(Invited) Photoluminescence-Based Circular Polarization Convertors for Multiplexing of Optical Information

Abstract

Polarized light has a great potential to provide a variety of optical information at once such as light intensity (brightness), wavelength (color), and polarization. In particular, circularly polarized (CP) light is expected to be used not only for 3D display but also for optical data encryption and anti-counterfeiting, because the polarization plane of CP light rotates during light propagation resulting in no angular dependence on information transmission. The previously reported approaches for creating CP light from unpolarized light can be roughly classified into the filtration using a circular polarizer, the selective reflection by chiral liquid crystals, and the circularly polarized luminescence (CPL) from chiral luminophores. Meanwhile, we have recently proposed a new approach for creating highly-pure CP light by converting linearly polarized luminescence (LPL) using luminescence-based CP convertor (Figure 1a).[1] The unique advantage of the luminescence-based CP convertor lies in the spectral conversion properties of the LPL films which allows multiplexing of optical information by simply laminating LPL films. In this presentation, we introduce the multilayer-type luminescence-based CP convertors (Figure 1b) fabricated by using two or three LPL films showing different PL wavelength.In this study, we selected quantum rods (QRs) and π-conjugated luminescent polymers as one-dimensional (1D) luminophores. As a stretchable transparent polymer, poly(ethylene-co-vinyl acetate) (EVA) was used. LPL films were prepared by uniaxial stretching of the luminophore/EVA composite films. When yellow-, orange-, and red-color-emissive QRs were used as a luminophore, yellow-, orange-, and red-LPL were obtained as shown in Figures 1c-e. By laminating LPL film on the quarter-wave film with the angles between polarization plane of LPL and fast-axis of quarter-wave film were -45˚, 0˚, and +45˚, left-handed (LH-), parallel LP, and right-handed (RH-) CP light were produced, respectively. When the yellow-, orange-, and red-LPL films were laminated at three different angles (-45˚, 0˚, and +45˚) against the fast axis of the quarter-wave film, 3×3×3=27 different pieces of optical information were produced as shown in Figure 1f. Furthermore, time information on CP light can also be multiplexed theoretically by laminating several LPL films showing different fluorescence lifetimes. In this presentation, we will also discuss about time-multiplexing of optical information by multilayer-type luminescence-based CP light convertor consisting of multiple LPL films showing different PL lifetimes.[1] Y. Okazaki et. al., J. Mater. Chem. C, 2022. DOI: 10.1039/d2tc03955a. Figure 1