Abstract:In this paper， n-type CdTe thin films were prepared by sputtering method. The morphology， structure and optical properties of n-type CdTe thin films deposited with different time and the influence of film thickness and annealing process on the photoelectrochemical （PEC） characteristics of n-type CdTe thin films were studied. The experimental results demonstrated that CdTe thin films with sputtering time of 25 min had better PEC performance. Annealing process could enhance the PEC properties of deposited n-type CdTe thin films. When CdTe thin films were coated with saturated CdCl₂ solution and annealed in vacuum at 400 °C， the photocurrents of n-type CdTe thin films achieved 301 μA/cm².

Abstract:This letter reports on a lateral linear mode avalanche photodiode through 0.35 μm high voltage CMOS process. The linear mode avalanche photodiode is designed and fabricated with the lateral separate absorption， charge and multiplication （SACM） structure using an epitaxial wafer. The DNTUB layer， DPTUB layer， Pi layer and SPTUB layer are used for the lateral SACM structure. This improves freedom of the design and fabrication for monolithic integrated avalanche photodiode without high voltage CMOS process modifications. The breakdown voltage for the lateral linear mode avalanche photodiode is about 114.7 V. The dark currents at gain M = 10 and M = 50 are about 15 nA and 66 nA， respectively. The effective responsive wavelength range is 450 ~ 1050 nm. And the peak responsive wavelength is about 775 nm at 20 V while M = 1. With unity gain （M = 1）， the responsivity at 532 nm is about half of the maximum.

Abstract:The HgCdTe is a narrow band gap semiconductor. As the operating temperature increases， the intrinsic carrier concentration of the material will increase， the detector cut-off wavelength will become shorter， and the dark current will increase， which will cause the performance of the detector to decrease. HgCdTe infrared detectors usually work near 77 K temperature and obtain good detection performance， but low temperature operation will increase the preparation cost， power consumption， volume and weight of the detector. In order to solve these problems， under the premise of ensuring the normal working performance of the detector， increasing the operating temperature of the detector is an important research direction of the HgCdTe infrared detector. The p-on-n structure HgCdTe infrared focal plane detectors has the characteristics of low dark current and long minority carrier life， which is conducive to obtaining better detector performance under high operating temperature conditions. The performance of the p-on-n long-wave focal plane detectors is tested and analyzed at different operating temperatures. At 110 K， the noise equivalent temperature difference （NETD） of the p-on-n long-wave HgCdTe infrared focal plane detectors is 25.3 mK， and the operability is 99.48%， have better working performance under high temperature conditions.

Abstract:Ti TES-based superconducting single-photon detectors with different dimensions between 5 μm×5 μm and 20 μm×20 μm were developed. The measured system detection efficiency （η_sys） is 72% at 1550 nm， and energy resolution （ΔE） is 0.26 eV by integrating an optical cavity during the TES fabrication. Based on the two-fluid model， we extract the key parameters （i.e.， temperature sensitivity， current sensitivity， heat capacity， et. al） of Ti TES-based superconducting single-photon detectors with different dimensions， and calculate the effective response time and ΔE， which are consistent with the measured ones. The obtained results show that it''s possible to realize high η_sys and ΔE by optimizing TES dimension and critical temperature， paving the way for high performance single-photon detectors at telecommunication band.

Abstract:To satisfy the need of Thulium-doped fiber laser pump source， 793 nm high-power semiconductor laser emitters and fiber-coupled module were developed. The laser epitaxy adopts the large asymmetric optical cavity waveguide structure to reduce the mode loss. The waveguide adopts aluminum free GaInP material which improves the facet damaged threshold combined with vacuum cleavage passivation process. Through the optimization of epitaxial structure and facet coating， the output power of the developed laser reaches 12 W@11A， passed the 300 h aging test of 8 W. Seven single emitters were space coupled to 100 μ m 0.22 NA fiber modules. The output power of the model is 40 W@7A， and the electro-optical efficiency is 49.5% @ 40 W.

