Robust Dual-Wavelength DRoF Link by Quasi-2-bit 256-QAM OFDM With Delta-Sigma Modulation

We experimentally demonstrated a robust dual-wavelength digital radio-over-fiber (DRoF) link by quasi-2-bit delta-sigma modulated 256- quadrature amplitude modulation orthogonal frequency-division multiplexing (QAM OFDM) data. By optically constructing the 2-bit delta-sigma modulated data with the optical group delay compensation technique, the proposed system combined the advantages from either the conventional 2-bit or 1-bit system. Due to the benefits of higher signal-to-noise ratio and robust anti-nonlinearity to the optical links, the proposed approach performed the widest dynamic ranges of 25.78, 17.81, and 13.46 dB after 25-km single-mode fiber (SMF) transmission by using the 400-MHz 16-, 64-, and 128-QAM OFDM data, respectively. These values were much better comparing with either the conventional 2-bit or 1-bit system. Up to 256-QAM OFDM data with 400-MHz bandwidth was supported by the proposed system for transmitting over 25-km SMF at the lowest overall receiving power of -10.72 dBm. This work provided a good solution for the beyond 5G or 6G DRoF link applications.