Abstract:Terahertz (THz) communication is considered to be one of the demanding technology for the upcoming 5G standards. The incredible demand for high rate through wireless channel necessitates the use of THz frequency for communication. The development of communication systems in this frequency band possess technical challenges as the characteristic of THz band is very much different from the present wireless channel. However, the advancements in the development of transceiver and antenna systems are rapidly bringing the THz communication into reality. The high path loss in THz band limits the communication range of this channel. Even, for a distance of few meters (>5m), the absorption coefficient is very high and hence the performance of the system is poor. Performance over this frequency channel can be enhanced by considering transmission windows over this band instead of the entire band. The transmission windows are the frequencies over which the absorption is relatively low. Though there is an improvement in the performance with this adaptive modulation scheme, but not sufficient for longer distance. Apart from path loss, the frequency selective nature of this high bandwidth channel is also a major reason for the poor performance of THz channel. Orthogonal Frequency Division Multiplexing (OFDM) is a promising solution to mitigate the effects of frequency selective nature of the wireless channel. OFDM has been exploited in this paper to improve the performance of terahertz channel. The results show that the Bit Error Rate (BER) of the terahertz channel is considerably improved with OFDM.

Abstract:Due to the ultra high electron mobility, graphene has been proposed as a prospetive candidate for the photodetection. Nevertheless the relatively low photo absorption limits its potential application. On the other hand, the semiconductor quantum dots has exhibited high quantum efficiency and strong optical absorption. A novel photodetector by the incorporation of graphene with InAs quantum dots on GaAs substrate has been proposed. The performance of the fabricated photodetector, such like photoresponse, dark current, and time response, have been extensively studied. The photodetector based on graphene/InAs QDs/GaAs hybrid hetero-junction demonstrated that for the visible range of 637 nm a responsivity of about 17.0 mA/W, and detectivity of 2.3×1010 cmHz1/2 W-1, with an on/off ratio of about 1×103 could be achieved. Moreover a stronger dependence of dark current, Schottky barrier height and ideality factor on temperature has also been observed.

Abstract:Impacts of the total period number for the In_0.83Al_0.17As/In_0.52Al_0.48As digitally-graded metamorphic buffer (DGMB) on the performances of 2.6 μm In_0.83Ga_0.17As photodiodes (PDs) have been investigated. An increase of the total period number from 19 to 38 for the In_0.83Al_0.17As/In_0.52Al_0.48As DGMB with the same thickness has shown improved crystal qualities for the In_0.83Ga_0.17As/In_0.83Al_0.17As photodiode layers grown on such pseudo-substrates. An increased strain relaxation degree up to 99.8%, a reduced surface roughness, enhanced photoluminescence intensities as well as photo responsivities, and suppressed dark currents are observed simultaneously for the In_0.83Ga_0.17As photodiode on the DGMB with a period number of 38. These results suggest that with more periods, DGMB can restrain the transmission of the threading dislocations more efficiently and reduce the residual defect density.

Abstract:The ZnTe:Cu crystals grown under microgravity and on ground are characterized by optical and energy dispersive spectrum analysis. The radial and axial spectra of the largest crystal at the end of the ingot are analyzed. For the axial component of the tail section, the compositional uniformity of Cu in the space sample is better than that of the ground sample, and the Te/Zn ratio of the ground sample is higher than that of the space sample. The radial compositional uniformity of Cu in the space sample in the tail section is better than that of the ground sample, and the Te segregation of the ground sample is more serious.

Abstract:As a main instrument of FY-4 which was launched on Dec.11, 2016, Geostationary Interferometric Infrared Sounder (GIIRS) is the first hyperspectral infrared atmospheric vertical sounder working on geostationary orbit internationally. This instrument is mainly used for vertical atmospheric sounding and gains atmospheric temperature, humidity and disturbances. The observed data of FY-4 GIIRS is assimilated into the GRAPES Global Forecast System in real time. It is the first time realizing the satellite hyperspectral detection and real-time data assimilation of wide range sensitive area sat a high frequency and will have a significant impact on the current meteorological forecasting capability, in particular, for the prediction of typhoon intensity and track, the accuracy can be greatly improved. In this paper we present the measuring principle of the atmospheric vertical sounder and the on-orbit performance and operation of GIIRS, and the development of hyperspectral infrared atmospheric vertical sounder in the future is also prospected.