Abstract:A monolithic ridged half-mode waveguide bandpass filter with a periodic defected ground array has been successfully fabricated. Utilizing the high-pass characteristic of the waveguide and the rejection band generated by the periodic defected ground structure， an effective passband was created. The measured results show a 3 dB passband from 39.4 to 45.4 GHz， centered at 42.4 GHz with a 3-dB fractional bandwidth of 14.1%. The lowest insertion loss of 2.4 dB locates at 44.2 GHz. The suppression in upper rejection band reaches 40 dB at 58 GHz. Compared to conventional rectangular waveguide filters， the width of the proposed filter is reduced by 64%， which benefits to the integration and miniaturization. With the development of the next generation wireless communication （5G） towards millimeter-wave band， the miniaturized millimeter-wave filter has promising potential for 5G communication.

Abstract:Graphene has the excellent characteristics of low defect density， easy large-area transfer and high carrier mobility. However， the zero-bandgap band structure of graphene leads to a short lifetime of photogenerated carriers， which restricts its application in highly sensitive photodetectors. In this work， ferroelectric material CuInP₂S₆（CIPS） was used as the top gate to control the photoelectric characteristics of graphene， and the possibility of improving the sensitivity of graphene terahertz detector was explored. The detection mechanism of graphene photothermoelectric effect and plasma wave effect under ferroelectric control was studied， and a high-performance graphene detector was obtained. At 0.12 THz， the responsivity of detector at room temperature reaches 0.5 A/W， with the response time of 1.67 μs and the noise equivalent power（NEP） of 0.81 nW/Hz^1/2 under a bias voltage of 40 mV and a gate voltage of 2.12 V. At 0.29 THz， the responsivity is determined to be 0.12 A/W， and a NEP is 1.78 nW/Hz^1/2. This work demonstrates the great potential of two-dimensional ferroelectric heterostucture at THz band.

Abstract:In this paper， the effect of misaligned electron beam on the beam-wave interaction has been studied for a 0.22 THz confocal waveguide gyrotron traveling wave tube （gyro-TWT） with linear and nonlinear theory. The effect of electron beam misalignment on linear gain， critical current of absolutely instability and the exciting situation of backward wave oscillation is investigated by dispersion equation. A self-consistent nonlinear theory for confocal gyro-TWT is introduced to analyze the influence of electron beam misalignment on output power and beam-wave interaction efficiency. Meanwhile， the velocity spread is also taken into account to investigate the effect of electron beam quality on the confocal waveguide beam-wave interaction. The results show that the electron beam misalignments can cause efficiency degradation.

Abstract:In order to improve the longitudinal resolution of terahertz imaging detection， a novel longitudinal resolution enhancement method based on empirical mode decomposition of continuous wavelet was proposed. Firstly， the frequency domain signals of the sample are processed by continuous wavelet transform to obtain the corresponding continuous wavelet transforms coefficients. Then， the obtained continuous wavelet coefficients are decomposed by empirical mode decomposition， which is adaptive decomposed into a series of intrinsic mode functions and a residual signal. And the first-order intrinsic mode functions are extracted as the imaging parameter for 3D reconstruction to obtain the final 3D intrinsic mode function image， so as improving the longitudinal resolution of terahertz detection image. In order to verify the effectiveness of the method， the 150～220 GHz high frequency terahertz frequency modulated radar imaging system was used to detect two kinds of sandwich structure composite material with internal adhesive debonding defects， and the proposed method was used to process them. The detection results images of the longitudinal resolution effectively enhanced and the sharpness effectively improved was obtained， which provides a new idea of future terahertz computer tomography imaging and terahertz non-destructive testing research.

Abstract:A metal-tellurene-metal terahertz photodetector， and realized optical detection under millimeter wave-terahertz wave are fabricated. The results show that the terahertz photodetector based on logarithmic antenna tellurene has a high optical responsivity （40 mA/W， 0.12 THz） under zero bias， a response time of 8 μs， and a noise equivalent power （NEP） of 4 pW·Hz^-0.5. This research results provide a new development path for high-performance room temperature terahertz optical detection.

Abstract:This paper reports the material characteristics of In_0.66Ga_0.34As/In_yAl_1-yAs high electron mobility transistor （HEMT）. The linearly graded In_yAl_1-yAs buffer layer was grown on InP substrates by gas source molecular beam epitaxy （GSMBE）. The influence of In_yAl_1-yAs graded buffer layer with different thickness and different indium contents on the surface quality， the electron mobility and the concentrations of two-dimensional electron gas （2DEG） was studied. It was found that the electron mobility and concentration at 300 K （77 K） were 8570 cm²/（Vs）^-1 （23200 cm²/（Vs）^-1） and 3.255×10¹² cm^-2 （2.732×10¹² cm^-2）. The surface morphology of the material was also well improved and the root mean square （RMS） was 0.154 nm when the InAlAs graded buffer layer thickness was 50 nm. And this study can provide strong support for the improvement of HEMT performance.

