Abstract:The influence of different Cu contents (Cu/(Ga+In)=0.748~0.982) on the microstructure of Cu(In,Ga)Se2 (CIGS) thin films was reported. The CIGS thin films were grown via a two-step process including DC sputtering deposition of metallic precursor and following selenization. Presence of a series of chalcopyrite diffraction peaks in the X-Ray diffraction (XRD) patterns confirms the existence of chalcopyrite CIGS (CH-CIGS) phase in these CIGS films. The Raman spectra indicate that as the Cu content increases from low to high, the CIGS film sequentially goes through three phase regimes: coexistence of OVC and CH-CIGS phase, single CH-CIGS phase and coexistence of CuxSe and CH-CIGS phase. Moreover, the full width at half maximum of CIGS Raman peaks changes with Cu/(Ga+In) and reaches its minimum near Cu/(Ga+In)=0.9 due to better crystallinity and less disorder. Some empirical FWHM-Cu/(Ga+In) relationships were also observed. These results show that Raman spectroscopy is more sensitive to the microstructure of CIGS film than XRD, and can be used for preliminary estimation of the crystal phases and Cu content of CIGS film in a fast and non-destructive way.

Abstract:Scaled InAlN/GaN heterostructure field-effect transistors (HFETs) with high unity current gain cut-off frequency (fT) on sapphire substrate were fabricated and characterized. In this device, scaled source-to-drain distance (Lsd) of 600 nm was realized by metal organic chemical vapor deposition (MOCVD) based on regrow nonalloyed n+-GaN Ohmic contacts. Moreover, a 50 nm rectangular gate was fabricated by self-aligned-gate technology. A high drain saturation current density (Ids) of 2.11 A/mm @ Vgs= 1 V and a peak extrinsic transconductance (gm) of 609 mS/mm were achieved in the InAlN/GaN HFETs. In addition, from the small-signal RF measurements, the values of fT and maximum oscillation frequency (fmax) for the device with 50-nm rectangular gate were extrapolated to be 220 GHz and 48 GHz. To our best knowledge, the value of fT is the best reported one for InAlN/GaN HFETs in China.

Abstract:Terahertz time-domain spectroscopy (THz-TDS) is a significant technique for characterizing materials as it allows fast and broadband measurement of optical constants in the THz regime. The measurement precision of the constants is highly influenced by the complicated measurement procedure and data processing. With particular emphasis on normal reflection measurement, the sources of error including amplitude errors and positioning error and sample misalignment in determining the dielectric properties of materials were analyzed. The uncertainty that characterizes the influence on the optical constants for each source was formulated independently. Several simulations were carried out to illustrate the relations between the error sources and the uncertainty of the optical constants.

Abstract:A new near-infrared monolithically integrated multichannel spectral sensor (MCSS) serves as a key component of Spectral-sensing Internet of Things (SSIOT). A wavelength calibration method for the MCSS was proposed. The method is based on the relative spectral response and includes specific principles of wavelength allocation. Several pixels comprised a channel with the calibrated wavelength. Experimental tests were conducted in the calibrated MCSS and other two commercial spectrometers. The compared spectrum results demonstrated calibration accuracy of 1.8 nm on average, with performance as good as a commercial spectrometer equipped with similar FWHM and sampling intervals, which can meet the application demand.

Abstract:The threshold power of 1.2 μm laser generated from the Ho3+: LLF crystal was discussed. Two typical quasi-three-level theoretical models were used to analyze the effectiveness of 1194 nm laser's threshold power in the in-band pumping source of 1.15 μm fiber laser with different parameters, such as the absorption coefficient of laser medium, the laser beam radius, the crystal length and reflectivity of the output mirror. It was found that the re-absorption loss was the most important factor leading to the different results for the two models, and the second model was close to the practice because of the narrow bandwidth pumping beam(<6 nm). The results provided reliable data of Ho3+-doped 1.2 μm solid-state laser systems for the design and experimental research in further.

