Dynamic Out-Coupling Grating for Near-Eye Display Light Utilization
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Solution Overview
Problem
Pupil-replicating lightguides in near-eye displays suffer from low light utilization efficiency, leading to reduced image brightness and increased battery size and weight, making them uncomfortable to wear, especially in bright environments where outside light competes with augmented reality imagery.
Innovation Solution
Incorporating an out-coupling grating with spatially-selective and time-variant tunable efficiency in the pupil-replicating lightguide to optimize image light distribution based on eye position and orientation, using a controller and eye tracking system to adjust the grating efficiency and ensure light energy is directed only to the eyebox, thereby enhancing light utilization efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a brighter light source is used to compensate for low light utilization efficiency, then image brightness is improved, but battery size and weight increase
Solution Approach 1:
The out-coupling grating implements spatially-selective out-coupling efficiency, creating different out-coupling characteristics at different locations within the eyebox. This allows light to be preferentially directed toward the pupil region while reducing light in non-pupil regions, improving light utilization efficiency without requiring increased overall light source brightness.
Solution Approach 2:
The system performs preliminary light distribution optimization within the lightguide before light reaches the eyebox. By pre-shaping the light intensity distribution through the out-coupling grating to match the expected pupil position and size, the system ensures that light energy is already optimally positioned when it reaches the user's eye, eliminating the need for over-brightening the light source.
2Illumination intensity
If a brighter light source is used to compensate for low light utilization efficiency, then image brightness is improved, but device complexity increases
Solution Approach 1:
The out-coupling grating modifies the uniform out-coupling characteristic of conventional lightguides by introducing spatially-variable out-coupling efficiency. This creates a non-uniform light distribution pattern within the eyebox that concentrates light in the pupil region, improving light utilization without adding complex optical elements or requiring brighter light sources.
3Ease of operation
If light is distributed uniformly across the entire eyebox, then ease of operation is improved, but light utilization efficiency decreases
Solution Approach 1:
The out-coupling grating creates a non-uniform light intensity distribution across the eyebox by implementing spatially-selective out-coupling. Light intensity is enhanced in regions corresponding to the pupil position while reduced in non-pupil regions, thereby concentrating light energy where it is needed and reducing waste in unused regions.
Solution Approach 2:
The system pre-configures the light intensity distribution within the eyebox to match the anticipated pupil characteristics (position and size) before the user views the display. This preliminary optimization ensures that when the user looks through the device, light energy is already concentrated in the correct region, improving both usability and efficiency.
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 improves light utilization efficiency by ensuring that image light is focused on the eyebox, reducing the need for a brighter light source and minimizing battery size and weight, enhancing comfort and visibility in various lighting conditions.
Implementation Method 1
an out-coupling grating for out-coupling spaced apart portions of the image light towards an eyebox
Data Source
AI summary
A display device includes an image projector and a pupil-replicating lightguide having an out-coupling grating with configurable dynamic spatial distribution of out-coupling efficiency that may be adjusted depending upon several factors including currently displayed portion of the field of view as well as the eye position and orientation at the eyebox of the display device. For scanning display systems, the out-coupling grating may be configured to have a high-efficiency grating area that “runs” along the grating in coordination with the scanning to provide a more efficient light utilization in the display device.