Contents 1. Introduction
Chromatic dispersion compensation is critical for high bitrate lightwave systems. Reconfigurable optical networks introduce a need for tunable dispersion compensation since different routes may have different cumulative dispersions. Because of the large number of channels in dense WDM systems, periodic filters are advantageous compared to single channel devices which require a unique filter for every WDM channel Several periodic dispersion compensators based on feed-forward [1], [2] and feedback filters have been realized. Allpass filters are a particularly advantageous feedback filter since they allow any phase response to be approximated and, in the ideal lossless case, have a unity magnitude response. Physical implementations include both etalons [3] and ring resonators [4]. Planar waveguides provide a platform for integrating multi-stage, tunable filters using ring resonators [5]. A ring resonator-based allpass filter with a dispersion tuning range of 4000 ps/nm and passband width of 15 GHz has been used to compensate 10 Gb/s NRZ signals [6], and filter bandwidths up to 22 GHz have been reported [7]. In this paper, we demonstrate filters with up to 60 GHz constant-dispersion passbands, and compensation of 40 Gb/s non-return-to-zero (NRZ) and carrier-suppressed return-to-zero (CSRZ) signals.
