Clone-comb-enabled high-capacity digital-analogue fronthaul with high-order modulation formats

Abstract

Access to the internet by mobile terminals relies on the transmission of information from the optical fibre backbone to wireless networks. Fronthaul, as the last mile of fibre-wireless convergence, determines the overall transmission performance in terms of capacity and fidelity. Orders-of-magnitude increases in both bandwidth and signal-to-noise ratio (SNR) are urgently desired to cope with the large growth in wireless traffic. Here we demonstrate a self-homodyne digital-analogue radio-over-fibre fronthaul using cloned optical frequency combs that meets these needs. The approach simultaneously supports an unprecedented 14.1 Tb s−1 common public radio interface equivalent data rate and a 1,024 quadrature-amplitude-modulated format. The clone-comb configuration, which possesses the properties of frequency and phase locking, is the key to enabling a high-performance coherent digital-analogue radio-over-fibre system. Besides exploiting the quadruple capacity for a single channel thanks to coherent detection, the clone-comb approach can also provide multiple parallel channels concurrently, boosting the overall data throughput. We further demonstrate the potential of the technique, showing its ability to transmit 65,536 quadrature-amplitude-modulated signals and a data rate of 32.8 Tb s−1. Our architecture is promising for fibre-based and free-space optical fronthaul, bringing full-band and coherent-lite access networks into reach.