Non-axisymmetric Curved Light Guide for Compact Head-Mounted Displays
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Solution Overview
Problem
Existing virtual image display apparatuses for head-mounted displays face challenges in achieving a wide viewing angle, compact size, and lightweight design while maintaining clear visibility of external scenes without obstructing the field of view, as previous solutions either obstruct the view, reduce image quality, or increase the thickness and weight of the device.
Innovation Solution
A virtual image display apparatus featuring a light guide member with non-axisymmetric curved surfaces and a projection lens with non-axisymmetric aspheric surfaces, where the first and third surfaces are arranged to face each other, allowing for total reflection and transmission of video light, and the light guide member is shaped to minimize diopter error and aberration, enabling a compact and lightweight design with a wide viewing angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a relay optical system with a projection lens is used to reduce the size of the optical system, then the overall size is reduced, but the projection lens becomes large in size and obstructs reduction in size and weight
Solution Approach 1:
The optical system is divided into multiple functional components: a light guide member with curved reflection surfaces for light guiding, a projection lens for imaging, and a video display device. This segmentation allows each component to be optimized independently, with the light guide member handling light routing and the projection lens focused on image formation, thereby reducing the overall size while maintaining performance
Solution Approach 2:
The light guide member utilizes curved three-dimensional surfaces (first, second, third, and fourth surfaces with specific curvatures) to guide light through complex paths. This spatial arrangement in multiple dimensions allows compact integration of optical functions without requiring large planar dimensions, enabling miniaturization of the projection lens and overall system
2Volume of moving object
If a light guide member with curved emission and reflection surface is used, then the optical system can be compacted, but video light is reflected by the half mirror surface twice causing video to become very dark
Solution Approach 1:
Different surfaces of the light guide member are designed with different optical properties: the first and third surfaces have curvature for total internal reflection to guide light efficiently, while the second surface has a half mirror coating with specific reflectance characteristics. This local differentiation of surface properties optimizes both light guidance and brightness, ensuring video light maintains sufficient intensity after multiple reflections
Solution Approach 2:
The optical system parameters are precisely controlled: the curvatures of the first, second, third, and fourth surfaces are specifically designed, and the half mirror reflectance is optimized to balance between reflecting video light for display and allowing transmission of external light. These parameter optimizations ensure that video brightness remains high even after double reflection, while maintaining compact system size
3Loss of energy
If a concave mirror and polarization half mirror are combined to enhance reflection efficiency, then reflection efficiency is improved, but a compensation lens must be attached resulting in an increase in thickness
Solution Approach 1:
The light guide member integrates multiple optical functions into a single component: light guidance through curved total internal reflection surfaces, half mirror reflection for video light extraction, and external light transmission. This merging eliminates the need for separate compensation lenses and multiple discrete optical elements, maintaining high reflection efficiency while reducing overall device thickness
Solution Approach 2:
The light guide member serves multiple functions simultaneously: it guides video light from the projection lens to the observer's eye through total internal reflection, extracts video light via the half mirror surface, and allows external scene light to pass through to the observer. This multi-functionality in a single component achieves high reflection efficiency without requiring additional thickness-compensating elements
4Device complexity
If the video display device is disposed above the eyes, then the optical system can be arranged, but it obstructs the field of view and reduces fit and appearance
Solution Approach 1:
The video display device is repositioned from above the eyes to across the face (bridge area), utilizing a different spatial dimension for mounting. The optical system uses curved light paths through the light guide member to deliver video light to the eyes from this new position, avoiding field of view obstruction while maintaining proper optical alignment and improving overall fit and appearance
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 virtual image display apparatus with a wide viewing angle, high performance, and a compact, lightweight design that allows for clear visibility of both virtual images and external scenes without obstructing the field of view, achieving zero diopter and magnification errors.
Implementation Method 1
a light guide member having a curved emission and reflection surface, and a projection lens which makes video light enter the light guide member
Data Source
AI summary
A light guide member includes three surfaces of a second surface, a fourth surface, and a fifth surface as two or more non-axisymmetric curved surfaces, and a projection lens includes a lens surface as a non-axisymmetric aspheric surface. With this, on the light guide member side, even when there is a shape constraint that the first surface or the third surface which is a surface contributing to light guide is a flat surface, and correction of asymmetric aberration is limited, it becomes possible to perform sufficient aberration correction as the whole of an optical system including the projection lens. Therefore, the virtual image display apparatus can have a wide viewing angle and high performance, and can be made small and lightweight.