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Partial response (PR), or correlative coding techniques, most commonly employed in the form of duobinary or polybinary schemes, can shape signal spectra, thus mitigate performance penalties due to non-ideal channel. In this work, we investigate the advantages of a family of PR encoders of the type (1+ D ) n , which are applied digitally to pulse amplitude modulation (PAM) in a bandwidth-limited intensity modulation and direct detection (IM/DD) system. Precoding is applied to enable memoryless decoding of PR signals based on a multilevel slicer and modulo operation. To quantify the improvements possible with the schemes under study, we simulate the signal-to-noise (SNR) advantage achievable with PR signaling in comparison to PAM for various transmitter and receiver bandwidths. The simulation results show that PR signaling can improve the performance when operating under a bandwidth constraint of approximately 0.44 symbol rate and lower. An experiment involving a high-speed IM/DD transmission is conducted, wherein the performance between different PAM and PR signals is compared. Highest net bitrate is achieved using (1+ D )-PAM-8 signal at 200 GBd, yielding a record net bitrate of 510 Gbit/s for an IM/DD link employing baseband modulation.
Hu et al. (2024) studied this question.