10 Tb/s PM-64QAM Self-Homodyne Comb-Based Superchannel Transmission with 4% Shared Pilot Tone Overhead
Journal article, 2018
We demonstrate transmission of a comb-based 10 Tb/s 50 × 20 Gbaud PM-64QAM superchannel using frequency comb regeneration to reduce carrier offsets and allow for self-homodyne detection. The regeneration is enabled by transmitting two optical pilot tones which are filtered and recovered in the receiver using optical injection locking and an electrical phase-locked loop. We show that by utilizing frequency combs together with optical pilot tones, self-homodyne detection similar to systems using one pilot tone per wavelength channel, can be achieved. Sharing the overhead for pilot tones reduces the complexity and limits the overhead to 4%. This enabled a total superchannel spectral efficiency of 7.7 b/s/Hz. To evaluate the performance, we perform both back-to-back measurements and transmission over 80 km of standard single-mode fiber. Successful self-homodyne detection of all 50 data channels in the 10-nm-wide superchannel demonstrates that the spectral coherence from frequency combs, combined with the use of optical pilots, can overcome limitations arising from frequency offset and phase noise in high-order QAM transmission while keeping the pilot overhead low.