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- Front Matter: Volume 9522
- Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics 2014, Part II
Front Matter: Volume 9522
Front Matter: Volume 9522
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This PDF file contains the front matter associated with SPIE Proceedings Volume 9522, including the Title Page, Copyright information, Table of Contents, Authors, Introduction (if any), and Conference Committee listing.
Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics 2014, Part II
An extraction method of the tank characteristic quantities in infrared thermal images
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In order to analyze the tank characteristic in infrared thermal image quantitatively, an extraction method of tank characteristic quantities in infrared thermal images by using MATLAB was discussed, and a group of characteristic quantities which identified tank in infrared thermal image were summarized. By calculating and processing infrared thermal image of tank which was created by simulation, the results showed that the characteristic quantities which were extracted using this method can described tank feature in infrared thermal image roundly, and provided the study foundation for target recognition technology development.
Effect of residual gas on cathode photoelectric emission life in generation III L-L-L tube
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In order to solve the sensitivity’s degression in the GaAs NEA photocathode, our crew dissected the Gen. III Low-Light-Level（L-L-L）tube and analyzed the residual gas from the tub e while functionally operating via mass spectrometer. The photoemission-harmful gas like C，CO，CO2 were the principal reason cause the photocathode sensitivity to drop most. Applying the theory of dipole layer, this paper had this thorough discussion over the impact the residual pernicious gas had upon the photocathode. The residual gas on the emission layer enlarged the interface barrier and dwindled the chance of overflow about the same time.There were none photoemission when the single molecule gas were all over the emission layer, and so the life-span has came to an end as well. Our crew bring forward “carbon-contamination precaution measure” on account of lo wering potential barrier, which resolve problems like unstable photocathode sensitivity and limited life-span.
Design of an infrared four-mirror optical system with large relative aperture
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Reflective optics is used widely in optical systems for their achromatization, large aperture and lightweight compared with refractive systems. An infrared four-mirror optical system with large relative aperture working in the 7.7～10.3 micron long wavelength infrared band is designed by using four reflective mirrors. The design principle, design results are described in this paper. The system has a circinal wide field of view with 1.5°×1.5°. The MTF of the system is diffraction-limited and the distortion is less than 1.0%. The ratio of focal length to total length is about 1/1.04,so the structure of the system is compact. The image quality is evaluated for each field, which shows that the design makes a good system with high image quality.
Simulation of surface deformation for the lithographic object lens by Zernike polynomials
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Surface deformation is the crucial factor for the imaging performance of the lithographic object lens in the manufacturing process. Simulation of surface deformation can predict the degradation of the wavefront error caused by surface deformation, find the lens which is most sensitive to the surface deformation even in the design phase. We develop a method to simulate the surface deformation by Zernike polynomials in this paper. In fact, the surface deformation generated in the manufacturing process is random. However, it does not mean that they have no rules at all. We analysize the Zernike coefficients distribution of the interferential data, and build a model to simulate the surface deformation. The model can generate random-surface-deformation according to the input RMS/PV bound in the form of INT file type, which can be added to the lens surface directly in the optical design program CODEV. The results show that the surface deformation generated by our model can simulate the interferential data very well.
Geometric correction method of rotary scanning hyperspectral image in agriculture application
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In order to meet the demand of farmland plot experiments hyperspectral images acquisition, an equipment that incorporating an aerial lift vehicle with hyperspectral imager was proposed. In this manner, high spatial resolution (in millimeter) imageries were collected, which meets the need of spatial resolution on farm experiments, but also improves the efficiency of image acquisition. In allusion to the image circular geometric distortion which produced by telescopic arm rotation, an image rectification method that based on mounted position and orientation system was proposed. Experimental results shows that the image rectification method is effective.
High precision digital control LED spot light source used to calibrate camera
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This paper introduces a method of using LED point light source as the camera calibration light. According to the characteristics of the LED point light source, the constant current source is used to provide the necessary current and the illuminometer is used to measure the luminance of the LED point light source. The constant current source is controlled by ARM MCU and exchange data with the host computer though the mode of serial communications. The PC is used as the host computer, it adjust the current according to the luminance of the LED point light source until the luminance achieve the anticipated value. By experimental analysis, we found that the LED point light source can achieve the desired requirements as the calibration light source, and the accuracy is quite better that achieve the desired effect and it can adaptive control the luminance of LED well. The system is convenient and flexible, and its performance is stable and reliable.
Effect of random phase errors on coherent beam combining based on liquid crystal phased array
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The effect of random phase errors on coherent beam combining based on liquid crystal phased array is studied. Utilizing the Fraunhofer propagation principle and probability theory, the analytical expressions of the far-field intensity distribution functions of the output beam are derived. According to these expressions, it can be concluded that as the phase errors increase, the peak intensity of the combined beam in the far-field decreases, the main lobe width widens and the error of deflection angle becomes greater. Considering the influence of random phase errors on the three parameters, a threshold of phase control precision can be designated. When the phase errors are less than the threshold, the performance degradation of the CBC system caused by the phase errors can be accepted. The computer simulations illustrate that the conclusions obtained from analytical expressions are reasonable. In the simulation parameters, the threshold of the phase control precision is λ / 20. The results in this paper can be employed to research methods to reduce the adverse effects of random phase errors and can also be used to determine the phase control precision when using phase-locking algorithms to lock the phase of the beams to be combined in the CBC system.
A fiber DBR laser based vector hydrophone for ultrasonic medical applications
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An ultrasonic hydrophone based on a dual polarization distributed Bragg reflector (DBR) fiber laser is described, and its application to detecting the vector medical ultrasound is demonstrated. The principle of the hydrophone is based on the detection of output beat frequency signal modulated by ultrasound. The amplitude, frequency and orientation of the ultrasound can be determined by the using the upper and lower sideband frequency. It has been found that the hydrophone has an orientation recognizable ability which the piezoelectric ultrasonic immersion transducer doesn’t have. It suggests that the type of hydrophone can provide an alternative to piezoelectric hydrophone technology.
Concept and realization of measuring spatial structure of atmospheric optical turbulence by the fiber optical turbulence sensor array
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In this article, a high quality fiber optical turbulence sensing array contains several sensors is proposed to obtain time series of air refractive index fluctuations. A fixed sensor is supposed to be set as the origin and others to be arranged in Cartesian coordinates respectively. Under the spatial configurations above, two-point correlation algorithm is used to give two order structure parameters and multipoint correlation algorithm for more structure information about scalar turbulence. For each direction, two-point spatial correlation coefficients varying with distance are provided. Meanwhile spatial power spectrum and outer-scales according to the data are introduced. Multipoint correlations can give more structure information such as the interactions between scales and the spatial structure of relevant fluctuations. In the one-dimension circumstance for instance the x-axis, spatial correlation coefficient tends to take oscillation. After a short-time averaging, it tends to decrease with the increase of spatial displacement, and then tends to zero after outer scale. Further study show that within the limit of outer scale, diurnal variation of the spatial correlation coefficient and intensity reveal a higher similarity, the relevancy is about 60% and keeps stable; once the distance goes across the outer scale, they are uncorrelated. In short, utilizing the fiber optical turbulence sensing array is a new method for measuring spatial correlation of optical turbulence. It can overcome some problems from single-point measurement, especially when using Taylor’s frozen-turbulence hypothesis. Some structural information of optical turbulence not only makes the theory of scalar field more abundant, but also in favor of some problems about optical propagation.
Integrated multi-channel receiver for a pulsed time-of-flight laser radar
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An integrated multi-channel receiver for a pulsed time-of-flight (TOF) laser rangefinder has been designed in this paper. The receiver chip as an important component of the laser radar device has been implemented in a 0.18um CMOS process. It consists of sixteen channels and every channel includes preamplifier, amplifier stages, high-pass filter and a timing discriminator which contains a timing comparator and a noise comparator. Each signal paths is independent of other channels. Based on the simulations, the bandwidth and transimpedance of the amplifier channel are 652MHz, 99dBΩ. Under the simulation condition of TT corner and 27℃, the propagation delay of the discriminator is 2.15ns and the propagation delay dispersion is 223ps. The power consumption during continuous measurement is 810mW, and the operating temperature range of the device is -10~60℃.
Test and analysis of the infrared characteristic of the plume-smoke
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The plume-smoke is one of the main infrared characteristic signal sources of the engine. In this paper, the infrared signal characteristic of a small test engine’s plume-smoke is studied. We conduct a quantitative observation of some specific points in the movement path of the plume-smoke by the MW and LW infrared thermal imager. Through the analysis of the smokeless and smoke infrared sequential images, we can get the infrared radiation and the transmission characteristics of the plume-smoke and their variation law with time. Experiments show that there exists a critical temperature of the plume-smoke; the radiation of background can increase when the temperature of the plume-smoke is higher than the critical temperature. On the contrary, the radiation of background decreases when the temperature of the plume-smoke is lower than the critical temperature. In this paper, the research provides a reference for further study on the infrared characteristic of the plume-smoke.
Directional force measurement technology based on fiber optical laser heterodyning demodulation
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Distributed Bragg Reflector (DBR) polarimetric optical fiber laser sensors have been attracting great interests due to harsh environment capability and high signal-to-noise ratio .We demonstrate directional force measurement technology using dual-polarization DBR optical fiber laser as a sensor. The influences of external force (bending, current and ultrasonic signal) could be analyzed by inducing a DFB polarimetric laser sensor to detect the beating signals shifts when the cavity is perturbed. We present the analysis of sensing mechanism on the DBR geometric construction and demodulation of directional information by separating the dual orthogonal polarization modes. With loading angles at 35°, 45°, 55°with 10° interval, the DBR laser sensor has shown orientation recognization ability corresponding to beating signals shifts, offering a potential for vector force directional detection.
The signal detection technology of photoconductive detector with lock-in amplifier
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The noise of photoconductive detector is so weak that the PAR 124A lock-amplifier is main test facility despite of discontinuation by long-gone manufacturer for decades. The paper uses 124A and 7124 lock-in amplifier system to test noise and response signal of several photoconductive detectors while use the SR830 internal oscillator and thermal noise of pure resistance as standard signal and noise source respectively. The results indicate that the data of two test system can fit each other except the background noise. The 124A lock-in amplifier with 116 transformer is 0.2nV/√Hz and 7124 lock-in amplifier with 5184 preamplifier is 0.8 nV/√Hz at 1kHz. The impedance of 116 transformer is small and the impedance of 5184 preamplifier is 5MΩ, so the signal of 116 transformer will decay and the 5184 preamplifier won’t in case of testing the performance of photoconductive detector with larger source resistance. Finally we suggest to use 7124 lock-in amplifier system in case of testing photoconductive detector with larger source resistance and use 124A lock-in amplifier system prior to 7124 lock-in amplifier system in case of testing photoconductive detector with small source resistance.
Research on mechanical vibration impacts of GaAs photocathode photoemission performance
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The GaAs photocathode has widely been used in optoelectronic devices such as image intensifiers, photomultiplier tubes, but these devices is inevitable to withstand a variety of mechanical vibration. In order to study the mechanical vibration impact on the photoemission performance of GaAs photocathode, GaAs photocathode image intensifier is researched in this paper. The spectral response of the GaAs photocathode before and after 5~55Hz scan frequency, 14Hz, 33Hz, 52Hz stay frequency, 5～60Hz scan frequency mechanical vibration respectively was tested, then the parameter of photocathode was calculated by MATLAB software according to quantum efficiency formula, the quantum efficiency curve were fitted. The results show that surface escape probability is increased after photocathode is subjected to mechanical vibration, so that its photoemission performance will be improved. We think this phenomenon is due to the GaAs photocathode surface Cs-O reconstruction. This finding provided a new method to enhance the photoemission performance of photocathode.
