Constraints on the design of 2-fiber bi-directional WDM rings with optical multiplexer section protection

Bi-directional WDM ring architectures with optical multiplexer section protection (OMSP) can be implemented with 2 or 4 fibers. The 2 fiber configuration has a significant cost advantage over the 4-fiber counterpart, because requires half the number of switches, optical amplifiers and optical fibers. As a drawback, the number of wavelengths needed to implement a full-mesh connection duplicates, since half the wavelengths in each fiber are reserved for protection. A sensible step in the design of a WDM ring is the selection of optical add-drop multiplexers (OADM) to use as network nodes. A possible strategy to construct OADMs consists on using arrayed waveguide gratings (AWG) in a loop-back, or foldback configuration. The fold-back configuration is more advantageous, since it offers a better crosstalk performance and avoids the instabilities that can occur in rings with loop-back. In this paper, we investigate the main constraints that limit the size of 2-fiber full-mesh WDM bi-directional OMSP rings using OADMs based on AWGs in a fold-back confguration.