Abstract:Crosstalk characteristic is closely correlated to higher sensitivity and higher resolution imaging of focal plane array (FPA). The electrical crosstalk of typical planar and mesa In0.53Ga0.47As/InP FPAs as a function of illumination wavelength, incidence, as well as the etching depth in the mesa structures was investigated quantitatively in detail by simulation. It was demonstrated that mesa structures possess better electrical crosstalk characteristics compared with the planar designs. Significantly, the crosstalk is lower for shorter wavelength radiation while the front-side illumination devices show better electrical crosstalk characteristics than do the back-side illuminated devices. It is ascribed to the influence of material absorption depth and the p-i junction depletion width of such structures. It was also found that the electrical crosstalk appears to be greatly suppressed when the etching depth of the mesa structure covers the entire absorption layer of the device. The results suggest design rules for InGaAs FPA with low electrical crosstalk.

Abstract:The diode microbolometer uncooled IRFPAs (infrared focal plane arrays, IRFPAs) have shown broad prospects in recent years. The performance of the IRFPAs is limited by sources of noise from the detector itself which must be further studied and decreased to achieve better performance. This paper outlines sources of noise from the detector, quantifies the RMS (root-mean-square, RMS) noise voltages from different noise sources, discusses their implications and finally obtains performance limits of the diode microbolometer IRFPA. Moreover, the optimum structural parameters are also studied. The theoretical computation results show that the temperature fluctuation noise-limited NETD (noise-equivalent temperature difference, NETD) of the detector is 2.36mK with a corresponding radiation-limited conductance of 2.06 nW/K. In addition, the optimum NETD of 46.5 mK can be obtained when the detector operates in the forward bias current of 33 μA and the ratio of temperature sensing area is 54% in a 25 μm×25 μm micromachined structure.

Abstract:Free-standing infrared detector with an Al/P(VDF-TrFE)/NiCr structure was fabricated. A semitransparent NiCr metal thin film on top of the device served as both electrode and absorption layer. The experimental results reveal that P(VDF-TrFE) has good ferroelectric and pyroelectric properties with remanent polarization 7.1 μC/cm2 and pyroelectric coefficient 27 μC/m2K respectively. The voltage responsivity RV and detectivity D* of the device at 10 Hz with blackbody source temperature at 500 K are around 1 500 V/W and 5×107 cmHz1/2W-1, respectively. The thermal conductance of unit area to the environment and absorption of the detector were estimated to be 2.5×10-3 W/cm2K and 0.1, respectively, from the frequency dependence of the voltage responsivity. Using the detector, the thermal image of target was obtained.

Abstract:The influence of Ti dopant in the titanium-doped Ge2Sb2Te5 film upon its optical and structural characteristics has been investigated by spectroscopic ellipsometry and x-ray diffraction. Temperature-dependent resistance tests have further revealed that Ti-doped Ge2Sb2Te5 films have better thermal stability than undoped one. Based on the Arrhenius extrapolation results from data retention tests, the endurance temperature corresponding to 10-year data retention of a Ti-doped Ge2Sb2Te5 cell is higher than that of a common Ge2Sb2Te5 cell without dopant. All these experimental results have confirmed that the Ti-doped Ge2Sb2Te5 films are more suitable for the application in phase-change random access memory.

Abstract:The thickness and dielectric constants of thin films usually have certain correlation in the fitting procedure of spectroscopic ellipsometry (SE). The choice of different dispersion models may also influence the results and cause errors. As the fitting is influenced by the dispersion models adopted in the analysis, the uniqueness test has been introduced into SE fitting. The results of uniqueness test have been compared with different dispersion models, different film thicknesses, different wavelength ranges and different incident angles using titanium dioxide samples as an example. It is indicated that uniqueness test is efficient in evaluating the fitting for SE measurement. Uniqueness test can also provide quantitative comparison among different dispersion models and contribute to fitting precision.

