Abstract:The molecular beam epitaxy growth of InAsSb film is presented. Dependence of Sb compositions on Sb4 fluxes was studied. Utilizing the high combination tendency of In and Sb atoms, the composition of InAsSb layer is highly controlled.

Abstract:A broadband terahertz quasi-optical detector has been developed with frequency from 140 GHz to 325 GHz. The terahertz quasi-optical detector consists of a silicon lens with high resistivity and a monolithic detector chip. A double slot antenna was fabricated on the chip with a Schottky diode assembled cross the terminals of the antenna. This compact structure endows the chip with the functions of receiving THz radiations from space and converts them into baseband. To improve the directivity of the antenna on chip, the hyper-hemispherical silicon lens was designed and optimized by MLFMM (Multilevel Fast Multipole Method)) algorithm, resulting in good radiation performance. The antenna gains at 220 GHz and 324 GHz was calculated to be 26 dB and 28 dB, respectively, from the measured radiation patterns. The measured responsivities of the detector achieve 1 000~4 000 V/W from 140 GHz to 325 GHz and the noise equivalent powers (NEP) were estimated to be 0.68~2.73 pW/Hz.

Abstract:A novel low dark count rate single-photon avalanche diode (SPAD) device was designed and fabricated with the 0.18 μm CMOS Image Sensor (CIS) technology in this paper. The device is comprised of an effective P+/LNW (light N-well doping) junction for photon detecting and a low concentration N-type diffusing circular guard-ring formed by the deep N-well diffusion. The latter prevents premature edge breakdown (PEB) of the junction and ensures it to operate in Geiger mode. The measured results show that the SPAD achieves a low dark count rate (DCR), and the DCR is 260 Hz at an excess bias voltage of 2V for 8 μm diameter active area structure at room temperature.

Abstract:In conventional terrain classification for the polarimetric SAR (PolSAR) images, color features are rarely involved unless in one recent supervised work. Unlike that work, the color features are exploited in a novel framework for the unsupervised classification of urban areas in this paper. Firstly, based on the recent four-component decomposition model of the PolSAR data, the common color spaces, such as YUV, RGB, HSI, and CIELab are calculated. The color feature is quantitatively selected from these color spaces by introducing the color entropy. Then together with the texture feature and the extended scattering power entropy, the adaptive mean-shift algorithm is used to segment the PolSAR data into clusters. Finally, the clusters are merged according to the G0 distribution-based distance measurement. The proposed framework is verified by the experiments on one AIRSAR L-band and two Radarsat-2 C-band PolSAR data. The classification accuracy indicates that the proposed method has superior discriminative ability for urban areas compared with existing works.

Abstract:The band structure of a GaAs/AlGaAs double quantum well was calculated via shooting method and finite element method. The energy needed for a ground-excited state transition is 43.3 meV, indicating that a 1.2 to 1.8 kV/cm electric field can cause a horizontal transfer of carriers. The designed double quantum well structure was grown by MBE. Good metal-semiconductor contact was obtained via optimizing annealing conditions. The negative resistance effect was obtained in a 1.5 kV/cm parallel electric field, which is differs from the electric field for GaAs Gunn effect. It was concluded that the mechanism for negative resistance effect is electrons transfer from high mobility layer to low mobility layer, namely real space transfer(RST).

Abstract:A series of variable-area photodiode devices with different P/A ratio were prepared by different passivation processes. The relationship between R0A of the devices and 1 000/T was analyzed in temperature range 77～147 K. The result shows that the dark current of device is dominated by diffusion current in the temperature range. The distribution of R0A was studied. The bulk defects and non-uniformity in HgCdTe thin films have an important influence on the performance of the device at 77 K. Due to the increase of the bulk diffusion current at 127 K, the effect of the defect on the device is significantly weakened. R0A values of the devices decrease with the increase of P/A ratio, which indicates that the surface passivation has an important effect on the device at 77 K and 127 K. The relationship between R0A of the devices and P/A ratio was analyzed based on Vishnu Gopal model. The surface leakage of the device is confirmed, and the effect of surface passivation on the performance of the device is effectively reduced by the improvement of the passivation process.

Abstract:Equivalent circuit for the Schottky diode was established based on measurement results of I-V and C-V curves. The design of 0.67THz sub-harmonic mixer included three-dimensional structures and broadband matching circuits. Results show that the 3dB bandwidth of RF is 47GHz with the center frequency at 0.685THz. The double-sideband conversion loss is between 13.1dB and 16dB. The lowest double-sideband noise temperature is 11500K at 685GHz.

