Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
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Abstract:To study the guardring suppression effect on the extension of the photosensitive area in planartype front illuminated InP/InGaAs heterostructure detector，the InGaAs photo detectors with different distances between guardring and PN junction were designed and fabricated. The actual distance between guardring and PN junction of the detector was calculated based on the atomic force microscopy (AFM) and scanning capacitance microscopy (SCM) measurements. The characteristics of the photo response of the detectors with guardring were carried out with laser beam induced current (LBIC) method. It was indicated that LBIC signal of the photo detector without guardring fit well with the exponential decay function, while that of detector with guardring followed the Gaussian distribution. The extension value of the photosensitive area decreased linearly as the distance between the guardring and PN junction decreased. It was concluded that the appropriate gap between the guardring and PN junction should be in the range of 7 to 12 μm.
Abstract:Poly (vinylidene fluoridetrifluoroethylene) (P(VDFTrFE)) thin films were deposited on polyimide substrate using horizontal LangmuirBlodgett(LB) technology. Xray diffractions indicate that the films have good crystallinity with (110) preferential orientation for films with different thickness. The optical dispersion of the films were measured by variableangle spectroscopic ellipsometry. The data Ψ and Δ at multiple incident angels (θ=75° and 85°) were fitted using the Cauchy model. The refractive index, extinction coefficient，absorption coefficient and thickness of each film were obtained. The ferroelectric of the films were studied. The remnant polarization is up to 6.3μC/cm2. The coercive field is 100MV/cm. The dielectric measurement for the film shows two distinctive phase transitions, ferroelectricparaelectric phase transition and β relaxation.
Abstract:An airborne inspection technique of natural gas transport pipeline based on the near infrared wavelength modulation spectroscopy is proposed. The physical principle of this technique was interpreted. The applicability of this technique to the helicopter station was discussed. The field experiments were carried out on a homemade system to validate the engineering feasibility of the technique.
Abstract:The results of 128×128 SW/MW twocolor HgCdTe infrared focal plane arrays (IRFPAs) were presented. By B+implantation, mesaisolation etching, sidewall passivation, sidewall metallization and flipchip hybridization with readout integrated circuit (ROIC),128×128 SW/MW twocolor HgCdTe IRFPAs detector was fabricated from a fourlayer ppPN heterojunction of Hg1-xCdxTe film grown by molecular beam epitaxy and insitu doping techniques. The micromesa fillfactor of (50×50)μm2 twocolor detector arrays was doubled by optimizing the wetchemical etching process. The staring SW/MW twocolor HgCdTe IRFPAs detector performed high uniformity and normal photoelectric properties. At liquid nitrogen temperature, the cutoff wavelengths of the twocolor IRFPAs were 2.7μm and 4.9μm, respectively, and the peak detectivities (D*λp) were 1.42×1011cmHz1/2/W and 2.15×1011cmHz1/2/W respectively.
Abstract:Based on primary parameter analysis of the thermal infrared hyperspectral imaging system, several methods were proposed to overcome the difficulties in detecting objects with low signal energy, serious thermal infrared background radiation and other problems. A pushbrooming infrared hyperspectral imaging system was developed, which can suppress the high background radiation effectively, and the groundbased imaging experiment was realized. Based on the low background experimental results, the relationship of the system performance with different factors was analyzed, and feasibility to optimize the system performance was comfirmed.
Abstract:Thinfilms of lead tellurium selenide were evaporated on silicon substrates from a resource of PbTe0.92Se0.08 bulk crystal grown by Bridgman method. Xray diffraction (XRD), scanning electron microscope (SEM), and energydispersive analysis by Xray (EDAX) were used to characterize the structural and surface morphological properties, as well as chemical compositions of the thinfilms. The results indicate that thinfilms of lead tellurium selenide have a polycrystalline structure and a preferred orientation during the deposition. It was also revealed that the grains appear as rectangles. By comparison of the optical properties of the thinfilms deposited at different substratetemperatures, it was found that substrate temperature has an important effect on the infrared optical properties of thinfilms. The refractive index of the lead tellurium selenide thinfilms lies between 5.2 and 5.8, and the extinction coefficient is lower than 0.1. When the wavelength is greater than 6μm, the extinction coefficient of the thinfilms is as less as 10-3. It can be inferred that lead tellurium selenide is a potential material to be used in the infrared coatings.
