Abstract:The effect of resonant cavity structure on the performance operation of InAs/GaAs quantum ring inter-subband photodetector is studied for detection of terahertz radiations range. In order to confinement of optical field within active region and consequently enhancement in responsivity of device, two periods of Al2O3/GaAs distributed bragg reflectors are used as bottom dielectric mirror and a thin layer of Au material as top mirror of device. For further improvement in detectivity, Al0.3Ga0.7As/ In0.3Ga0.7As resonant tunneling barriers are included in absorption layers to reduce dark current of device. Proposed photodetector shows a peak responsivity of about 0.4 (A/W) and quantum efficiency of 1.2% at the wavelength of 80μm (3.75THz). Furthermore, specific detectivity (D*) of device is calculated and results are compared to conventional quantum ring inter-subband photodetector. Results predict a D* of ~1011(cm.Hz1/2/W) for device at T=80K and V=0.4V which is two orders of magnitude higher than that of conventional QRIPs.

Abstract:In order to reveal the scattering characteristics of targets at terahertz frequencies, high resolution radar imaging was studied based on the high frequency (HF) electromagnetic calculation data. Considering huge data flow of 3D image formation, a novel azimuth-elevation imaging theory with its result similar to a photograph of targets was proposed. The point spread function is derived for revealing the high resolution performance and scatterers identification capability. Simulation results demonstrated that HF method can solve radar cross section of perfectly electrical conducting (PEC) target accurately and fast at terahertz frequencies. The high resolution images show that the sub-wavelength features of targets are resolvable. It also implies that terahertz radar can attain more fine information about targets, which will be helpful for target recognition.

Abstract:This paper presents an Ultra-wideband (UWB) low-noise amplifier (LNA) based on a single-ended common-gate (CG) in cascade with cascode configuration. The proposed LNA is implemented by a standard 90-nm RF CMOS technology and it features that the measured flat gain is more than 10 dB from 28.5 to 39 GHz, the -3 dB bandwidth is 15 GHz from 27 to 42 GHz which covers almost the entire Ka band, the minimum noise figure (NF) is 4.2 dB, the average NF is 5.1 dB within the 27-42 GHz range, the S₁₁ is better than -11 dB over the overall testing band, and the input 3rd-order intermodulation point (IIP3) is 2 dBm at 40 GHz. The DC power dissipation of the whole circuit is as low as 5.3 mW. The chip occupies an area of 0.58*0.48 mm2 _{including all pads.}

Abstract:The absorption spectra of H2CO were recorded at room temperature with a typical equivalent sensitivity of 3.61 × 10-6cm-1Hz-1/2 by utilizing a QCL based gas detection set-up. Relative frequency calibration based on F-P etalon and absolute frequency calibration based on CH4 spectrum are calculated and shown in this paper. Frequency tuning spectra are also measured and processed when changing the operation temperature from -15℃ to 20℃ with increment of 5℃. As nonabsorbent gases, He, Ne, Kr, O2 and CO2 were used to determine the line intensity of H2CO line centered at 1253.14392cm-1. Buffering spectrum in N2 and the corresponding statistical residuals were given to show broadening characteristics and the difference between the observed absorption data and the expected Voigt fit value with increasing the pressure of buffer gas.

Abstract:The growth and fabrication of a 320×256 type-Ⅱ InAs/GaSb superlattice long wavelength infrared focal plane array detector were reported. The superlattice material was grown on GaSb substrate using molecular beam epitaxy (MBE) technology with a PBIN structure. The structure of infrared absorption layer is 14ML (InAs)/7ML(GaSb), the focal plane array had a pixel size of 27μm×27μm and a pitch of 30μm. The device fabrication process consisted of mesa dry etching, side-wall passivation, metallization and flip-chip hybridization with readout integrated circuit (ROIC). At 77K, the detector had a 100% cut-off wavelength of 10.5μm, and a peak detectivity of 8.41×109cmHz1/2W-1. Concept proof of infrared imaging was also demonstrated with the focal plane array at liquid nitrogen temperature.

Abstract:This paper proposed a one-dimensional soil moisture content data assimilation system based on the ensemble Kalman filter (EnKF), the distributed hydrology-soil-vegetation model (DHSVM), microwave radiative transform model (advanced integration equation model, AIEM) and optically semi-empirical model (temperature-vegetation dryness index, TVDI) for soil moisture content retrieval in bare soil. Numerical experiments were conducted at the middle reaches of the Heihe River Basin from June 1 to July 2, 2008. The results indicate that EnKF is an efficient approach to handle the strongly nonlinear problem. By assimilating multi-source remote sensing observations, the assimilation method works successfully with DHSVM and significantly improves the soil surface moisture estimation in the surface layer and root layer, the root mean square error (RMS) and mean bias errors (MBE) decrease 0.0217 and 0.0329 in surface layer and 0.0193 and 0.025 in root layer respectively, both in Yingke station. In the Linze station, the retrieve precision was also improved. It is practical and effective for soil moisture content estimation by assimilation of multi-source remote sensing data.

