# Ultrasonic liquid crystal tunable light diffuser

## TL;DR

This paper introduces a new type of light diffuser using liquid crystals and ultrasound that can control and rotate light diffusion without moving parts.

## Contribution

The novel use of ultrasound to control the optical directivity of a nematic liquid crystal diffuser is presented.

## Key findings

- The diffusion angle of transmitted light can be controlled by input voltage amplitude, reaching a maximum at 16.0 V.
- The diffuser's directivity can be rotated by adjusting voltages to different electrodes.
- The design allows for a thin, mechanical part-free tunable light diffuser.

## Abstract

Conventional light diffusers have periodic surface profiles, periodic refractive index distributions, or light scattering layers containing colloids. In all such structures the optical directivity of the light diffuser is cannot typically be controlled. Here we propose an electrically tunable light diffuser based on the application of ultrasound to a nematic liquid crystal (LC) material. The ultrasonic LC diffuser consists of an LC layer sandwiched by two glass discs and an ultrasonic transducer. The electrodes of the transducer are divided in a circumferential direction so that a resonant non-coaxial flexural vibration mode can be generated on the diffuser by controlling the electrical input signals. A continuous reversed-phase sinusoidal electric signal to the transducer generates the non-coaxial resonant flexural vibration mode on the glass disc, inducing an acoustic radiation force acting on the boundary between the LC layer and glass discs. This effect changes the molecular orientation of the LC and the transmitted light distribution. The diffusion angle of the transmitted light depends on the input voltage amplitude, and the diffusion angle was maximized at 16.0 V. The vibrational distribution and the diffusion directivity could be rotated by adjusting the input voltages to different electrodes, meaning that an ultrasonic LC diffuser with a thin structure and no moving mechanical parts provided a tunable light-diffusing functionality with rotatable directivity.