Lightguide Diffractive In-Coupler Spatially Variable Pitch
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Solution Overview
Problem
Conventional head-mounted display devices are cumbersome due to their large, bulky, and heavy design, which affects user comfort, especially when equipped with heavy batteries, as they struggle to provide efficient illumination and a large enough eyebox for diverse user interpupillary distances.
Innovation Solution
A display apparatus featuring a pupil replicating lightguide with a diffractive optical element having a spatially variable pitch, which enhances light throughput by projecting images into the eye pupil at multiple positions within the eyebox, allowing for a compact and efficient configuration with improved illumination and accommodation of various user positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional head-mounted display devices use traditional lightguide configurations, then the device structure is simple, but the light throughput is insufficient and the eyebox is too small
Solution Approach 1:
The lightguide is divided into multiple functional zones along the propagation direction: an input region with a first diffraction grating for light coupling, a middle propagation region, and an output region with a second diffraction grating for light extraction. This segmentation allows each region to be optimized independently for its specific function, improving overall light throughput while maintaining manageable structural complexity.
Solution Approach 2:
Different regions of the lightguide are assigned different optical properties and structures. The input region uses a first diffraction grating with specific pitch and orientation optimized for coupling light from the display element, while the output region uses a second diffraction grating with different parameters optimized for extracting light toward the user's eye. This local optimization of properties throughout the lightguide enhances light throughput efficiency.
2Volume of moving object
If the lightguide uses a small out-coupler, then the device becomes more compact, but the eyebox size is reduced
Solution Approach 1:
The patent extends the light coupling and extraction process from a single point (small out-coupler) to a distributed linear structure along the propagation direction. By placing diffraction gratings that extend in the vertical direction (perpendicular to the display element plane), the system creates an elongated eyebox in the vertical dimension, allowing compact horizontal footprint while maintaining adequate vertical eyebox size.
Solution Approach 2:
The out-coupling function is segmented into multiple locations along the lightguide propagation path. Instead of relying on a single large out-coupler, the second diffraction grating is distributed along the output region, creating multiple extraction points that collectively form a sufficiently large eyebox while keeping individual coupler elements small.
3Ease of operation
If the display device is made compact, then user comfort improves, but illumination efficiency decreases
Solution Approach 1:
The patent replaces traditional bulk optical elements with diffractive optical structures (diffraction gratings) that achieve light manipulation functions with minimal material and compact dimensions. The diffraction gratings use optical interference effects rather than mechanical light redirection, enabling efficient light coupling and extraction in a compact form factor that maintains illumination efficiency while improving user comfort.
Solution Approach 2:
The patent optimizes the pitch, orientation, and depth parameters of the diffraction gratings to maximize light coupling and extraction efficiency within a compact lightguide structure. By carefully tuning these parameters, the system achieves high illumination efficiency in a reduced-size device, balancing compactness with performance.
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 increases the lightguide's throughput, making images appear brighter and more comfortable for users by accommodating different interpupillary distances, reducing the need for large out-couplers and alleviating the vergence-accommodation conflict, thus enhancing the overall user experience.
Implementation Method 1
an in-coupler including a diffractive optical element (DOE) having a spatially variable pitch; the DOE configured to couple the image light into the substrate
Implementation Method 2
the substrate having two opposing surfaces for guiding the image light within the substrate by total internal reflection from the surfaces
Implementation Method 3
a grating out-coupler supported by the substrate for out-coupling the image light from the substrate toward the eyebox
Data Source
AI summary
A display apparatus includes a lightguide for conveying images to an eyebox. The lightguide includes a substrate, a diffractive optical element (DOE) configured to couple the image light into the substrate. The DOE has a spatially variable pitch configured to provide the DOE with a positive optical power. The lightguide further includes a grating out-coupler supported by the substrate for out-coupling portions of the image light from the substrate toward the eyebox.