Theoretical modelling has been used to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for any defined input and output beam angles. The approach is used to facilitate the design and fabrication of diffractive coupling elements through a holographic process that avoids the use of coupling prisms during recording and will help in the design of recording arrangements that better suit the mass production of low-cost elements, especially those designed for non-normal incidence. In this study, the recording angles needed for a range of recording wavelengths were explored for VHOE couplers designed for input angles (in air) ranging from 0° to −55°. Then, in order to validate the model, holographic recording in Bayfol HX 200 photopolymer at 532 nm was used to fabricate photopolymer VHOE couplers for 633 nm light (−45° input angle in air). Bragg curves obtained experimentally for different probe wavelengths (403 nm, 532 nm and 633 nm) confirm the recording of the desired grating structures to a precision of ±1°, and coupling is demonstrated at 633 nm with a diffraction efficiency of up to 72%. Furthermore, the model is used to identify the origins of some weaker spurious gratings observed alongside the expected ones.

A theoretical model has previously been developed to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for operation as a coupler for different input and output angles. In this paper, the experimental study is extended to further validate the VHOE coupler design and fabrication approach for additional incident beam angles, comparing -40° -45° and -50° (in air). The output angle for each VHOE is +45° within the medium and the coupler operational wavelength is 633nm. Holographic recording in Bayfol HX 200 photopolymer at 532nm is used to fabricate the VHOE couplers. The experimental Bragg curves for each VHOE coupler obtained at 633 nm demonstrate agreement of the measured angles to within ±1.5° (in air) with the expected values.