A novel millimeter-wave-band radio-over-fiber system with dense wavelength-division multiplexing bus architecture

In this paper, we propose a novel millimeter-waveband radio-over-fiber (RoF) system with a dense wavelength-division multiplexing (DWDM) bus architecture. Two lasers with a small wavelength difference, phase locked and polarization aligned, are allocated at a central station (CS) for connecting the CS and each base station (BS), one laser for transmitting and the other for detection (the remote local oscillator). For the conceptual illustration, we consider a DWDM RoF system with a channel spacing of 12.5 GHz and RF of similar to 30-GHz millimeter-wave band. In the downlink system, a single-sideband (SSB) subcarrier is used with low RF imposed on an optical carrier at the CS, and an millimeter-wave-band RF signal is obtained at each BS using direct photodetection by the SSB subcarrier beat with the remote oscillator. In the uplink system, the received millimeter-wave-band RF signal at each BS is imposed on the two optical carriers simultaneously, one optical carrier with the closest SSB subcarrier is optically filtered out and fed into in the uplink transmission fiber without frequency interleaving; the electrical signal with a low IF can be photodetected directly at the CS. Such an RoF system has simple, cost-effective, and maintenance-reduced BSs, and is immune to laser phase noise in principle.