Gerchberg-Saxton Based FIR Filter for Electronic Dispersion Compensation in IM/DD Transmission Part II: Experimental Demonstration and Analysis

In this article, the first experimental demonstration of a non-iterative electronic dispersion compensation (EDC) solution implemented at the transmitter using a finite impulse response (FIR) filter optimized with the Gerchberg-Saxton (GS) algorithm, is presented, for intensity-modulation and direct-detection (IM/DD) systems. The theoretical framework for the GS FIR filter and preliminary simulations have been presented in Part I of this work. Here, the performance of the GS FIR filter is compared to that of the iterative GS algorithm in the transmissions of 56-Gb/s on-off keying (OOK) over 80&#x00A0;km of single mode fiber (SMF) with a post feed-forward equalizer (FFE) for combating residual inter-symbol interference (ISI). Furthermore, the influence of the pulse shape (raised cosine or rectangular) and modulation format (return-to-zero (RZ) or non-return-to-zero (NRZ)) on the measured bit error ratio (BER) is experimentally investigated, while changing the number of FIR taps, the number of post-FFE taps, and the number of post-FFE samples-per-symbol. It is shown that within the range of the target digital extinction ratios (DERs) for which the original iterative GS algorithm offers benefit, both analytical and numerical methods for calculating the optimum FIR taps, outlined in Part I of this work, produce similar BER performance as predicted. To that end, the former method is extended, here, through a non-recursive frequency response formula, which offers insight into the action of the GS filter with different pulse shaping and enables the derivation of the explicit GS impulse response. It is also shown that rectangular RZ pulse shaping exploits the full benefit of GS filtering through a uniform spectrum, enabling a BER below the 7&#x0025; hard-decision forward error correction (HD-FEC) limit, with a 641-tap <italic>T</italic>/2-spaced pre-EDC FIR filter and a 3-tap adaptive <italic>T</italic>-spaced post-FFE.