Abstract:The effect of CdZnTe substrates with different polarity （111） plane on slider liquid phase epitaxalgrowth of Hg_1-xCd_xTe was studied. The experimental results show that the composition and thickness of HgCdTe films grown by slider liquid phase epitaxy on （111）A surface CdZnTe substrate were equivalent to those on conventional （111）B surface CdZnTe substrate. The contact angles between HgCdTe melt and （111） A surface and （111） B surface of HgCdTe films grown on CdZnTe substrate were respectively （50±2）° and （30±2）°.It is confirmed that the surface tension between HgCdTe melt and （111） A surface of HgCdTe film is larger combined with micro model analysis. The difference between the surface morphology of HgCdTe film grown on （111） A surface and that on （111） B surface was observed and discussed. The FWHM of the HgCdTe film grown on （111） A surface was 33.1 arcsec. The effect of （111） plane polarity on melt droplet is reported for the first time， and the results show that slider liquid phase epitaxy of Hg_1-xCd_xTe on （111） A surface CdZnTe substrate can greatly reduce melt droplet of the film without reducing the crystal quality.

Abstract:In this work， the surface treatment of InAs/GaSb type-II super-lattice long-wavelength infrared detectors is studied. An optimizing process of N₂O plasma treatment and rapid thermal annealing was developed， which can improve the performance of long-wavelength detector with λ_{50% ?cut-off}=12.3 μm from 5.88×10^-1 A/cm² to 4.09×10^-2 A/cm² at liquid nitrogen temperature， -0.05 V bias. Through variable area device array characterization， the sidewall leakage current was extracted. Under zero bias， the surface resistivity improved from 17.9 Ωcm to 297.6 Ωcm. However， the sidewall leakage couldn’t be ignored under large inverse bias after optimizing process， where surface charge might induce the surface tunneling current. It is verified by gate-control structure that there are two main leakage mechanisms in long-wave device： pure sidewall parallel resistance and surface tunneling. At last， the surface charge was calculated to be 3.72×10¹¹ cm^-2 by IV curve fitting after optimizing process.

Abstract:This paper presents the design method and test results of a switchable dual-wavelength vertical-external-cavity surface-emitting laser （VECSEL）. The two lasing wavelengths with the separation of 50 nm are generated at different pumping powers using one single gain chip. During the operation of the VECSEL， the thermal rollover of output power is observed twice. The first rollover indicates the first switch of lasing wavelength， which is due to the temperature rise within the gain chip and its tuned gain spectrum. The maximum output power of each emitting wavelength exceeds 1.5 W at 0 °C. The lasing wavelength can be switched between 950 nm and 1000 nm with the change of pump power， and dual-wavelength emission with output power of more than1.5 W is demonstrated. We believe that this kind of switchable dual-wavelength VECSEL device has great application potential as dual-wavelength laser sources for providing technical support for mid-infrared radiation.

Abstract:High-power semiconductor laser with nearly diffraction limited narrowband emission was designed and fabricated. The monolithic master oscillator power-amplifier （MOPA） diode laser consists of distributed Bragg gratings， a narrow ridge waveguide and a tapered amplifier. The ridge waveguide with length of 8 mm and width of 3 μm is used as the single-mode seed source. A tapered gain section with length of 7 mm and a full taper angle of 3.3° amplify the seed power. The fabricated device reach an output power of 10.3 W with a slow axis beam quality M² （1/e²） factor of 1.06 and an electro-optic efficiency of 50.5% . The spectral linewidth is 40 pm （3 dB）， and a central wavelength tuning range of 4 nm was realized by the integrated Bragg gratings micro heater.

Abstract:Sheet beam is a kind of electron beam， whose cross-section is approximate rectangular or elliptical shape with high aspect ratio. Compared with conventional pencil beam， sheet beam has many advantages， such as high beam current and large interaction area. Terahertz science and technology have got rapid development in recent years owing to its high frequency， wide bandwidth， high-speed transmission rate， and other advantages of terahertz waves. As a kind of new-type vacuum electron devices， terahertz sheet beam devices have excellent performance such as high power， high gain， high efficiency， and miniaturization. However， it is difficult for sheet beam to keep stable transport over a long distance due to the existence of Diocotron instability， which cannot lead to fully demonstrating its technical advantages. This paper briefly summarizes the generation， formation， and focusing methods of sheet beam， and then introduces the state-of-the-art of terahertz sheet beam devices. Finally， the challenges and development tendencies are discussed.

