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Accepted papers to appear in an upcoming issue

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Enhanced Four-Wave Mixing Process Near the Excitonic Resonances of Bulk MoS₂

Brian Ko, Alexei Sokolov, Marlan Scully, Zhang Rong, and Ho Wai Lee

Doc ID: 349643 Received 31 Oct 2018; Accepted 11 Dec 2018; Posted 11 Dec 2018  View: PDF

Abstract: Two-dimensional materials are generating great interest due to their unique electrical and optical properties. In particular, transitional metal dichalcogenides such as MoS₂ are an attractive material due to the existence of a direct band gap in the monolayer limit that can be used to enhance nonlinear optical phenomena, such as Raman spectroscopy. Here, we have investigated four-wave mixing processes in bulk MoS₂ using a multiplex coherent anti-Stokes Raman spectroscopy setup. The observed four-wave mixing signal has a resonance at approximately 680 nm, corresponding to the energy of the A excitonic transition of MoS₂. This resonance can be attributed to the increased third-order nonlinear susceptibility at wavelengths near the excitonic transition. This phenomenon could open the path to using MoS₂ as a substrate for enhancing four-wave mixing processes such as coherent anti-Stokes Raman spectroscopy.

Wideband adaptive microwave frequency identification using an integrated silicon photonic scanning filter

Xu Wang, Feng Zhou, Dingshan Gao, Yanxian Wei, Xi Xiao, Shaohua Yu, Jianji Dong, and Xinliang Zhang

Doc ID: 345236 Received 06 Sep 2018; Accepted 09 Dec 2018; Posted 11 Dec 2018  View: PDF

Abstract: Photonic-assisted microwave frequency identification with distinct features including wide frequency coverage and fast tunability, has been conceived as a key technique for applications such as cognitive radio and dynamic spectrum access. The implementations based on the compact integrated photonic chips have exhibited intriguing advantages in footprint miniaturization, light weight and low power consumption, in stark contrast to the discrete optical-fiber-based realization. However, the reported chip-based instantaneous frequency measurements can only operate at a single-tone input, which stringently limits their practical deployment that require wideband identification capability in modern RF and microwave applications. In this article, we demonstrate, for the first time, a wideband, adaptive microwave frequency identification solution based on a silicon photonic integrated chip, enabling the identification of different types of microwave signals from 1 to 30 GHz, including single-frequency, multiple-frequency, chirped-frequency, frequency-hopping microwave signals, and even their combinations. The key component is a high-Q-factor scanning filter based on a silicon microring resonator, which is used to implement frequency-to-time mapping. This demonstration opens the door to a monolithic silicon platform that enable the wideband, adaptive and high speed signal identification subsystem with a high resolution and a low SWaP for mobile and avionic applications.

Effective suppression of stimulated Raman scattering in half 10 kilowatt tandem pumping fiber lasers using chirped and tilted fiber Bragg gratings

Meng Wang, Zefeng Wang, Le Liu, Qihao Hu, Hu Xiao, and Xiaojun Xu

Doc ID: 347322 Received 02 Oct 2018; Accepted 08 Dec 2018; Posted 11 Dec 2018  View: PDF

Abstract: The average power of fiber lasers have been scaled deep into the kW regime in the past years. However, stimulated Raman scattering (SRS) is a major factor limiting the further power scaling. Here, we have demonstrated for the first time, to the best of our knowledge, the suppression of SRS in a half 10 kilowatt tandem pumping fiber amplifier using chirped and tilted fiber Bragg gratings (CTFBGs). With specially self-designed and manufactured CTFBGs inserted between the seed laser and the amplifier stage, a maximum SRS suppression ratio of >15 dB in spectrum is observed with no reduce in laser efficiency. With one CTFBG, the effective output power is improved to 3.9 kW with beam quality M2 factor of ~1.7 from <3.5 kW with M2 factor of >2; with two CTFBGs, the effective laser power reaches to 4.2 kW with an increasing ratio of 20% and M2 factor of ~1.8, and further power promotion is limited by the power and performance of the 1018 nm pump sources. This work provides an effective SRS suppression method for high-power all-fiber lasers, which is very useful for the further power scaling of these systems.

