Fluorescent light source with continuously tunable polarization via modification of molecular orientation

Abstract

We demonstrate that the polarization of emitted light from a photoluminescent cholesteric liquid crystals (PL-CLC) cell with well-designed electrodes can be electrically switchable among the linearly polarized, circularly polarized, and un-polarized states. Moreover, the degree of polarization can be continuously tunable from zero to the maximum degree of polarization of emitted light from the cell, that is, from 0 to 0.8 and 0 to 0.45 for circularly and linearly polarized light, respectively. The degrees of circular and linear polarizations are mainly governed by the perfectness of the CLC photonic bandgap, and the Sμ order parameter of the PL molecules, respectively. By continuously electrically manipulating the molecular ordering between the planar helicoidal state with a perfect photonic bandgap, the focal conic state with a macroscopic random ordering, and the unwound state with a highly uniaxial ordering, one can selectively produce those types of polarized emitted light with any degree of polarization. The wavelength dependency of the degree of polarization significantly varies depending on the types of polarization and LC alignment states.