A photoconductive switch with 4H-SiC as the substrate material and the same-side electrode structure is developed. The test results show that when using a hundred picosecond laser pulse as the trigger source, the device can achieve an ultra-short electrical pulse response of hundred picoseconds, that is, it can output Gigahertz-level wide-spectrum signal. Through the experimental circuit built, under the condition of certain bias voltage and light pulse width, the pulse width of the electrical signal is tested when the energy of the light pulse changes within the range of 0.3-4.4 mJ. The experimental results show that the stronger the energy of the irradiated light pulse, the wider the pulse width of the response electrical signal of this switch.
A coplanar photoconductive switch based on vanadium-nitrogen doped 4H-SiC bulk material was developed. The test results show that the combination of vanadium doping and coplanar electrode structure, the voltage capability of 4H-SiC photoconductive switch is significantly improved and the conductive resistance of 4H-SiC photoconductive switch under low light intensity is reduced. The bias voltage of 4H-SiC photoconductive switch is 10kV. The conductive resistance of 4H-SiC photoconductive switch excited by 0.5mJ 532nm laser is 21Ω. In the conjugate matching link, the ouput peak power on the load is 0.3MW. The conductive resistance of 4H-SiC photoconductive switch excited by 2.5mJ 532nm laser is less 1Ω. In the conjugate matching link, the ouput peak power on the load is 6.25MW. The results show that the developed vanadium-nitrogen doped 4H-SiC photoconductive switch has the characteristics of stable output waveform, small jitter and high power. Low conductive resistance can be obtained at low light intensify. The developed vanadium-nitrogen doped 4H-SiC photoconductive switch has certain application value.
A complementary coplanar interdigital electrode photoconductive switch based on vanadium-nitrogen doped 4H-SiC bulk material was developed. The test results show that the combination of vanadium doping and coplanar interdigital electrode structure, the voltage capability of 4H-SiC photoconductive switch is significantly improved and the conductive resistance of 4H-SiC photoconductive switch under low light intensity is reduced. The bias voltage of 4H-SiC photoconductive switch is 10kV. The conductive resistance of 4H-SiC photoconductive switch excited by 0.4mJ 532nm laser is 50Ω. In a 50 Ω microwave system, the peak power output by the load is 0.5MW. By continuously increasing the injected laser energy to 2mj, the on resistance can be reduced to 6 Ω. The results show that the developed vanadium-nitrogen doped 4H-SiC photoconductive switch has the characteristics of stable output waveform, small jitter and high power. The developed vanadium-nitrogen doped 4H-SiC photoconductive switch has certain application value.
When the spatial visible light camera images the detection target, non-imaged light in the space also reaches the imaging surface through the lens, forming an image on the detector. Some of the light is imaged on the image surface after multiple reflections inside the lens. These non-target images affect the image quality of the camera. In severe cases, the camera may not work properly. In order to reduce the influence of stray light on the imaging system and improve the imaging performance of the camera, firstly, the generation mechanism of stray light in the visible light system is analyzed, and the stray light suppression measures are proposed. Secondly, the system is then analyzed using ZEMAX software. The optical system design of the camera with the previous stray light problem was improved, and the stray light modeling analysis was performed on the improved result, and finally the space reconnaissance camera that satisfies the use requirements was obtained.
This paper reviews the research progress of liquid crystal optical phased array (LCOPA) devices in space laser communication applications. According to the constraints of space applications and system requirements, in the design and key technologies of array devices, the research progresses on the implementation methods such as wide-point range, large-aperture optical aperture, short response time, and space environment adaptability are emphatically introduced. In introducing the wide beam pointing range, the beam control method and the digital concatenation scheme are mainly described. In the study of large aperture, the area filling module and the area selection module are separately analyzed. And comparatively expounded the realization of sub-millisecond order rapid response of liquid crystal materials, and finally gave the United States Air Force laboratory's research on the liquid crystal optical phased array device irradiation environment adaptability research results.
Ship target detection is increasingly important to the current war today. Space-based Detection is an important way for getting the remote-sensing image included the ship target. Ship target characteristics analysis is the key of infrared image reorganization. It includes the thermal radiation of the target and background, Atmospheric transmission characteristics, imaging characteristics of detector and target characteristics. In order to get the simulation image in the infrared long-waveband, it analyses the characteristics of the infrared ship target and background. The target characteristics are known clearly, it could make the extraction process of target more effective and accurate. The target characteristics analysis is more conducive to the detection and recognition of the target.
The image pattern recognition can accurately identify and locate the target, but image pattern recognition is unable to
accurately recognize the distorted targets (the targets rotated in plane or scale changed), which has restricted the
development of the image pattern recognition. In order to solve the problem of inaccurate recognition for distorted target
in cluttered background among the image pattern recognition, the distorted target images and the training images are
edge extracted by canny operator. The Optimum Trade-off Maximum Average Correlation Height (OT-MACH) filter is
synthesized with the edge extracted training images. The low frequency information of the distorted target images and
the filter is enhanced. Then the edge extracted distorted target image is filtered by the OT-MACH filter. Thereby, the
distortion tolerance of the OT-MACH filter is expanded. It can respond higher correlation peaks and have higher
distortion tolerance to recognize various types of distorted targets in cluttered background. By this method, which the
space edge extraction combines with frequency domain filtering, the scale distortion tolerance is 0.72~1.42 times; the
rotation distortion tolerance can reach up to 70 degrees. In order to prove the feasibility of this method, a lot of computer
simulation experiments have been done with the canny operator and the OT-MACH filter.
With the development of the technology of infrared, infrared optical system has been widely used in many fields, especially in tank target detection and recognition. The difficulty and key in the designing of LWIR optical systems for working under temperature range of -60°C~80°C is athermalization. In this paper, the infrared telephoto lens is designed which is composed of four pieces of lenses. The working temperature range is -60°C~80°C. In order to balance the chromatic aberration and thermal aberration, two aspherical surfaces are used in this cooled athermalized infrared optical system. The effective focal length is 100mm and the F-number is 2.The full field of view is 7.0°. The curve of MTF is close to diffractionlimit curve. Within the working temperature, the value of MTF at 17cy/mm is always large than 0.4. The result shows that the infrared optical system achieved better athermal performances at the working temperature range.
In order to solve the problem of inaccurate recognition for distorted target (the targets rotated in plane or scale changed)
in cluttered background among the image pattern recognition, combined with the Mexican Hat mother wavelet and the
Optimum Trade-off Maximum Average Correlation Height (OT-MACH) algorithm, the Mexican Hat Optimum Trade-off
Maximum Average Correlation Height (Mexican Hat OT-MACH) matched filter is designed. The Mexican Hat OT-MACH filter is obtained to recognize distorted target in cluttered background. The wavelet functions have the
multi-scale characteristic and can analyze the specific frequency information. Moreover, the Optimum Trade-off Maximum Average Correlation Height algorithm (OT-MACH) has three characteristics, namely high distortion tolerance,
suppressing noise and sharpening the correlation peak. Therefore, the new designed matched filter contains all the characteristics of the wavelet function and OT-MACH algorithm. In order to balance all the performances of the new designed Mexican Hat OT-MACH matched filter, the performance control parameters and the scale coefficient of the
Mexican Hat OT-MACH matched filter need to be set. Thus, the new designed Mexican Hat OT-MACH matched filter has high versatility. It can respond higher correlation peaks and has higher distortion tolerance to recognize various types of distorted targets in cluttered background. In order to prove the feasibility of the Mexican Hat OT-MACE filter and determine its distortion tolerance, a lot of computer simulation experiments have be done with the filter. Good effect can be obtained.
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