Abstract:Key problem of sub-millimeter waves or terahertz system is the very small output power of the source. Power combining technology is a suitable approach to increase the output power. However the conventional power combining methods used in microwave and low millimeter wave bands such as circuits combining or waveguide spatial combining all suffer from the higher loss and difficult for manufacture and so on at sub-millimeter waves. In this paper an approach of beam power combining based on quasi-optical technology is proposed. It has advantages of low loss, high combining efficiency and relative easy for manufacture. The analysis, simulation and experiments results are presented. High combining efficiency has been obtained.

Abstract:In this work, a composition dependent model based on the Cr-W alloy structure has been studied to make it possible be put into practical application. In terms of the optical properties of the Cr-W alloy with defined composition, a simpler 4-layered structure with single Cr-W alloy absorption layer has been designed to show the merit of high photon-to-heat conversion efficiency in the broad spectral region of 300-1000 nm.

Abstract:In this paper, two D-band (110~170 GHz) monolithic millimeter-wave integrated circuit (MMIC) amplifiers have been designed and realized using 90-nm InAlAs/InGaAs/InP high gain electron mobility transistors (HEMT) technology. The amplifiers are developed in common source and microstrip technology. The three-stage MMIC amplifier A is designed based on device A and measured on wafer with a small-signal peak gain of 11.2 dB at 140 GHz and 3 dB bandwidth is 16 GHz with a chip size of 2.6×1.2 mm2. The two-stage MMIC amplifier B is designed based on device B and measured on wafer with a small-signal peak gain of 15.8 dB at 139 GHz and 3dB bandwidth is 12 GHz and the gain higher than 10 dB from 130 GHz to 150 GHz with a chip size of 1.7×0.8 mm2, the amplifier also shows an excellent noise character with noise figure of 4.4 dB with the associated gain of 15 dB is acquired at 141 GHz and the average noise figure is about 5.2 dB over the bandwidth. The amplifier B exhibits a higher gain-per-stage, competitive gain-area ratio and lower noise figure. The successful realization of MMIC amplifiers is of great potential for receiver-front-end applications at D-band.

Abstract:A 0.18-μm CMOS process single photon avalanche diode (SPAD) was examined in this study in an effort to inhibit premature edge breakdown (PEB) and secure large photo current and low dark count rate (DCR). The SPAD consists of a p-well/deep n-well photosensitive junction and a guard ring as-formed by a deep n-well up-diffused region and an edge STI. The size of the STI layer related to the light current and dark rate was determined via test. The results indicate that the photo current and dark count of the SPAD are optimal when the overlapping length between the STI and guard ring is 1-μm at room temperature. The SPAD with 10-μm diameter has high photon detection probability (PDP), wide spectral response, dark count rate as low as 208 Hz, and 20.8% peak PDP when the wavelength is 510 nm.

Abstract:this paper introduces two designs of balanced frequency triplers in 0.68 THz and 1.00 THz bands. The proposed triplers are based on discrete antiparallel Schottky diodes and quartz glass instead of terahertz integrated circuit. The merits of this work are attributed to the improvement of the diode model, the thinned quartz glass film and the machining accuracy of the waveguide. The improved LEC diode model considers not only the current voltage (I/V) and capacitance voltage (C/V), but also plasma resonance and skin effect. The quartz glass film is thinned to 15um and can be used for up to 1.2 THz. The machining accuracy of the waveguide is ±3um for terahertz applications with channel size 60um. The measurement shows a peak output power above 160 μW and 60 μW for the 0.68 THz and 1.00 THz triplers, respectively. Moreover, the efficiency of the 0.68 THz and 1.00 THz triplers is around 1% and 0.6% correspondingly, and the 1.00 THz tripler is around. The output frequency bandwidth is both more than 10%.

Abstract:The tunable high performance multi-channel wavelength demultiplexer (WDM) based on metal-insulator-metal (MIM) plasmonic ring resonators is designed and numerically investigated. By the resonant theory of ring cavity, we find that the channel wavelength of WDM can be easily manipulated by adjusting the radius and refractive index of the ring cavity, which is in good agreement with the results obtained by finite element method (FEM) simulations. The multi-channel WDM structure consisting of a plasmonic waveguide and several ring resonators increases the transmission up to 80% at telecommunication regime, which is two times higher than the results reported in a recent literature. The proposed compact multi-channel wavelength demultiplexer can find more applications for the ultra-compact WDM systems in highly integrated telecommunication circuits.

Abstract:In this paper, a method to accurately measure supercooling of HgCdTe film grown by LPE has been proposed. Influence of supercooling on the thickness uniformity of HgCdTe film has been studied by combining with optical Microscope, Fourier transform infrared (FTIR), step profiler and White-light Interferometer (WLI). Result shown that, thickness in the center of a 20 mm × 25 mm film decreased when supercooling is less than 2 ℃, while it is increased significantly when supercooling is more than 3 ℃, attached with cross-hatch pattern on micrograph. Thickness variation of a 20mm × 25mm film could be less than 0.5 μm, and surface roughness is comparable with CZT substrate when supercooling is around 2.5 ℃.

