A Method for Improving the Detection Accuracy of the Spot Position of the Four-Quadrant Detector in a Free Space Optical Communication System

Abstract

In a free space optical communication system, the beacon light will lose most of its energy after long-distance transmission, and the background light from the universe will strongly interfere with it. The four-quadrant detector (4QD) has been widely used in optical communication systems as a high-precision spot position detection sensor. However, if the light signal falling on the 4QD is too weak, the electrical signal of the output position will be very weak, and it will easily be affected by or even submerged in noise. To solve this problem, we propose a method for improving the spot position detection accuracy. First, we analyzed the solution relationship between the actual position of the spot and the output signal of the 4QD, with a Gaussian spot as the incident light model. The output current signal of the detector was then transimpedance-amplified by an analog circuit and the output voltage signal with noise was digitally filtered. An error compensation factor and the gap size of the detector were introduced into the traditional spot position detection model. High-precision spot position information for the 4QD in a complex environment was then obtained using the improved spot position detection model. Experimental results show that the maximum spot position detection error for this method was only 0.0277 mm, and the root mean square error was 0.0065 mm, when the 4QD was in a high background noise environment. The spot position detection accuracy was significantly improved compared with traditional detection algorithms. Real-time detection can therefore be achieved in practical applications.

High-Precision Position Detection and Communication Fusion Technology Using Beacon Spread-Spectrum Modulation with Four-Quadrant Detector

“…In [9], the nonlinear characteristics of spot detection positions are analyzed, and a linear correction method based on the Boltzmann function is proposed. In [10], error compensation factors and detector gap sizes are introduced into the spot position-detection model while digital filtering is applied to the detected light signals, thus enhancing the precision of spot position detection. In [11,12], a neural network for backpropagation is constructed by analyzing measurement data, and a neural network-based method that enhances the measurement precision of QD is presented.…”

Cartridge-type piezostack deformable mirror with reduced cross-section of control elements

“…Traditional closed-loop adaptive optical system contains three main elements: control unit [20] , wavefront sensor [21] and wavefront corrector -key element [22] . However, such systems could be equipped with additional elements like quadrant sensors [23] , tip-tilt correctors [24] , extra cameras for imaging [25] . Nevertheless, crucial role in aforementioned systems plays wavefront correctors.…”

Research on Quadrant Detector Multi-Spot Position Detection Based on Orthogonal Frequency Division Multiplexing

“…In [9], the relationship between the position of the spot position and the output signal of QD is obtained by combining the opposite error characteristics of the infinite integral method and Boltzmann method, which reduces the position detection error of a different spot radius. In [10], an error compensation factor and the gap size of the detector are introduced into the traditional spot position detection model. The high-precision spot position information of the QD in a complex environment is obtained by using the improved spot position detection model.…”