Optical Assembly Waveplate Ghost Image Reduction
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Solution Overview
Problem
Head-mounted displays (HMDs) suffer from ghost images due to Fresnel reflections caused by multiple reflective surfaces in their optical assemblies, which are distracting and bothersome for users.
Innovation Solution
The optical assembly incorporates a waveplate configuration in the first optical element, reducing the number of reflective surfaces that display light encounters, thereby minimizing ghost images by converting linearly polarized light to circularly polarized light and using a partially reflective layer and anti-reflection coatings to manage reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple optical layers are used in the optical assembly, then optical functionality is improved, but Fresnel reflections increase causing ghost images
Solution Approach 1:
The patent applies anti-reflection coatings that convert harmful Fresnel reflections into beneficial effects by reducing the reflection coefficient at optical interfaces. The coatings are designed with specific refractive indices and thicknesses to minimize reflected light intensity, thereby converting the harmful reflection phenomenon into a benefit where ghost images are suppressed while maintaining optical layer functionality
Solution Approach 2:
The patent introduces anti-reflection coatings as intermediary layers between optical elements. These coating layers act as mediators that reduce the abrupt refractive index changes at interfaces, thereby minimizing Fresnel reflections. The intermediary coatings enable light to transition smoothly between layers with different refractive indices, reducing ghost image formation while preserving the necessary optical layer structure
2Adaptability or versatility
If waveplate is positioned in the second optical element closer to the eye, then polarization conversion is achieved, but ghost images are still generated due to multiple reflective surfaces
Solution Approach 1:
The patent applies anti-reflection coatings preliminarily to optical elements before light undergoes multiple reflections. By pre-treating the optical surfaces with anti-reflection coatings, the system reduces the intensity of Fresnel reflections at each interface before ghost images can form, thereby suppressing harmful reflections while maintaining the waveplate's polarization conversion function
Solution Approach 2:
The patent changes the optical parameters of interface surfaces by applying anti-reflection coatings with specific refractive indices and thicknesses. This parameter modification reduces the reflection coefficient at optical interfaces, thereby minimizing ghost image formation while preserving the waveplate's ability to convert linearly polarized light to circularly polarized light
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 significantly reduces the magnitude of ghost images by minimizing Fresnel reflections, resulting in a more comfortable user experience with fewer distracting reflections compared to prior designs.
Implementation Method 1
The first optical element includes a waveplate such as a quarter waveplate
Implementation Method 2
using a partially reflective layer and anti-reflection coatings to manage reflections
Implementation Method 3
An optical assembly can be included in a head mounted display (HMD) in order to focus image light emitted from a display to an eye of a user
Implementation Method 4
layers of the optical assembly may generate Fresnel reflections
Data Source
AI summary
A lens assembly includes a first optical element and a second optical element. The first optical element includes a partially reflective layer and a waveplate. The second optical element includes a reflective polarizer configured to reflect a first polarization orientation of display light back to the first optical element and transmit a second polarization orientation of the display light.