Abstract:Based on the 70 nm InP HEMT process， a 230~250 GHz low noise amplifier terahertz integrated circuit （TMIC） is designed. The amplifier adopts cascade structure of five common-source amplifiers to achieve low noise amplification. Based on the bias network which consists of microstrip radial stub and transmission line to isolate RF signals and DC bias signals. The first and second stages of the amplifier are designed based on noise matching technology， the middle two stages are designed based on power matching technology， and the last stage focuses on output matching. The on-chip test results show that the small signal gain of the LNA is greater than 20 dB in the frequency range of 230~250 GHz. The Y-factor method is used to complete the noise test of the encapsulated low noise amplifier module. The noise figure of the MMIC amplifier is better than 7.5 dB in the frequency range of 243~248 GHz. Compared with HBT and CMOS processes， the low noise amplifier based on HEMT process has a noise figure advantage of more than 3 dB.

Abstract:An open rhombus metamaterial structure is proposed to suppress the parasitic mode oscillations and improve the beam-wave interaction efficiency of a U-shaped meander-line slow wave traveling wave tube. The effect of the metamaterial on the surface E-field enhancement of the beam-wave interaction and the suppression of the parasitic oscillations were discussed through the combination of the circuit design with the numerical simulation optimization by considering the resonant performance of the metamaterial unit， the coordination of the matamaterial with the slow wave structure， the realizability and simplicity of the circuit structure. The simulated results of a Ka-band U-shaped meander-line slow wave traveling wave tube show that this metamaterial is effective in suppressing the parasitic oscillations and improving beam-wave interaction efficiency， which is of great significance of improving the stability of this kind of traveling wave tube.

Abstract:Video spectral imaging technology is an important direction in the development of remote sensing detection. It can achieve 4-dimensional information acquisition （two-dimensional space + spectrum + time）， which is of great significance for application such as dynamic target detection. The current technical means are mainly based on the filter method， and do not have the high-resolution advantage of grating. Uncoupled Slit Array Scan Hyperspectral imager （uSASHI） and Coded Slit Array Scan Hyperspectral imager （cSASHI） are proposed in this paper， both use multiple slits to achieve simultaneous acquisition of multiple fields of view information to improve the information acquisition rate， and enables video-level spectral imaging. The information obtained by each slit of uSASHI will not be coupled， and n slits can achieve n times the improvement of information acquisition efficiency. The slits of cSASHI are arranged according to the compressed sensing theory， which can achieve under-sampling conditions （sampling rate α≤ 1） video spectral imaging， the information acquisition efficiency can be improved by n/α times. The system designed in this paper finally realizes the 1024*490*30 spectral data cube 10 Hz video spectral imaging method， and cSASHI achieves a higher frame rate. The proposed system provides a new direction for the video spectral imaging technology and lays a better foundation for future applications.

Abstract:Imaging sensors in medium and long-wave infrared spectrum are extremely expensive. Therefore， for most consumers， remote high-resolution imaging and real-time display in these spectrums are still a challenge. This paper proposes an effective block compressed sensing method called Multi-block Combined Compressed Sensing （MBCS） adapting to Focal Plane Array Compressed Imaging system （FPA CI）， which combines parallel sampling and fast reconstruction. The high-resolution images can be reconstructed from low-resolution measurement results in real-time using a low-resolution infrared sensor. The results showed that， compared with the traditional CS-based super-resolution method， this method could greatly improve the quality of the reconstructed high-resolution image and achieve a higher reconstruction speed. The optical prototype architecture and construction of the MBCS measurement matrix for the reconstruction model are also discussed. This study evaluated the reconstruction performance in terms of the block size and found that the optimal block size needed to consider both speed and reconstruction quality. Furthermore， the MBCS reconstruction algorithm with GPU acceleration was implemented to improve the image reconstruction speed of the highly parallel image system. In the experiment， the optical system and the strategy of rapid imaging and reconstruction were verified via simulation and optical experiments， which showed that the imaging speed of 512×512 resolution could reach 5 Hz.

