The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters.
These typically require corrugations widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, on the realization of SOI Bragg filters based on sub-wavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints.
Based on this concept, we experimentally demonstrate a single-etch, 220 nm thick, Si Bragg filter featur- ing a corrugation width of 150 nm, a rejection bandwidth of 1.1 nm and an extinction ratio exceeding 40 dB. This represents a ten-fold width increase compared to conventional single-periodicity, single-etch
counterparts with similar bandwidths
