Abstract:Quantum cascade lasers ( QCLs) are promising high output power semiconductor-based terahertz (THz) sources with narrowlinewidths and wide operating frequency. We have grown and fabricated THz-QCLs based on GaAs/AlGaAs superlattices under the guidance of a newly developed simulation tool based on the framework of Non-Equilibrium Green's Function ( NEGF) method. The latest THz-QCLs demonstrated 270 mW peak power and 2.4 mW average power at 10 K, which is comparable to the highest reported value but with a size of more than 4 times larger than ours. Temperature dependence of the device performance are analyzed through the detailed calculations by using the NEGF method.

Abstract:Flexible high-efficiency III-V multijunction solar cells are being developed for use in unmanned Aerial Vehicles ( UAVs) , wearable devices and space applications. The solar cell epitaxial layers are grown on GaAs substrate by metalorganic chemical vapor deposition ( MOCVD) and then are transferred to flexible substrates by coldbonding and epitaxial lift-off process ( ELO) . Through the design of ELO apparatus and a large number of experiments on the optimal parameter, GaAs solar cell structure can be effectively separated from 4-inch GaAs wafer without defects and degradation in performance. Recently, 30 cm2 large area flexible GaInP/GaAs/In GaAs 3-junciton solar cells on 50 μm polyimide film achieved a 1-sun, AM0 conversion efficiency of 31. 5% with an open-circuit-voltage of 3. 01 V, a short-circuit current-density of 16. 8 mA/cm2, and a fill factor of 0. 845. By using the very light PI substrate, the unit weight of the solar cell is only 168. 5 g/m2 and the specific power is up to 2 530 W/kg.

Abstract:Ultrafast terahertz ( THz) modulation characteristics of organolead halide perovskite films ( CH3 NH3 Pb I3 and CH3 NH3 Pb I3-xClx) were investigated on picosecond time scales using time-resolved THz spectroscopy. Upon photo-excitation, a transient decrease in THz transmission was observed. Compared with CH3NH3PbI3, CH3NH3PbI3-xClx showed a better modulation depth ( 10%) within the range of the photo-excitation powers used.The mechanism underpinning this photoconductive ultrafast response was determined by measuring the transmission properties and calculating the carrier density. The larger crystalline bulk of the CH3NH3PbI3-xClx film produced higher carrier densities than the CH3NH3PbI3 film. These results demonstrate that CH3NH3PbI3-xClx films are promising materials for developing high-performance THz modulators and ultrafast switchable THz photoelectric devices.

Abstract:As CMOS technology scales down, the size of the detector itself becomes an impediment to the further scaling of CMOS single photon avalanche diode (SPAD) arrays. In order to further scale the SPAD detector, the guard ring size of p-well/DNW (deep n-well) SPAD was designed, and SPADs with varied guard ring sizes were fabricated in a 0.18 μm CMOS Image Sensor (CIS) technology. The measured results show that, the guard ring with its size decreased to 0.4 μm is effective in preventing premature edge breakdown (PEB), and SPADs with guard ring size more than 0.4 μm exhibit good avalanche breakdown characteristics with a breakdown voltage of 16 V. Moreover, the guard ring size does not have a significant impact on the dark count rate (DCR) and the photon detection probability (PDP) of p-well/DNW SPADs, and the SPADs for 20 μm diameter active area structure achieve a low DCR of 638 Hz at 25 ℃ and a broader spectral response with a PDP peak of 16% at 530 nm.

Abstract:In this paper, a composite structure metamaterial absorber is designed and simulated with dual metallic particles and holes array. The absorption peak of the proposed metamaterial absorber is excited by the resonance of localized surface plasmon (LSP) modes. The vertical distance (along the x-axis) and horizontal distance (along the y-axis) between two metallic particles are optimized. The absorption of the proposed metamaterial absorber is enhanced due to new LSP modes are excited. Moreover, new absorption bands are obtained with optimizing vertical distance and horizontal distance.

