Research of range image on non-scanning LADAR based on APD arrays

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.