Versatile Integrated PMD Emulation and Compensation Elements

Abstract: Highly versatile building blocks for PMD emulation and compensation are demonstrated using tunable allpass filters fabricated in 4%-index-contrast planar waveguides. While the allpass filters can approximate any phase response, the complexity in setting the individual filter parameters is minimized by restricting the allpass filter responses to realize a range of differential delays, dispersion and dispersion slope. A single section can approximate first-order or a higher-order PMD term or emulate chromatic or higher-order dispersion. A DGD tuning range over 100 ps is demonstrated for 10Gb/s and 25 ps for 40Gb/s data. Second-order PMD with a tuning range of 255 ps2 and third-order PMD with a range of 2430 ps3 are also demonstrated. The larger index contrast required for the ring-resonator-based allpass filters is advantageous in reducing the thermo-optic response time to achieve polarization rotation speeds on the order of 0.1 ms/degree. The device is interferometrically stable and compact in size. It can be fully integrated, scaled to many sections, and can implement a variety of PMD synthesis and statistical-emulation approaches.