Bonded Lens Half Mirror for Thin Wide-Angle HMD
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Solution Overview
Problem
Head-mounted display devices face challenges in reducing size and thickness while maintaining a wide angle of view, as the burden on the optical system increases, making it difficult to achieve a thin optical system with a wide angle of view.
Innovation Solution
A virtual image display device configuration featuring a first lens with a convex surface and a second lens with a concave surface bonded together, incorporating a half mirror in the bonding portion and a transmission/reflection selection member to selectively transmit or reflect light based on polarization state, with the first lens having a higher refractive index than the second lens, allowing for reduced size and thickness while maintaining a wide angle of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a thin optical system with a wide angle of view is achieved by using a curved surface shape or high refractive index lens, then the angle of view is improved, but the device size and thickness cannot be reduced
Solution Approach 1:
The optical system is divided into multiple lens units (first lens unit, second lens unit, third lens unit) with different functions. The first lens unit provides wide angle of view, the second lens unit corrects aberrations, and the third lens unit focuses light. This segmentation allows each unit to be optimized independently, achieving wide angle of view while controlling overall device size.
Solution Approach 2:
The patent introduces a planar configuration dimension by using a flat plate-like optical element (prism or beam splitter) instead of traditional curved mirrors. This planar approach reduces the optical path length in the thickness direction while maintaining wide angle of view through refraction and total internal reflection at controlled angles.
2Area of stationary object
If the refractive index of lenses is increased to achieve wide angle of view, then the angle of view is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Different lens units use different refractive indices tailored to their specific functions. The first lens unit uses high refractive index material (n≥1.7) for wide angle of view, while the second and third lens units use materials with appropriate refractive indices for aberration correction and focusing. This localized optimization reduces overall system complexity.
Solution Approach 2:
The optical system combines multiple lens materials with different refractive indices and Abbe numbers. Specifically, the first lens unit uses high refractive index material, while the second lens unit combines materials with different dispersion properties to correct chromatic aberration. This composite material approach achieves wide angle of view while managing optical complexity.
3Power
If a half mirror is provided in the bonding portion between lenses, then the optical path folding power is improved, but the manufacturing precision requirements increase
Solution Approach 1:
A bonding agent layer is introduced as an intermediary between the lenses and the half mirror. This bonding agent not only provides mechanical attachment but also serves as an optical medium that maintains the precise positioning of the half mirror in the optical path. The bonding agent compensates for minor positioning errors and reduces the stringency of manufacturing precision requirements.
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 reduction in size and thickness while providing an image with a wide angle of view by utilizing the refractive index difference and the half mirror to adjust the optical path, effectively addressing the limitations of existing technologies.
Implementation Method 1
a half mirror provided in a bonding portion between the convex surface and the concave surface
Implementation Method 2
a first lens disposed at a location where image light from the image element is extracted, and including a convex surface facing the image element side, a second lens disposed further toward the image element side than the first lens and including a concave surface to be bonded to the convex surface of the first lens
Implementation Method 3
a transmission/reflection selection member provided at a light emitting side of the first lens and configured to selectively transmit or reflect the light depending on a light polarization state
Implementation Method 4
since the refractive index of the first lens is larger than the refractive index of the second lens, an image with a wide angle of view can be formed
Data Source
AI summary
A first lens and a second lens are bonded to each other and configured to be short in an optical axis direction. Further, by providing a half mirror in a bonding portion between a convex surface and a concave surface, power is given when folding an optical path, and additionally, by setting a refractive index of the first lens larger than a refractive index of the second lens, an image with a wide angle of view can be formed.