Experimental Study of Free Space Coherent Optical Communication on 1km

Abstract

A 1.3km free-space coherent optical communication experimental platform is set up. The changing polarization, wavefront of the laser after transmission over the atmospheric channel is analyzed, and the influence on the intermediate frequency (IF) signal is also analyzed. The results show that the polarization state of the laser is slowly changing after 1.3km transmission. When the polarization state of the signal light is controlled, the peak value of the output IF signal is increased by 0.5V and the mixing efficiency increased by 19%. The slowly changing of wavefront can directly affect the coupling efficiency of spatial light coupling into the fiber. Importantly, after the wavefront correction, the coupling efficiency is increased by 30 times, and the peak value of the IF signal is increased by 1V, thus, the mixing efficiency is increased by 20%. Moreover, both ends of the communication can complete continuously and smoothly transmission of the video signal, and the bit error rate of the communication system is below 10-9.