High-power and high-energy laser generation at 1834 nm in a Nd:YAG single-crystal fiber laser oscillator

Bin Xu, yaqi cai, Yunshan Zhang, qingyu tian, Xiaodong Xu, Qingsong Song, Dongzhen Li, Jun Xu, and Ivan Buchvarov

Doc ID: 351312 Received 08 Nov 2018; Accepted 06 Dec 2018; Posted 07 Dec 2018  View: PDF

Abstract: We report on diode-end-pumped high-power and high-energy Nd:YAG single-crystal fiber laser at 1834 nm. Two 808-nm diodes injecting about 58-W pump power into the Nd:YAG fiber have generated 3.28-W continuous-wave and 1.66-W Cr:ZnSe-based passively Q-switched lasers. Slope efficiencies with respect to pump powers are 8.7% for the continuous-wave laser and 4.9% for the Q-switched laser. The extracted maximum pulse energy is about 266.9 μJ and the corresponding maximum pulse peak power is 2.54 kW. These performances greatly surpass previous results regarding this specific laser emission because laser gain medium in the form of fiber can significantly mitigate thermally induced power saturation thanks to its significantly reduced thermal lensing effect. Single-crystal fiber lasers show great potential for high average power, pulse energy and peak power.

Silicon on insulator based microwave photonic filter with widely adjustable bandwidth

Lu Xu, Jie Hou, Haitao Tang, Yuan Yu, Yu Yu, Xuewen Shu, and Xinliang Zhang

Doc ID: 340537 Received 25 Jul 2018; Accepted 04 Dec 2018; Posted 05 Dec 2018  View: PDF

Abstract: We demonstrate a silicon based microwave photonic filter (MPF) with flat-top passband and adjustable bandwidth. The proposed MPF is realized by using a tenth-order microring resonator (MRR) and a photodetector (PD), both of which are integrated on a photonic chip. The full width at half maximum (FWHM) bandwidth of the optical filter achieved at the drop port of the tenth-order MRR is 21.6 GHz. The ripple of the passband is less than 0.3 dB while the rejection ratio is 32 dB. By adjusting the deviation of the optical carrier wavelength from the center wavelength of the optical bandpass filter, the bandwidth of the MPF can be greatly changed. In the experiment, the FWHM bandwidth of the proposed MPF is tuned from 5.3 to 19.5 GHz and the rejection ratio is higher than 30 dB.

Self-Powered Lead-Free Quantum Dot Plasmonic Phototransistor with Multi-Wavelength Response

yu yu, Yating Zhang, lufan King, Zhiliang Chen, Yifan Li, Qingyan Li, Mingxuan Cao, Yongli Che, Haitao Dai, Junbo Yang, and Jian-Quan Yao

Doc ID: 344728 Received 05 Sep 2018; Accepted 28 Nov 2018; Posted 30 Nov 2018  View: PDF

Abstract: Possessing with excellent visible light absorption properties, lead-free colloidal copper-based chalcogenide quantum dots (QDs) have emerged in photoelectronic fields. By means of localized surface plasmonic resonance (LSPR), the absorption properties of QDs can be enhanced. In this paper, we fabricate lead-free CuInSe2 QDs field effect phototransistor (FEpT) by utilizing the enhancement of LSPR of Au nanoparticles (NPs). The plasmonic FEpT demonstrates responsivity up to 2.7 μAW–1 and a specific detectivity of 7×103 Jones at zero bias, which are enhanced by approximate 200 % times than devices without Au NPs. Particularly, the FEpT exhibits multi-wavelength response, which is photoresponsive to the 405 nm, 532 nm and 808 nm irradiations, and presents stability and reproducibility in the progress of ON-OFF cycles. Furthermore, the enhancement induced by Au NPs LSPR can be interpreted by finite-difference time domain (FDTD) simulations. The low cost solution-based process and excellent device performance strongly underscore lead-free CuInSe2 quantum dot as a promising material for self-powered photoelectronic applications, which can be further enhanced by Au NPs LSPR. © 2018 Chinese Laser Press

