Digital subcarrier optical networks and cross-connects

Abstract

This paper describes a rate flexible network transport solution to achieve sub-wavelength circuit provisioning between edge node pairs. Sub-wavelength circuits are obtained by concatenating spectrally efficient digital subcarrier channels along the network path, with each subcarrier frequency carrying only a fraction of the wavelength bandwidth. By reserving one or more such subcarrier frequencies along a path connecting two edge nodes, a dedicated end-to-end sub-wavelength circuit is provisioned. At an intermediate node, incoming frequencies are switched to outgoing frequencies via a cross-bar electronic circuit switch or cross-connect. By performing digital subcarrier multiplexing (DSCM) using CMOS based advanced digital signal processing (DSP) algorithms, spectral guard-bands between adjacent channels are not necessary, thus yielding good bandwidth efficiency when multiplexing multiple subcarrier channels onto the same wavelength.

Compared to current TDM based transport network solutions, e.g., OTN/SONET/SDH, the described solution offers the unique advantage of implementing two key transport functionalities in the same DSP system, which is capable of (1) performing compensation of fiber transmission impairments in the electronic domain to ensure good signal integrity, and (2) multiplexing (demultiplexing) subcarrier channels after (before) add/drop and switching circuit operations. Because of this design advantage, system complexity and fabrication of the network equipment are ameliorated, possibly leading to tangible cost and electric power consumption reductions.