Abstract:Dispersive imaging spectrometers that use back-illuminated CCDs have interference fringes in near-infrared band. These fringes are sensitive to the distribution of incident light wavelength and stable in spatial frequency. Therefore, they are very suitable for measuring and calibrating spectral deviation. In this paper, we built a grating dispersion push-broom imaging spectrometer prototype. We then estimated the distribution law of fringes and use band-pass filter and least squares method to extract the phase information of the interference fringes. Finally, we calculated the spectrum offsets based on this information. Experiments show that when the incident light intensity changes by more than 130%, the maximum uncertainty of fitting line positions is 0.0073nm. We change the spectral position and compare the spectral deviations calculated by using fitting algorithm and measured by using mercury spectrum. The maximum error of spectral position is 0.1358nm. Our fitting algorithm can effectively reduce dependence on light stability of the calibration system, and improve detection accuracy for slight offsets in spectral dimension.

Abstract:A novel hybrid Freeman/eigenvalue decomposition with general scattering models was proposed for polarimetric synthetic aperture radar (PolSAR) data. A unit matrix represents the volume scattering model, and eigenvectors corresponding to the two larger eigenvalues of the coherency matrix are used as the surface scattering model and double-bounce scattering model for non-reflection symmetry condition. There are three advantages in the proposed hybrid decomposition. Firstly, the surface and double-bounce scattering models are free from the reflection symmetry constraint which is more general and realistic for common media. Secondly, since the scattering powers of the proposed method are solved as linear combinations of the eigenvalues derived from the coherency matrix, they are all roll-invariant parameters. Thirdly, negative powers of surface scattering and double-bounce scattering are avoided with non-rotation of the coherency matrix. Fully PolSAR data on San Francisco are used in the experiments to prove the efficacy of the proposed hybrid decomposition.

Abstract:For fast design of millimeter-wave non-resonant slotted waveguide antennas (SWAs) with more accuracy, an improved analytical method is presented by introducing a modified factor into the traditional Stevensons formula. The modified factor can greatly improve analytical calculation accuracy of slot displacement of longitudinal shunt slots cut in the broad face of a waveguide. Generally, the traditional Stevensons formula is valid for only narrow slots of a length-to-width ratio of 10∶1. However, the proposed method allows for fast design of millimeter-wave SWAs of very low-sidelobe levels and wide slots of an approximately 4∶1 length-to-width ratio. A theoretical explanation of the modification was provided. With the improved method, a prototype of non-resonant SWAs operating in 60 GHz band was designed and fabricated. The measured gain and sidelobe level are 14.8 dB and -25 dB. Good agreement between the simulation results and measured data indicate the effectiveness of this improved method.

Abstract:Optical signals of two different wavelengths in the IR regime were generated in atomic Rb vapor using broad bandwidth laser pulses. Competition between the two signals was observed. The effects of pump laser intensity, chirp of laser pulses and Rb number density on the characteristics of the two signals were investigated. The results show that the two signals were generated from two coupled parametric six-wave mixings processes and the competition between the two signals was dominantly governed by phase matching conditions related to Rb number density.

Abstract:The aspect ratio of trenches is one of the key parameters in processing the HgCdTe infrared focal plane arrays (IRFPAS)．The divergence angle of the two-grid Kaufman ion-beam source that is widely used in China at present is typically large. Using such an ion beam source, the aspect ratio of HgCdTe isolation trenches is comparatively low. Several methods were employed in the etching process to increase the aspect ratio of trenches etched by Ar+ ion beam apparatus, such as with different types of photoresists, changing the incidence angle of ion beam, and utilizing three-grid Kaufman ion-beam source. The cross-section profile of the trenches on HgCdTe arrays was studied with scanning electron microscope (SEM ) and the aspect ratio was calculated. The influences of these methods on etching profiles were given and many results desirable for the design of high aspect ratio of ion beam etched trenches were achieved.

Abstract:In order to extend the response of InGaAs short-wave infrared detectors to visible wavelength band, a InGaAs etch stop layer was added to the standard InGaAs epitaxial structure. After the fabrication of 32×32 pixel planar InGaAs detectors, the InP substrate was removed with mechanical thinning and chemical wet etching. The results indicated that the response of detectors after substrate removal covered the wavelength band from 400nm to 1700nm. Quantum efficiency is approximately 16% at 500nm, 54% at 850nm, and 91% at 1550nm. The detectors achieved almost the same low dark current as they did before the substrate removal process. The effect of parameters of epitaxial material on the quantum efficiency has been analyzed and simulated, and then the method to optimize the visible response of detectors was given.

