Experimental Demonstration of Non-Integer Fractionally-Spaced Equalization for Flexible Coherent Receivers

In this paper we present a general approach for dual polarization non-integer butterfly fractionally-spaced equalization (FSE) combined with a static frequency-domain electronic dispersion compensation (EDC). We experimentally demonstrate the ability of the above mentioned digital signal processing (DSP) scheme to compensate for linear impairments in optical transmission systems for various sampling rates corresponding to a number of samples-per-symbol (SPS) ranging from 1.25 to 2.5. We successfully transmit a 10 GBaud quaternary phase-shift keying (QPSK) signal over up to 3666 km standard single mode fiber (SSMF) using the suggested DSP. The non-integer FSE shows similar performance with enhanced flexibility in the receiver DSP, together with the capability of relaxing the required analog-to-digital conversion (ADC) sampling rates, compared with an integer FSE. The non-integer FSE with less than two SPS, shows a comparable performance with FSE realizations with two SPS or more, and outperforms symbol-spaced equalization by up to 4 dB in Q factor.