Optical Axis Deviation Detection Technique Based On The Balanced Detector

Coherent optical communication has the advantages of high sensitivity and long transmission distance,so it is widely used in satellite communications.In order to achieve the detection of weak signals,we need to increase the sensitivity of the detector?Because we cannot get a result that the laser transmission power and the signal reception quality are all very high.The balanced detection method has higher detection sensitivity and signal-to-noise ratio than other detection modes,even close to the quantum limit.In laser communication,the communication distance is so far that the signal light going through the atmosphere will be subjected to the secondary modulation of the atmospheric channel,which will lead to the signal quality deterioration at the receiver part.This will make a very high demand of the alignment accuracy on the receiver side.Receiver-side optical axis alignment is the key to achieving satellite communication.In other words,how to use the signal light to complete the optical axis angle deviation precision detection has become the main point of this paper.This paper studies these problems which have a close relationship with the actual needs.It has an important application value.In this paper,we propose to detect the deviation angle of the optical axis under weak signal light.Then correct the error signal through the feedback circuit to adjust the angle of the fast mirror to realize the purpose of fine tracking.The theoretical solution shows that the technical scheme is reasonable and feasible.In this paper,the working principle of the balanced detector and the principle of optical axis deviation detection are described in detail.The isolation experiment is carried out to verify the error through analyzing the experimental results.Finally,the effect of the balanced detector is analyzed.The relationship between signal-to-noise ratio and response coherence coefficient under different bandwidth conditions is given by MATLAB simulation.The simulation results show that it can improve the signal-to-noise ratio and suppress the intensity noise of the local oscillator compared with single-ended detection.These works have some reference value for the design of coherent optical communication optical terminal system.