Abstract:Many kinds of typical crystal defects can be observed in the Cadmium Zinc Telluride (CdZnTe) single crystals. X-ray diffraction topography is a powerful method for investigating the structural integrity and homogeneity of single crystals. In this paper, the defects of CdZnTe substrate and Mercury Cadmium Telluride (MCT) epitaxial layer grown by liquid phase epitaxy (LPE) were investigated by X-ray diffraction topography in reflection. The X-ray diffraction topography and etched surface morphology of the same substrate were compared to characterize the defects. Six types of X-ray diffraction topography of defects in the CdZnTe substrate were observed including perfect structure, mosaic structure, twin crystals, low-angle grain boundary, inclusions/precipitates, and scratches. At present, most of the X-ray diffraction topographies of the samples show perfect structure of the CdZnTe substrates, free of scratches and mosaic structure defects. Low-angle grain boundary is the major type of defects in the CdZnTe substrates. Comparing the X-ray diffraction topography of CdZnTe substrate and MCT epitaxial layer grown on the same substrate by LPE, the low-angle grain boundary defects on the substrate were also observed on the MCT epitaxial layer. These results suggested that the quality of MCT epitaxial layer was closely related to the defects of CdZnTe substrate. The substrate with perfect structure was the foundation for the growth of MCT epitaxial layer with high quality.

Abstract:PbZr0.4Ti0.6O3 (PZT) multilayers were prepared by sol-gel method using chemical solutions containing polymer of Polyvinylpyrrolidone (PVP). Effects of PVP content on optical properties of PZT multilayers have been investigated. Tests demonstrated that these multilayers display a layered structure consisting of dense and porous PZT layers and these dense and porous layers are alternately arranged in the layered structure. The reflectance spectra in visible region exhibit a single optical reflection-band with high reflectivity. The central wavelength of the reflection-band shifts to longer wavelength with the increase of PVP concentration within a given polymer content range. The multilayer derived from chemical solution containing PVP with a relative molar ratio of x = 1.0 exhibits the optimal performance with highest optical reflectivity of 89% and largest stop-band width of 44 nm.

Abstract:To realize remote sensing at sub-millimeter wavelengths, a 450GHz sub-harmonic mixer was studied. An anti-parallel pair of Schottky diodes is the key component in the mixer. The length of the diodes is 74μm, and the cut-off frequency of diodes is up to 8THz. The suspended microstrip matching circuit was built on quartz, and the metal block was cut into two halves. The diode embedding impedance was calculated. The diode package and the matching circuit were integrated in the mixer model. The predicted single side band(SSB) conversion loss is 8.0dB, with 4mW of local oscillator power. Measured results indicate that the lowest measured SSB conversion loss is 14.0dB, with 5mW of local oscillator power. The loss is below 17.0dB in the band from 433~451GHz, with a 3dB bandwidth of 18GHz.

Abstract:The characteristics of the planar ladder-type multi-gap resonant cavity are investigated, including the mode distribution, characteristic impedance (R/Q), coupling coefficient and the operating stability. The high-frequency interaction system for a W-band high-power extended interaction klystron was designed. The nonlinear performances such as the saturated power, gain, efficiency, as well as bandwidth are predicted by using the three-dimension Particle-in-Cell technology. The modulation and bunching of the beam and the physics of the interaction between the beam and the multi-gap resonant cavity were explored. PIC simulation results show that the output power is up to 1.8kW at the frequency of 94.52GHz with the voltage of 16 kV and beam current of 0.6 A. This power corresponds to a gain of 47.7dB and an efficiency of 19.4% respectively. The sweep-frequency simulations with the same drive power show that the 3-dB bandwidth of 210MHz can be achieved.

Abstract:Based on the accurate electromagnetic model and an improved equivalent circuit model of Schottky diode, the design and fabrication of a W-band eighth harmonic mixer for broadband operation is presented in this paper. With the analysis of the Schottky diode physical structure, a three-dimensional electromagnetic model and an improved equivalent circuit model up to 180GHz were established. According to the mixing product energy distribution characteristics and bandwidth requirements, broadband RF and LO matching networks were designed, which extend the mixer operation bandwidth to the entire W-band. The measurement result indicates that the conversion loss of the W-band eighth harmonic mixer is less than 28dB in the range of 75～110GHz, and the minimum is 18dB.

Abstract:For the “dual-band dual-modulation dual LO (DFDMDL)” range and range-rate detection ladar with large ranging dynamic range and high-repetition-rate, we analyzed the LFM modulator linearity of the signal, the “amplitude-frequency ” characteristic of the local and emitted light signal, the period stability of the symmetrical triangular linear frequency modulation (STLFM) signal, which are needed to be considered in the ladar design. The signal modulation scheme for the system was proposed by comparison, simulation and measurement of different parameters. In the desgin, we used the acousto-optic frequency shifter (AOFS) to provide external modulation for high linearity STLFM signal, and the direct digital frequency synthesis device (DDS) to drive AOFS. We also proposed and used the DAC to adjust the RF drive source power to compensate the non-flat “amplitude-frequency” characteristics of the AOFS, the High Precison FPGA based TDC measures the STLFM period and the time between multiple STLFM signals. The result demonstrated that the DFDMDL system has a high accuracy of ranging and has the potential ability of pulse integration by using this scheme.

