bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical nonreciprocity with blue-detuned driving in two-cavity optomechanics
Authors: Zhang Li-Wei , Li Xian-Li , Yang Liu ,   College of Electronic Science, Northeast Petroleum University, Daqing 163318, China,   College of Automation, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Radiation pressure in an optomechanical system can be used to generate various quantum phenomena. Recently, one paid more attention to the study of optical nonreciprocity in an optomechanical system, and nonreciprocal devices are indispensable for building quantum networks and ubiquitous in modern communication technology. Here in this work, we study how to realize the perfect optical nonreciprocity in a two-cavity optomechanical system with blue-detuned driving. Our calculations show that the optical nonreciprocity comes from the quantum interference of signal transmission between two possible paths corresponding to the two interactions in this system, i.e. optomechanical interaction and linearly-coupled interaction. According to the standard input-output relation of optical field in cavity optomechanics, we obtain the expression of output optical field, from which we can derive the essential conditions to achieve the perfect optical nonreciprocity, and find there are two sets of coupling strengths both of which can realize the perfect optical nonreciprocal transmission. Because the system is driven by blue-detuned driving, the system is stable only under some conditions which we can obtain according to the Routh-Hurwitz criterion. Due to the blue-detuned driving, there will be transmission gain (transmission amplitude is greater than 1) in the nonreciprocal transmission spectrum. We also find that the bandwidth of nonreciprocal transmission spectrum is in proportion to mechanical decay rate if mechanical decay rate is much less than the cavity decay rate. In other words, in a realistic optomechanical parameter regime, where mechanical decay rate is much less than cavity decay rate, the bandwidth of nonreciprocal transmission spectrum is very narrow. Our results can also be applied to other parametrically coupled three-mode bosonic systems and may be used to realize the state transfer process and optical nonreciprocal transmission in an optomechanical system.
Terahertz wave absorption for alkylcyclohexyl-isothiocyanatobenzene liquid crystal materials
Authors: Yan Hao-Lan , Cheng Ya-Qing , Wang Kai-Li , Wang Ya-Xin , Chen Yang-Wei , Yuan Qiu-Lin , Ma Heng ,   College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China,   Department of Computing Technology, Henan Information Engineering School, Zhengzhou 450000, China
Published: December 2020

According to density functional theory, in this paper we report a simulation result obtained by using the Gaussian09 package. Adopted in the calculation are an optimized Opt Freq and a base group of B3LYP/6-311g to simulate the absorption of 16 kinds of liquid crystal (LC) molecules of 4-(trans-4-n-alkylcyclohexyl) isothiocyanatobenzenes (CHBT) in a 0.1−5.0 terahertz band (THz). The results show that in the low terahertz band, the absorption is caused mainly by the vibration and rotation of the molecules. So for convenience, we present an novel analytical method of studying the influence of molecular moment of inertia and mass center of gravity shift on absorption. An important result is found that the length of the molecular alkyl chain can lead to different molecular mass, mass center of gravity and moment of inertia, which causes the rotation and vibration of the molecule to be different. These factors lead to the difference in terahertz wave absorption. In the 0.1−5.0 terahertz band, the molecules with 3−7 alkyl chain carbon atoms show a strong absorption. As a reference, reducing and increasing the carbon atoms in the alkyl chain will cause the molecules to reduce the absorption of terahertz waves . In the end, the calculated results are compared with the experimental results obtained from 10 molecules according to the reference data in a frequency range of 0.3−3.0 terahertz. It is found that in the low frequency band there exist some differences between the calculation results and the experimental measurements, in which the difference in the position of the absorption peak may originate from a hydrogen bond. Comparing the relative magnitudes of the absorption intensities, it is found that the experimental measurements are consistent with the calculated results, indicating that the absorption intensity comes from the absorption of dipole vibration and rotation, which demonstrates the positive significance of computational simulation. We look forward to the experimental measurements in the future, and correct the calculation methods and keywords as well as the parameters such as temperature calculation that is to be done in future work. As a theoretical basis, the calculation results can better reflect the absorption of molecular materials, and it is expected to provide useful suggestions for designing and synthesizing the liquid crystal molecules.
