Coherent subcarrier multiplexing system with distributing local oscillator in local loop

The proposed system can realize multichannel transmission with one optical carrier by using the subcarrier multiplexing (SCM) technique and has no need for LOs at each station. The SCM system uses a bandpass filter to select a specific channel. The carrier-to-noise ratio (CNR) of the system is analyzed with frequency-shift keying (FSK) in a multioctave configuration. A general expression of the CNR is derived and is shown for parameters such as the number of channels, the position of the station on the loop, and the number of stations on the loop. The optimal CNR, the minimum required power of the lasers, and the maximum number of stations that the system can serve are shown. The CNR of the system is compared with that of a system having LOs at each station in the local loop. It is shown that the proposed system can obtain good performance at the expense of a slight increase of the output power of only two lasers at the central station. Therefore, the system is cost-effective and practical