Phase-shifted volume Bragg gratings in photo-thermo-refractive glass

Narrow-band filters based on phase shifted Bragg gratings have been widely investigated in fiber configuration. However, up to now, no experimental demonstration was performed using volume Bragg gratings in free space configuration. In this paper both theoretical and experimental study of this new type of filters is presented. The phase matching conditions that allow obtaining a resonant filter are analyzed. Narrow bandwidth transmission filters based on the coherent combination of two non slanted reflecting Bragg gratings in photo-thermo-refractive glass are studied. A filter with 25 pin bandwidth and 90%+ transmission at 1064 nm is demonstrated. The effect of the phase matching between the two volume Bragg gratings is presented and perfect accordance of experimental and theoretical data are shown. Based on these results, we show that the phase-shifted reflecting volume Bragg gratings recorded photo-thermorefractive glass pave a way to the fabrication of large aperture extremely narrow band filters with high transmission at resonance and high rejection.