2021

• Record 361 of
  
  Title:Preparation and Electromagnetic Wave Absorbing Mechanism of Helical Amorphous Carbon Nanotube/Bismaleimide (HACNT/BMI) Resin Composites
  
  Author(s):Zhu, Ruoxing(1,2); Zhao, Tingkai(2); She, Shengfei(3); Li, Tiehu(2)
  Source: Cailiao Daobao/Materials Reports  Volume: 35  Issue: 10  DOI: 10.11896/cldb.20030156  Published: May 25, 2021  
  Abstract:New electromagnetic wave absorbing materials are the hotspot and focus of research in national defense science and technology. Carbonmaterials, as light absorbing materials, have been widely valued by researchers. In this study, we prepared helical amorphous carbon nanotube/bismaleimide (HACNT/BMI) resin composites and investigated their electromagnetic wave absorbing properties. We used helical amorphous carbon nanotubes as adsorbing agents, bismaleimide as matrix to prepare HACNT/BMI resin composites. Helical amorphous carbon nanotubes were prepared by floating catalytic chemical vapor deposition method. Scanning electron microscope (SEM), transmission electron microscope(TEM), X-ray diffractometer (XRD) and Raman spectroscopy were used to characterize the morphology and structure of samples. The electromagnetic parameters of HACNT/BMI composites were measured by vector network analyzer. The results showed that the increasing in the content of absorbing agent enhanced the electromagnetic wave absorbing properties of HACNT/BMI composites. The maximum absorption peak reached -18.35 dB, the widest absorbing bandwidth reached 2.56 GHz(9.52~12.08 GHz) when the RL belows -10 dB, and the reflection loss exceeded 97%. Moreover, the absorption peak of HACNT/BMI composites with higher content of HACNTs shifted towards lower frequency compared to that of the sample with lower content of HACNTs. Our results indicate that the helical structures of HACNTs plays an important role in enhancing the electromagnetic wave absorbing performance of HACNT/BMI composites. The HACNTs could increase the possibility of multiple reflection of electromagnetic wave and the path length of scattered waves. As a result, the energy loss of incident electromagnetic wave was increased. © 2021, Materials Review Magazine. All right reserved.
  Accession Number: 20212510535091
• Record 362 of
  
  Title:Testing Characterization and Simulating Optimization of High-power Laser Diode Array Chips
  
  Author(s):Du, Yu-Qi(1,2); Wang, Zhen-Fu(1); Zhang, Xiao-Ying(3); Yang, Guo-Wen(1); Li, Te(1); Liu, Yu-Xian(1,2); Li, Bo(1,2); Chang, Yi-Dong(1,2); Zhao, Yu-Liang(1,2); Lan, Yu(1,2)
  Source: Faguang Xuebao/Chinese Journal of Luminescence  Volume: 42  Issue: 5  DOI: 10.37188/CJL.20210014  Published: May 2021  
  Abstract:Due to small size, light weight, high efficiency and long operation life, high power semiconductor laser array chips have gradually entered into mass-markets and emerged applications, such as laser pumping, materials processing, medical therapy and lidar. However, limited by high-temperature working environments such as material processing, the development of high power semiconductor laser is hindered. Since laser diode arrays work in high-temperature working environments and generate great quantity during operating, the output power and reliability of high power semiconductor laser is decreased, which is caused by reducing in slope efficiency, increasing in threshold current, and wavelength redshift. Hence, it is vital to research the optoelectronic performance and laser diode array optimization of semiconductor laser under high temperature. To improve the high temperature performance of high-power semiconductor laser chips, firstly, the influence mechanism of environment temperature on internal quantum efficiency is analyzed theoretically. Secondly, in order to quantify the main factors affecting the stability of the chip, the high-power semiconductor laser array chips test system was built to study the characteristics of the laser diode array chips at 15-60℃, and analyze energy loss distribution at various temperatures. The experimental results show that when the temperature rises from 15℃ to 60℃, the percentage of carrier leakage loss increases sharply from 2.30% to 11.36%, which is the main factor affecting the high temperature operation of semiconductor laser array chips. Finally, the chip structure simulation shows that increasing the Al composition of the waveguide layer to 20% can effectively limit carrier leakage, balance the increase in series resistance caused by the increase of Al composition, and obtain high electro-optical conversion efficiency. This research can provide a reference for the design of high-temperature laser diode array chips. © 2021, Science Press. All right reserved.
  Accession Number: 20212110414100
• Record 363 of
  
  Title:High-performance solid-state photon-enhanced thermionic emission solar energy converters with graded bandgap window-layer
  