Abstract:Push-broom camera has been widely applied to aviation and spaceflight remote sensing for the earth.Due to its big optical gain, it is prone to laser jamming. Jamming problem of laser to push-broom camera is noticed at all times. In allusion to jamming effects and mechanism difficulty problem of laser to push-broom camera, a jamming experiment system of laser to push-broom camera has been constructed. Laser jamming experiment to push-broom camera has been done, experiment result is presented. Laser jamming mechanism was analyzed on basis of the configuration of linear CCD detector and image processing principle. The relation of camera pupil entrance laser power and image jamming area was established using experiment data. Most factor of affecting camera image jamming area was analyzed. Jamming of laser to push-broom camera and gaze camera was compared. This result can be used for evaluating laser jamming effect to push-broom camera and researching camera laser protection method.

Abstract:The design of a 220GHz high power coaxial gyrotron is presented. The device operates in the fundamental harmonic TE04circular electric mode. The operation parameters for cavity were 50kV, 10A, and 8.4 Tesla which were optimized by self-consistent nonlinear theory. The electron beam is produced by a coaxial triode magnetron injection gun (MIG) with an average perpendicular-to-parallel velocity ratio 1.5 and perpendicular velocity spread of 5.2%. Particle-in-cell (PIC) simulations have been performed for the whole gyrotron. Both the results from theoretical analysis and PIC simulations show that the designed gyrotron can produce more than 200kW output power with power conversion efficiency of more than 40%.

Abstract:Sheet-beam formation has been studied using the combination method of theory analysis and simulation verification. A design theory of the sheet-beam electron gun has been proposed. The beam voltage, the beam current, the half-thickness of beam at the waist position, the half-thickness of the cathode, and the width of the cathode are used to calculate the parameters of the sheet-beam electron gun such as the cathode cylindrical radius, the anode-cathode spacing, the anode cylindrical radius, and the throw. Then through simulation, the sheet-beam electron gun for millimeter-wave vacuum electron devices are set up based on the theoretical results.

Abstract:A high-power and narrow-linewidth MgO-doped periodically poled LiNbO3 optical parametric oscillator was reported, which is based on a volume Bragg grating output coupler pumped by a linearly polarized Q-switched Nd: YAG laser. Maximum output power of 8.4W at a wavelength of 2.1μm with beam quality factor M2 of 3.8 and 4.1 in horizontal and vertical directions was obtained using a double-pass pump four-mirror standing-wave geometry. The spectral bandwidths are 0.41nm and 0.53nm for signal and idler waves, respectively, which are confined within 2nm.

Abstract:Carbon black (CB) was dispersed into high density polyethylene (HDPE), which was transparent to terahertz wave, by melt-mixing and compressing method. The dielectric properties of the composites in terahertz region were then investigated. Reversed effective medium approach (REMA) was firstly applied to the analysis of the composites. The real part and imaginary part of dielectric constants, refractive index and absorption coefficient of the pure CB particles were extracted with REMA from that of the composites with fixed concentration and an alterable parameter of depolarization factor. The results indicate that the calculated dielectric constants, absorption coefficient and refractive index of CB from different concentrations coincide well with each other. Combined with the direct current conductivity test, the depolarization factor was found to be correlated to the CB concentration and its distributing state in the composites. It has an apparent decrease at the percolation threshold of CB/HDPE composites. The extracted results were then analyzed with the dipole relaxation model. The relaxation time, relaxation strength and dc conductivity of the pure CB particles were obtained.

Abstract:Plasmonics paves the way for controlling electromagnetic waves at the nanoscale by coupling light to coherent electronic excitations(surface plasmon resonances, SPRs)at the interface between dielectric and metallic materials. Plasmonic resonances in metallic nanostructures have drawn increasing attention because of their extensive applications, including waveguides, microscopies, sensors, lasers, and light emitting diodes. The strong confinement of light associated with surface plasmon resonances can give rise to the fast development of different kinds of sub-wavelength photonic components and devices. The photon-electron excitations allow solid confinement of the electromagnetic waves to nanoscale dimensions which may lead to strong field enhancement. To manipulate the plasmonic resonances, diversified designs have been used to modify the features, sizes, and spacing of the metallic structures. In comparison with these physical approaches, varying the separations of optically functional nanoelements is a much more efficient method. Here, we investigate the optical response of plasmonic crystal arrays composed of square-and circle-shaped particles with different separations. Using focused ion beam milling, plasmonic crystal arrays with normal separation(relatively large size)are first fabricated, leading to weak coupling regime between adjacent particles. To minimize redeposition effects and achieve fine patterns, small beam current and parallel milling method are applied. In order to further generate plasmon-enhanced reflection, the separation between neighboring plasmonic crystals is remarkably decreased. As the separation reduces, the coupling effects become stronger, enabling strong coupling regime. It is found the reflection can be significantly enhanced by strong coupling effects and the resonance wavelength redshifts with decreasing separation when the gap size is smaller than 30nm. To verify the experimental results, finite-difference time-domain calculations are carried out. Simulations agree well with the measured data. By combining gold(Au)nanoparticle structures with ATR-FTIR spectroscopy technique, the absorbance of glucose can be effectively enhanced. The plasmonic crystal structures and new findings under investigation in this work may find extensive applications in chemical sensing, detecting and optical waveguiding.

