Off-Axis 4f Optical Relay for Mixed Reality Image Combining
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Solution Overview
Problem
Existing augmented reality display technologies face challenges in achieving a high field of view (FOV) with a small form factor while effectively controlling wavefront curvature, amplitude, and polarization, and suffer from inefficiencies in waveguide combiners and reflective optics.
Innovation Solution
A novel optical system using a free space relay system with off-axis 4f-systems and surface relief diffractive optical elements (SRDOEs) to relay virtual images onto the eye pupil plane, combining them with real-world scenery, allowing for a large eyebox and FOV while maintaining a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If waveguide combiners are used to combine virtual and real light, then the optical system can be compact, but the efficiency is reduced and chromatic aberrations occur
Solution Approach 1:
The patent extracts the diffractive optical elements from the waveguide structure and places them in free space, eliminating the waveguide while maintaining compactness through the off-axis 4f-system configuration. This allows high-efficiency diffraction without waveguide losses.
Solution Approach 2:
The patent introduces free space as an intermediary medium between the display optics and the eye, using diffractive optical elements to couple light into the eye's pupil. This intermediary approach achieves both compactness and high efficiency by avoiding direct waveguide coupling losses.
2Volume of moving object
If waveguide combiners are used to combine virtual and real light, then the optical system can be compact, but chromatic aberrations increase
Solution Approach 1:
The patent uses diffractive optical elements with wavelength-dependent diffraction angles to differentially redirect different colors of light. By adjusting the diffraction parameters of multiple DOEs, the system compensates for chromatic aberrations while maintaining a compact off-axis 4f-system configuration.
3Volume of moving object
If reflective optics are used, then the optical path can be folded for compactness, but the vergence-accommodation conflict increases
Solution Approach 1:
The patent replaces reflective optics with diffractive optical elements that operate in transmission rather than reflection. This substitution eliminates the vergence-accommodation conflict caused by reflective paths while maintaining compactness through the off-axis 4f-system's folded optical arrangement.
4Area of moving object
If the eyebox is enlarged to support alignment tolerances, then the optical system complexity increases according to the etendue invariant
Solution Approach 1:
The patent uses dynamic pupil steering through gaze tracking to actively adjust the exit pupil position and size, matching it to the user's eye pupil in real-time. This dynamic adaptation achieves a large functional eyebox without requiring a statically complex optical system, as the system adapts to user movement rather than providing a fixed large eyebox.
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 system provides high efficiency and flexibility in controlling light field properties, reducing chromatic aberrations, and minimizing the vergence-accommodation conflict, thereby enhancing the mixed reality experience.
Implementation Method 1
at least one lens formed from at least one resonance-domain surface relief diffractive optical element (SRDOE) operable for combining said virtual image light field with the real-world light field
Implementation Method 2
A novel optical system using a free space relay system with off-axis 4f-systems and surface relief diffractive optical elements (SRDOEs) to relay virtual images onto the eye pupil plane
Data Source
AI summary
An optical system is presented for use in a near-eye mixed reality system. The system comprises a relay system defining an eyebox of the optical system, said relay system being configured and operable to relay a virtual image light field from a light-engine onto an eye pupil plane while combining said virtual image with real-world light field. The relay system is configured as a free space relay system configured for free space propagation of said virtual image light field being relayed, said free space relay system comprising at least one off-axis 4f-system. Each of said at least one off-axis 4f-system comprises at least one lens formed from at least one resonance-domain surface relief diffractive optical element (SRDOE) operable for combining said virtual image light field with the real-world light field, said at least one SRDOE being configured with a predetermined global surface relief pattern characterized by global variation of at least some of pattern parameters across said SRDOE.