  Author(s):Yang, Yang(1,4); Xu, Peng(1,2); Cao, Weiwei(1,2,3); Zhu, Bingli(1,5); Wang, Bo(1); Bai, Yonglin(1,4); Qin, Junjun(2,5); Bai, Xiaohong(4); Chen, Zhen(1)
  Source: Journal of Physics D: Applied Physics  Volume: 54  Issue: 5  DOI: 10.1088/1361-6463/abbb04  Published: February 4, 2021  
  Abstract:To realize a high-performance solid-state photon-enhanced thermionic emission (SPETE) solar energy converter, in this study, a graded bandgap window layer is therefore adopted, throughout which the bandgap gradation is generated via the variation of Al composition in the layer in the SPETE converter with a GaAs absorber. Based on one-dimension steady-state equation, an analytical model is formed in analyzing performance of the proposed device in our study. Theoretical simulation results indicate that not only are the losses of contact surface recombination being decreased via the bandgap-gradation-induced build-in electric field of the window layer, but also the photon-generated electrons are effectively collected, thereby improving the conversion efficiency. Moreover, the effect of bandgap energy of the contact surface and the width of the window layer on device performance is discussed. A trade-off of high-efficient SPETE converters is therefore realized between large contact surface bandgap and thin window layer width, to which the rationale lies in the improved process of electron collection facilitated by the enhanced build-in electric field rather than reducing the photon absorption in the window layer. Threshold values for barrier height at the emitting interface are presented to guarantee the ideal voltage-current characteristic. It is found that the threshold values of barrier increase with the increase in temperatures. © 2020 IOP Publishing Ltd.
  Accession Number: 20205009610622
• Record 364 of
  
  Title:Free-carrier-assisted mid-infrared microcavity soliton generation
  
  Author(s):Fan, Weichen(1,2); Sun, Qibing(1,2); Lu, Zhizhou(1,2); Wang, Leiran(1,2); Zhao, Wei(1,2); Zhang, Wenfu(1,2)
  Source: Journal of Applied Physics  Volume: 129  Issue: 8  DOI: 10.1063/5.0037921  Published: February 28, 2021  
  Abstract:Multi-photon absorption (MPA) and free-carrier (FC) effects, usually considered to be detrimental to microcomb generation by introducing strong nonlinear loss, also offer opportunities to overwhelm the thermal-optic effect by modifying the refractive index. Here, we derive the theoretical expression of solitons expanded with MPA and FC effects, accompanied by numerical simulations to reveal the dynamics and mechanism for capturing steady mid-infrared solitons in both Si and Ge microcavities. It is found that with increased FC lifetime, the intensity-dependent MPA underlies non-monotonous variation of nonlinear detuning which enables soliton generation. More interestingly, proper control on the FC lifetime admits bidirectional switching of soliton states (i.e., both decreasing and increasing the number of solitons) as well as self-starting solitons, yielding different technique routes toward microcavity solitons. This research could contribute to a better understanding of nonlinear behaviors influenced by FC effects and find practical applications by releasing the demand on precise control of laser sources, which is especially meaningful for the mid-infrared region. © 2021 Author(s).
  Accession Number: 20210909995006
• Record 365 of
  
  Title:Femtosecond Chirped Pulse Amplification System with Liquid Crystal Spatial Light Modulator for Spectral Modulation
  
