Precise switching control of liquid crystalline microgears driven by circularly polarized light

Kiminori Ito,Hiroshi Frusawa,Masahiro Kimura

doi:10.1364/oe.20.004254

Abstract

Liquid crystalline molecules carrying photopolymerizable end groups absorb photon energy via a two-photon process, enabling the photofabrication of 3D structures. In this work, we prepared microgears with different heights and tooth lengths. These birefringent microgears can be induced to rotate by circularly polarized light. Here, we demonstrate that the use of phase plate for switching between left- and right-handed polarization reverses the optically induced rotation while maintaining the same rotational frequency. Due to the precise switching control, these birefringent microgears have advantages over previous microrotors that are fabricated from non-birefringent light-curing resins.

Highlights

Micro-objects are optically rotated by light with inherent angular momentum, including lasers with a helical phase structure and circularly polarized light [1,2,3,4,5,6,7,8,9], because micro-objects can extract the angular momentum of such light due to their absorptive or birefringent optical properties [9]
We prepared microgears with different heights and tooth lengths. These birefringent microgears can be induced to rotate by circularly polarized light
We demonstrate that the use of phase plate for switching between left- and right-handed polarization reverses the optically induced rotation while maintaining the same rotational frequency

Summary

Introduction

Micro-objects are optically rotated by light with inherent angular momentum, including lasers with a helical phase structure (e.g., the Laguerre-Gaussian mode) and circularly polarized light [1,2,3,4,5,6,7,8,9], because micro-objects can extract the angular momentum of such light due to their absorptive or birefringent optical properties [9]. Laser tweezers can be used to rotate liquid crystalline (LC) droplets, birefringent liquid particles that are surrounded by solvents, with circularly polarized light, the shapes of such birefringent micro-objects have been limited to simple configurations of spheres or cylinders [4,5,6,7,8,9]. Yang et al reported that continuous rotation of chiral nematic LC droplets is driven by a linearly polarized light [10]. Another alternative strategy is to use micro-objects that can scatter light in a helical manner [11,12,13]. The photopolymerization of light-curing resins can create microscopic propellers, which have been demonstrated to rotate efficiently due to helical scattering

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