Low-Latency Synchronous Clock Distribution and Recovery for DWDM-OFDMA-Based Optical Mobile Backhaul

In this paper, we propose and experimentally verify a low-latency digital signal processing (DSP)-free synchronous clock distribution and recovery scheme for high-speed dense wavelength division multiplexing orthogonal frequency division multiple access (DWDM-OFDMA)-based mobile backhaul (MBH) systems. The synchronous clock distribution is achieved jointly with high-speed OFDMA data signal transmission through a simple and low-cost intensity-modulation direct-detection (IMDD) optical backhaul architecture that also guarantees clock time and frequency stability. We experimentally verify aggregate 41.09-Gb/s (7λ × 5.87 Gb/s/λ) DWDM-OFDMA data rates with distribution and recovery of 50-MHz square wave and 4-GHz sinusoid clocks over 40 km standard single mode fiber (SSMF) with spectrally-efficient 25-GHz channel spacing and no remote optical amplification. To demonstrate the flexibility of the proposed system, aggregate 51.31-Gb/s (7λ × 7.33 Gb/s/λ) DWDM-OFDMA transmission with 50-MHz square wave and 5-GHz sine wave clocks is also experimentally evaluated. Highly precise time and frequency accuracy is achieved, featuring an order of magnitude improvement with respect to LTE-Advanced (LTE-A) synchronization requirements. By supporting high bit rates, high spectral efficiency, and low-latency synchronization, the proposed approach is promising for future optical MBH.