Abstract:A novel ship detection method using cascaded convolutional neural network (CCNet) with multispectral image is proposed to achieve high-speed detection. The CCNet employs two cascaded convolutional neural networks (CNN) for extracting regions of interest (ROIs), locating and segmenting ship objects sequentially. Benefit from the abundant details of the multispectral image, CCNet can extract more robust feature for achieving more accurate detection. The efficiency of CCNet has been validated by the experiments on SPOT 6 satellite multispectral images. In comparison with the state-of-the-art deep learning based ship detection algorithms, the experimental results indicate that the proposed ship detection algorithm accelerates the processing by more than 5 times with a high accurate detection performance.

Abstract:A D-band (110-170 GHz) transmitter module, based on a novel self-aligned microstrip-to-waveguide transition, is demonstrated. The simulated average insertion loss of the transition is about 0.6 dB and return loss is better than 10 dB during working band. A D-band transmitter module is developed using such transition with resistive mixer and multiplier chips. The transmitter module operates between 110-153 GHz and provides a peak saturated output power of -4.6 dBm at 150 GHz and with 13.5 GHz 3-dB bandwidth from 145.8 to 159.3 GHz. 3 Gb/s wireless communication with this module at 145 GHz is demonstrated with spectrum efficient 64-QAM modulation.

Abstract:Staggered double vane traveling wave tubes have been given a lot of attentions in recent years due to its high power capacity and easy fabrication. However, the loss seriously limits the performance of traveling wave tube with the increasing of frequency, especially in THz wave band. In this paper, a more practical design about staggered double vane structure is proposed with the consideration of the loss and fillets caused by fabrication. The simulation results indicate that the tube with uniform period slow wave structures can obtain over 5W output power in the frequency range from 320GHz to 342GHz. The method of phase-velocity taper is used to enhance the output power and the simulation results show an obvious improvement of the power with more than 28% in the operating wave band. Based on these, the experiment of the fabricated high frequency system with filleted staggered double vane slow wave structure is carried out. The tested S21 of pillbox window is above -2.1 dB in the frequency range from 330GHz to 360GHz and VSWR (voltage standing wave ratio) is below 1.35 in the frequency range from 334GHz to 355GHz. And the tested VSWR of the high frequency system including the pillbox window is below 2 in the frequency range from 335GHz to 344GHz, which matches with the simulation results.

Abstract:This letter presents a 340-GHz cavity-backed on-chip patch antenna design and fabrication using standard 0.13-μm SiGe BiCMOS technology. The patch placed at AM layer is fed by a stripline at LY layer through via holes from LY to AM layer. The via holes are built between the top metal layer (AM layer) and the ground plane (M1 layer) to form a cavity which improves the impedance matching bandwidth and the radiation performances of the antenna. The proposed antenna shows a simulated impedance bandwidth of 9.2 GHz from 335.6 to 344.8 GHz for S11 less than -10 dB. The simulated gain of the antenna at 340 GHz is 3.2 dBi. The total area of the antenna is 0.5×0.56 mm2.

Abstract:In this paper, a novel and simple design of dual-stop-band frequency selective surface (FSS) for infrared stealth applications is investigated. The designed structure consists of three layers, metallic four multiplexed cross resonators located at the front and metal well structure at the back separated by a dielectric layer. The simulated results show that the proposed dual-stop-band FSS has high reflectivity in the two atmospheric windows (3.0-5.0μm and 8.0-14.0μm) for normal incidence waves, and the transmissvity is suppressed completely under 0.1. The effects of incident angle, polarization angle, period size and dielectric thickness on reflectivity and transmittance were investigated. the proposed structure also shows good transmission stability in a wide range of incident angles θ for both TE and TM incidences at azimuthal angle φ = 0°. Moreover, we demonstrate that such structure has good transmission stability for a wide range of azimuthal angles due to four-fold rotational symmetry of the designed unit cell. The principle of the resonant the proposed structure is formed not only by the electric resonance but also by the magnetic resonance.

