Ridge Resonance in Silicon Photonics Harnessing Bound States in the Continuum

The theoretical analysis and experimental demonstration of a waveguide resonator are presented based on bound states in the continuum in an integrated photonic chip platform. The continuum has the form of a collimated beam of light which is confined vertically in a transverse electric (TE) mode of a silicon slab. The bound state is a discrete transverse-magnetic (TM)-like mode of a ridge on the silicon slab. The coupling between the slab and ridge modes results in a single sharp resonance at the wavelength where they phase match. This phenomenon is experimentally demonstrated on a silicon photonic chip using foundry-compatible parameters and it is interfaced on-chip to standard single-mode silicon nanowire waveguides. The fabricated chip exhibits a single sharp resonance near 1550 nm with a line width of a few nanometers, an extinction ratio of 25 dB, and a thermal stability of 19.5 pm degrees C-1. It is believed that the demonstration of a resonance operating near a bound state in the continuum realized using guided wave components will form the basis of a new approach to on-chip wavelength filtering and sensing applications.