Optical System With Equal-Retardance Plates for VR Ghost Image Elimination
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Solution Overview
Problem
Existing optical systems for VR head-mounted displays suffer from ghost images and reduced brightness due to incomplete conversion of light wavelengths by quarter wavelength plates, leading to deviations in polarization function and decreased optical path efficiency.
Innovation Solution
The optical system employs equal retardance first and second quarter wavelength plates, composed of laminated optically anisotropic layers, with a mirror-symmetric arrangement and orthogonal optic axes, and includes a reflective polarizer with cholesteric liquid crystal layers and retardation layers to ensure complete polarization conversion and minimize ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional quarter wavelength plates are used in the optical system, then the structure can be simplified, but ghost images occur and brightness is reduced due to incomplete polarization conversion
Solution Approach 1:
The patent applies parameter changes by precisely controlling the retardation values of the quarter wavelength plates. Specifically, the first quarter wavelength plate has a retardation value of 80-120 nm and the second quarter wavelength plate has a retardation value of 90-130 nm, ensuring complete polarization conversion across the visible spectrum while avoiding ghost images
Solution Approach 2:
The patent uses composite materials by combining multiple quarter wavelength plates with different retardation characteristics. The first quarter wavelength plate (80-120 nm) and second quarter wavelength plate (90-130 nm) work together as a composite optical system to achieve broadband polarization conversion without the drawbacks of single-material designs
2Reliability
If quarter wavelength plates with different retardation values are used, then polarization conversion can be achieved, but deviation in polarization function occurs leading to ghost images
Solution Approach 1:
The patent applies parameter changes by establishing specific retardation value ranges for each quarter wavelength plate. The first quarter wavelength plate is controlled at 80-120 nm and the second at 90-130 nm, ensuring consistent polarization conversion across wavelengths while preventing ghost image formation through precise parameter control
3Productivity
If light conversion is incomplete in quarter wavelength plates, then some wavelengths cannot reciprocate properly, but this causes main images to appear dark
Solution Approach 1:
The patent applies parameter changes by optimizing the retardation values to ensure complete polarization conversion. The first quarter wavelength plate (80-120 nm) and second quarter wavelength plate (90-130 nm) are designed to convert all wavelengths completely, enabling full reciprocation of light and preventing main image darkening while maximizing optical path efficiency
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 configuration enhances brightness and eliminates ghost images by maintaining consistent polarization across different wavelengths, improving the overall image quality and reducing optical path length in VR head-mounted displays.
Implementation Method 1
light is completely converted into circularly polarized light in the quarter wavelength plate through which the light first passes, and is completely converted into linearly polarized light in the quarter wavelength plate through which the light second passes
Implementation Method 2
retardance of the first quarter wavelength plate and retardance of the second quarter wavelength plate are equal to each other
Implementation Method 3
light is reciprocated between the half mirror and the reflective polarizer to increase the optical path length
Implementation Method 4
a reflective polarizer with cholesteric liquid crystal layers and retardation layers to ensure complete polarization conversion and minimize ghost images
Data Source
AI summary
An object is to provide an optical system capable of improving the brightness of a main image while eliminating a ghost image. In an optical system including: an image display device that emits an image; a linear polarizer through which light associated with the image passes; a first quarter wavelength plate which receives the light from the linear polarizer; a half mirror; a reflective polarizer; and a second quarter wavelength plate provided between the reflective polarizer and the half mirror, retardance of the first quarter wavelength plate and retardance of the second quarter wavelength plate are equal, and thus the object is achieved.