MEMS Micro-Mirror Prism for Speckle Reduction
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Solution Overview
Problem
Current micro-projection systems using laser light sources suffer from speckle interference and parasitic light reflections due to coherent light, leading to image deterioration and visual discomfort, and existing solutions are complex, expensive, and inefficient.
Innovation Solution
An optical MEMS scanning micro-mirror with a transparent prism covering the reflection side, where the outer and inner faces are non-parallel, providing a dual anti-speckle and anti-reflection effect, reducing parasitic reflections and speckle interference without additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transparent window or prism is added to protect the MEMS mirror, then the mirror surface is protected from dust and mechanical degradation, but parasitic light reflections occur at the air-window interfaces
Solution Approach 1:
The patent introduces an anti-reflective coating as an intermediary layer between the air and the transparent window/prism. This coating mediates the optical interaction by reducing the refractive index mismatch at the interface, thereby minimizing parasitic reflections while maintaining the protective function of the window.
Solution Approach 2:
The patent modifies the optical parameters of the window-prism interface by applying anti-reflective coatings with specific refractive indices. This parameter change (refractive index matching) reduces the reflection coefficient at the interfaces, eliminating the harmful parasitic reflections while preserving the protective enclosure.
2Object-affected harmful factors
If conventional speckle reduction techniques are used (diffusing elements, rotating refracting devices), then speckle interference is reduced, but the system complexity and cost increase significantly
Solution Approach 1:
The patent merges the protective window function with the speckle reduction function into a single integrated component. The transparent prism serves both as the protective enclosure for the MEMS mirror and as the speckle-reducing optical element, eliminating the need for separate diffusing elements or rotating refracting devices.
Solution Approach 2:
The transparent prism is designed to perform multiple functions simultaneously: it protects the MEMS mirror from environmental damage, provides the necessary optical path for light reflection, and reduces speckle interference through its specific geometric configuration. This multi-functionality simplifies the overall system while achieving speckle reduction.
3Loss of energy
If anti-reflective coatings are applied to reduce parasitic reflections, then reflection losses are minimized, but the manufacturing process becomes more complex
Solution Approach 1:
The patent employs self-service manufacturing techniques where the anti-reflective coatings are deposited directly onto the window or prism during the same fabrication process. This integrated approach allows the coatings to be applied automatically as part of the standard manufacturing sequence, minimizing additional process complexity while achieving the energy loss reduction.
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 and parasitic reflections, improving image quality and user comfort while maintaining system simplicity and reducing costs by integrating the prism into the MEMS packaging, ensuring efficient performance without degrading image sharpness.
Implementation Method 1
different speckle patterns are formed over time at the target with a temporal frequency greater than a temporal resolution of an illumination sensor or an eye of an observer so that speckle contrast ratio in the observed illumination is reduced
Implementation Method 2
A standard way to reduce these reflections is the deposition of anti-reflective coatings on both sides of the window, enabling the reduction of the parasitic reflections down to approximately 0.1% of the incoming light intensity
Implementation Method 3
Classically, MEMS mirrors are used in various optical applications and are usually delivered as stand-alone unprotected chips. When used in scanning applications for example, the incoming light is directly reflected on the mirror
Implementation Method 4
Speckle is a phenomenon created with laser light sources, due to the fact that laser light is coherent. Parallels and synchronized wavefronts simultaneously hit the projection surface. When the light hits the surface, it creates constructive and destructive interference.
Data Source
AI summary
Optical MEMS scanning micro-mirror comprising: —a movable scanning micro-mirror (101) pivotally connected to a MEMS body (102) substantially surrounding the lateral sides of the micro-mirror; —an transparent prism (500, 600) substantially covering the reflection side of the micro-mirror; —wherein said prism has its outer face non-parallel to the micro-mirror neutral plane N-N, thereby providing a dual anti-speckle and anti-reflection effect, namely against parasitic light. The invention also provides the corresponding micro-projection system and method for reducing speckle.