Po-Hung Yao

Sub-15 nm linewidth gratings using roll-to-roll nanoimprinting and plasma trimming to fabricate flexible wire-grid polarizers with low colour shift

Sub-15 nm-wide gratings with a high aspect ratio of up to 16:1 were fabricated using roll-to-roll nanoimprinting and plasma trimming to achieve high optical performance (up to 12 000:1 extinction ratio with an average transmittance of 82%) and low colour shift (transmittance variation less than 3%) flexible wire-grid polarizers for display applications. We applied two imprint platforms onto glass and plastic substrates to identify the optical properties and characteristics of each fabrication process. To enhance the tolerance, reproducibility, and optical performance of the process, the grating profile symmetry and varying residual layer thicknesses were precisely simulated and controlled to achieve the design targets.

Low speckle laser illuminated projection system with a vibrating diffractive beam shaper

Currently the major issues in applying the laser as an illumination source for projectors are beam shaping and laser speckle. We present a compact total solution for both issues by using a diffractive beam shaper associated with a cylindrical lens for the illumination optics and a vibrating motor attached to the beam shaper to eliminate speckle on the projection screen. The diffractive beam shaper features a double-sided microlens array with a lateral shift to each other. The illumination pattern is free of zero diffraction order mainly due to the continuous and spherical surface relief of the lenslet, which can be accurately fabricated with diamond turning and injection molding without quantizing surface relief, so that the illumination pattern on the microdisplay can match the design very well with high diffraction efficiency. In addition, the vibration of the diffractive beam shaper in the longitudinal mode has been found effective for eliminating the dot pattern in the illumination and reducing laser speckle on the projection screen. The proposed laser illuminator has been implemented on a three-panel LCoS projector engine to replace the traditional UHP lamp. The uniformity and speckle contrast are measured to be 78% and 5.5% respectively, which demonstrates the feasibility and potential of the proposed scheme.

Polarized backlight with constrained angular divergence for enhancement of light extraction efficiency from wire grid polarizer.

Efficiency of liquid crystal displays highly depends on the amount of polarized light emerging from the backlight module. In this paper, a backlight architecture using a nanoimprint wire grid polarizer for polarization recycling is proposed and studied, in which the extraction efficiency of polarized light is the major concern. The backlight module is composed of the stack of a wire grid polarizer, a lenticular array and a light guide plate. The light guide plate features interleaving v-groove and trapezoidal ridge coated with aluminum on the top surface, and scattering dot array on the bottom. The angular divergence of emerging light from the light guide plate can be well constrained so as to exploit the angular range with the best transmission of polarized light for the wire grid polarizer. The prototype of a 2.5-inch module has demonstrated an angular divergence of 48°. The overall extraction efficiency of polarized light enhanced by 21% and uniformity of 76% have been achieved.

Double side lenslet array for illumination optics of laser projector

Laser is an ideal illumination light source for liquid crystal projection displays in terms of source Etendue and polarization. In order to make a conversion from a circular Gaussian laser beam profile to a rectangular uniform distribution on the microdisplay, a double side microlens array has been proposed as a homogenizer, and a cylindrical lens is exploited for shaping the aspect ratio of illumination pattern. The design and simulation based on scalar diffraction theory have shown that two identical lenslet arrays on each side of a thin plastic substrate with a lateral shift of half diagonal pitch can convert laser beam into a uniform square illumination at a specified near field. The pitch and curvature of the lenslet are major parameters for modifying the illumination distance, area and uniformity. The proposed lenslet array will provide an economical solution for the illumination optics of laser based light valve projector due to its regular and circular lenslet profile.

Strategy for developing high efficiency backlight module for LCD

The major efficiency loss in current liquid crystal displays(LCD) are the absorption in polarizers and color filter, and both can be resolved with decent backlight design which takes light polarization and color separation into consideration. Those improvement schemes on the backlight normally will not trade off the image quality readily achieved in the commercial LCD. Both polarization and color separation schemes for the backlight are reviewed with categorization on the basic concept, followed by the proposal of possible combinations for both direct lit and edge lit configuration with the consideration on the availability of associated components. Two total solutions, including polarization conversion module for LED and pixelized backlight with RGB LED for direct lit and edge lit respectively, are given with demonstration of preliminary result achieved so far as the efficiency improvement schemes for LCD backlight.

74.3: Color Separation Backlight System with Mosaic Pixel Arrangements

A color separation LCD backlight by pixelized illumination is described to eliminate conventional absorbing-type color filters, which is expected to enhance the gain factor of power efficiency. Several pixel mosaic configurations (RGBG stripe, RGBG diagonal and RBGG quad arrangements) are proposed for different applications.

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

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. 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 (Tp) 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.