Abstract:Based on the curved circular waveguide coupling theory and regular circular waveguide junction mode matching method, the TE01-HE11 Mode Converter model was designed using the optimization parameter of the waveguide mode conversion structure obtained from relevant numerical calculation program, and was successfully simulated and verified by the CST software. The system is mainly composed of three parts: a TE01-TE01 mode transition, two circular waveguide mode converters for TE01-TE11 and TE11-HE11. The calculations showed that the conversion efficiency of the TE01-HE11 mode converter system is over 99% within the bandwidth of 5% relative to 24.13 GHz. The results of simulations and test are consistent with that of calculation.

Abstract:Filters are essential components of communication systems. A rapid and accurate fabrication method is presented in this paper for the design and fabrication of a waveguide filter. The filter was fabricated by using a multi-layer coating and one-time ultraviolet exposure lithography (SU-8 resist on a silicon wafer) to have dimensional fabrication errors of less than 3 μm in height and 1.1° in vertical angle deviation. We demonstrated the feasibility of the proposed class of filters and the fabrication method used and achieved a superior performance (with regard to: insertion loss, return loss, and bandwidth). Consequently the minimum passband insertion loss, which is practically negligible, was measured as being less than 0.5 dB while the return loss is greater than 10 dB during the passband, demonstrating that the chosen rapid fabrication technology is an effective method of terahertz device fabrication. The new technology should become a major driving force forging the future development of terahertz RF devices.

Abstract:A novel W-band digital variable polarimetric radar for target characteristic measurement is presented in this paper. The main components of the digital variable polarimetric radar are the two-subarrays variable polarized antenna, the two-channels T/R modules, and the digital signal processing unit. This radar transmits arbitrary polarized electromagnetic wave by spatial polarimetric synthesis, and receives arbitrary polarized echo by digital polarimetric synthesis. The experimental results illustrate that the W-band digital variable polarized measurement radar can extract the polarimetric scattering matrix accurately under various polarimetric modes, has the ability of measuring full-pol RCS of the target and can be used for target polarimetric information analyzing and research.

Abstract:With high spatial resolution of 250 m, MERSI images obtained from FY-3 satellite not only reveals information about the long term distribution of sea ice in large scale, but also contains information about its detailed shape characteristics, such as ice block area and roundness. Based on the spectral feature of sea ice and gray distribution feature of ice block, an integral method and process for extracting the macroscopic sea ice distribution and detail ice block shape parameters was proposed in this paper. This method consisted of sea ice recognition, ice block detection and sea ice parameters extraction. In the summer of 2014, the detail sea ice information of the marginal ice zone in the Fram Strait was extracted accurately by using the proposed method. And consequently this method can provide methodological support and information security for the study on the change of Arctic sea ice and interaction between atmosphere and ocean.

Abstract:High performance Hg1-xCdxTe epitaxial materials with the size of 50 mm×50 mm were produced by Te-rich vertical LPE technology. The sample holder with triangle cylinder structure and a function to prevent HgCdTe solution soaking into the back of the substrates was designed and used to obtain 3 epitaxial materials for each growth process. In order to obtain uniform epilayers, the temperature uniformity and composition uniformity of HgCdTe solution during the process were improved. The STDDEVs for x-value and thickness distributions of 50 mm×50 mm epitaxial material are 0.000 4 and 0.4 μm, respectively. The average values of x-value and thickness of three epitaxial wafers grown at the same time have a very small difference, less than 0.0004 and 0.1 μm, respectively. The differences of average x-values and thickness values from run-to-run are about ±0.002 and ±2 μm, respectively. In order to control the defects of HgCdTe epilayers, the lattice parameters and defects of CdZnTe substrates have been strictly controlled. The full width at half maximum (FWHM) of X-ray double-crystal rocking curve for HgCdTe epilayers was controlled within 30″. The dislocation density is less than 1×105 cm-2, and the surface defect density is less than 5 cm-2. Utilizing annealing technique, the carrier concentration of Hg vacancy doped p-type Hg0.78Cd0.22Te epilayers at 77 K were controlled in a range of 8 ~ 20×1015 cm-3 and their hole mobility exceed 600 cm2/Vs. The material performance and production capacity based on the LPE technique described above can satisfy the demand for fabricating large format HgCdTe infrared focal plane arrays.

Abstract:The laser beam induced current (LBIC) and the I-V test at liquid-nitrogen temperature were applied to characterize the PN junction region extension effect in the HgCdTe device processing. By LBIC and I-V test, it was found that the area of n-type region of p-type HgCdTe material implanted by Boron ion or etched by ion beam milling is larger than the nominal values. The transverse dimension of n-type region was measured. At the same time, it was found that the results obtained by both methods were comparable.