Abstract:A design example of diffractive telescope is presented and the aperture of objective is 3 meters. The operating wavelength of the system is 7.7~10.3 μm and spectral bandwidth |Δλ/λ| is about 1/3. It is shown that the system approximately attains diffraction limit. We developed a small scale diffractive telescope and its’ image quality was perfect.

Abstract:An integrated order blocking filter covering the wavelength range from 0.4μm to 25μm was designed and fabricated for the hyperspectral imaging system. Based on the characteristics of the reflective Offner convex grating dispersion, the optical substrate is divided into three areas with different working band to block the high-level spectra. The optical transmittance efficiency of each band is higher than 93%. Fine mask technique was adopted to ensure the size of adjacent area between different band less than 30 μm. The spectra utilization efficiency is improved effectively.

Abstract:A folded waveguide traveling-wave tube (FW-TWT) amplifier which is driven by backward-wave has been studied in this paper. Folded waveguide backward oscillator (FW-BWO) is used as driven source and drives the traveling-wave tube amplifier. The working frequency of FW-BWO is 216GHz. The optimized results were simulated by 3D-Magic. By optimizing the length and height of the loss-material and the current of cathode, the output power of the FW-TWT is 96W. The length of the waveguide is only about one centimeter.

Abstract:Based on resonant subband transitions, the second-order and third-order nonlinear optical effects in an asymmetric quantum well (AQW) with the structure of GaAs/Al0.2Ga0.8As/Al0.5Ga0.5As have been theoretically investigated on the conditions of parabolic and non-parabolic bands. With the increase of two pump wavelengths λp1 and λp2 separately, the second-order nonlinear difference frequency susceptibility χ(2)DFG and the two third-order nonlinear susceptibilities χ(3)ω1 and χ(3)ω2 increase to a maximum value, and then drops down rapidly. In comparison with the condition of parabolic subband, the curves of χ(2)DFG, χ(3)ω1 and χ(3)ω2 show obvious red-shift as a function of the short pump wave λp1 on the condition of nonparabolic subband. However, with the increase of long pump wave λp2, no changes of peak position have been discovered. The physical origin of all red-shift in nonlinear optical effects is the different energy level gaps on the two conditions of subband, which causes the changes in resonant condition. The primary reason for different peak values is the different transition matrix elements, and the other reason is energy level gaps.

Abstract:A laser coherent detection system with wavelength of 1 550 nm was established. The stability of the system has been improved because of the all-fiber optical path. The underwater vibration signals with different frequency, intensity and depth have been studied in experiments. The results show that the fluctuations of water surface are detected by the laser coherent detection system. The vibration characteristics of the underwater acoustic field can be extracted effectively by the time-frequency analyses. Experimental results indicate that the detection system can be used to detect real-time underwater acoustic signals at frequency from 40 Hz to 10000 Hz with test error less than a few Hz. Therefore the laser coherent radar can be used for feature extraction and recognition of underwater target in real time.

Abstract:We presented a novel approach for accurate temporal coherence decorrelation analysis of InSAR echo signal. The proposed algorithm is divided into three steps: Firstly, using the modified Intensity-Driven Adaptive Neighborhood (IDAN) algorithm to estimate interferometric coherence; then using least squares fitting to remove deviation; finally, obtaining accurate temporal coherence decorrelation component with coherence decomposition technique by separating approximate unbiased coherence. We analyzed the ENVISAT ASAR data from the area of Los Angeles with the new method. The result was compared with the existing methods. The result shows that the new fusion algorithm is able to obtain more reliable and accurate temporal coherence decorrelation component. Meanwhile, the characteristics for the new method of non-threshold and almost adaptive performance were proved.

Abstract:Based on 86 satellite-ground synchronous samples taken from four measurement campaigns in Lake Hongze in 2014~2015, a single band (671 nm) model was developed to estimate the suspended particulate matter (SPM). The model performed well (R2=0.74, RMSE=8.58 mg/L), with validation (R2=0.72, RMSE=11.98 mg/L). Then, 464 VIIRS images (2012~2015) were used to estimate SPM concentrations. The results show that the concentrations of SPM increase in the autumn and winter and decrease in the spring and summer. While it is higher in the east and central area of the lake than in the north and west sections of the lake. Inter-annual comparisons show a decrease of suspended particulate matter(SPM) over the short four year period. The visible/infrared imager radiometer suite(VIIRS) performs well in estimating SPM in Lake Hongze, allowing for an extension of MODIS analysis approaches and improving the remote sensing of inland lakes in the future.

