Compact integrated tunable dispersion compensators

Tunable dispersion compensators for 10 and 40 Gb/s signals using planar waveguide ring-resonator allpass filters are reviewed. Recent work using tunable ring-resonators as building blocks for PMD emulation, compensation and monitoring are also discussed.

Precise chromatic dispersion compensation is critical for high bitrate lightwave systems. Furthermore, reconfigurable optical networks require tunable dispersion compensators because different routes have different cumulative dispersions. Approaches requiring a unique filter for every channel are cumbersome because dense WDM systems have a large number of channels. With networks evolving to wavelength routing, periodic compensators are needed for next generation systems. Several periodic dispersion compensators based on feedforward [1] and feedback filters [2], [3] have been demonstrated. Allpass filters are a particularly useful feedback filter since they allow any phase response to be approximated adaptively and, in the ideal lossless case, have a unity magnitude response. Physical implementations include both etalons [3] and ring resonators.