Design and Demonstration of Apodized Comb Filters on SOI

We report on the design, modeling, and characterization of apodized comb filters in the silicon-on-insulator platform. These devices are based on sampled gratings, wherein the comb response is generated by a convolution of a regular grating by a predetermined periodic sampling function. We show that dual and complementary apodization of the etch depth in the marks and spaces ensures a near-zero dc index change over the length of the device and avoids the unwanted sidelobes obtained in a single apodized device. Comb filters with a 40-dB side-mode suppression ratio, a 92-GHz clear bandwidth, 200-GHz channel spacing, and a 120-dB/dec rolloff have been theoretically proposed. An experimental demonstration of the fabricated devices is also presented, and the performance is compared with the numerical simulations.