Topological invariants and edge states in one-dimensional two-tile lattices
Authors: Lu Man-Xin , Deng Wen-Ji ,   School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, China
Published: December 2020

The existence of robust conducting edge states is one of the most prominent properties of topological insulator, which is often simply illustrated as a consequence of bulk-boundary correspondence. Then here arises a new question whether similar robust edge states appear in some other topological-trivial systems, or rather, given a general answer of fundamental mathematics such as harmonic analysis or K-theory to this problem, we study one-dimensional two-tile lattices and show that the robust edge states can exist in topological-trivial complex lattices. Under the tight-binding approximation, all kinds of one-dimensional two-tile lattices with staggered hopping matrix elements can be described by the Su-Schrieffer-Heeger model or the Rice-Mele model, depending on their site energy. The site energy values of the Su-Schrieffer-Heeger model are equal, and often assumed to be zero, and the Rice-Mele model is constructed to describe the one-dimensional two-tile lattices having two different site energy values. With the help of the generalized Bloch theorem, the eigen-state problem of electrons in one-dimensional two-tile complex lattices are solved systematically, and the analytical expressions for the wavefunctions of the edge states in the corresponding finite lattice are obtained. The numerical and analytical results show that the edge states can also emerge in any of one-dimensional two-tile lattices beyond the Su-Schrieffer-Heeger lattice, i.e., provided that the magnitude of intracell hopping is less than the intercell hopping, a pair of edge states can also emerge in Rice-Mele lattice. Unlike the Su-Schrieffer-Heeger edge states, the two Rice-Mele edge states are locally distributed at one end of the finite lattice: one at the left and another one at right. The Zak phase is a topological invariant of the Su-Schrieffer-Heeger model, but it is no longer invariant for the Rice-Mele model because of the breaking of spatial inversion symmetry, and therefore the Rice-Mele lattices are topologically trivial. However, the Rice-Mele edge states are also robust to the non-diagonal disorder of the lattice. In addition, it is proven that the winding number can provide a general criterion for the existence of a couple of edge states in any one-dimensional two-tile lattice whether it is the Su-Schrieffer-Heeger lattice or not. These results lead to a conclusion that the topological invariant is not necessary for the robust edge states to occur.
Influence of discharge parameters on pulsed discharge of coaxial gun in deflagration mode
Authors: Zhao Chong-Xiao , Qi Liang-Wen , Yan Hui-Jie , Wang Ting-Ting , Ren Chun-Sheng ,   Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams of the Ministry of Education, School of Physics, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Coaxial gun can produce high-speed and high-density plasma jet and has some potential applications in many research areas such as space thruster, space debris impact simulation, nuclear fusion, and material processing. The coaxial gun is usually composed of a pair of coaxial cylindrical and hollow electrodes. The pulsed discharge of coaxial gun has two discharge modes, i.e., deflagration mode and pre-fill mode. Compared with the pre-fill mode, deflagration discharge mode can induce a plasma jet with few impurities, high collimation, and fast speed. In this paper, the effect of gas injection mass and discharge voltage on the discharge characteristic of deflagration mode are studied with electrical and optical diagnosis including the emission spectrum, plasma velocity and discharge current measurements. The experimental results show that when the gas injection mass is relatively low, such as 1.4 mg, many plasma clusters eject from the muzzle. As the gas flowing into the coaxial gun bottom increases, the plasma density increases and the jet velocity decreases. Eventually, when the gas injection mass increases to 2.6 mg, one cluster of plasma is found and ejects from the muzzle of the gun. In the discharge process, as a small quantity of gas flows into the bottom of the coaxial gun through the electromagnetic valve continuously, new current paths will be generated at the bottom of the coaxial gun and move forward. This results in the observation of multiple plasma jet at the exit of the coaxial gun. It is noted that the plasma densities are different for different gas mass flowing into coaxial gun bottom, but the currents have little effect in the first discharge half cycle due to the small plasma inductance in discharge circuit. Meanwhile, the plasma characteristics under different voltages with the fixed gas mass of 2.6 mg flowing into the coaxial gun bottom are experimentally measured. The results show that the plasma density and speed increase with voltage increasing, which is attributed to the stronger discharge current and larger self-induced Lorentz force. More neutral particles can be ionized into plasma with discharge voltage increasing, and the transport speed becomes faster under the enhanced force. In addition, the multiple ionization phenomena are observed again when the discharge voltage increases from 5 kV to 8 kV. This study provides an insight into how to better apply the coaxial gun discharge plasma to practical engineering field. The article further verifies the phenomenon of multiple discharges at the bottom of the coaxial gun by changing the charging capacitance and analyzing the magnetic probe signals.