Abstract:FY-4 is the satellite on geostationary three-axis stable satellite platform. Due to the influence of severe external heat flux on the daily cycle and annual cycle, temperature of the scanning fame and telescope of the imager on board will be fluctuated above 40℃. How to adapt the optical machine structure to the severe environment temperature change and ensure the good image quality are the international problem. Matching design with various material and using proper structure is avoiding and reducing distortion of structure and debasing of image. The data on board indicating, the imager has overcame adverse effect for severe fluctuate when day and night. When star sensing, each diffuse spot almost covers only one pixel, and there is not much difference between midday and midnight.

Abstract:In view of GIIRS, a hyperspectral vertical detector equipped on the FY-4A geostationary satellite, a channel selection experiment for the retrieval of temperature is carried out. Using line-by-line radiative transfer model, according to the information content, channels are selected by step-by-step iterative method, which can be used to describe the effective information of various atmospheric parameters in the infrared hyperspectral data. Finally, sensitive channels using for retrieval of temperature profile are obtained，56 channels in global and 58 in FY-4A detection range. The selected channels have small correlation with each other,and they have high information content, which can be used as the representative channel set for temperature profile retrieval research and data assimilation.

Abstract:Hyperspectral remote sensing technology contribute significantly to earth observation. In hyperspectral images (HSIs), the spectral vector of each pixel contains hundreds or even thousands of elements, which provides rich spectral information to efficiently identify and distinguish different types of land cover. However, due to the limited spatial resolution and the complexity of surface features, mixed pixels are common in HSIs. The existence of numerous mixed pixels conflicts with the demands for accurate recognition and interpretation of the material properties of the pixels. Hyperspectral unmixing (HU), which decomposes the mixed pixels into a set of constituent materials called “endmembers”, as well as the corresponding mixture coefficients referred to as “abundances”, was developed to alleviate the mixed pixels problem. Linear unmixing as the basis of HU, due to its physical explanatory and mathematic maneuverability, has been widely concerned. At the beginning, there are many mathematical models to handle Linear Hyperspectral Unmixing(LHU). However, the observation noise, the environmental conditions, the endmember variability and dataset size provide lots of challenges to the inverse problem of ill-posedness. The paper summarizes the literature of the past five years from four aspects: matrix decomposition, archetype analysis, bayesian method and sparse regression to unveil the state-of-art models and problems of linear unmixing.

Abstract:Radiometric calibration was of critical importance for information quantification of satellite remote sensing of environment,and in the field of optical remote sensing,the calibration of remote sensors played key roles. Now, transfer the standard cryogenic absolute radiometer to trap detector was the highest accuracy standard method. With a gold-plated hemisphere reflector added to a thermopile detector with electrical substituted pins, an infrared trap detector is designed and brought forward technical proposals of calibration. Established a high accurate calibration system based on cryogenic absolute radiometer and infrared spectrum calibration facility based on infrared monochromatorto calibrated the linearity, stability, spatial uniformity and absolute spectral responsibility of infrared trap detector. The combined relative uncertainty in the spectral responsivity of infrared trap detector from 1.1μm to 3.0μm was below 1%. From the results of experiment, we can conclude that the calibration technology based on this transfer detector will effectively improve the calibration accuracy of sensors through its shorter calibration chain, and increase the calibration accuracy of infrared absolute responsibility. This improvement will create a one-step scale transfer between the monochromator-based calibration systems and the cryogenic absolute radiometer.

Abstract:In this paper, a simplified nonlinear Eulerian beam-wave interaction theory model for helix traveling wave tubes is developed. Next, derived from the nonlinear model, a second-order Eulerian large-signal analytic solution is obtained by the method of successive approximation. Then, the analytic solution of AM/PM conversion is obtained and the relationship between AM/PM conversion and electron phase is also found. Finally, the Eulerian large-signal analytic solution and the analytic solution of AM/PM conversion are compared to a Lagrangian beam-wave interaction theory model and traditional Eulerian nonlinear models. All the simulations are conducted on a set of millimeter-wave traveling wave tube parameters which are based on a single pitch section of a Q-Band traveling wave tube. It is found that the gain, phase and AM/PM conversion of Eulerian large-signal analytic solution agree well with Lagrangian beam-wave interaction theory model before saturation occurs. The maximum error of gain is less than 8.5% near saturation. The Eulerian large-signal analytic solution gain more accuracy than traditional Eulerian models. The present Eulerian large-signal analytic solution can describe saturation effects which is caused by electron overtaking that cannot be found by traditional Eulerian analysis. Results validate the correctness and effectiveness of our Eulerian large-signal analytic solution and the analytic solution of AM/PM conversion. The analytic model of AM/PM conversion is expected to be useful as a first-hand design and simulation tool of AM/PM conversion for millimeter-wave traveling wave tubes.

