Speckle Reduction in Scanning Laser Projectors
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Solution Overview
Problem
Scanning laser projectors face the issue of 'speckle' artifacts, which degrade image quality due to coherent light sources and randomly diffusing surfaces, causing intensity variations that appear as patches of light and dark, affecting the viewer's perception based on their position.
Innovation Solution
A scanning laser projector design that introduces temporal incoherence in the laser light by splitting it into P and S polarization components, using a polarizing beam splitter and solid figure elements to internally reflect and recombine the light, creating a relative delay between the components, resulting in reduced speckle through the averaging of uncorrelated speckle patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent laser light is used as the light source, then the brightness and coherence of the projected image is improved, but speckle artifacts appear that reduce image quality
Solution Approach 1:
The patent divides the coherent laser light into multiple incoherent components by passing it through a rotating diffuser that segments the light into multiple scattered paths, thereby reducing speckle while maintaining brightness
Solution Approach 2:
The patent introduces dynamic elements (rotating diffuser or acousto-optic modulator) that continuously change the optical path of the laser light during projection, creating temporal variations that average out speckle patterns over time
2Object-affected harmful factors
If a speckle reduction component is added to the projector, then speckle is reduced, but the device complexity increases
Solution Approach 1:
The patent introduces an intermediary component (rotating diffuser or acousto-optic modulator) placed in the optical path between the laser source and projection lens, which mediates the speckle reduction function without requiring complete system redesign
Solution Approach 2:
The patent changes temporal parameters of the light by introducing controlled time delays and variations in the optical path, transforming coherent light into temporally varying light that reduces speckle while maintaining system compactness
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 reduces speckle in projected images by introducing temporal incoherence, improving image quality while maintaining a compact device size and high optical power efficiency, with a speckle reduction factor of √2 when the optical power split is approximately 50/50 and the delay matches the coherence length of the laser light.
Implementation Method 1
splitting it into P and S polarization components, using a polarizing beam splitter
Implementation Method 2
using a polarizing beam splitter and solid figure elements to internally reflect and recombine the light
Implementation Method 3
The recombined light beams are then passed to at least one scanning mirror and reflected into a raster pattern of scan lines to form a projected image
Data Source
AI summary
Devices and methods are described herein that use a first solid figure element, a polarizing beam splitter, and a second solid figure element to reduce speckle in projected images. Specifically, laser light is generated and split into two portions having orthogonal polarizations. The first portion of laser light is internally reflected off at least three internal faces of the second solid figure element and is then spatially recombined with the second portion of laser light in the first solid figure element. The difference in path length followed by the two portions generates a temporal incoherence in the recombined laser light beam, and that temporal incoherence reduces speckle in the projected image.