Manipulating leaky mode in silicon waveguides harnessing bound states in the continuum

A low-loss ridge waveguide is proposed and demonstrated with a novel, to the best of our knowledge, bound state in the continuum (BIC)-based structure on the silicon-on-insulator (SOI) platform. The presented waveguide is designed appropriately to suppress TM-mode leakage, and has a theoretically low propagation loss of ∼0.0027 dB/cm at 1550 nm. In the wavelength range from 1530 nm to 1600 nm, the 2-mm-long waveguide can achieve an average loss suppression of ∼30 dB in the experiment. Such a novel ridge waveguide structure can also be introduced into narrowband optical filters. The fabricated Bragg grating filter working at the TM mode can achieve a narrow bandwidth of ∼1 nm and an extinction ratio of ∼14.8 dB.