Influence of grating shift in Fabry-Perot interferometer with two waveguide grating mirrors

Abstract

Fabry-Perot interferometer with two identical waveguide gratings mirrors is studied. Earlier we studied the case of oblique light incidence and in this paper normal incidence is considered. Normal incidence case is special because two waveguide modes propagating in the opposite directions are excited simultaneously. It is found that for the filter having small distance between the waveguide grating mirrors the reflection spectrum depends on the phase shift between the gratings. One or two additional resonances appear in the case of phase shift not being equal to 0 or π. We attribute the appearance of these resonances to the symmetry breakdown in the waveguide system and coupling between the waveguides.