Tilted Partial Faces Light Guide for Compact HMD Beam Management
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) face challenges in designing compact input coupling structures due to large field angles, which result in increased size and conspicuousness, and anatomical issues with beam alignment, limiting their social acceptance and practicality.
Innovation Solution
A light guide with an extensive output coupling structure featuring two tilted partial faces allows for manipulation of beam distribution, enabling input coupling via a perimeter face and reducing the cross-sectional area, facilitating compact design and efficient beam management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If beams are guided as collimated beams in the light guide, then the beam path can be maintained, but the cross-sectional area becomes larger with increasing distance from the eye, requiring larger input coupling structures
Solution Approach 1:
The patent transforms the beam guidance from purely collimated propagation to a converging beam path that focuses toward a focal point within the light guide. This dimensional change in beam geometry allows the cross-sectional area to decrease with distance from the input coupling structure, enabling smaller coupling structures while maintaining effective beam transport over the required optical path length.
2Adaptability or versatility
If large field angles are used to represent large initial image fields, then the field of view is improved, but the cross-sectional area of beams increases, requiring larger input coupling structures
Solution Approach 1:
The patent applies different optical properties to different regions of the light guide by implementing separate imaging channels with dedicated reflective elements for left and right eye fields. Each channel is optimized for its specific field region, allowing large overall field angles while keeping individual beam cross-sections manageable through localized beam convergence in each separate channel.
3Reliability
If the distance between spectacles and head is increased to accommodate beam alignment, then beam coupling can be achieved, but the anatomical acceptability deteriorates
Solution Approach 1:
The patent incorporates imaging optical units and reflective elements that pre-converge and pre-position the beams before they enter the light guide. This preliminary optical action ensures that beams are properly aligned and coupled into the light guide at the required angles, eliminating the need for increased spectacle-to-head distance while maintaining reliable beam coupling.
4Reliability
If beam combiners are attached at the front of spectacles, then optical function is achieved, but the spectacles become front-heavy and conspicuous
Solution Approach 1:
The patent extracts the beam combining function from a separate front-mounted component and integrates it into the spectacle lens itself through the light guide structure. The light guide is embedded within the lens, and the output coupling structure is formed as part of the lens rear face, eliminating the need for external beam combiners and achieving a more balanced, cosmetically acceptable design.
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 solution enables the use of smaller input coupling structures, allows for larger field angles, and optimizes the arrangement of image generators, resulting in a more compact and practical HMD design that maintains direct perception of surroundings.
Implementation Method 1
Guiding the light of the electronic image by way of total internal reflection in the spectacle lens
Implementation Method 2
In the case of a diffraction grating, the beam path of the electronic image is coupled out from the spectacle lens e.g. via the 1st order diffraction maximum
Data Source
AI summary
A light guide for an imaging apparatus for generating a virtual image from an initial image with at least two different initial image field regions is provided. The light guide includes an input coupling structure for coupling beams coming from the initial image into the light guide, and an extensive output coupling structure for coupling the beams that were coupled into the light guide out of the light guide. The extensive output coupling structure includes at least two partial faces. Each partial face is assigned to a different one of the initial image field regions and couples out the beams coming from the corresponding initial image field region. The partial faces of the output coupling structure are tilted about two non-parallel axes. The light guide can be part of an imaging apparatus, which can be used in particular in a head-mounted display.