Activation processes on GaAs photocathode by different currents of oxygen source
Zhuang Miao,
Feng Shi,
Hongchang Cheng,
et al.
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In order to know the influence of activation processes on GaAs photocathodes, three GaAs samples were activated by a fixed current of cesium source and different currents of oxygen source. The current of caesium source is same during activation to ensure initial adsorption of caesium quantum is similar, which is the base to show the difference during alternation activation of caesium and oxygen. Analysed with the activation data, it is indicated that Cs-to-O current ratio of 1.07 is the optimum ratio to obtain higher sensitivity and better stability. According to double dipole model, stable and uniform double dipole layers of GaAs-O-Cs:Cs-O-Cs are formed and negative electron affinity is achieved on GaAs surface by activation with cesium and oxygen. The analytical result is just coincident with the model. Thus there is an efficient technological method to improve sensitivity and stability of GaAs photocathode.
The influences of vacuum pressure and gas components on the stability of GaAs photocathode
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The photocurrent attenuation of GaAs photocathode within one hour after activation under three different vacuum pressure (5×10-9Pa, 5×10-8Pa, 5×10-7Pa) were recorded by automatically activated monitor. The results show that: the photocurrent quickly descend in the beginning and then descend linearly at a low slope; the amplitude of the quickly descending area were 10%, 14.74% and 36%separately, with the respective slope of the linear descending area were -0.00653, -0.01132and -0.02. Three samples’ gas components of H2, CH4, CO, H2O, O2, CO2 etc under the same vacuum pressure (5×10-8Pa)during photocurrent attenuation were collected by quadrupole mass spectrometer. By comparing the gas components content and the attenuation law of the photocurrent, it has been found that H2O and H2 had a greater impact on the stability of GaAs photocathode in the ultra-high vacuum environment and H2O was the predominant effect. This paper has important guiding significance and reference value in studying the stability of GaAs photocathode and the improvement of semiconductor photocathode process.
Investigation on choosing technical parameters for pulse thermography
Huijuan Li
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Composite material connected by glue has gained popularity as a replacement for conventional materials and structures to reduce weight and improve strength in the aerospace industry, with the development of material science and structural mechanics. However, the adhesive bonding process is more susceptible to quality variations during manufacturing than traditional joining methods. The integrality, strength and rigidity of product would be broken by disbonding. Infrared thermography is one of several non-destructive testing techniques which can be used for defect detection in aircraft materials. Pulsed infrared thermography has been widely used in aerospace and mechanical manufacture industry because it can offer noncontact, quickly and visual examinations of disbonding defects. However the parameter choosing method is difficult to decide. Investigate the choosing technical parameters for pulse thermograpghy is more important to ensure the product quality and testing efficiency. In this paper, two kinds of defects which are of various size, shape and location below the test surface are planted in the honeycomb structure, they are all tested by pulsed thermography. This paper presents a study of single factor experimental research on damage sample in simulation was carried out. The impact of the power of light source, detection distance, and the wave band of thermography camera on detecting effect is studied. The select principle of technique is made, the principle supplied basis for selection of detecting parameters in real part testing.
A novel approach to improve digital signal performance by placement and routing with manual intervention
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This paper describes how placement and routing with manual intervention to improve the digital signal performance. According to studying and analyzing the features of Field Programmable Gate Array (FPGA) devices which include chip architecture and timing characteristics, a new approach is presented that some key logic modules can be relocated reasonably with manual intervention after completing successful place-and-route automatically. An example is given to illustrate this method. In this example, in order to improve remote sensing Charge Coupled Device (CCD) camera performance, signal-skew and delays among CCD driving timing signals must be controlled accurately and easily. This method can make CCD driving timing signals obtain the zero-skew which means tCO (clock to out) values for all these signals are equal, and finally hardware tests are carried out and experiment results are measured precisely by oscilloscope.
Investigation on the interface of polysilicon/oxide in CCD image sensors
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The morphology of interface between polysilicon and its thermal oxide is very important for the fabrication of charge-coupled device (CCD) image sensors. Poor quality of polysilicon/oxide interface may lead to leakage current, low charge transfer efficiency, image deficiency, and then reduce the product yield and device reliability. In this paper, the effects polysilicon/oxide interface morphylogy on thermal oxide breakdown characteristics of polysilicon grown by low-pressure chemical vapor deposition (LPCVD) are studied by means of scanning electron microscopy (SEM) and electrical measurement. The breakdown characteristics of the oxide are related to the polysilicon/oxide interface smoothness. As the smoothness of polysilicon/oxide interface becomes worse, the breakdown strength of thermal oxide of the polysilicon decreases. Doping process of polysilicon remarkably affects the smoothness of polysilicon/oxide interface and the breakdown strength of the oxide. Saturated doping of polysilicon improves the polysilicon/oxide interface smoothness, so the breakdown strength of polysilicon may increase.
Study on the repetition rate locking system of the femtosecond laser
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The new technique known as “The femtosecond frequency comb technology” has dramatic impact on the diverse fields of precision measurement and nonlinear optical physics. In order to acquire high-precision and high-stability femtosecond comb, it’s necessary to stabilize the repetition rate fRep and the offset frequency f0. This article presents the details of stabilizing and controlling the comb parameter fRep and finally phase lock the repetition rate of femtosecond laser to a radio frequency reference, derived from an atomic clock. In practice, the narrower the bandwidth of lock system (close-loop system), the higher stability we can achieve, but it becomes easier to be unlocked for external disturb. We adopt a method in servo unit to avoid this problem in this paper. The control parameters P and I can be adjusted and optimized more flexibly. The lock steps depend on the special servo system make it easier to find the right parameters and the lock becomes more convenient and quickly. With this idea, the locked time of repetition rate can be as long as the mode-locking time of the laser. The stability of laser can be evaluated by allan deviation. In this research, the contrast of stability of fRep between the locked laser and the unlocked is given. The new lock system is proved reasonable.
High speed global shutter image sensors for professional applications
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Global shutter imagers expand the use to miscellaneous applications, such as machine vision, 3D imaging, medical imaging, space etc. to eliminate motion artifacts in rolling shutter imagers. A low noise global shutter pixel requires more than one non-light sensitive memory to reduce the read noise. But larger memory area reduces the fill-factor of the pixels. Modern micro-lenses technology can compensate this fill-factor loss. Backside illumination (BSI) is another popular technique to improve the pixel fill-factor. But some pixel architecture may not reach sufficient shutter efficiency with backside illumination. Non-light sensitive memory elements make the fabrication with BSI possible. Machine vision like fast inspection system, medical imaging like 3D medical or scientific applications always ask for high frame rate global shutter image sensors. Thanks to the CMOS technology, fast Analog-to-digital converters (ADCs) can be integrated on chip. Dual correlated double sampling (CDS) on chip ADC with high interface digital data rate reduces the read noise and makes more on-chip operation control. As a result, a global shutter imager with digital interface is a very popular solution for applications with high performance and high frame rate requirements. In this paper we will review the global shutter architectures developed in CMOSIS, discuss their optimization process and compare their performances after fabrication.
A vehicle photoelectric detection system based on guidance of machine vision
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A vehicle photoelectric detection system based on guidance of machine vision is described in detail, which is composed of electric-optic turret, distributed perception module, position orientation system and data process terminal, etc. Simultaneously, a target detection method used in the system based on visual guide is also discussed in this paper. This method, based on the initial alignment of camera position and the precise alignment of target location, realizes the target acquisition and measurement by using the high-definition cameras of distributed perception module installed around the vehicle as the human eyes to guide the line of sight of optoelectronic devices on the turret to the field of view of one camera quickly and carry on small-scale target alignment operations. Simulation results show that the method could achieve the intelligent dynamic guide of photoelectric detection system, and improve the detection efficiency and accuracy.
Study of a sensor based on the series of micro-rings with dual coupling points
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A novel type of humidity sensor based on the series of micro-rings with the same radius is proposed, and the humidity is measured by detecting the spectrum drift. Experimental results show the sensitivity can achieve about 16pm/10%RH and the sensing range of the humidity sensor is 10~60%RH. The proposed structure will provide an effective way for integrated humidity sensors with simple structure, high sensitivity and low cost.
Dual-band infrared optical imaging system design by wavefront coding
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The revolution in dual-band infrared focal plane arrays over the past ten years has induced a significant impact on dual-band imaging system design. There are numerous challenges facing dual-band imaging system design using traditional methods. In this paper, Wavefront Coding technique is used to offer the potential implementation of infrared dual-band achromatic and diffraction-limited imaging by using simple optics. An example in terms of a one-element dual-band infrared imager is given.
Evaluation of thermo-radiation characteristics of IR windows in hypersonic vehicles
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When hypersonic vehicles have high-hypersonic flights in the atmosphere, high-temperature IR windows become the main factor of complicated aero-thermo-radiation effects, which would reduce the performance of IR detection systems, or even make these systems fail. By analyzing thermal radiation transfer in IR windows, an experimental platform is established to measure thermo-radiation characteristics of IR window materials. And a method is proposed to evaluate thermo-radiation characteristics of IR windows with uneven temperature distribution. Take a MWIR detection system of a hypersonic vehicle as an example, thermo-radiation characteristics of a sapphire IR window is evaluated. The results indicate that, thermo-radiation characteristics of the sapphire IR window material in 3.7μm-4.8μm have an approximate cubic relationship with temperature at 100°C~350°C. With the rise of temperature, the transmittance of the sapphire material decrease, while the window self-radiation increase. As the sapphire IR window is exposed in high-temperature and high-speed airflow, the transmittance drops 4%, still bigger than 95%, self-radiation enhance about 9 times, while temperature of the window rises rapidly. Self-radiation can drive detector into saturation easily, of which the influence on the MWIR detection system is bigger than that of transmittance.
Rotational analysis of birefringent crystal particles based on modified theory in optical tweezers
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In order to achieve high-precision, controllable rotation of uniaxial birefringent crystal particles, we study the principle of optical rotation due to the transfer of spin angular momentum from light to birefringent crystal particles. The interaction process between the beam and particles is affected by various factors existed actually, for instance: the reflection of beam on the crystal surface, laser power, the set of angle between the crystal optical axis and surface, radius, phase difference between the ordinary ray and extraordinary ray. According to the analysis of these factors, the theoretical model of optical rotation is reconstructed. The theoretical curves of calcium carbonate and silicon particles chosen as experimental material between the rotational frequency and the radius are simulated and calculated. The result shows that the rotation frequency is inversely proportional to the cube of radius, and compared the performance of modified model with traditional model. The birefringent particles are rotated by optical tweezers in the experiment, and rotation frequency is measured with the same laser power. According to the experimental results of optical rotation, the modified Friese theoretical model is proved to be the reasonably and excellence, in addition, the result shows the maximum frequency of calcium carbonate is 19.1Hz, and the maximum frequency of silicon particles is 11.5Hz. The rationality of our experiment is testified by compared with theoretical analysis. Our study has great directive significance to the design of optical driven micro-mechanical motor and the material selection of rotor.
Automatic bias control system of high speed electro-optic modulator in DPSK Systems
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In DPSK communication system, the traditional way for bias voltage is loading a fixed bias voltage on the electro-optic modulator. For the influence of the temperature changes, the half-wave voltage of the electro-optic modulator may change and the DC bias supply voltage will have a certain degree of random fluctuations at the meantime which will cause the DC bias point of the modulator drift and consequently the communication systems are affected. To enhance the stability of the DPSK optical communication system and control the bias of Mach-Zehnder electro-optic modulators automatically, a PID control method has been proposed in this paper. After the actual operation, a DPSK signal transmission with transfer rate of 5Gb/s is built. Using the complex spectrum analyzer, stable signal and the constellation can be received. The automatic control system basically meets the needs of the DPSK transmission system of high stability, high accuracy and capacity of resisting disturbance.
