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.

We propose two types of structures to achieve the control of Fano and electromagnetically induced transparency (EIT) line shapes, in which dual one-dimensional (1D) photonic crystal nanobeam cavities (PCNCs) are side-coupled to a bus waveguide with different gaps. For the proposed type Ⅰ and type Ⅱ systems, the phase differences between the nanobeam periodic structures of the two cavities are π and 0, respectively. The whole structures are theoretically analyzed via the coupled mode theory and numerically demonstrated using the three-dimensional finite-difference time-domain (3D FDTD) method. The simulation results show that the proposed structure can achieve several kinds of spectra, including Fano, EIT and asymmetric EIT line shapes, which is dependent on the width of the bus waveguide. Compared to the previously proposed Fano resonator with 1D PCNCs, the proposed structures have the advantages of high transmission at the resonant peak, low insertion loss at non-resonant wavelengths, a wide free spectral range (FSR) and a high roll-off rate. Therefore, we believe the proposed structure can find broad applications in optical switches, modulators and sensors.