Polarization-Independent Nematic Liquid Crystal Phase Modulators

In this paper, we investigate the potential of achieving polarization independent phase modulation using supertwisted nematic (STN) liquid crystal (LC) devices. Here, we describe the use of a burst driving voltage applied to a 180° STN LC device to obtain a twist symmetric H (T-Hs) state, which enables simultaneous modulation of light for all polarizations, demonstrating a polarization independent characteristic in the time domain. Additionally, we consider a 90° twisted nematic (TN) LC device for comparison, as this can also exhibit polarization independent characteristics. Simulations were carried out using a numerical model based on the Ericksen-Leslie continuum equations, which was employed in conjunction with the Jones calculus to simulate the optical properties of the device. The time-dependent optical phase modulation of the device was subsequently measured by using a phase-shifting Mach-Zehnder interferometer. The experimental results demonstrate that an STN device with an 8.9 μm thick LC layer operating in the T-Hs state exhibited a π/2 optical phase modulation in 1 ms for a burst voltage of 30 Vrms that was found to be independent of the incident polarization. These measurements were obtained at room temperature in a single optical path configuration and were found to be in good agreement with the results from the simulations.