Abstract:First-principles calculations based on density functional theory have been performed on the nonmagnetic 2p light element carbon-doped rutile TiO2, which is very appealing for spintronics and infranics. The results show that carbon dopants tend to couple ferromagnetically around the Ti atom in the rutile structure, and the magnetic moment per C is about 1.3 μB. The ferromagnetism is predicted to be the collective effects from a p-d exchange hybridization and a p-d exchange-like p-p coupling interaction, between the impurity (p-like t2g) and valence (p) states.

Abstract:In this paper, 90-nm T-shaped gate InP-based In0.52Al0.48As/In0.65Ga0.35As pseudomorphic high electron mobility transistors (PHEMTs) with well-balanced cut-off frequency ft and maximum oscillation frequency fmax are reported. This device with a gate-width of 2×25 μm shows excellent DC characteristics, including a maximum saturation current density Idss of 894 mA/mm, and a maximum extrinsic transconductance gm,max of 1640 mS/mm. The off-state breakdown voltage (BVoff-state) defined at a gate current of 1mA/mm is 3.3 V. The RF measurement is carried out covering the full frequency range from 1 to 110 GHz, an extrapolated ft of 252 GHz and fmax of 394 GHz are obtained, respectively. These results are obtained by the combination of gate size scaling, parasitics reduction and the on-wafer measurement in the full frequency band from 1 to 110 GHz.

Abstract:GaSb-based laterally coupled distributed feedback (LC-DFB) quantum well lasers with a wavelength of 2 μm were successfully prepared. Second order Bragg gratings are fabricated by holographic lithography and inductively coupled plasma etching (ICP). The etching conditions for grating preparation are optimized and a single longitudinal mode lasing at room temperature is obtained. The room temperature peak power output per facet exceeds 5 mW with a maximum side-mode suppression ratio of more than 24 dB.

Abstract:Abundance estimation (AE) plays an essential role in the hyperspectral image processing and analysis. Owing to the simplicity and mathematical tractability, various methods based on the constrained linear regression are usually developed to estimate abundance matrix. The obvious limitation of these approaches is that the fitness between the estimated data and ground-truth data does not include the structural information, e.g. row difference and column difference. In this paper, a novel linear regression algorithm is proposed by jointly adding the multi-structured information to the traditional linear regression model. And it is employed to modify sparse and low-rank abundance estimation model to improve estimated accuracy and robustness. Firstly, a new linear regression model is established by taking into account the structural information. Then, mathematical proof of the new linear regression method is presented. Afterwards, it is applied to modify the sparse low-rank abundance estimation model. Finally, Alternating Direction Method of Multipliers(ADMM) technique is adopted to solve the new model. The experimental results demonstrate that the proposed algorithms can capture structural information and improve the estimated performance on the simulated dataset and the real hyperspectral remote sensing images.

Abstract:The spectral features and differences in bright vegetation area, shaded vegetation area and water area were investigated by the experimental data from four medium resolution remote sensing images of ALOS AVNIR-2, CBERS-02B CCD, HJ1A-CCD2 and Landsat 7 ETM. Based on the near-infrared band and normalized difference vegetation Index (NDVI), Normalized Shaded Vegetation Index (NSVI) was constructed and the enhancements of spectral differences and classification effect were also evaluated. The results show that NSVI has increased the relative diferences of the spectra in bright vegetation area, shaded vegetation area and water area, and reduced probability of misapplication for the spectral data. The NSVI threshold method was employed to classify the four experimental images. The overall accuracy is over 97%, and the overall Kappa coefficient is above 0.96. The detection accuracy of the shaded vegetation area is over 94% and the Kappa coefficient is also higher than 0.96. By using radiation differences of the near-infrared band between the ground objects, NSVI can solve the problem that NDVI can only partially weaken the topographic effect and enlarge the spectral differences among the ground objects. NSVI enhances the validity of the ground objects especially in the shadow detection and avoids the “saturation” problem of NDVI. It can provide a new solution to remove the shadow in remote sensing images.

Abstract:In this paper, an improved 16-element small-signal topology for InAlAs/InGaAs InP-based HEMTs has been proposed. The gate-source resistance (Rgs) is introduced into the topological structure to characterize the gate leakage current caused by the short gate channel spacing. The output conductance (gds) and drain delay factor (τds) are proposed to characterize the impact of drain voltage on channel current and also the phase change by drain-source capacitor (Cds), which can improve the fitting accuracy of S22. The parasitic elements are calculated through open and short dummy structures, and the intrinsic parameters are extracted by Y-parameters after de-embedding the external parasitic parameters. The ultimate values of parameters are determined by optimization procedure to gain the best fitting precision. The results show that the simulation values of S-parameters and frequency characteristics fit well with the measured values, and the introduction of Rgs and τds reduces the model error. The accurate and appropriate small signal model for InP-based HEMTs would be of great importance in the design of high-frequency circuits.

