Dispersion compensation of a 1x N passive optical router with low loss, a flat passband, and low cross talk

A 1xN interferometer-based router with single-stage all-pass filters in the arms has low loss, a flat passband, and low cross talk. However, we show that the router has substantial cubic dispersion over the channel passband, which is identical from channel to channel. For a 1x4 router with a free spectral range of 100 GHz, the average dispersion slope over a 60% passband is -8x10(3)ps/nm(2), and thus a cascade of four routers incurs a significant system power penalty. A three-stage all-pass filter placed on the input arm reduces the dispersion of all channels by a factor of 16. The router is quite insensitive to variations in the all-pass filter design parameters.