Polarization-independent tunable optical filters using bilayer polarization gratings.

Department of Electrical and Computer Engineering, North Carolina State University, 2410 Campus Shore Drive, Raleigh, North Carolina 27606, USA.
Applied Optics (Impact Factor: 1.69). 07/2010; 49(20):3900-4. DOI: 10.1364/AO.49.003900
Source: PubMed

ABSTRACT We demonstrate a polarization-independent tunable optical filter based on switchable polarization gratings (PGs) formed using reactive and nonreactive liquid crystals (LCs). PGs are anisotropic diffraction gratings that exhibit unique properties, including a zero-order transmittance that is independent of incident polarization and that can vary from approximately 0% to approximately 100%, depending on wavelength and applied voltage. A stack of several PGs of varying thicknesses combined with an elemental angle filter yields polarization-independent bandpass tuning with minimal loss. We introduce a novel hybrid PG consisting of both reactive and nonreactive LC layers, which allows very thick gratings to be created with thin active LC layers. We demonstrate a tunable optical filter with a peak transmittance of 84% of unpolarized light, a minimum full width at half-maximum of 64 nm, and a maximum tuning range of 140 nm.

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