Wide angular aperture holograms in photorefractive crystals by the use of orthogonally polarized write and read beams

Abstract

We demonstrate a method of simultaneous holographic recording and readout in photorefractive crystals that provides high write-read beam isolation and wide angular bandwidth. The method uses orthogonally polarized read and write beams and parallel tangent diffraction geometry near the equal curvature condition to provide spatially separable, orthogonally polarized diffracted output beams with high isolation and wide Bragg-matched angular bandwidth. The available angular bandwidth of this read-write technique is analyzed, simulated, and experimentally investigated. The measured angular bandwidth internal to the crystal is approximately 18° × 6° for our 45°-cut BaTiO(3) crystal, yet the entire hologram still demonstrates high Bragg selectivity. In contrast, traditional nonparallel-tangent geometries yield angular apertures of the order of 1° × 4°.

Experimental demonstration of a broadband adaptive processor for phased-array antennas

“…The parallel-tangents, equal-curvature condition 16 is an effective geometry that has been previously used to achieve a high degree of read-write isolation while simultaneously maximizing the Bragg-matched angular aperture between the writing and reading beams. The process involves matching the tangents and curvatures of the ordinary and extraordinary momentum surfaces.…”

<title>Photorefractive phased array antenna beam-forming processor</title>

“…The array input field will interfere at the PRC with the diffracted output from the reference Bragg cell. This diffracted term, propagating nominally in the z direction, can be expressed as Er(X,t) = e'umn[]i(t -x/v)e' (13) The function ITI[x/X] describes the uniformly illuminated aperture of the AO device. We introduce a linear operator notation L {.…”

“…We introduce a linear operator notation L {. }, to express the Fresnel propagation of the incident fields given by (12) and (13). In particular, In the operator notation, the grating evolution inside the PRC created by the interference of the x propagating array field and the z propagating diffracted Bragg cell field is described by…”