Birefringent Light Guide Plate for LCD Backlight Polarization
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Solution Overview
Problem
Existing edge light type illuminating devices for liquid crystal display devices have an insufficient increase in the percentage of p-polarized light component, leading to reduced use efficiency of backlight light due to a high percentage of s-polarized light component remaining in the light guide plate.
Innovation Solution
The implementation of a light guide plate with birefringence and a polarization state converting structure that includes a high refractive index layer and an optical sheet to refract light, converting the polarization state of light emitted from the light guide plate, thereby increasing the percentage of p-polarized light component and reducing the s-polarized light component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional light guide plate is used in an edge light type backlight, then the device structure is simple, but the percentage of p-polarized light component is insufficient and s-polarized light component remains high
Solution Approach 1:
The patent introduces a birefringent layer with specific refractive index anisotropy (nx ≠ ny) to change the optical parameters of the light guide plate. This causes different propagation velocities for s-polarized and p-polarized light, resulting in polarization state conversion that increases the p-polarized light component in the emitted light
Solution Approach 2:
The patent creates a composite structure by combining the light guide plate with a birefringent layer (such as a stretched polymer film or liquid crystal layer). This composite material approach allows the system to maintain the light guiding function while adding polarization control capabilities
2Loss of energy
If the percentage of p-polarized light component is increased using conventional methods, then use efficiency of backlight light improves, but the degree of polarization remains insufficient
Solution Approach 1:
The patent optimizes the refractive index parameters of the birefringent layer (nx, ny, and thickness) to achieve maximum polarization conversion efficiency. By carefully selecting these parameters, the system converts a high percentage of s-polarized light to p-polarized light, achieving both high use efficiency and high degree of polarization
Solution Approach 2:
The patent addresses the polarization conversion by introducing a new dimension of optical anisotropy through the birefringent layer. This adds a dimensional aspect to the light propagation control, enabling effective polarization state transformation that conventional isotropic materials cannot achieve
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly increases the degree of polarization of light emitted from the light guide plate, enhancing the use efficiency of backlight light in liquid crystal display devices by increasing the p-polarized light component and reducing power consumption.
Implementation Method 1
the light guide plate has birefringence in at least an in-plane direction of the front surface and is formed of a transparent medium having a slow axis in parallel to a longitudinal direction of the end surface
Implementation Method 2
an optical sheet which changes a propagation direction of the surface light ray emitted from the light guide plate
Data Source
AI summary
An illuminating device includes: a light source; a light guide plate which converts light emitted from the light source into a surface light ray and emits the surface light ray through a front surface of the light guide plate; and an optical sheet which changes a propagation direction of the surface light ray emitted from the light guide plate. The light source is arranged in opposition to one end surface of the light guide plate. A polarization state converting structure to convert a polarization state of the light propagating through the light guide plate is provided in a rear surface of the light guide plate. The polarization state converting structure contains an inclination plane having a ridge line extending in a direction perpendicular to the extension direction of the one end surface.