53.4: Highly Polarized Backlight Consisting of an Aperture‐limited Light Guide Plate and a Hybrid Wire‐Grid Polarizer

Abstract

On the purpose of improving the transmittance of LCD panels, the study of polarized illumination has been emphasized as one of the urgent topics to reduce the energy loss at the present absorptiontype polarizer of LCD cells. The polarization-selection property of nano-wire-grid structures has been widely studied for a reflective polarizer and applied to increase the transmittance of LCD. For a determined wire-grid polarizer, the transmittance of P polarization (T p ) depends on wavelength and incident angle. The effective incident angle is limited by total internal reflection (TIR) condition of selected polymer materials for wire-grid substrates. This paper presents a polarized backlight unit consisting of an aperture-limited light-guide plate featured by plurality of aluminum-coated trapezoid ridges on the output surface and a hybrid nano wire-grid which has been proposed to improve the transmittance of LCD by polarization recycling and emission angle control. Gain of central brightness was achieved up to 2.1x. IntroductionThe transmittance of current LCD panels is around 4-7% of the backlight emission mainly caused by the energy absorption of the down polarizer (>50% loss) and the color filter component (>67% loss). On the purpose of improving the transmittance of LCD panels the study of polarized illumination has been emphasized as one of the urgent topics to reduce the energy loss at the present absorption-type polarizer of LCD cells. Thus, the birefringence materials and components exhibiting polarization selection through transmission and reflection mechanism are studied and applied as the reflective polarizer for the LCD panels [1]. With highly flexible design freedom the texture-controllable birefringence property of the nano wire-grid (NWG) component consisting of metal grating or metal-dielectric grating at scale of 100s-200s nm has attracted lots of research works in the past decade. The geometric features of the NWG, like stack orientation, pitch, aspect ratio (AR), and duty cycle (DC), relates directly to its birefringence property denoted mainly by transmission of P polarization (Tp) and transmission of S polarization (Ts) and extinction ratio (Ext.R, defined by the ratio of Tp to Ts). In the edge-lit backlight units, many research works have applied the NWG structure onto the LGP to manipulate the polarization property for the emission light [2,3]. In order to control the angular distribution that determines the total extraction efficiency of P polarization from the NWG and the brightness concentration on the central axis of backlight units as the preferred illumination condition for LC cells the light extraction structure which generally comprises the plurality of micro vgrooves on the surface opposite to the NWG side of the LGP [2-5] is also required. However, it is difficult to fabricate the LGP with two individual structures at extremely different scales using current tooling arts.For the purpose on improving the efficiency of polarization extraction and also considering satisfactory uniformity...

Strategy for developing high efficiency backlight module for LCD

“…1(a). The reflective polarizer being used includes multilayer stacking of isotropic and birefringence film [4], wire grid polarizer [5-7] and cholesteric liquid crystal [8,9] etc., and the polarization recycling scheme include scattering [10] and retarder film [11,12]. Polarization conversion basically shares the same mechanism as polarization recycling but the light is conceptually fully polarized with single pass through the conversion module, as shown in Fig.…”