Light Guide Lens Bonding to Prevent AR Projection Stray Light
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Solution Overview
Problem
Existing projection devices used in augmented reality (AR) experience total reflection on the outer surface of light guides, leading to stray light and the need for miniaturization and improved optical performance.
Innovation Solution
A projection device design where a lens is bonded to the light guide surface to prevent total reflection, with a lens group including a first side lens and an Nth lens in contact with the light guide, and optical axes orthogonal to each other, minimizing flare and allowing for a reduced total track length (TTL).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional light guide structure is used without bonded lenses, then the device structure is simpler, but total reflection occurs on the outer surface causing stray light and degraded optical performance
Solution Approach 1:
A lens is introduced as an intermediary component bonded to the light guide surface. This lens mediates between the light guide and the external environment, preventing total reflection while maintaining structural feasibility. The lens acts as a transition element that modifies the optical interface without requiring complete structural redesign.
2Length of moving object
If the light guide size is reduced for miniaturization, then the total track length is reduced, but optical performance deteriorates due to increased total reflection
Solution Approach 1:
The optical parameters at the light guide surface are changed by bonding a lens with specific refractive index and curvature. This parameter change prevents total reflection by modifying the critical angle condition, allowing miniaturization without optical performance degradation. The lens parameters are optimized to maintain light extraction efficiency in compact configurations.
3Reliability
If lenses are bonded to the light guide surface to prevent total reflection, then optical performance is improved and stray light is eliminated, but device complexity increases
Solution Approach 1:
The lens is merged with the light guide structure through direct bonding, creating an integrated optical assembly. This merging reduces the number of separate components and simplifies assembly while maintaining the optical performance benefits. The lens and light guide function as a unified optical element rather than separate components.
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 design effectively eliminates stray light and enables miniaturization of the light source, reducing the total track length and enhancing optical performance.
Implementation Method 1
a lens is bonded to a surface, through which light is emitted, of a light guide such that total reflection does not occur on an outer surface of the light guide
Implementation Method 2
a lens is bonded to a surface, through which light is emitted, of a light guide
Data Source
AI summary
An embodiment provides a projection device comprising: a light guide; a first light source disposed at a first side of the light guide; a lens group disposed at a fourth side of the light guide; and a first-side lens disposed between the first side of the light guide and the first light source, wherein: the lens group comprises first to Nth lenses; the first lens is located farthest from the fourth side of the light guide; the first side of the light guide overlaps the fourth side of the light guide in the optical-axis direction of the lens group; and the first-side lens and the Nth lens come into contact with the light guide.