Abstract:In accordance with the requirements of a real-time spectral detection system, the Fourier transform spectral theory is utilized to obtain the spectral information to be detected. First, the basic operation principle of the real-time spectral detection system is presented and a radix-2 FFT algorithm is optimized. Then, the design of the hardware structure of the algorithm is described in detail, the address generation and control process designed by an Algorithm State Machine (ASM) is illustrated emphatically and the hardware design of the FFT module is completed by using a XC3S400 chip with an IP core produced by Xilinx Inc. on an ISE9.1 software development platform. Finally, the Testbench program written in VerilogHDL language is used to simulate the functions of the FFT module on ModelsimSE6.3f, a third-party simulation software. The simulation result is compared with the result calculated by Matlab in theory. It shows that the FPGA hardware is designed correctly. It takes about 8.6μm for the chip operating at 100MHz to implement 256-point 16 bit radix-2 FFT data, which can meet the real-time requirement for spectral detection.

Abstract:In the field of polarization imaging and laser power measurement, an obvious error can be produced due to the effect of light polarization state on a photodetector in any polarization-dependent quantitative measurement. This phenomenon is mainly caused by the fact that many kinds of photodetectors are sensitive to light polarization. In this paper, the polarization-dependent responsivity (PDR) of a photodetector is analyzed, the stokes model of polarization-dependent loss (PDL) is deduced and the effect of a SiNx passivation film on the PDR of an InGaAs photodetector is analyzed. The analysis result shows that when the SiNx passivation film is not used, the PDL increases with the increasing of an incident angle and decreases with the increasing of wavelength; and when the SiNx passivation film is used, the PDL firstly decreases and then increases with the increasing of wavelength. Because the central anti-reflection wavelength of the designed SiNx passivation film is at 1550nm, the PDL at the wavelength of 1310nm is greater than that at the wavelength of 1550nm.

Abstract:The effect of quantum confinement on the shallow acceptor transition in δ-doped GaAs/AlAs multiple-quantum wells with a width of 30A～200A is studied by using photoluminescene spectra. The samples used in the experiment are the Be δ-doped GaAs epilayers grown by molecular beam epitaxy (MBE) and a series of GaAs multiple-quantum wells in the center of which shallow acceptor Be are δ-doped. The photoluminescene spectra of the samples are measured at a low temperature of 4.2K and the two-hole transition of the acceptor-bound exciton from the ground state, 1S3/2(Γ6), to the excited states, 2S3/2(Γ6) and 3S3/2(Γ6), are observed clearly. It is found that the transition energy of acceptors increases with the enhancement of quantum confinement. The study of the quantum confinement effect used to tune the transition energy of acceptor states has further enhanced the understanding of the acceptor states and has provided a new way to develop terahertz far infrared light emitters or lasers.

Abstract:Because of the advantages of low average power, high recurrence frequency and low coherence requirement for light sources, pulse laser ranging technology has wide applications in military industry. The precision of the pulse laser ranging technology can be improved directly by improving the time-gap measurement accuracy in pulse laser ranging. In order to reach the ps-level measurement accuracy, a single chip microcomputer is used to control a time measurement chip. So, the time measurement chip not only can measure the time delay between the emitted pulse signal and the returned pulse signal, but also can correct the measurement result automatically. Compared with the traditional methods for measuring the time-gap in pulse laser ranging, this method can simplify the design of a device and improve its measurement speed.

Abstract:The polarization characteristics of a camouflage material in the direction of specular reflection are tested by using a multispectral polarization CCD camera in visible and infrared wavebands. The polarization characteristics of a camouflage material with rough sufaces are studied under different incident conditions and the polarization spectrum of the material is obtained. In the direction of specular reflection, high linear polarization is exhibited at the surfaces of the camouflage material and very low linear polarization is exhibited against the meadow background. The polarimetric scattering at the rough surfaces are analyzed by using Kirchhoffs scattering theory. The analysis result is in agreement with the measured polarization spectrum. Since the polarization scattering spectrum of the camouflage material is different from that of the background, the use of polarization information in imaging is very helpful to the identification of targets against complex background. Polarization remote sensing is of important value to the detection of camouflaged military targets.

Abstract:Aluminium oxide (Al2O3) thin films are widely used in mechanical, optical and microelectronic applications and have attracted more and more attention because of their excellent physical and chemical properties. However, Al2O3 has a variety of phases and their properties are different. So, the study of the effect of different structures on the luminenscence properties of Al2O3 is of significance in the practical application. The Al2O3 thin films are grown on silicon substrates by radio frequency (RF) magnetron sputtering and are annealed in the nitrogen gas at different temperatures. The structures and photoluminescence (PL) spectra of these films are compared with each other before and after annealing. Two fluorescence peaks are observed near 384nm and 401nm. Both fluorescence peaks are generated by the color center. With the increasing of annealing temperature, the crystallization of the films becomes better. At the same time, the position and intensity of the fluorescence peaks are changed correspondingly, too.

Abstract:Vanadium dioxide (VO2) is a kind of thermochromatic material. When phase transformation occurs, its resistance, optical transmittance and reflectivity will be changed obviously. Some preparing parameters, such as gas flow ratio of argon to oxygen, sputtering atmospheric pressure and substrate temperature, are changed by using a direct current reactive magnetron sputtering method. The effect of those preparing parameters on the structure and resistance-temperature characteristics of a VO2 film is studied. The result shows that when the ratio of argon to oxygen is 1.0∶15 and the gas pressure is 2.0Pa, the prepared film contains more VO2; and when the substrate temperature is 250℃, the prepared VO2 film has its best resistance-temperature abrupt capability.

Abstract:The variation of the current characteristics of a Si-based Ge PIN infrared detector with the strain, thickness and doping concentration of a Ge absorption layer is numerically simulated on the basis of a drift-diffusion model and an optimized device design scheme is given. The research result shows that when the tensile strain of the Ge absorption layer is increased from 0 to 0.3%, the dark current of the device is increased by about 50%; when the thickness of the Ge absorption layer is increased from 1μm to 4μm, the dark current of the device is decreased by about 80% and its quantum efficency is nearly doubled; and when the doping concentration of the Ge absorption layer is increased from 1×1014cm-3 to 1×1016cm-3, the dark current of the device is decreased by about 60%. In view of the effect of absorption layer thickness on the quantum efficiency and dark current of the device and the effect of doping concentration of the absorption layer on photocurrent, the Ge absorption layer of the Si-based Ge PIN infrared detector is designed to have a thickness of 4μm and a doping concentration of 1×1014cm-3. It is expected that this design can provide a good basis for the improvement of device performance and the fabrication of practical devices.

Abstract:Information fusion technology is one of the key technologies of millimeter wave/infrared (MMW/IR) combined guidance. Its target tracking algorithm can directly affect the performance of a MMW/IR combined guidance system. According to the target tracking of MMW/IR combined guidance, the measurement data from both a MMW sensor and an IR sensor are fused firstly and an improved alpha-beta tracking filter algorithm is proposed. The algorithm can obtain the filter gain in light of the maneuver situation of a target in real time and adjust the filter equations in time, so as to obtain good tracking performance. Finally, the linear motion and the course-changed linear motion of the target are simulated with the improved algorithm. The simulation result shows that compared with other filter algorithms, the improved algorithm has a better tracking effectiveness, a higher tracking accuracy and a less computation quantity.

Abstract:A simple method for calculating the field angle of a candy shape cold shield with the Monte Carlo method and MATLAB is presented. Compared with other calculation methods, this method has the features of simple programming, controllable accuracy and convenient operation etc..