KEYWORDS: Signal to noise ratio, LIDAR, Sensors, Semiconductor lasers, Amplifiers, Avalanche photodetectors, Signal detection, Target detection, Photodetectors, 3D acquisition
Active multi-spectral detection technology is used to acquire the information of the targets,such as spectrum, distance,
intensity, and location and so on. So the active multi-spectral detection technology becomes one of the main trends of
development of detection system in the future. Based on the analyzing the theory of streak tube lidar active multi-spectral
detection system, we design a wavelength conversion circuit which can be applied to implement wavelength conversion
in the streak tube lidar in the active multi-spectral detection. Through the O-E-O conversion mode, the wavelength of
laser echo signal which contains the target information is transformed into another wavelength which represents the
spectral peak response wavelength of the stripe tube photocathode. The simulation results show that when the input laser
echo signal wavelength is 1.55um, and the after-converted wavelength is 0.85um , the photon conversion efficiency can
reach 2.2×106 ,the signal to noise ratio can reach 19.3dB. And when the target distance or the signal bandwidth
increases, the signal to noise ratio(SNR) will decrease accordingly.
Compared to scanner imaging ladar, non-scanning LADAR plays a more prominent role in the militarily imaging
scenarios. Non-scanning LADAR has many advantages, such as structure simplicity, high reliability, imaging efficiency
and etc. However the range accuracy is low. This paper proposes a technique to use a designed delay line module in the
APD array LADAR systems, which could significantly improve the range accuracy in all channels. A semiconductor
laser is used as light source. A 5×5 APD array detector is adopted as the sensitive unit. A 25 channel parallel amplifier
circuit is designed to process the signal with bandwidth 240 MHz . Field Programmable Gate Array (FPGA) is used to
process these 25 signals paralleled, with a delay line module designed, to significant improve the ranging accuracy .The
clock frequency of FPGA is 400MHz with accuracy 2.5ns. The delay lines module are used to measure part of pulse
flying time, which is shorter than the clock cycle and could not be directly measured by the clock, and that is the cause of
the ranging accuracy. Every delay cell is 46picoseconds , total timing accuracy is less than 500picoseconds. By using
above technique, a short distance imaging experiment is presented and get the 5 ×5 pixels range image. The result is
analyzed together with the factors, which influence the accuracy of ranging image, it shows the ranging accuracy of each
pixel is 10cm. And some advanced methods are proposed to improve the accuracy of the system in the future.
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