Research On Isolation Of Laser Communication Ground Testing Equipment

Laser communication technology is a long-distance wireless communication technology that uses laser as an information carrier,and is one of the important components of communication technology in today's era.Before the space laser communication terminal is put into useing,it is necessary to perform performance tests and index verification tests under laboratory conditions,so developing laser communication ground detection equipment is very important.Compared with the actual communication distance,the distance between the terminal under test and the ground detection equipment is very limited.The echo between the two terminals becomes an important influencing factor of the test,which will reduce the test credibility.Furthermore,current laser communication terminals mostly use a duplex mode of operation.The backward reflection and scattering of optical components of the optical system will cause crosstalk of the transmitted and received beams,which will limit the isolation level between the transmitting and receiving branches of the laser communication ground detection equipment.Based on the above background,in order to improve the detection accuracy of the laser communication ground detection equipment,this article has conducted a detailed study on the isolation between two terminals and the isolation of transmission and reception.The details are as follows:1)After Analyzing and comparing various typical optical antennas,we select common off-axis three-reflection optical antennas and Cassegrain optical antennas according to the design indicators,and use Zemax software to complete two optical antennas and each rear branch Optical design and image quality analysis.2)Aiming at the short distance between the laser communication ground detection equipment and the terminal under test,the definition and calculation method of the isolation between the terminals are proposed.Through theoretical analysis,it is found that the isolation level between the terminals is proportional to the isolation level of the optical antenna,and the isolation of the optical antenna is related to the structure type and mirror roughness of the optical antenna.The simulation experiment with tracePro software proves that the isolation of the off-axis three-reflection optical antenna is better than the Cassegrain optical antenna,and the isolation level of the optical antenna increases with the decrease of the roughness.Under laboratory conditions,the equivalent isolation between terminals was verified by experiments.3)Aiming at the problem of signal optical crosstalk between the transmitting and receiving branches of the laser communication ground detection equipment,the various optical splitting methods of the transmitting and receiving branches are analyzed and compared,and a scheme of using the polarization splitting principle to realize the separation of the receiving and transmitting beams is proposed.The principle of polarization beam splitting is derived theoretically,and the definition and calculation method of the transmit and receive isolation of laser communication ground detection equipment are proposed.According to theoretical analysis,it is found that this parameter is mainly affected by stray light reflected by the quarter-wave plate and the optical antenna.Based on two main influencing factors,a scheme for improving the isolation of transmission and reception is proposed.Under laboratory conditions,polarization splitting and transceiver isolation improvement schemes were experimentally verified.This paper's research on the optical design and the isolation between terminals and the transceiver isolation of the integrated laser communication ground detection equipment has some guiding significance for practical engineering applications.