Abstract:According to the surface micro-element bidirectional reflectance distribution function (BRDF), the polarization effect of the object’s surface is analyzed. Based on infrared polarization characteristics in long wave band, a model combining the infrared reflected effect and emitted effect is developed to calculate the polarization degree. The simulation result of this model indicates that, the degree of polarization is determined by the value of the ratio of emitted radiation to reflected radiation. With the use of RadThermIR, the emitted radiation and reflected radiation of the sea surface and ship targets can be obtained. Based on radiation results and the proposed polarization calculation model, the polarization degree of the ship and sea water surface in different time and different detected angle is simulated. Experiments were conducted to measure the polarization degree in sea scenarios, and the results show that experimental data are consistent with simulated data, which validates the effectiveness of the proposed model.

Abstract:The reflectance of thermochromatic material vanadium dioxide (VO2) and its fluctuation (noise spectrum) were measured simultaneously during the semiconductor-metal phase transition via self-built experimental system. The noise spectra were measured by a Data-Acquisition Card with real time fast Fourier transforms (FFTs-DAC) , showing the same phase-transition temperature (55 ℃) of the sample as that measured via reflectance measurement. A significant noise peak (around 15-20 MHz) was found in high temperature regime (the metal phase), while being almost flat in low temperature regime (the semiconductor phase). Such a noise peak also reflects that the low-temperature semiconductor phase and the high-temperature metallic phase have different crystal structures. Noise spectroscopy may be widely used to study phase-transtion materials.

Abstract:The direction of thermal radiance is one of the key problems in thermal infrared remote sensing retrieval and product validation. Aiming at row crop, a directional thermal radiance model is built by considering the sunlit/shaded leaf, sunlit/shaded soil, multiple scattering and field of view. The accuracy and sensitivity of the model are discussed and the results show that the model can not only explain the row crop structure and hot spot effect well, but also be suitable for simulating the thermal radiance of continuous canopy. Compared with the FRA97 and the FovMod model, the directional distributions of directional brightness temperature are in good agreement. The root mean square error is 0.18 K and 0.36 K respectively.

Abstract:Ice clouds measurement technology plays an important role in improving the accuracy of the weather forecast and monitoring extreme weather phenomena and so on. Considering the physical dimension and shape distribution of ice-cloud particles, the problem of ice-clouds detecting could be solved by using terahertz passive remote sensing instrument. As an important detecting channel, the 664GHz RF front-end of receiver mainly includes a 664GHz sub-harmonic mixer, a 332GHz doubler and a 166GHz high power source. Based on the design of terahertz doubler, a 166GHz high power frequency multiplying source has been realized by using two way power-combined technology. The measured results show that the output power of above-mentioned source is more than 46mW in 164~172GHz and the highest output power is 59mW at 168GHz. The above-mentioned research could solve the problem of lacking of the G band high power source in the LO chain, and provide technical support for the design of terahertz system working at higher frequency.

Abstract:Instrument line shape function ( ILS) is one of the important physical characterization parameters of the fourier spectrometer, which affects the accuracy of the spectrometer. With the high-precision demand for remote sensing applications such as space measurement and atmospheric detection, howto measure and update the ILS of the on-orbit spectrometer in real time is an important means to improve the accuracy of on-orbit ultrahigh resolution spectrometer. This paper used Fourier spectrometer as an example, according to the principle of ILS, used the characteristics of the measured solar spectral calibration data of the on-orbit ultrahigh resolution spectrometer, which have independent Fraunh9 fer line and less influenced by atmospheric aerosols, to monitor and update the ILS of the on-orbit ultrahigh resolution spectrometer. In this paper, the Kurucz solar spectrum model is used as the reference spectrum, the characteristic peaks of the measured solar calibration spectra and reference spectra are selected in the corresponding band, by adjusting the slit model of the spectrometer, the characteristic peak residuals are iteratively compared to calculate the ILS parameters of the instrument. Finally, after making a convolution between the updated ILS and the theoretical limb spectrum, we compared the results with the measured limb calibration spectrum. The error range is-6% ~ 8%. These results showthat thismethod can provide a reference for supervising and updating the ILS of on-orbit ultrahigh resolution spectrometer.

