Modeling holographic optical element performance with an extended source; Experimental investigation using misaligned point sources

Holographic optical elements (HOEs) have the potential to enable more compact, versatile, and lightweight optical designs, but many challenges remain. Volume HOEs have the advantage of high diffraction efficiency, but they present both chromatic selectivity and chromatic dispersion, which impact their use with wide spectrum light sources. Single-color light emitting diode (LED) sources have a narrow spectrum that reduces these issues and this makes them better suited for use with volume HOEs. However, the LED source size must be taken into consideration for compact volume HOE-LED systems. To investigate the design limits for compact HOE-LED systems, a theoretical and experimental study was carried out on the effects of an extended source on the HOE output for different holographic lenses, with focal lengths from 25-100 mm. The lenses were recorded in a commercially available photopolymer [Bayfol HX200], and their diffraction efficiency was characterized across the lens aperture by measuring the Bragg angular selectivity curve at each location. Offset point sources were used to experimentally study the effects of a non-point source on the HOEs, and the system was modeled using Matlab and Zemax.