  Author(s):Duan, Yufei(1,2); Li, Feng(1); Yang, Zhi(1); Li, Qianglong(1); Yang, Yang(1); Wu, Tianhao(1,2); Wang, Yishan(1); Yang, Xiaojun(1)
  Source: Zhongguo Jiguang/Chinese Journal of Lasers  Volume: 48  Issue: 11  DOI: 10.3788/CJL202148.1101001  Published: June 10, 2021  
  Abstract:Objective: Compared with traditional solid-state lasers, such as slats and wafers, femtosecond fiber lasers have many advantages, including compact structures, good beam quality, stable systems, and good heat dissipation. They are widely used in various application fields, particularly in the field of fine material processing. The current femtosecond fiber laser is mainly used to reduce the problems of nonlinearity and device damage in the amplification process using the chirped pulse amplification technology to obtain a femtosecond laser with its peak power and narrow pulse width meeting processing requirements. Owing to the increase in the energy demand of an industrial fiber laser, the amplification classes also gradually increase, rendering the narrowing effect due to an uneven gain medium increasingly severe and influencing the final spectral width. Thus, its occurrence increases the compressed pulse width limit, reduces the pulse peak power, and severely impacts the thermal diffusion in processing. Currently, the gain narrowing problem of a femtosecond fiber laser can be solved using self-phase modulation, a new amplifying stage system, or dielectric layer filters. However, these approaches can only form fixed spectral modulation, which cannot solve the gain narrowing problem in different amplification or laser systems with different power requirements of the same amplification system. Therefore, programmable devices are proposed to achieve the controllability of spectral modulation. Among them, the liquid crystal spatial light modulator, a common element for beam shaping and pulse shaping, exhibits higher regulating precision than the general acousto-optic filter. For a fiber laser seed source, its spectral width is only a few nanometers or tens of nanometers; the liquid crystal spatial light modulator is more suitable for fiber laser spectral modulation. This study focuses on the characteristics of the spatial light modulator and the requirement of a chirp pulse amplification system for spectral modulation. The solutions of a spectral shaping system are proposed based on the two-dimensional (2D) intensity-type liquid crystal spatial light modulator for spectral modulation. The chirped pulse amplification system eliminates the gain narrowing problem and achieves a narrower output pulse duration. Methods: Herein, the 2D intensity-type liquid crystal spatial light modulator was used for spectral modulation. First, the seed source is amplified using the single-mode amplification system and enters the spectral shaping system, which comprises the polarization-splitting prism, grating, and the intensity of reflection-type liquid crystal spatial light modulator to perform various spectral modulation shapes and verify the programmability and high precision of the spectral shaping system. Then, the subsequent multi-mode amplification and main amplification systems with an optical fiber aperture of 25 μm were established. The shape required for spectral shaping, which can be compared with the initial spectrum function to achieve a 2D grayscale map, was obtained using the step-by-step Fourier transform method combined with reverse operation. Next, the grayscale image was loaded into the spatial light modulator, and the spectral widths before and after the addition of the grayscale image were compared to investigate the influence of the shaping system on the spectra and the reasons for the spectral shape formation. Finally, the near-limited output pulse duration of the femtosecond laser was obtained by compressing an appropriate distance by the 1450 line/mm grating, and the pulse duration was measured using an autocorrelation instrument to determine the optimization results of pulse duration. Results and Discussions: The spectrum can be reshaped into flat-top, central-depression, triangle, continuous- depression, and other shapes using the spectral shaping system (Fig.4). Generally, as the spectral shaping becomes more complex and its shaping effect becomes worse, the modulation of the liquid crystal void generated using the liquid crystal spatial light modulator becomes increasingly obvious. After adding the main amplification system, the spectral width before entering the amplification system is reduced by approximately 1.5 nm (Fig.5) and the gain narrowing effect is evident. The grayscale map obtained using reverse operation was loaded on the 2D liquid crystal spatial light modulator to obtain the super-Gaussian spectral shape (Fig.6) after spectral shaping and amplification. The full width at half maximum of this spectrum is approximately 9.5 nm. The spectral width is approximately 2.5 nm, and the corresponding limited pulse duration is reduced from 222 fs to approximately 164 fs. Finally, the pulse duration of 170 fs, close to the limit, can be obtained after the laser with spectral shaping is compressed through the grating. Compared with that of direct compression, the pulse duration is decreased by 86 fs. Moreover, the pulse shape has a side lobe owing to the liquid crystal spacing problem of the liquid crystal spatial light modulator (Fig.7). Conclusions: Results show that the spectral shaping system can realize the arbitrary spectral modulation using the liquid crystal spatial light modulator. It can also set the spectral bandpass characteristics by regulating the function of different spectral component gains and realize dynamic matching using the subsequent amplification spectrum. Thus, this system is suitable for different conditions of gain spectrum modulation demand and can achieve a pulse duration close to the limit to meet the narrow output pulse duration and peak power of a femtosecond laser. Moreover, it achieves the purpose of efficient material cold working and satisfies the high requirements of the thermal effect for femtosecond laser applications. However, the improved results can be obtained using a modulator with a higher filling rate and smaller clearance for spectral shaping. © 2021, Chinese Lasers Press. All right reserved.
  Accession Number: 20213410819650
• Record 366 of
  
  Title:Compact 2D serpentine optical phased array
  
  Author(s):Ren, Yangming(1,2); Zhang, Lingxuan(1,2); Zhao, Wei(1,2); Wang, Guoxi(1,2); Feng, NingNing(1,2); Wu, Wei(1,2); Sun, Xiaochen(1,2); Zhang, Wenfu(1,2)
  Source: Applied Optics  Volume: 60  Issue: 24  DOI: 10.1364/AO.431942  Published: August 20, 2021  
  Abstract:We present a two-dimensional (2D) Si photonics optical phased array (OPA) using a serpentine design which eliminates the long directional couplers used in many 2D OPA designs. It significantly reduces the distance between the antenna benefitting far-field sidelobe reduction while maintaining high optical power use efficiency. © 2021 Optical Society of America
  Accession Number: 20213310780852
• Record 367 of
  
