Dispersion-compensating optical digital filters for 40-Gb/s metro add-drop applications

Optical digital filters that employ optical delay lines are proposed. Properly locating the zeros in the transfer function is shown to enable interleaver pairs to be designed with the same amplitude responses but opposite phase responses. In metro add-drop applications, the interleaver pair can provide up to 50% of the adding and dropping of the total traffic while simultaneously reducing the insertion loss of the express channel. Both experiments and Monte Carlo simulations demonstrated that the cascaded dispersion of seven pairs of interleavers within the +/-30-GHz passband is less than 1 ps. A total dispersion near zero considerably increases the effective bandwidth and greatly increases the number of cascadable add-drop nodes.