Abstract:In this paper, a single-stage W-band low noise amplifier (LNA) monolithic millimeter-wave integrated circuit (MMIC) has been designed and fabricated using our own InP-based high electron mobility transistor technology. The LNA MMIC is developed in Cascode topology and coplanar waveguide technology, which result in a very compact chip with size of 900 μm × 975 μm and a rather high linear gain over 10 dB from 84 GHz to 100 GHz with the maximum value of 15.2 dB at 95 GHz. To our knowledge, this single-stage LNA MMIC exhibits the highest gain-per-stage and competitive gain-area ratio among reported W-band LNA MMICs. Additionally, the amplifier also demonstrates a relatively low noise figure of 4.3 dB at 87.5 GHz and a fairly high saturated output power of 8.03 dBm at 88.8 GHz at room temperature. The successful fabrication of LNA MMIC is of great significance on building a W-band signal receiver-front-end system.

Abstract:A gradient-based steering kernel (GradSK) reconstruction strategy for compressed remote sensing is proposed. It aims to solve the artifacts and blurriness caused by the none-strictly sparsity and the noisy Fourier undersamples. Semi-random Fourier measurements are presented for encoding, which can preserve approximating components of images and retain the incoherence by random undersamples in the periphery of K-space. The steering kernel derived from multistep gradients is exploited to encapsulate with finite-difference Total Variance (TV) in the unconstrained convex framework for decoding. Numerical results demonstrate the superior performance of this algorithm in the case of noiseless and noisy measurements for compressed remote sensing.

Abstract:A high performance PIN diode single-pole-single-throw (SPST) switch for W-band application using a low cost approach was developed. By utilizing flip-chip PIN diodes mounted onto a separately fabricated passive circuit having a quartz substrate, a W-band quasi-monolithic millimeter-wave integrated circuit (Q-MMIC) switch was achieved. A 3-D PIN diode model and a compensation structure were adopted to acquire a low loss and high isolation switch. The measurement results show the minimum insertion loss is about 0.5 dB at 88 GHz and less than 2 dB over the frequency range of 80 to 101 GHz. The isolation is greater than 30 dB from 84 to 105 GHz. The total size of the switch is 1.5 mm× 3.0 mm.quasi-monolithic millimeter-wave integrated circuit（Q-MMIC）,

Abstract:We report a stable, high-power, continuous-wave (cw) optical parametric oscillator (OPO) pumped at 1064nm by a commercial Nd:YVO4 solid-state laser. The oscillator is singly resonant, based on an angle-polished MgO-doped periodically poled LiNbO3 (MgO:PPLN) in a four-mirror ring cavity. Maximum output idler up to 2.15 W is achieved at 3069.1 nm with 9.8 W of pump power, corresponding to a pump-to-idler conversion efficiency of 21.9%. The device exhibits excellent power stability better than 0.19% rms over 30 minutes, which is related to the reduced intracavity residual reflections and thermal self-locking effect.

Abstract:This paper investigated the magnetotransport properties of the two-dimensional electron system in an asymmetrical In0.53Ga0.47As/In0.52Al0.48As quantum well, in which the expected beatings in the Shubinikov-de Haas oscillations of the longitudinal magnetoresistance Rxx were not observed. Zero-field spin splitting was extracted by measuring the weak anti-localization effect and the high field effective g-factor, g*, was extracted by fitting the tilt angle θ-dependent spacing of spin-splitted Rxx peaks. The Dingle plot is shown to be nonlinear, which can be attributed to the long-range scattering potential from the doping Be atoms near the substrate.

Abstract:A stable single-longitudinal-mode dual-wavelength (SLM-DW) multiple ring fiber laser with a tunable wavelength spacing was proposed and demonstrated. In the multiple ring cavities, the mode selection is made by the tunable digital micro-mirror device (DMD) filter and two different length passive sub-ring cavities. The DMD filter can select and couple any two wavelengths from the gain spectrum of the erbium-doped fiber (EDF). The SLM lasing is guaranteed by the two sub-ring cavities which serve as a mode filter. The stable and uniform dual-wavelength oscillation is obtained by the highly-nonlinear photonic crystal fiber (HN-PCF), which can generate the four-wave-mixing (FWM) effective. By loading different gratings on the DMD filter without any mechanically shift, the tunable wavelength spacing from appropriately 0.165 nm to 1.08 nm within a tuning accuracy of 0.055 nm is achieved at room temperature.

