Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
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Abstract:InAs/InGaAs digital alloy strain-compensated quantum well lasers have been grown on InP substrate by gas source molecular beam epitaxy. Multiple quantum wells composed of compressive InAs/In0.53Ga0.47As digital alloy triangular wells and tensile In0.43Ga0.57As barriers were used as the active region. X-ray diffraction measurements confirmed the pseudomorphic growth and high crystalline quality of the QW structures. The peak emission wavelength of the laser is 1.94μm at 100K under continuous-wave driving current of 130mA, and the threshold current density is 2.58kA/cm2. An unusual blue shift of the laser spectral with the increase of the temperature was found, which is originated from the reduced slope of maximum gain function, due to the relatively high internal absorption and weak optical confinement in the laser structure.
Abstract:The silicon-on-insulator(SOI) diode uncooled infrared focal plane array(IR FPA) uses single-crystal silicon PN junction diodes as a temperature sensor, and has various advantages over other MEMS-based uncooled IR FPAs. The basic principle and the advances of the two different SOI diode uncooled IR FPA are describes, including operation of the diode temperature sensor, the design of the pixel structure, the theory calculation and the simulation results. The improved structure, the IR absorbing structure was made in the upper level to cover almost the entire pixel area, in which the fill factor can increase from 21% to 80%. The calculated results show that the sensitivity of the improved structure raises to 7.75×10-3V/K and the noise equivalent temperature difference(NETD) decreases to 43mK(f/1.0) in a 35μm×35μm micromachined structure, which is close to the international advanced level. Meanwhile, the simulation results also confirm the improved performance and the possibility for large format uncooled IR FPAs.
Abstract:A simple SF57 soft glass photonic crystal fiber (PCF) with a rhombic array of four elliptical holes in the core region and a hexagonal lattice of elliptical air hole cladding was proposed. The birefringence and effective mode area of the proposed PCF were studied by the full vectorial finite element method with anisotropic perfectly matched layers. A high birefringent SF57 soft glass PCF with low effective mode area has been obtained, which shows good polarization stability and large tolerance to fabrication errors. The proposed PCF has high birefringenceup to 1.01×10-1, low mode areas of 1.52μm2 and 1.55μm2 for x and y polarizations at 1.55μm.
Abstract:The transmission, negative refractive index (NRI) and figure of merit (FOM) of metal-dielectric-metal (MDM) sandwiched metamaterial, which is perforated with different length of rectangular holes, are numerically studied. The low-frequency transmission peak and maximum transmission peaks of rectangular hole are red-shifted with the increasing of the length of holes. The NRI and the frequency bandwidth of NRI of the rectangular holes are reduced with the increase of the length of holes. It becomes possible to obtain a higher transmission or NRI of metamaterial by adjusting the length of the rectangular holes on MDM metamaterial arrays.
Abstract:A low cost chemical solution method for the preparation of CuInSe2 thin films was proposed. The changes of film properties were studied, which were caused by several parameters of the experiments, including the annealing temperature of the precursor films, the annealing temperature for selenization and different substrates. Copper nitrate and indium chloride were used to prepare the precursor solution. The precursor films were processed by the spin-coating method from the solution, and then selenized at 480℃ to obtain CIS thin films. XRD results show chalcopyrite structure with high crystallinity. SEM images show large grains and relatively smooth and dense surface. EDX analysis results indicate that the ratios of components were in a reasonable range, slightly poor in copper and rich in selenium. The sample films were sandwiched into CIS prototype solar cells as the absorbing layer. The photovoltaic response of a single CIS layered cell reaches 1.6%.
Abstract:Based on the electron motion equation, the propagation of terahertz (THz) wave in plasma is studied. The complex refractive index of THz wave is determined by the plasma electron density and collisions. It decides the propagation of the THz in plasma, which means the change of the THz wave phase and amplitude. THz time-domain spectroscopy system can measure the THz wave phase and amplitude, so it can be used to diagnose the electron density and collisions. Limited by the dispersion relation in plasma, there is a limitation for this method in the electron density measurement. The diagnosis works well for plasmas with density in the range 1012~1016/cm3.
Abstract:To meet the multi-band and integration requirements of the communication apparatus, the coupling and resonance mechanism can be exploited to design a miniaturized-element frequency selective surface (FSS) with two independent pass-bands at Ku-band and millimeter wave (MMW) frequency. The interaction of the layers was analyzed based on the structure, and the precise transmissions for different parameters were obtained using the vector modal matching method. The results show that the structure has two independent and largely separated pass-bands: the first one has miniaturization characteristic with a unit cell size of about λ1/10, where λ1 is the wavelength at the center frequency of the first pass-band; the second one is a rectangular pass-band with a “shallow vale” of -0.828 dB at 47.4 GHz between two peaks at 42.6 GHz and 49.6 GHz, respectively. The transmission and resonant frequency are stable as the incident angle was varied from normal to 60°. The multifunctional FSS can satisfy the engineering requirements via parameters optimization.
