The filter made up of two gratings performs as a two-dimensional non-spatial filtering.This paper reports that the volume Bragg gratings are fabricated by interfering two collimated coherent laser beams in photopolymer.Diffraction efficiency of a single grating is up to 78% in Bragg's condition,then a two-dimensional non-spatial filter,which consists of two volume Bragg gratings and a half-wave plate,enables the laser beam filtered in two dimensions with the diffraction efficiency of 54%.The Bragg's condition and effect of polarisation on performances of the two-dimension filter are also discussed.
Diffraction efficiency of volume Bragg grating,whose period is in the same order as the incident wavelength, is related to the polarization direction of the incident linear polarized beam.When two linearly polarized recording beams with the same polarization direction are used for recording volume Bragg gratings in a photopolymer with diffusion amplification,the azimuth of polarization of the reconstruction beam influences the diffraction efficiency of the grating.When the probe beam is linearly polarized and oriented orthogonally to the grating vectors,the±1-order diffraction beams are also linearly polarized with polarization direction parallel to that of the probe beam.According to the results,a two-dimensional nonspatial optical filter consisting of the volume Bragg gratings would achieve significantly higher efficiency.