Vertical-cavity surface-emitting lasers for data communication and sensing

Anjin Liu, Philip Wolf, James Lott, and Dieter Bimberg

Doc ID: 352384 Received 07 Sep 2018; Accepted 27 Nov 2018; Posted 30 Nov 2018  View: PDF

Abstract: Vertical-cavity surface-emitting lasers (VCSELs) are the ideal optical sources for data communication and sensing. In data communications, large data rates, combined with excellent energy efficiency and temperature stability have been achieved based on advanced device design and modulation formats. VCSELs are also promising sources for photonic integrated circuits due to their small footprint and low power consumption. Also, VCSELs are commonly used for a wide variety of applications in the consumer electronics market. These applications range from laser mice to three-dimensional (3D) sensing and imaging, including various 3D movement detection, such as gesture recognition, or face recognition. Novel VCSEL types will include metastructures, exhibiting additional unique properties, of largest importance for next generation data communication, sensing, and photonic integrated circuits.

Bound states of solitons in a harmonic graphene-mode-locked fiber laser

Daniel Popa, Bo Fu, Jin Li, and Zhang Cao

Doc ID: 348920 Received 26 Oct 2018; Accepted 25 Nov 2018; Posted 30 Nov 2018  View: PDF

Abstract: We report bound states of solitons from a harmonic mode-locked fiber laser based on a graphene saturable absorber. A simple all-fiber ring cavity exploits a graphene-based solution for both bound states and harmonic mode-locking generation. The laser generates stable bound states of solitons 26.2 ps apart with 720 fs duration. Harmonic mode-locking, corresponding to the 26th harmonic, is also detected with 409.6 MHz repetition rate. This is a low-cost, versatile multi-function laser that could be used for many applications.

Wide tunable laser based on electrically regulated bandwidth broadening in polymer-stabilized cholesteric liquid crystal

Hongbo Lu, Cheng Wei, Qiang Zhang, Miao Xu, Yunsheng Ding, Guobing Zhang, Jun Zhu, Kang Xie, Xiaojuan Zhang, Zhijia Hu, and Longzhen Qiu

Doc ID: 348249 Received 15 Oct 2018; Accepted 24 Nov 2018; Posted 30 Nov 2018  View: PDF

Abstract: Electrically responsive photonic crystals represent one of the most promising intelligent material candidates for technological applications in optoelectronics. In this research, dye doped polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy were fabricated, and mirrorless lasing with electrically tunable wavelength was successfully achieved. Unlike the conventional LC lasers, the proposed laser aided in tuning the emission wavelength though controlling the reflection bandwidth based on gradient pitch distribution. The principal advantage of the electrically controlled dye doped PSCLC laser is that the electric field is applied parallel to the helical axis, which changes the pitch gradient instead of rotating the helix axis, thus preserving the heliconical structure intact to lasing. The broad tuning range (~110 nm) of PSCLC lasers, coupled with stable emission performance, continuous tunability, and easy fabrication lead to its enormous potential application in intelligent optoelectronic devices, such as sensing, medical, and display.

Kelly sidebands suppression and wavelength tuning of conventional soliton in a Tm-doped hybrid mode-locked fiber laser with all-fiber Lyot filter

Jianfeng Li, Yazhou Wang, Hongyu Luo, Yong Liu, Zhijun Yan, Zhongyuan Sun, and Lin Zhang

Doc ID: 343083 Received 23 Aug 2018; Accepted 19 Nov 2018; Posted 20 Nov 2018  View: PDF

