Abstract:The dynamic current-voltage (I-V) characteristics of mid-wavelength HgCdTe photovoltaic detectors under steady-state gamma irradiation have been measured as a function of gamma dosage. Two obvious effects were observed due to gamma radiation. One is the ionization effect demonstrated by the generation of the photocurrent in the diodes. The other is the displacement damage effect reflected by the increased resistivity in the neutral region. Both effects showed dosage dependence. Qualitative analysis showed that the photo electron yield became small with increasing gamma dosage, which meant the radiation-induced defects played a significant role in large dosage range.

Abstract:Germanium carbon (Ge1-xCx) thin films were deposited by ion beam sputtering deposition of Ge target in a CH4/Ar discharge. The surface morphology, chemical structure, infrared optical and mechanical properties of the Ge1-xCx films were investigated by atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy(XPS), Fourier transform infrared (FTIR) spectroscopy and nano-indentation, respectively. The relationship between ion beam voltage and film properties was discussed. The results show that the surface roughness decreases with increasing of the ion beam voltage. The film deposited at a higher voltage has lower carbon content and higher fraction of Ge-C bonds. The film has excellent infrared optical and mechanical properties. The films show good transparent over a wide range. Due to the content of the carbon decreasing with increasing of voltage, the refractive index increases obviously as the ion beam voltage increases from 300 V to 800 V. The hardness of the film is above 8 GPa. With the Ge-C bonds instead of the C-C bonds and C-Hn bonds, the hardness of the film increases with increasing ion beam voltage

Abstract:In this paper, a model for the photocurrent of the quantum dot infrared photodetector (QDIP) including the continuous potential distribution of the electrons and the total electron transport is improved with the consideration of the dependence of the photoconductive gain on the applied bias, and this improved model can be further used to estimate the responsivity of the photodetector. The corresponding calculated results show a good agreement with the published results, which verifies the validity of the improved model.

Abstract:The capacitance-voltage (C-V) curves of Au/P(VDF-TrFE)/Al capacitor were investigated from 200 K to 310 K. An asymmetry of capacitance value at 0 bias voltage under two polarization orientations was observed at room temperature region, which can be applied in the field of non-volatile memory. The capacitance asymmetry decays with reduced temperature and disappears as the temperature is below 230 K. The phenomena is attributed to a pinned dipole layer between P(VDF-TrFE) films and Al metal electrode.

Abstract:The properties of polarization preservation of partially coherent Hermite-Gaussian beams propagating along different atmospheric turbulence paths were studied. The analytical expressions for the polarization of partially coherent Hermite-Gaussian beams propagating through atmospheric turbulence along different paths have been derived. It is shown that the larger the coherence length is, and the larger the beam order m, n are, the less the polarization is changed. We found that the evolution properties of the polarization in slant-down paths through turbulent atmosphere are similar to the case in free space if the condition zenith angle ξ<π/4 is satisfied. While at a long propagation distance, evolution properties of polarization in horizontal paths of turbulent atmosphere differs much from those in free space and in slant paths. The results may allow one to choose the optimal propagation path in terms of specific applications, which is helpful for future experimental implementation of multiple-degrees-of-freedom free-space communication.

Abstract:Bandwidth,gain and gain-flattening of Raman fiber amplifier(RFA) directly impact on the transmission quality of fiber communication system. RFA with two-pump cascade tellurite fiber was put forward that it will aim for optimizing these parameters according to the features of tellurite fiber Raman gain spectrum(RGS). And the constraints of fiber lengths and pumping parameters were derived when achieving gain-flattening. Quintic polynomial fitting on RGS can accurately reflect the information of RGS and simplify the conditions of achieving gain-flattening. Through Matlab simulation verification,when the two fibers are respectively 0.339 km and 0.16 km, the peak gain is 17.81 dB, gain-flattening is 0.66 dB, and amplified bandwidth is 48 nm. This project supplies a new approach for designing RFA with wide bandwidth, high gain and low gain-flattening.

Abstract:A new complete scheme for urban rectangle building detection and height estimation was proposed using one high-resolution optical image and one synthetic aperture radar (SAR) image. The scheme exploited adequately the complementarities of both data and consisted of a sequential processing chain: building boundary extraction from both data, registration from optical image to SAR image based on an integrated criterion and building height estimation based on a “hypothesis generation-simulation-matching” procedure. Especially, the proposed method performed well also for partially occluded buildings. The method was tested and validated over two different scenes.

Abstract:A novel and efficient quantum detection scheme based on statistical theories was proposed. The feasibility was verified by simulation. The simulation results show that the scheme is efficient and secure. Considering the integrity of the scheme, we constructed a complete model of links to obtain the threshold of the scheme.