Abstract:To fulfil quantitative monitoring of fire line contour (location, length and area) for forest fire prevention and suppression, the algorithm for fire identification have been developed using dynamic thresholds of window combining the images obtained in thermal band, short wave infrared band and near infrared band of Landsat TM/ETM+. In order to get the quantitative result of fire line contour, the identified fire image has been processed by a series method such as the connectivity identification, hole filling, little speckle elimination and edge smooth. An automatic fire line contour identification program has also been developed using Landsat TM/ETM images in ENVI 4.8 IDL condition. The method and program have been validated by selected typical forest fires which had taken place in northeast forest region of China and Амрская бласть of far east region of Russian. The validation results showed that the total accurate percent is 86.44%, the total false percent is 13.56% (the total omission is 1.77% and the commission is 11.79%). So, the methodology can be satisfied the need to knowing the fire line contour parameters for forest fire prevention and suppression operation.

Abstract:The scattering properties of multi-walled carbon Nanotubes(MWCNTs)were investigated by using modal technique based on Bessel and Hankel function. It was found that the results of scattering vary with radius and numbers of carbon nanotubes. Under transverse magnetic(TM)wave conditions, the different structure of MWCNTs is not sensitive to the frequency, and the scattering intensity on the TM wave of the same radius nanotubes increases with the increasing of the number of nanotubes. Under transverse electric(TE)wave conditions, the different structure of MWCNTs exhibit high selectivity for frequency range, and the scattering intensity increases with the increasing of the radius and number of nanotubes. It is very helpful to detect infrared wave using carbon nanotubes.

Abstract:Two fuzzy adaptive resonance neural networks were utilized to build the background models of thermal and visible components. According to the multiple-valued immune network model, a series of immune response strategies were designed to cooperate B cell with T cell to build the interactive model, which takes the infrared background model as B cell and the visible background model as T cell. With the interactive model, the targets are detected according to the degree of fuzzy match between pixels and models. Experimental results show that the F1 measurement of the proposed approach is up to 96.4%. It is able to complement information between thermal and visible components effectively. The method is capable of detecting targets in complex scenes effectively.

Abstract:Based on the smooth cylindrical waveguide structure, an novel polarization converter for high-order TEmn mode is presented. Using the general coupled wave theory and numerical optimization method, a polarization converter for 94GHz TE5,1 mode is studied. The proposed polarizer, consisting of transition section and phase shift section, features structurally simple and easy construction. From 88GHz to 98GHz, the maximum axial ratio of the polarizer is less than 1.18. The performance of polarizer was veritfied by comparing the ideal radiation field and the measured one. The research work provides a physics model for designing low-order waveguide mode polarizer with high conversion effciency.

Abstract:The Gaussian model was used to describe the algae vertical profiles and analyze the influence of algae vertical profiles on band ratio algorithm via Hydrolight simulation. It indicated that there was no definite relationship between reflectance of water surface and the algae biomass because of different algae vertical profiles. The algae blooms at the water surface could lead to the failing of retrieval algorithm. Excluding algal bloom case, there were good correlation between band ratio algorithm and chlorophyll-a concentration at 0.25m water depth or averaged chlorophyll-a concentrations at 0~0.25 / 0~0.5m water depth, which is independent on the algae biomass and algae vertical profiles. Comprehensive consideration on chlorophyll-a concentration retrieved from remote sensing algorithm and algae vertical profiles should be an executable approach to obtain algae biomass of inland lakes.

Abstract:Limited labeled samples is used adequately as a hard constraint into matrix factorization. Meanwhile, the local graph of data is constructed to exploite the manifold structure and maintain the local invariance. As a result, feature extraction on matrix factorization for hyperspectral data(FEMF)was proposed. Through matrix decompose process, the nearby data in original space is still close after dimensionality reduction, and the congeneric labeled data is projected into the same position. Such low-dimensional representation has more powerful discriminate performance for classification and clustering. This issue is a non-convex programming problem, and an iterative multiplicative updates algorithm is introduced to achieving the local optimization. The efficiency of the proposed method was verified in real hyperspectral data feature extraction.

Abstract:The simple symmetrical triangular linear frequency modulation(STLFM) continuous wave range and range-rate detection ladar system and its limitations were analyzed. Dual-LO, dual-modulation dual-LO, dual-frequency dual-modulation dual-LO coherent ladar systems were proposed, which will enhance the simple STLFM systems dynamic range of detection range, the detection repetition frequency, and other performances of this system. The simulation and analysis of the key theory for these three systems and the detection accuracy were presented. Methods for further improving the ranging accuracy were proposed. The possibility to reduce the need of emitted power by pulse integration was simulated and analyzed. Comparison of those systems demonstrated that dual-frequency dual-modulation dual LO symmetrical triangular linear frequency modulation continuous wave range and range-rate detection ladar system has advantages of large dynamic range of ranging, high-repetition-rate of detection, effective ability of reduce the need of emitted power and so on.