Continuously Geometric Phase Modulation by using a reflective liquid crystal structure

Distinguished from the dynamical phase gained by optical path difference, the geometric phase (GP) is an additional phase delay produced by the variation of polarization states when light propagates in an anisotropic medium. Its modulation amount does not depend on the thickness of the medium or the wavelength of the light, therefore, it is expected to realize smaller and faster phase modulation unit. Based on the principle that the geometric phase generated by two passes through a wave plate of circularly polarized light with the same rotation direction is four times the rotation angle of optical axis of the wave plate, a reflective phase modulation structure composed of an In-plane Switching (IPS) liquid crystal (LC) cell, a mirror and two quarter wave plates is proposed in this paper. Under the action of IPS electrodes, the LC director can rotate nearly 80 degrees in-plane to realize a 320 degrees GP modulation. Finite Difference Time Domain (FDTD) method is used to simulate the GP modulation, and an optical path for interferometric measurement is built. The experimental results are in good agreement with the simulation results. This method uses only a single layer of driving electrodes and a LC cell to achieve 320 degrees GP modulation, which avoids the alignment problem and provides a new idea for the spatial light dynamic modulator.

Automated summary

Geometric phase is an additional phase delay produced by the variation of polarization states when light propagates in an anisotropic medium. In this paper, a reflective phase modulation structure is proposed to achieve geometric phase modulation under the action of IPS liquid crystal cell.