Abstract:Long-wavelength VCSELs on an InP substrate was designed and fabricated with an active layer of 1550 nm. The top Distributed Bragg Reflection （DBR） mirror system has been constructed by fabricating 4.5 pairs of SiO₂/Si top DBRs. The threshold current was 20 mA and maximum output power around 7 μW under continuous wave （CW） operation at room temperature. More importantly, the lasing spectrum is 1554 nm and the full width at half maximum is 3 nm.

Abstract:Based on the first principles study, this paper investigates the control of the work function and optical properties of graphene absorbed with metal atoms. The work is conducted with eight different kinds of metal that are of most reactive (Na, K, and Al) and commonly used in experiments (Ti, Ag, Ru, Au, and Pt). The results show that all the adatoms loss electrons, resulting in the Dirac cone of graphene moves toward the direction of the low energy except for the adsorption of Ti and Ru atoms. The work functions of all the adsorption structures arelower than that of graphene. Particularly, the smaller work functions of Tiand Ru adsorption are observed due to the strong interaction between the Ti or Ru atom and graphene. Furthermore, the optical properties change greatly owing to the existence of adatoms. ?₁(0) varies greatly with the different adsorption structures, the absorption intensity of the visible light and the infrared increased greatly.

Abstract:In infrared radiation temperature measurements of wide-dynamic, high-resolution and wide-spectrum, Fourier Transform infrared (FTIR) spectrometer is a commonly used measurement unit. The nonlinearity of the spectral responsivity is one of the main uncertainty contributions to wide dynamic infrared spectrum measurements of radiation sources. Based on the flux superposition principle, nonlinearity measurement system of FTIR spectrometer measurement system was established. The experimental research on the drift characteristics of the blackbody radiation source and FTIR spectrometer measurement system during the representative nonlinearity measurement time were carried out. The quasi-linear drift effects on the nonlinearity measurement were eliminated by permuting the aperture measurement order. The nonlinear characteristics of FTIR spectrometer measurement system were experimentally measured at 200~1 000℃. The nonlinearity measurement results and associated uncertainties at 3.9 μm and 10.6 μm are reported respectively.

Abstract:To apply Si-based photodetectors in the near-infrared band and improve their responsivity. A regular and orderly microstructure array was formed on the surface of silicon-based photodetectors by plasma lithography. Besides, an film was grown on the microstructure surface by atomic layer deposition (ALD) to study its anti-reflection and passivation effects. The surface reflectivity and characteristic curves of the device were compared and the light responsivity of the device under 808 near-infrared light was calculated. It is found that the responsivity of the device is increased from 0.063 to 0.83.

Abstract:To develop high frequency, broad bandwidth and low voltage traveling wave tube (TWT), the folded rectangular coaxial waveguide slow wave structure (FRCW-SWS) is proposed in this paper. Operating at overmoded condition, the proposed FRCW-SWS has relatively high operating frequency and acceptable transmission characteristics. A double ridge-loaded waveguide-to-coaxial-waveguide converter is designed and applied as the input/output coupler to incorporate the broadband characteristics of the FRCW-SWS. The hot performance of this overmoded FRCW-TWT at W-band is investigated using particle-in-cell (PIC) simulation. The simulation results indicate that the output power can be over 13.7 W in the frequency range of 76～110 GHz, when the length of the SWS, the beam voltage and beam current are 32 mm, 3230 V and 150mA, respectively. The maximal output power is about 27.4 W at the frequency of 108 GHz, corresponding to the RF efficiency of 5.65%.

Abstract:A terahertz photo-excited tunable metamaterial sensor is investigated. It is composed of a hybrid metal-semiconductor structure (which is a split ring resonator (SRR)) and a flexible polyimide substrate. Silicon is filled in the gaps of the structure. Simulation results reveal that the conductivity of the semiconductor component can be tuned by changing the external pump light’s power, resulting in resonant peak shift of the composited metamaterial structure. The electric field and surface current density distributions of this structure under different resonant frequencies are also analyzed. The physical mechanism of this device has been further discussed. Moreover, the resonant peak will be red-shift as the concentration of the surrounding environment (calcium chloride, CaCl₂) increases, and the sensitivity is 11.4 GHz/M, which makes it a possible application in liquid sensing in terahertz region.

Abstract:In terahertz imaging, the sparse design of the array can cause degradation of the grating-lobes. In this paper, based on the traditional coherence factor(CF) weighting method, phase coherence factor(PCF) and sign coherence factor(SCF) are designed, which are applied to multi-input and multi-output(MIMO) terahertz sparse array imaging grating-lobes suppression. The simulation results of the point target show that the peak side lobe ratio(PSLR) is reduced by 17.81 dB, 24.56 dB and 22.74 dB after grating lobes suppressed by CF, PCF and SCF, respectively. The results measured in the 340 GHz 4T16R sparse array imaging system also show that the suppression effect of PCF and SCF on grating lobes is 6dB and 4dB better than CF, respectively.

