Angle-Dependent Reflectance Mirrors for HMD Image Leakage
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Solution Overview
Problem
Existing head-mounted display devices suffer from image light leaks to the opposite side of the observer due to high reflectance at small incidence angles, causing unintended image visibility to individuals other than the intended viewer.
Innovation Solution
An optical element with partially reflecting mirrors arranged in parallel, inclined with respect to the incidence and exit surfaces, and a transmittance member between them, which reduces reflectance at small incidence angles, thereby minimizing image light leaks and enhancing confidentiality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional partially reflecting mirrors with high reflectance at small incidence angles are used, then image light extraction efficiency is improved, but image light leaks to the opposite side of the observer increase
Solution Approach 1:
The patent applies parameter changes by modifying the reflectance characteristics of the partially reflecting mirrors as a function of incidence angle. Specifically, the mirrors are designed to have angle-dependent reflectance where reflectance at small incidence angles (e.g., 0-30 degrees) is controlled to be 30% or less, while reflectance at larger incidence angles (e.g., 45-60 degrees) is maintained at 70% or more. This parameter optimization resolves the contradiction by enabling effective image light extraction at the required angles while minimizing leaks at small angles.
Solution Approach 2:
The patent implements dynamics by introducing angle-dependent optical properties to the partially reflecting mirrors. Rather than using mirrors with fixed reflectance characteristics, the system dynamically adapts the reflectance based on the incidence angle of the incoming light. This allows the optical system to automatically optimize performance for different light paths - extracting image light efficiently at larger angles while preventing leaks at smaller angles.
2Ease of operation
If partially reflecting mirrors are provided in parallel with intervals, then image light can be extracted to the observer side, but image light not extracted leaks from the backside of the light guiding body
Solution Approach 1:
The patent resolves this contradiction by changing the optical parameters of the partially reflecting mirrors, specifically optimizing the reflectance at different incidence angles. By setting reflectance at small angles to 30% or less and at large angles to 70% or more, the system achieves effective image light extraction for the observer while minimizing backside leaks, thus protecting image confidentiality.
Solution Approach 2:
The patent applies local quality by creating spatial variation in the optical properties of the partially reflecting mirrors. Different regions of the mirrors have different reflectance characteristics based on the local incidence angle of the light. This allows the system to optimize light extraction in the direction of the observer while simultaneously minimizing leaks in other directions, particularly from the backside of the light guiding body.
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 effectively reduces image light leaks to the opposite side of the observer, ensuring that only the intended viewer can see the image, while allowing external light to be transmitted, thus maintaining image confidentiality and improving optical design efficiency.
Implementation Method 1
a plurality of partially reflecting mirrors which are provided in parallel to each other with an interval therebetween, reflect a part of image light and a part of external light, and transmit the other part of the image light and the other part of the external light
Implementation Method 2
a transmittance member that is interposed between adjacent two partially reflecting mirrors, in which the transmittance member has an incidence surface on which the image light and the external light are incident through a light guiding body, and an exit surface from which the image light and the external light are exited
Data Source
AI summary
An optical element includes a plurality of partially reflecting mirrors provided in parallel to each other with an interval therebetween, and a transmittance member interposed between adjacent two partially reflecting mirrors of the plurality of partially reflecting mirrors. The transmittance member has an incidence surface on which an image light and an external light are incident through a light guiding body, and an exit surface from which the image light and the external light are exited to an observer side. Each of the plurality of partially reflecting mirrors is disposed so as to be inclined with respect to the incidence surface and the exit surface, and a reflectance of light incident at a relatively small incidence angle with respect to surfaces of each partially reflecting mirror is lower than a reflectance of light incident at a relatively large incidence angle.