Iterative Algorithm for Electronic Dispersion Compensation in IM/DD Systems

A novel iterative algorithm for electronic dispersion compensation (EDC) at the transmitter is described and demonstrated for intensity modulation and direct detection (IM/DD) systems. The proposed algorithm is based on the Gerchberg-Saxton (GS) algorithm, where the link dispersion performs time-to-frequency mapping, while the unconstrained phase at the direct detection receiver acts as a degree of freedom. Simulation results for a transmitter employing a single drive Mach-Zehnder modulator (MZM) operating at 28 Gb/s non-return-to-zero on-off keying (NRZ-OOK), show pre-compensation of upto 100 km of single mode fiber (SMF), with 1 dBQ margin above the forward error correction (FEC) bit error rate (BER) limit of 3.8 \times 10^{-3}. It is shown that with five iterations of the proposed EDC algorithm in digital-signal processing (DSP) coupled with an 8-bit 56 GSa/s digital-to-analog converter (DAC), the transmission reach is extended by a factor of 5 in unamplified SMF links. Simulations for a 56 Gb/s four-level pulse-amplitude-modulation (PAM-4) show the compensation of upto 10 km with five iterations of the EDC algorithm at 1 dBQ above the FEC limit.