Abstract:In silicon solar cells, carriers are generated under illumination of laser, and excess minority carriers emit infrared radiation via a radiative recombination process. A model for minority carrier density in a pn junction induced by modulated laser was developed based on 1D carrier transport equation of semiconductor. The influences of carrier lifetime, diffusion coefficient, surface recombination rate, and photovoltage on radiation recombination, thus on infrared radiation were investigated. The laser-induced photocarrier radiometry signal was monitored using an InGaAs detector (0.9~1.7μm). The amplitude and phase of infrared radiation were obtained by a digital lock-in amplifier. Carrier transport parameters of m-Si solar cell were obtained by frequency-scanning experiments.
Abstract:Terahertz Schottky varistor diode with cutoff frequency of 3.2THz was developed based on GaAs process of Nanjing Electronic Devices Institute (NEDI). The performances of diodes are optimized by optimization of active layer (expital layer and buffer layer) doping, thickness, and Schottky contact area. Physical structure of the nonlinear diode was setup, and EM software and circuit software were combined together for impedance matching analysis. For the D-band doubler, highest measured multiply efficiency is 2.7% at 152.6GHz, and typical efficiency is 1.3% in 147.4～155GHz. For the G-band doubler, highest measured multiply efficiency is 2.1% at 172GHz, and typical efficiency is 1.0% in 150～200GHz.
Abstract:The continuous dehydration processes of adipose, muscle and skin from pork were investigated by transmitted terahertz time-domain spectroscopy (THz-TDS). The changes of terahertz spectroscopy during the dehydration have been observed, and the difference of absorption coefficient and refractive index at the beginning and end of the dehydration among three biological tissue samples were compared. The results show that terahertz spectroscopy is sensitive to the change of water content in the fresh tissues, and water content is the primary factor to influence the absorption coefficient of fresh tissues. Moreover, there are significant differences in the absorption of the terahertz spectroscopy for different tissues, indicates that the transmitted THz-TDS enable to distinguish different biological tissues.
Abstract:Design, simulation and test of a Denisov quasi-optical mode converter, which convert a 96 GHz whispering-gallery mode into Gaussian beam, was introduced. Based on the mode coupling theory, the design method of Denisov launcher is shown. To meet the layout requirement for the 96GHz TE6,2 Denisov quasi-optical mode convertor, a Denisov launcher was optimized. The configuration of the launcher is 6.4 mm for input radius and 52 mm in length. The amplitude of current at the cut edges of the launcher wall decrease to 10% of the focused current in the center. The energy conversion efficiency of output quasi-Gaussian beam reached 96.51%. The tested output field of Denisov mode converter is obtained. The diameter of beam waist is 22.4 mm. The vector conversion efficiency is greater than 95%.
Abstract:Based on the heat transfer model of vertical external cavity surface emitting semiconductor laser with heatspreader, the change in temperature of the quantum well active region has been calculated under different conditions with the finite element method. The equivalent thermal resistance model has been proposed and calculation formula has been derived for the maximum temperature of quantum well, the parameters of which are determined by fitting curves. The calculation shows that the maximum temperature of the quantum well increases linearly with the pump power, while it is nearly inversely proportional to the light spot area. The heatspreader can significantly reduce temperature and its unevenness in the active region of the quantum well. The equivalent thermal resistance model shows that a larger thermal resistance forms due to the difficulty of heat flux to spread in the radial direction, thus thermal diffusion capacity of the heatspreader tends to saturation. As a result the thermal performance of silicon carbide is approximately 75% of that of the diamond.
Abstract:Raman spectra of internal transitions of shallow Be acceptors confined in the center of multiple-quantum GaAs/AlAs wells were studied. A series of Be δ-doped GaAs/AlAs multiple-quantum wells with doping at the well center and wells widths ranging from 30～200 were grown on (100) GaAs substrates by molecular beam epitaxy. Raman and photoluminescence spectra were measured at 4.2 K respectively. The transitions of Be acceptors from the 1S3/2(Γ6) ground state to the 2S3/2(Γ6) first-excited state were clearly observed in Raman spectra. An iterative shooting algorithm and a variational principle were introduced to obtain the 1～2s transition energy of quantum confined Be acceptors as a function of the well width. It was found that the acceptor transition energy increases with the decreasing of quantum wells widths, and the experimental results are in good agreement with the theoretical calculation.
Abstract:An optimized method was proposed to get high resolution and wide-view images of infrared target. To overcome the shortcoming in the traditional ways that had the contradiction between wide-view and high resolution, this experiment scheme was designed that adopted pendulum scanning of whole system along with synchronal image motion compensation. It was shown that the precise speed control and image motion compensation performed decisive roles for the successful achievement of the whole system. Whats more, optimized design had been made for these two parts. The experiment and simulation results are in good agreement. Accordingly, the engineering feasibility of the proposed design method has been validated. The experiment results show that the velocity error of the system is 0.19%. After synchronal image motion compensation, the obtained infrared images have both wide-view and high resolution.
