HMD Light Guide with Oriented Output Coupling for Compact Vertical Field
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) with large vertical field angles face challenges in maintaining compact dimensions due to the need for extensive light guides, which can result in aesthetically unappealing designs, especially when trying to couple light from the side to output coupling structures, leading to increased height and bulkiness.
Innovation Solution
A light guide system for HMDs with oriented output coupling structures that adjust the wave vectors' ky/kxz ratio to guide beams at larger vertical angles at smaller angles within the light guide, allowing for a compact design by dividing the angular spectrum into parts and using multiple input and output coupling structures to achieve field stitching and avoid crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If light is coupled from the side to output coupling structures in conventional HMDs, then large vertical field angles can be achieved, but the vertical extent and height of the light guide increase, resulting in bulky and aesthetically unappealing designs
Solution Approach 1:
The angular spectrum is divided into multiple parts (first angular spectrum portion and second angular spectrum portion) that are transmitted through different beam paths within the light guide. This segmentation allows each portion to be optimized for compact transmission, enabling large vertical field angles without increasing the overall vertical extent of the light guide structure.
Solution Approach 2:
The patent utilizes the lateral dimension of the light guide to transmit different angular spectrum portions, rather than solely relying on vertical stacking. By guiding light beams laterally through the light guide and using multiple output coupling structures at different lateral positions, the system achieves large vertical field angles while maintaining a compact vertical profile.
2Reliability
If multiple input and output coupling structures are used to divide the angular spectrum, then field stitching and avoidance of crosstalk are achieved, but the device complexity increases
Solution Approach 1:
Multiple output coupling structures are combined within a single light guide system, where each structure handles a specific portion of the angular spectrum. The light guide integrates these multiple coupling structures into one unified device, achieving field stitching and crosstalk prevention without proportionally increasing overall device complexity.
Solution Approach 2:
Different regions of the light guide are assigned different functions: input coupling structures are positioned at specific locations for coupling in light, while output coupling structures are positioned at different lateral positions for coupling out specific angular spectrum portions. This local differentiation enables precise field stitching and crosstalk avoidance through optimized spatial arrangement.
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
Enables the transmission of large vertical fields with a compact light guide design, maintaining aesthetic appeal by reducing the vertical extent of the light guide and preventing crosstalk, thus providing flexibility in shaping the light guide to fit various HMD forms.
Implementation Method 1
Guiding the light of the electronic image by way of internal reflection in the spectacle lens
Implementation Method 2
The output coupling structure can be embodied as a diffraction grating, as a partially transparent, inclined mirror or in the form of partially transparent Fresnel elements. 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 first order diffraction maximum
Implementation Method 3
The output coupling structure can be embodied as a diffraction grating, as a partially transparent, inclined mirror or in the form of partially transparent Fresnel elements
Data Source
AI summary
A light guide for guiding light for an HMD includes at least one input coupling structure and at least one output coupling structure. The output coupling structure can be oriented such that for all the rays that are coupled out by the output coupling structure and for which the wave vector k has a negative ratio ky/kxz after they have been coupled out, the wave vector k in the light guide has a ratio of ky/kxz of greater than −0.2, and/or that for all the rays that are coupled out by the output coupling structure and for which the wave vector k has a positive ratio ky/kxz after they have been coupled out, the wave vector k in the light guide has a ratio of ky/kxz of less than +0.2.