Online learning method based on artificial neural network to optimize magnetic shielding characteristic parameters
Authors: Peng Xiang-Kai , Ji Jing-Wei , Li Lin , Ren Wei , Xiang Jing-Feng , Liu Kang-Kang , Cheng He-Nan , Zhang Zhen , Qu Qiu-Zhi , Li Tang , Liu Liang , Lü De-Sheng ,   Key Laboratory for Quantum Optics and Center of Cold Atom Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Magnetic shielding plays an important role in magnetically susceptible devices such as cold atom clocks, atomic interferometers and other precision equipment. The residual magnetic field in a magnetic shield under a varying external magnetic field can be calculated by the Jiles-Atherton (J-A) hysteresis model and magnetic shielding coefficient. According to the calculation results, the variation of internal magnetic field can be compensated for the active compensation coils. However, it is difficult to practically obtain the exact values of the five magnetic-shielding-related parameters in the J-A hysteresis model and the other two magnetic-field-attenuation-related parameters. It usually takes a lot of time to match the parameters manually according to the measured hysteresis loop and it is difficult to ensure that the final parameters are the global optimal values. The machine learning method based on artificial neural network has been used as an efficient method to optimize the parameters of complex systems. Owing to the powerful computing capability of modern computers, using the artificial neural network to optimize parameters is usually much faster than manual optimization method, and has a greater probability of finding the global optimal parameters. In this paper, the five J-A parameters and the other two parameters relating to magnetic field attenuation are optimized by the method of online learning based on artificial neural network, and the residual magnetic field in the magnetic shield is predicted under the simulated satellite magnetic field environment. By comparing the measured residual magnetic field with the predicted value, it is found that the machine learning method can optimize the magnetic shielding characteristic parameters more quickly and accurately than the manual optimization method. This result can not only help us to compensate for the magnetic field better and optimize the parameters of our cold atom system, but also validate the application of neural network in a multi-parameter physical system. This proves that the in-depth learning neural network can be conveniently applied to other physical experiments with multi-parameter interaction, and can quickly determine the optimal parameters needed in the experiment. This application is especially effective for remote experiments with slow response to parameter adjustment, such as scientific experiments carried out on satellites or deep space.
Characteristics of latch-up current of dose rate effect by laser simulation
Authors: Chen Qian , Ma Ying-Qi , Chen Rui , Zhu Xiang , Li Yue , Han Jian-Wei ,   National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China,   College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Due to the parasitic PNPN structure, the complementary metal oxide semiconductor (CMOS) integrated circuit may be affected by the latch-up effect, and the latching induced by the transient high dose rate Gamma ray has unique characteristics. In order to explore the complex physical mechanism of the latch-up by transient dose rate effect, in this paper we select the pulsed laser with 1064 nm wavelength as an radiation source to simulate the gamma ray radiation environment, select bulk silicon CMOS deserializer FIN1218MTDX, and use transient dose rate effect laser simulation experiments to explore its latch-up threshold and latch-up current characteristics. The test obtains that the dose rate latch-up threshold optical power density of the device at 3.3 V operating voltage is (8.5 ± 1.2) × 104 W/cm2, a latch-up voltage of the device is 2.8 V, only the device latches when the supply voltage is greater than 2.8 V. At the same time, it is found that under the working voltages of 3.3 V and 3.6 V and the optical power density between 1.9 × 106 W/cm2 and 1.6 × 107 W/cm2, the latch-up current significantly decreases, the latch-up current " window phenomenon” appears. Based on the equivalent circuit model, the multi-path latching mechanism is used to construct the HSPICE model. The mechanism of the transient dose rate latching characteristics exposed by the laser test is analyzed by circuit-level simulation. The results show that the latch-up current and the latch-up voltage are related to its own latch structure when the device is latched. The phenomenon of latch-up current window in laser test is due to the multi-path latch mechanism, which will be in the specific circuit structure, and causing the multiple latch-up paths of the device to be switched. The reason of the latch-up path is switched is that the different holding voltages and trigger conditions between the latch-up paths, distributed resistance in the circuit reduces the voltage of latch-up path, so that the holding voltage of the latch-up path cannot be satisfied and the latch-up path is released. At the same time the other latch-up path is latched.
