Bandwidth-Flexible WDM System Based on Homodyne Detection and Power Splitting Configuration

Abstract

Conventional WDM systems multiplex channels with different signal bandwidths using fixed and equal channel spacing. As a result, their spectral efficiency is rather poor. If the wavelength and the bandwidth of each channel in a WDM system could be freely changed as needed, a variety of services with different signal bandwidths could be accommodated efficiently. This is expected to yield high spectral efficiency. For this purpose, this paper proposes a WDM optically amplified system that combines optical power splitting with homodyne detection; its use in three configurations, point to point, ring (center to remote nodes), and peer to peer, is described. Coherent optical systems generally need a frequency stable local light source in addition to a sending light source in each WDM channel. We improve cost effectiveness by proposing that the output of one light source be divided to yield the local light for frequency selection by homodyne detection and the sending light source whose output is externally modulated by transmission signal. In this configuration, the local light level is low to permit high levels of sending power. The key problem is how to get high SNR with limited low-level local lights. This paper derives the optimum receiving loss condition that can maximize the SNR with local light levels as low as -20 dBm for the point to point configuration. For the ring configuration, the system overcomes the optical power loss created by splitting numbers over 1,000 even if the local lights are as low as OdBm. The ring configuration can, therefore, flexibly accommodate many users and services. We also elucidate the relation between SNR and BER for DPSK homodyne detection in a bandwidth-flexible system.