Block Length Effect on 5.0 Gbit/s Real-time QPSK Intradyne Receivers with a Standard DFB Laser

For intradyne QPSK receivers, block phase estimation based on the Viterbi & Viterbi algorithm [1] has been reported to yield better OSNR results than differential detection. When a laser with large phase noise such as distributed feedback (DFB) laser is used, typically a higher error floor is observed with block phase estimation. With shorter block length, the bit-error rate (BER) floor for a 5.0Gbit/s real-time intradyne receiver was improved without large sacrifice in the low BER performance.