PERFORMANCE EVALUATION OF COHERENT SUBCARRIER MULTIPLEXED OPTICAL-DISTRIBUTION SYSTEMS WITH COMMON LOCAL OSCILLATORS

Abstract

Coherent subcarrier multiplexed local distribution systems using a common local oscillator (LO) in which the LO is provided by a distribution centre instead of locally generated at the subscriber premise are described. Both single and multiple optical carrier systems are considered. Because of the low path loss in a local optical network, a common LO system is possible with a LO shared by many subscribers, and indeed provides many advantages. First, a simplified receiver is achievable which eliminates a tunable LO, an automatic frequency control (AFC) circuit, a polarisation controller, and an optical coupler. Secondly, the system cost is decreased due to the reduction of components. Thirdly, laser phase noise and intermediate frequency (IF) drift are expected to be minimised. Fourthly, because no active optical components are placed at the subscriber premises, the system reliability is increased. Fifthly, the common LO system can be expanded with optical amplifiers without increasing the number of LO and simultaneous amplification of the message, and LO signals are achievable. By sharing high power, highly frequency stabilised, and very narrow linewidth LO lasers provided by the centre, it is expected that a simple and reliable coherent optical distributing network can be constructed by using common LO.