AR Display Optical Elements for Fovea Light Intensity
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Solution Overview
Problem
Existing augmented reality (AR) display devices, such as head-mounted displays, often suffer from reduced light intensity at the fovea, the most critical part of the visual field, leading to a darkened display area.
Innovation Solution
The implementation of an image display device with a configuration of optical elements, including a first optical element with a deflection function and a second optical element with a lens function, where the incidence and diffraction angles of light are strategically aligned to prevent light loss and ensure optimal light transmission to the fovea, using a combination of volume-type hologram, diffraction grating, or meta-surface optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional optical systems are used in AR head-mounted displays, then the overall display range is covered, but the light intensity at the fovea becomes insufficient causing darkened display
Solution Approach 1:
The optical system is divided into multiple optical elements with distinct functions: a first optical element (deflection holographic optical element) that deflects incident light, and a second optical element (lens holographic optical element) that focuses light. This segmentation allows each element to optimize light transmission to specific regions, ensuring sufficient light intensity at the fovea while covering the overall display range.
Solution Approach 2:
Different optical elements are designed with different optical characteristics tailored to specific functional requirements. The first optical element has deflection characteristics optimized for directing light toward the fovea, while the second optical element has focusing characteristics optimized for forming images on the retina. This local optimization ensures high light intensity where needed without compromising overall system performance.
2Illumination intensity
If optical elements are configured to improve light transmission to fovea, then display brightness at center is improved, but the alignment precision of incidence and diffraction angles becomes more critical
Solution Approach 1:
The optical elements are pre-designed with specific diffraction angle characteristics that anticipate the required light deflection. The first optical element is designed with a diffraction angle that pre-deflects light toward the fovea region, and the second optical element is positioned and oriented to receive this deflected light at the correct incidence angle. This preliminary design of angular relationships reduces the sensitivity to manufacturing tolerances during assembly.
Solution Approach 2:
The optical system utilizes changes in diffraction angles as a key parameter to control light direction. By designing the first optical element with specific diffraction angle characteristics and the second optical element with corresponding incidence angle requirements, the system transforms the light path in a controlled manner that maintains brightness at the fovea while managing alignment precision requirements through parameter optimization.
3Area of stationary object
If the optical system uses fixed incidence angles, then the optical path is simplified, but the visual field coverage is reduced when the eyeball rotates
Solution Approach 1:
The optical system is designed to dynamically adapt to eyeball rotation. The first optical element deflects incident light at a predetermined diffraction angle that maintains the optical path geometry even when the eyeball rotates within a certain range. This dynamic design allows the visual field coverage to be maintained across different gaze directions without requiring complex active adjustment mechanisms.
Solution Approach 2:
The optical elements are designed with asymmetric diffraction and refraction characteristics that are optimized for the specific geometry of the human eye and typical viewing conditions. The deflection angle of the first optical element and the lens function of the second optical element work together in an asymmetric configuration that expands the effective visual field coverage while maintaining a relatively simple optical 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
This configuration effectively enhances light transmission to the fovea, preventing darkening of the display area and maintaining a clear visual field, while also considering the rotation of the eyeball to ensure robustness and wide visual field coverage.
Implementation Method 1
the first optical element has a deflection function of deflecting incident light which has a predetermined wavelength and is incident on the first optical element at a predetermined incidence angle to a side of the first optical element on which the incident light is incident, and emits first diffracted light deflected by the deflection function
Implementation Method 2
the second optical element has a lens function for the first diffracted light which has a predetermined wavelength and is incident on the second optical element at a predetermined incidence angle
Data Source
AI summary
To provide an image display device capable of improving display at a fovea of an eye, which is the most important part in a display range, such that display at the fovea of the eye is not darkened. There is provided an image display device including: at least one optical element unit including two optical elements facing each other, in which one optical element unit included in the at least one optical element unit includes a first optical element and a second optical element, an image is formed on the basis of image display light which transmits through the first optical element and is emitted to outside of the image display device, the first optical element has a deflection function of deflecting incident light which has a predetermined wavelength and is incident on the first optical element at a predetermined incidence angle to a side of the first optical element on which the incident light is incident, and emits first diffracted light deflected by the deflection function, the second optical element has a lens function for the first diffracted light which has a predetermined wavelength and is incident on the second optical element at a predetermined incidence angle, and a direction of the incidence angle of the incident light and a direction of a diffraction angle of the first diffracted light are different from a direction of an optical axis of the second optical element.