Enhanced memory architecture for massively parallel vision chip
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Local memory architecture plays an important role in high performance massively parallel vision chip. In this paper, we propose an enhanced memory architecture with compact circuit area designed in a full-custom flow. The memory consists of separate master-stage static latches and shared slave-stage dynamic latches. We use split transmission transistors on the input data path to enhance tolerance for charge sharing and to achieve random read/write capabilities. The memory is designed in a 0.18 μm CMOS process. The area overhead of the memory achieves 16.6 μm2/bit. Simulation results show that the maximum operating frequency reaches 410 MHz and the corresponding peak dynamic power consumption for a 64-bit memory unit is 190 μW under 1.8 V supply voltage.
Noise analysis for high speed CMOS image sensor
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Noise performance of the high speed image sensor is a bottle neck for its low illumination applications. As the foremost stage circuit, pixel noise is an important portion of high speed image sensor system. This paper has discussed and analyzed the different noise source of the 4T pixel and influence on the image quality of high speed image sensor in detail. We proposed circuit model of pixel with ideal correlated double sampler to simulate the noise source distribution in the pixel and noise reducing methods. Pixel random readout noise can be effectively reduced to 5.44e by optimizing the gate size of the reset transistor.
A detection method of infrared dim small target under complex cloud background
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Based on the analysis of the characteristics of infrared dim small target under complex cloud background, A detection algorithm is proposed for infrared dim small target. Firstly, median filtering algorithm is employed to remove the noise effectively. Secondly, according to the characteristics of the cloud background and targets, a frequency-domain processing method based on Fourier transform and second-order Butterworth high pass filtering is proposed. The cutoff frequency of the filter is adaptively decided by establishing the relationship between the background complexity and the cutoff frequency. Lastly, target detection is achieved by threshold segmentation. Experiments showed that the algorithm can effectively detect infrared dim small target under complex cloud background.
Recent development of infrared tunable filter
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Researchers are engaging on tunable infrared (IR) filters, miniature Fabry-Perot optical devices, to operate IR detector like a spectrometer. This kind of devices was used in astronomical detection field in the 1950s. To meet the miniature, lightweight requirements of the optical detection system, researchers began to make small, lightweight, and cheap tunable IR filters. Nowadays researchers have applied a variety of different structures and the IR filter, and are attempting to integrate them with IR detectors directly. Tunable filter thin film mechanical and thermal properties, and working conditions will affect the tunable filter optical performance. In this article we give two main influencing factors, interface roughness and curvature effect. we also present and discuss the current development of FPF in different groups around the world.
The quantitative detection analysis to infrared polarization characteristics of targets
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We made quantitative detection analysis to infrared polarization characteristics of target using a non-real time infrared polarization detection system. First, the detection system must be calibrated, so according to our detection system, we presented a calibration method of doing radiometric calibration in four polarization detection channels. Second, based on the analysis of the infrared polarized mechanism, we made some theoretical simulation models. The target infrared radiation include spontaneous radiation and reflected radiation, and the combination of them lead to depolarization effect. The energy distribution between spontaneous and reflected radiation of the target is affected by target temperature, light conditions etc. So we created a experimental environment of low temperature and reflected radiation to validate theoretical model of spontaneous radiation, and found the experimental data has good consistency with theoretical prediction in a certain error range.
Study on the premixed laminar flames of iso-octane
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Propagation characteristics of premixed laminar iso-octane flames at atmosphere and equivalence ratios from 0.8 to 1.4 are studied in a constant combustion bomb using a schlieren technique, the laminar burning velocity at different initial pressure, temperature, equivalence ratio are calculated through CHEMKIN program. The experimental and calculation results show that the laminar burning velocity of iso-octane rise with the decreasing of initial pressure and rise with the rising of initial temperature . Only changing the initial temperature or pressure ,the maximum laminar burning velocity of iso-octane were both obtained at equivalence ratio 1.1. Flame stability become weak ,when increased the equivalence ratio. The problem of the chemistry reaction mechanism to predict the laminar burning velocity were analysed.
A new 9T global shutter pixel with CDS technique
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Benefiting from motion blur free, Global shutter pixel is very widely used in the design of CMOS image sensors for high speed applications such as motion vision, scientifically inspection, etc. In global shutter sensors, all pixel signal information needs to be stored in the pixel first and then waiting for readout. For higher frame rate, we need very fast operation of the pixel array. There are basically two ways for the in pixel signal storage, one is in charge domain, such as the one shown in [1], this needs complicated process during the pixel fabrication. The other one is in voltage domain, one example is the one in [2], this pixel is based on the 4T PPD technology and normally the driving of the high capacitive transfer gate limits the speed of the array operation. In this paper we report a new 9T global shutter pixel based on 3-T partially pinned photodiode (PPPD) technology. It incorporates three in-pixel storage capacitors allowing for correlated double sampling (CDS) and pipeline operation of the array (pixel exposure during the readout of the array). Only two control pulses are needed for all the pixels at the end of exposure which allows high speed exposure control.
Modeling and characteristic of the SMT Board Plug connector in high speed optical communication system
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Modeling and characteristic of the SMT Board Plug connector, which is used to connect micro optical transceiver to the main board, are proposed and analyzed in this paper. When the high speed signal transfers from the PCB of transceiver to main board through SMT Board Plug connector, the structure and material discontinuity of the connector causes insertion losses and impedance mismatches. This makes the performance of high speed digital system exacerbated. So it is essential to analyze the signal transfer characteristics of the connector and find out what factors affected the signal quality at the design stage of the digital system. To solve this problem, Ansoft's High Frequency Structure Simulator (HFSS), based on the finite element method, was employed to build accurate 3D models, analyze the effects of various structure parameters, and obtain the full-wave characteristics of the SMT Board Plug connectors in this paper. Then an equivalent circuit model was developed. The circuit parameters were extracted precisely in the frequency range of interests by using the curve fitting method in ADS software, and the result was in good agreement with HFSS simulations up to 8GHz with different structure parameters. At last, the measurement results of S-parameter and eye diagram were given and the S-parameters showed good coincidence between the measurement and HFSS simulation up to 4GHz.
Quenching and temperature dependence of perpendicular magnetic anisotropy of Pt/Co multilayers
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Magnetic metallic multilayers separated by nonmagnetic metal films are of great importance in magnetoelectronics and spintronics, due to their capacity of giving rise to giant magneto-resistance as well as the electric field control of ferromagnetism. Co/Pt multilayers are one of the typical platforms that own perpendicular magnetic anisotropy which can be tuned in various ways. Since previous investigations focus on the anomalous Hall(transverse) resistivity which characterizes the magnetization of the multilayers, much less attention has been paid to the longitudinal resistivity. In this work, we find that the longitudinal resistivity also gives rich phenomena that need further theoretical treatment. We have grown two Co/Pt multilayer structures that have different spacings between neighboring ferromagnetic layers. The one with smaller spacing shows a superparamagnetic behavior in its Hall resistivity even at a temperature as low as 1.5 K, but the longitudinal resistivity shows a well established hysteresis. The other sample shows square hysteresis in the Hall resistivity at all available temperatures up to 300 K, while the longitudinal resistivity gives no significant signals because they are mostly engulfed in the noises. The corresponding temperature dependence of the coercive field are also different. While the former gives an approximately exponential function of the temperature T, the latter can be divided to two zones, each of which can be characterized by a lnTs dependence, where s is not necessarily an integer. Such distinct features may be deeply related to the microstructures as well as the magnon scattering, which require further investigations.
Study on application of adaptive fuzzy control and neural network in the automatic leveling system
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This paper discusses the adaptive fuzzy control and neural network BP algorithm in large flat automatic leveling control system application. The purpose is to develop a measurement system with a flat quick leveling, Make the installation on the leveling system of measurement with tablet, to be able to achieve a level in precision measurement work quickly, improve the efficiency of the precision measurement. This paper focuses on the automatic leveling system analysis based on fuzzy controller, Use of the method of combining fuzzy controller and BP neural network, using BP algorithm improve the experience rules .Construct an adaptive fuzzy control system. Meanwhile the learning rate of the BP algorithm has also been run-rate adjusted to accelerate convergence. The simulation results show that the proposed control method can effectively improve the leveling precision of automatic leveling system and shorten the time of leveling.
An enhanced moment matching method to destriping EO-1/Hyperion data
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The striping noise can obscure the true radiation information in the images, reduce the accuracy of hyperspectral images, and have serious effect for visual interpretation and further results based on spectral analyses. This paper introduces the principle of moment matching method, emphasizes the analysis of the formative reason for “edge effect”, and then proposes an enhanced method to destripe EO-1/Hyperion data. The method for destriping has been introduced as well in this paper to compare with the moment matching method from both visual effect and quantitative assessment. It shows that the proposed method could achieve the greater effect for destriping EO-1/Hyperion data.
GaN ultraviolet detector based demonstrator board for UV-index monitoring
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Currently, various types of III nitride-based materials have been successfully used for short-wavelength optoelectronic devices. The GaN ultraviolet detector has been wildly used for UV-Index(UVI) monitoring, UV curing and water disinfection. The global solar UVI describes the levels of solar UV radiation at the Earth’s surface. The higher the UVI value, the greater the potential damage to the skin and eyes. The UVI monitoring demonstrator board with GaN detector is briefly introduced in this paper.
Two methods for characterizing the electrical properties of InAsSb film grown by liquid phase epitaxy
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High-quality InAs1-xSbx films with x=0.06 have been successfully grown on InAs (100) substrates by liquid phase epitaxy. Two methods are used to characterize the electrical properties of InAsSb film. One is to grow InAsSb epilayer on p-type InAs substrate, which, in combination with the n-type epilayer, forms a p-n junction to prevent the parallel conduction from the substrate. The other is that both the conductive InAs substrate and the dislocation layer between InAs and InAsSb are removed completely by chemical mechanical polishing method to get InAsSb film glued onto insulating sapphire substrate. The influence of conductive InAs substrate on the electrical properties of InAsSb film is eliminated effectively.
Enhancement dark channel algorithm of color fog image based on the local segmentation
Lijun Yun,
Yin Gao,
Jun-sheng Shi,
et al.
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The classical dark channel theory algorithm has yielded good results in the processing of single fog image, but in some larger contrast regions, it appears image hue, brightness and saturation distortion problems to a certain degree, and also produces halo phenomenon. In the view of the above situation, through a lot of experiments, this paper has found some factors causing the halo phenomenon. The enhancement dark channel algorithm of color fog image based on the local segmentation is proposed. On the basis of the dark channel theory, first of all, the classic dark channel theory of mathematical model is modified, which is mainly to correct the brightness and saturation of image. Then, according to the local adaptive segmentation theory, it process the block of image, and overlap the local image. On the basis of the statistical rules, it obtains each pixel value from the segmentation processing, so as to obtain the local image. At last, using the dark channel theory, it achieves the enhanced fog image. Through the subjective observation and objective evaluation, the algorithm is better than the classic dark channel algorithm in the overall and details.
New bionic navigation algorithm based on the visual navigation mechanism of bees
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Through some research on visual navigation mechanisms of flying insects especially honeybees, a novel navigation algorithm integrating entropy flow with Kalman filter has been introduced in this paper. Concepts of entropy image and entropy flow are also introduced, which can characterize topographic features and measure changes of the image respectively. To characterize texture feature and spatial distribution of an image, a new concept of contrast entropy image has been presented in this paper. Applying the contrast entropy image to the navigation algorithm to test its’ performance of navigation and comparing with simulation results of intensity entropy image, a conclusion that contrast entropy image performs better and more robust in navigation has been made.
