Alternating Mirror Light Guide for Smartglasses Imaging
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Solution Overview
Problem
Conventional optical systems for smartglasses suffer from limited imaging quality and field of view due to the use of free-form Fresnel surfaces, which result in reduced eyebox size and potential for ghost images, making it difficult to achieve high imaging quality while maintaining a compact and aesthetically pleasing design.
Innovation Solution
The optical system employs a configuration with multiple individual mirrors arranged in alternating fashion along the light propagation direction, allowing for high imaging quality and a large field of view without additional imaging units, and subdivides the source image into multiple imager regions with corresponding mirror groups to ensure seamless image overlay and avoid distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a free-form Fresnel surface with multiple reflecting Fresnel segments is used for output coupling, then the optical system can be made compact, but the imaging quality deteriorates due to surface discontinuities and restricted field of view
Solution Approach 1:
The optical system is divided into multiple independent partial systems, each comprising an imager region and associated optical elements. This segmentation allows each partial system to be optimized independently for high imaging quality while maintaining overall compactness through the folded beam path in the light guide.
Solution Approach 2:
The beam path is folded back on itself within the light guide thickness direction, transforming a potentially long linear path into a compact three-dimensional configuration. This allows the optical system to achieve high imaging quality with sufficient optical path length while maintaining a thin, compact form factor suitable for smartglasses.
2Volume of moving object
If the output coupling arrangement is placed close to the exit pupil to maintain compactness, then the system size is reduced, but imaging quality deteriorates due to sensitivity to surface trueness
Solution Approach 1:
The output coupling is divided into multiple discrete reflecting elements (Fresnel segments or individual mirrors) distributed along the beam path rather than a single continuous surface. This segmentation reduces the cumulative effect of surface errors and relaxes the trueness requirements while maintaining compact positioning near the exit pupil.
Solution Approach 2:
Each reflecting element in the segmented output coupling arrangement can be independently optimized for its local function, allowing tolerances to be distributed across multiple elements rather than requiring high precision across a single large surface. This local optimization approach maintains imaging quality while reducing overall manufacturing difficulty.
3Ease of manufacture
If individual Fresnel segments are used for output coupling, then the system can be manufactured with simpler surfaces, but ghost images are generated due to shadow regions between segments
Solution Approach 1:
The harmful shadow regions between Fresnel segments are eliminated by extracting the problematic discontinuities and replacing them with individually optimized mirror elements. Each mirror element is positioned and shaped to eliminate shadow casting, removing the source of ghost images while maintaining the segmented structure's manufacturing advantages.
Solution Approach 2:
The segmented structure, which initially causes shadow regions and ghost images, is transformed into a beneficial configuration by individually optimizing each segment's position and shape. The segmentation allows for precise control of light paths from different imager regions, converting the potential harm of discrete elements into the benefit of tailored light beam control that eliminates ghost images.
4Area of stationary object
If multiple imager regions are used to provide the source image, then the field of view is improved, but the device complexity increases due to additional optical paths
Solution Approach 1:
The light guide structure serves multiple functions simultaneously: it guides light from multiple imager regions, provides the optical path for multiple partial systems, and acts as the structural framework for the entire smartglasses system. This multi-functionality reduces overall device complexity despite the increased field of view requirements.
Solution Approach 2:
Multiple optical paths from different imager regions are merged within the shared light guide structure. The light guide consolidates what would otherwise be separate optical systems into a single integrated structure, reducing component count and overall system complexity while maintaining the expanded field of view provided by multiple imager regions.
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 configuration enables a compact and aesthetically pleasing smartglasses design with improved imaging quality and a larger field of view, reducing the need for additional optical components and minimizing the impact on the 'see-through' function, while ensuring consistent image representation.
Implementation Method 1
The coupling of the light propagating in the light guide, typically by way of total-internal reflection, at the outer surfaces of the light guide out of the light guide to the eye of the user
Implementation Method 2
the output coupling arrangement comprising a plurality of individual mirrors, which in each case are arranged at a distance from one another in the light propagation direction
Data Source
AI summary
An optical system includes a light guide to be worn in front of one eye, which guides light beams from the source image into the light guide and towards a reflective outcoupling arrangement, which couples the light beams out of the light guide to the eye. The outcoupling arrangement has a plurality of individual mirrors, which are spaced apart from one another in the light propagation direction. A first group of individual mirrors couples first light beams, which originate from a first imaging region, out of the light guide towards the eye, and at least one second group of individual mirrors couples second light beams, which originate from a second imaging region, out of the light guide towards the eye. The individual mirrors of the first group and the second group are each arranged alternating in the light propagation direction.