Abstract:Transmission enhancement is simulated verification based on a non-hollowing double layer of metamaterial filter. The proposed structure contains a continuous metallic film covering on a continuous dielectric layer. The transmission of the proposed double layer structure can be enhanced obviously comparing the single metal layer structure. The effects of the dielectric layer thickness and the incident angle on the transmission enhancement are simulated verification. It is found that the maximized transmittance enhancement is achieved when the thickness h1 is 20nm. Moreover, the proposed double layer metamaterial filter shows a stability of transmittance enhancement when the incident angle reaches to 45°. The proposed double layer metamaterial filter can be applied in many potential fields due to its non-hollowing design strategy.

Abstract:Infrared photo-thermal absorption effect was used extensively in detecting the micro-defects in semiconductor materials (silicon wafers) as a nondestructive and noncontact technology. This effect was adopted initially to detect the structural characteristic of the defects in CdZnTe (CZT) crystal and images with obvious coherent fringes were obtained, which were investigated systemically. It was confirmed that the coherent fringes of the Infrared photo-thermal absorption images of CZT wafers come from the interference of incident light relative to parameters of incident light, wafer thickness, thermal conductivity and band gap of materials. Finally, the micro-defects of CZT materials and their distribution along depth direction were obtained by optimizing the test conditions.

Abstract:A numerical model was established by the level set method to simulate the etching profile evolution in HgCdTe ion beam etching. The input parameters are: mask thickness、the slope of mask sidewall、trench width、ion angular distributions, etching speed, et al. Etching lag and etching profile of HgCdTe were simulated and compared with experimental results. The results shows that, given nominal trench width 4?10?m, the errors between simulated etch depths and that of experiments are 6~20%. The profile evolution of etching mask was simulated and an example was given to illustrate how to design the mask thickness to improve the aspect ratio.

Abstract:A high-sensitivity long wavelength infrared detection system was developed based on the type-II superlattice 320 × 256 long wavelength infrared detector. The technical specifications of the type-II superlattice infrared detector and the main structure and working mode of the infrared system are introduced. In order to give full play to the sensitivity of the infrared detector, a high-sensitivity information acquisition system was developed. The software and hardware design of the information acquisition system is introduced. The information acquisition system adopted an adaptive signal conditioning technology to reduce information acquisition noise and improve sensitivity and dynamic range of the infrared system. Finally, the information acquisition noise test, system performance test and outfield imaging experiment are carried out for the whole long wavelength infrared detection system. The experimental results show that the information acquisition noise of the long wave infrared detection system is 0.065mV, the NETD is19.6mK, and the blackbody detectivity is 7.72×1010cm√Hz/W. The quality of outfield imaging is good, the details of the images are clear and the contrast is high. The long wavelength infrared detection system is conducive to the application of type-II superlattice infrared detectors in high sensitivity long wavelength infrared remote sensing.

Abstract:The equivalent circuit models for the open and short structures used in InP DHBT on-wafer testing are presented. The model topologies are physically based. The high frequency parasitics of the structures are considered in the model topologies completely. The capacitive and resistive parasitics are extracted from the low-frequency measurements of the open structure directly. Tradition physical formulations are employed to have an initially determination of the inductive and skin effect elements of the models, and further corrected by using the analytically extracted results from the low-frequency measurements of the short structure, which enables an instance accurate formulations for the test structures modeling. The models and the modeling methodology are verified using the open and short structures manufactured at a 0.5 um InP DHBT technology, excellent agreements of the model simulated and measured results are achieved over the frequency range of 0.1-325 GHz.

Abstract:Aiming for remote wide-area detection of weak and small aerial target under space-based complex observation conditions, we in this paper analyze the radiation interaction mechanism between complex background environment, e.g., solar illumination, clouds and earth surface, and aerial target based on the full link of space-based optical detection. We then summarize main environmental factors that affect the target radiation characteristics. After that, combined with the detectability characterization, we investigate the influence rules of environmental factors, e.g., different illuminations, various surface background types and clouds, on the target detection performance under different detection spectrum. Finally, taking a typical target as an example, we combine existing target characteristics cognition and theoretical modeling to rank the influence order of different environmental factors, and give the detection spectral optimal selection suggestions according to the variation of signal-to-noise ratio and the variation characteristics of the spectrum. This provides theoretical basis and scientific guidance for the design of stealth/anti-stealth aircraft, space-based detection system and information processing optimization algorithm.

