Misalignment Analysis of a High-speed Uplink OWC System Based on a 940-nm VCSEL

In this letter, we experimentally proposed a high-speed long-distance uplink optical wireless communication (OWC) system based on a commercial 940-nm VCSEL for the first time. To the best of our knowledge, the system can reach a record-high data rate of 4.81 Gbps over 12-m transmission with a BER lower than the FEC floor of $3.8\times 10 ^{-3}$ among existing commercial VCSEL based long-distance OWC systems. Orthogonal frequency division multiplexing (OFDM) with adaptive bit-power-loading scheme is applied to improve the performance. We also built an mathematically equivalent model over 1.3 m to facilitate setting up optical link, reducing impact of link variation, and analyzing effect of link misalignment for a relatively long distance. Based on experimental and theoretical results, we presented a closed-form expression of the data rates versus the receiver offset distance by curve fitting. Newly calculated results differ from the actual measurements by no more than 4%, which demonstrates the validity of this empirical evaluation model of link misalignment.