Abstract:We investigated experimentally and theoretically the mode competition and output power characteristics in terahertz second-order distributed feedback quantum cascade lasers. The experiment results demonstrated that the lasers operate stably on the fundamental transverse/longitudinal mode during the whole laser dynamic range. High-order transverse modes are suppressed due to the absorbing boundaries set along the laser ridge. In addition, the fundamental mode and the high-order longitudinal modes are very close in frequency, and their electromagnetic fields have strong overlap. The spectral or spatial hole burning effect is therefore effectively avoided, leading to a stable operation of the fundamental longitudinal mode. The experimental results also show that the slope efficiency of output power decreases with the length of the distributed feedback grating. As a result, only in certain grating length, the output power reaches its maximum. Our work provides experimental and theoretical supports for the studies of high performance THz lasers and the phase locked laser arrays.

Abstract:A prototype of optically-pumped terahertz (THz) gas laser (OPTL) with metallic waveguide was designed and manufactured. The output power of THz laser radiation is 150 mW, pumping by a 44 W, 9P36 (9.69 μm) cw CO2 laser. The THz laser medium is CH3OH vapour, and the pressure is 30 Pa. The photon conversion efficiency is 8.4%. The relationships of THz laser power versus working gas pressure and pump power are given. The stability of the output power in ten minutes was measured. The variation of THz laser power was measured by adjusting the length of the THz laser cavity precisely through a piezoelectric translator. The characteristics of the longitudinal modes in the metallic waveguide THz laser are discussed. The experimental work and results are helpful for further researches on the compact folded all-metal waveguide OPTL.

Abstract:Infrared spectrum is very useful in the field of hyperspectral remote sensing. Because of the weak energy of infrared spectrum, the difficulty of the development of infrared focal plane, and the strong background, the development of the Infrared Hyperspectral Imaging System is very difficult. So far, the field is still in the laboratory research stage. This paper presents an airborne infrared hyperspectral imager. It can acquires 180 wavebands in the range of 8.0~12.5 μm.The spectral resolution of this imager is better than 44 nm and the absolute spectral calibration accuracy is better than 1 nm. The field of view of this imager is about 14° and the spatial resolution is better than 1mrad. Its noise equivalent temperature difference (NETD) is less than 0.2 K@300 K. The imager was carried out in Zhoushan, Zhejiang, China in June 2015. Analysis shows that the infrared hyperspectral image data can plays an important role in the field of surface emissivity inversion and geological mineral recognition.

Abstract:A comparison of the feasibilities of adulteration detection for chondroitin sulfate using terahertz time-domain spectroscopy(THz-TDS)and infrared spectroscopy(IR) was conducted. The shark-derived chondroitin sulfate (SCS) mixed with sodium hexametaphosphate (SHMP) adulteration was used as the materials for detection in this research. The results have shown that the spectra of SHMP, SCS and the adulterated samples of them were significantly different in either THz-TDS spectra or IR spectra, indicating that these two spectroscopic techniques have a potential for the identification of chondroitin sulfate adulteration. The lowest adulteration ratios(mass to mass)of SHMP to SCS which can be identified were 1: 15 and 1: 1 for THz-TDS and IR, respectively. THz-TDS is more sensitive in the detection performance than IR and is superior to IR for the detection of SCS adulteration. This study has provided an experimental foundation for developing an accurate, rapid and nondestructive spectroscopic technique which can be used to identify the adulteration of SHMP in SCS.

Abstract:Recent advances on diversified 3-D printed passive waveguide devices operating from microwave to terahertz frequencies have been reviewed. Developed by the authors' group, several waveguide filters fabricated using a stereolithography (SLA)-based 3-D printing technique have been presented. They are two X-band bandpass filters based on novel high-quality-factor single-mode and dual-mode spherical cavity resonators, and two W-band bandpass filters based on a slotted rectangular waveguide and a compact on-plate structure. The presented filters demonstrate good agreement between the measured and simulated RF performances. Compared with their conventional counterparts made from copper, these SLA-printed devices exhibit a significant weight reduction over 80% due to the use of nonmetallic printing materials, without any penalty of degrading their RF performances.