Abstract:CO₂ and CO are called the key indicators of combustion efficiency. Accurate measurement of CO₂ in the combustion flow field is very important for energy conservation and emission reduction in industrial combustion process and engine combustion state diagnosis. Researching intensity, self-broadening coefficient, temperature-dependence exponent and other parameters of CO₂ in high temperature, may improve the accuracy and reliability of measurements for CO₂ concentration. A precise temperature control and pressure control gas spectroscopic parameter measurement system with a design temperature up to 2073K based on absorption spectroscopy has been developed for the measurement of spectroscopic parameters of the R(50e) line at 5007.787cm-1 of CO₂. A large number of high temperature survey spectra of the CO₂ R(50e) line were recorded at temperatures between 1212K and 1873K and many pressures through the system. Through background subtraction, baseline fitting, time-frequency conversion, multi-line combination and nonlinear least squares fitting, and other data processing based on the CO₂ R(50e) survey spectra, intensity, self-broadening full-width and temperature-dependence exponent at temperatures between 1212K and 1873K were obtained. The uncertainty of line strength is less than 1.5%, the uncertainty of self-broadening full-width is less than 4.5%. These parameters are supplement and improvement to the existing database. They are helpful for the detection of CO₂ concentration in combustion diagnosis to ensure the accurate inversion of CO₂ concentration in the combustion process.

Abstract:Starting from the key problems of spectral image recognition, the improved Histogram of Oriented Gradient (Spectral Histogram of Oriented Gradient) and "Spectral total reflectance" were applied to the polarized spectral recognition study, and five dry plants and three bare soils could be recognized. In the study, the hierarchical clustering analysis was carried out by combining the length of Spectral Histogram of Oriented Gradient and Spectral total reflectance, and six study objects could be identified. Then, the length of Spectral Histogram of Oriented Gradient was used to identify the remaining two study objects by the hierarchical clustering analysis alone. As a result, the polarized spectrum of all the study objects could be recognized.

Abstract:A new deep convolutional network for detecting small targets in infrared images is proposed. The problem of small targets detection is transformed into the classification of small targets’ location distribution. First, a Fully Convolutional Networks is used for enhancing and initially screening the small targets. After that, the original image and the background suppressed image are selected as the inputs for classification network which is used for the follow-up screening, and then the SEnet (Squeeze-and-Excitation Networks) is used to select the feature maps. The experimental results show that the detection network is superior to multiple typical infrared small target detection methods and has an excellent result on different signal-to-noise ratio,different scenes and motion blur targets.

Abstract:Based on upstream products of FY-4A and A-Train satellites data, an estimation algorithm of cloud base height for FY-4A has been presented utilizing Random Forest model. The algorithm is evaluated in the comparison with CloudSat and CALIPSO. The results show that cloud base height for top layer cloud can be generated by using upstream products of FY-4A. Compared with CloudSat and CALIPSO, the mean absolute error is less than 1km and the relationship coefficient is bigger than 0.8. The presence of multi-layer clouds may result in underestimate of cloud base height, the error in cloud top height may also introduce uncertainties in estimation of cloud thickness and cloud base height. In addition, error of the cloud base height tend to increase as the cloud thickness increasing.

Abstract:Near-infrared spectroscopy is a promising method to monitor the characteristics of biological samples noninvasively in biomedical field, food safety field, agricultural field, etc. But most study focus on the measurement of optical properties of biological samples in these fields. Utilizing the latest developed diffuse correlation spectroscopy device and 30% intralipid as the phantom of biological sample, we demonstrated how to obtain both the optical property and dynamical property of 30% intralipid. The absorption coefficient and reduced scattering coefficient of 30% intralipid are 0.037cm-1 and 303 cm-1 respectively. The Brownian diffusion coefficient of the diluted 30%intralipid (0.85%, volume/volume) is 8.40×10-9cm2/s and the radius of intralipid particle is about 253nm deduced by Stokes-Einstein relation. The stability of the diluted 30% intralipid is also studied. The scattering coefficient increases by 106% and the Brownian diffusion coefficient decreases by 63% for seven days. This study suggest that diffuse correlation spectroscopy can not only measure the optical properties but also measure the dynamical property of biological sample, which may be a powerful tool in biomedical field, food safety field , agricultural field, etc.