Abstract:As an important part of metamaterials, the dielectric layer is one of the key factors influencing the properties of metamaterials. When the size and surface metal-pattern of metamaterials had been fixed, control rules related to the permittivity and thickness of dielectric layer were analyzed within terahertz band. For the first time, the formula related with the frequency and permittivity was defined in this article. The results show that, with other parameters kept constant, the frequency response of metamaterials mainly depends on the real part of permittivity, while the absorption mainly depends on the thickness of the dielectric layer. According to the conclusions, we further proposed a new method for designing the metamaterials: firstly, putting the required response frequency into the deduced frequency equation and calculating the permittivity, by which suitable dielectric material in accordance with the calculation can be chosen; secondly, under the chosen frequency, the highest or desirable terahertz absorption can be obtained by adjusting the thickness of the dielectric layer. This design method can effectively predict and control the response properties of the metamaterials just by changing the parameters of the dielectric layer. Importantly, our method not only can obviously shorten the design cycle, but can also greatly reduce the difficulty in designing the metamaterials.

Abstract:The 4×4 transfer matrix method is used to investigate the broadband optical isolation property of two different one-dimensional magneto-photonic crystal structures. The results show that the first structure makes broadband optical isolation come true. When the angle between the applied magnetic field and optical axis is set as 41.0°, its bandwidth achieved 3nm with a 22.90μm-thickness, the Faraday rotation angle fluctuated from 45° to 48.89° and transmittance achieved 99.86~99.95%. The other structure with total thickness of 18.61μm achieves a 1nm-bandwidth optical isolation with the Faraday rotation angle fluctuated from 45.83° to 45.89° and transmittance fluctuated from 98.53% to 98.78%, when the applied magnetic field is nearly parallel to the optical axis. This structure ensures the achievement of optical isolation without adjusting the applied magnetic field.

Abstract:Spectroscopic ellipsometry was used to investigate the optical properties of Mn film deposited with different sputtering pressures on silicon substrates in the photo energy range of 2.0~4.0eV. Parameterized analyses, based on Drude-Lorenz model and Bruggeman effective-medium approximation model, were used to fitting the elliptic parameters. The results imply that the density of Mn films first increases and then decreases with increasing of Ar pressure, whereas the refractive index changes with Ar pressure in a contrary way. Meanwhile, the extinction coefficient has a complex relationship with Ar pressure at lower photo energy, the extinction coefficient changes in line with the refractive index when photo energy exceeds 2.8eV. Moreover, the effects of Ar pressure on optical constant of the film depend strongly on the variation of the Mn atomic density.

Abstract:A prototype of frequency 8-tupling millimeter-wave photonic generator based on improved two-step heterodyne was proposed and analyzed. In the proposal, two step heterodyne technique was employed to eliminate the phase noise of two phase uncorrelated lasers. Millimeter-wave signal with frequency eight time of driving frequency was obtained. We theoretically analyzed the generators principle and the issue of power penalty induced by lasers phase noise, fiber dispersion and optical time delay. To verify the mechanism and the discussion, simulation was carried out to verify the principle.

Abstract:Based on the visible near-infrared (VNIR) data acquired by TG-1 hyperspectral imager on March 6, 2012, synchronous and non-synchronous alternative spectral calibration were assessed at the oxygen band. In order to improve the reliability of non-synchronous alternative spectral calibration result, other two images with similar imaging date were used to achieve multiple calibrations. The results show that non-synchronous alternative spectral calibration results based on three images are similar, difference is less than 0.2nm, and standard deviation is less than 0.11. Difference between synchronous and non-synchronous alternative spectral calibration results is less than 0.3nm. Compared with the TG-1 on-board spectral calibration results, the error of the two alternative spectral calibration methods is 0.384nm and 0.489nm, respectively. The accuracy difference is relatively small. Non-synchronous alternative spectral calibration method can be used to achieve high-frequency spectral calibration for hyperspectral imager.

Abstract:Based on field-matching theory, the general transmission matrix of pill-box windows and a new concept of hybrid transmission modes pill-box window were presented to extend the bandwidth of output window. With guidance of the new concept, the primitive structure and parameters of the extremely broad bandwidth pill-box output window, working over 34~52GHz, had been obtained. Afterward, HFSS was employed to optimize the parameters of the window and to examine the optimized mode. Through amount of thermodynamic analysis and optimization design, the extremely broad bandwidth pill-box window, with average power capacity 10kW over 40% bandwidth whose insert loss is less than －18dB, was attained. The cold test verifies the results of the design.

Abstract:State-of-the-art methods for airport detection in panchromatic remote sensing images utilize very limit geometrical features of airport line segments. This paper proposed a new method which uses both bottom-up and top-down saliency. Because the airport runways have features of vicinity and parallelity, and their lengths are among certain range, the concept of near parallelity is introduced after using an improved line segments detector (LSD). It is used as a priori knowledge which can fully exploit geometrical relationship of airport runways to get top-down saliency. Meanwhile, a simplified graph-based visual saliency (GBVS) model is used to extract bottom-up saliency. Candidate regions can be gotten by combining those two clues. After that, scale-invariant features transform (SIFT) and support vector machine (SVM) are used to finally determine whether the regions contain an airport or not. The proposed method is tested on an image dataset composed of different kinds of airports. The experimental results show that the method has advantages in terms of speed, recognition rate and false alarm rate. Also, the method is more robust to complex background.