AR Optical Combiner with Four-Pass Collimation
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Solution Overview
Problem
Existing augmented reality (AR) display systems, particularly off-axis retinal scanning displays (ORSDs), face challenges such as small eyeboxes, limited field of view, and the need for complex or bulky optical components, which affect user experience and practicality.
Innovation Solution
The optical system comprises an image generator and an optical combiner configured to transmit ambient light while reflecting and controlling the divergence of image light, allowing it to traverse the optical combiner four times and exit as collimated light. This design replicates the exit pupil at multiple positions, expanding the eyebox and reducing the thickness of the eyepiece, resulting in a more compact and efficient AR display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transmissive optical combiner with beam splitter is used in the eyepiece, then ambient light can be transmitted, but a proportion of image light is lost and power is wasted
Solution Approach 1:
The patent replaces the transmissive beam splitter with a reflective optical combiner that uses polarization-dependent reflection. The combiner reflects image light back through the waveguide while transmitting ambient light, eliminating the need for light-absorbing beam splitters and associated polarizing beamsplitters, thereby reducing energy loss and simplifying the optical path.
Solution Approach 2:
Instead of discarding absorbed light through a beam splitter, the reflective combiner recovers and redirects image light back through the waveguide by using polarization-dependent reflection. This allows the image light to be reused multiple times (up to four passes) before exiting, maximizing light utilization efficiency.
2Area of stationary object
If pupil replication is used to increase eyebox size, then the eyebox expands, but bulky optics such as prisms are required
Solution Approach 1:
The patent implements nested optical paths where the image light traverses the waveguide multiple times (up to four passes) in a compact folded geometry. The waveguide itself is folded to create multiple reflection paths, effectively nesting the optical path within a small volume, eliminating the need for bulky external prisms while achieving pupil replication and eyebox expansion.
Solution Approach 2:
The patent uses folded waveguide geometry to convert a linear optical path into a three-dimensional folded path. By reflecting light at angles within the waveguide structure, the system achieves multiple passes (up to four) within a compact footprint, effectively using spatial folding to expand the optical path length without increasing the physical device volume.
3Area of stationary object
If a folded optical path with multiple traversals is used, then the eyebox expands and field of view increases, but the optical path becomes more complex
Solution Approach 1:
The folded waveguide structure serves multiple functions simultaneously: it guides image light through multiple reflections, transmits ambient light, and creates the folded optical path for pupil replication. The same waveguide structure that provides mechanical support also performs the optical functions of light guidance, reflection, and path folding, reducing the need for separate optical components and simplifying the overall system despite the complex light path.
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
The solution achieves a practical eyebox size, maintains a compact optical system, and provides a wide field of view while minimizing the use of complex or bulky components, thus enhancing user experience and manufacturing simplicity.
Implementation Method 1
the optical combiner is configured to transmit ambient light from the scene towards an eye of the user
Implementation Method 2
the optical combiner is configured to reflect, and control the divergence of, the image light so that the image light traverses the optical combiner four times
Implementation Method 3
exits the optical combiner as collimated light from the second side of the optical combiner
Data Source
AI summary
An optical system for AR displays includes an image generator for generating image light, and an optical combiner for location in a field of view of a user of the optical system between the user and a scene. The optical combiner transmits ambient light from the scene towards a user eye, the ambient light being incident on a first side of the optical combiner. The image generator and the optical combiner are arranged so image light is incident on a second side of the optical combiner, the second side of the combiner being opposite to the first side of the optical combiner. The optical combiner reflects and controls the divergence of the image light so the image light traverses the optical combiner four times and exits the optical combiner as collimated light from the second side of the optical combiner, whilst the ambient light traverses the optical combiner only once.