Birefringent Layer Ghost Image Suppression in Near-Eye Displays

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Solution Overview

Problem

Near-eye displays, such as head-mounted displays, suffer from loss of visual contrast and ghost image problems due to reflections within the display panel, particularly in compact and integrated designs where pancake lenses are used, leading to cumbersome and uncomfortable user experiences.

Innovation Solution

Incorporating a quarter-wave birefringent layer between the top polarizer and a finite reflectivity layer within the display panel to convert reflected image light to an orthogonal polarization state, which is then blocked by the polarizer, thereby suppressing ghost images and reflections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a compact near-eye display design with pancake lenses is used, then the device size and weight are reduced, but visual contrast is lost and ghost images appear due to reflections within the display panel

Engineering Contradiction:

Improvedisplay device sizeVSAvoidreflections and ghost images

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful reflected light into a beneficial effect by using a quarter-wave birefringent layer to transform linearly polarized reflected light into circularly polarized light, which then passes through a circular polarizer to become linearly polarized light oriented perpendicular to the original reflection, effectively directing reflected light away from the viewer's eye and eliminating ghost images while maintaining compact design

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the polarization state parameter of reflected light by introducing a quarter-wave birefringent layer that converts linearly polarized light to circularly polarized light and back to linearly polarized light with perpendicular orientation, thereby changing the direction of reflected light to eliminate ghost images without affecting device compactness

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If multiple layers including birefringent layers are added to suppress reflections, then visual contrast is improved, but device complexity increases

Engineering Contradiction:

Improvevisual contrastVSAvoidnumber of layers

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The quarter-wave birefringent layer serves multiple functions simultaneously: it converts linearly polarized light to circularly polarized light, transforms reflected light to perpendicular polarization orientation, and works with the existing circular polarizer to eliminate ghost images, thereby achieving reflection suppression without proportionally increasing device complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The quarter-wave birefringent layer acts as an intermediary element between the reflection source and the circular polarizer, transforming the polarization state of reflected light in a way that enables the circular polarizer to effectively block ghost images while maintaining overall system simplicity

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution effectively reduces ghost images and enhances visual contrast by ensuring that reflected light is not re-reflected back to the viewer, resulting in improved image quality and user comfort in compact near-eye display designs.

Implementation Method 1

a first birefringent layer for receiving polarized light emitted by a backlight

Methodology Applied

Scientific EffectBirefringence: Birefringence

Implementation Method 2

a second birefringent layer for receiving the light propagated through the finite reflectivity layer. The second birefringent layer is configured to convert a polarization state of an image light portion propagating in sequence through the first polarizer, the second birefringent layer, reflected from the finite reflectivity layer, and propagating back through the second birefringent layer towards the first polarizer, to an orthogonal polarization state that is blocked by the first polarizer

Methodology Applied

Scientific EffectBirefringence: Birefringence

Implementation Method 3

reflected from the finite reflectivity layer

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11493800B2Display panel with backreflection suppression comprising first and second birefringent layers and a reflectivity layer

Publication Date: 2022.11.08 META PLATFORMS TECHNOLOGIES LLC

AI summary

Ghost image formation due to reflections of image light by a display panel to an ocular lens may be suppressed by ensuring that the image light reflected by the lens does not get reflected by the display panel back towards the lens. To that end, the display panel may include a quarter-wave birefringent layer between the top polarizer of the display panel and a layer inside the display panel that the image light reflects from, such as a black grid layer or an active matrix layer.