Abstract:A parameter-extraction approach for the stacked on-chip transformer, which combines the analytical approach and the empirical optimization procedure, was developed. The model parameters determined from the analytical expressions were considered as an initial guess of a subsequent optimization procedure leading to the final model parameters. Good agreement was obtained between simulated and measured results for a stacked transformer on silicon substrate in the frequency range 100 MHz~60 GHz.

Abstract:To improve the precision and effectiveness of crown-volume measurement and calculation, the authors have analyzed the characteristics of existing methods for processing the point cloud and have proposed a crown-surface reconstruction algorithm using a triangulated irregular network and voxel-based volumetric algorithms. This algorithm, after reconstructing the surface of the point-cloud crown, can extract the crown volume. This paper compares classic Delaunay grid-construction results with those from the proposed algorithm using a visualization method and carries out algorithm complexity analysis. These efforts have confirmed that the method presented in this paper is better than the traditional algorithm from the viewpoints of grid-construction accuracy and efficiency. This research, examined 30 trees in the study area. T-LiDAR was used to obtain point-cloud data for the crown. The classical manual dendrometric method, the point-cloud measurement method, the classical Delaunay algorithm, and the method proposed in this paper were used to calculate crown volume, and the results were compared. The four methods showed a good correlation (R2>=0.831), while the improved Delaunay method presented in this paper achieved good precision, good stability, and the least calculation time. The results of these experiments proved that the proposed algorithm has a considerable advantage in crown-volume extraction from point clouds (especially from T-LiDAR data). The combination of the proposed algorithm with T-LiDAR data could extract crown properties such as surface area and biomass quickly and precisely.

Abstract:A novel method for the realization of high selectivity millimeter wave band pass filters is presented. A small perturbing notch was etched at sidewall of a dual-mode circular cavity to improve cross coupling between two orthogonal modes. By properly changing the perturbing angle, the bandwidth is expanded and location of the transmission zero can be easily adjusted to significantly enhance the filter selectivity. The V-band filters have been designed, fabricated and measured. The experiment results showed an excellent agreement with simulation results. Unlike conventional filters, the proposed prototypes do not need any additional mechanical tuning element. It has merits of simple design process, high selectivity, compact size and quasi-planar structure.

Abstract:The impact of (N+1)×1 coupler pump arm numbers on the pump coupling efficiency was numerically studied firstly. It is shown that pump coupling efficiency decreases with more pump arms built on the coupler, yet in a slightly decreasing manner. According to the simulation results, side-pumped (1+1)×1 and (2+1)×1 couplers were made. The total output power of the (2+1)×1 coupler is about 681 W, almost two times that of the (1+1)×1 coupler, enhancing the pump light injection capacity of the fiber laser system significantly.

Abstract:A coupler for coupling terahertz radiation into a waveguide was designed, which is the combination of a conical column and a short cylinder made of aluminum. The performance of the coupler in the cases of a broadband collimated terahertz wave and a single frequency collimated terahertz wave from free-space into an anti-resonate waveguide was simulated by theory and verified by experiment. The results confirm that the coupler is a high efficiency and broad band THz coupler. By optimizing the dimension parameters of the coupler, the amplitude coupling ratio of 71% and the amplitude concentration factor of 6.125 in the terahertz time domain spectroscopy system have been achieved.

Abstract:Near infrared (NIR) spectroscopy was used to identify the origins of two representative of Shandong green tea (Laoshan green tea and Rizhao green tea) rapidly and non-destructively. Several preprocessing methods of NIR, such as smoothing, first-and second-derivative were compared. Moving window back propagation artificial neural network (MW-BP-ANN) was used to select characteristic spectral variables. It was found that the first-derivative and MW-BP-ANN processing techniques improved the predictive abilities of the support vector machine (SVM) classification models. The best estimated identification accuracy can be improved to 98.33%, which demonstrates that the spectral variables selection method is significant for the predictive ability of origin identification models.

Abstract:The initial heteroepitaxial growth stages of GaAs on Ge(100) by all-solid-source molecular beam epitaxy(MBE) were studied by means of reflection high-energy electron diffraction (RHEED), high resolution X-ray diffraction (XRD) and atomic force microscopy, as well as the effects of different growth conditions to the epitaxial layer qualities. It was indicated that high growth temperatures or low growth rates enabled a layer-by-layer growth mode of initial GaAs nucleation layer which was evidenced by RHEED patterns. However, the combination of low growth temperatures and low growth rates for the initial GaAs layer gave lower full-width at half-maximum value of rocking curves and lower surface roughness of the epitaxial materials, owing to the decrease of the lattice mismatch between substrates and epi-layers.

Abstract:In the process of the quantum key distribution based on the polarization coding of photons, the polarization state will be affected strongly and randomly by the birefringence effect of the single-mode fibers, which will lead to decrease the final secure key rate. Fortunately, this undesirable effect of single-mode fibers can be corrected by the combination of two quarter-wave plates and a half-wave plate. Utilizing the combination of three wave plates as the actuator, we build a simulation model of real-time polarization compensation based on stochastic parallel gradient descent algorithm. We study the relationship among the amplitude of the random disturbance, the gain factor and the convergent rate. Furthermore, we implement an experiment to demonstrate the algorithm we proposed. The results of the experiment show that the polarization extinction ratio of the simulation system can be corrected well after a certain number of iterations.

