Optimization of Time-Division Hybrid-Modulation and its Application to Rate Adaptive 200Gb Transmission

Today 100G transmission systems are well established on market using coherent dual polarization QPSK technique. The evolution towards 400G implies the application of a dual carrier approach with 16QAM modulation each. The application of the more complex modulation scheme requires a ~+7dB increased OSNR leading to a drastic decrease in maximum transmission reach. Increased overhead error correction has been proposed to extend the reach limits further. The power consumption of strong FECs is huge [1] and rate adaptive FEC may be a good solution to minimize the FEC processing to the reach requirements [2]. Rate adaptive FEC at constant net rate requires a variable gross rate. In this paper we target the application of time-division hybrid-modulation formats (TDHM) for rate adaptive FEC, which has been introduced recently to increase the spectral efficiency granularity given by regular nQAM modulation schemes [3,4,5], to vary the gross rate and therewith the FEC overhead of 200G channels. As a benchmark we are considering systems with either 32 GBaud or 28 GBaud and 16QAM modulation. The paper targets the theoretical and experimental optimization of the 16QAM /8QAM TDHM technique including sFEC decoding as well as the final comparison of optimized formats in maximum transmission reach.