System design of Fourier transform imaging spectrometer using tunable lateral shearing splitter
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The Fourier transform spectrometer without slit has the advantages of high radiation throughput and high spatial resolution. It can be used for detecting more details of the spectral and spatial information. We present the initial structure of the collimator and objective based on the analysis of the principle of the Fourier transform spectrometer. Then the collimator and objective are optimized by Zemax. The MTF of the cut-off frequency is great than 0.7. The tunable lateral shearing splitter is used as the interferometer, which makes the system more compact compared with the system using Sagnac lateral shearing splitter. The method to calculate the geometric dimension of the splitter is presented. Then the complete Fourier transform spectrometer is designed. The MTF of the cut-off frequency is great than 0.6. And the largest RMS of the spot is less than 6μm.
Analysis of system parameters for interferometric imaging spectrometer
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The technology of interferometric imaging spectrometer can detect spatial information and spectral information of targets simultaneously. It has been the research hotpot because of its advantages of high throughput, high spectral resolution, high spatial resolution and so on. In order to obtain the spectral images of scene at different distance, a system of interferometric imaging spectrometer is presented, which consists of two imaging lens, a collimating lens, a Sagnac transverse shearing splitter and a detector. Based on the analysis of the optical paths and structure of spectrometer, system parameters of interferometric imaging spectrometer were researched, especially the ones of the transverse shearing splitter, incident plane width, mirror offset, optical parallelism error, and the clear aperture of the imaging lens and collimating lens . Optimal system parameters were given by discussing the relationship of parameters including transverse shearing splitter, detection distance, imaging lens, collimating lens and detector. Experimental prototype is set up to verify the impact of the error of system parameters on the imaging properties.
Observation and analysis of flow field in laser ablation plume of POM
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When using YAG laser emit strong laser pulses to bombardment solid POM, in the areas of interaction will produce a plume. A shadowgraph photography technique was employed for visualizing temporal evolution of plume. The experiment results show that in the plume flow field, multi-density discontinuities were observed. The plume has a high speed towards laser source, and plume uneven expansion makes the shape and position of discontinuities change. Plume velocity affect the propulsive efficiency, enhance the pulse laser energy can speed up the plume, energy increase to a certain degree of plume speed will reach a steady-state value.
Research progress and perspective of hyperspectral image projectors
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As a new hyperspectral image projection technology developed in recent years, hyperspectral image projectors(HIP) provides an economical, practical and effective solution for the detection, evaluation and nonlinear calibration of hyperspectral imager. HIP, based on the spatial light modulation technology used in DMD and LCD, is capable of projecting an arbitrary spectrum into each spatial pixel to simulate a realistic scenes. We describes the concept of a generic hyperspectral image projector, and presents an overview of its applications in a number of areas. The possibilities of development direction in the future are proposed.
A high performance constant fraction discriminator for pulsed laser proximity fuze
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A novel high performance timing discrimination circuit architecture for a pulsed laser proximity fuze based on constant fraction discrimination technique is constructed and tested. A LC resonant circuit is designed to replace the traditional transmission delay-line to accommodate the special requirements of laser proximity fuze for low size, power consumption, weight and cost. The walk error of the improved constant fraction discriminator is analyzed with lots of detailed experiments. The experiment results indicate that the discriminator eliminates the dependency of the echo pulse amplitude from the timing result, the walk error caused by the amplitude variation and the noise variation of the received echo pulse is less than 125ps, when the SNR is more than 20 and the echo pulse is 0.2V to 2.134V (20.12dB dynamic range). The error is less than 100ps when the SNR more than 60. Furthermore, Detection on the whole system integrating the timing discrimination circuit verifies that, the laser repetition frequency can reach 10 KHz, the accuracy of the system with a measurement time of 0.1ms is 1.45cm in the case of a noncooperative target at a measurement range from 2m to 24m at room temperature, which improve greatly the fixed distance precision of pulsed laser proximity fuze.
The modification of ultraviolet Total Ozone Unit (TOU) for absorbing aerosol index
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Aerosol Absorbing Index (AAI) can be used for the observation of the absorbing aerosol including dust, biomass burning and volcano ash etc. Recently, with much more aerosol pollution events occurring, atmospheric environment is getting worse in China. The AAI derived from FY-3/TOU has been used for the atmospheric aerosol pollution observation since 2013 by China Meteorological Administration. In this paper, the precision factors analysis of AAI retrieval from TOU is made. Based on the analysis, the wavelengths most suitable for AAI retrieval are 354 nm and 388 nm. Besides, considering the low spatial resolution of TOU (50×50 km2), a modified UV sensor is proposed with characters of much smaller size, higher sensitivity (SNR<4000) and higher spatial resolution (<5 km) which is much more suitable for observing aerosol pollution events, especially in urban areas.
A novel data transmission circuit for digital image sensors
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A novel data transmission circuit for digital image sensors is presented. Large amounts of data are divided into m groups of n bits each. Each group of data is stored in an n-bit shift register. Under the control of a column scanner, at a time, only one group of data is selected to output serially to a common output line. Thus, as the scanner scans all the groups of data, the large amounts of data are serially output through the common line. A current-mode circuit transforms the output data into a low voltage swing signal which propagates over the common output line fast. A sense amplifier receives the low voltage swing signal and then recovers the full swing signal. Finally, a low-voltage differential signaling ( LVDS ) transmitter, which is fed with the full swing signal, transmits the data out chip. Because there is always only one of the m shift registers operating, the power consumption is greatly reduced. The simulation results show that the proposed circuit works correctly at a date rate of 400Mb/s. For n=14, and m=8, 32, 128, and 256, the power consumption of the prototype is as low as 1/4, 1/15, 1/50, and 1/80 that of the traditional serial link respectively.
Test of reflective MTN liquid crystal cell for the LCOS microdisplay by guided wave method
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In order to confirm the function of MTN model in our LCOS microdisplay device, we made the MTN test cell, in which low substrate is also glass instead of silicon. Since a standard commercial-like liquid crystal cell with low index glass( with an index close to 1.52) plate is to be investigated by a guided model technique to unravel the director profile through the cell, the low index improved fully leaky guided model(IFLGM) technique are chosen. At higher applied voltages (in our study U≥5.0 V(rms), the voltage-dependent reflectance can not be distinguished. In this range of the applied voltage, the electric fields create tiny difference in the distribution of the director only near the substrates and waveguide signals are just sensitive to this difference. Fitting the data in reflection by using the modeling-program based upon multilayer optical theory together with continuum theory gives the information about the pre-tilt and twist of the director as well as the parameters of different optical layers. We found that the pre-tilt angle on the top substrate is smaller 1° than that on the bottom in the best fit, this suggests that the ITO and the aluminum coatings have different effects on the alignment layers.
Terahertz digital holography image processing based on MAP algorithm
Guang-Hao Chen,
Qi Li
Show abstract
Terahertz digital holography combines the terahertz technology and digital holography technology at present, fully exploits the advantages in both of them. Unfortunately, the quality of terahertz digital holography reconstruction images is gravely harmed by speckle noise which hinders the popularization of this technology. In this paper, the maximum a posterior estimation (MAP) filter is harnessed for the restoration of the digital reconstruction images. The filtering results are compared with images filtered by Wiener Filter and conventional frequency-domain filters from both subjective and objective perspectives. As for objective assessment, we adopted speckle index (SPKI) and edge preserving index (EPI) to quantitate the quality of images. In this paper, Canny edge detector is also used to outline the target in original and reconstruction images, which then act as an important role in the evaluation of filter performance. All the analysis indicate that maximum a posterior estimation filtering algorithm performs superiorly compared with the other two competitors in this paper and has enhanced the terahertz digital holography reconstruction images to a certain degree, allowing for a more accurate boundary identification.
Temperature sensor and display researched based on micro-deformation of beam splitting mirror in holographic system
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The 45° beam splitting mirror plays a vital role on image quality in the Holographic system, in order to study the influence of environment temperature variation on the 45° beam splitting mirror in the Holographic system, finite element analysis method is used to simulate the anti-three through seven mirror deformation at 27℃, 28℃ and 29℃ temperature in theory. A new real-time monitoring and displaying photoelectric system for ambient temperature and beam splitting mirror distortion detection is designed to provide real-time temperature change and deformation detection , which is made up of laser speckle interferometer, chip temperature sensor, two-operational amplifier, MCU and LED indicator. And the out-plane displacement value measured in the experiment under the condition of temperature correspondingly are 406nm, 420nm and 427 nm. Finally, the relation equation of temperature and mirror deformation is established by the method of exponential equation fitting, which will provide preliminary theoretical and experimental reference for further research.
A background suppression algorithm for infrared image based on shearlet
Ruibin Zou,
Caicheng Shi,
Xiao Qin
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Because of the relative far distance between infrared imaging system and target or the wide field infrared optical, the imaging area of infrared target is only a few pixels, which is isolated or spots to be showed in the field of view. The only available is the intensity information (gray value) for the target detection. Simultaneously, there are many shortcomings of the infrared image, such as large noise, interference and so on, therefore the small target is always buried in the background and noises. The small target is relatively difficult to detect, so generally, it is impossible to make reliable detection to this target in a single frame image. Summarily, the core of the infrared small target detection algorithm is the background and noise suppression based on a single frame image. Aiming at the infrared small target detection and the above problems, a shearlets-based background suppression algorithm for infrared image is proposed. The algorithm demonstrates the performance of advantage based on shearlets, which is especially designed to address anisotropic and directional information at various scales. This transform provides an optimally efficient representation of images, which is greatly reduced the amount of the information and the available information representation. In the paper, introducing the principle of shearlets first, and then proposing the theory of the algorithm and explaining the implementation step. Finally, giving the simulation results. In Matlab simulations with this method for several sets of infrared images, simulation results conformed to the theory on background suppression based on shearlets. The result showed that this method can effectively suppress background, and improve the SCR and achieve a satisfactory effect in the sky background. The method is very effectively for target detection, identification, track in infrared image system for the future.
Development of optically immersed, near-room-temperature HgCdTe photovoltaic detectors
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Optically immersed HgCdTe photovoltaic detectors in the 2.5 to 3.2 μm wavelength region operating at near room temperatures have been developed based on HgCdTe graded structure materials grown by opened tube isothermal vapor phase epitaxy (ISOVPE) method on lattice matched CdZnTe substrate. Fourier transformation infrared spectroscopy (FTIR) measurement combined with continuous step wet etching was applied to adjust the cutoff wavelength. The devices were designed and fabricated by traditional n-on-p planar junction process. Optical immersion of micro-lenses by CdZnTe substrate was used to improve the performance of the devices and the hyper-hemispherical micro-lens with a diameter of 1.5mm was made by single point diamond turning method. The optical response area was tested by laser beam induced current (LBIC) scanning measurement, and the result showed that the devices with hyper-hemispherical immersion micro-lens could get a 1mm×1mm response area as designed. The current-voltage characteristic of the devices were measured, and all the devices showed a little increase in the values of zero biased resistance, which was due to a decreased background radiation acceptance angle caused by a hyper-hemispherical structure. The photo response signal and dark noise were also measured before and after the micro-lens fabrication. The signal showed an increase by 20-30 times due to the enlarged photo response area, and the dark noise showed a little decrease which was also due to a limited background radiation acceptance angle. As a result, a multiple factor of four in detectivity enhancement could be achieved by the adoption of hyper-hemispherical immersion micro-lens structures.
