Head-Up Display Light Guide Unit Polarization Control

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Solution Overview

Problem

Conventional head-up display (HUD) devices face challenges in maintaining high visibility and contrast of virtual images due to luminance reduction and background light reflection, particularly when projecting linear polarized light onto windshields.

Innovation Solution

The HUD device incorporates a light guide unit with a first phase shifter converting linear polarized light to circularly polarized light, a reflection surface, and a second phase shifter adding a ¼ wavelength phase difference to convert it back to linear polarized light, combined with a linear polarizer aligned with the light guide axis to minimize light shielding and enhance contrast.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If linear polarized light is projected onto the windshield, then the image can be displayed, but luminance loss occurs and background light reflection reduces visibility

Engineering Contradiction:

Improveluminance of virtual imageVSAvoidbackground light reflection

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the polarization state parameter of light by introducing phase shifters that convert linear polarized light to circular polarized light and back, with a 1/4 wavelength phase difference. This parameter transformation allows the system to maintain high luminance while reducing background light reflection through optimized polarization control.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a linear polarizer as an intermediary component on the optical path. This polarizer selectively transmits display light with polarization direction along the light guide axis while shielding ambient light with perpendicular polarization, thereby improving contrast and visibility without significant luminance loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Illumination intensity

If a light guide unit with multiple phase shifters is used to optimize polarization, then visibility and contrast improve, but device complexity increases

Engineering Contradiction:

Improvevisibility and contrast of virtual imageVSAvoidnumber of optical components

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The patent combines multiple optical functions into an integrated light guide unit that incorporates both phase shifters and a linear polarizer within a single optical path structure. This merging approach achieves optimized polarization control and improved image visibility while minimizing the overall device footprint and complexity.

Inventive Principle:

Principle #5Merging (Combining)

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 reduces luminance loss and ambient light reflection, resulting in improved visibility and contrast of virtual images by optimizing the projection and shielding of display and ambient light.

Implementation Method 1

a first phase shifter that is disposed on the optical path to convert the display light as the linear polarized light from the projection unit into a circularly polarized light

Methodology Applied

Scientific EffectPhase modulation: Phase Modulation

Implementation Method 2

a second phase shifter that is disposed on the projection member side of the first phase shifter on the optical path and gives a phase difference of a 1/4 wavelength to the display light converted into the circularly polarized light by the first phase shifter to convert the display light into a linear polarized light

Methodology Applied

Scientific EffectPhase difference: Phase Modulation

Implementation Method 3

a linear polarizer that is disposed on the projection member side of the second phase shifter on the optical path to guide a light whose polarization direction is along a light guide axis and to shield a light whose polarization direction is along a light shield axis perpendicular to the light guide axis

Methodology Applied

Scientific EffectPolarization filtering: Polarisation

Implementation Method 4

which includes a reflection surface, which is provided to be directed to the projection member and to be capable of reflecting a light from the projection member side to the projection member side

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11474349B2Head-up display device

Publication Date: 2022.10.18 DENSO CORP

AI summary

A light guide unit includes a first phase shifter disposed on the optical path to convert the display light as the linear polarized light from the projection unit into a circularly polarized light and including a reflection surface directed to the projection member and capable of reflecting a light from the projection member side to the projection member, a second phase shifter disposed on the projection member side of the first phase shifter on the optical path and giving a ¼ wavelength phase difference to the display light converted into the circularly polarized light by the first phase shifter to convert the display light into a linear polarized light, and a linear polarizer on the projection member side of the second phase shifter on the optical path. The linear polarizer guides the display light converted into the linear polarized light by the second phase shifter toward the projection member.