Abstract:Compared with other targets, it is more difficult to detect infrared small targets due to several aspects such as the low signal to noise ratio, low contrast, small size, the lack of shape and texture information of the targets, especially under complex background. A novel infrared small target detection method based on peer group filter (PGF), bi-dimensional empirical mode decomposition (BEMD) and local inverse entropy (LIE) was proposed to overcome these difficulties. The PGF is implemented to remove noise and improve signal-to-noise ratio of the initial image. The proposed BEMD algorithm is able to estimate background effectively, which gets target image by removing background from original image and segmenting the Intrinsic Mode Functions (IMFs) by local inverse entropy. Experimental results demonstrated that the novel method can extract the small targets validly and accurately.

Abstract:A 3-D imaging system based on sparse MIMO (Multiple Input and Multiple Output) array at 340 GHz is presented. The imager incorporates a linear array containing 4 transmitters and 16 receivers (4Tx-16Rx) as electronic beam former in horizontal dimension and an elliptic cylinder as focusing reflector in elevation to get high cross-range resolution. Each emitter transmits frequency-modulated continuous-wave (FMCW) waveform with 16 GHz bandwidth and high range resolution is achieved by using pulse compression technique. Experimental results indicate that the 3-D imaging resolution is 14 mm, 10mm and 12mm in horizontal direction, vertical direction and range dimension at 4-m distance, respectively. The personal screen experiments also imply that concealed threats such as guns can be detected by this 3-D imager.

Abstract:An adaptive directional filter method was proposed for the photon counting Lidar point cloud data. The method defines a filter kernel with its main filter direction adjustable. The density of the best filter direction were achieved by traverse and the noise points away from the objects were removed. The noise points adjacent to the objects were eliminated according to the density difference between the point and points in its neighborhood. The filtering method provide here is validated through the point cloud data obtained in an aerial experiment. The results show that the filtering method is able to eliminate the noise points very close to the ground effectively and is fit for the low density object point cloud recognition, while the filter accuracy is 91.86% for vegetable points and 97.89% for ground points.

Abstract:Power combining technology is an effective method to improve the output power of a system when the output power of a single amplifier does not meet the requirement of the system. In this paper, a new type of waveguide E-T junction power divider/combiner based on thin film resistor was studied in detail, and a novel waveguide E-T junction based on thin film resistor was designed. The structure has the advantages of high isolation, low insert loss, small size, and wide band. In order to increase the power which the waveguide E-T junction based on thin film resistor can bear, we try to increase the area of the thin film resistor by designing the length to width ratio of the thin film resistor reasonably, and use the aluminum nitride substrate with high thermal conductivity as the dielectric substrate of the microstrip and thin film resistor. The novel waveguide E-T junction based on thin film resistor was simulated in 3D electromagnetic simulation software HFSS. After testing, the insert loss was less than 0.2 dB, the return loss was better than-15 dB, the isolation was better than 10dB in 25~34 GHz. The measured results were consistent with the simulated results, and the structure has a good engineering application value..

Abstract:According to the latest Sentinel-1 radar system parameters and the surface characteristic parameters of the study area, this paper established a database of surface microwave scattering characteristics under the sparse vegetation cover condition by AIEM model. On the basis of AIEM model numerical simulation analysis, soil moisture inversion model was constructed. The results showed that: 1) Under the different incident angles and polarization mode, the backscatter coefficient response of soil moisture (Mv) and the composite surface roughness (Zs) have obvious logarithmic correlation, respectively. Soil moisture response of VV polarization is sensitive, the optimal response range is for Mv 0~30%, Zs 0~0.06 cm. 2) GammaMAP filtering has good denoising effect in the sentinel-1 radar data preprocessing. The spatial distribution of soil moisture extracted from sentinel-1 images has good consistency with the actual situation in the same period field in the study area. In April, the soil moisture spatio-temporal distribution of Weigan-Kuqa river basin shows spring drought characteristics. 3) For 0~10 cm surface soil moisture, the correlation coefficient between the measured value and simulated value reaches 0.76, showing that this model is suitable for the extraction of soil moisture in the arid area of a certain regional scale.