Modeling for infrared readout integrated circuit based on Verilog-A
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Infrared detectors are the core of infrared imaging systems, while readout integrated circuits are the key components of detectors. In order to grasp the performance of circuits quickly and accurately, a method of circuit modeling using Verilog-A language is proposed, which present a behavioral simulation model for the ROIC. At first, a typical capacitor trans-impedance amplifier(CTIA) ROIC unit is showed, then the two essential parts of it,operational amplifier and switch are modeled on behavioral level. The op amp model concludes these non-ideal factors, such as finite gain-bandwidth product, input and output offset, output resistance and so on. Non-deal factors that affect switches are considered in the switch behavioral model, such as rise and fall time, on-resistance and so on. At last time-domain modeling method for noise is presented, which is compared with the classical frequency domain method for difference. The analysis results shows that in the situation that noise interested bandwidth(NIBW) is more than 5MHz, the difference between the two methods leads to less than 1% if the sample rate of noise is larger 4 times of the NIBW
Simulation for spectral response of solar-blind AlGaN based p-i-n photodiodes
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In this article, we introduced how to build a physical model of refer to the device structure and parameters. Simulations for solar-blind AlGaN based p-i-n photodiodes spectral characteristics were conducted in use of Silvaco TCAD, where device structure and parameters are comprehensively considered. In simulation, the effects of polarization, Urbach tail, mobility, saturated velocities and lifetime in AlGaN device was considered. Especially, we focused on how the concentration-dependent Shockley-Read-Hall (SRH) recombination model affects simulation results. By simulating, we analyzed the effects in spectral response caused by TAUN0 and TAUP0, and got the values of TAUN0 and TAUP0 which can bring a result coincides with test results. After that, we changed their values and made the simulation results especially the part under 255 nm performed better. In conclusion, the spectral response between 200 nm and 320 nm of solar-blind AlGaN based p-i-n photodiodes were simulated and compared with test results. We also found that TAUN0 and TAUP0 have a large impact on spectral response of AlGaN material.
On simulation and verification of the atmospheric turbulent phase screen with Zernike polynomials
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Atmospheric turbulence is one of the main factors that influence the spread of laser communication in the atmosphere affect, which will change the random distribution of the refractive index of air, and affect the image quality of the beam through the atmosphere seriously. To study atmospheric turbulence in order to grasp changes in atmospheric turbulence, by taking the appropriate methods to control and reduce the effects of atmospheric turbulence on the beam quality. In addition to studying atmospheric turbulence using experimental methods and theoretical analysis. Numerical simulation is an effective means to study the problem of turbulence. Zernike polynomials were used to produce atmospheric turbulence phase screen in this article. The phase structure function and the atmospheric coherence length were used to check whether the atmospheric turbulence phase screen is right or not. Simulation results were studied show that, the atmospheric turbulence phase screen generated with Zernike polynomial method was consistent with the theoretical values in the low spatial frequency components, but, the simulation results had big difference with the theoretical values in the high spatial frequency components. The reason is that Zernike polynomials method has some limitations. In addition, the distribution of turbulence in the atmospheric turbulence phase screen can be changed by increasing the Zernike polynomials of orders or changing the receiving apertures, but which involves great and complex calculation. Therefore, in the specific application of the laser communication system, the best experimental program should be considered. Statistical properties of atmospheric turbulence phase can be described by the phase structure function. Therefore, the structure of the function will be used to determine the phase screen simulation phase screen is accurate. To give a better understanding of both methods the difference between simulation results, the simulation results of Zernike polynomials and power spectral inversion simulation results were compared. At last to give the corresponding power spectrum inversion method to simulate atmospheric turbulence phase screen simulation results and shows that the theory without making the introduction.
Simulation of hyperspectral imaging based on tunable Fabry-Pérot interferometer
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Fabry–Pérot interferometer is a multi-beam interferometer, with the advantage of high spectral resolution, and can be used to research the fine structure of the matter. The application of Fabry–Pérot interferometer in spectral imaging instrument will improve the spectral resolution. And it can also enhance the structural efficiency and promote the miniaturization of the spectral imaging instrument, which makes it convenient to be used in aviation and space applications. Here, we propose a method of hyperspectral Imaging based on Tunable Fabry–Pérot interferometer. At first, the time-domain interferogram is obtained by adjusting the cavity length during shooting, then, the corresponding relationship between the interferogram and the spectral curve can be described by the theoretical model of multi-beam interference, and linear equations can be obtained by discretizing the theoretical model. Finally, the spectral curve can be obtained by solving the equations. Good results come out of the simulation of this method. It has high precision and spectral resolution.
Fabrication and surface profile simulation of sapphire microlens array
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In this paper, photoresist reflow method was used to fabricate microlens array on the sapphire substrate which possesses high mechanical strength and transmittance in broad spectrum. High etch selectivity of sapphire over photoresist was obtained through adjusting ICP etching parameters. To test the fabrication process, a geometric model of square aperture microlens was built by finite element method. The validation of this model was done by comparing the surface profiles of three samples reflowed under different condition with the geometric model. In all three cases the simulation results were close to the experiment results. So the model was justified. On the other hand, the fabrication process was found to be repeatable because the surface profile of fabricated microlens was close to the theoretical surface profile of reflowed photoresist. The geometric model can be used to check the repeatability of photoresist reflow process and to predict the surface profile of microlens with irregular aperture.
The integrated platform of controlling and digital video processing for underwater range-gated laser imaging system
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Laser range-gated imaging is one of the effective techniques of underwater optical imaging. It could make the viewing distance up to 4 to 7 times with the video image processing technology. Accordingly, the control and image processing technologies come to be the key technologies for the underwater laser range-gated imaging system. In this article, the integrated platform of controlling and digital video processing for the underwater range-gated laser imaging system based on FPGA has been introduced. It accomplishes both the communication for remote control system as the role of lower computer and the task of high-speed images grabbing and video enhance processing as the role of high-speed image processing platform. The host computer can send commands composed to the FPGA, vectoring the underwater range-gated laser imaging system to executive operation.
Research on dual spectrum solar-blind ultraviolet corona detection system
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A dual spectrum solar-blind ultraviolet (UV) corona detection system is designed in this paper. A common optical axis using a dichroic mirror is applied to this system in order to make visible light and ultraviolet light spectroscopy to ultraviolet detector and visible detectors. A high speed circuit of image processing based on TMS320DM642 DSP and a circuit that is used into system control and power management based on microcontroller are designed for the presented system. On the basis of the multi-threaded programming ideas, real-time image acquisition of ultraviolet and visible detectors, ultraviolet image noise reduction, image registration, dual spectral integration, Characteristic superimposing, serial communication and image display are achieved by using the DSP image processing circuit. Experimental results show that the dual spectrum solar-blind ultraviolet corona detection system has a good performance of corona detection based on ultraviolet and visible image fusion.
Research and experiment of InGaAs shortwave infrared imaging system based on FPGA
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The design and imaging characteristic experiment of InGaAs shortwave infrared imaging system are introduced. Through the adoption of InGaAs focal plane array, the real time image process structure of InGaAs shortwave infrared imaging system is researched. The hardware circuit and image process software of the imaging system based on FPGA are researched. The InGaAs shortwave infrared imaging system is composed of shortwave infrared lens, InGaAs focal plane array, temperature controller module, power supply module, analog-to-digital converter module, digital-to-analog converter module, FPGA image processing module and optical-mechanical structure. The main lock frequency of InGaAs shortwave infrared imaging system is 30MHz. The output mode of the InGaAs shortwave infrared imaging system is PAL analog signal. The power dissipation of the imaging system is 2.6W. The real time signal process in InGaAs shortwave infrared imaging system includes non-uniformly correction algorithm, bad pixel replacement algorithm, and histogram equalization algorithm. Based on the InGaAs shortwave infrared imaging system, the imaging characteristic test of shortwave infrared is carried out for different targets in different conditions. In the foggy weather, the haze and fog penetration are tested. The InGaAs shortwave infrared imaging system could be used for observing humans, boats, architecture, and mountains in the haze and foggy weather. The configuration and performance of InGaAs shortwave infrared imaging system are respectively logical and steady. The research on the InGaAs shortwave infrared imaging system is worthwhile for improving the development of night vision technology.
Study on damage of K9 glass under 248nm ultraviolet pulsed laser irradiation
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The damage of K9 glass under 248nm ultraviolet pulsed laser irradiation was studied. The laser pulse energy was kept within the range of 60mJ to 160mJ, and the repetition rate was adjusted within the range of 1Hz to 40Hz. The damage morphologies of single-pulse and multi-pulse laser irradiation were characterized by optical microscope, and the damage mechanism was discussed. The experimental results indicated that the damage of K9 glass irradiated by 248nm ultraviolet laser mainly followed the thermal-mechanical coupling mechanism and the damage threshold of K9 glass was 2.8J/cm2. The intensity of damage area increased gradually with the increase of the laser pulse number. It was shown that accumulation effect of laser induced damage to K9 glass was obvious.
Dual cameras acquisition and display system of retina-like sensor camera and rectangular sensor camera
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For a new kind of retina-like senor camera and a traditional rectangular sensor camera, dual cameras acquisition and display system need to be built. We introduce the principle and the development of retina-like senor. Image coordinates transformation and interpolation based on sub-pixel interpolation need to be realized for our retina-like sensor’s special pixels distribution. The hardware platform is composed of retina-like senor camera, rectangular sensor camera, image grabber and PC. Combined the MIL and OpenCV library, the software program is composed in VC++ on VS 2010. Experience results show that the system can realizes two cameras’ acquisition and display.
Discussion of beam quality of semiconductor lasers
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Based on the beam characteristics of semiconductor lasers, a new parameter for evaluating beam quality of semiconductor lasers is introduced. The shortcomings of M2 factor used in evaluating beam quality of semiconductor lasers are discussed and its limitations are pointed out. Moreover, some important aspects of the beam quality factor are discussed. The main factors to influence collimating the beam of semiconductor lasers are analyzed. Our results give us grounds to make the following conclusions: the new propagation parameter succeeds in its universality and adaptability.
Study on the relationship of dark current characteristics and materials surface defects of extended wavelength InGaAs photodiodes
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Extended wavelength InGaAs photodiodes in 1.0~2.5μm spectral rang based on two types of material structures were investigated systematically. The first type InGaAs photodiode, marked by sample 1#, was fabricated using MOCVD epitaxial materials with P-i-N structure. The second type InGaAs photodiodes, marked by sample 2#, was fabricated using MBE epitaxial materials with P-i-N structure. The two types of photodiodes were fabricated by mesa etching technique, side-wall and surface passivation film. Dark current and voltage curves were measured by semiconductor parameters analyzer at different temperature, and dark current characteristics were analyzed using different perimeter to area method. The mechanism of the devices has been analysed. Polarization microscopy and conductive atomic force microscopy (c-AFM) have been used to investigate the local conductivity of the photodiodes’ sensitive area. Combining the optical and c-AFM micrographs with dark current characteristics, we intended to characterize the relationships of the leak current and the defect. The results indicate that sample 1# has relative much more leak defects than that of sample 2#, and thus the dark current sample 1# is higher than that of sample 2# and. The defects are generated at the body of material and spread to the surface, and these defects cause very high dark current of sample 1#.
Performance of four-stage thermoelectric cooler for extended wavelength InGaAs detectors
De-feng Mo,
Li-yi Yang,
Da-fu Liu,
et al.
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Experimental setup for evaluating four-stage thermoelectric cooler’s performance was designed. Effects of input power, heat dissipation condition and heat load on the temperature difference (ΔT) of four-stage thermoelectric coolers’ hot and cold faces were obtained experimentally. The result shows that, the ΔT increases as the input power increases. A linear relationship exists between input current and feedback voltage. In different cooling conditions, the ΔT of thermoelectric cooler (TEC) increases with the temperature of hot face. As the temperature increasing on hot face is 1K, the ΔT increasing of TEC can be about 0.5K. Meanwhile, the power consumption of TEC also increases slightly. Water condensation can be prevented in either dry nitrogen environment or vacuum environment, but the vacuum level has great influence to the ΔT, especially in low operation temperature. The better the vacuum level is, the smaller the convection heat loss has. When the operation temperature of focal plane array (FPA) is lower than 220K, it is prior to use vacuum packaging. Considering the Joule-heat of readout circuit and the heat loss of wire conduction, the minimum working temperature of FPA can reach below 200 K when the temperature of the hot face is 285K. And the coefficient of performance (COP) of TEC can increase sharply from 0.8% to 4% when the controlled operation temperature is 220K rather than 200K.
