Low complexity sub-baud rate sampling reception in a bandwidth-limited IM/DD system

This Letter presents what is to our knowledge a novel approach to reduce the digital signal processing (DSP) complexity in intensity modulation and direct detection (IM/DD) systems, which is critical for short-reach optical communication systems with severe bandwidth limitations. We propose a sub-baud rate sampling reception method utilizing a polyphase feedforward equalizer-based maximum likelihood sequence estimation (PFFE-MLSE), which could operate effectively under a sampling rate of 0.6 samples per symbol. This new architecture eliminates the need for resampling, allowing the adaptive equalizer to operate with significantly reduced complexity-over 60% compared to traditional FFE-MLSE. An offline experiment, transmitting a 100-Gbaud on-off keying (OOK) signal over a 5-km single-mode fiber (SMF) link, demonstrates the feasibility of our approach with bit error ratio (BER) meeting the KP4-forward error correction (KP4-FEC) threshold in the optical back-to-back (OBTB) scenario and 7% hard-decision FEC (HD-FEC) threshold in the 5-km SMF transmission.