All-Optical and Polarization-Independent Tunable Guided-Mode Resonance Filter Based on a Dye-Doped Liquid Crystal Incorporated with Photonic Crystal Nanostructure

This work presents the design, fabrication, and characterization of a novel two-dimensional (2D) all-optical and polarization-independent tunable guided-mode resonance filter. This filter is composed of a 2D sub-wavelength photonic crystal nanostructure with a dye-doped liquid crystal layer in a doped-nanoparticle-induced homeotropic alignment. Experimental results show that the resonant wavelength of the filer can be all-optically and polarization-independently tuned for red- and blue-shifting if the cell is illuminated successively by UV and green beams. The all-optical and polarization-independent tunability of the filter is attributed to the phase transition between homeotropic (H) and isotropic (I) state, resulting in variations in the LC refractive index between the ordinary index (n_o) and refractive index in I state (n_i) via either UV-beam-induced trans-cis or green-beam-induced cis-trans back isomerization. In addition, the optically tunable cycle of the filter is repeatable for many times without significant decay or damage. This filter has potential applications, such as optical filters in signal processing, optical switches in communications technology, and optical sensors.