Virtual Image Display Diffractive Elements Chromatic Aberration

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Solution Overview

Problem

Conventional virtual image display devices for vehicles suffer from chromatic aberration, which reduces the visibility of projected images due to differences in diffraction angles for lights of varying wavelengths, leading to insufficient visibility and increased device size.

Innovation Solution

Incorporating a light guide unit with diffractive reflective elements that cause diffraction, resulting in opposite color shifts between the display-unit-side and projection-portion-side reflective elements, effectively cancelling chromatic aberration and reducing optical path width, thereby enhancing visibility and mountability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a conventional virtual image display device projects an image using direct diffraction reflection, then the device structure is simple, but chromatic aberration occurs causing poor visibility

Engineering Contradiction:

Improvedevice structureVSAvoidvisibility

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent divides the single diffractive reflective element into two separate elements: a display-unit-side diffractive reflective element and a projection-portion-side diffractive reflective element. This segmentation allows each element to be optimized for different functions - one for efficient light reflection and the other for chromatic aberration correction, thereby resolving the contradiction between simple structure and good visibility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different diffraction grating characteristics to different locations in the optical path. The display-unit-side element uses a first diffraction grating with specific properties, while the projection-portion-side element uses a second diffraction grating with different properties. This local differentiation enables chromatic aberration correction while maintaining efficient light reflection, addressing the visibility issue without significantly increasing overall device complexity.

Inventive Principle:

Principle #3Local quality

2Reliability

If chromatic aberration is corrected using multiple diffractive elements, then visibility improves, but optical path width increases

Engineering Contradiction:

ImprovevisibilityVSAvoidoptical path width

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The patent utilizes the angular dimension of light propagation to correct chromatic aberration. By designing the two diffractive reflective elements with different incident and emission angle relationships, the system corrects chromatic aberration in the angular domain rather than requiring increased spatial separation. This dimensional approach allows effective chromatic correction while maintaining a compact optical path width.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Quantity of substance

If diffractive reflective elements with different diffraction angles are used for various wavelengths, then wavelength separation occurs, but chromatic aberration increases reducing visibility

Engineering Contradiction:

Improvewavelength separationVSAvoidvisibility

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent converts the harmful effect of wavelength-dependent diffraction angle differences into a beneficial chromatic aberration correction mechanism. By intentionally designing the two diffractive reflective elements to produce opposite color shifts, the system utilizes the natural wavelength separation property of diffraction to cancel out chromatic aberration. The first element's color shift is counterbalanced by the second element's opposite color shift, transforming what was previously a visibility-reducing effect into a correction mechanism.

Inventive Principle:

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

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 significantly reduces chromatic aberration and optical path width, improving the visibility of virtual images while maintaining compact device size, thus addressing both visibility and mountability issues.

Implementation Method 1

The light guide unit includes a diffractive reflective element configured to reflect the display light by causing diffraction such that an incident angle and an emission angle of the display light are different from each other

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS11435582B2Virtual image display device

Publication Date: 2022.09.06 DENSO CORP

AI summary

First and second diffractive reflective elements form an optical path that guides a display light from a display unit toward a projection portion. The first diffractive reflective element is placed on the optical path to reflect the display light toward the projection portion by causing diffraction such that an incident angle and an emission angle of the display light are different from each other. The second diffractive reflective element is placed between the display unit and the first diffractive reflective element on the optical path to reflect the display light from the display unit toward the first diffractive reflective element by causing diffraction such that an incident angle and an emission angle of the display light are different from each other.