Abstract:For the traditional Fabry-Perot cavity laser， the field perpendicular to cavity wall will be resonantly enhanced until it breaks with the threshold and escapes out of the cavity， while the field emitted obliquely dissipates outside the cavity leading to the low efficiency. Here a high-efficiency laser cavity is proposed resorting to metamaterials. Based on the multipath positive feedback mechanism， the photons emitted form atoms in any direction can only leak out of the cavity along one direction and no photons run out of the cavity which showed potential for improving the efficiency. Furthermore， this combination of cavity is almost independent of atom position. In addition， we designed a realistic dielectric micro-structure system made of two-dimensional photonic crystals to confirm our proposal. When the gain medium is introduced into the system， the cavity can provide both a lower lasing threshold and a higher maximum emission intensity， compared with the individual zero-index materials cavity， demonstrating improved lasing efficiency.

Abstract:Thermophotovoltaic systems perform the characteristics of high efficiency， high power intensity and wide range of heat sources. To further enhance its energy conversion performance， the physical mechanism of opt-electrical conversion and its influence factors need to be analyzed in detail. Therefore， based on the spectral opt-electrical conversion process in the thermophotovoltaic cell， the microscopic carrier transport model in the cell is established. The coupled opt-electrical model is used for the simulation of GaSb thermophotovoltaic cell to explore the effects of spectral characteristics and power intensity of the incident radiation on the cell performance. The results show that under the fixed incident radiation power intensity， the energy conversion efficiency of the cell shows obvious non-monotonicity with the change of wavelength and the peak appears at 1.42 μm. In addition， under the fixed wavelength， with the rise of radiation power intensity， the maximum electrical output power intensity accordingly increases while the rise of the energy conversion efficiency gradually slows down. At 1.42 μm， the rise of the energy conversion efficiency reaches the maximum about 4.85%.

Abstract:Photomultiplier tubes （PMT） have unique advantages in photon-counting LIDAR applications due to its photon-level sensitivity and lack of photon detection dead time. However， the output pulse height of PMT responds to the single photon follows the Gaussian random distribution， and there may produce pile up between different pulses. When using the fixed threshold method to identify the photo-events， the traditional single photon model can not accurately describe the photon detection process of PMT. By analyzing the influence of PMT output pulse height distribution， pulse pile up and the amplitude of photo-event discrimination threshold on the photo-events detection probability， a new PMT photon detection theoretical model was built， and the mode was simplified according to the practical application scene. The applicability of the simplified model was verified by Monte Carlo simulation. The correlation characteristics of the new model in photon-counting ranging are analyzed. A photon-counting LIDAR system is built， compared with Geiger mode APD， the PMT photon detection model has a slight loss of photon detection probability， but it has a smaller ranging walking error and higher ranging accuracy in photon-counting ranging applications. The experiment also proves that the new model is more consistent with the photo-event detection probability of PMT than the traditional single photon detection model. The new model has important guiding significance for the system design and theoretical analysis of PMT photon-counting LIDAR.

Abstract:The images captured by the Division-of-Focal-Plane （DoFP） infrared polarimeters have checkboard effect. Thus， a polarization demosaicking processing of DoFP images is demanded to recover the full resolution polarization images， based on which， the subsequent tasks are then performed. However， the demosaicking processing is usually time-consuming and may introduce demosaicking errors. To achieve object detection by directly using infrared polarization DoFP image， a polarization-weighted local contrast object detection method is proposed. The difference of polarization characteristics between the object and background is first analyzed. Then， a convolution kernel is designed to calculate the Stokes vector directly from original infrared polarization DoFP images. A polarization-weighted saliency map of the degree of polarization image is also proposed， which is used for object detection with the adaptive thresholding. In addition， an edge detection method is used to refine the target detection results and obtain more complete detection results. The experiment results on the infrared polarization DoFP images dataset demonstrate that the proposed object detection algorithm is robust to the conditions of complex background and bad weather.

