Cascadability of Optical 3R Regeneration for NRZ Format Investigated in Recirculating Loop Transmission Over Field Fibers

This letter demonstrates optical 3R regeneration in 10-Gb/s nonreturn-to-zero field transmission. The 3R regenerator utilizes semiconductor-optical-amplifier-based Mach-Zehnder interferometer wavelength converters, a synchronous modulator, and a Fabry-Perot filter to realize optical 3R regeneration including all-optical clock recovery. The cascadability of the 3R regenerator is investigated in recirculating loop transmission experiments with various regeneration spacings up to 462 km (corresponding to an input optical signal-to-noise ratio (OSNR) of 22 dB). Transmission with the 3R regenerator shows significant performance improvement over that without 3R regeneration. A 66-km-spaced 3R regeneration with a 33-dB input OSNR achieves 1000-hop cascaded error-free transmission (66 000 km in distance) with no hop-to-hop power penalties. A 264-km-spaced 3R regeneration with a 25-dB input OSNR also achieves 100-hop cascaded transmission (26 400km in distance) with a bit-error-rate error floor at ~1times10^-8