Efficiency improvements in a dichroic dye-doped liquid crystal Fresnel lens

A dichroic dye-doped liquid crystal Fresnel lens was fabricated and investigated to observe the combination of phase and amplitude modulation based focusing. An anthraquinone dichroic dye was doped into a liquid crystal host, which when in the Fresnel lens configuration generates a Fresnel zone plate with alternating “transparent” and “opaque” zones. The zones were induced by using photo-alignment of a light-sensitive alignment layer to generate the alternating pattern. The voltage dependency of efficiency for the dye doped and pure liquid crystal Fresnel devices were investigated. Incorporation of dyes into the device yielded a significant 4 % improvement in relative efficiency in the lens, giving a maximum of 37 % achieved in the device, much closer to the theoretical 41 % limit when compared with the non dye doped device. The input polarization dependence of efficiency was also investigated, showing very small fluctuations (±1.5 %), allowing further insight into the effect of fabrication method on these liquid crystal Fresnel devices.