Abstract:Acousto-Optic Tunable Filter （AOTF） based spectroscopy instruments have been widely applied in biomedical， agricultural， aerospace， and other fields. However， the conventional AOTF spectrometers struggle to achieve increased system luminous flux while maintaining spectral resolution and reducing the number of samples. To address the above problems， this paper proposes an AOTF spectral measurement method based on the compressed sensing （CS） theory. Sparse randomly coded composite optical signal modulation in the spectral domain using the multi-frequency acousto-optic diffraction of AOTF. A modulated composite optical signal is obtained in the spectral domain and recorded sequentially using a single-element detector or a focal-plane detector array. The original spectrum or spectral image data cube is then obtained by using compressed sensing reconstruction algorithms. In order to verify the effectiveness of the present method， we constructed a sensing matrix using the actual measured AOTF spectral response bandwidth data and simulated the effect of compressed sampling and target data reconstruction with the spreading spectrum as the recovery target. The simulation results show that the method can reconstruct the spectral data of 512 wavelength points with 202 compressed samples， and the spectral data sampling rate and compression ratio is 0.39. Under this sampling rate， the method can recover the spectral curve with high accuracy， and the PSNR index reaches 41.75 dB， and the SAM and GSAM indexes are 0.9998 and 0.9754. With the simultaneous multi-frequency drive， the system optical throughput is improved by a factor of 5 on average. Compared with the traditional wavelength-by-wavelength point scan sampling method， this method can reduce the total number of samples and improve the luminous flux of the system while maintaining the original spectral resolution， and also compressing the spectral data， which is of great importance in the fields of weak signal detection， rapid identification of substances， and spectral data transmission and storage.

Abstract:Uncooled infrared imaging technology has a very broad application prospect. However， there are some urgent problems to be solved， such as non-uniformity correction， image detail enhancement and stripe noise. This paper proposes and designs a special SoC chip for image processing for uncooled infrared imaging. The chip integrates a CPU， two DSP processors and a special accelerator for infrared image processing. A single chip can realize real-time image processing such as non-uniformity correction， image filtering， histogram equalization， digital image detail enhancement， stripe elimination and target detection and tracking. At the same time， research and development of uncooled low-power infrared image processing algorithms for chip applications. The 65-nm CMOS process is used to realize the special processing SoC chip for uncooled infrared images， and a small and low-power uncooled infrared imaging system based on the uncooled infrared imaging chip and the image processing SoC chip is realized. The test results show that the imaging system can realize functions such as clear uncooled infrared imaging， target detection and target tracking. The power consumption of the system is less than 2 W， and the volume is reduced by 50% compared with the traditional system. It meets the application requirements of systems with high requirements for volume， power consumption and performance， and has high engineering application value and prospect.

Abstract:A compact polarization splitter rotator （PSR） based on the principle of mode evolution is proposed. The device consists of a tapered TM₀-TE₁ mode converter and a mode splitter with an asymmetric directional coupler （ADC） structure， optimized by particle swarm optimization （PSO） and the principle of spline interpolation. The device is simulated using the finite difference time domain method （FDTD）. The numerical results show： for TE₀ mode input， a low insertion loss （<0.007 dB）， low crosstalk （<-28.7 dB）， and high polarization extinction ratio （>49.1 dB） in the 100 nm （1500~1600 nm） bandwidth is achieved within a device length of only 45μm. On the other hand， for TM₀ mode input， a low insertion loss （<0.34 dB）， low crosstalk （<-47.1 dB）， and high polarization extinction ratio （>15.5 dB） in the whole C-band is achieved. The insertion loss value at 1550 nm is reduced to 0.06 dB. In addition， the tolerance of the device is analyzed and the results reveal that the proposed device is robust. The designed PSR has small loss， compact size， and low crosstalk， which are important for future applications in large-scale photonic integration.