Longitudinal stratified liquid crystal structures to enable practical spatial light modulators in the terahertz regime

Abstract

Electro-optic (EO) modulation of the amplitude and phase of electromagnetic waves using liquid crystals (LCs) is commonplace in the optical and infrared regions. This effort has led to commercially available components used in spectral filtering, polarization management, beam steering, transmitters, displays, etc. However, electro-optic techniques have had limited success in the terahertz (THz) region due to several practical design challenges. The growth in applications has led to an interest in the development of a spatial light modulator (SLM) for the terahertz region. In the visible region, the most common SLMs use electro-optic materials such as liquid crystals to spatially modulate a beam. However, this approach to achieve a practical SLM in the terahertz regime has been difficult. The primary barrier for components is the long interaction lengths required to modulate a THz wave. Since the EO modulation depth is directly proportional to the multiplication of the change of permittivity and the ratio of interaction length over wavelength, THz systems with wavelengths ranging from 150 μm to 1mm pose a challenge. To overcome this barrier, longitudinal stratified sub-wavelength liquid crystal structures have been engineered and fabricated. The stratified structures introduce the challenge in the selection and design of the electrodes. By using multiple layers the tunable films can be maintained at manageable thicknesses (25 to 200 μm). The reduced individual film thickness will significantly improve the requisite drive voltage and response time. However, the layered structure with multiple conducting layers adds considerable challenges to the design of the transparent electrode. Both simulation and experimental data will be presented.