Polarization-independent tunable optical filters based on bilayer polarization gratings

Abstract

We report enhanced polarization-independent tunable optical filters based on liquid crystal (LC) and reactive mesogen (RM) polarization gratings (PGs). This new design achieves tunable passbands with significantly smaller bandwidth and allows for potential applications in spectroscopy and beyond. Analogous to Lyot and Solc filters, our filter is constructed of multiple bilayer polarization gratings (BPGs) of varying thicknesses, with the potential for highly compact implementation. BPGs are a hybrid of a switchable/tunable liquid crystal (LC) PG and a reactive mesogen (RM) PG. By adding the RM layer, the BPG provides a significant advantage over LCPGs for the filter application in that it allows very thick gratings to be created with thin active LC layers. As such, the difficulty in fabricating LCPGs with arbirtrarily large thicknesses is much less of a concern. BPGs exhibit the unique properties of PGs, including polarization independent zero-order transmittance, as well as diffraction at visible and infrared wavelengths. Our unique design enables a high peak transmittance (~ 90%) as well as a significantly improved full-width-at-half-maximum (FWHM). Here, we present preliminary data, discuss the unique capabilities and compelling advantages of our filter. We analyze performance in terms of finesse, 3dB bandwidth (FWHM), and free-spectral-range by comparison to theoretical simulation.