Tunable-focus liquid crystal Fresnel zone lens based on harmonic diffraction

Abstract

We propose and demonstrate a tunable-focus liquid crystal Fresnel zone lens (TLCFZL) based on harmonic diffraction. The physical mechanism of the focus tuning is based on a multi-order diffraction process using a shallow surface relief type harmonic diffractive structure with uniform electrodes which results in significantly reduced fabrication complexity and excellent electro-optic performances. A rapid fabrication process including imprinting technique is studied, from which a high performance TLCFZL with three switchable focus lengths and high diffraction efficiency (about 70%) is fabricated. Focusing and imaging properties of the TFLCFZL are tested. The highest resolution of the lens reaches 22.6 lp/mm with low operating voltage of less than 7.2 Vrm and response time of ∼200 ms.