Experimental Investigation of a Recurrent Optical Spectrum Slicing Receiver for Intensity Modulation/Direct Detection systems using Programmable Photonics

Photonic computing and signal processing are rapidly regaining attention, capitalizing on the saturation of digital electronics capabilities, owed to the ending of the Moore's law era. Optical communications are among the fields in which digital signal processing (DSP) struggles to offer a viable long-term solution, as its power consumption rises significantly in the latest generation optical links. For example, the traditional intensity modulation and direct detection (IM/DD) systems suffer from challenging problems such as the chromatic dispersion induced power fading effect, which necessitates the use of powerful digital equalizers in the 800G and 1.6T optical transceivers. In this paper, we experimentally validate our previous numerical works in recurrent optical spectrum slicing (ROSS) accelerators for dispersion compensation in high-speed IM/DD links. For this, we utilize recurrent filters implemented both through a waveshaper and by exploiting novel integrated programmable photonic platforms. Different recurrent configurations are tested. The ROSS accelerators exploit frequency processing through recurrent optical filter nodes in order to mitigate the power fading effect, which hinders the transmission distance and baudrate scalability of IM/DD systems. By equalizing even 80 km of 64 Gb/s PAM-4 transmission in C-band, we prove that our system can offer an appealing solution in highly dispersive channels. We employ the simplest digital equalization in the form of a feed-forward equalizer (FFE), avoiding throughput, latency, and complexity restrictions that the decision feedback equalizer (DFE) and the maximum-likelihood sequence estimator (MLSE) impose. We achieve, with the use of programmable photonics, to reduce the bit error rate (BER) from 0.11 to less than 1x10-2 with the use of only two filter nodes, whereas BER approaches 10-3 when three nodes are incorporated. These results correspond to almost two orders of magnitude BER gain. © 2024 The Authors