Abstract
In this article we disclose a method to fabricate a polarization independent dual frequency liquid crystal (DFLC) Fresnel lens (FL) with relatively high efficiency. The switchable FL is based on a patterned hybrid photo-aligned nematic (HPAN) DFLC cell assembled by one substrate providing the homeotropic anchoring and the other one providing the in-plane patterned alignment, with mutually orthogonal easy axis in the neighboring alignment domains, which has been prepared by means of two-step photo-alignment technique. Due to the electro-optical properties of dual frequency LC, the proposed HPAN DFLC FL, which manifests relatively high diffraction efficiency of 38.5% and low driving voltage, has the possibility of achieving a fast response by alternatively switching between high frequency and low frequency electric fields. Thus, with an excellent rewritable performance leading to the alternative focus/defocus switch, the HPAN DFLC FL would definitely be practical and promising in many modern devices.
Highlights
The fast switchable lens with high efficiency is broadly desirable for variety of applications
Thanks to the photo-alignment technology which provides us an opportunity to facilely control Liquid crystal (LC) alignment, exhibiting a phase profile as Fresnel zones, a polarization independent dual frequency liquid crystal (DFLC) Fresnel lens (FL) with high diffraction efficiency and fast responsiveness behavior was achieved by confining the DFLC with a low crossover frequency in a patterned hybrid photoaligned nematic (HPAN) cell, whose rising and decay time were controlled by the external field with alternate high frequency and low frequency voltage signals
The Fresnel zones pattern with a certain focal length of the proposed hybrid photo-aligned nematic (HPAN) DFLC FL can be erased and rewritten for another one with different focal length by using a polarized laser (λ = 450 ± 10nm) [35].The response time of the erasing and rewriting depends on the elastic parameters of the LC and the anchoring energy of the alignment layer which can be tuned by doses of the exposing energy [36]
Summary
The fast switchable lens with high efficiency is broadly desirable for variety of applications. W. Hsieh, “Polarization-independent and high-diffraction-efficiency Fresnel lenses based on blue phase liquid crystals,” Opt. Lett.
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