Spectroscopic properties of Nd3+/Yb3+ co-doped in lithium aluminum silicate glass for 1.0 μm fiber laser
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The Nd3+, Yb3+ singly doped and Nd3+ /Yb3+ co-doped lithium aluminum silicate glasses are fabricated by using a conventional melt quenching technique in air atmosphere, with the molar composition of (60-a-b)SiO2-3Al2O3-20Li2O-12MgO-5CaO-aNd2O3-bYb2O3 (with a=0, 0.25, 0.5, 1 and b=0,2). The Spectroscopic properties of 1.0 μm emission and Luminescence lifetime in Nd3+ /Yb3+ co-doped lithium aluminum silicate glasses are investigated under 808 nm excitation. The Judd–Ofelt theory is used to study the spectroscopic properties of Nd3+ . Meanwhile, the emission cross-section of Yb3+ are obtained by using the reciprocity method. A broad emission band from 950 to 1,100 nm is detected when the Nd3+ /Yb3+ co-doped in lithium aluminum silicate glasses excited by 808 nm LD. The energy transfer process from Nd3+ →Yb3+ co-doped in lithium aluminum silicate glasses is described in this paper.
Photo-and-dark-current-voltage characteristics of normal-incidence GaAs photodetectors with two types of electrode configurations
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The characteristics of photo-current-voltage and dark-current-voltage for two-photon-response semi-insulating GaAs photodetectors responding to near-infrared wavelengths of 1.31 μm and 1.55μm are investigated. The semi-insulating GaAs photodetectors were fabricated into hemisphere on whose bottom two types of electrodes were deposited. In experiments, the incident laser was adjusted to travel normally to the photodetector and focus at the center of the bottom so as to improve the nonlinear photo-responsivity markedly. It is observed that the photocurrent dependent on bias exhibits quadratic nonlinearity for both lasers and both electrode configurations, which reflects frequency-doubled absorption responsible for the physical mechanisms of the photodetectors; and the reasonable analysis demonstrates the important role of the electric-field-induced frequency-doubled absorption in two-photon response. Furthermore, it is found that the photocurrent is quite more greater when the electrode positioned at the bottom center of the photodetectors (central electrode for short) is negatively charged than that in the case of it positively charged under the conditions of the identical bias voltage and the same incident optical power; while the dark-current varies in exactly the opposite mode compared to the photocurrent. The aforementioned disparate variations of the photocurrent and the dark-current are well interpreted by the theory of surface band-bending of semi-insulating GaAs, and such variations result in a large ratio of photo-current to dark-current in the case of the central electrode negatively charged. The investigated results also indicate that the optimization of electrode structure is essential to improve the photo-responsivity of the photodetector.
Electroluminescence of cubic boron nitride single crystal flakes with color-zoning
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The current-voltage (I-V) characteristics and phenomena of electroluminescence of cubic boron nitride (cBN) single crystal flakes with color-zoning under extremely non-uniform electric fields (ENUEFs) induced by needle-plate electrodes were observed. When a cBN flake with sizes of 0.3×0.3×0.1 mm3 was tightly fixed between the tungsten needle and brass plate electrodes in the atmosphere, the I-V relationship exhibited nonlinearity, and peculiar phenomena of electroluminescence with bright blue-violet light appeared at the bias voltage in a range of 700-1200 V. The current-controlled differential negative resistance was synchronously observed. The electroluminescent phenomena were somewhat different for cases of the needle electrode respectively contacting to the amber and transparent zones. The electroluminescent radiations of cBN flakes biased at voltages with a range of 600-1550 V were also investigated in vacuum. In a vacuum chamber, the green emitting phosphor spread around the cBN flake might be excited by the vacuum ultraviolet (VUV) emission from the cBN crystal, and the green fluorescence was observed by naked eyes. The VUV radiation spectrum with a peak wavelength of 149 nm was measured. In the atmosphere, the blue-violet light emission may be the gas discharge resulted from the air ionization induced by the VUV emission from the cBN crystal under the ENUEF, and the ENUEF subsequently keeps the air discharging. The VUV emission from the cBN crystal under the ENUEF can be caused by the original interband transition and the subsequent intraband transfer for electrons, and the final electron-hole direct recombination.
Measurement and analysis of aircraft and vehicle LRCS in outfield test
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The measurement of aircraft and vehicle Laser Radar Cross Section (LRCS) is of crucial importance for the detection system evaluation and the characteristic research of the laser scattering. A brief introduction of the measuring theory of the laser scattering from the full-scale aircraft and vehicle targets is presented in this paper. By analyzing the measuring condition in outfield test, the laser systems and test steps are designed for full-scale aircraft and vehicle LRCS and verified by the experiment in laboratory. The processing data error 7% below is obtained of the laser radar cross section by using Gaussian compensation and elimination of sky background for original test data. The study of measurement and analysis proves that the proposed method is effective and correct to get laser radar cross section data in outfield test. The objectives of this study were: (1) to develop structural concepts for different LRCS fuselage configurations constructed of conventional materials; (2) to compare these findings with those of aircrafts or vehicles; (3) to assess the application of advanced materials for each configuration; (4) to conduct an analytical investigation of the aerodynamic loads, vertical drag and mission performance of different LRCS configurations; and (5) to compare these findings with those of the aircrafts or vehicles.
High performance InAs/GaSb superlattice long wavelength photodetectors based on barrier enhanced structures
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The barrier enhanced InAs/GaSb long wavelength photodetectors were designed and demonstrated in this paper. A PBIN detector with an electron barrier inserted between P type contactor and absorption region show significantly improved electrical performances compared to a PIN structure. The RmaxA product of the PBIN detector was measured to be 104 Ωcm2 at 80K and 7360 Ωcm2 at 50K. Temperature dependent measurements show that the tunneling currents dominate the dark current below 50K, the generation-recombination (GR) currents dominate from 50K to 90K, and the diffusion current dominate over 90K. The PBIN structure benefits from a lower electric field in the absorption region and therefore, suppressed the tunnel currents and GR currents. To improve the quantum efficiency, Be-doping was employed to convert the conductivity of the long wavelength SL structure, the PN junction moves away from the B-I hetrostructure to the π-N interface, which loses the barrier effect. Therefore, the hole barrier was needed to form a PBπBN structure. In this paper, hole barrier was designed without Al element to form a PBπBN structure. The RmaxA product of the PBπBN detector was measured to be 77 Ωcm2 and the dark current density under -0.05V bias was measured to be 8.8×10-4A/cm2 at 80K. The peak current responsivity at 9.8 μm was 2.15A/W and the quantum efficiency was 26.7%.
Noise characteristic of AlGaN-based solar-blind UV avalanche photodiodes
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A particular system for excess noise of avalanche photodiode (APD) measurement was build. Then the signal-noise ratio at different reverse voltage and the noise spectrum are measured and analyzed on different devices. First, the noise measurement system was constructed to fulfill the requirement that a high DC voltage can be applied on, and the measurement system was carefully shielded to protect from disturbance of electromagnetic radiations. Than we measured the noise spectrums of separate absorption and multiplication (SAM) type solar-blind APDs. The noise spectrums of SAM APDs which have different dark current levels were also measured. The results show that the low-frequency noise is dominant across a wide frequency range. And as the dark current goes higher, shot noise and low-frequency noise go higher at the same time. And the low-frequency noise will also takes more proportion in the spectrum when dark current goes higher. On the other hand, noise measurements at different reverse voltage and in either UV illumination or dark show that the excess noise factor increase faster as the gain increase. This leads to a decrease of signal-noise ratio at very high gain. In order to get a higher signal-noise ratio, a proper high gain should be adopted, rather than a gain “higher and better”.
Analysis of pixel circuits in CMOS image sensors
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CMOS image sensors (CIS) have lower power consumption, lower cost and smaller size than CCD image sensors. However, generally CCDs have higher performance than CIS mainly due to lower noise. The pixel circuit used in CIS is the first part of the signal processing circuit and connected to photodiode directly, so its performance will greatly affect the CIS or even the whole imaging system. To achieve high performance, CMOS image sensors need advanced pixel circuits. There are many pixel circuits used in CIS, such as passive pixel sensor (PPS), 3T and 4T active pixel sensor (APS), capacitive transimpedance amplifier (CTIA), and passive pixel sensor (PPS). At first, the main performance parameters of each pixel structure including the noise, injection efficiency, sensitivity, power consumption, and stability of bias voltage are analyzed. Through the theoretical analysis of those pixel circuits, it is concluded that CTIA pixel circuit has good noise performance, high injection efficiency, stable photodiode bias, and high sensitivity with small integrator capacitor. Furthermore, the APS and CTIA pixel circuits are simulated in a standard 0.18-μm CMOS process and using a n-well/p-sub photodiode by SPICE and the simulation result confirms the theoretical analysis result. It shows the possibility that CMOS image sensors can be extended to a wide range of applications requiring high performance.
The field distribution in a finite number of nanostructured metal waveguide arrays
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We investigative the field distribution in nanostructured metal waveguide arrays. Firstly, we analyze a simple discrete system containing two adjacent metallic waveguides (N=2). The propagation constants β1 and β2 can be calculated by a rigorous field analysis approach. According to the supermode theory of conventional dielectric waveguide arrays, we can also obtain the expressions of propagation constants. So we can obtain the coupling constant and the perturbation constant of the expressions in the supermode theory. Next, we consider a system that contains five adjacent metal waveguides (N=5). The propagation constants and the wavefunctions of the supermodes can be obtained according to the coupling constant, the perturbation constant, and the supermode theory. The incident light is located at the input of the 4st waveguide. The initial excited field can be expressed as a sum of supermodes. The total field is formed by the superposition of supermodes. The variation of field amplitude with propagation distance is obtained and can predict the precise positions of the field distribution. To demonstrate the analytical results, we numerically simulate the field distribution in the waveguides (N=5) constructed with silver by the finite-difference time-domain method. The numerical simulation results show a good agreement with theoretical expectations.
Research on micro-deformation of beam splitting mirror in holographic system by laser speckle method
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In order to study the influence of environment temperature variation on the quality of holographic images, the change of transmit path in the holographic optical system is analyzed for both objective beam and reference beam before and after mirror deformation. In theory, finite element analysis method is used to simulate the anti-three through seven mirror deformation at 27℃, 28℃ and 29℃. And a new real-time monitoring and displaying laser speckle system is designed for measuring ambient temperature and beam splitting mirror distortion detection. The deformation value measured in the experiment are 406nm, 420nm and 427nm respectively at the same temperature mentioned above. The results show that theoretical and experimental values are in good agreement, and errors are less than 0.5%.
Dark-current characteristics of GaN-based UV avalanche photodiodes
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For UV detecting, it needs high ratio of signal to noise, which means high responsibility and low noise. GaN-based avalanche photodiodes can provide a high internal photocurrent gain. In this paper, we report the testing and characterization of GaN based thin film materials, optimization design of device structure, the device etching and passivation technology, and the photoelectric characteristics of the devices. Also, uniformity of the device was obtained. The relationship between dark current and material quality or device processes was the focus of this study. GaN based material with high aluminum components have high density defects. Scanning electron microscope, cathodoluminescence spectra, X-ray double crystal diffraction and transmission spectroscopy testing were employed to evaluate the quality of GaN-based material. It shows that patterned sapphire substrate or thick AlN buffer layer is more effective to get high quality materials. GaN-based materials have larger hole ionization coefficient, so back incident structure were adopted to maximize the hole-derived multiplication course and it was helped to get a smaller multiplication noise. The device with separate absorption and multiplication regions is also prospective to reduce the avalanche noise. According to AlGaN based material characteristics and actual device fabrication, device structure was optimized further. Low physical damage inductively coupled plasma (ICP) etching method was used to etch mesa and wet etching method was employed to treat mesa damage. Silica is passivation material of device mesa. For solar-blind ultraviolet device, it is necessary to adopt a wider bandgap material than AlGaN material. The current-voltage characteristics under reverse bias were measured in darkness and under UV illumination. The distribution of dark current and response of different devices was obtained. In short, for GaN-based UV avalanche photodiode, dark current was related to high density dislocation of thin film materials and device processes, especially the mesa etching and passivation. More and more proofs reveal that the mesa formation course even plays the most important role in generation of dark current.