Abstract:The transient photocurrent generated by femtosecond laser excitation on the surface of Dirac semimetal ZrTe₅ were measured through the reflected terahertz time-domain spectroscopy. Experimental results reveal several physical mechanisms of terahertz radiation generated from ZrTe₅. The results show that the polarization-independent photocurrent is the main component of the surface current， and the terahertz amplitude is related to polarization of the pump laser pulse， which indicates that part of the current is caused by nonlinear optical rectification effect. Under circularly polarized laser pumping， the terahertz amplitude changes four times periodically with the pump laser pulse， which confirms that circular photogalvanic effect of ZrTe₅. Besides， we have analyzed the terahertz time-domain electric field excited by ultrashort laser pulses. The ZrTe₅ inversion symmetry is broken under the excitation of the femtosecond laser pulse， which produces B_1u phonons， forming a transient Weyl point， and undergoing a phase transition from the Dirac state to the Weyl state. This is of great significance to the study of topological phase transitions and other topological states.

Abstract:A high efficiency 285 GHz Schottky diode tripler has been demonstrated based on the face-to-face differential configuration. The proposed concept could improve the power handling capability by a factor of two compared to the traditional balanced circuit based on on-chip capacitors. Meanwhile， the tripler could provide improved DC bias networks with perfect amplitude and phase balance， which shows lower insert losses by leaving out the high required on-chip bypass capacitor. The proposed triple frequency multiplier features inherent suppression on even-order harmonics with the face-to-face differential topology， which ensures better conversion efficiency with doubled anodes. The fabricated tripler has been proved to exhibit a 12% peak efficiency for a nominal driven power of 140~210 mW.

Abstract:A radar/infrared compatible stealth structure based on metamaterial was successfully designed in this paper， and the structure consists of an infrared stealth layer （IRSL）， two microwave absorption layers （MAL） and a microwave reflection layer （MRL） based on indium tin oxide （ITO） film. The IRSL is composed of frequency selective surface of ring hollow structure. The MALs are composed of square ring structures with different period and square resistance. The MRL is composed of continuous conductive film. Each layer is separated by a polymethacrylimide （PMI） materials with different thickness. Experimental results show that the structure can achieve more than 90% microwave absorption in the range of 2～18.6 GHz， and its infrared emissivity is lower than 0.3.

Abstract:Photo-conductive terahertz source （PCA） has been widely used in the terahertz time-domain spectral system （THz-TDS）. In the THz-TDS system， the biased PCA is triggered by a femtosecond laser to radiate terahertz waves to free space due to the accelerated motion of photogenerated carriers under the bias electric field， and a pulse current is formed in the PCA bias loop. Generally， the circuit that loads bias voltage to PCA has different circuit designs， so there is inevitably a specific inductance in the base circuit of PCA mounting. The electromagnetic inertia caused by this will significantly affect the pulse width of the current in the circuit. The pulse width of the current pulse will be widened with the increase of the circuit inductance. Therefore， whether the inductance of The PCA circuit will affect the character of the THz wave radiated from PCA to free space is a problem faced by the circuit design based on PCA. In this paper， inductance elements with different inductance values are added to the PCA circuit， and the time domain waveform and spectrum of THz wave radiated by PCA are tested experimentally. The results show that the inductance value in the PCA circuit has no noticeable effect on the THz wave released by PCA， thus providing an experimental basis for t designing the THz PCA substrate circuit applied to different occasions.

Abstract:A two-dimensional polarization-independent subwavelength grating structure suitable for long wave infrared band have been proposed. Symmetric two-dimensional structure is used to eliminate polarization dependence of one-dimensional grating and increase luminous flux. The evaluation function of grating optimization was proposed， and then the optimization of grating structure parameters was transformed into a path optimization problem. Finally， the ant colony algorithm was used to solve the optimal grating structure parameters. Simulation results show that the proposed two-dimensional multilayer structure has the advantages of polarization independence， narrow grating period， narrow spectral bandwidth and low side band in 10～13 μm band. The convergence speed of the proposed optimization design method is fast. The transmittance of the polarization direction of transverse electric （TE） and transverse magnetic （TM） reaches 70%， and the spectral bandwidth is 260 nm.

