Abstract:The surface leakage current and thermal stability of the infrared detector are highly related to the sidewall surface of the mesa. This work focused on researching the sidewalls'' properties of InAs/GaSb type-II superlattice middle-wavelength infrared detectors by gate-control techniques. It was found the I-V curves for samples with or without annealing showed significant difference at 80 K， and the dark current density of the annealing sample increased from 2.17×10^{-?7 ?}A/cm² to 6.96×10^-5A/cm² comparing with the sample without annealing at the bias of -?0.05 V. The results of gate-control experiment proved the surface fixed charge was increased by 2.76×10¹² cm^-?2 after annealing， which caused severe surface tunneling leakage. And the XPS showed the elemental Sb increased after annealing.

Abstract:By studying the relationship between Everson etch pits on CdZnTe （112）B surface and （111）B surface， the correspondence of Everson etch pits on the （112）B surface and the defects in CdZnTe materials were revealed. The results show that the rod-shaped etch pits on the （112）B surface originate from the bulk defects in the material， or develop from the residual pyramidal etch pits after the extending defects terminate. Three kinds of different pyramidal etch pits on the （112）B surface come from the extending defects with the extending directions in <110>， <211> and <123>， respectively. Results also show that the habit etching faces of some pyramidal etch pits on （111）B surface can no longer form pyramidal etch pits on （112） surface. By observing the lateral shift of etch pits during prolonged etching， it was confirmed that Everson etchant could only reveal the extending defects with the crystal orientations situated near the connection line of ［011］ and ［101］ on the （112） pole figure. Based on the experimental results， the relationship between etch pit density on CdZnTe （112）B surface and the defect density of CdZnTe materials was discussed. The results will be helpful for HgCdTe molecular beam epitaxy to identify the defects in HgCdTe epilayers originating from CdZnTe substrates and better control the quality of CdZnTe （112）B substrates.

Abstract:Photodetectors play a key role in various demanding applications， such as remote sensing， night vision， reconnaissance， medical imaging， thermal imaging and chemical detection， etc. Structures and features of the photodetecting materials directly affect the performance of the photodetectors. In recent years， carbon nanotubes （CNT） have rapidly grown into the alternative materials in photodetection due to their unique optical and electrical properties. The early researches were mainly focused on photodetectors based on individual carbon nanotubes， while potential applications require carbon nanotube thin films as the detecting layers to maximize the photo absorption ability and the detective efficiency. Therefore， preparation of large-area， high-density， high-orientation， and high-uniformity carbon nanotube thin films， and fabrication of the photodetectors based on these thin films， have attracted great research interest in the field of CNTs. Herein we elaborate the development of preparation methods of CNT thin films as well as the recent progress in the CNT-based photodetectors with a discussion on its development tendency in the near future..

Abstract:When an infrared wave is incident on the traditional epitaxial blocked impurity band detector， part of wave energy would be reflected by the device due to its special structural design and the properties of the constituent materials. The energy loss is obviously detrimental to the performance of the device. Here， a kind of bilayer metasurface-based microstructure array is introduced into the epitaxial blocked impurity band infrared detector for suppression of reflection. Experimental results show that the reflectance of the proposed metasurface-based device is lower than 20% in the wavelength range of 25.3～32.2 μm， particularly， which is even less than 3% at the wavelength of 30 μm. Meanwhile， the proposed metasurface antireflection coating also has strong polarization selectivity for incident wave， which meets the requirement for the fourth-generation focal plane arrays development.

Abstract:The photocurrent spectra of metallic cavity quantum well infrared photodetectors under oblique incidence have been measured with incident plane being perpendicular to or parallel to the long axis of the device. The dependence of the resonant mode of the metallic cavity on the incident angle is investigated experimentally and theoretically. The experimental results show that the resonant wavelength of the cavity mode does not change with the incident angle when the incident plane is perpendicular to the long axis of the device， while it moves to shorter wavelength with the increase of the incident angle when the incident plane is parallel to the long axis of the device. The measured results are in good agreement with the calculated results of the derived formula which describes the relationship of the resonant wavelength and the incident angle. The angle dependences of the Fabry-Pérot filter and the plasmonic filter are also analyzed and compared. The results show that the metal cavity quantum well infrared detector has relatively good angle robustness， and it is expected to develop a quantum well infrared photodetector whose response wavelength is completely insensitive to the incident angle by using three-dimensional metal cavity.