Abstract:The results of a Cl2/ N2 inductively coupled plasma (ICP) reactive ion etching process on InAs/GaSb superlattices infrared focal plane arrays were reported. A standard PIN device structure based on GaSb substrate was applied in all samples grown by molecular beam epitaxy. The etching results including etching rate and mesa sidewall profile were affected by gas flow directly, The higher the chlorine content, the higher the etching rate, when the argon content increased, the etching rate decreased and tended to a certain value. When other parameters such as chamber pressure et al. were fixed, the etching rate and selection ratio increased linearly with temperature, and the mesa tended to be right angle, layered texture profile gradually disappeared, but the channel became rough and even pitted. Within the scope of the experimental study, the ICP power and RF power had little effect on the etching results.

Abstract:The MW HgCdTe avalanche photodiodes (HgCdTe APDs) were prepared by different processes. The pn junction characteristic and the relation between gain and bias voltage for HgCdTe APDs were characterized by different methods. The gain-bias curves of APDs were fitted based on the Beck model and Shockley,s analytical expression. The results show that the widths of the saturated depletion region for APDs fabricated by different processes are 1.2μm and 2.5μm respectively. The wide depletion region effectively suppresses the tunneling current at high reverse bias, and Shockley,s analytical expression has been found to give an excellent fit to the gain–bias curves of HgCdTe APDs, and fitting parameters are similar to the results of Rothman at Sofradir.

Abstract:An infrared imaging simulation method for aerial targets is proposed. According to energy conservation law, the thermal equilibrium equation of the target in the sky background is used to solve the surface temperature field. A suitable bidirectional reflection distribution function model is selected to describe the reflection characteristics of the target surface element in the infrared band, which improves the realism of the infrared reflection of face element. Taking into account the geometric model of air target, the infrared radiation of target itself and the reflected radiation to background render the infrared image of aerial target in combination with the relevant theories of computer graphics. The modeling and simulation methods provide reference for the detection, identification and tracking of air targets.

Abstract:Based on microsatellite constellation, meteorological forecast has been greatly improved in terms of temporal and spatial resolution. To separate frequency in RF front-end system of the microsatellite atmospheric microwave sounder, a waveguide diplexer with compact size and low insertion loss is adopted. A 166/183GHz diplexer is designed using equivalent circuit method and mode-matching technology. According to the actual situation of machining, the effects of iris steepness and iris thickness on the performance of diplexer are analyzed in simulation. Through the analysis of the split-block realization and the machining defects, the way of machining is continuously optimized to obtain a satisfactory machining sample. Maximum measured insertion loss is 1.5dB, and minimum measured return loss is 15dB. Measured out-band rejection is higher than 27dB. Good agreement between simulation and measurement has validated the feasibility of designing method.

Abstract:A Tunable Mid-IR dual frequency laser based on Single-Resonant Optical Parametric Oscillator is presented. The mid-infrared wavelength tunability of 3-3.8 μm is achieved by adjusting the temperature and polarization period of MgO:PPLN crystal. When the pump power is 6.9 W and the temperature of the MgO:PPLN is 75°C, output power of 1.25W is obtained. The highest optical-optical conversion efficiency of the idler light with respect to pump light is 18.2%. The beat note frequency is equal to the beat note frequency of the pump, which can be tuned from 125 to 175 MHz. The modulation index of the beat note of idle could be adjusted with different dual-frequency power radio of pump.

Abstract:Land surface temperatur is one of thr important parameters of geogas interaction and energy exhange.In order to obtain high spatial resolution land surface temperature data. The research improved a method of downscaling thermal infrared remote image, and verified it with Shanghai Landsat 8OLI/TIRS image as the data source. The Normalized Difference Vegetation Index (NDVI) was decomposed into low frequency layer and edge layer and detail layers, in which the edge layer and the detail layer are scaled up to the thermal infrared data, and compared with the classical thermal infrared downscaling method DisTrad algorithm and TsHARP algorithm, the simulated surface temperature (LST) ( 270m) LST downscaling (90m) as a downscaled data source.The results show that: 1) All three downscaling methods preserve the spatial characteristics of the original land surface temperature, but the DisTrad algorithm and the TsHARP algorithm increase the detailed information that does not exist in original land surface temperature data.; 2)The improved three-layers decomposition model has a root mean square error of 0.9130k,which is 0.9373k and 0.8320k higher than the DisTrad method and the TsHARP method.

Abstract:Low excitation-power density photoluminescence (PL) spectra suffered from poor spectral signal-to-noise ratio ( SNR）and hence restricted the study of the band-tail states in GaAs1-xBix. We in this work conduct laser spot-size-dependent PL measurements on two GaAs1-xBix epitaxial films by Fourier transform infrared spectrometer-based PL system with enhanced sensitivity, and observe that (i) with constant excitation power, increase of laser-spot diameter leads to a redshift of the PL-peak position and a linewidth evolution of first decreasing and then increasing, which is attributed to the decrease of the equivalent excitation power density, and (ii) with a constant excitation power density of 5.1W/mm2, the PL lineshape is unchanged while the SNR is significantly improved as the laser spot diameter rises. As a result, the weak transition features are well resolved in the PL spectra taken at low excitation power density, and can be safely treated by spectral fitting analysis. The result indicates that adequate increase of excitation spot-size contributes to the improvement of the SNR and sensitivity as well for PL measurement at low excitation-power density.