Abstract:The valence band shift in Pb1-xSrxTe thin films with different Sr compositions was studied. The ratio of conduction band offset and valence band offset in this heterostructure has been determined. Without considering the strain effect, the conduction band offset ratio is Qc=ΔEc/ΔEg=0.71, and with considering the strain effect, the energy band of PbTe is degenerated into longitudinal and oblique valleys. The conduction band offset ratio for longitudinal valley is QLC=0.47 and for oblique valley is QOC=0.72, respectively. Pb1-xSrxTe/PbTe heterostructure has a type Ⅰ alignment at the interface, which implies the confinement of both electrons and holes. The accurate determination of band alignment of Pb1-xSrxTe/PbTe heterostructure has great benefits in the research and development of mid-infrared opto-electronic devices.

Abstract:A compound regularized multiple sparse bayesian learning algorithm for sparse unmixing is presented, in which sparse bayesian learning model is integrated in the linear hyperspectral pixel unmixing. On the framework of sparse Bayesian Learning model based on MMV (Multiple Measurement Vectors), the parameters in the model is established with the probability, and a L2,1 norm regularization-based multiple sparse bayesian learning model for spectral unmixing is constructed by bayesian inference, taking the non-negativity and sum-to-one property of abundances into the convex objective function. The compound regularization problem is decomposed into several single regularization problems solving by a variable separation method, and the regularization parameters of the model are updated by an adaptive adjustment algorithm. Experimental results on both synthetic and real hyperspectral data demonstrate that the proposed method outperforms the greedy algorithms and the convex algorithms with a better spectral unmixing accuracy, and is suitable for complex combination of endmembers and low signal-to-noise ratio hyperspectral data.

Abstract:The optical properties of VO2 nano periodic array were studied in order to obtain low phase transition temperature and high quality optical material widely used in the field of intelligent window. Optical properties of VO2 nano periodic array at different filling ratios were calculated with finite difference time domain method, and the best VO2 nano periodic array was selected. Vanadium film was deposited on the glass substrate by magnetic DC sputtering, then VO2 film was formed by annealing under air condition, and VO2 nano periodic array was gained by photolithography and etching technology. Its microstructure and optical properties were tested by SEM, XRD and XPS as well as spectrophotometer. The results show that the phase transition temperature of VO2 nano periodic array with filling ratio 0.74 decrease about 25 ℃ and the transmittance has changed 39% between the metallic and semiconducting states at 1700 nm.VO2 nano periodic array exhibits the better optical properties than VO2 film before and after phase transition. It is indicated that the optical properties can be improved through regulating the structure of VO2 nano periodic array.

Abstract:The Electromagnetic (EM) scattering characteristics in terahertz (THz) band of non-uniform unstable electrical conducting target with different roughness surface is studied in this paper. The modeling concept of randomly rough surface is applied to model the target with non-uniform unstable roughness surface. Here, the root mean square (RMS) height and the correlation length of rough surface are applied to describe the roughness of different target surfaces. Firstly, the Gaussian surface is generated to model a non-uniform random unstable target, then a combined method of physic optics and equivalent current is employed to simulate the EM scattering in THz band. The scattering characteristics of the target with different roughness scales at different incident angles and radar frequencies are analyzed and discussed.

Abstract:The nonlinear theory of large-orbit gyrotron traveling wave amplifier (gyro-TWA) was developed with consideration of misaligned electron beam. The effects of misaligned electron beam on both working mode and backward oscillation mode were studied using this theory. The results show that, for working mode, the average gain is decreased by the effect of misalignment, while for backward oscillation mode, the misalignment leads to changes of possible oscillation modes which makes the mode competition in large-orbit misaligned electron beam is more complex.

Abstract:A novel sub-micron optical waveguide based on silicon-on-germanium (Ge-on-Si,GOS) is proposed and by adjusting second-order dispersion curves the waveguide structure were optimized and designed .Then this article studied its wavelength conversion properties between 3μm and 6μm.The numerical results show that this waveguide can achieve high conversion efficiency in broadband infrared wavelength conversion when the pump light wavelength near the zero dispersion point at negative wavelength region of the second-order dispersion curves at the optimized waveguide structure which the ridge width is 2.8μm,ridge high is 1.6μm and slab thickness is 0.48μm.The 3dB conversion bandwidth reaches 1664nm and the maximum conversion efficiency can reach -2.479dB at the 0.05GW/cm2 power density of the pump light .This waveguide has potential applications in terms of future photonic networks and communications space due to it’s large wavelength bandwidth and high conversion efficiency advantages.