利用光纤无源器件制作了光学90°混频器,实现了混频器90°相移的精确控制与监测,稳定时间达到12 h以上,利用此混频器研究并实现了数字相干光检测。对差分相移键控(DPSK)信号光和本振光进行混频,高速模数转换器(ADC)对混频后的基带信号采样,利用离线数字信号处理算法进行光载波相位估计和色散补偿,利用有限冲击响应(FIR)数字滤波器补偿了经过90 km光纤传输的8 Gb/s速率DPSK信号的色散失真,测量无误码。

An optical 90° hybrid based on fiber passive devices is developed to enable optical coherent detection. By introducing the optical phase difference monitoring and control,the hybrid is stabilized over 12 hours without apparent deterioration. With the help of this hybrid,the differential phase shift keying (DPSK) signal is demodulated by mixing signal light with local light,and then,is sampled and digitalized by high-speed Analog-to-digital converters(ADCs). Off-line algorithm is used to estimate the phase error between the signal light and local light and compensate chromatic dispersion. We restore the constellation diagrams of 8 Gb/s DPSK signal transmited over 90 km single mode fiber using FIR filter to compensate the fiber dispersion and get an error free result in our experiment.