Analog processing based carrier phase recovery and equalization for coherent optical receivers

Semiconductor lasers with unstable emission frequencies and large linewidths pose a big challenge for high degree of integration in coherent optical systems. Carrier phase & frequency offsets due to finite laser linewidths and the dispersion introduced by fiber non-idealities would be the major limiting factors in achieving higher data rates in future fiber optic links. Fortuitously, CMOS based digital signal processing has shown promise for these links. However carrier synchronization in digital domain can be slow for feedback loops and impose stringent constraints on the laser linewidths. Additionally, digital processing requires large power budget including overheads. To overcome these problems we propose an analog signal processing based QPSK receiver incorporating carrier phase recovery and adaptive equalization. A 20 Gbps QPSK receiver is demonstrated using simulations for 1 MHz laser linewidth and 50 km distance.