  Title:Stray Light Suppression in Sweep Mirror Field-Widened Space-Borne Fourier Transform Imaging Spectrometer
  
  Author(s):Zhang, Zhinan(1,2); Li, Libo(1); Zou, Chunbo(1); Hao, Xiongbo(1); Sun, Jian(1,2); Liu, Xuebin(1); Wang, Pengchong(1); Liu, Jie(1,2)
  Source: Guangxue Xuebao/Acta Optica Sinica  Volume: 41  Issue: 10  DOI: 10.3788/AOS202141.1029001  Published: May 25, 2021  
  Abstract:The field widening of a sweep mirror field-widened Fourier transform imaging spectrometer is achieved by adding a sweep mirror before its optical system. However, the addition of the sweep mirror causes the cross distribution of rays from different fields and different channels, which presents a difficulty in the suppression of stray light, and thus the traditional stray light suppression design is no longer valid. To solve this problem, a new design of stray light suppression is proposed. Based on the stray light suppression design, the point source transmittance (PST) stimulation and analysis of the visible and near-infrared optical system and the shortwave infrared optical system is presented for the sweep mirror at different field of view locations of 0°, 15°, and -15°. The analysis results show that as for all sweep mirror locations, the PST along the spatial direction and spectral direction at 0.5° off-field angle can be reduced to 10-3. Based on the observation mode, the signal source and stray light source of the on-orbit imaging spectrometer are analyzed. In addition, based on the PST stimulation results, the stray light irradiance at the focal plane is studied and the signal-to-stray ratio is calculated. It shows that the signal-to-stray ratio of the visible and near-infrared optical system is 0.1% and that of the shortwave infrared optical system is 0.6%. The results indicate that the proposed stray light suppression method is effective and can meet the requirement of the space-borne imaging spectrometer. © 2021, Chinese Lasers Press. All right reserved.
  Accession Number: 20213410810256
• Record 368 of
  
  Title:A sealed X-ray microchannel plate imager with CsI photocathode to improve quantitative precision of framing camera
  
  Author(s):Yang, Yang(1,2); Zhu, Bingli(1,2); Gou, Yongsheng(1); Chen, Zhen(1,2); Bai, Xiaohong(1,5); Qin, Junjun(1,5); Bai, Yonglin(1,2); Liu, Baiyu(1); Cao, Weiwei(1,4); Wang, Bo(1,2); Xu, Peng(1,3)
  Source: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  Volume: 1005  Issue:   DOI: 10.1016/j.nima.2021.165404  Published: July 21, 2021  
  Abstract:In this paper, we propose a hermetically sealed X-ray microchannel plate imager as a more effective and stable alternative to the traditional open-structured imager. With two microstrip photocathodes of 100 nm Au and 100 nm CsI, respectively, the proposed imager has a measured exposure time of 65 ps when applied with a 200 ps width gate pulse. The static response test shows that the image intensity of the CsI microstrip photocathode is 3.4 times that of the Au microstrip photocathode when illuminated by a non-monochromatic portable X-ray source with high energy photons. The sealed imager not only enhances the sensitivity and stability of the framing camera, but also has the potential to reduce crosstalks and artifacts, thus further improves the precision of measurement in practice. © 2021
  Accession Number: 20211910328976
• Record 369 of
  
  Title:Theoretical and Technical Research of X-ray Communication in Plasma Sheath
  
  Author(s):Su, Tong(1); Sheng, Lizhi(1); Liu, Yongan(1,2); Zhang, Xuehan(1,2); Liu, Yifan(1,2); Zhao, Baosheng(1)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 11  DOI: 10.3788/gzxb20215011.1134001  Published: November 25, 2021  
  Abstract:Because of the imperfect theoretical model and insufficient experimental verification technologies, the problem of information transmission in the plasma sheath has not yet been resolved. In this paper, the interaction mechanism between X-ray photons and plasma is studied firstly, and a modified theoretical model is provided through numerical calculation and theoretical modeling. Different from the conclusion that X-rays can penetrate plasma without attenuation in the traditional wave model, the modified theoretical model established in this paper points out that the transmittance of X-rays in plasma is closely related to plasma electron density and incident X-ray flux. Secondly, an experimental system was built using a grid-controlled X-ray modulation emission source, a single-photon X-ray detector, and a dynamic plasma generator. Using this system, the non-uniform plasma which electron density ranges from 109/cm3 to 1014/cm3 is generated, and the X-ray communication with 1 Mbps communication rante and 10-5 bit error rate is also verified. The experimental results indicate that the modified theoretical model can explain and predict the experimental phenomena, and the experimental system can provide the solution for solving the communication problems in the plasma sheath. © 2021, Science Press. All right reserved.
  Accession Number: 20215011321997
• Record 370 of
  