Abstract:Cyanobacteria is the dominant algae species in inland eutrophic water bodies, and the phycocyanin ( PC) is its unique pigment which can be used as an indicator of its presence. Therefore, the retrieval of PC concentration by remote sensing is of great significance to early warning of cyanobacteria bloom. In this paper, the Random Forest retrieval Model for estimating PC concentration based on the sentinel 3 A-OLCI bands was developed using in situ data collected from Taihu Lake, Dianchi Lake andHongzehu Lake. The results of the importance analysis of input variables in random forest demonstrated that the seventh band ( 674 nm) , the eighth band ( 665 nm) and the ninth band ( 620 nm) have significant impact on the PC estimation. The accuracy assessment showed that the Mean Absolute Percentage Error ( MAPE) of this PC retrieval model is only 34. 86% with the Root Mean Square Error ( RMSE) of38. 67 μg/L. The comparison between the mode developed by this paper and other models, i. e., Simis semi-analytic algorithm and PCI exponential model was extensively conducted, and it was found that compared with other two models, the MAPE was improved by 85. 65% and 15. 65% respectively, and the RMSE was improved by 26. 08 μg/L and 19. 86 μg/L respectively. The atmospheric correction accuracy was further analyzed using the in situ samples and synchronous satellite image, and the result showed that the Management Uint Mathematical Model ( MUMM) method can be successfully used for the OLCI image. The atmospheric corrected spectral curves are consistent with the measured spectral curves, and the MAPEs of 8 bands are all less than 30% at the wavelength range between 560 and 779 nm. The random forest model developed for estimating PC concentration in this paper can be successfully applied to Sentinel 3 A-OLCI images, which provides a newalgorithm for remote estimation of phycocyanin concentration in inland lake.

Abstract:Nonlinear spectral unmixing for hyperspectral remote sensing images can overcome the shortage of linear unmixing methods that failing in explaining the nonlinear mixing effect in more complex scenarios. Meanwhile, bilinear mixture models and their corresponding algorithms are the hot topic of related researches. A nonlinear spectral unmixing algorithm based on the geometric characteristics of bilinear mixture models was proposed. By representing the models' nonlinear mixing terms as the linear contribution of one extra vertex concentrating the common nonlinear mixing effect, solving the complex bilinear mixture models was converted to do the simple linear spectral unmixing. Further, a traditional linear spectral unmixing algorithm was adopted to estimate the abundances directly in an iterative way.Experimental results on simulated and real hyperspectral images indicate that the proposed algorithm can overcome the collinearity effect and the adverse impact caused by fitting too many parameters, and improve both unmixing accuracy and computational speed.

Abstract:In this paper, based on the principle of range finding of FMCW, the range finding system of the double light path FMCW is constructed and improved and the optical fiber delay line is added in the measuring optical path to expand the measuring distance to 65 m. The influence of dispersion in equal optical frequency resampling is also researched and the resampling model with dispersion and optical fiber delay line is deduced in this paper. Therefore, the dispersion correction method that uses frequency amplitude to adjust the phase compensation coefficient in large-length range finding of FMCW is proposed. The experiments show that the optical fiber delay line is added within the range of 45-65 m and the dispersion is corrected effectively. After dispersion correction, the maximum error between the range fining at 65.165 m and the measuring value of interferometer is less than 500 μm. The standard error is 246 μm and the frequency spectrum resolution reaches 123 μm, quite close to the theoretical resolution. The research in this paper provides feasible reference for the large-length range finding of FMCW.