Super receiver design for superchannel coherent optical systems

Abstract

Recently efforts have been focused on ultra-high speed optical communication systems which can support 1Tb/s per channel transmission. However, 1Tb/s over a single carrier requires either or both very high-level modulation format (i.e. PDM-1024QAM) and high baud rate. Therefore, grouping a number of tightly spaced "sub-carriers", to form a terabit channel has been considered and this has been refered to as a superchannel. Nyquist-WDM and Coherent Optical- OFDM (CO-OFDM) are the two approaches to achieve ultra-high spectral efficiency in superchannel coherent optical systems. In Nyquist-WDM systems, optical subcarriers are tightly packed at channel spacing near or equal to the baud rate, potentially inducing strong inter-channel interference (ICI). The traditional way to mitigate the impact of ICI is by applying aggressive optical filters to each channel; however this typically induces severe inter-symbol interference (ISI). In this paper, we investigate receiver architectures for Nyquist-WDM superchannel coherent systems, and propose a new "super receiver" architecture, which jointly detects and demodulates multiple channels simultaneously. Several joint DSP algorithms are developed and tested through experimental and simulated data. The simulation results showed that more than 5 dB ONSR gain was achieved comparing to conventional method at narrow channel spacing conditions.