Side-Coupled Fabry-Perot Resonator Filter Based on Dual-Waveguide Bragg Grating

We propose, analyze and demonstrate a side-coupled Fabry-Perot (F-P) resonator filter composed of two dissimilar waveguides with
π
phase-shifted Bragg grating. The resonance circuit is formed by the mode conversion between the fundamental transverse electric (TE
₀
) modes of the two waveguides. It can realize a wide free spectral range (FSR) or an FSR-free response with a single strong resonance at the central wavelength of mode conversion. In addition, compared with the conventional F-P resonator, only one transverse mode in the proposed resonator can be coupled to the bus waveguide. Thus, it has some advantages including no intrinsic reflection to the bus waveguide and low resonance loss. The experimental results on silicon-on-insulator (SOI) platform have shown that the extinction ratio, full width at half maximum (FWHM) and quality factor (
Q
-factor) of the proposed resonator are 52.5 dB, 0.125 nm and 1.24 × 10
⁴
, respectively. The fabrication error and add-drop filters based on the proposed resonator are discussed then. The proposed resonator is believed to benefit the practical applications of optical filters and sensors.