Abstract:A novel classification algorithm of hyperspectral remote sensing image based on nonlinear kernel mapping artificial immune network was proposed. An artificial immune network model was constructed according to natural immune network theory. The training samples of hyperspectral imagery are projected to high feature space with nonlinear kernel function, which improved the sorting method based on similarity in kernel space in artificial immune network. The number of antibodies which are used to recognize training samples is reduced, and the accuracy and efficiency of the algorithm are enhanced. To evaluate the advantage of the proposed algorithm, some other kinds of hyperspectral image classification algorithms were compared with it in the experiment using two hyperspectral image data. Experimental results demonstrated that the proposed algorithm, which acquires higher accuracy and computing speed than traditional hyperspectral image classification algorithms, is a new improved classification algorithm of hyperspectral remote sensing image based on artificial immune network.
Abstract:The integral time adjustment is the primary means to extend the dynamic range of the infrared radiation measuring system. A real-time integral time adjustment method based on radiation calibration was put forward according to the radiation dramatic changes for the re-entry high-speed target, tracking affection and image saturation when integral time is adjusted. Radiation calibration can get the response and the bias of different integral time; the target radiance and the background radiance at the entrance pupil can be calculated by the target information and the background information. Then, the targets and the backgrounds signal value on the other integral time can be computed by the target radiance and the background radiance. The optimal integral time can be predicted by the tracking criterion. Experimental results show that the method can accurately locate the optimal integral time, reduce the number of integral time adjustment in the measurement process, and realize the target continuous tracking accuracy rate of 100%.
Abstract:Retrieval of land surface temperature (LST) is one of the key issues in mid- and thermal-infrared quantitative remote sensing. Compared with thermal-infrared (8~14μm) channel, mid-infrared (3~5μm) channel with the advantages, such as more transparent of atmospheric window and less sensitive to the surface emissivity, might be used to retrieve the LST. A two-channel LST retrieval algorithm, which only uses the night-time data of two mid-infrared channels and introduces the experience of thermal infrared LST retrieval method, has been proposed in this paper. The retrieval accuracies of two channel-combination models, i.e., narrow-channel model (3.929~3.989 μm and 4.020~4.080 μm) and wide-channel model (3~4μm and 4~5μm), were analyzed in detail. The results show that the LST retrieval accuracies of wide-channel and narrow-channel models are approximate ~ 0.5K and ~ 0.3K, respectively. However, compared with the wide-channel model, the noise equivalent temperature difference (NEΔT) and the error of land surface emissivity (LSE) can produce a greater influence on the narrow-channel model.
Abstract:To make full use of the multi-source remotely sensed data for classification, a novel method was proposed based on the integration of full-polarization SAR (HH, HV, VH, VV) data, features of polarization coherence matrix, spectral features provided by optical data, texture features extracted from optical and SAR data and multi-classifier ensemble. Preprocessing for full-polarization data was performed and polarimetric features are extracted from polarization coherence matrix. Spatial textural features including contrast, dissimilarity, second moment, etc., are extracted from PALSAR full-polarization data and optical image using Grey-level Co-occurrence Matrix (GLCM) method. Features of polarization coherency matrix, full-polarization SAR channels, spectral and textures are integrated by 6 strategies. Some well-known classification techniques, including Support Vector Machine (SVM), Minimum Distance (MD), Back Propagation Neural Network (BPNN), Multi-Layer Perceptron (MLP), Random Subspace (RSS), Random Forest (RF) classifiers were selected to test different combination strategies. The parallel and sequential ensemble learning techniques were selected to integrate single classifier for land cover classification. The results indicate that the proposed approach integrating multi-source, multi-features and multi-classifier strategy can make full use of the potential of optical and SAR remotely sensed data for landscape types, and improve the overall accuracy and the accuracy of single land cover type effectively.
Abstract:A combined fluorescence-optical tomography methodology of steady-state is developed to enhance the applicability of the breast-dedicated diffuse optical tomography (DOT). The system employed a 4-channel gated photon-counting technique working in a fiber-switch-based tandem series-to-parallel mode to achieve the tradeoff among the measuring time, probing sensitivity and cost effectiveness. Based on the graphics-processing-unit accelerated Monte Carlo modeling of photon migration, a fluorescence-guided hemoglobin DOT reconstruction algorithm was proposed, which can effectively alleviate the ill-posedness of the hemoglobin DOT using the localization prior provided by the high-contrast fluorescence DOT. The phantom experiments demonstrate that the reconstruction accuracy and quantitative performance can be improved efficiently comparing with the standalone-DOT.
Abstract:AOTF has become an important dispersive device in the field of deep-space remote sensing because of its characteristics such as small size, light weight. For the purpose of developing a method to obtain high-precision spectral inversion data from SWIR spectrometer based on AOTF under the condition of wide temperature range in deep-space exploration, firstly, the principle of AOTF, as well as the configuration of SWIR spectrometer based on AOTF were introduced. Then, the temperature effect on AOTF, RF amplifier and InGaAs detector with TEC in the spectrometer was analyzed theoretically. Through the temperature simulation experiment, a date pre-processing model for temperature effect correction was set up and validated finally, which provided a guarantee for acquiring high-accuracy data in deep-space exploration application.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335