Abstract:Big-bore and flexible dielectric-coated metallic waveguides were fabricated with various dielectric film thicknesses. Transmission characteristics were measured for the metallic waveguides and dielectric-coated metallic waveguides in G band, 4.3 THz, and mid-infrared regions. Measured results show that waveguide loss in G band increases with the increase of dielectric film thickness. Loss for the 2.6 mm-bore metallic waveguide was 2.1 dB/m at the frequency of 160 GHz and the additional loss caused by bending for the waveguide is small. Waveguide loss at 4.3 THz decreases with the increase of dielectric film thickness. And the additional loss caused by bending for the dielectric-coated metallic waveguide decreases with the increase of dielectric film thickness. Loss for the 3.6 mm-bore dielectric-coated metallic waveguide with 1.2 ?m dielectric film thickness is 2.84 dB/m. Measured beam profiles show that energy is more concentrated in the low-order transmission mode as the film thickness increases.

Abstract:HgCdTe APD is one of the developing trends of third generation inferred FPA detectors. This article presents a new method to fabricate HgCdTe APD by Ion Beam Etch (IBE), and discusses the relation of gain to cutoff wavelength and depletion region thickness. A gain of 1000 at a bias of 17V was achieved in a HgCdTe APD with a cutoff wavelength of 4.8μm fabricated by this method. The noise factor, F, is calculated after a noise spectrum test.

Abstract:The high resistance and severe optical absorption brought by the traditional P-side distributed Bragg reflectors (P-DBRs) has been the bottleneck of the development of 2 μm GaSb based vertical cavity surface emitting lasers (VCSELs). For this reason, a P-side mirror with high contrast subwavelength grating (HCG) is designed and simulated by the rigorous coupled wave analysis method. The testing results show the HCG mirror,easy to make, has 278nm bandwidth with reflectivity more than 99.5% and 148nm bandwidth with reflectivity greater than 99.9% around the central wavelength of 2 μm for TM mode. Such a mirror can fully meet the requirements of VCSEL, and can effectively avoid the problem of diffraction characteristics deterioration caused by heteroepitaxy and so on.

Abstract:For the problem of tracking infrared weak targets, a box particle labeled multi-bernoulli multi-target detection and tracking algorithm is proposed. To begin with, the algorithm using the mean filter to denoise the grayscale image, Then, the region with higher intensity is selected as the interval measurement at current time by sorting the intensity of all the pixels, Finally, the box particle labeled multi-bernoulli filter is applied to tracking. Simulation are presented to demonstrate that the BOX-LMB-DT algorithm has stable, effective performance. In the same conditions, compared with the LMB particle filter under interval measurement, the operation efficiency of the BOX-LMB filtering is improved by 22.59% when the same tracking performance is achieved.

Abstract:The identification of supercooled water droplets in the cloud is of great significance for the physical process of cloud-precipitation and warning aircraft icing. In this paper, the spectral peak recognition algorithm is established by the U.S. ARM-AMF2 spectral data of the 35GHz cloud radar in Finland. The spectral separation of the total spectrum is obtained, and then the supercooled water droplets are identified. Next the supercooled water droplets are identified. Next, the reflectivity, doppler velocity and spectral width of different types of particles are calculated by spectral moment. Finally, the liquid water content in the cloud is retrieved from the empirical relationship and compared with the detection results of the microwave radiometer. The results are as follows:(1)The radar reflectivity factor of mixed-phase clouds mainly depends on snow. Therefore, it is considered that the effective volume of radar is snow. The cloud liquid water content will be underestimated according to the total reflectivity;(2) The gradient of Doppler velocity(V) of ice and snow particles in the supercooled water layer(SWL) larger than that in the ice and snow layer(ISL);(3) The liquid path(LWP) obtained by the Doppler spectrum is good agreement with the microwave radiometer. It shows that the millimeter wave radar can effectively estimate the liquid water path in the cloud.

Abstract:Terahertz frequency comb, which is generated from femtosecond frequency comb, is applied to measurement of the spatial intensity of terahertz source. Two technologies, electro-optic sampling and photoconductive detection, are applied to generate terahertz frequency comb, and the spatial intensity of a 100 GHz source is measured with both of these two techniques. The total radiant power is traceable to a standard terahertz radiometer, and the absolute intensity of the terahertz source is obtained. The measurement results with both of the two techniques, electro-optic sampling with 800 nm femtosecond optical pulse in free space and photoconductive antenna detection with 1550 nm femtosecond optical pulse in fiber, are analyzed and compared. Moreover, the spatial intensities of the terahertz radiation at different distance away from the terahertz source are measured, and the involvement of the terahertz radiation in free space is experimentally studied.