Fresnel Lens Using Nanoscale Liquid Crystals

5 Fresnel Lens Using Nanoscale Liquid Crystals 

Ren et al. reported the fabrication of a Fresnel lens using a photomask with zone plate patterns [9]. The LC monomer in the zones cured with more UV intensity would lead to smaller LC droplets. Conversely, the zones with weaker UV exposure would result in larger nanoscale droplets. When a uniform voltage was applied to the zone plate, the refractive index (or phase) of the 

Left Method for fabricating Fresnel lens. Right Photomask showing Fresnel zone structure. (Source Ren, H.W., Y.H. Fan, and S.T. Wu. 2003. Applied Physics Letters, 2003. 83(8) 1515-1517. With permission.) 

In a binary phase Fresnel lens, the focal length/is related to the innermost zone radius rj as / = r lE, where X is the wavelength of the incident beam. The primary focal length of the lens was -50 cm (for X = 633 nm). Due to the higher order Fourier components, a Fresnel zone lens has multiple foci a.t f, f/3, f/5, etc. Flowever, most of the incident light diffracts into the primary focus. The theoretical diffraction efficiency of the primary focus for the binary-phase Fresnel lens is 41%. 

Li et al. applied LC microlenses for adaptive ophthalmic lenses [10]. A Mach-Zehnder interferometer operating at 543.5 nm was used to measure wavefront quality immediately behind the lens and determine the focal length. The technique is based on interference between the spherical wave after the lens and a reference plane wave. 

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H. Ren, Y. H. Fan, and S. T. Wu, Tunable Fresnel lens using nanoscale polymer-dispersed liquid crystals, Appl. Phys. Lett. 83, 1515 (2003). 

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