Optical System Polarizer Partial Reflector Ghosting Reduction
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Solution Overview
Problem
Virtual image display devices face challenges in reducing ghosting or flaring, particularly in bright external conditions, due to external light reflecting off partial reflectors within the light guide.
Innovation Solution
An optical system comprising a light guide, partial reflectors, and a polarizer is employed, where the polarizer has higher transmittance for one polarization direction and lower reflectance for external light, and the partial reflectors are strategically placed to minimize external light reflection, thereby reducing ghosting or flaring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dimming film is formed on the glass lens to reduce external light, then ghosting or flaring is reduced, but the see-through properties and visibility of external environment are degraded
Solution Approach 1:
The patent applies parameter changes by using a polarizer with specific transmittance characteristics (first transmittance in first polarization direction, second transmittance in second polarization direction) and a partial reflector with specific reflectance characteristics (first reflectance in first polarization direction, second reflectance in second polarization direction). By controlling the polarization parameters of light interaction, the system reduces ghosting while maintaining see-through properties without requiring a dimming film that would degrade external visibility.
Solution Approach 2:
The patent employs a composite optical system combining a polarizer and a partial reflector with complementary polarization characteristics. The polarizer has higher transmittance in the first polarization direction and lower in the second, while the partial reflector has lower reflectance in the first polarization direction and higher in the second, creating a composite structure that selectively manages light based on polarization state to reduce ghosting while preserving external scene visibility.
2Use of energy by moving object
If the polarizer has high transmittance in first polarization direction, then image light transmission is improved, but external light reflection by partial reflector increases causing ghosting
Solution Approach 1:
The patent resolves this contradiction by changing the polarization parameter of the partial reflector's reflectance characteristics. The partial reflector is designed with first reflectance in the first polarization direction that is lower than the second reflectance in the second polarization direction. This parameter adjustment ensures that when the polarizer transmits image light with high transmittance in the first polarization direction, the partial reflector simultaneously exhibits low reflectance for external light in the same polarization direction, thereby preventing ghosting while maintaining image light transmission.
3Object-affected harmful factors
If the partial reflector has high reflectance for external light, then ghosting is reduced, but visibility of virtual image in bright environments is degraded
Solution Approach 1:
The patent applies parameter changes by designing the partial reflector with polarization-dependent reflectance characteristics where the first reflectance in the first polarization direction is lower than the second reflectance in the second polarization direction. Simultaneously, the polarizer is configured with higher transmittance in the first polarization direction and lower transmittance in the second polarization direction. This coordinated parameter adjustment allows the system to maintain low ghosting (through the reflectance difference) while preserving virtual image visibility in bright environments (through the transmittance characteristics).
Solution Approach 2:
The patent employs a composite optical system where the polarizer and partial reflector work together with complementary polarization characteristics. The polarizer's transmittance profile and the partial reflector's reflectance profile are coordinated such that image light transmission is optimized while external light reflection causing ghosting is minimized, enabling clear virtual image display in bright conditions without excessive ghosting suppression.
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 ghosting and flaring while maintaining equivalent see-through properties, allowing for improved visibility of virtual images even in bright environments and preventing external light interference.
Implementation Method 1
The polarizer has a first transmittance in a first polarization direction higher than a second transmittance in a second polarization direction orthogonal to the first polarization direction, with respect to vertical incident light incident perpendicularly on the polarizer
Implementation Method 2
The partial reflector in the light guide reflects a part of the image light guided in the light guide to an outside of the light guide through the light-emission surface
Data Source
AI summary
An optical system includes a light guide, a partial reflector, and a polarizer. The light guide has a light-emission surface; and an outer surface opposite to the light-emission surface. The polarizer is on the outer surface to transmit a part of incident light incident on the polarizer. The polarizer has a first transmittance in a first polarization direction higher than a second transmittance in a second polarization direction orthogonal to the first polarization direction, with respect to vertical incident light incident perpendicularly on the polarizer. The partial reflector has a first reflectance in the first polarization direction lower than a second reflectance in the second polarization direction, with respect to the vertical incident light.