Speckle Reduction in Scanning Projectors via Polarization Splitting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Scanning laser projectors face the issue of 'speckle' artifacts, which reduce image quality due to coherent light being projected onto randomly diffusing surfaces, causing intensity variations that appear as patches of light and dark to the human eye, and these variations change with the observer's position.
Innovation Solution
The introduction of a speckle reduction component that splits laser light into P and S polarization components, with one portion being internally reflected off multiple surfaces before recombination, creating a temporal incoherence that reduces speckle by averaging out uncorrelated speckle patterns, and this is achieved using a polarizing beam splitter and solid figure elements or an array of mirrors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent laser light is used for projection, then high brightness and sharp images are achieved, but speckle artifacts appear reducing image quality
Solution Approach 1:
The invention segments the coherent laser beam into multiple independent coherent sub-beams by passing it through a diffuser. Each sub-beam maintains coherence but has a slightly different wavefront. When these sub-beams are recombined and projected, they create multiple independent speckle patterns that average out to reduce visible speckle artifacts, while preserving the high brightness of laser light
Solution Approach 2:
The invention changes the spatial parameter of the laser beam by introducing random phase variations through a diffuser. This transforms the uniform coherent wavefront into multiple coherent beams with different spatial characteristics. The parameter change allows the system to maintain laser brightness while reducing speckle through statistical averaging of multiple independent speckle realizations
2Object-affected harmful factors
If a speckle reduction component is added to the optical path, then speckle is reduced by creating temporal incoherence, but device complexity increases
Solution Approach 1:
The invention introduces a diffuser as an intermediary element in the optical path between the laser source and the projection lens. This diffuser acts as a mediator that randomly scatters the coherent light into multiple sub-beams, creating temporal incoherence and reducing speckle. The diffuser is a simple passive optical element that achieves speckle reduction without requiring complex active control systems or multiple moving components
Solution Approach 2:
The invention employs a rotating diffuser or oscillating diffuser that periodically changes the scattering pattern over time. This periodic action creates temporal incoherence by ensuring that the speckle pattern changes during the exposure time, causing the human eye to perceive an averaged, reduced speckle image. The periodic motion is simple to implement and effectively reduces speckle without complex optics
3Object-affected harmful factors
If laser light is split and internally reflected off multiple surfaces, then temporal incoherence is created for speckle reduction, but optical power efficiency may be reduced
Solution Approach 1:
The invention segments the laser beam into multiple coherent sub-beams using a diffuser, where each sub-beam undergoes internal reflections off multiple surfaces. This segmentation creates temporal incoherence between sub-beams while maintaining high optical power efficiency because the diffuser and reflection surfaces are designed to minimize absorption and scattering losses. The multiple reflections are arranged to preserve beam intensity while achieving the desired incoherence effect
Solution Approach 2:
The invention uses composite optical structures including dielectric coating layers on reflection surfaces and potentially multiple diffuser materials with different scattering properties. These composite structures are engineered to provide high reflectivity and low absorption, maintaining optical power efficiency while creating the necessary temporal incoherence through controlled multiple reflections and scattering events
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 effectively reduces speckle in projected images by introducing temporal incoherence, improving image quality while maintaining compact size and high optical power efficiency, and can improve pixel size and resolution by ensuring the recombined beams are coaxial.
Implementation Method 1
splits laser light into P and S polarization components
Implementation Method 2
one portion being internally reflected off multiple surfaces before recombination
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 or array of mirrors 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 reflected in the second solid figure element or the array of mirrors 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.