Abstract:To improve the retrieval accuracy of cloud macro-physical parameters （cloud base height， CBH； cloud top height， CTH； cloud thickness， CTK；and cloud layer number，CLN） over the plateau area using millimeter-wave radar （MMCR） measurements， this study proposed an improved retrieval method. Differences between MMCR- and ceilometer CL31- derived CBHs， and between MMCR- and Himawari-8（HW8）- retrieved CTHs were analyzed. The vertical distribution and diurnal variation of clouds over the Nagqu of Tibetan Plateau in summer observed by these three instruments were also investigated and compared in detail. Results indicate that the presented method can avoid the influences of range sidelobe and cloud layer misclassification compared with the previous method. MMCR-derived CBHs and CTHs are both higher than the counterparts of CL31 and HW8， respectively. Whereas， their vertical distributions and diurnal variations are significantly coherent. The MMCR has a better performance on the CBH observation of multiple-layered clouds than CL31， and similarly can obtain more accuracy measurements of CTHs than HW8. The radar sidelobe echo has apparent influences on the retrievals of cloud macro-physical parameters for both different cloud types.

Abstract:A folded diamond shaped waveguide slow wave structure （SWS） is proposed and investigated in this paper. Compared with the conventional folded rectangular waveguide SWS， the folded diamond shaped waveguide SWS is larger with the same frequency band， and the bandwidth is broader with the same dimension. The input-output waveguide transition structure and attenuator appropriate for this kind of SWS are put forward. Based on the proposed folded diamond shaped waveguide （FDSWG） SWS， we designed the whole SWS for a 340 GHz traveling wave tube （TWT）， in which the negative phase-velocity tapering technique is adopted to improve the gain. The particle-in-cell results show that its output power and gain at 343 GHz can reach 8 w and 33 dB， respectively. Its 3-dB bandwidth is from 330 GHz to 348 GHz， with a circular electron beam of 15.3 kV and 35 mA.

Abstract:The thermodynamics of La_0.7Ca_0.3MnO₃ film by terahertz transient spectroscopy were presented. The temperature of metal-insulator phase transition of La_0.7Ca_0.3MnO₃ film is observed to occur around 260 K， which is almost the same as that of the ferromagnetic-paramagnetic phase transition. It indicates that the conductivity of the La_0.7Ca_0.3MnO₃ film is closely related to the order of magnetic moments in the film. We find the conductivity of the La_0.7Ca_0.3MnO₃ film can be reproduced with Drude model at low temperature range from 40 K to 200 K， and Drude-Lorentz model at high temperature region from 210 K to 290 K.

Abstract:To monitor the working state of a space target， attitude direction estimation of parabolic antenna loads from a multi-view sequence of the terahertz （THz） inverse synthetic aperture radar （ISAR） images is developed. A space-based THz radar imaging system， which aims to achieve surveillance of high earth orbit satellite targets and small satellite targets， is proposed. Under the theorem that the projection of the parabolic antenna edge （a circle） along arbitrary observation direction is an ellipse， an improved Randomized Hough Transform is proposed to automatically detect and calculate the five key parameters of ellipse components from each THz ISAR image. To ensure the efficiency， accuracy， and robustness of the estimated attitude direction， a two-level estimation algorithm is proposed. The radius and three-dimensional center location of the antenna edge are estimated first. Then， taking these parameters as prior information， the attitude direction is estimated by solving an optimization to minimize the joint error about the length of semi-minor axis and the inclination angle of an ellipse. Electromagnetic scattering data of satellite model targets illustrate the effectiveness and robustness of the proposed method in attitude direction estimation of parabolic antenna loads.

Abstract:Mid-infrared supercontinuum generation in dispersion-engineered ZnSe rib waveguides was investigated for the first time. Numerical results showed that the zero-dispersion wavelength can be shifted to a shorter wavelength by adjusting structural parameters and refractive index contrast between the core and cladding layers in the waveguide. The optical field can be well confined in the 4- and 8-μm wide waveguides with a 2-μm thick cladding layer of Ge₅As₁₀S₈₅ glass. The effect of waveguide parameters on the bandwidth of the supercontinuum spectrum at a 5-cm-long waveguide was also simulated to understand the effect of the pump wavelength and structure parameters on the supercontinuum generation. Our results showed that supercontinuum output could vary over a wide range depending on structural parameters of the waveguide， the pump power and wavelength. An ultrabroad supercontinuum spectrum from 3.0 up to 12.2 μm （> 2 octaves） was confirmed in a 4 μm-width waveguide with a peak pump power of 20 kW and a pump wavelength of 4.5 μm， which is promising as one of the on-chip supercontinuum light sources for many applications such as biomedical imaging， and environmental and industrial sensing in the mid-infrared.