Abstract: We demonstrate a stable conventional soliton in a Tm-doped hybrid mode-locked fiber laser by employing a home-made all-fiber Lyot-filter (AFLF) and a single-wall carbon nanotube (SWCNT). The AFLF, designed by sandwiching a piece of polarization maintained fiber (PMF) with two 45° tilted fiber gratings (45°-TFGs) which inscribed by a UV laser in PMF with phase-mask scanning technique, shows large filter depth of ~9 dB and small insertion loss of ~0.8dB. By optimizing the free spectral range (FSR) of the AFLF, the Kelly sidebands of conventional soliton centered at 1966.4 nm can be dramatically suppressed without impairing the main shape of soliton spectrum. It gives the pulse duration of 1.18ps and bandwidth of 3.8 nm. By adjusting the temperature of the PM fiber of the AFLF from 7 °C to 60 °C, wavelength tunable soliton pulses ranging from 1971.62 nm to 1952.63 nm are also obtained. The generated soliton pulses can be precisely tuned between 1971.62 nm and 1952.63 nm by controlling the temperature of the AFLF.

Vacuum-Ultraviolet Photovoltaic Arrays

Feng Huang, Wei Zheng, Richeng Lin, and Lemin Jia

Doc ID: 345923 Received 14 Sep 2018; Accepted 19 Nov 2018; Posted 20 Nov 2018  View: PDF

Abstract: As one of the most ideal tools for monitoring the formation and evolution of solar storms, vacuum ultraviolet (VUV) detector should be both of fast temporal response and with an array structure that enables image formation. Here, by combining non-traditional graphene processing technique with traditional MOCVD epitaxy technology, we created hybrid-heterostructure (HH) arrays of p-Gr/AlN/p-Si with VUV photovoltaic response capability and silicon integration potential. The HH arrays not only exhibit ultra-fast temporal response (rise time of only 120 ns) and extremely high Ion/Ioff ratio of 107, but also achieve the imaging demonstration of VUV pattern for the first time. The technique of hybrid heterostructure provides a possible new path for the development of VUV imaging devices.

Observation of Controllable Tightly and Loosely Bound Solitons with An All-Fiber Saturable Absorber

tianyu zhu, Wang Zhaokun, Dongning Wang, Fan Yang, and liujiang Li

Doc ID: 348021 Received 11 Oct 2018; Accepted 19 Nov 2018; Posted 20 Nov 2018  View: PDF

Abstract: A hybrid no-core fiber (NCF) - graded index multimode fiber (GIMF) structure is used as a saturable absorber (SA) for mode-locked laser operation. Such a SA supports various types of soliton outputs. By changing the cavity parameters, not only the spatiotemporal mode-locking states with a stable single pulse but also tightly and loosely bound solitons are generated. Single 35.5 pJ solitons centered at 1568.5 nm have a 4 nm spectral full-width half-maximum (FWHM) value and an 818 fs temporal duration. Tightly bound soliton pairs with continuously tunable wavelength from 1567.48 to 1576.20 nm, featured with ∼700 fs pulse train with separation of 2.07 ps have been observed by stretching the NCF-GIMF structured device. Meanwhile, several different pulse separations from 37.57 to 56.46 ps of loosely bound solitons have also realized. The results obtained help in understanding the nonlinear dynamics in fiber lasers.

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.

Efficient InGaN based Yellow Light-emitting Diodes

Fengyi Jiang, Jun Liu, Zhang jianli, Xu Longquan, Ding Jie, Guang Wang, Xiaoming Wu, Xiaolan Wang, Chunlan Mo, Zhijue Quan, Xing Guo, Chang Zheng, and Shuan Pan

Doc ID: 345588 Received 10 Sep 2018; Accepted 10 Nov 2018; Posted 11 Dec 2018  View: PDF

Abstract: Realization of efficient yellow light-emitting diode (LED) was always a challenge in solid state lighting, great efforts was made but slight advancement have been done in the past a few decades. After a comprehensive work on InGaN based yellow LED on Si substrate, we successfully make a breakthrough and push the wall-plug efficiency (WPE) of yellow LED to 22.8%. The success of yellow LED can be credited to the improved material quality and reduced tensile strain of InGaN quantum wells by prestrained layer and substrate, as well as enhanced hole injection via V-defects.

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.

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.

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