Investigation of a thin-film grating filter under oblique-incidence conditions

An experimental investigation and calculations were made of the principal characteristics of a reflection filter representing a waveguide section with a diffraction grating on its surface. The grating period was selected so that the projection of the wave vector of the incident radiation on the normal to the grating was equal to half the reciprocal lattice vector. When the radiation was incident at 45°, corresponding exactly to the Bragg condition, the reflection coefficient was 94%. The angular selection was better than 5'.