Fast Visible-Near Infrared Switchable Liquid Crystal Filter

Abstract

A conventional liquid crystal display consists of a liquid crystal cell between two crossed polarizers. By applying a voltage, the liquid crystal can be switched and the transmission of light can be manipulated. For thick devices, the transmission shows a strong wavelength dependency and this can be used to construct a tunable Lyot-Öhman filter. Such a filter consists of several liquid crystal cells with polarizers in between with a narrow transmission band that can be shifted over a certain wavelength range. Instead of aiming for a narrow transmission peak, in this work the aim is to achieve a wide transmission wavelength range. In this way the transmission band can be switched, for example, from the visible wavelength range to the near-infrared range. Because the device needs only two different states, bistable surface-stabilized ferroelectric liquid crystal devices can be used which offer short switching times in the order of 100 μs. Numerical optimization of this switch reveals that high contrast ratios can be achieved by using 2 fixed and 2 switchable retarders.

Keywords:

• ferroelectric liquid crystals
• Lyot-Öhman filter
• wavelength tunable filter

Acknowledgments

This work was supported by the Photonics@be IAP network of the Belgian Science Policy.

Additional information

Notes on contributors

Jeroen Beeckman

Jeroen Beeckman is postdoctoral fellow of the Research Foundation – Flanders (FWO-Vlaanderen).