Wavelength multiplexing recording of vHOEs in Bayfol HX photopolymer film

Photopolymer films (Bayfol® HX) have been recently introduced into the market place and prove themselves as easy to process for volume holographic optical element (vHOE) recording. The new Bayfol® HX instant developing holographic photopolymer film provides full color capability and adjustable diffraction efficiency as well as an unprecedented optical clarity when compared to classical volume holographic recording materials like silver halide emulsions (AgHX) or dichromated gelatin (DCG). Besides the recording step no pre- or post-processing is necessary and easy mass production of vHOEs in a completely dry roll to roll process is possible. Due to the nature of vHOEs, multiplexing recording can be used to superimpose multiple optical functions in a single layer. This enables to merge angular wise precise full color diffractive combiner optics in one layer by spectral multiplexing, like RGB recording in Bayfol® HX film. Further optical sensing functions may be added by additional angular multiplexing. For reflection type vHOE recording the necessity of additional partial reflective layers or using total internal reflection (TIR) in a light guide becomes obsolete. Obviously, these unique properties of vHOEs could significantly simplify the layer structure of immersive displays like in Head-Mounted-Displays (HMD) and Head-Up- Displays (HUD). In this paper we investigate and demonstrate wavelength multiplexing recording in Bayfol® HX film with a specific focus on the design of the optical recording setup and its system and stability margins. Well controlled RGB recording power conditions enable high repeatability over extended operation periods of the RGB efficiency balance of reflective vHOEs.