Abstract:An inverted surface relief vertical-cavity surface-emitting laser (ISR-VCSEL) with annular light emitting window has been presented and investigated. The most prominent structural feature of the device is that the stable single-higher-order transverse mode emission is supported. The laser emits output power up to 9.8 mW at about six times threshold current with an SMSR close to 30 dB, and it can still keep the output power of 4 mW even at as high ambient temperature as 360 K. The measured far field power intensity shows a Gaussian-shaped beam profile with low divergence.

Abstract:Photoacoustic spectroscopy is the most sensitive approach of trace gas analysis reaching part per trillion by volume level and available for engineering practice, but not sufficiently satisfy the measurement demand of gases with weak absorption in near infrared zone. This paper presents a simple interrogation method using a dual-wavelength schema to switch effectively between the absorption and unabsorption lines of the gas to be measured, which takes good advantage of the current modulation characteristic of laser diode. Measurement results of methane demonstrate the feasibility and a relatively simple way to reach resolution of 0.46 ppm of the dual-wavelength method when the laser power is 2.1 mW.

Abstract:In order to solve problem of the limited training samples and keep consistency in one region, a new two-level classification scheme is proposed, which combines sparse auto-encoder (SAE) and Boundary-preserved Wishart-markov random fields (BWMRF). In the first layer, an SAE classifier is applied to obtain an initial classification and more accurate regional boundaries. In the second layer, Boundary-preserved Wishart-markov random fields have been used to correct the previous classification results. Meanwhile, the boundaries classified by sparse auto-encoder are preserved, and a new error correction strategy is applied to ensure the classification accuracy. Therefore, accurate region boundaries supplied by SAE are explored to divide different regions, and the coherent in each region will be realized during the BWMRF process. Compared with other classification methods, this method obtains higher classification accuracy and proves the validity of the new scheme.

Abstract:The doping distribution in the multiplication zone of n+-p-π-p+ structured linear avalanche photodiode (APD) based on standard CMOS process greatly determines the device performance. The influences of implanting dose and the depth of its peak concentration of the p-layer on device characteristics are simulated using Silvaco. The simulation results show that, at a given gain of 50, the optimized doping dose of P layer is 1.82×1012/cm2 with depth of peak concentration 2.1 μm. Under optimized conditions, the reverse bias voltage is 73.1 V, the excess noise factor is 4.59, and the excess noise index is 0.34~0.45 (λ=800 nm),which are better than those reported. The performance of the APD may be further improved through process optimization.

Abstract:The effects of the interface traps on the quantum efficiency and the crosstalk of a back-illuminated p-on-n mesa InSb photovoltaic infrared detector were studied based on Silvaco 2D numerical simulation. The distributions of the recombination rate, the hole current density and the electric field change with the position and the density of the interface traps, and their relationships were analyzed. The results show that the interface traps has a profound effect on the inherent physical mechanisms of the steady-state performance of the InSb detector. The traps at the N-InSb/passivation interface both on the back and between the pixel mesas improve the crosstalk performance at the cost of the decrease in the quantum efficiency. Because the regions they affect are different, the influence extents of the traps at different positions on the two steady-state performance are different.

Abstract:An accurate design approach of full WR-3 waveguide band balanced frequency tripler is proposed in this paper. Compact Suspended Microstrip Resonator Cell (CSMRC) is adopted for input filtering and circuit matching. CSMRC brings relatively higher out-of-band rejection and reduce the size and the channel width of the tripler. The entire tripler is composed of two waveguide-to-suspended stripline transitions, a pair of two anti-parallel diodes, a CSMRC and two matching lines. The design approach is verified by comparing the measured results with the simulated ones. The measured output power of two samples is between 45 to 95 μW at frequencies from 225 to 330 GHz, and the average output power is 60 μW. The conversion efficiency is from 1.5% to 3%, and the optimum efficiency is 3% with +5 dBm drive power.

Abstract:We report the selection of the lidar instrument operating wavelengths, the Monte Carlo simulation was made, knowledge that imprecise temperature affect on the systemic bias and random errors of surface pressure measurement was developed. When 764.765 nm and 765.094 nm were selected as detection wavelengths, then 764.948 nm between both online was selected as reference wavelengths, the emulation research show that measurement error is least. Excellent detection wavelength was neither in absorption peak value wavelength, nor was in trough between two absorption line, that were on wing of p13 and p14 absorption line of A band. This result has directive function to build up an IPDA for measurement of surface pressure.

Abstract:This paper focuses on point target detection with single frame under complicated background and suggests the conception of valid pixel detection. A modified point target detection method based on Markov Random Field was proposed in terms of local correlation of point target and local difference of target and background. This algorithm conducted initial configuration of iterative optimization for MRF by a signal-to-clutter ratio criterion based on complex background separability measure. Moreover, the prior probability model of MRF label field was improved by designing a new prior probability energy function based on Euclidean metric: firstly the label field probability response model of MRF to Euclidean space distance was built; secondly the response ability of the target probability to neighborhood label change was improved by a higher order energy function. The results indicate that: the performance of the detection algorithm in structured background is better; the target’s radiation-dimension detection ability of the modified label field prior probability model is more vigorous compared to the traditional Potts model. The proposed algorithm is a more robust one.