Abstract:A compact airborne coherent Doppler lidar （ACDL） was developed by Ocean University of China. The system design， methods of motion compensation， velocity correction and wind inversion have been explained in this paper. The data analyzed in this paper are based on the first domestic UAV-borne Doppler lidar experiment for offshore wind at Hailing Island， Guangdong Province in 2016. The reliability of correction and inversion algorithms have been proved with ground-based Doppler lidar. ACDL has been proved to be an effective tool to achieve offshore wind observation.

Abstract:Remote sensing image scene classification is one of the current hot topics in the field of remote sensing image processing. Since convolutional neural networks （CNNs） have powerful feature extraction capabilities， they have been widely applied in remote sensing image scene classification. However， the current methods have not fully considered and utilized the complementary information between different layers of CNN and the spatial context information of remote sensing images， resulting in that the corresponding classification accuracy needs to be improved. In order to address these issues， a multilayer feature context encoding （MFCE） network is proposed and utilized to solve the problem of scene classification for remote sensing images. The proposed network is composed of two parts： 1） A densely connected backbone； 2） A multiscale context encoding （MCE） module. The former is adopted to fuse the feature information of different layers of CNN， and the latter is utilized to encode and exploit the spatial context information that resides in the multilayer features. Experimental results on two large-scale remote sensing image datasets demonstrate that compared with the existing remote sensing image scene classification methods， the proposed network framework can achieve a significant gain in classification accuracy.

Abstract:Vertical space characteristics of infrared hyperspectral hyperspectral atmospheric sounder data are indirectly determined by spectral performance indicators of the sounder， and are related to the interested atmospheric parameter and its variation. Based on removing those invalid channels whose atmospheric parameter sounding signal-to-noise are too low， the sounding altitude， sounding altitude resolution， sounding vertical asymmetry and sounding vertical coverage of water vapor and ozone are evaluated for FY-4A satellite infrared hyper-spectral atmospheric sounder GIIRS data. Then， they are compared with the vertical space characteristics of atmospheric temperature sounding. The results show that， 1） similar to atmospheric temperature， FY-4A GIIRS can sound the vertical distribution of atmospheric water vapor， where the vertical coverage of water vapor sounding is troposphere lower than 12km （the sounding peak altitude is below 11km）， and atmospheric temperature can sound the entire troposphere and lower-and-middle stratosphere. 2） FY-4A GIIRS can sound total ozone in 10～21 km， and the sounding altitudes are distributed concentratedly near 16.4 km. This study is helpful to grasp the application ability of FY-4A GIIRS infrared hyperspectral data from the perspective of sounding vertical space characteristics.

Abstract:The symmetry of lattice points in a two-dimensional topological photonic insulator has not been explored as a design freedom. In this study， the influence of the symmetry of the lattice points on the photonic bandgap of an all-dielectric valley photonic crystal （VPC） structure is analyzed by using elliptical lattice points with lower symmetry. The central wavelength and width of the photonic bandgap of the VPC can be modified by varying the direction of the long axis of the elliptical lattice points. The all-dielectric VPC structures with different bandgap widths and central wavelengths are combined in a mirror-symmetrical manner to form all-dielectric photonic topological insulator waveguides， which achieve anti-scatter robust unidirectional optical transmission. This study adds new degree of freedom and provides new possibilities to all-dielectric VPC designs.

Abstract:Aiming at the problem of insufficient samples of infrared aircrafts and low accuracy of fine-grained classification， a method of infrared aircraft few-shot classification based on meta learning is proposed. Based on meta learning and combined with multi-scale feature fusion， this method can effectively extract commonness among different classification tasks while reducing computation， and then classify different tasks with fine-tuning. The experiments proved that this method could improve the classification accuracy of mini-ImageNet dataset while reducing the calculation amount by about 70%. The accuracy of fine-grained classification for infrared aircrafts with few samples reached 92.74%.

Abstract:Phosphorene provides a new choice for the construction of optoelectronic devices based on two-dimensional materials because of its adjustable band gap， high carrier mobility and in-plane anisotropy. Plasmon-induced transparency in the π-cascade and compact structure of phosphorene was numerically simulated by the finite difference time domain method. By changing the structure distribution and Fermi energy level of phosphorene and other parameters， a wide range of tunable plasmon-induced transparency from mid-infrared to far-infrared was realized. Among them， the number， intensity and position of transparent windows are flexibly modulated. In addition， the sensitivity of induced transparent window to the angle of polarization is studied. The results provide a reference for the development of biosensors， photo-detectors and optical switches based on the surface plasmon of phosphorene.