A 15-bit incremental sigma-delta ADC for CMOS image sensor
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An incremental sigma-delta ADC is designed for column-parallel ADC array in CMOS image sensor. Sigma-delta modulator with single-loop single-bit structure is chosen for power consumption and performance reasons. Second-order modulator is used to reduce conversion time, without stability problem and large area accompanied by higher order sigma-delta modulator. The asymmetric current mirror amplifier used in integrator reduces more than 30% power dissipation. The digital filter and decimator are implemented by counters and adders with significantly reduced chip area and power consumption. A Clock generator is shared by 8 ADCs for trade-off among power, area and clock loading. The ADC array is implemented in a 0.18-μm CMOS technology and clocked at 10 MHz, and the simulated resolution achieves 15-bit with 255 clock cycles. The average power consumption per ADC is 118 μW including clock generator, and the area is only 0.0053 μm2.
Blind image deblurring with edge enhancing total variation regularization
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Blind image deblurring is an important issue. In this paper, we focus on solving this issue by constrained regularization method. Motivated by the importance of edges to visual perception, the edge-enhancing indicator is introduced to constrain the total variation regularization, and the bilateral filter is used for edge-preserving smoothing. The proposed edge enhancing regularization method aims to smooth preferably within each region and preserve edges. Experiments on simulated and real motion blurred images show that the proposed method is competitive with recent state-of-the-art total variation methods.
A limb atmospheric radiance inversion method based on a sun-synchronous orbit satellite
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It is always affected by the influence of limb atmosphere when the space-based remote sensing systems detect spatial targets using limb observation mode. In this paper, the characteristics of the limb atmosphere and the impact of limb atmosphere to target observation are theoretical modeled. Based on the model, we propose an algorithm to compute the vertical structure of atmosphere radiance through the image of limb atmosphere as well as the star image. Realization of atmosphere radiance under similar situation can then be computed based on inversion algorithm proposed in the paper. The stellar images of different areas including areas over Antarctic and Equator are captured by in-orbit space borne camera. The method of how to inverse from the gray image to atmosphere limb radiance in engineering applications is described in detail and statistical analysis of the result of inversion to limb atmosphere radiance is conducted whose trend is consistent with simulation result of MODTRAN which increases at lower altitude to a peak value then drop to zero slowly while there are two peaks in the statistical radiance distribution curves illustrating the polar light over Antarctic.
The application of IR detector with windowing technique in the small and dim target detection
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The performance of small and dim IR target detection is mostly affected by the signal to noise ratio(SNR) and signal to clutter ratio(SCR), for the MWIR especially LWIR array detector, because of the background radiation and the optical system radiation, the SCR cannot be unlimited increased by using a longer integral time, so the frame rate of the detector was mainly limited by the data readout time especially in a large-scale infrared detector, in this paper a new MWIR array detector with windowing technique was used to do the experiment, which can get a faster frame rate around the target by using the windowing mode, so the redundant information could be ignore, and the background subtraction was used to remove the fixed pattern noise and adjust the dynamic range of the target, then a local NUC(non uniformity correction) technique was proposed to improve the SCR of the target, the advantage between local NUC and global NUC was analyzed in detail, finally the multi local window frame accumulation was adopted to enhance the target further, and the SNR of the target was improved. The experiment showed the SCR of the target can improved from 1.3 to 36 at 30 frames accumulation, which make the target detection and tracking become very easily by using the new method.
New design of a hybrid plasmonic waveguide
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A new design of hybrid plasmonic waveguide based on nanostructure has been proposed. Compared with the previous mixed plasmonic waveguides, the design make a vertical dielectric-slot configuration embed within the middle of the metal surface and the high-index dielectric structure. The closed structure can provide the ultra-compact mode confinement. The propagation loss due to the presence of the air slot can be greatly reduced. The design could improve the development of integrated photonic circuits.
Blind image deblurring based on trained dictionary and curvelet using sparse representation
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Motion blur is one of the most significant and common artifacts causing poor image quality in digital photography, in which many factors resulted. In imaging process, if the objects are moving quickly in the scene or the camera moves in the exposure interval, the image of the scene would blur along the direction of relative motion between the camera and the scene, e.g. camera shake, atmospheric turbulence. Recently, sparse representation model has been widely used in signal and image processing, which is an effective method to describe the natural images. In this article, a new deblurring approach based on sparse representation is proposed. An overcomplete dictionary learned from the trained image samples via the KSVD algorithm is designed to represent the latent image. The motion-blur kernel can be treated as a piece-wise smooth function in image domain, whose support is approximately a thin smooth curve, so we employed curvelet to represent the blur kernel. Both of overcomplete dictionary and curvelet system have high sparsity, which improves the robustness to the noise and more satisfies the observer's visual demand. With the two priors, we constructed restoration model of blurred images and succeeded to solve the optimization problem with the help of alternating minimization technique. The experiment results prove the method can preserve the texture of original images and suppress the ring artifacts effectively.
Defect structure and optical damage resistance of Zr:Ce:Fe:LiNbO3 crystals
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The congruent Zr:Ce:Fe:LiNbO3 crystals have been grown by the Czochralski method with fixed concentrations of CeO2 and Fe2O3 and various concentrations of ZrO2. The Ultraviolet(UV)-Visible(Vis) absorption spectra were measured in order to investigate their defect structures and their optical damage resistance was characterized by the transmission light spot distortion method. The results show that the optical damage resistance of the Zr:Ce:Fe:LiNbO3 crystals improves with the doping concentration of ZrO2 increasing. The dependence of the optical damage resistance on the defect structure of Zr:Ce:Fe:LiNbO3 crystals was discussed.
Growth and photorefractive properties of Zr:Cu:Fe:LiNbO3 crystals with various Li/Nb ratios
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A series of Zr(1 mol%):Cu(0.1 mol%):Fe(0.03wt%)LiNbO3 single crystals with various Li/Nb ratios having compositions varying between 48.6 and 58 mol% Li2O in the melt were grown by the Czochralski method in the air. The OH− transmittance spectra was investigated to characterize the structure defects of these crystals. The OH− absorption peaks shift to longer wavelength as the [Li]/[Nb] ratio increases and an obvious absorption peak at 3468 cm-1 was observed at the Li/Nb ratio of 1.05. The photorefractive properties of the crystals were experimentally studied using the two-wave coupling method. The results show that as the [Li]/[Nb] ratio increases, the holographic response time and the diffraction efficiency increase under the Li/Nb ratio of 1.2.
A fast and practical calibration method for the phase measuring profilometry
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In the traditional PMP calibration, the system calibration and phase measurement were performed dividedly, and the measurement result was the relative height to the reference plane. A fast calibration was proposed, in which two gauge blocks were used to replace the standard plane controlled by the mechanical shifting device in the traditional calibration, and fewer datum points were sampled from the surface of the gauge blocks to calibrate the system. With this method, both system calibration and phase measurement can be implemented simultaneously. The real height of the object relative to the supporting plane can be obtained when the supporting plane was not superposed on the reference. A cuboid block of normal height 14.00mm was successfully measured by this method. Its mean relative error was no more than 1.35% and the root-mean-square error was less than 0.15mm. The calibration of the PMP was simplified and became more flexible with the proposed method.
Discuss on the two algorithms of line-segments and dot-array for region judgement of the sub-satellite purview
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When satellite is flying on the orbit for special task like solar flare observation, it requires knowing if the sub-satellite purview was in the ocean area. The relative position between sub-satellite point and the coastline is varying, so the observation condition need be judged in real time according to the current orbital elements. The problem is to solve the status of the relative position between the rectangle purview and the multi connected regions formed by the base data of coastline. Usually the Cohen-Sutherland algorithm is adopted to get the status. It divides the earth map to 9 sections by the four lines extended the rectangle sides. Then the coordinate of boundary points of the connected regions in which section should be confirmed. That method traverses all the boundary points for each judgement. In this paper, two algorithms are presented. The one is based on line-segments, another is based on dot-array. And the data preprocessing and judging procedure of the two methods are focused. The peculiarity of two methods is also analyzed. The method of line-segments treats the connected regions as a set of series line segments. In order to solve the problem, the terminals’ coordinates of the rectangle purview and the line segments at the same latitude are compared. The method of dot-array translates the whole map to a binary image, which can be equal to a dot array. The value set of the sequence pixels in the dot array is gained. The value of the pixels in the rectangle purview is judged to solve the problem. Those two algorithms consume lower soft resource, and reduce much more comparing times because both of them do not need traverse all the boundary points. The analysis indicates that the real-time performance and consumed resource of the two algorithms are similar for the simple coastline, but the method of dot-array is the choice when coastline is quite complicated.
Polarization of focal spot for high numerical aperture radially polarized beam
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According to Wolf and Richards vectorial diffraction theory, an electric field intensity model of focal spot for high numerical aperture radially polarized beam is established to analyze the intensity distributions of the focal spot and the polarization components of the electric field along the x, y and z axis, separately. In the reflection-mode confocal of imaging system, the intensity distributions of focal spot is obtained utilizing the gold nanoparticles, and the intensity distributions of the polarization components of the electric field along the x, y and z axis are obtained utilizing the gold nanorods. In the incident light, the polarization component along the z axis is nonexistent in front of the objective. But there is the polarization component along the z axis, which is relative to the numerical aperture, in the focal spot behind the objective. When the numerical aperture increases from 0.8 to 1.4, the ratio of the polarization component maximum along the z axis to that along the x axis or y axis increases from 0.57 to 3.16. The results show that the focal spot of radially polarized beam through high numerical aperture objective have the polarization component along the x, y and z axis, separately, and polarization component along z axis is much more than the other.
Visual saliency detection based on modeling the spatial Gaussianity
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In this paper, a novel salient object detection method based on modeling the spatial anomalies is presented. The proposed framework is inspired by the biological mechanism that human eyes are sensitive to the unusual and anomalous objects among complex background. It is supposed that a natural image can be seen as a combination of some similar or dissimilar basic patches, and there is a direct relationship between its saliency and anomaly. Some patches share high degree of similarity and have a vast number of quantity. They usually make up the background of an image. On the other hand, some patches present strong rarity and specificity. We name these patches “anomalies”. Generally, anomalous patch is a reflection of the edge or some special colors and textures in an image, and these pattern cannot be well “explained” by their surroundings. Human eyes show great interests in these anomalous patterns, and will automatically pick out the anomalous parts of an image as the salient regions. To better evaluate the anomaly degree of the basic patches and exploit their nonlinear statistical characteristics, a multivariate Gaussian distribution saliency evaluation model is proposed. In this way, objects with anomalous patterns usually appear as the outliers in the Gaussian distribution, and we identify these anomalous objects as salient ones. Experiments are conducted on the well-known MSRA saliency detection dataset. Compared with other recent developed visual saliency detection methods, our method suggests significant advantages.
