Curved Light Guide Grating Eyebox Aberration Control
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Solution Overview
Problem
Display devices with curved light guide elements face challenges in maintaining a large eyebox and field of view due to the influence of curved surfaces on light beams during total reflection, leading to aberrations and uneven image intensity.
Innovation Solution
The design involves an imaging optics system where light bundles strike the outcoupling grating a maximum of n times, with decoupling occurring at specific consecutive impacts, allowing for adaptation to achieve a large eyebox and field of view, and incorporating an imaging or reflective grating to compensate for aberrations and ensure homogeneous intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the light guide element has a curved front and/or curved back, then the eyebox can be enlarged, but the light beams are influenced by the curved surfaces during total reflection, causing different wave states after each reflection and leading to aberrations
Solution Approach 1:
The patent applies parameter changes by carefully controlling the curvature radius of the curved surfaces in the light guide element. By selecting specific curvature radii that satisfy certain mathematical relationships with the optical parameters, the system achieves a balance between enlarging the eyebox and minimizing aberrations caused by multiple reflections on curved surfaces.
Solution Approach 2:
The outcoupling grating is divided into multiple zones corresponding to different pixel positions. Each zone is independently optimized to control the decoupling of light bundles at different locations, allowing the system to maintain image quality while achieving a large eyebox through spatially varying optical control.
2Area of stationary object
If sequential multiple outcoupling is performed via the outcoupling grating, then a large eyebox can be achieved with a plane-parallel plate, but the field of view is limited
Solution Approach 1:
The patent introduces dynamic control of the outcoupling process by making the outcoupling grating's characteristics position-dependent. The grating's diffraction efficiency and orientation vary across different zones, enabling the system to dynamically adapt the light decoupling to achieve both a large eyebox and an expanded field of view simultaneously.
Solution Approach 2:
The patent transitions from a two-dimensional plane-parallel plate to a three-dimensional curved light guide element with spatially varying optical properties. By introducing curvature and position-dependent grating characteristics, the system adds dimensional complexity that enables simultaneous optimization of eyebox size and field of view.
3Manufacturing precision
If the in-coupling and out-coupling gratings are designed as imaging gratings, then aberrations can be compensated, but the device complexity increases
Solution Approach 1:
The outcoupling grating is designed to serve multiple functions simultaneously: it acts as both a diffraction grating for light decoupling and an imaging element for aberration correction. By integrating these functions into a single position-dependent grating structure, the patent reduces overall device complexity while achieving effective aberration compensation.
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 enables a larger eyebox and field of view while minimizing aberrations and ensuring uniform image intensity, allowing for effective imaging with curved light guide elements.
Implementation Method 1
an in-coupling grating (10) which is designed in such a way that light bundles (L1, L2, L3) emitted by the imaging device can be coupled into the light guide element (3, 4)
Implementation Method 2
the light bundles guided between the two gratings in total reflection are influenced by the curved front and/or the curved back
Implementation Method 3
the light bundles are decoupled depending on the position of the associated pixel at exactly 1 to m consecutive impingements on the decoupling grating
Data Source
Figure 1~2
Figure 3a~4
Figure 5a~6
AI summary
The invention relates to a display device, comprising an image generator (8) having several pixels, from which pixels light bundles (L1, L2, L3) are emitted in order to generate an image, a control unit (7) for controlling the image generator (8), and an imaging optical system (14), which comprises a light guiding element (3, 4) having a front side (5, 5') and a rear side (6, 6'), which light guiding element has an input grating (10) formed on the front or rear side (6, 6'; 5, 5') and an output grating (11) formed on the front or rear side (5, 5'; 6, 6'), wherein the light bundles (L1-L3) are input into the light guiding element (3, 4) by means of diffraction at the input grating (10), are guided in the light guiding element (3, 4) to the output grating (11) by means of total internal reflection, and are output by means of diffraction at the output grating (11) in such a way that a user can perceive the generated image, wherein the front side (5, 5') and/or the rear side (6, 6') is curved and the imaging optical system (14) is designed in such a way that the light bundles (L1-L3) hit the output grating (11) at most n times depending on the position of the associated pixel, wherein n is an integer greater than or equal to three, and that the light bundles (L1-L3) are output upon 1 to m consecutive hits of the output grating (11) depending on the position of the associated pixel, wherein m is an integer greater than or equal to one and less than n and the output begins upon the (n-m+1)th hit at the latest.