Robust channel estimation in optical OFDM via IQ separation pulse compression noise rejection.

We introduce an innovative channel estimation technique, in-phase and quadrature separation pulse compression noise rejection (IQS-PCNR), for intensity modulation and direct detection (IMDD) optical orthogonal frequency division multiplexing (OFDM) systems. IQS-PCNR uses pulse compression to estimate the channel impulse response (CIR) and employs a noise rejection window to mitigate residual noise, resulting in significant performance improvements. Experimental results show that IQS-PCNR outperforms conventional methods, such as least squares (LS) and intra-symbol frequency-domain averaging (ISFA), while preserving comparable complexity. Specifically, IQS-PCNR provides a 2.87 dB and 0.61 dB enhancement in optical receiver sensitivity, along with a 3.65 Gbps and 1.85 Gbps increase in achievable bitrate at the hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10^-3, after transmission over a 2-km standard single-mode fiber (SSMF) link, compared to LS and ISFA, respectively. Additionally, IQS-PCNR enables the generation of real pilot signals with greater hardware efficiency.