Enhanced Speed and Tunability of Liquid Crystals in Nanocavities via Engineering the Local Electromagnetic Field

Abstract

The speed of nematic liquid crystals (LCs) is usually limited by the viscoelastic relaxation time, determined by the viscosity, elastic constant, and device thickness. Here, we demonstrate breaking this limit by confining the LC in a resonant nanocavity and designing the electromagnetic field to be concentrated within a specific region of the LC where the molecules react strongly to the applied voltage. Confining the LC within a subwavelength deep silicon (Si) grating of 712 nm height and 566 nm space, we achieve a guided mode resonance that results in high field confinement at the center of the LC space at the resonance wavelength. Conversely, outside the resonance wavelength, the field confinement shifts to the Si lines. This configuration reduces the rise time by an order of magnitude, from 2 ms to 200 μs at the resonance wavelength. The optimized field overlap integral at the center of the LC space indicates that most of the light–matter interactions occur in this region. As a result, this central region responds faster to an increasing voltage than does the entire LC region, thereby explaining the faster response observed at resonance. Similarly, the tunability in response to voltage and temperature can be enhanced if the alignment inside the nanocavities is better controlled. This method paves the way for ultrafast devices that utilize faster LC modes and innovative resonant nanocavity designs.