Abstract:A high aperture efficiency W-band Cassegrain dual-reflector monopulse antenna is proposed for helicopter collision avoidance radar applications. Aperture field approach method has been investigated to increase the whole performance of the proposed antenna with unequal phase aperture distribution in W-band. The proposed monopulse antenna integrated with the aperture size of 135 mm and focal length of 40.5 mm was fabricated. A sum-difference network based on the E-plane branch line bridge was designed to test the antenna. Measured results show that the gain of the antenna is 38.6 dBi at 93 GHz, corresponding to the aperture efficiency of 54.7%. In addition, it owns the null-depth better than -24 dB and the side-lobe below -18 dB. Measured results are in good agreement with predicted ones. It is demonstrated that the proposed structure is an attentive candidate of high aperture efficiency W-band monopulse antenna.

Abstract:A novel broadband circuit model for millimeter-wave Marchand balun using three-conductor coupled line was proposed. Based on the c-mode and π-mode theory, the three-conductor coupled line was analyzed and modeled by the transmission line and several ideal transformers. The model parameters are extracted from the electromagnetic simulation and then the coupled line model is utilized to build the model of the Marchand balun. Using the proposed model, a millimeter-wave Marchand balun was designed and fabricated in GaAs process. The balun works at the frequency range from 15 GHz to 55 GHz, the measurement results show that the balun has good amplitude and phase imbalance performance and verify the model as well.

Abstract:In this paper, an improved scene-based non-uniformity correction (SBNUC) algorithm called space projection estimator and temporal iteration (SPETI) is proposed. This method estimates the global translation by the projection estimator and iterates between several adjacent frames. The detailed method includes three main steps. First, we develop a new projection estimator for the registration with a criterion. Then, correlation of adjacent frames, together with iteration strategy between them, is used in order to get fast and reliable fixed-pattern noise (FPN) reduction with low few ghosting artifacts. Finally, this algorithm is immigrated into an FPGA-based hardware system. We test the performance of our algorithm by the evaluation indexes, and demonstrate the actual effect of correcting the non-uniformity under a monotonous motion on the system. In order to compare with the gated adaptive least mean square (GALMS) method and the total variation (TV) method, a clean infrared image sequences with synthetic non-uniformity is studied. Normal distributed gain and offset non-uniformity are applied to the image sequences to study the relationship of iteration times and level of non-uniformity.

Abstract:In this paper, we report research results of 256×256 dualcolor midwavelength infrared InAs/GaSb superlattice focal plane arrays. The detector structure is PNNP epitaxial multilayer and the signal is read out by sequential mode. The superlattice structure was grown on GaSb substrate using molecular beam epitaxy (MBE) technology. The respective structure of each absorption region are 7ML (InAs) /7ML (GaSb) and 10ML (InAs) /10ML (GaSb). The pixel center distance of the detector is 30μm. At 77 K measurement, the detector has 50% cutoff wavelength of 4.2 μm and 5.5 μm respectively; The NonP detector has a peak detectivity of 6.0×1010 cmHz1/2W-1 and dead pixels rate of 8.6%; The PonN detector has a peak detectivity of 2.3×109 cmHz1/2W-1 and dead pixels rate of 9.8%. Infrared images of both wavebands have been taken using infrared imaging test by adjusting devices voltage bias.

Abstract:The contact characteristics of Au/ p-InP in hetero-junction InP/InGaAs detector were studied in this work. Under the annealing condition of 480℃ for 30s, the ohmic contact was formed with the room-temperature special contact resistance 3.84×10-4Ω·cm2. Temperature-dependent characteristics of ohmic contact were investigated. The results indicate that the special contact resistance increases with decreasing temperature, the current transmission mechanism at the interface is thermion-field emission mechanism (TFE) at the temperature of 243 K to 353 K; while below 240 K, the contact performance presents schottky property. By means of scanning electron microscope (SEM) and X-ray diffractometer, the diffusion degree and metallurgical reaction at the Au/InP interface were investigated，and the penetration degree is very heavy at the interface of sample after annealed at 480℃for 30s and the generation of Au10In3 produced by metallurgical reaction contributes to improve the contact performance of Au/p-InP.

