Flat-Top, Narrow-Band, Thermally Tunable Optical Filters Based on Multi-Phase-Shifted Bragg Gratings and Suspended Waveguide

Tunable optical filters are key components in optical communication systems. In this paper, a multi-phase-shifted Bragg gratings (MPSBGs) filter based on a laterally supported suspended waveguide is designed and fabricated. Optimized design of phase-shift segments location and length in MPSBGs combined with thermal tuning of the suspended waveguide to achieve a flat-top, narrow-band filter response. By tuning the heater in the phase shift section, a transmission window with a -3 dB bandwidth of 270 pm is obtained, while out-of-band rejection of is about 30 dB, shape factor (the ratio of -20 dB to -3 dB bandwidth) is 2.3, and thermal tuning efficiency is about 40 pm/mW.