Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
- Most Read
- Most Cited
- Most Downloaded
Abstract:0.15 μm gate-length InP-based In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors (HEMTs) were successfully fabricated with gate-width of 2×50 μm and source-drain space of 2 μm. The maximum extrinsic transconductance (gmext) of 1 052 mS/mm was obtained under gate-source voltage (VGS) of 0.1 V and drain-source voltage (VDS) of 1.7 V at room temperature. Transmission Line Method (TLM) measurements revealed the contact resistance of 0.032 Ω·mm and the specific contact resistivity of 1.03×10-7 Ω·cm-2 on linear TLM patterns. Thus, markedly enhanced gmext was achieved by the superb Ohmic contact and the short source-drain space for minimizing series source resistance. These devices also demonstrated excellent RF characteristics. The fT and fmax extrapolated using the S-parameters measured from 100 MHz to 40 GHz were 151 GHz and 303 GHz, respectively. The HEMTs were promising for millimeter-wave band integrated circuits.
Abstract:The new advanced very high resolution (VHR) synthetic aperture radar (SAR) sensors are capable of achieving sub-metric spatial resolution, which offers the opportunity for a fine level of analysis of man-made structures in such data. In this paper, we first proposed a decomposed model to analyze the signature of rectangular buildings in VHR SAR images. In the model, the scattering effects were subdivided according to different contributors. Accordingly, detailed geometrical structures and spatial distributions of image features of building objects with respect to varied SAR illumination conditions were exploited. Then, based on the generalized effects, a new detection and reconstruction algorithm was proposed for 3-D reconstruction from single VHR SAR images. Specifically, a matching procedure was applied to extract image features, and prior knowledge was employed in the reconstruction steps to jointly perform dimensions retrieval and building type identification. Finally, the proposed approach was applied to VHR SAR imagery and the reconstruction results were discussed.
Abstract:The design of a W-band four-cavity gyroklystron amplifier is presented. The device operates in the fundamental harmonic TE01 circular electric mode. The 70 kV, 6 A beam is produced by a double anode magnetron injection gun (MIG) with an average perpendicular-to-parallel velocity ratio of 1.5 and a parallel velocity spread of less than 4%. Particle-in-cell (PIC) simulations have been performed to predict general RF performance for various parameters. The simulated results show that the designed gyroklystron amplifier can produce about 35 dB gain, 800 MHz bandwidth and 100 kW peak output power with power conversion efficiency of 23.8% for a beam with 4% axial velocity spread.
Abstract:A 12.5 μm long wavelength infrared detector based on InAs/GaSb Type-II superlattice was presented in this work. Superlattice materials were grown on GaSb substrates using MBE technology. Absorber structure for long wavelength detector was designed to be 15ML(InAs)/7ML(GaSb). The detector used a PBIN multiple heterostructures to decrease the dark current. The dark current I-V curve, responsivity spectra and blackbody current responsivity were measured at 77 K. At this temperature, RmaxA product was 2.5 Ωcm2 for the device with a photo sensitive area of 100 μm× 100μm. At zero bias, a current responsivity of 1.29 A/W was measured for the detector, which correspond to a blackbody detectivity of 2.1×109 cmHz1/2/W. Quantum efficiency at 11 μm was measured to be 14.3%. Dark current characteristics were simulated with four kinds of probable transport mechanisms. The results showed that the dominated dark current of the detector is Generation-Recombination current.
Abstract:32×32 element mesa-type back-illuminated InGaAs detector arrays were fabricated on the MBE- grown In0.8Al0.2As/In0.8Ga0.2As epitaxial materials by ICP etching. The characteristics of I-V curves, signal and noise were measured and analyzed. The results indicated that the thermal activation energy is 0.443eV at 210~300 K. By fitting with experimental data, R0A and I-V at different temperature were calculated theoretically. Mechanism of dark current was analyzed and some methods of reducing dark current were put forward. The detector arrays were In-bonded to readout integrated circuits (ROICs) and the characteristics of the FPA was measured. The result of the tested structure with different integrate capacitance indicates that the parasitical capacitance is about 10fF.
Abstract:The results on the growth of GaSb quantum dots (QDs) by liquid phase epitaxy (LPE) were reported. The dot Morphology in term of size, shape, density and uniform was studied by atomic force microscopy (AFM). The effects of growth conditions such as substrate, melt composition, and melt-substrate contact time on the morphology of GaSb QDS were investigated. It was found that it’s easier to get high quality GaSb QDs in condition of GaAs substrate, Ga-rich melt and shorter of contact time.
Abstract:The effect of LPE HgCdTe longitudinal composition distribution on device’s spectral response was studied. A new model was proposed to calculate the spectral response of HgCdTe IR detector. This model considered the real composition distribution in HgCdTe film. The coherent and incoherent light transmission among the device were also included. The calculated result indicates that the composition gradient of LPE HgCdTe film and the built-in electric field can evidently improve the response of the device. The calculated result agreed with the measured data, and proved the accuracy of the model.
Abstract:As a nonlinear dimension reduction algorithm, Gaussian process latent variable model (GPLVM) has been widely applied in pattern recognition and computer vision for its capability in dealing with small size and high-dimensional samples. As GPLVM can discover low-dimensional manifolds in high-dimensional data given only a small number of samples, a new SAR target recognition method was proposed, in which a modified GPLVM was used for feature extraction and Gaussian process classification was employed as the classifier. In GPLVM, the likelihood was optimized by using the scaled conjugate gradient. In order to avoid the noise effect to gradient estimate and overcome the disadvantage that the performance is severely affected by the step length, the immune clone selection algorithm based GPLVM was developed for target feature extraction where the immune clonal selection algorithm characterized by rapid convergence to global optimum was utilized to improve the performance. The experimental results show that the method not only reduces the dimension but also gets higher accuracy.
