Saturation of multiplexed volume Bragg grating recording.

Recording of volume Bragg gratings (VBGs) in photo-thermo-refractive glass is limited to a maximum refractive index change about 0.002. We discuss various saturation curves and their influence on the amplitudes of recorded gratings. Special attention is given to multiplexed VBGs aimed at recording several gratings in the same volume. The best shape of the saturation curve for production of the strongest gratings is the threshold-type curve. Two-photon absorption as a mechanism of recording also allows increasing the strength of multiplexed VBGs.

Crossed-gratings volume hologram: backward reflection with high angular and spectral selectivity.

A new type of reflective hologram with both high angular and spectral selectivity is suggested. With novel design of crossed gratings inside the volume hologram, unusual angular selectivity is achieved via coupling of four waves. Analytic solution with spectral and angular detuning from Bragg regime is derived. The compensation between these two detuning forms an interesting figure of saddle shape.