Angle Multiplexed Diffractive Combiner for Compact AR Eyebox
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Solution Overview
Problem
Existing off-axis retinal scanning displays for wearable heads-up displays have limited design flexibility and are bulky due to the requirement for pupil replication to occur at specific optical planes, which restricts the positioning of optical elements and results in a small eyebox, making them inefficient for mass production and user comfort.
Innovation Solution
The use of a splitting element, such as a diffractive splitting element, positioned away from the image and Fourier planes, combined with a volume phase holographic (VPH) element that applies individual optical functions to replicated beams based on their angle of incidence, allows for replication and collimation of light to expand the eyebox and provide greater design flexibility, enabling a more compact and efficient optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pupil replication is performed at traditional image or Fourier planes, then the optical system can be designed with conventional elements, but the system becomes bulky and design flexibility is limited
Solution Approach 1:
The patent moves pupil replication from traditional 2D planes (image or Fourier planes) to a 3D volumetric space using a volume phase holographic element. This allows replication to occur throughout a volume rather than constrained to specific planes, enabling compact integration while maintaining design flexibility. The VPH element creates multiple exit pupils at different positions and orientations within the optical path, achieving the desired adaptability without increasing system volume.
2Ease of operation
If conventional pupil replication methods are used, then the optical functions can be collected by single optical elements, but the eyebox remains small and positioning flexibility is restricted
Solution Approach 1:
The patent segments the optical functions by using a volume phase holographic element that can simultaneously perform multiple operations: splitting incident light into multiple directions, collimating beams with different angles, and directing them to different exit pupil positions. This segmentation of optical functions within a single volumetric element allows for a larger effective eyebox while simplifying the positioning requirements compared to multiple separate optical elements.
Solution Approach 2:
The VPH element serves multiple optical functions simultaneously - it acts as a beam splitter, collimator, and directional steering element all in one component. This multi-functionality allows the system to achieve a larger eyebox and greater positioning flexibility without increasing device complexity, as a single element performs what would traditionally require multiple separate components.
3Productivity
If the optical system is designed for mass production, then manufacturing efficiency improves, but custom fitting for individual head shapes becomes impractical
Solution Approach 1:
The patent enables easy adjustment of optical parameters (such as exit pupil positions, beam angles, and replication geometry) by modifying the VPH element's holographic gratings or repositioning it within the optical path. This allows the same mass-producible optical system to be quickly adapted to different user head shapes and sizes by changing optical parameters rather than requiring custom manufacturing for each user, thus maintaining high productivity while achieving adaptability.
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 results in a thinner, more compact, and efficient optical system with a larger eyebox, allowing for greater flexibility in positioning optical elements and improved user experience by reducing the need for bulky components and accommodating different head shapes and sizes.
Implementation Method 1
a splitting element configured to split incident light into a plurality of directions
Implementation Method 2
a first volume phase holographic (VPH) element comprising a plurality of multiplexed holograms, each hologram configured to selectively collimate incident light according to a respective angle of incidence on the first VPH element
Data Source
AI summary
An optical system for a wearable heads-up display includes an image projector configured to project an image towards an eye of a user and a combiner element positioned in a field of view of the user and in an optical path between the image projector and the eye of the user. The combiner element is configured to replicate the image onto a plurality of positions in a plane at the eye of the user. The combiner element includes a splitting element configured to split incident light into a plurality of directions and a first volume phase holographic (VPH) element. The first VPH element includes a plurality of multiplexed holograms, each hologram configured to selectively collimate incident light according to a respective angle of incidence on the first VPH element.