Research on photoelectric signal preprocessing of four-quadrant detector in free space optical communication system

Abstract

In the free space optical communication system, the detection accuracy and detection speed of the beam deflection angle have an important influence on the tracking accuracy and tracking speed of the precision tracking system. The beam deflection angle is equivalent to the position detection of the laser spot on the photo-sensitive surface of the precision tracking detector. Using a four-quadrant detector to detect the spot position error in real time can effectively eliminate the spot jitter error through the correction mechanism. By analyzing the signal characteristics of the four-quadrant detector, a photoelectric signal preprocessing circuit for the four-quadrant detector output is designed and implemented. Including the transimpedance amplifier module, low-pass filter module, main amplification module. Finally, the spot position is calculated by the photocurrent in the four quadrants. Through theoretical calculation, physical modeling, simulation, the designed signal preprocessing circuit is verified by simulation. The simulation results show that the magnification of designed signal preprocessing circuit is 2×108 and the bandwidth is 1.97MHz, which can provide a strong guarantee for the calculation of the spot position of the four-quadrant detector.