  Title:Theoretical and Experimental Research of X-ray Communication in Shielded Environment
  
  Author(s):Zhang, Xuehan(1,2); Su, Tong(1); Sheng, Lizhi(1); Liu, Yongan(1); Zhao, Baosheng(1)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 11  DOI: 10.3788/gzxb20215011.1134002  Published: November 25, 2021  
  Abstract:Based on the theoretical model of the interaction between X-rays and matter, the transmission characteristics of X-rays in an electromagnetic shielding environment are studied, and the feasibility of X-rays communication for information transmission in an electromagnetic shielding environment is theoretically demonstrated. After that, a numerical simulation model of X-ray communication in a shielded environment is established, and the communication parameters of X-rays in an electromagnetic shielded environment are analyzed to achieve the index constraint of the core components. Finally, based on the key technologies of X-ray modulated emission and single-photon X-ray detection, an equivalent verification experiment of X-ray passing through the shielding material is conducted to realize the experimental verification of X-ray communication with a communication rate better than 23 kbps. The results are expected to provide some theoretical basis and experimental foundation for solving the radiation data transmission in a shielded environment. © 2021, Science Press. All right reserved.
  Accession Number: 20215011321631
• Record 371 of
  
  Title:Force and Torque Analysis of Micro-sized Particles in Perfect Optical Vortex Beams
  
  Author(s):Zhang, Yanan(1,2); Li, Manman(1); Yan, Shaohui(1); Zhou, Yuan(1,2); Li, Xing(1,2); Yao, Baoli(1,2)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 3  DOI: 10.3788/gzxb20215003.0308002  Published: March 25, 2021  
  Abstract:Based on the tightly focusing approach, the perfect optical vortex beams are generated at the geometric focal plane. The optical forces and torques exerted on the micro-sized particle in the perfect optical vortex beams are calculated. Numerical results show that the micro-sized particle is trapped on the ring of perfect optical vortex beams and is driven to rotate around the optical axis. The orbital torque will firstly increases and then tends to be stable with the increase of the topological charge value. In addition, the influence of circular polarization state, radial polarization state and azimuthal polarization state on the force and orbital torque of micro-sized particles are investigated in perfect optical vortex beams. The results show that the state of polarization of perfect optical vortex beams will affect the optically induced orbital motion to some extent. The circular polarization state of perfect optical vortex beams is superior to drive the orbital motion of the particle. © 2021, Science Press. All right reserved.
  Accession Number: 20211910311300
• Record 372 of
  
  Title:Unobtrusive vital signs and activity monitoring based on dual mode fiber
  
  Author(s):Xu, Wei(1,2); Bian, Shihang(3); Dong, Bo(1,2,4); Shen, Ying(3); Han, Shuying(3); Yu, Changyuan(5); Zhao, Wei(1,2,4); Wang, Yishan(1,2,4)
  Source: Optical Fiber Technology  Volume: 64  Issue:   DOI: 10.1016/j.yofte.2021.102530  Published: July 2021  
  Abstract:A solid unobtrusive fiber-optic sensor based on modal interference in dual mode fiber (DMF) embedded in a thin mat is proposed and investigated theoretically and experimentally, realizing real-time vital signs and activity monitoring. The whole sensing setup only consists of one laser diode, one section of DMF, one photo-detector and few standard single mode fibers (SMFs). The DMF fiber is sandwiched into the SMFs using core-offset splicing, i.e., SMF-DMF-SMF structure. The optimal value of the core offset is numerically simulated and experimentally validated. It has to be noted that all the fibers used in the experiment are with 900-μm protection jacket, which can effectively avoid fiber breaking. The proposed sensor is both investigated in different postures and different subjects. And the results of vital signs monitoring performance show great consistency compared with commercial monitors. Besides, the activity monitoring is also addressed with one-second discrimination resolution, identifying three basic states, i.e., on bed, body movement and off bed. It is easy to fabricate and shows great potential in future non-invasive vital signs and activity monitoring applications. © 2021 Elsevier Inc.
  Accession Number: 20211810295262