Long-range, high-precision absolute distance measurement technology based on alternately oscillating optoelectronic oscillator
Authors: Xie Tian-Yuan , Wang Ju , Wang Zi-Xiong , Ma Chuang , Yu Yang , Li Tian-Yu , Fang Jie , Yu Jin-Long ,   School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Absolute distance measurement plays an important role in many areas, such as aerospace and scientific research. Traditional measurement methods generally cannot meet requirements for long-range and high-precision at the same time. In this paper, an absolute distance measurement method based on alternately oscillating optoelectronic oscillator is proposed. This method places the distance to be measured in the loop of optoelectronic oscillator and takes advantage of accumulative magnification effect to achieve high accuracy. The measurement and the reference optoelectronic oscillators are established and selected by an optical switch, and a microwave switch is used to choose the high-order or low-order oscillating frequency. The high-order frequency and low-order oscillating frequency of the measurement and reference optoelectronic oscillators are measured in turn by frequency counter to calculate the loop lengths of two optoelectronic oscillators. The low-order frequencies are used to measure the fundamental frequency roughly and the high-order frequencies are used to calculate loop length precisely. Although the mode hopping occurs in the measurement process, it does not affect the loop length calculation by substituting the corresponding oscillating mode number. Note that the loop length measurement moments of two optoelectronic oscillators are different due to the switching order of optical switch and microwave switch. In order to calculate the absolute distance, which is the length difference between two optoelectronic oscillators at the same moment, the measured loop lengths should be averaged.In this way, systematic error accumulation caused by slow drift of environment can be eliminated, and this method does not need to control the length of reference optoelectronic oscillator. Meanwhile, the measurement system is simple. In the experiment, 1 km, 5 km and 8 km fibers are placed in a common part of the measurement and reference optoelectronic oscillators to simulate different long-range distances in space. A high-resolution optical delay line is placed in the measurement optoelectronic oscillator to verify the performance of the measurement system. The experimental results show that the measurement error is 3.5 μm with a 3.5 μm maximum standard deviation of each measurement distance at an emulated round trip distance of 6 km. The relative measurement accuracy reaches 5.8 × 10－10. This method provides a feasible idea for solving the technical problems of long-range and high-precision absolute distance measurement.
NO2 measurement using fiber coupled broadband LED source combining a Herriott multi-pass cell
Authors: Cao Yuan , Tian Xing , Cheng Gang , Liu Kun , Wang Gui-Shi , Zhu Gong-Dong , Gao Xiao-Ming ,   School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, China,   Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

An NO2 sensor based on a fiber coupled broadband LED source with a Herriott multi-pass cell is developed and demonstrated for calibrating aerosol absorption photoacoustic (PA) spectrometer. At first, a Herriott multi-pass cell with an effective optical path of 26.1 m is designed based on the theory of light transmission, for increasing the light absorption of NO2 in the cell. It is difficult to obtain a high-quality beam of LED by using the conventional collimating method that enables the collimated output beam to transmit back and forth in the multi-pass cell, due to the large emitting surface and divergence angle of the LED. So, in the present work, the emission of the LED is coupled into a single model fiber, and then collimated by using a lens. The LED spectrum does not change before and after fiber coupling. The collimated beam with a central wavelength of 438.5 nm is coupled into the multi-pass cell. The output beam passing through the multi-pass cell is detected by using a spectrometer for retrieving the NO2 concentration. Finally, an expected concentration detection limit of 1 μmol/mol (3σ) is achieved within 1 s acquisition time and the signal-to-noise ratio (SNR) is 40. By analyzing the result measured with 46 μmol/mol NO2, a measurement precision of 0.1% is achieved. In order to calibrate the aerosol absorption PA spectrometer, the NO2 sensor and the aerosol absorption PA spectrometer based on 450 nm are used to measure different concentrations of NO2, simultaneously. The results show that the measured NO2 concentration has a good linear relationship with the PA spectrum signal, and the linearity is better than 99.9%. This good linear relationship further shows the feasibility and reliability of the NO2 sensor. The slope of calibration curve after normalizing the power is 0.95 nV/(mW·Mm-1). Using this calibration result, the PA signal measured with aerosol absorption PA spectrometer is transformed into the absorption coefficient. The developed NO2 measuring system based on a broadband LED light source and Herriott multi-pass cell has the advantages of low cost, simple structure and easy use. It can be used to calibrate the aerosol absorption PA spectrometer, and also to measure NO2 in industry.