Abstract:Based on chemical solutionprocess method, red, green, and blueluminescent CdSe/ZnS semiconductor core/shell quantum dots were successfully prepared by utilizing ethylxanthates as precursors of shell layers. Greenluminescent (542nm) and blueluminescent (483nm) core/shell quantum dots were synthesized by capping the CdSe core quantum dots with ZnS shell layers from zinc ethylxanthate precursors and manipulating reaction temperature with the presence of oxygen. The red color (612nm) CdSe/CdS/ZnS core/multishelled quantum dots were prepared by capping of CdS and ZnS shell layers from cadmium ethylxanthate and zinc ethylxanthate precursors. Results from UVvis absorption spectra, photoluminescence spectra and transmission electron microscopy (TEM) indicated that the emission redshifted if the ZnS capping of CdSe dots is processed at a lower temperature (about 230 ℃ ), while blueshifted at a higher temperature (about 260 ℃ ). Trichromatic white light was obtained via mixing of red, green, and blueluminescent quantum dots.
Abstract:Based on viscoplastic Anand model, von Mises stress distribution of the infrared focal plane array detector is analyzed by finite element method. Simulation results show that as the diameters of the indium bump decreases from 36μm to 18μm in step of 2μm, the maximum stress existing in InSb chip reduces at first, then increases linearly with indium bump diameters. Yet the stress distribution in the indium bump is almost unchangeable and its maximum value keeps at 15.7MPa. Furthermore the maximum stress in SiCMOS readout integrated circuit is smaller than that of InSb chip, and its changing tendency chart is almost the same as that of InSb chip. When the diameter of the indium bump is set to 30μm, the maximum stresses existing in both InSb chip and Si CMOS readout integrated circuit reach the minimal value 260MPa and 140MPa, respectively. Simulations also show that the stress distribution at the contact areas is uniform and concentrated, the stress value in the whole infrared focal plane array detector is smallest, and its distribution is promising.
Abstract:The dependency of the characteristics of 980nm high power verticalcavity surfaceemitting Lasers (VCSELs) on the distributed Bragg reflector (DBR) reflectivity was analyzed theoretically. The output characteristics of the VCSELs with different active region diameters were calculated. The output characteristics at different DBR reflectivities were analyzed. It is found that the variation of DBR reflectivity exerts different influences on the VCSELs with different diameters of active region. The test experiment was carried out in order to validate the theoretical analysis. The experimental results show that the output powers of VCSELs with 500μmdiameter active region under the injected current of 6A are 2.01W and 2.09W when the NDBR reflectivities are 99.7% and 99.2%, respectively. However， the output powers of VCSELs with 200μmdiameter active region under the injected current of 3A are 0.64W and 1.12W when the NDBR reflectivities are 99.7% and 99.2%, respectively. It was concluded that the theoretical results are validated by the experiment effectively.
Abstract:The eight neighborhood algorithm (ENA) was developed for estimating the variance of suspended sediment concentration (SSC) distribution in a pixel based on the current knowledge about the SSC retrieval models' scaling effect. Taking advantage of the results of ENA, further study developed the scaling correcting methods for linear quantitative models, exponential quantitative models and logarithmic quantitative models. Applied these methods to the results of the Landsat/TM imagery and the field spectral experiments in Tai Lake, it was found that the scale effect errors are strongly correlated with the SSC predicting models. The scale effect could result in 16% relative errors for reflectance measurement in complicated Case Ⅱ water bodies such as Tai Lake.
Abstract:Pumping a 30cm length of photonic crystal fiber with a femtosecond Tisapphire laser, the supercontinuum spectrum scource of light in the near infrared region were generated. The wavelength ranges from 465nm to 2500nm, covering a wide band over 2000nm.The mechanism of the supercontinuum origination was studied.
Abstract:To improve the detection range of pyroelectric infrared sensor on the target (the pedestrian) , the passive infrared sensor detection system and IR signal were studied. The pyroelectric infrared sensor signal is affected by the perception parts on the target (pedestrians), temperature difference between the environment and objectives, lens size and sections related to the number. A detection system for testing infrared sensors distance were designed. Experiments showed that after taking into account several factors which affect the detection range, the detecting distance was improved from 10 meters to 40 meters while keeping the signal level of infrared detection unchanged. Test methods and results offer some guidance and reference for other similar detection systems.
