Experimental Investigation of Ultra-Fast CDR Scheme for High-Speed Free-Space Optical Data Transmission With Multiple Access

Time-division multiple access schemes such as time-slot coding (TSC) provide an effective and simple multi-user access framework for indoor free-space optical communications (FSO) with limited inter-user interference. For realistic multi-user scenarios employing TSC, clock data recovery is indispensable to achieve timing synchronization for different users, which lacks investigation in the previous study on TSC. In this paper, for the first time, we experimentally demonstrate a time-slot coded multi-user FSO system employing clock data recovery, in which a sum data rate of 40-Gb/s with bit-error-rate (BER) of each user around the 7% hard-decision forward error correction (HD-FEC) limit can be achieved. Moreover, to further improve the system performance, we propose a novel clock data recovery scheme for multi-user FSO systems employing TSC. Experimental results show that more than 3dB received optical power gain can be obtained to achieve the reference BER level of the 7% HD-FEC limit as compared to the system employing the conventional clock data recovery scheme. Higher-precision timing synchronization and ultra-fast convergence speed can also be achieved via our proposed clock data recovery scheme.