Laser Backlight Speckle Reduction via Polarization Recycling
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Solution Overview
Problem
Laser-based display systems suffer from image artifacts known as speckle due to narrow band light on random rough surfaces, which reduce image resolution and aesthetic quality, and existing de-speckling techniques often compromise efficiency, cost, reliability, and power consumption.
Innovation Solution
A polarization enhancement film is used in liquid crystal displays (LCDs) to increase the polarization of light, allowing only desired polarization to pass through while recycling undesired polarized light back into the backlight for random re-polarization, thereby enhancing the amount of polarized light reaching the LCD panel and reducing speckle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If narrow band laser light is used for illumination, then color saturation and purity are improved, but speckle artifacts are introduced that reduce image quality and resolution
Solution Approach 1:
The patent segments the narrow band laser light into multiple wavelength components using a diffuser, which spatially separates different wavelengths to reduce speckle while maintaining color saturation. This segmentation approach allows the system to process each wavelength component separately, reducing the coherence effects that cause speckle.
Solution Approach 2:
The patent introduces spatial dimensionality by using a diffuser to create multiple spatial paths for different wavelength components. This transforms the problem from a temporal coherence issue to a spatial distribution problem, where speckle patterns from different paths interfere destructively, reducing overall speckle visibility.
2Object-affected harmful factors
If de-speckling techniques are applied to reduce speckle artifacts, then image quality is improved, but efficiency and power consumption are compromised
Solution Approach 1:
The patent applies preliminary action by incorporating the diffuser at the light source level before light enters the display system. This early intervention in the optical path prevents speckle formation rather than correcting it later, avoiding the efficiency losses associated with post-processing de-speckling techniques.
Solution Approach 2:
The diffuser acts as an intermediary element between the laser light source and the display panel. It mediates the interaction by randomly scattering light to reduce coherence while maintaining overall light transmission, thus reducing speckle without significant efficiency loss.
3Object-affected harmful factors
If broad spectral bandwidth is used to reduce speckle, then speckle artifacts are minimized, but color purity and saturation are reduced
Solution Approach 1:
The patent applies local quality by allowing different spatial regions of the light distribution to have different spectral characteristics. The diffuser creates local wavelength separation where each spatial region contains primarily one wavelength component, maintaining color purity locally while achieving speckle reduction globally through the combination of all regions.
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 approach improves the efficiency and reliability of laser-based displays by minimizing speckle noise while maintaining color purity and increasing the transmission efficiency and image contrast, leading to a more effective and cost-compatible solution for high-resolution imaging applications.
Implementation Method 1
A polarization enhancement film increases the polarization of light from the light distributor by allowing light of a first polarization to pass through the film. Light that is not of the first polarization is reflected back into the backlight for random re-polarization within the backlight.
Implementation Method 2
Light that is not of the first polarization is reflected back into the backlight for random re-polarization within the backlight.
Data Source
AI summary
A flat panel display includes a backlight with a plurality of lasing elements. A light distributor distributes light from the lasing elements across the flat panel display. In edge-lit backlights, the light distributor may be a light guide. In direct-lit backlights, the light distributor may be one or more light diffusers that randomize the polarization of light. A polarization enhancement film increases the polarization of light from the light distributor by allowing light of a first polarization to pass through the film and reflecting light that is not of the first polarization back into the backlight. The light reflected back into the backlight is randomly re-polarized within the backlight. An array of light modulators arranged across the flat panel display modulates light emitted by the backlight.