Sound insulation performance of thin-film acoustic metamaterials based on piezoelectric materials
Authors: He Zi-Hou , Zhao Jing-Bo , Yao Hong , Jiang Juan-Na , Chen Xin ,   Graduate School, Air Force Engineering University, Xi'an 710051, China,   Department of Basic, Air Force Engineering University, Xi'an 710051, China
Published: December 2020

Aiming at the isolation of low-frequency sound, a kind of thin-film acoustic metamaterialis designed and obtained by implanting PZT into thin film. The finite element method (FEM) of the structure is built, and 1st–14th order eigenfrequencies and transmission loss between 20–1200 Hz are calculated. The reliability of finite element calculation is verified experimentally and the existence of adjustable sound insulation peak is monitored in the experiment. The results show that the acoustic metamaterial has good sound insulation performance in a frequency range between 20 and 1200 Hz, and has two sound insulation peaks of more than 50 dB, and there is a sound insulation peak which can be changed by adjusting the parameters of the outer circuit. By analyzing the first resonance mode of simple structure and building its equivalent model, the effect of structural parameter on the sound insulation performance of thin film acoustic metamaterial is investigated theoretically, and the rationality of the equivalent model is verified by the finite element calculation. The sound insulation mechanism of the structure is further illustrated by taking into consideration the eigenfrequencies, transmission loss curve and vibration mode diagrams at various frequencies. It is found that at the resonance frequency, the flapping motion of the film will cause the sound wave in the subsequent propagation to cancell the interference, therefore realizing the attenuation of the sound wave. Based on Fano resonance theory, the reasons for the different characteristics of transmission loss curves at different resonance points are investigated. The PZT and outer circuit can form a LC oscillator. At the resonant frequency of the oscillator, the vibration of the piezoelectric material can absorb the energy of sound wave to cause a sound insolation peak. The resonant frequency of the circuit can be adjusted by changing the parameters of the outer circuit, thereby realizing the adjustability of the sound insulation performance. The influence of eccentricity of piezoelectric mass block on sound insulation performance of material is explored, proving that the sound insulation performance can be further optimized by improving structure. And through the finite element calculation, it is proved that the sound insulation performance of material is adjustable by changing the parameters of the outer circuit. The results provide a theoretical reference for designing the thin film acoustic metamaterials.
Fabrication and physical measurement accuracy of nanoscale standard samples for vector beams confocal laser scanning microscopy
Authors: Li Xiao-Nan , Guan Guo-Rong , Liu Yi-Kun , Liang Hao-Wen , Zhang Ai-Qin , Zhou Jian-Ying ,   State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, China,   School of Electronic and Information Engineering, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

Various kinds of super-resolution optical microscope techniques have been developed to break the diffraction barrier in the past decades. Confocal laser scanning microscopy is the super-resolution microscopy. It is widely used due to high resolution and depth selectivity in obtaining images. However, there are neither accurate nor rigorous measurement methods with a nanoscale resolution. In order to measure the resolution of vector beam confocal laser scanning microscopy accurately and rigorously, a nanoscale resolution standard sample is proposed and experimentally realized. This sample is composed of a series of accurate measure patterns and a couple of arrays of triangle finding structures. It allows a wide measurement range between 40 nm to 1000 nm, and provides appropriate measurement steps and high measurement accuracy. The measurement patterns can be efficiently figured out by using the found structures, and their structure line width can be easily calculated. The first standard sample is produced on a piece of amorphous silicon by electron beam lithography and inductive coupled plasma etching technology, and measured by the scanning electron microscopy. According to the test, the sample meets the requirements of accuracy for nanoscale resolution measurement. Optical testing is applied to the sample by a vector beam confocal laser scanning microscope. And the sample shows that the resolution is 96 nm (oil immersion, refractive index 1.52) under the irradiation of 405 nm radially polarized beams, which is far beyond the diffraction barrier. Furthermore, a metal structure standard sample, which is based on a piece of indium tin oxide glass, is produced to improve the signal contrast ratio of the silicon standard sample. The measurement patterns are fabricated by electron beam lithography and electron beam evaporation and made of 10 nm titanium and 100 nm gold. It works for both reflective and transmissive confocal laser scanning microscopy, and would obtain high resolution images with a better contrast ratio. These standard samples are able to test the performance of microscope system efficiently, and provide a more rigorous way to make sub-100 nm resolution measurement and a calibration guidance for point scanning super-resolution microscope. In the meantime, we find that nanoscale opticalimaging is affected not only by sample morphology, but also by the photoelectron property of the sample. Further study is required to understand the underlying mechanism.