Abstract:Based on the multi-frequencies mode of Acousto-Optical Tunable Filter (AOTF), the technique of spectral programmability for imaging spectrometer has been proposed. The principles of this technique were presented, and the test results of spectral programmability were introduced, including controls on the filtered wavelength, spectral resolution and passband shape of AOTF via software. Then a prototype system of spectrally programmable imaging spectrometer was established. Primary imaging experiments was carried out to validate the engineering feasibility and technical advantages of the technique. A novel method was provided for increasing the efficiency and flexibility of imaging spectrometers.
Abstract:A W-band sub-harmonic mixer was presented employing microstrip hybrid microwave integrated circuit. The parasitic parameter introduced by package structure of the diode was analyzed. Then a method is proposed to reduce the parasitic capacitance of the diode. In order to avoid grounding with via-hole and usage of edge-coupled band-pass filter in the W-band which are commonly encountered in traditional sub-harmonic mixers, a modified configuration of sub-harmonic mixer was proposed. The measured minimum single side conversion loss is 8 dB at a LO of 45 GHz and an IF of 2.4 GHz. The conversion loss is less than 10.5 dB in the range of 90~100 GHz.
Abstract:A new read-out IC (ROIC) architecture with substrate temperature compensation was introduced for the uncooled microbolometer detector. The influence of responsivity on the substrate temperature was evaluated. Numerical simulation and measurement of the proposed ROIC architecture demonstrated high quality of signal over wide temperature range without using multiple corrections. A 320×240 uncooled microbolometer focal plane array(FPA) based on the proposed circuit was implemented on silicon using a 0.5 μm CMOS technology. The measurement data show that the maximum difference of the output voltages is only 2mV over the change of 20K in the substrate temperature. This architecture is expected to allow removal of the thermoelectric cooler (TEC) from uncooled systems. Thus it is ideally suited for low-cost, low-power, and low-weight production applications.
Abstract:The design of an infrared multiple FOV optical system with a MWIR/LWIR dual-band staring focal plane array detector was introduced. Wide medium narrow FOV was realized by inserting different sets of lens groups in narrow optical path. The harmonic diffraction theory and aspheric design method were used in the aberration balance. The operating wavelength region is 3 to 5 μm and 7.7 to 9.5 μm, F-number is 3, and zoom ratio is 18∶1. The results indicate that the modulation transfer functions (MTF) of all FOV are approaching to diffraction limit, 70 percent medium-wave infrared encircled energy and 60 percent long-wave infrared encircled energy are concentrated in one pixel of detector. Moreover, it could obtain well optical performance in all temperature range. The dual-band optical system could be widely applied in military and civilian opto-electronic detective fields.
Abstract:The aircraft with an elliptical dome acquires excellent aerodynamic performance, but the non-rotationally symmetric structure characteristic of the dome makes the airborne infrared search/track system difficult to meet the requirements of wide field-of-regard (FOR) and high imaging quality at the same time. In order to overcome this problem, a design method for the elliptical dome optical system based on the combination of an arch corrector and a dynamic corrector was proposed. A mid-wave infrared optical system with an ellipsoid dome was designed as an example. The system has a super wide FOR of ?54?, and the imaging quality of the system approaches to the diffraction limit across the entire FOR and instantaneous field-of-view.
Abstract:Echo removal is an important way to improve the spectral resolution of terahertz time-domain spectroscopy. In order to study the echo removal method for the cases of nonlinear absorbent samples, the absorption and group delay effects were considered based on de-convolution algorithm. Two of the four parameters needed in conventional algorithms were abandoned and the remaining two are not related to the exact material and thickness of the sample, which improves the accuracy of terahertz spectrum recovery. Results show that the presented algorithm can eliminate echoes generated by GaAs antenna and ZnTe detection crystal effectively. The width of the time window is doubled so that the spectral resolution is improved up to 20 GHz.
Abstract:According to different characters of infrared image and panchromatic image, a new image registration method was proposed based on the gradient structure information of the image. Firstly, the gradient of infrared image and panchromatic image were calculated. Then the structure similarity between two gradient images was measured to generate homologous points. RANSAC was used to robustly remove the wrong homologous points. Finally, after dividing image into small regions on triangle irregular network (TIN), the registered image was obtained by transforming the triangle. Experiment results show that the proposed approach is efficient and the register accuracy is high.
Abstract:Monitoring of aerosols in a large-region can be achieved by remote sensing, which is very important to the regional ecology and environment study. Data obtained from environment and disaster monitoring and forecasting satellite, which was launched in September 2008, has the advantages of high temporal resolution and spatial resolution in comparison with the common remote sensing data which are used to estimate AOD like TM, MODIS and so on. In order to promote the application of HJ data in land aerosol area, a method combining the HJ CCD data and IRS (a sensor which is also carried by HJ satellite) 1.6 μm data to estimate AOD was presented.
Abstract:The snow albedo which is influenced by the snow grain size, plays an important role in regional or global radiation balance and climate change. The degree of influence depends on the microphysical and optical properties of snow. In this paper, the influence of snow grain size on sensitivity of snow bidirectional reflectance was simulated and analyzed by the radiative transfer equation based on the studies of snow optical characteristics in 550 nm, 1030nm and 1 640 nm. The results indicate that the near-infrared channel 1 030 nm is the sensitive wavelength to retrieve snow grain size. In this band, snow bidirectional reflectance changes significantly when grain size and view angle change. This study provides the theoretical basis for retrieving snow grain size with the multi-angular remote sensing data.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335