An Experimental Demonstration of Rate-Adaptation Using Shaped Polar Codes for Flexible Optical Networks

In this paper, we propose a polar-coded transmission system with adjustable data rate for coherent optical transmission employing quadrature amplitude modulation (QAM). The proposed system is based on a many-to-one constellation shaping method for achieving a range of data rates with arbitrarily small rate steps. An implicitly punctured polar-coded modulation system is then designed by combining polar coded bit-interleaved coded modulation system with many-to-one labelings. The scheme is experimentally evaluated in a wavelength division multiplexed (WDM) system with five carriers modulated at 16 GBaud with polarization multiplexed (PM) 256QAM. Data rates ranging from 121 to 182 Gb/s per carrier are experimentally demonstrated and the system can be directly extended to achieve higher data rates. Synchronization and equalization of PM-256QAM received symbols are performed with a pilot rate of 5%. The experimental results show 1.2 dB of shaping gain over the conventionally punctured polar codes in the optical back-to-back scenario. The maximum transmission system reach is increased by 200 to 400 km w.r.t the conventionally punctured polar codes. It is shown that the rate adaptation does not require a change of modulation format and/or underlying forward error-correction code. Finally, the performance of all five WDM channels is validated for the optimal input power.