Microwave photonic frequency up-converter with LO doubling based on carrier suppression single-sideband modulation
Authors: Xu Jia-Hao , Wang Yun-Xin , Wang Da-Yong , Zhou Tao , Yang Feng , Zhong Xin , Zhang Hong-Biao , Yang Deng-Cai ,   College of Applied Sciences, Beijing University of Technology, Beijing 100124, China,   Beijing Engineering Research Center of Precision Measurement Technology and Instruments, Beijing University of Technology, Beijing 100124, China,   Science and Technology on Electronic Information Control Laboratory, Chengdu 610036, China
Published: December 2020

Frequency up-converter as an essential component of the transmitter, which is used to implement the frequency up-conversion by mixing a low-frequency intermediate frequency (IF) signal with a local oscillator (LO) signal. However, only the 1st-order sideband of the LO signal and the IF signal are used in the tradtioanal microwave photonic up-converser, thus the frequency of the up-conversion signal is ωLO + ωIF. In this case, an LO with a higher frequency is needed for generating a high-frequency up-converted signal. In order to reduce the frequency requirement of the LO signal, the high-order LO singals or secondary modulation can be used to achieve high-frequency up-conversion. A microwave photonic up-converter with LO doubling based on carrier suppressing single-sideband modulation is proposed based on the cascaded structure of a Mach-Zehnder modulator (MZM) and a dual-parallel Mach-Zehnder modulator (DPMZM). The MZM is driven by an LO signal biased at the minimum transmission point for carrier suppressing double-sideband (CS-DSB) modulation. A fiber Bragg grating (FBG) is used to separate the +1st-order from －1st-order of the LO signal. The －1st-order of LO signal is then sent to a DPMZM for the secondary modulation, and the carrier suppressing single-sideband (CS-SSB) modulation is realized in order to generate the －1st-order of the IF signal by using an electrical 90° hybrid coupler. The modulated IF signal is then combined with the +1st-order LO signal reflected by the FBG and sent into the photodetector (PD) to implement the photoelectric detection. The upconverted signal with a frequency of 2ωLO + ωIF can be detected by a PD. The experimental results show that the spur suppression ratio of the optical spectrum and the up-converter signal reach 22.5 dB and 23.6 dB, respectively. The spurious-free dynamic range of the system is 96.1 dB·Hz2/3. The proposed system can effectively reduce the frequency requirement of LO signal, and the purity of the electrical spectrum is largely improved which benefits from the CS-SSB modulation. The proposed microwave photonic up-converter provides an effective way for high-frequency emissions in systems such as radio-over-fiber and optically controlled phased array radar.
Interactions between photons and excitons in micro-nano photonic structures
Authors: Duan Xue-Ke , Ren Juan-Juan , Hao He , Zhang Qi , Gong Qi-Huang , Gu Ying ,   State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China,   Nano-optoelectronics Frontier Center of Ministry of Education (NFC-MOE) and Collaborative Innovation Center of Quantum Matter, Peking University, Beijing 100871, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China,   Beijing Academy of Quantum Information Sciences, Beijing 100193, China
Published: December 2020

The strong localized field in micro-nano photonic structures brings new opportunities for the study of the light-matter interaction. By designing optical modes in these structures, photons and excitons in micro-nanostructures can exchange energy reversibly or irreversibly. In this paper, a series of our recent studies on the strong and weak photon-emitter coupling in micro-nano structures especially in plasmonic and their coupled structures are reviewed, such as the principle of efficient, tunable and directional single photon emission, and engineering the electromagnetic vacuum for enhancing the coupling between photon and exciton. These results provide new physical contents for the light-matter interactions on micro and nanoscale, and have potential applications in the on-chip quantum information process and the construction of scalable quantum networks.
Femtosecond laser 3D printing temperature sensitive microsphere lasers
Authors: Hou Zhi-Shan , Xu Shuai , Luo Yang , Li Ai-Wu , Yang Han ,   State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
Published: December 2020

The whispering gallery mode (WGM) microcavity has been widely used for sensing and detection because of its high quality factor, small mode size, simple and diverse manufacturing process, and high sensitivity to the surrounding environment. Microsphere cavityand microdisk cavity are typical whispering gallery mode microcavities. However, the real controllable size of the on-chip three-dimensional microsphere cavity has rarely been reported because it is difficult to prepare by photolithography. At the same time, most of the current microsphere cavity are prepared by hot melting, which have the poor ability to control the size. In this article, we have mainly demonstrated the fabrication of a dye-doped polymer whispering gallery mode microsphere by femtosecond laser two-photon polymerization, which shows good surface smoothness with a fabrication spatial resolution beyond the diffraction limit. The microsphere cavity consists with commercial photoresist SU-8 as the cavity material and Rhodamine B as the gain medium. With the 532 nm pump, the RhB-doped SU-8 can emit fluorescence in the spectral range of 600–700 nm, and thus resonant whispering gallery laser modes in this spectral region can be eventually formed in the microsphere cavities. The microcavity shows excellent lasing performance with a quality factor of ~2000. Due to the special luminescence mechanism of organic dyes, the fluorescence spectrum of the dye drifts with the change of ambient temperature, and it will form a new resonance excitation with the eigenmode of the cavity. Within a certain temperature range (20 ℃－35 ℃), the wavelength of the main lasing peak is linearly related to temperature. The results shows that the organic dye doped micro-resonator has a unique laser mechanism which can be used to construct a new type of microlaser. Moreover, the tunable microsphere laser can be used as a temperature sensor after further optimized. We believe our work will provide a positive inspiration for the rational design of miniaturized lasers with ideal performance.
