Integrated waveguide allpass filter tunable dispersion compensators

As the bitrate per channel increases in optical systems, the allowable tolerance for dispersive effects, such as chromatic and polarization mode dispersion, decreases substantially. At 40 Gb/s and beyond, the tolerance window has shrunk to an extent where adjustable dispersion compensation is required to accommodate beginning-of-life distributions, wavelength dependence, measurement uncertainties, and temperature fluctuations in the fiber dispersion. We focus on optical allpass filters. Allpass filters are unique in their ability to provide a flexible phase response that can approximate any desired dispersion over a bandwidth which is large relative to the filter period and, in the limit of low feedback path losses, which is decoupled from the magnitude response.