Abstract:Cu(In, Al)Se2 (CIAS) thin films have been obtained by rapid thermal processing selenization of magnetron sputtering Cu-In-Al precursor thin films. The influence of selenization temperatures on the structural and optical properties of CIAS thin films has been investigated. The result reveals that the crystal structure of CIAS thin films depends on selenization temperature and the band gap energy has a red shift with the increase of selenization temperature. It is noted that the optimum selenization temperature of the CIAS thin films is 540℃, and it has a pure chalcopyrite structure with a band gap energy of 1.34 eV, which corresponding to the band gap energy of the theoretical maximum efficiency of solar cell absorber layer materials.

Abstract:A newly designed terahertz quantum-well photodetector (THz QWP) sandwiched between GaAs and GaAs/Al0.04Ga0.96As material was demonstrated. Experimentally, we measure the response photocurrent spectra and the current-voltage curve and obtain the peak response of 6.78 THz and background-noise-limited performance (BLIP) temperature of 16 K. Theoretically, we investigated the many body effect to the band structure of THz QWP and calculate the peak response of 6.64 THz which is in agreement with the experiment. So, many-body effect must be included in the design of THz QWPs. Then, we calculate the BLIP temperature of 17.5 K which is fitted well with the measurement. However, the low BLIP temperature is the main factor limiting applications of THz QWPs; we propose two schemes to improve the operating temperatures. Firstly, a scheme using an optical antenna to increase the BLIP temperature is proposed. Calculation shows the device is expected to achieve BLIP at 76 K when employing a 106 enhancement antenna. The second scheme is to use a THz quantum cascade laser as signal source to achieve photon-noise-limited performance (PLIP) at high temperatures. Simulations show that when the illumination intensity reaches 0.01 mW/μm2, the operation temperature could be 77 K.

Abstract:To get actual response spectra of quantum type photodetectors from measured photo-current spectra using FTIR method, two feasible and convenient correction schemes of calculated instrument function scheme and standard detector transfer scheme are proposed. The feasibility, limitations and matters need attention are discussed in detail. Based on those schemes, consistent response spectra of various shortwave infrared InGaAs photodetectors have been gained. A comparison have been made to the response spectrum measured using a precisely calibrated grating monochromator system, the validity of the schemes is confirmed.

Abstract:In this paper, based on optical feedback theory and V-shaped cavity-enhanced absorption spectroscopy, combined with quantum cascade laser, a detection system for CO was built up. The optical feedback effect, even and odd modes effect, and threshold current lowering effect were studied. The effective reflectivity of 99.979% and the effective absorption path of 4.48 km in a cavity with physical length of 47 cm were obtained. By adjusting the length of V-shaped cavity automatically, the spectral resolution was improved to 0.001 1 cm-1 from 0.005 3 cm-1. With the best integration time of 53 s obtained by allan variance, this optical system allows detection for the R(6) band of CO with high accuracy of (97.79±0.07)% and the detection limit of (0.49±0.04) ppb at pressure of 40 torr and temperature of 20 °C. The effects of gas pressure on the absorption peak value, detection accuracy and detection limit for CO were also analyzed and demonstrated.

Abstract:Based on in situ data from Chaohu Lake, a novel algorithm was developed to estimate POC concentrations in eutrophic lakes. This two-step algorithm examined changes in absorption aph(665) and associated to POC concentrations though a measured relationship between aph(665) POC determined in extensive measurements in this large eutrophic lake. Two different aph(665) algorithms were explored. While both provided good estimates of POC concentrations, Gons algorithm (RMSErel=2190%) was superior to that of Simis (RMSErel=23.81%). This approach was developed for medium-spectral resolution satellite senors, such as MERIS or Sentinel 3-OLCI. The application of this approach will provide new insights to our understanding of the aquatic carbon cycle in inland waters.

Abstract:An image motion compensation technique based on real-time Line of Sight (LOS) tracking was proposed to solve the serious problem of image motion in the process of frame scanning infrared imaging originating from wingspan pendulum sweep. The compensation accuracy is up to ±0.005° and the compensation effect is no more than 1 pixel for the imaging system with an instantaneous Field of View of 100 μrad. This method enables high-frequency compensation of image motion derived from wingspan pendulum sweep, promoting the development of airborne infrared imaging technology with WFOV and high spatial resolution.