Abstract:This paper presents a 76～81 GHz CMOS millimeter wave quadrature down-mixer for automotive radars. The transformer-based gm-boosted method is utilized in the pre-amplifier for improving gain performance. A parallel inductor and two cross-coupled transistors with dynamic current-bleeding are combinatorially exploited to resonate the parasitic capacitance between the transconductance stage and the switching stage and improve noise figure and conversion gain. The proposed mmW down-mixer is implemented in a 55-nm CMOS process and the measurement results show that the BW_-3dB is 5.5 GHz, the peak gain is up to 4.1 dB with <0.16 dB I/Q mismatch （at 50 Ω load）, the input P1dB is -6 dBm and the minimum noise figure is of 19 dB while consuming 40 mW of power. Excellent FOM is achieved by combining above-mentioned techniques.

Abstract:The EMI filter of infrared cryocooler driving system was designed and simulated. With considering the characteristic of the crucial device in system, the co-simulation model of the system was built by using the appropriate algorithm. The interference mechanism was extracted and analyzed with the assist of the co-simulation model. Based on the impedance mismatch theory, the relationship of the filter performance and the impedance of the source and load was analyzed. Finally, based on interference mechanism, a method for filter design and optimization was raised, and it can optimize the filter’s performance and reduce redundancy effectively. A test was established and proved the feasibility and accuracy of the method.

Abstract:Directional polarimetric camera （DPC） can acquire multi-spectral, multi-angle, radiometric and polarimetric reflectance data from the earth. A method for the inversion of aerosol optical depth was presented according to the multi-spectral, multi-angle and polarimetric data. Firstly, the polarized land surface reflectance is calculated using the Nadal-Breon semi-empirical model to deduct the land surface radiation from the measured value. Secondly, the vector radiation transfer model derived from double-accumulation method is used to construct the lookup table of aerosol optical parameters. Then, the minimum residual is calculated to determine the aerosol model dynamically for the retrieving of aerosol optical thickness over the land. Using the L1 products of DPC, the aerosol optical thickness in eastern China is retrieved. The values are compared with the product of MODIS and the data measured at the same time from AERONET ground station displaced at several places. Results show that the distribution of aerosol optical thickness retrieved from DPC data is in good agreement with MODIS aerosol product. And also, the results of DPC and AERONET ground station are highly correlated. The correlation coefficients of 670 nm and 865nm bands are above 0.8. It demonstrates the feasibility of the algorithm and what we have considered over land.

Abstract:This paper introduces the research situation of low-level wind shear identification, and proposes a low-altitude wind shear recognition algorithm based on airport application for laser wind radar. The key monitoring areas and warning methods are designed in a targeted manner. Low-level wind shear data in this paper are collected form the LIDAR wind field detection tests conducted from January to April 2016 and December 2017 to June 2018 at several airports with different climate and terrain complexity. The shear identification capability of the algorithm was evaluated by comparing with the results of a foreign company"s LIDAR and aircraft voice report. The experimental results show that the algorithm can effectively detect low-level wind shear in the detection range of laser wind radar, and the hit rate can reach over 88%.

Abstract:Semantic segmentation of very high resolution (VHR) remote sensing images is one of the hot topics in the field of remote sensing image processing. Traditional supervised segmentation methods demand a huge mass of labeled data while the labeling process is very consuming. To solve this problem, a semi-supervised semantic segmentation method for VHR remote sensing images based on Generative Adversarial Networks (GANs) is proposed, and only a few labeled samples are needed to obtain pretty good segmentation results. A fully convolutional auxiliary adversarial network is added to the segmentation network, conducing to keeping the consistency of labels in the segmentation results of VHR remote sensing images. Furthermore, a novel adversarial loss with attention mechanism is proposed in the paper in order to solve the problem of easy sample over-whelming during the updating process of the segmentation network constrained by the discriminator when the segmentation results can confuse the discriminator. The experimental results on ISPRS Vaihingen 2D Semantic Labeling Challenge Dataset show that the proposed method can greatly improve the segmentation accuracy of remote sensing images compared with other state-of-the-art methods.

Abstract:With the development and maturity of the photon-counting ldiar technology, photon-counting ldiars are increasingly used in marine mapping. Based on the JONSWAP wave spectrum theory and micro-face model theory, this paper first establishes a photon-counting lidar simulation model via the Monte Carlo method. By substituting the system parameters of a spaceborne lidar into the proposed model, the photon distributions reflected by sea surfaces with different wind speed conditions are simulated and verified by comparing the averaged numbers of photons measured by the ICESat-2 spaceborne lidar. Then, the ranging errors under different wind speed conditions are discussed. The results indicate that the elevation value measured by photon counting lidars will be smaller than the actual elevation of sea surfaces, and the bias and standard deviation of photon counting lidars will increase when the wind speed is rising. When the wind speed is 10 m/s, the cumulative pulse number is 100, the elevation bias is approximately -2.5 cm and the standard deviation is 3.6 cm. The proposed simulation model and analysis results have important reference for optimizing the system parameter design of a photon-counting lidar for sea surface observations and correcting the bias on sea surface observations.