Interaction of pulsed laser energy with bow shock in Mach 5 flow
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Pressure sensing and schlieren imaging with high resolution and sensitivity were applied to the study of the interaction of pulsed laser energy with bow shock at Mach 5. A Nd:YAG laser operated at 1.06μm, 100mJ pulse energy was used to breakdown the hypersonic flow in shock tunnel. 3 dimensional Navier-Stokes equations were solved with upwind format to simulate the interaction. Stagnation pressure of the blunt body was measured and calculated to examine the pressure variations during the interaction. Schlieren imaging was used in conjunction with the calculated density gradients to examine the process of the interaction. Results showed that the experimental stagnation pressure and schlieren imaging fitted well with the simulation. Stagnation pressure would increase when the transmission shock approached to the blunt body and decrease with the reflection of the transmission shock. Bow shock was deformed during the interaction. Schlieren imaging supplied important phenomenon to investigate mechanism of the interaction.
A non-destructive readout circuit of the linear array image sensor with over 90dB dynamic range and 190k fps for radar system
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This paper presents a non-destructive readout circuit of the linear array image sensor with wide dynamic range and high speed readout for radar system. A multi-capacitor and self-regulated capacitive trans-impedance amplifier (CTIA) structure is employed to extend the dynamic range. The gain of the CTIA is auto adjusted by switching different capacitors to the integration node asynchronously according to the output voltage. A class AB OPA is utilized to drive all the additional capacitors to achieve high speed readout. A photo response curve presents as a polyline with 5 segments, which enables a 101.7 dB dynamic range. In addition, the exposure time is 5.12us in the simulation, then an over 190k fps is achieved.
Modeling and simulation of time-gated FLIM SPAD image sensors
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A mathematical model of time-gated FLIM SPAD image sensors was established in behavioral level by MATLAB. The process of time-gated detection was simulated which includes photons emission, avalanche triggering and the restoration of fluorescence lifetimes. A fluorescence lifetime map was used to model the virtual scene being photographed. In order to guide the design of FLIM SPAD image sensors, the impacts of some parameters of FLIM SPAD image sensors, such as DCR and timing jitter, were analyzed by the proposed model. The impacts of the above parameters on sensors quantified by the simulation results indicated that the FLIM SPAD image sensor can get a better performance with smaller DCR and shorter timing jitter.
Probability-based saliency detection approach for multi-features integration
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There are various saliency detection methods have been proposed recent years. These methods can often complement each other so combining them in appropriate way will be an effective solution of saliency analysis. Existing aggregation methods assigned weights to each entire saliency map, ignoring that features perform differently in certain parts of an image and their gaps between distinguishing the foreground from the backgrounds. In this work, we present a Bayesian probability based framework for multi-feature aggregation. We address saliency detection as a two-class classification problem. Saliency maps generated from each feature have been decomposed into pixels. By the statistic results of different saliency value’s reliability on foreground and background detection, we can generate an accurate, uniform and per-pixel saliency mask without any manual set parameters. This approach can significantly suppress feature’s misclassification while preserve their sensitivity on foreground or background. Experiment on public saliency benchmarks show that our method achieves equal or better results than all state-of-the-art approaches. A new dataset contains 1500 images with human labeled ground truth is also constructed.
Automatic target locating system through cooperative dual-field imaging
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This paper proposes an automatic targeting locating system based on dual-field imaging to improve the stability of light weapons. The system consists of a wide field of view (WFOV) camera and a narrow field of view (NFOV) camera. The WFOV camera searches the pedestrian in the scenery, the other camera tracks the pedestrian and aims it accurately. Video signal is send to the processing unit PC and control signal is send back to the imaging system. This automatic target tracking algorithm is integrated by Adaboost and Median-Flow algorithm. It is used to track the pedestrians and locate the head of the target. Experiment results show that the dual-field imaging system and proposed algorithm has robust target tracking performance.
Backscattering metal gratings in QWIPs to increase the long wavelength infrared light absorption
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Nowadays, traditional infrared detectors such as MCT infrared photo detectors performance nearly reached their detect theory limits. As lead to an increased interest in detectors such as QWIPs, T2SL, QCD and so on. Due to the low cost, high integration level and high performance, QWIPs is a mainstream infrared photo detector in the areas of military, medicine industries. The problem blocked the QWIPs industry development is the low quantum efficiency because of the polarization dependence of the incident light. As decided by the absorption mechanism, the QWIPs cannot absorb the normal incident infrared light. Various methods is developed to couple the normal incident light to the QWIPs. The introduction of metal gratings proved to be efficient to improve the absorption of the normal incident light which can introduce a SPPs coupling on the interface of the gratings and the QWIPs. But in the method used before usually are transmission gratings on the surface of the QWIPs devices. A kind of backscattering metal grating patterns is designed and simulated in our work to get a higher performance. It is nearly 4 times of the coupling efficiency than the transmission gratings in simulation. We also discuss some grating parameters such as grating thickness and cycle duties for their effects on the coupling efficiency and optimize these parameters to reach a highest performance. The simulation results show a new promising structure use in the QWIPs especially in the dual-band QWIPs to enhance the absorption of the long wavelength infrared light.
An infrared image non-uniformity correction algorithm based on pixels’ equivalent integral capacitance
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In the infrared focal plane array (IRFPA) imaging system, the non-uniformity (NU) of IRFPA directly affects the quality of infrared images. Especially applying in the infrared weak small targets detection and tracking system, the impact of the spatial noise caused by the non-uniformity of IRFPA detector, often more serious than the temporal noise of imaging system. In order to effectively correct the non-uniformity of IRFPA detector, we firstly analyze main factors that cause the non-uniformity of IRFPA detector in imaging. Secondly, according to photoelectric conversion mechanism of IRFPA detector, and the analysis of the process of the target energy accumulation and transfer, we propose a calculation method of pixels' integral capacitance. Then according to the calculation results, we correct the original IR image preliminary. Finally, we validate this non-uniformity correction algorithm by processing IR images collected from actual IRFPA imaging system. Results show that the algorithm can effectively restrain the non-uniformity caused by the differences of the pixels' capacitance.
Surface morphology of LPE-growth GaSb quantum dots
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The self-assembled type-II GaSb quantum dots (QDs) were successfully grown on semi-insulting GaAs (100) substrate by the liquid phase epitaxy (LPE) technique with growth temperature ranging from 520 to 580 oC. The morphology of GaSb QDs including size, shape and density was investigated by atomic force microscopy measurement and scanning electron microscope measurement, respectively. The cap layer with scores of nanometers, which is characterized by Profile-system, is obtained for the photoluminescence measurement and device fabrication.
A hyperspectral image optimizing method based on sub-pixel MTF analysis
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Hyperspectral imaging is used to collect tens or hundreds of images continuously divided across electromagnetic spectrum so that the details under different wavelengths could be represented. A popular hyperspectral imaging methods uses a tunable optical band-pass filter settled in front of the focal plane to acquire images of different wavelengths. In order to alleviate the influence of chromatic aberration in some segments in a hyperspectral series, in this paper, a hyperspectral optimizing method uses sub-pixel MTF to evaluate image blurring quality was provided. This method acquired the edge feature in the target window by means of the line spread function (LSF) to calculate the reliable position of the edge feature, then the evaluation grid in each line was interpolated by the real pixel value based on its relative position to the optimal edge and the sub-pixel MTF was used to analyze the image in frequency domain, by which MTF calculation dimension was increased. The sub-pixel MTF evaluation was reliable, since no image rotation and pixel value estimation was needed, and no artificial information was introduced. With theoretical analysis, the method proposed in this paper is reliable and efficient when evaluation the common images with edges of small tilt angle in real scene. It also provided a direction for the following hyperspectral image blurring evaluation and the real-time focal plane adjustment in real time in related imaging system.
Quality evaluation of adaptive optical image based on DCT and Rényi entropy
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The adaptive optical telescopes play a more and more important role in the detection system on the ground, and the adaptive optical images are so many that we need find a suitable method of quality evaluation to choose good quality images automatically in order to save human power. It is well known that the adaptive optical images are no-reference images. In this paper, a new logarithmic evaluation method based on the use of the discrete cosine transform(DCT) and Rényi entropy for the adaptive optical images is proposed. Through the DCT using one or two dimension window, the statistical property of Rényi entropy for images is studied. The different directional Rényi entropy maps of an input image containing different information content are obtained. The mean values of different directional Rényi entropy maps are calculated. For image quality evaluation, the different directional Rényi entropy and its standard deviation corresponding to region of interest is selected as an indicator for the anisotropy of the images. The standard deviation of different directional Rényi entropy is obtained as the quality evaluation value for adaptive optical image. Experimental results show the proposed method that the sorting quality matches well with the visual inspection.
Terahertz digital holography image denoising using stationary wavelet transform
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Terahertz (THz) holography is a frontier technology in terahertz imaging field. However, reconstructed images of holograms are inherently affected by speckle noise, on account of the coherent nature of light scattering. Stationary wavelet transform (SWT) is an effective tool in speckle noise removal. In this paper, two algorithms for despeckling SAR images are implemented to THz images based on SWT, which are threshold estimation and smoothing operation respectively. Denoised images are then quantitatively assessed by speckle index. Experimental results show that the stationary wavelet transform has superior denoising performance and image detail preservation to discrete wavelet transform. In terms of the threshold estimation, high levels of decomposing are needed for better denoising result. The smoothing operation combined with stationary wavelet transform manifests the optimal denoising effect at single decomposition level, with 5×5 average filtering.
Strategies to improve system resolution in multiple configuration sensors
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System resolution in multiple configuration sensors is a typical problem in optimum research, facing among all kinds of image sensor, esp. in structured configuration system. Inspired to in order to reveal the configuration to improve system resolution, further technical requirement is proposed of the function and influence on the development of smart image sensors. To break the diffraction limit, multiple configuration is applied effectively. Criterion, such as MTF, PSF and so on is used to evaluate the features of the system. Therefore, The results show that they are effective solutions.
Integrated optics to improve resolution on multiple configuration
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Inspired to in order to reveal the structure to improve imaging resolution, further technical requirement is proposed in some areas of the function and influence on the development of multiple configuration. To breakthrough diffraction limit, smart structures are recommended as the most efficient and economical method, while by used to improve the system performance, especially on signal to noise ratio and resolution. Integrated optics were considered in the selection, with which typical multiple configuration, by use the method of simulation experiment. Methodology can change traditional design concept and to develop the application space. Our calculations using multiple matrix transfer method, also the correlative algorithm and full calculations, show the expected beam shaping through system and, in particular, the experimental results will support our argument, which will be reported in the presentation.
Fabrication of super-hydrophobic duo-structures
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Recently, super-hydrophobicity has attracted increasing attention due to its huge potential in the practical applications. In this paper, we have presented a duo-structure of the combination of micro-dot-matrix and nano-candle-soot. Polydimethylsiloxane (PDMS) was used as a combination layer between the dot-matrix and the soot particles. Firstly, a period of 9-μm dot-matrix was easily fabricated on the K9 glass using the most simple and mature photolithography process. Secondly, the dot-matrix surface was coated by a thin film of PDMS (elastomer: hardener=10:1) which was diluted by methylbenzene at the volume ratio of 1:8. Thirdly, we held the PDMS modified surface over a candle flame to deposit a soot layer and followed by a gentle water-risen to remove the non-adhered particles. At last, the samples were baked at 85℃ for 2 hours and then the duo-structure surface with both micro-size dot-matrix and nano-size soot particles was obtained. The SEM indicated this novel surface morphology was quite like a lotus leaf of the well-know micro-nano-binary structures. As a result, the contact angle meter demonstrated such surface exhibited a perfect super-hydrophobicity with water contact angle of 153° and sliding angle of 3°. Besides, just listed as above, the fabrication process for our structure was quite more easy, smart and low-cost compared with the other production technique for super-hydrophobic surfaces such as the phase separation method, electrochemical deposition and chemical vapor deposition etc. Hence, this super-hydrophobic duo-structure reported in this letter was a great promising candidate for a wide and rapid commercialization in the future.