Initial configuration design of off-axis reflective optical system based on vector aberration theory
Authors: Cao Chao , Liao Zhi-Yuan , Bai Yu , Fan Zhen-Jie , Liao Sheng ,   Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The traditional method of designing the initial configuration of off-axis reflective optical system is to first obtain the initial configuration of coaxial reflective optical system, and then achieve the unobscured design with an offset aperture stop or a biased input field, or both. Because the aberration distribution of coaxial reflective optical system is not applicable to the off-axis reflective optical system, the obtained unobscured off-axis reflective optical system has large aberration, and the unobscured design process is complicated. In this paper we present a method of designing an initial configuration of off-axis reflective optical system based on vector aberration theory. With this design method, a good unobscured initial configuration of off-axis reflective optical system can be directly obtained by using an offset aperture stop or a biased input field, or both. Based on the vector aberration theory and gaussian brackets, the third-order aberration coefficient is derived for off-axis reflective optical system. Initial configuration performance is important for optical design, especially for the complicated optical system design. The selection of initial configuration highly affects the final system imaging performance, fabrication difficulty and alignment difficulty. An error function is established to evaluate the performance of off-axis reflective optical system, and it consists of aberration coefficients and other constraints. The genetic algorithm is a highly parallel, random and adaptive global optimization algorithm. To obtain a good initial configuration for the off-axis reflective optical system, the genetic algorithm is used to search for the initial configuration with minimum residual aberration. This method can obtain a good initial configuration of off-axis reflective optical system for further optimization. The benefit of this design method is demonstrated by designing an off-axis three-mirror optical system. For the focal plane array, a long-wave infrared off-axis three-mirror optical system is designed. A good initial configuration is obtained with the proposed method, which achieves the unobscured design by using an offset aperture stop and a biased input field. To improve the performance of initial configuration, the obtained initial configuration is optimized with the optical design software. The designed optical system has good imaging quality. As the mirrors are free from the tilts and decenters, the designed optical system is aligned easily.
Inkjet printed perovskite solar cells: progress and prospects
Authors: Xia Jun-Min , Liang Chao , Xing Gui-Chuan ,   Joint Key Laboratory of the Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Macau 999078, China
Published: December 2020

In the field of photovoltaic materials, perovskite has attracted extensive attention during the past years, owing to its excellent photovoltaic properties, including high charge carrier mobility, low exciton binding energy, long charge carrier diffusion length, broad light absorption spectrum, large absorption coefficient, and low-cost solution processability. However, due to the limitations of film preparation methods (typical spin coating), industrial large-scale production of perovskite solar cells is still in infancy. The inkjet printing technology is a significant manufacturing technology developed from home and office printing and widely used in various printing electronics industries. Compared with other deposition methods, it possesses many advantages, including low cost, high material utilization, high patterning precision, etc. As a direct writing technology, the inkjet printing has shown great industrial potential and is expected to be employed in the industrialization of perovskite solar cells. In this paper, we review the research progress of perovskite solar cells fabricated via the inkjet printing and the application of inkjet printing technology to various functional layers (electrode, hole transport layer, electron transport layer, perovskite active layer). Finally, the challenges of inkjet printed perovskite solar cells at this stage are discussed, and the commercialization direction of inkjet printed perovskite solar cells is also pointed out.
Controllable growth of InAs quantum dots on patterned GaAs (001) substrate
Authors: Wang Hai-Ling , Wang Ting , Zhang Jian-Jun ,   Nanoscale Physics and Devices Laboratory, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

InAs/GaAs quantum dot (QD) is one of the promising material systems for the quantum information processing due to their atomic-like optical and electrical properties. There are many previous researches reporting the InAs QDs which can be implemented as solid-state single-photon sources for quantum information and quantum computing. However, the site-controlled growth of QDs is the prerequisite for addressability and integration. There are very few researches focusing on the systematic study of preferential nucleation of InAs QDs on a patterned GaAs (001) substrate. In this work, we study the preferential nucleation sites of InAs QDs on a patterned GaAs (001) substrate with different trench sidewall inclinations. With small inclination angle of the trench sidewalls, the InAs QDs nucleate preferentially inside the trenches, while with large inclination angle, the edges of the trenches appear to be the preferential nucleation sites. By utilizing the established method, a pair of InAs dots can be uniformly achieved in the patterned pits through tuning the inclination angle of the pits. The site-controlled single InAs QD and InAs QD molecules on the patterned substrates could have potential applications in quantum information processing and quantum computing.