Abstract:In this paper, two coherent Doppler lidars were used to observe the low-level wind shear induced by dry thunder storms and terrain at Beijing Capital International Airport. The experiments respectively adopted Doppler Beam Swing (DBS) and Glide Path wind shear identification method to alert the wind shear of the above two types. The results show that the DBS method and Glide Path mode can respectively identify horizontal wind shear caused by dry thunderstorms and terrain. Dry thunderstorms bring sudden increase of wind velocity, abrupt change of wind direction and strong convection of updrafts and downdrafts, which causes the low-level wind shear. Terrain-induced wind shear with the transient and sporadic nature is mainly produced by the interaction between high-speed airflow and complex underlying surface.

Abstract:An effective polarimetric synthetic aperture radar (PolSAR) image classification technology is the basis of the successful application of PolSAR. However, compared with relatively mature PolSAR imaging technology and system design, PolSAR image classification technology lags behind. Aiming at the main problems existing in the research of object-oriented classification of PolSAR images, this paper proposed a new object-oriented classification method, which combines multi-target polarimetric decomposition, ReliefF-PSO_SVM and ensemble learning. First, polarimetric decomposition is implemented for PolSAR image using various methods. Polarimetric parameters extracted using different polarimetric decomposition methods are combined into a multichannel image. Second, the multichannel image is divided into numerous image objects by implementing multi-resolution segmentation. Third, features are extracted from the multichannel image. Fourth, ReliefF-PSO_SVM algorithm is applied for feature selection, and N feature subsets with the highest fitness are retained for classification. Each feature subset corresponds to a classification result. Finally, ensemble learning technology is used to integrate the classification results. The study site is located at the southeastern part of Changchun City, Jilin Province. A RADARSAT-2 Fine Quad-Pol image was selected as the data source for this study. The proposed method was applied to land-use classification, and good classification results were obtained. The overall accuracy was 85.06% and the kappa value was 0.8006. In addition, three other classification methods were performed for comparison. The comparison results further proved the superiority of the proposed method in PolSAR image classification.

Abstract:In order to effectively detect weak and small infrared targets under complex background, a single-frame method based on horizontal-vertical multi-scale grayscale difference （HV-MSGD） is proposed to enhance weak targets, and the strong edges of background are suppressed by the difference between the distance and grayscale values. There is discontinuity between the target area and the surrounding area. To strengthen their differences, HV-MSGD combined with bilateral filtering （BF） can increase the intensity of the target while suppressing the background. Candidate targets are further extracted by adaptive local threshold segmentation and global threshold segmentation. In order to further verify the impact on single-frame detection, the above-mentioned single-frame detection algorithm is combined with an improved untraced Kalman particle filter （UPF） to implement trajectory detection. The experimental results show that this method is better than other methods under weak signal-to-noise ratio （SNR）. It can enhance the target while suppressing the background, and the enhancement effect is 6-30 times that of other methods. In the experiments, the input signal-to-noise ratios were 2.78, 1.77, 1.79, 1.13, and 1.16, respectively. After image processing, the background suppression factors （BSF） are 13.48, 21.33, 11.73, 20.63, and 121.92, and the signal-to-noise ratio gains （GSNRs） are 40.09, 71.37, 27.53, 12.65, and 131, respectively. The probability of detection （Pd） of this method is also superior to other algorithms. When the false alarm rate （FAR） is , , , , and , the Pd values of the five sets using real sequence images are calculated to be 94.4%, 92.2%, 91.3%, 95.6% and 96.7% respectively.

Abstract:Aiming at the fusion of infrared intensity-polarization image, an intelligent fusion method based on spatially weighted averaging method optimized by fireworks algorithm is proposed. Based on the optimization model, the boundary conditions of fireworks algorithm are determined. The fitness function based on comprehensive relative-entropy is established by introducing the weight of relative-entropy. Finally, the fusion experiments on three groups of infrared image “ground”, “truck” and “car” are carried out with LP, PCA, GP, MP, DWT and SIDWT methods, and the fusion results are evaluated objectively and compared with the visual effects. The experimental results show that the proposed method can effectively achieve the fusion of infrared intensity map and polarization map, and retain the infrared intensity and polarization characteristics. Combining the visual effect and objective evaluation results, the method in this paper is superior to the comparison algorithm in relative-entropy, similarity of summary structure and total mutual information index.