Laser Despeckler Using Micro Scanner and Holographic Diffuser
Solution Overview
Problem
Current laser display technologies suffer from speckle, a granular structure caused by the high spatial and temporal coherence of lasers, which reduces image sharpness and is distracting to viewers, and existing methods like rotating diffusers and polarization diversity fail to completely eliminate speckle.
Innovation Solution
A despeckler device combining a micro scanner with a holographic diffuser, where the micro scanner deflects laser light into a variable refractive index medium with temporally varying electrodes to create a diffuse illumination patch, and the holographic diffuser further diffuses the light to reduce speckle contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a rotating diffuser is used to reduce speckle contrast, then speckle reduction is achieved, but mechanical complexity and reliability are worsened
Solution Approach 1:
The patent replaces the mechanical rotating diffuser system with an electrically controlled liquid crystal display (LCD) system. The LCD modulates the phase of light waves electronically through voltage-controlled pixel elements, eliminating moving parts while achieving the same speckle reduction effect through phase diversity. This substitution of mechanical system with electronic/optical system directly resolves the contradiction between speckle reduction and mechanical complexity.
Solution Approach 2:
The patent introduces an LCD as an intermediary device between the laser source and the diffuser. The LCD acts as a phase modulator that divides the light into multiple phase-shifted beams, which then interfere to reduce speckle contrast. This intermediary electronic phase modulation layer enables speckle reduction without requiring mechanical rotation, resolving the contradiction by adding an electronic mediation layer instead of mechanical complexity.
2Object-affected harmful factors
If a rotating diffuser is used to reduce speckle contrast, then speckle reduction is achieved, but reliability is worsened
Solution Approach 1:
The patent replaces the mechanical rotating diffuser system with an electrically controlled liquid crystal display (LCD) system. The LCD modulates the phase of light waves electronically through voltage-controlled pixel elements, eliminating moving parts while achieving the same speckle reduction effect through phase diversity. This substitution of mechanical system with electronic/optical system directly resolves the contradiction between speckle reduction and mechanical complexity.
Solution Approach 2:
The patent uses dynamically controllable LCD pixels that can rapidly switch phase states in response to electrical signals. This dynamic electronic phase modulation creates time-varying phase patterns that reduce speckle contrast without mechanical motion. The dynamic control is achieved through electrical rather than mechanical means, improving reliability by eliminating wear and mechanical failure modes.
3Object-affected harmful factors
If polarization diversity is used to reduce speckle, then speckle contrast is reduced, but device complexity increases
Solution Approach 1:
The patent segments the light beam into multiple spatial regions (pixels) on the LCD, where each pixel independently modulates the phase of the light passing through it. This segmentation creates multiple phase-shifted beams that interfere to reduce speckle contrast. The segmentation approach uses a single integrated LCD device rather than multiple separate polarization components, reducing overall device complexity while achieving speckle reduction.
Solution Approach 2:
The patent transitions from polarization-based speckle reduction (working in the polarization dimension) to phase-based speckle reduction using LCD pixels (working in the phase dimension). This dimensional change allows speckle reduction through phase modulation across the spatial profile of the beam, using a single device plane rather than multiple polarization components, thereby reducing 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
The device effectively reduces speckle contrast by generating unique speckle patterns within an eye resolution cell, providing a solid-state solution that improves image sharpness and reduces subjective speckle, achieving better results than traditional mechanical scanning methods.
Implementation Method 1
the micro scanner deflects laser light into a variable refractive index medium with temporally varying electrodes to create a diffuse illumination patch
Implementation Method 2
the holographic diffuser further diffuses the light to reduce speckle contrast
Implementation Method 3
speckle may be reduced by using an electro optic device to generate variations in the refractive index profile of material such that the phase fronts of light incident on the device are modulated in phase and or amplitude
Implementation Method 4
An SBG is formed by recording a volume phase grating, or hologram, in a polymer dispersed liquid crystal (PDLC) mixture
Implementation Method 5
During the recording process, the monomers polymerize and the HPDLC mixture undergoes a phase separation, creating regions densely populated by liquid crystal micro-droplets
Data Source
AI summary
A device for reducing laser speckle using a micro scanner and a holographic diffuser. The micro scanner includes a first transparent optical substrate with an input surface and an output surface and a second transparent optical substrate with an input surface and an output surface and a variable refractive index medium sandwiched between the output surface of the first substrate and the input surface of the second substrate. Transparent electrodes are applied to the output surface of the first substrate and the input surface of the second substrate. The electrodes are coupled to a voltage generator. The input surface of the first substrate is optically coupled to a laser source. The input surface of the second substrate is configured as an array of prismatic elements. At least one of the input surface of the first substrate or the output surfaces of the second substrate is planar.