Effect of plume motion path on heat transfer characteristics in two-dimensional turbulent thermal convection
Authors: Bao Yun , He Jian-Chao , Gao Zhen-Yuan ,   School of Aeronautics and Astronautics, Sun Yat-Sen University, Guangzhou 510275, China
Published: December 2020

The Grossman and Lohse (GL) theory is an important theory for studying the heat transfer characteristics of the turbulent convection. Previous computational studies have found that when the Ra number is higher than a certain value, the change of the heat transfer Nu number with Ra number in two-dimensional turbulent thermal convection is different from that in the three-dimensional thermal convection, deviating from the multiples line of the GL theory prediction. Therefore, the value of studying the two-dimensional numerical calculation of turbulent thermal convection with high Ra number is questioned. The numerical calculations of a series of two-dimensional turbulent thermal convection events with high and very high Ra number(specifically, maximum Ra = 1013 with Pr = 0.7 and 4.3) are carried out in this paper. The results show that there exists a good correlation between the heat transfer Nu number and the variation of large scale circulation path length(that reflects the plume motion) with Ra number in the two-dimensional turbulent convection, and they have two Ra number transition points. The first transition point appears in the large scale circulation from the ellipse to the circle, when its circumference CLSC of the large scale circulation suddenly decreases with Ra number increasing. The second transition point appears at the minimum circumference CLSC, and then the plume rheology becomes vortex group and the circumference CLSC increases with Ra number increasing. The Ra number at transition point for a smaller Pr number is lower. The variation of the heat transfer Nu number after Ra0.3 compensation shows that the local scale law of Nu number decreases as the circumference CLSC of the large scale circulation becomes small, and a phenomenon of deviating from the multiples line of GL theory prediction appears. When Ra number is higher than the second transition point, the local scale law of the Nu number varying with Ra number is in good agreement with the multiples line of GL theory prediction again in 2D turbulent thermal convection. It means that the numerical results of two-dimensional turbulent thermal convection can correctly reflect the heat transfer characteristics of turbulent thermal convection under the condition of very high Ra number.
Recent advances in photo-stability of lead halide perovskites
Authors: Lou Hao-Ran , Ye Zhi-Zhen , He Hai-Ping ,   State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Lead halide perovskites, which can be grown by solution process, are very suitable for various optoelectronic applications, such as in solar cells, light-emitting diodes, lasers and photo-detectors, due to their outstanding electrical and optical properties. However, lead halide perovskites are unstable under continuous light illumination, which severely degrades the performance and lifetime of optoelectronic devices based on them. Therefore, the photo-stability of perovskites and the mechanisms have received more and more attention. In this article we review the main phenomena in perovskites, induced by continuous light illumination, namely photo curing, photo dissociation, photo-induced phase separation, and photo-induced phase transition. The proposed mechanisms for the instability from the perspectives of defect states, ion migration, thermodynamics and chemical bonds, respectively, are also introduced. Finally, the complexity presented in the studying of photo-stability, and the issues should be addressed in the future are also briefly discussed.
Prediction of time reversal channel with neural network optimized by empirical knowledge based genetic algorithm
Authors: Yuan Lin , Yang Xue-Song , Wang Bing-Zhong ,   School of Physics,University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Because of the strong non-linear fitting capability, the artificial neural network (ANN) can be used to establish the mapping relationship between the terminal position and the received signal for obtaining the channel characteristics at different locations. The accuracy of an ANN model is, in general, determined by the number of the training sets used in constructing the model. The more the training sets, the better the accuracy is. However, getting a large number of training sets by deterministic model is expensive. Therefore, under the same number of training sets, improving the accuracy of the model is crucial to develop an effective time reversal (TR) modeling method based on ANN. In this paper, a new TR channel modeling method based on the back propagation neural network is proposed. Genetic algorithm (GA) with excellent global search capability is used to optimize the weight and threshold of the ANN to avoid the possibility of the ANN falling into local minimum. According to the basic principle of time reversal, the peak characteristics are obtained by the fitting method. In order to improve the accuracy of the model, the peak value characteristics are integrated into the GA as empirical knowledge to change the fitness function. Meanwhile, the principal component analysis technology is utilized to process data, which reduces the data dimension and the training time of ANN while data characteristics are ensured. Once the terminal antenna positions are input to the proposed model, the accurate TR received signals can be quickly obtained. Finally, the deconvolution operation of the received signal is performed by the clean algorithm to obtain the channel characteristics. A simple indoor TR scenario is used as an example to demonstrate the effectiveness of the proposed method. The results show that the three channel characteristics obtained by the model, i.e., channel impulse response peak value, 15 dB multipath number, and average delay, have high accuracy. Furthermore, the proposed model has more excellent performance than the other two ANN models under the condition of the same number of training samples. Based on the basic principle of TR technology, the electromagnetic waves have better focusing effect in more complex environments. Therefore, the proposed method is also applicable to more complicated environments than the simple indoor scenario.