See-Through Optic Baffle Layout for Ghost Reflection Reduction
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Solution Overview
Problem
Existing head-mounted display systems with see-through optics suffer from secondary or ghost images that obscure and blur the actual image due to techniques that block large portions of light, reducing image brightness and clarity.
Innovation Solution
An optic with internal baffles positioned at oblique angles to intercept and redirect ghost images, using diffusing or light-absorbing structures that do not obstruct the desired image, maintaining the integrity of the projected image while reducing ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If shielding coatings are applied to exterior surfaces of optical elements to block ghost images, then ghost images are reduced, but light transmission is blocked and image brightness is reduced
Solution Approach 1:
The optical element is divided into functional zones: exterior surfaces remain uncoated for full light transmission, while interior surfaces receive selective coatings only in regions where ghost images are generated. This segmentation allows the system to block harmful reflections without sacrificing overall light transmission and image brightness.
Solution Approach 2:
Rather than applying uniform shielding coatings across entire exterior surfaces, the invention applies coatings locally only to specific interior surfaces where ghost images originate. This local quality approach ensures that light blocking is concentrated exactly where needed to eliminate ghost images, while preserving light transmission in all other areas.
2Object-affected harmful factors
If blocking plates are used to reduce ghost images, then ghost images are reduced, but large portions of relevant light are blocked and image brightness is reduced
Solution Approach 1:
The harmful reflective function is extracted from the exterior light-blocking plates and relocated to interior surfaces. By applying coatings only to specific interior surfaces where ghost images are generated, the system eliminates ghost images without requiring large exterior blocking plates that would obstruct relevant light and reduce image brightness.
3Object-affected harmful factors
If projections and depressions are added to scatter incident light, then ghost images are reduced, but relevant light is scattered and image clarity is reduced
Solution Approach 1:
The scattering function is applied locally only to interior surfaces where ghost images are generated, rather than across entire exterior surfaces. This localized approach ensures that scattering affects only the harmful ghost image light paths, while leaving the main image-forming light paths unaffected, thereby preserving image clarity.
4Object-affected harmful factors
If exterior coatings are applied to entire prisms to block ghost images, then ghost images are reduced, but all light passing through the prism is impeded and image brightness is reduced
Solution Approach 1:
The prism is segmented into coated and uncoated regions based on functional requirements. Interior surfaces that generate ghost images receive reflective coatings, while exterior surfaces and other interior surfaces remain uncoated to maintain full light transmission. This segmentation eliminates ghost images without impeding the light paths that form the main image.
Solution Approach 2:
Coatings are applied with local quality, meaning only specific interior surfaces where ghost images originate receive the reflective coating. This selective application ensures that light blocking occurs precisely where needed to eliminate ghost images, while preserving light transmission and image brightness in all other areas of the prism.
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 ghost images without obstructing the viewer's line of sight, enhancing image clarity and brightness by selectively blocking ghost rays while allowing unaltered transmission of desired light rays.
Implementation Method 1
The optic includes a beam splitter that provides transmission of at least a portion of incoming light rays to continue through the optic, and which may further provide reflectance of certain other light rays out of the optic.
Implementation Method 2
U.S. Pat. No. 5,838,504 discloses projections and depressions to create an uneven surface that scatters incident light, reducing the perception of the corresponding image.
Implementation Method 3
The light blocking portions of the plate reduce ghost images by blocking the corresponding light rays.
Data Source
AI summary
An optic providing reduction in secondary or ghost images includes a beam splitter, a reflective surface, and at least one baffle therebetween. A transmissive surface may be located between the beam splitter and the reflective surface. The baffle is positioned to intercept internally reflected ghost rays while being substantially parallel to outside light rays along a line of sight of the viewer, permitting use in see-through optics. The baffles may be formed of light absorbing material, diffusing structures, and combinations of both. Baffles intercept and absorb ghost rays to the exclusion of projected image rays that provide a desired projected image which are internally reflected through the optic. An assembly including such optic integrated with a wearable vision system, such as a head-mounted display, is also disclosed for near-eye application.