Research On The Optical Receiver In Coherent Optical Communication System

The coherent optical receiver does not only have a high sensitivity, a long relay distance, a good selectivity, and a high communication capacity; it also supports multiple modulation modes. The coherent optical receiver has been attracting more attention again, when optical devices and digital signal process technologies have gained huge improvements in recent years.This paper describes the design of an optical receiver with wide-band and high sensitivity. This optical receiver is used for processing base-band signal in coherent receiving. The PIN-TIA with high sensitivity and the LA-CDR with low jitter were chosen to compose the optical receiver and the chip PTCM965-002 and AND 2812 were selected. The optical receiver was carefully designed with basic diagrams and the PCB design was debugged and tested. The result indicated the optical receiver achieved a good performance. It can receive the optical signal with high modulate frequency from 1Gbps to 2.5Gbps and the sensitivity can reach -24.8dBm, -23.5dBm, -22.7dBm, -21.7dBm at 1Gpbs, 1.25Gpbs, 2.5Gbps, 2.7Gpbs respectively.In this paper, the theory of coherent detection and the coherent demodulation schemes were introduced. The designed heterodyne coherent optical receiver with balanced detection and asynchronous demodulation schemes has been simulated to demonstrate how linewidth of laser, power of local laser and modulate frequency influence the performance of the coherent optical receiver. The simulation results show that narrow linewidth of laser, high power of local laser and low modulate frequency generate a coherent optical receiver with high sensitivity.In this paper, the high gain, wide band and low noise amplifier was designed to amplify the intermediate frequency signal in coherent optical receiver. The tap transmission lines and the amplifying chip AMMP-6220 were adopted in the design scheme. The gain ripple of the amplifying chip can be improved by adjusting the size of the tap transmission lines, include its width and length, which is also proved by the simulation. Finally the PCB of the amplifier was designed based on the optimized simulation and was tested after debugging. The result indicates that the band-width of the amplifier is from 6GHz to 14GHz; the gain is 20dB; and the gain ripple keeps below 1dB from 6GHz from 12GHz.