High-Q tunable Fano resonances in the curved waveguide resonator with mirrors with spatially variable reflectivity

High-Q Fano resonances are demonstrated, as well as effects similar to electromagnetically induced transparency arising in a curved Fabry-Perot waveguide resonator with variable-reflection mirrors. It is shown that these effects arise as a result of coupling the fundamental mode of the bent waveguide core with whispering gallery cladding modes. An influence of the main geometrical parameters of the resonator on the resonance features in its reflection and transmission spectra is studied. The results obtained can be used in the creation of new functional elements of photonics based on curved waveguides, in particular, highly sensitive portable refractometers for bio- and chemosensory systems, as well as optical sensors of mechanical effects.