Narrowband Bragg filters based on subwavelength grating waveguides for silicon photonic sensing

Subwavelength grating (SWG) waveguides have been shown to provide enhanced light-matter interaction resulting in superior sensitivity in integrated photonics sensors. Narrowband integrated optical filters can be made by combining SWG waveguides with evanescently coupled Bragg gratings. In this paper, we assess the sensing capabilities of this novel filtering component with rigorous electromagnetic simulations. Our design is optimized for an operating wavelength of 1310 nm to benefit from lower water absorption and achieve narrower bandwidths than at the conventional wavelength of 1550 nm. Results show that the sensor achieves a sensitivity of 507 nm/RIU and a quality factor of 4.9 × 10⁴, over a large dynamic range circumventing the free spectral range limit of conventional devices. Furthermore, the intrinsic limit of detection, 5.1 × 10^-5 RIU constitutes a 10-fold enhancement compared to state-of-the-art resonant waveguide sensors.