Abstract:A complex structure feature enhancement （CEA） algorithm was proposed， and in which the complex structure is represented by high-order total direction variation （HOTDV） regular operator， and the sparse feature of SAR imaging targets is represented by regular operator. The algorithm uses Alternating Direction Method of Multipliers （ADMM） to establish a multi-regular constraint optimization framework， and designs complex structure splitting variables and sparse splitting variables. The analytic solutions of split variables are obtained to enhance the complex structure features and sparse features of SAR imaging targets. The thinking of “dual-decomposition” in the multi-regular constraint optimization framework guarantees the multi-feature processing capability， while the use of Augmented Lagrange term guarantees the convergence and robustness of the algorithm. Finally， simulation and measured SAR data complex structure feature enhancement experiments are designed to verify the effectiveness of the proposed algorithm， and several traditional structure feature enhancement algorithms are compared to verify the superiority of the proposed complex structural feature enhancement algorithm.

Abstract:In order to meet the aerosol retrieval application requirements of polarized scanning atmospheric corrector （PSAC） over land， the information content and a posterior error analysis is applied to the synthetic data in this paper， which inherits from the optimal estimate theoretical framework. We discussed the angle dependence of the degrees of freedom for signal （DFS） of the aerosol and surface parameters in different scenarios， and analyzed the posterior errors of the aerosol and surface parameters. On this basis， the variation trend of the aerosol and surface parameters DFS with aerosol optical depth （AOD） and surface reflectivity is analyzed. The results show that： 1） Under different observation geometry， the total DFS of aerosol parameters vary greatly， and the optimal scattering angle range of aerosol parameters is . 2） The columnar aerosol volumes（ and ） for the coarse mode dominated aerosols and the columnar aerosol volumes（） for fine-dominated aerosol models can be inverted at any observation angle， and some parameters of particle size distribution and refractive index can be obtained at large scattering angle. 3） The increase in polarization information is helpful to the inversion of aerosol parameters under the bright surface， and the increase of short-wave infrared band can improve the ability to obtain surface parameters under the condition of high AOD.

Abstract:A low-power digital readout integrated circuit （DROIC） with 15-bit pixel-level single-slope analog-to-digital converter （ADC） for mid-wave infrared imagers is proposed. A novel pulse comparator featured power-self-adaption is presented for the pixel-level ADC to reduce power consumption. Only when the ramp signal approaches the integration voltage， there is current flowing through the comparator. Furthermore， the pulse output of the comparator also reduces dynamic power consumed by the 15-bit pixel conversion result memories. For achieving the requirement of 15 μm pixel pitch， the memories adopt a 3-transistor dynamic structure and only occupy about 54 μm². The current mode transmission is used to read out the analog-to-digital conversion results to column for robustness against voltage crosstalk between adjacent column bus lines. The 640×512 DROIC with this structure is fabricated in 0.18 μm CMOS process. The experimental results demonstrate the DROIC consumes 48 mW at 120 fps. The total integration capacitor is about 740 fF and the charge handling capacity is 8.8 Me^-. The equivalent noise voltage on the integration capacitor is 116 μV and the peak signal-to-noise ratio is 84 dB at the full well.

Abstract:In recent years， many advances have been made in polarization control and dispersion control of artificial microstructure. However， it is still a challenge to realize achromatic control of arbitrary polarization because the traditional way to calculate the manipulation of metasurface on elliptic polarization have to solve the equation for each piece of data. A direct calculation method based on coordinate transformation is proposed to quickly calculate the manipulation of metasurface elements on arbitrary polarization states. An achromatic focusing metasurface lens based on all-Si elliptic cylinder structure is designed to manipulate elliptical polarization states in the mid-infrared band. The result shows that this method and design can effectively control the elliptic polarization state under the condition of greatly simplifying the calculation process. Compared with the previously reported design based on circular polarization or non-polarization dependence， the application scope of the dispersion control of the metasurface is further expanded.