Modelling HOE 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 HOE’s have the advantage of high diffraction efficiency but they present both chromatic selectivity and chromatic dispersion which impact on their use with wide spectrum light sources. Single-colour 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 o f a n e xtended s ource o n t he H OE output for different h olographic l enses, w ith f ocal l engths f rom 2 .5-10 c m. T he l enses w ere r ecorded i n B ayfol HX200 material and their diffraction e fficiency was cha racterised acr oss the len s ape rture by mea suring the Bragg angular selectivity curve at each location. Offset p oint s ources w ere u sed t o e xperimentally s tudy t he e ffects of a non-point source on the HOEs and the system was also modelled using Matlab and Zemax.