High-contrast filtering by multipass diffraction between paired volume Bragg gratings.

High-contrast filtering via multiple reflections between matched volume Bragg gratings (VBGs) is demonstrated. The use of multiple reflections serves to increase the suppression ratio of the out-of-band spectral content such that contributions of grating sidelobes can be mitigated. The result is a device that retains spectral and angular selectivity and diffracts light into a single order with high efficiency but reshapes the spectral/angular response to achieve higher signal-to-noise ratios. We demonstrate that multipass spectral filters can be recorded with extremely high suppression ratios using reflecting Bragg gratings (RBGs) in three different configurations. These filters demonstrate roll-offs of over 150 dB/nm. Similarly, we demonstrate angular filtering by multipass transmitting gratings.