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.
A highly-sensitive, reliable, simple and inexpensive chemical detection and identification platform is demonstrated. The
sensing technique is based on localized surface plasmon enhanced Raman scattering measurements from gold-coated
highly-ordered symmetric nanoporous ceramic membranes fabricated from anodic aluminum oxide. To investigate the
effects of the thickness of the sputter-coated gold films on the sensitivity of sensor, and optimize the performance of the
substrates, the geometry of the nanopores and the film thicknesses are varied in the range of 30 nm to 120 nm. To
characterize the sensing technique and the detection limits, surface enhanced Raman scatterings of low concentrations of
a standard chemical adsorbed on the gold coated substrates are collected and analyzed. The morphology of the proposed
substrates is characterized by atomic force microscopy and the optical properties including transmittance, reflectance and
absorbance of each substrate are also investigated.