Eyebox Expansion in Wearable Heads-Up Displays Using Optical Splitter
Solution Overview
Problem
Conventional wearable heads-up displays with scanning laser projectors typically have a small eyebox, limiting the range of eye positions from which content is visible, as they employ a fixed exit pupil that aligns with the user's entrance pupil, restricting the field of view and resolution when the user glances off-center.
Innovation Solution
The solution involves optically replicating and spatially distributing multiple exit pupils over a larger area using a holographic combiner, a split mirror, and an optical splitter, allowing light signals to be redirected from virtual positions, thereby expanding the eyebox while maintaining high image quality and minimal bulk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a fixed exit pupil is used to align with the user's entrance pupil, then image resolution is maintained, but the eyebox size is limited
Solution Approach 1:
The single exit pupil is segmented into multiple exit pupils (first exit pupil and second exit pupil) that are spatially distributed across different locations. This segmentation allows the system to maintain high image resolution for each individual pupil while collectively providing a larger eyebox area that accommodates multiple eye positions and gaze directions.
Solution Approach 2:
The patent transitions from a single-point exit pupil in one location to multiple exit pupils distributed across two spatial dimensions. The optical splitter and holographic combiner work together to project light from multiple virtual positions, effectively adding a spatial distribution dimension that expands the eyebox while maintaining the precision of individual pupil projections.
2Adaptability or versatility
If optical components are added to expand the eyebox, then the range of visible eye positions increases, but the device bulk increases
Solution Approach 1:
The patent combines multiple functions into integrated optical components. The optical splitter simultaneously creates multiple virtual image positions and directs light to multiple exit pupils. The holographic combiner merges the projection of multiple exit pupils into a single wearable display unit. This merging allows eyebox expansion without proportionally increasing device bulk, as each component performs multiple optical functions.
Solution Approach 2:
The holographic combiner serves multiple functions: it acts as a beam combiner, a waveguide, and a display element simultaneously. The optical splitter performs both image duplication and light routing functions. This multi-functionality reduces the number of separate components needed, thereby expanding the eyebox without proportionally increasing the overall device volume.
3Ease of operation
If the exit pupil is positioned for direct ahead gaze, then content is visible at that position, but content disappears when the user gazes off-center
Solution Approach 1:
The patent creates multiple copies of the exit pupil image at different spatial locations (first exit pupil and second exit pupil). Each copy is positioned to be visible from different eye positions and gaze directions. When the user's eye is at one position, they see content from one virtual position; when the eye moves to another position, they see content from another virtual position, effectively copying the display function across multiple spatial locations.
Solution Approach 2:
The system changes the spatial parameters of the exit pupil by creating multiple pupils at different locations rather than using a single fixed exit pupil. The optical splitter modifies the light path parameters to originate from multiple virtual positions, and the holographic combiner adjusts the projection parameters to deliver images to multiple exit pupil locations, enabling content visibility across different gaze directions.
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 approach effectively increases the eyebox size, ensuring that the display remains visible across a range of gaze directions without compromising image resolution or increasing the device's bulk, allowing users to see both the display and their environment.
Implementation Method 1
an optical splitter carried by the support structure, the optical splitter comprising at least one optical element arranged to receive light signals generated by the scanning laser projector and redirect each light signal towards the holographic combiner effectively from one of N spatially-separated virtual positions
Implementation Method 2
a split mirror carried by the support structure, the split mirror comprising at least two non-coplanar reflective surfaces to receive light signals from the scanning laser projector and redirect the light signals towards the optical splitter
Implementation Method 3
a holographic combiner carried by the support structure and positioned in a field of view of the user
Implementation Method 4
a holographic combiner carried by the support structure and positioned in a field of view of the user when the support structure is worn on the head of the user
Data Source
AI summary
Systems, devices, and methods for eyebox expansion in wearable heads-up displays (WHUD) are described. A WHUD includes a support structure, a scanning laser projector (SLP), a split mirror, an optical splitter, and a holographic combiner. When the WHUD is worn on the head of a user the holographic combiner is positioned in a field of view of the user. The SLP scans light signals onto the split mirror which reflects the light signals onto the optical splitter. The optical splitter redirects the light signals towards the holographic combiner such that subsets of the light signals originate from spatially-separated virtual positions. The holographic combiner redirects the light to the eye resulting in spatially-separated exit pupils. The spatial separation of the exit pupils results in an expanded eyebox. The indirect path of light from SLP to optical splitter enables a smaller and therefore more aesthetically desirable design for the WHUD.