Abstract:Aiming at the characteristics of infrared over-sampling scanning imaging, an infrared point target detection method based on DCNN (Deep Convolution Neural Network) is proposed. Firstly, a regressive-type DCNN is designed to suppress the background clutter of the scanning image. The network does not contain any pooling layer, so can input the original image of any size, with the size of output image after clutter suppression in accordance with the input image. Subsequently, the post-suppression image is tested and the original data of candidate target region is extracted. Finally, the candidate target area raw data is input into the classification-type DCNN to further identify the target and remove the false alarm. Meanwhile, a large number of training data of infrared over-sampling scanning images are designed, and two networks are trained effectively. The experimental results show that the proposed method is superior to multiple typical infrared small target detection methods in the target clutter ratio gain, detection probability, false alarm probability and running time under different clutter backgrounds, and is applicable to the point target detection of the infrared oversampling scanning system.

Abstract:Hapke model has been widely used in the photometric study of regolith as the parameters has specific photometric and physical meaning. To reverse these parameters, photometric observations are needed for a wide range of incidence, emission, and phase angles of the regolith. However, it is difficult to have such wide range angles in the remote sensing and in situ observation. So, it is very important to know how we can get precise result with the limited observations and we can do the research at laboratory. In this work, we got the reflectance of olivine with large range of phase angle by ASD spectrometer and got reflectance of two kinds of Lunar analog samples by Chang’E-3 VIS-NIR Imaging Spectrometer. Also we learned how to reverse Hapke model parameters. As a result, we find that we can get accurate result with limited measurements. Also, we have got some result of two Lunar analog samples (one with glass and the other without glass) with analysis of relative parameters of Hapke model.

Abstract:The slow wave characteristics of truncated sine waveguide are analyzed by the simulation method. The two-section high frequency electromagnetic system based on truncated sine waveguide is proposed, which can be used for the W-band Traveling Wave Tube (TWT). Meanwhile, the input/output coupler and attenuator are designed for the high frequency system. We obtain the beam-wave interaction results in the high frequency electromagnetic system by the Particle-in-cell（PIC）simulation method. The PIC simulation results indicate that the TWT can produce the output power over 200W and gain over 30dB in the frequency range of 92-101GHz.

Abstract:Bright supercontinuum was experimentally generated in an argon-filled hypocycloid-core Kagome fiber pumped by a femtosecond laser. The spectrum of the generated supercontinuum can be controlled by changing the gas pressure and input pulse energy. By use of a pump laser centered at 980 nm, a bright broadband supercontinuum ranging from 340 nm to 1550 nm was generated. The dynamics of the supercontinuum generation in the argon-filled Kagome fiber was investigated using an accurate carrier-resolving unidirectional pulse propagation equation.

Abstract:In this work, nanowire-nanocone double-layer nanoforests are prepared based on a plasma repolymerization technique, and then double-layer hybrid nanoforests are realized by introducing noble metal-nanoparticles on surface of the nanoforests using a magnetron sputtering step. The entire process is simple and fully compatible with conventional micro-fabrication, besides, it is a parallel technique, thus large area fabrication of the hybrid nanoforests is easy to achieve. Moreover, such a hybrid nanoforest is able to combine light trapping effect and surface plasmonic effect thus to achieve an average absorption as high as 84.1% in a broad wavelength range of 1.5~25 μm. With such a broadband high absorption property, the double-layer hybrid nanoforests are expected to be widely used to improve performance of infrared devices, and to expand applications of such devices.

Abstract:In order to enhance the photon flux and brightness of a synchrotron source, and improve the thermal stability of optical elements, synchrotron radiation source often operates in the qusi-constant current injection (Top-Up) mode. The Top-Up mode can maintain a stable beam current in the storage ring of Synchrotron Source. When the electron is injected into the storage ring from the booster, a noise induced by the instantaneous fluctuation of the beam current in the storage ring will cause a large fluctuation on the interferogram, which can be observed by the FTIR spectrometer used in IR experimental endstation. The median filtering algorithm is not sufficient to filter the noise according to the noise characteristics. Therefore, a zone median filter method is proposed to eliminate the noise introduced by the Top-Up mode. A set of the processes of zone median filtering algorithm is designed, which can eliminate the Top-Up mode induced noise on the interferogram automatically. Simulation results show that: the filtering algorithm can be applied to eliminate the noise on the interferogram introduced by the Top-Up mode effectively,so the method can be used to enhance the spectral SNR of the spectrum in the Top-Up mode.