Abstract:A sensor was proposed to measure temperature, concentration and pressure of the atmosphere based on scanning wavelength modulation spectroscopy. The method using 4fpeak/2fpeak and 2f/1f signals of H2O spectral lines was analyzed and the sensor design program was studied. Frequency division multiplexing technology is adopted to measure gas parameters of static cell in the temperature range of 300~1 200 K using the two H2O spectral lines (7 429.72 cm-1 and 7 454.45 cm-1). Experimental results show that the iterative algorithm has rapid convergence rate and high accuracy. The measured gas temperature, pressure and concentration of H2O are consistent with the predicted value with the largest relative errors 4%, 6% and 6%, respectively.

Abstract:A high-linear birefringence photonic crystal fiber is pumped by a femtosecond laser pulse generated by Ti: sapphire laser. The center wavelength of the pulse is 820 nm, which is located in the anomalous dispersion region of the photonic crystal fiber near zero dispersion. Experimental results show that the central wavelength of soliton is red shifted while that of dispersion wave is blue shifted into the visible wavelength with the increase of pump power. When the average power of the pump is increased to 0.45 W, the ratio of the dispersive wave to the residual pump intensity can be up to 42.67, while the spectral width of dispersion wave is broadened to 81 nm as well as the soliton bandwidth to 231 nm. Near infrared broad soliton and the highly efficient dispersive wave in the visible region was generated in the high nonlinear photonic crystal fiber, which provides an important reference for the frequency conversion and spectral broadening of the femtosecond laser.

Abstract:The design of a novel magnetron injection gun with curved emitter for a W-band gyrotron traveling wave tube has been presented. An axial velocity spread of 1.84% with beam velocity of 1.1 is obtained by manual optimization. To overcome the complexity and inefficiency of manual optimization, numerical optimizing methods are employed. Optimizing codes based on genetic algorithm (GA) and simulated annealing algorithm (SAA) are completed by using the MATLAB program language. 2-D electro-optic code EGUN is employed to calculate and optimize the electron trajectories and beam parameters. The achieved velocity spreads optimized by GA and SAA are 0.81% and 1.05%, respectively, when velocity ratio is kept at 1.1. Compared with manual optimization, the numerical optimizing methods do not need the designers to get involved in the optimizing process. Besides, the numerical optimizing methods feature automation and high-efficiency, and often, the optimizing results are better.

Abstract:This paper proposed a novel phase unwrapping method which unites beat-frequency localization, equivalent ground interferometric phase removing and ambiguity number estimation. First, a rough localization is conducted under the beat frequency with the information of beam pointing. Then, by introducing the technology of ground interferometric phase removing in interferometric synthetic aperture radar(InSAR), an equivalent approach is used to alleviate the pressure of phase unwrapping. At last, the ambiguity number is estimated by statistic processing. The practical data processing results showed that the proposed method can not only solve the relative phase wrapping caused by large target size, but also obtain the absolute phase, making three-dimensional(3-D) localization and 3-D imaging possible.

Abstract:As analytical fusion tracking algorithms based on visible and infrared images always have low robustness in complex environment, a novel adaptive analytical fusion tracking algorithm based on optimized co-training framework was proposed. Firstly, selecting the most discriminative weak classifiers from weak classifier pools based on infrared and visible images respectively are achieved by weighted multiple instance learning boosting technology, which relieving classifiers’ discriminative capacity decreasing owing to the added error positive samples. Then, classifiers’ sample bags are updated by co-training criterion under the help of adaptive prior knowledge import strategy. Lastly, efficiency analysis of the proposed algorithm was achieved based on error model. Comparative experiments on multiple sequences tracking show the contributions for improving tracking robustness from different parts of the proposed algorithm, and then, demonstrate that it outperforms state-of-the-art tracking algorithms based on single source image or other fusion schemes on robustness.

Abstract:Large aperture static interference imaging spectrometer (LASIS) is characterized by that all CCD chips of 180 spectral bands scan through the same field. Based on this, a novel method is proposed to achieve high accuracy band-to-band registration by re-imaging with virtual CCD based calibration. Considering the geometric factors that cause hyperspectral image mismatch, such as changes of attitude and orbit data, lens distortion and so on, this method reimages the hyperspectral images with the virtual CCD calculated from the calibrated interior orientation to remodel the error sources and eliminate the relative errors. Validation experiments using different area data of RS-14 show that with the proposed method, the band-to-band registration accuracy of LASIS is better than 0.16 pixels.