Optical Clock Recovery and 3R Regeneration for 10-Gb/s NRZ Signal to Achieve 10 000-hop Cascadability and 1 000 000-km Transmission

This letter experimentally demonstrates all-optical clock recovery and optical 3R regeneration for a 10-Gb/s nonreturn-to-zero (NRZ) format. The 3R regenerator has achieved 10 000-hop cascadability and 1 000 000-km transmission for a pseudorandom bit sequence (PRBS) of 2⁷-1. A semiconductor-optical-amplifier-based Mach-Zehnder interferometer (SOA-MZI) as an NRZ to pseudoreturn-to-zero converter and a Fabry-Perot filter perform the all-optical clock recovery from an NRZ signal. A pair of SOA-MZIs combined with a synchronous modulator provides the 2R regeneration and retiming functions. The cascadability of the 3R regenerator is investigated in a recirculating loop transmission experiment by eye diagram, bit-error rate, and Q-factor measurements. Transmission with the 3R regenerator shows significant performance improvement over that without 3R regeneration. A 100-hop cascadability is also demonstrated for PRBS 2³¹-1, enabling 10 000-km error-free transmission with a low power penalty of 1.2 dB