Polarization Recovery in Directional Display Backlights
Solution Overview
Problem
Spatially multiplexed autostereoscopic displays face issues with reduced spatial resolution, image flicker, and non-uniform viewing windows due to gaps between pixels, leading to limited viewing freedom and increased visual strain, with conventional backlight systems causing significant light loss through unpolarized illumination.
Innovation Solution
The implementation of an imaging directional backlight with a waveguide, light sources, and a polarizing reflecting element that separates and transforms polarization states, allowing for efficient directional illumination and increased brightness, utilizing a stepped waveguide structure and polarizing components to direct light into specific viewing windows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional backlight systems use unpolarized illumination, then the display can be illuminated, but significant light loss occurs reducing display brightness
Solution Approach 1:
The patent recovers polarized light that would otherwise be lost by using a polarizing beam splitter to separate and redirect polarized components back through the spatial light modulator, converting waste light into useful illumination and improving overall system efficiency
Solution Approach 2:
The patent changes the polarization state of light through the use of polarizing beam splitters and waveplates, transforming unpolarized or incorrectly polarized light into the desired polarization state for efficient SLM operation, thereby reducing light loss and increasing brightness
2Shape
If spatially multiplexed autostereoscopic displays use pixel aperture structures, then viewing windows are formed, but gaps between pixels produce non-uniform viewing windows and image flicker
Solution Approach 1:
The patent introduces a polarizing beam splitter and polarization control elements as intermediaries between the light source and the spatial light modulator, creating a more uniform illumination distribution that reduces flicker and improves viewing window uniformity without compromising the autostereoscopic effect
3Reliability
If defocusing is used to reduce image flicker, then flicker is reduced, but image cross talk increases and visual strain increases
Solution Approach 1:
The patent changes the polarization parameters of the illumination light to achieve flicker reduction without defocusing, using polarizing beam splitters and waveplates to control the polarization state and eliminate the need for defocusing that causes cross talk and visual strain
4Loss of energy
If a polarizing beam splitter is added to recover polarized light, then light efficiency increases, but device complexity increases
Solution Approach 1:
The patent designs the polarizing beam splitter and polarization control elements to serve multiple functions simultaneously: separating polarized light, redirecting it back through the SLM, and controlling the polarization state, thereby reducing the need for additional separate components and minimizing overall device complexity
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 solution enhances display brightness, extends battery life, and enables high-brightness operation in brighter environments while providing high-resolution, flicker-free autostereoscopic displays with improved viewing freedom and reduced cross-talk.
Implementation Method 1
the first guide surface being arranged to guide light by total internal reflection
Implementation Method 2
a reflective polariser disposed between the first guide surface of the waveguide and the spatial light modulator and arranged to transmit the first polarisation component and to reflect a second polarisation component
Implementation Method 3
a polarisation converter layer arranged to convert the polarisation of the rejected light supplied back to spatial light modulator into the first polarisation on reflection from a pair of corner facets
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
Disclosed is an imaging directional backlight polarization recovery apparatus including an imaging directional backlight with at least a polarization sensitive reflection component with optional polarization transformation and redirection elements. Viewing windows may be formed through imaging individual light sources and hence defines the relative positions of system elements and ray paths. The base imaging directional backlight systems provide substantially unpolarized light primarily for the illumination of liquid crystal displays (LCDs) resulting in at least 50% loss in light output when using a conventional sheet polarizer as input to the display. The invention herein introduces a polarization sensitive reflecting element to separate desired and undesired polarization states for the purposes of transformation and redirection of the reflected light for usable illumination. Polarization transformation and redirection can be provided by additional components such as retarder films and specular mirror surfaces.