Augmented Reality Display Waveguide Beam Expansion for Larger Eye Boxes
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Solution Overview
Problem
Conventional augmented reality (AR) displays face a trade-off between the size of the eye box and image quality due to the constraints imposed by the MEMS mirror, limiting the cross-section of the collimated light beam and the scanning rate, which affects the user's ability to maintain a stable perception of the AR image.
Innovation Solution
The integration of a waveguide system with a MEMS mirror and a semi-transparent combiner, where the waveguide expands the cross-section of the light beam downstream of the MEMS mirror, allowing for a larger eye box and improved image quality without constraining the MEMS mirror's size, and the use of a second waveguide for further expansion to mitigate banding effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the cross section of the collimated light beam is increased to enlarge the eye box, then the eye box size is improved, but the MEMS mirror size must be increased which reduces the scanning rate and image quality
Solution Approach 1:
The optical system is segmented into distinct functional components: a compact MEMS mirror for high-speed scanning, a waveguide for beam expansion, and a combiner for image superposition. This segmentation allows the MEMS mirror to maintain a small size for high scanning rates while the waveguide separately handles the beam expansion to achieve a large eye box, resolving the contradiction between eye box size and scanning rate.
Solution Approach 2:
The waveguide acts as an intermediary component between the MEMS mirror and the combiner. It receives the collimated light beam from the MEMS mirror, expands its cross section through total internal reflection, and delivers the expanded beam to the combiner. This intermediary function allows the MEMS mirror to remain small while achieving a large eye box, thereby maintaining high scanning rates.
2Area of stationary object
If the MEMS mirror reflective area is increased to allow larger light beam cross section, then the eye box is improved, but the mass of the MEMS mirror increases which limits the scanning rate
Solution Approach 1:
The functions of beam deflection and beam expansion are segmented into separate components. The MEMS mirror is responsible only for angular deflection with a small reflective area, keeping its mass low for high scanning rates. The waveguide handles the beam expansion to the required cross section, allowing the MEMS mirror to remain lightweight while achieving the necessary light beam dimensions.
Solution Approach 2:
The system changes the parameters of the light beam as it progresses through the optical train. The MEMS mirror changes the angular direction of the beam, while the waveguide changes the spatial distribution and cross section of the beam. This parameter transformation approach allows the MEMS mirror to operate with small dimensions while the final beam achieves the required cross section for a large eye box.
3Productivity
If the MEMS mirror size is reduced to achieve high scanning rate, then the scanning rate is improved, but the cross section of the deflected light beam is limited which reduces the eye box size
Solution Approach 1:
The waveguide serves as an intermediary that decouples the MEMS mirror size from the final light beam cross section. The compact MEMS mirror deflects the beam at high scanning rates, and the waveguide subsequently expands the beam cross section through its guiding and expanding sections. This intermediary function resolves the contradiction by allowing the MEMS mirror to be small for high scanning rates while the waveguide provides the necessary beam expansion for a large eye box.
Solution Approach 2:
The system separates the angular dimension (handled by the MEMS mirror for high-speed scanning) from the spatial dimension (handled by the waveguide for beam expansion). The MEMS mirror operates in the angular domain to achieve high scanning rates, while the waveguide operates in the spatial domain to expand the beam cross section. This dimensional separation allows both high scanning rates and large eye box to be achieved simultaneously.
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 configuration enables a high scanning rate and flicker-free AR image perception, with an adjustable eye box size and improved image quality, allowing for a wide range of user alignments and movements, and reduces brightness fluctuations.
Implementation Method 1
at least one of the in- and out-coupling sections of the first waveguide is formed by a diffraction grating
Implementation Method 2
the mirror is spaced apart from the out-coupling diffraction grating and configured to redirect any parts of the light originating from the out-coupling diffraction grating in a reverse direction back to the output direction of the out-coupling diffraction grating
Implementation Method 3
a guiding section configured to guide the collimated deflected light beam through the first waveguide
Data Source
Figure 1~2
Figure 3~5d
Figure 6~7
AI summary
The present invention relates to an augmented reality display (1) for displaying, in addition to a light field (2) of a surrounding (3), an image (4) to a user's eye (6), comprising a support (9), a light source (10) to emit a collimated light beam (14) carrying said image, a micro-electro-mechanical-system (MEMS) mirror (11) to deflect the collimated emitted light beam (14) as a collimated deflected light beam (15), a waveguide (12) having an in-coupling section (28), a guiding section (27) to guide the collimated deflected light beam (15) and an out-coupling section (29) to couple the collimated deflected light beam (15) out from the first waveguide (12) as a collimated expanded light beam (16), and a semitransparent combiner (13) to superpose the collimated expanded light beam (16) as an image light beam (17) with the light field (2) of the surrounding for displaying to the user's eye.