Versatile Integrated PMD Emulation and Compensation Elements
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Highly versatile building blocks for polarization-mode dispersion (PMD) emulation and compensation are demonstrated using tunable all-pass filters fabricated in 4%-index-contrast planar waveguides. While the all-pass filters can approximate any phase response, the complexity in setting the individual filter parameters is minimized by restricting the all-pass filter response 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 differential group delay (DGD) tuning range over 100 ps is demonstrated for 10 Gb/s and 25 ps for 40 Gb/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 all-pass filters is advantageous in reducing the thermooptic response time to achieve polarization rotation speeds on the order of 0.1 s/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.
