See-Through Display Free-Form Optics for Wider AR Eye Box
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Solution Overview
Problem
Existing augmented reality devices face challenges with narrow eye boxes due to off-axis aberrations caused by combiners, particularly when using holographic optical elements, which limit the viewer's ability to see clear images unless their eyes are accurately positioned at a small focal point.
Innovation Solution
Incorporating a free-form optical element that generates correction aberrations opposite to the off-axis aberrations generated by the combiner, utilizing a configuration that includes a spatial light modulator, collimating lens, beam splitter, and a free-form optical element to minimize aberrations and satisfy the Scheimpflug condition, thereby enhancing image clarity across a wider range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a holographic optical element (HOE) is used as a combiner to implement complex optical characteristics in a simpler structure, then device complexity is reduced, but off-axis aberration increases causing narrow eye box
Solution Approach 1:
A free-form optical element is introduced as an intermediary component between the image generator and the HOE combiner. This intermediate element generates correction aberrations that counteract the off-axis aberrations produced by the HOE, thereby resolving the contradiction between using a simple HOE structure and maintaining image quality across a wider field of view.
Solution Approach 2:
The invention changes the optical parameters by introducing a free-form optical element with specifically designed surface curvature (represented by Legendre, Chebyshev, Q-polynomials, or Zernike polynomials). This element modifies the wavefront of light to generate correction aberrations that offset the harmful off-axis aberrations from the HOE combiner.
2Adaptability or versatility
If the combiner is arranged off-axis to achieve a wider viewing angle, then adaptability is improved, but off-axis aberration increases causing image degradation
Solution Approach 1:
The invention converts the harmful off-axis aberration generated by the off-axis combiner into a beneficial correction. The free-form optical element is designed to generate specific correction aberrations that are opposite to and cancel out the off-axis aberrations, thereby allowing the off-axis combiner configuration to be maintained while achieving improved image clarity across a wider viewing angle.
3Measurement precision
If the focal point is made significantly small to achieve accurate image focusing, then measurement precision is improved, but eye box size becomes significantly narrow
Solution Approach 1:
The free-form optical element applies local quality correction by generating different correction aberrations for different regions of the optical field. The correction is tailored to compensate for off-axis aberrations at various viewing angles while maintaining accurate focusing at the central focal point, thereby extending the eye box without sacrificing image sharpness.
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 provides a see-through display device with improved image clarity and a wider eye box by offsetting off-axis aberrations, allowing viewers to see clear images regardless of their eye position within a larger viewing area.
Implementation Method 1
a free-form optical element provided on an optical path of the light corresponding to the image between the image generator and the combiner, the free-form optical element configured to generate a correction aberration with respect to the light corresponding to the image, the correction aberration being opposite to an off-axis aberration generated by the combiner
Implementation Method 2
The combiner may include a holographic optical element (HOE), and is further configured to focus the light corresponding to the image
Implementation Method 3
The combiner may include a diffractive optical element (DOE), and is further configured to focus the light corresponding to the image
Implementation Method 4
a beam splitter configured to transmit a part of light from the light source and reflect another part of the light
Data Source
AI summary
A see-through display device includes an image generator configured to emit image light, a combiner which is arranged off-axis with respect to the image light and is configured to generate an off-axis aberration with respect to the image light, and a free-form optical element which is disposed on an optical path of the image light between the image generator and the combiner and is configured to generate a correction aberration with respect to the image light, the correction aberration being opposite to the off-axis aberration.