynamic mechanism of light-graphene interaction. Here, we propose a power dependent modulation by using 980 nm pump light and 1064 nm signal light via graphene microfiber, and the results show a strong transmission reduction and frequency blue-shift as the increase of pump power. The experimental observation is attributed to a Stimulated Brillouin Scattering (SBS) process induced by the pump light. Power and frequency variation are a result of energy transition of the scattered phonon in the fiber. This work reveals the nonlinear effect process in the light-graphene interaction and provides a new method for power and frequency control with graphene all-optical modulation.

Intermodal group velocity engineering for broadband nonlinear optics

Jeffrey Demas, Lars Rishoj, Xiao Liu, Gautam Prabhakar, and Siddharth Ramachandran

Doc ID: 344703 Received 31 Aug 2018; Accepted 28 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Interest in the nonlinear properties of multi-mode optical waveguides has seen a recent resurgence on account of the large dimensionality afforded by the platform. The large volume of modes in these waveguides provide a new spatial degree of freedom for phase matching nonlinear optical processes. However, this spatial dimension is quantized, which narrows the conversion bandwidths of intermodal processes and constrains spectral and temporal tailoring of the light. Here we show that by engineering the relative group velocity within the spatial dimension, we can tailor the phase matching bandwidth of intermodal parametric nonlinearities. We demonstrate group-velocity-tailored parametric nonlinear mixing between higher-order modes in a multi-mode fiber with gain bandwidths that are more than an order of magnitude larger than that previously thought possible for intermodal four-wave mixing. As evidence of the technological utility of this methodology, we seed this process to generate the first high-peak-power wavelength-tunable all-fiber quasi-CW laser in the Ti:Sapphire wavelength regime. More generally, with the combination of intermodal interactions, which dramatically expand the phase matching degrees of freedom for nonlinear optics, and intermodal group velocity engineering, which enables tailoring the bandwidth of such interactions, we showcase a platform for nonlinear optics that can be broadband while being wavelength-agnostic.

Auxiliary-cavity-assisted vacuum Rabi splitting of semiconductor quantum dot in a photonic crystal nanocavity

Huajun Chen

Doc ID: 345940 Received 14 Sep 2018; Accepted 27 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: The coherent light-matter interaction has drawn enormous attention for its fundamental importance in cavity quantum-electrodynamics (C-QED) field and great potentials in quantum information applications. Here, we design a hybrid C-QED system consisting of a quantum dot (QD) driven by two-tone fields implanted in a photonic crystal (PhC) cavity is coupled to an auxiliary cavity with a single-mode waveguide, and investigate the hybrid system operating in the weak, intermediate and strong coupling regimes of the light-matter interaction via comparing the QD-photon interaction with dipole decay rate and the cavity field decay rate. The results indicate that the auxiliary cavity play a key role in the hybrid system, which affords a quantum channel to influence the absorption of the probe field. With controlling the coupling strength between the auxiliary cavity and the PhC cavity, the phenomenon of Mollow triplet can appear in the intermediate coupling regime even in the weak coupling regime. We further study the strong coupling interaction manifested by vacuum Rabi splitting (VRS) in the absorption with manipulating the cavity-cavity coupling under different parameters regime. This study provides a promising platform for understanding the dynamics of QD-CQED systems and paving the way towards on-chip QD-based nano-photonic devices.

Fabrication and properties of high quality InGaN-based LEDs with highly reflective nanoporous GaN mirrors

dezhong cao, Xiaokun Yang, lvyang shen, chongchong zhao, caina luan, Jin Ma, and Hongdi Xiao

Doc ID: 332758 Received 11 Jun 2018; Accepted 25 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Distributed Bragg reflectors (DBRs) are essential components for the development of optoelectronic devices. In this paper, we first report the use of the nanoporous GaN (NP-GaN) DBR as a template in growth of InGaN-based light emitting diode (LED). The wafer-scale NP-GaN DBR, which is fabricated by an electrochemical (EC) etching in a neutral solution for the first time, has smooth surface, high reflectivity (> 99.5%), and wide spectral stop-band widths (> 70 nm). Compared to the LED film regrown on unetched GaN thin film, the LED regrown on the DBR structure exhibits smoother surface and 5-fold enhancement in photoluminescence (PL) intensity. The performance enhancement is attributed to light reflection effect of the NP-GaN DBR and improved crystalline quality which can be further confirmed by PL lifetime.

Graphene-loaded metal wire grating for deep and broadband THz modulation in total internal reflection geometry

Yiwen SUN, Riccardo Degl'Innocenti, David Ritchie, Harvey Beere, Long Xiao, Michael Ruggiero, Axel Zeitler, Rayko Stantchev, Danni Chen, Emma Pickwell-MacPherson, Zhengchun Peng, and Xudong Liu

Doc ID: 342721 Received 20 Aug 2018; Accepted 24 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realise deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in the TIR geometry and in the subwavelength wire grating was combined to demonstrate a ~77% modulation depth (MD) in the frequency range of 0.2-1.4 THz. This MD, achieved electrically with SiO2/Si gated graphene device, was 4.5 times higher than the device without metal grating in transmission geometry. By optimizing the parameters of metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging.

