Laser Backlight Speckle Reduction via Wavelength Shift
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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 reduces image resolution and aesthetic quality, and existing de-speckling techniques are costly and complex, impacting efficiency, reliability, and cost compatibility.
Innovation Solution
A laser-lit flat panel display system utilizing a bandwidth-enhancing technique with multiple lasing elements of primary colors, where each element emits a laser beam with a specific center wavelength and spectral bandwidth, and the beams are wavelength-shifted to create an ensemble spectrum with a mean spectral overlap parameter greater than 1, reducing speckle while maintaining color purity.
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 noise increases reducing image quality
Solution Approach 1:
The patent divides a single laser source into multiple spatially separated laser beams (at least three beams) with different propagation paths. Each beam illuminates the same target area but through different optical paths, which randomizes the speckle patterns and reduces their visibility when combined, while maintaining the narrow band spectral properties for color saturation.
Solution Approach 2:
The patent introduces spatial dimensionality by using multiple laser beams traveling along different paths to illuminate the same area. This multi-dimensional approach transforms the single-beam illumination into a multi-beam system where speckle patterns from different paths superimpose and cancel each other's coherence artifacts, while preserving color purity through spectral filtering.
2Object-affected harmful factors
If de-speckling techniques are applied to reduce speckle noise, then image quality is improved, but system complexity and cost increase
Solution Approach 1:
Instead of using complex post-processing de-speckling techniques, the patent segments the illumination into multiple laser beams with different optical paths from the beginning. This preventive segmentation approach inherently reduces speckle through optical path randomization without requiring additional complex de-speckling components or processing stages.
Solution Approach 2:
The patent applies speckle reduction through preliminary action by randomizing optical paths before the light reaches the display surface. By using multiple beams with different propagation paths from the start, the speckle patterns are naturally minimized through constructive and destructive interference, eliminating the need for subsequent complex de-speckling operations.
3Object-affected harmful factors
If multiple laser beams with different optical paths are used, then speckle noise is reduced, but optical system complexity increases
Solution Approach 1:
The patent uses segmentation to divide the illumination into multiple laser beams that travel along different optical paths. This segmentation is achieved through relatively simple optical components such as beam splitters or spatially separated lasers, creating multiple paths without requiring complex optical systems, thereby reducing speckle through path diversity.
Solution Approach 2:
The patent applies local quality by ensuring that each laser beam maintains its specific optical path characteristics while all beams converge on the same target area. Each beam's unique path introduces different phase and spatial variations that randomize speckle patterns locally, while the combined effect provides overall speckle reduction without complex system-wide modifications.
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
The solution effectively minimizes speckle noise, preserves color saturation, and enhances image resolution and aesthetic quality, improving reliability and reducing power consumption by operating lasers at lower output power, thus offering a cost-effective and efficient solution for high-resolution displays.
Implementation Method 1
each lasing element emits a laser beam with a center wavelength λ0i, and a spectral bandwidth Δλi
Implementation Method 2
Laser radiation is inherently narrow band and gives rise to the perception of fully-saturated colors. Unfortunately, narrow band light incident on random rough surfaces also introduces an unacceptable image artifact known as 'speckle'
Data Source
AI summary
Laser lit flat panel displays are disclosed including edge-lit and direct lit backlights. In certain embodiments, laser assemblies are selected to obtain bandwidth distributions to reduce speckle.