Virtual Image Display Optics for Fresnel-Free Polarization Control
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Solution Overview
Problem
Existing virtual image display devices face issues with image formation deterioration due to the incorporation of a Fresnel-type half mirror between optical units, and using a meniscus lens instead can affect birefringence characteristics, leading to potential phase difference failures.
Innovation Solution
A virtual image display device with an optical member that folds image light twice by reflection, using a lens member, a transmissive reflective optical element, a reflective polarizing optical element, and wave plates made of liquid crystal material to convert and reciprocate image light, ensuring accurate polarization and image formation without complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Fresnel-type half mirror is incorporated between optical units, then polarization control is achieved, but the surface shape becomes complicated and image formation deteriorates
Solution Approach 1:
The patent removes the Fresnel-type half mirror from the optical system and replaces it with a reflective polarizing optical element that has a simple planar surface. This extraction of the problematic component eliminates the surface shape complexity while maintaining the polarization control function through the reflective polarizing element.
Solution Approach 2:
The patent uses a reflective polarizing optical element that copies the polarization control function of the Fresnel half mirror but implements it through a simpler mechanism. Instead of using a complex curved surface, the system uses a planar reflective element with polarization-selective properties to achieve the same functional outcome.
2Manufacturing precision
If a meniscus lens is used instead of a flat plate, then imaging capability is improved, but birefringence characteristics change due to curvature and phase difference effect is lost
Solution Approach 1:
The patent segments the optical system into distinct functional components: a lens member for imaging and separate wave plate elements for polarization control. This segmentation allows the lens to be optimized for imaging (using a meniscus shape if needed) while the wave plate elements handle polarization functions independently, preventing curvature-induced birefringence issues.
Solution Approach 2:
The patent introduces wave plate elements as intermediary components between the lens and the reflective polarizing element. These wave plates compensate for any phase differences and maintain proper polarization characteristics, acting as mediators that preserve the desired optical function even when curvature is present in the lens.
3Reliability
If multiple optical elements are used to control polarization and form images, then functional requirements are met, but device weight and cost increase
Solution Approach 1:
The patent merges the polarization control function and the reflective element into a single integrated reflective polarizing optical element. This combination reduces the total number of separate components, thereby reducing the overall weight of the optical system while maintaining both polarization control and imaging functions.
Solution Approach 2:
The reflective polarizing optical element serves multiple functions simultaneously: it acts as a polarizer, a reflector, and part of the optical path management system. This multi-functionality reduces the need for separate dedicated components, thereby reducing weight and cost while meeting all functional 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
The solution provides a simplified optical configuration with reduced weight and cost, maintaining image quality and brightness uniformity, while allowing for miniaturization and reduced aberrations.
Implementation Method 1
a wave plate that is provided between the reflective optical element and the polarizing optical element, is formed of a liquid crystal material, converts the image light having passed through the reflective optical element into linearly polarized light in a first polarization direction
Implementation Method 2
a reflective polarizing optical element that is provided facing a second optical surface of the lens member that is far from the display and reflects image light, that is linearly polarized light in a first polarization direction
Implementation Method 3
an optical member that folds back the image light twice by reflection to form a virtual image, in which the optical member includes a lens member
Data Source
AI summary
A virtual image display device includes a display, and an optical member, in which the optical member includes a lens member, a transmissive reflective optical element provided facing a first optical surface of the lens member that is close to the display, a reflective polarizing optical element provided facing a second optical surface of the lens member that is far from the display and reflects first polarized light, that is, image light linearly polarized light in a first polarization direction, and a wave plate provided between the reflective optical element and the polarizing optical element, is formed of a photo-crosslinkable polymeric liquid crystal material, converts the image light, that is, linearly polarized light in the first polarization direction, and converts the image light, that is reflected by the reflective optical element to reciprocate, into second polarized light in a second polarization direction.