Gradient Grating Perimeter for HMD Lightguide Outcoupler
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional head-mounted displays (HMDs) suffer from unwanted illumination on the world-side of the lightguide due to outcoupled display light, which can be distracting and interfere with the user's experience.
Innovation Solution
The implementation of a perimeter region with a gradient grating structure around the primary outcoupler region in the lightguide, which reduces the intensity of outcoupled light across the perimeter region, thereby softening the edges of the illuminated area and minimizing its visibility to observers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an outcoupler is used to direct light from the lightguide to the user's eye, then the display function is improved, but unwanted illumination appears on the world-side of the lightguide
Solution Approach 1:
The outcoupler is designed with spatially varying grating features where the first region (near the lightguide edge) has different grating characteristics than the second region (central area). This local differentiation allows the first region to redirect outcoupled light away from the world-side while the second region maintains normal display functionality, thus resolving the contradiction between achieving display function and eliminating unwanted illumination.
2Illumination intensity
If the outcoupler directs light efficiently to the user's eye, then the brightness of the virtual image is improved, but the illuminated area on the world-side becomes more visible
Solution Approach 1:
The outcoupler employs region-specific grating features where the first region near the edge redirects light away from the world-side and the second central region optimizes light direction toward the user's eye. This localized functional differentiation maintains high virtual image brightness while minimizing the visibility of the illuminated area on the world-side.
Solution Approach 2:
The outcoupler is segmented into distinct functional regions: a first region near the lightguide edge with grating features optimized for redirecting light away from the world-side, and a second central region with grating features optimized for directing light to the user's eye. This segmentation allows independent optimization of each region's light control characteristics.
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 effectively reduces the appearance of the illuminated area on the world-side, enhancing user experience by minimizing distractions and improving the aesthetic appeal of the HMD.
Implementation Method 1
an output optical coupling (i.e., an 'outcoupler'), which can also take the form of an optical grating
Implementation Method 2
the light beams are 'guided' through the substrate, typically by multiple instances of total internal reflection (TIR)
Data Source
AI summary
The present disclosure provides techniques to reduce the appearance of an illuminated area on the world-side of lens of a head mounted display (HMD) caused by display light that is outcoupled away from a user. A perimeter region is added to surround a primary region of an outcoupler, where the primary region includes a primary grating structure with one or more grating features to direct display light to the field of view (FOV) area of the user of the HMD. The perimeter region includes a perimeter grating structure with a perimeter grating feature that changes across the width of the perimeter region. In this manner, the perimeter region provides a perimeter grating structure gradient that gradually reduces the intensity of outcoupled display light across the width of the perimeter region, thereby having the effect of “softening” the edges of the outcoupler to reduce its appearance to observers.