Surface-related synergistic nonlinear optical enhancement of graphene/CdS nanohybrids under single pulse laser irradiation

Baohua Zhu, Fangfang Wang, Guixia Wang, and Yuzong Gu

Doc ID: 335482 Received 21 Jun 2018; Accepted 17 Oct 2018; Posted 18 Oct 2018  View: PDF

Abstract: Surface states is very important for altering the nonlinear optical (NLO) properties of graphene. To investigate the correlation between surface structure and the synergistic NLO response in graphene-based nanocomposites, we attached CdS nanocrystals on the surface of graphene (G) and prepared G/CdS nanohybrids (NHs) consisting of various oxygen-containing functional groups via chemical method. The NLO absorption and NLO refraction of G/CdS NHs under single pulse laser irradiation are enhanced 17.5 times with the concentration decrease of surface oxygen-containing groups, which might be attributed to the local field effects and synergetic effects stemming from charge transfer between the two components. But the optical nonlinearity is decreased with further concentration decrease, which might arise from sp2 fragments interconnection and surface defects in NHs. The NLO absorption transformation from two-photon absorption to saturable absorption with oxygen decrease is observed, and intensity-related NLO absorption and refraction in NHs are also discussed. Meanwhile, the G/CdS NHs exhibit superior NLO properties, implying the potential applications of this NHs material in NLO devices.

Phase-modulation nested structure optical fields for extending optical filament

Hui-Tian Wang, Jia-Qi Lv, Ping-Ping Li, Dan Wang, Chenghou Tu, and Yongnan Li

Doc ID: 339912 Received 18 Jul 2018; Accepted 17 Oct 2018; Posted 18 Oct 2018  View: PDF

Abstract: Extending the propagation length of femtosecond laser filamentation has always been expected since the needs in practical application. Here we achieve experimentally and theoretically great extending of single filament in BK7 glass by using phase modulated nested structure optical fields. The function for realizing the arising of filamentation and following energy replenishment are assembled in one nested optical field. The common path generating system insures the stability of generated filaments while the adjustable parameters provide the possibility to find the longest high-quality filament under the constraint of finite input power. Beside the significance of continuous replenishment has been discussed and the potential of generating more extended filament has been predicted.

Embedded whispering-gallery mode microsphere resonator in a tapered hollow annular core fiber

Jiawei Wang, Xiaobei Zhang, Ming Yan, Lei Yang, Fengyu Hou, Wen Sun, Xiaotong Zhang, Libo Yuan, Hai Xiao, and Tingyun Wang

Doc ID: 344719 Received 31 Aug 2018; Accepted 13 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We propose and demonstrate a tapered hollow annular core fiber (HACF) coupler for excitation of whispering-gallery modes (WGMs) of an embedded microsphere resonator. The coupler is simply fabricated by fusing splicing a segment of HACF with the single mode fiber (SMF), and then improved by tapering the splicing joint to reduce the cone-apex angle. Therefore, the coupling efficiency from the SMF to HACF is enhanced to excite various WGMs via evanescent field coupling. Normal positive, negative symmetrical Lorentzian and asymmetric Fano line shapes can be obtained by varying the resonator size and location. Another interesting phenomenon is observed that a higher Q-factor mode in a lower Q-factor mode has a contrast as high as 58. Temperature sensing with good stability is also demonstrated. This embedded WGM microsphere resonator in the tapered HACF is expected to promote the environmental adaptability in the practical application due to its simplify and robustness.

High efficient generation of tunable ellipse perfect vector beams

CHENLIANG CHANG, LIN Li, Caojin Yuan, Shaoteng Feng, Shouping Nie, Hui-Tian Wang, Jianping Ding, and Zhi-Cheng Ren

Doc ID: 335066 Received 13 Jun 2018; Accepted 12 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: We present a method of generating and shaping ellipse perfect vector beams (EPVB) with prescribed ellipse intensity profile and continuously variant linear polarization state. The scheme is based on the coaxial superposition of two orthogonally polarized ellipse laser beams of controllable phase vortex serving as base vector components. The phase-only CGH is specifically designed by means of a modified iteration algorithm involving complex amplitude constraint, which is able to generate EPVB with high diffraction efficiency in the vector optical field generator. We also discuss and demonstrate the simultaneous shaping of multiple EPVBs with independent tunable ellipticity and polarization vortex in both of transversal (2D) and axial (3D) focusing structures, proving potentials in a variety of polarization-mediated applications such as trapping and transportation of particles in a more complex geometry circumstances.

Resonance-assisted light-control-light characteristics of SnS₂ on microfiber knot resonator with fast response

Huihui Lu, zhongmin wang, zhijin huang, jun tao, hanqing xiong, Wentao Qiu, Heyuan Guan, Huazhuo Dong, Jiangli Dong, Wenguo Zhu, JianHui Yu, Yongchun Zhong, Yunhan Luo, Jun Zhang, and zhe chen

Doc ID: 347500 Received 04 Oct 2018; Accepted 08 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: An all optical light-control-light functionality with a structure of microfiber knot resonator (MKR) coated with tin disulfide (SnS₂) nanosheets is experimentally demonstrated. The evanescent light in the MKR (with a resonance Q of ~ 59,000 and an extinction ratio (ER) of ~ 26 dB) is exploited to enhance light matter interaction by coating a two dimensional material SnS₂ nanosheet onto it. Thanks to the enhanced light-matter interaction and the strong absorption property of SnS₂, the transmitted optical power can be tuned quasi linearly with an external violet pump light power where a transmitted optical power variation rate ΔT with respect to violet light power of ~ 0.22 dB/mW is obtained. In addition, the MKR structure possessing multiple resonances enables a direct experimental demonstration of the relationship between resonance properties (such as Q and ER etc) and the obtained ΔT variation rate with respect to violet light power. It verifies experimentally that a higher resonance Q and a larger ER can lead to a higher ΔT variation rate. In terms of the operating speed, this device runs as fast as ~ 3.2 ms. This kind of all optical light-control-light functional structure may find applications in future all optical circuitry and hand held fiber sensors etc.

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