Beam Splitter Transmittance Layout for Uniform HMD Luminance
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Solution Overview
Problem
The luminance difference in the vertical direction of a display image caused by varying incident angles of light on the beam splitter results in deteriorated display quality in head-mounted displays.
Innovation Solution
The implementation of a beam splitter with a spatially adjusted transmittance distribution, achieved through varying film thickness, reflective film patterns, or absorptivity, to equalize transmittance across different vertical positions, thereby reducing luminance differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a planar beam splitter is used, then the device complexity is reduced, but luminance uniformity deteriorates due to incident angle variations
Solution Approach 1:
The beam splitter is designed with spatially varying transmittance properties - the transmittance changes according to the incident angle of light at different positions. This local variation in optical properties compensates for the incident angle differences across the beam splitter surface, maintaining uniform luminance in the virtual image while keeping the overall structure simple.
Solution Approach 2:
The transmittance parameter of the beam splitter is changed as a function of position and incident angle. By making the transmittance dependent on the incident angle, the optical system compensates for the angle-dependent reflectance variations, thereby achieving uniform luminance distribution across the display image.
2Device complexity
If the incident angle varies across the beam splitter, then the optical path is simplified, but transmittance uniformity deteriorates
Solution Approach 1:
The beam splitter exhibits local quality variation where transmittance is tailored for each spatial position and incident angle. This local optimization ensures that despite varying incident angles across the optical path, each region contributes uniformly to the final virtual image luminance.
Solution Approach 2:
The beam splitter is pre-designed with compensatory transmittance characteristics that counteract the expected incident angle variations. By incorporating this preliminary compensation into the beam splitter design, the system proactively prevents luminance non-uniformity before it occurs in the 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 solution enhances the display quality by minimizing luminance differences, resulting in a more uniform and high-quality virtual image presentation.
Implementation Method 1
The beam splitter 122 reflects display light P11 from the display element unit 101 forward. The display light P11 reflected by the beam splitter 122 enters a combiner 121. The combiner 121 reflects the display light P11 backward. The display light reflected backward by the combiner 121 is referred to as display light P12. The display light P12 passes through the beam splitter 122 and enters an eye E of a user.
Implementation Method 2
The combiner 121 transmits outside light P21 from in front of the combiner 121. The outside light P21 and the display light P12 pass through the beam splitter 122 and enter the eye E of the user.
Data Source
AI summary
A head-mounted display according to the present embodiment includes a reflective member arranged in front of a user and configured to reflect at least part of display light for forming a display image toward the user, and a beam splitter arranged between the reflective member and an eye of the user and configured to reflect the display light toward the reflective member and to transmit the display light that has been reflected by the reflective member, in which transmittance of the beam splitter in a direction from a first position above the eye of the user toward the eye is equal to transmittance of the beam splitter in a direction from a second position below the eye of the user toward the eye.