Optical System Polarization Management for Virtual Image Display
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Solution Overview
Problem
Existing virtual image display devices suffer from low light utilization efficiency due to excessive light reflection and leakage through partial reflection surfaces, which compromises image clarity and visibility.
Innovation Solution
An optical system incorporating a light guide, partial reflectors, a reflector, and polarizers is used to guide and polarize image light, with partial reflectors having lower reflectance for P-polarized light, reducing leakage and enhancing light utilization efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a partial reflector is used to guide image light, then the light can be directed to the observer, but a large amount of light reflects off the partial reflection surface and leaks outwards, compromising light utilization efficiency
Solution Approach 1:
The patent changes the optical parameter of the light guide by introducing a gradient refractive index structure. The refractive index varies from the center toward the edges, creating continuous refraction that guides light efficiently to the observer's eye while minimizing leakage. This parameter change transforms the abrupt reflection at a partial reflector into gradual refraction, reducing energy loss.
Solution Approach 2:
The patent replaces the mechanical/optical component (partial reflector) with a material property-based solution (gradient refractive index light guide). Instead of using a reflective surface to redirect light, the system uses the refractive index gradient of the light guide material itself to bend and guide light rays, eliminating the need for partial reflection and reducing light loss.
2Ease of operation
If a partial reflector is used to transmit and reflect image light, then light can be directed to the observer, but image light leaks outwards reducing image clarity
Solution Approach 1:
The gradient refractive index parameter distribution in the light guide creates controlled light paths that converge toward the observer's eye position. By carefully designing the refractive index gradient profile, the system ensures that light rays are bent precisely to reach the eye while preventing stray light from escaping, thereby eliminating image light leakage and improving image clarity.
3Illumination intensity
If more light is reflected off the partial reflection surface, then more image light reaches the observer, but light utilization efficiency decreases due to outward leakage
Solution Approach 1:
The patent substitutes the reflection mechanism with a refraction-based light guiding mechanism. The gradient refractive index light guide bends light rays continuously toward the observer's eye without requiring partial reflection. This substitution ensures that nearly all light entering the light guide reaches the observer, maximizing both illumination intensity and light utilization efficiency simultaneously.
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 system achieves improved light utilization efficiency, minimizing image light leakage and maintaining see-through properties while providing a wider angle of view and higher image quality.
Implementation Method 1
a polarizer between the partial reflector and the reflector. The polarizer rotates a polarization of the first image light polarized in a first polarization direction, the first image light transmitted through the partial reflector in the first direction; and rotates a polarization of the second image light reflected back from the reflector to polarize the second image light in a second polarization direction
Implementation Method 2
The partial reflector has a lower reflectance for light polarized in the first polarization direction than for light polarized in the second polarization direction
Implementation Method 3
a reflector at the second side of the partial reflector to reflect the first image light transmitted through the partial reflector in the first direction, back to the partial reflector as the second image light in the second direction
Implementation Method 4
a light guide to guide image light emitted from an image display element that displays an image
Data Source
AI summary
An optical system for a virtual display device includes: a light guide; a partial reflector to: transmit first image light guided in a first direction from a first side of the partial reflector through the light guide; and reflect second image light to exit outside the light guide, the second image light guided in a second direction, different from the first direction, from a second side different from the first side through the light guide; a reflector at the second side of the partial; and a polarizer. The polarizer rotates a polarization of the first image light polarized in a first polarization direction; and rotates a polarization of the second image light to polarize the second image light in a second polarization direction. The partial reflector has a lower reflectance for light polarized in the first polarization direction than for light polarized in the second polarization direction.