Abstract:Metallic wire gratings in terahertz frequency were designed and fabricated by femtosecond micromaching and sputtering technique. The polarized transmission spectra of the gratings were characterized by terahertz (THz) time domain spectroscopy. The theoretical simulations based on FDTD method show a good agreement with experimental results. The physical origin of impacting transmittance in S and P polarization was analyzed. The results obtained from this work provide a useful referrence for the production of THz polarization devices.
Abstract:Vanadium oxide thin films were deposited by dual ion beam sputtering, and then annealled with different procedures of temperature elevating. Optical transmission properties were measured at different temperature by use of Fourier transform infrared spectrum, from which the relationship of transmission and temperature at a fixed wavelength of 5μm was obtained. The results show that the vanadium oxide thin film annealed with rapid elevating temperature has smaller and uniform crystal size, while the film annealed with normal elevating temperature has larger and wider distributed crystal size. All the films after annealing have abrupt change over 60% in transmission in infrared band. The phase transition temperature of vanadium oxide thin film after rapid elevating temperature annealing is 63.74℃, which is higher than that of vanadium oxide thin film after normal elevating temperature annealing, 60.31℃. The temperature range of phase transition of the former is also broader.
Abstract:Because of the nonuniformity and instability of atmosphere, it is very difficult to obtain realtimely and precisely a band of infrared atmospheric extinction coefficient with MODTRAN atmospheric transmission software and any other traditional methods. The nonlinear function relationship between the input and output of neural network can be obtained via the relation among the atmospheric optical properties at different wavelengths in the nearinfrared band by generalized regression neural network. Then the atmospheric optical properties at other wavelengths can be further derived through realtime inversion of the data at certain wavelength measured by laser radar. The method was proved to be effective in obtainning realtimely the nearinfrared atmospheric optical properties of a band in actual combat conditions.
Abstract:Midcourse ballistic target, releasing warhead and large numbers of decoys and forming dense cluster, presents a new challenge for target tracking with spacebased infrared focal plane array ( IRFPA ). The numbers of the identified target vary because of the finite resolution of IRFPA. The target trajectory on IRFPA shows strong nonlinear characteristic. To cope with these problems, a tracking algorithm based on random finite set was proposed. Random finite set is a theoretically unified framework of optimal Bayesian multitarget tracking filter, but the recursion of posterior joint multitarget distribution is not practical in use due to the computational hurdle. Probability Hypothesis Density(PHD) is the first moment of multitarget posterior distribution, and the PHD filter is the suboptimal and practical alternative within the framework of random finite set. Sequential Monte Carlo method was proposed to propagate PHD. The target quantity was estimated by summing up all particle's weight. The kmeans method was adopted to cluster PHD to estimate the target states. Scenario simulation was set up, where the algorithm was tested under the conditions of different handover tracking tasks，false alarm rates and target numbers. Simulation results show that, the algorithm can simultaneously track the numbers and states of the targets among midcourse ballistic target group on spacebased IRFPA.
Abstract:A new implementation method of simplex growing algorithm (SGA) is proposed based on support vector machine (SVM), which is free of dimensional reduction and makes use of distance measure instead of volume one. The unmixing equality of linear SVM and linear spectral mixing modeling (LSMM) is proved. The superiorities of linear SVM based spectral unmixing in two extended applications, combined use of endmember informations and nonlinearity use of the model, are explored. Experiments show that the computational complexity of the SVM based implementation method of SGA is decreased greatly, while the unmixing accuracy is obviously improved.
Abstract:To explore the effectiveness of TemperatureVegetation Angel Index in forecasting crop yield with MODIS, winter wheat yield forecast was taken as an example in Shijiazhuang and Xingtai city, Hebei province of China. Firstly, according to winter wheat biological characteristic, the four parameters of normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), temperaturevegetation angel index (TVA) and enhanced temperaturevegetation angel index (ETVA) were calculated in heading stage. Secondly, the regressive models between groundbased measurements of winter wheat yield and NDVI, EVI, TVA and ETVA data from MODIS were established. It was found that there was significantly linear regressive relationship between yield and NDVI, EVI, TVA and ETVA. The correlation coefficient R2 between yield and NDVI, EVI, TVA and ETVA were 0.61、0.65、0.68 and 0.74, respectively. The models based on TVA and ETVA were better than that based on NDVI and EVI, especially the ETVA. This research shows that TVA/ETVA, which integrated vegetation index and land surface temperature, can be applied in yield forecast with improved forecast accuracy.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335