Sawtooth Light Guide Optics for Wider HUD Viewing Without Stray Light
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Solution Overview
Problem
In head-up display devices, stray light from the interface between the light guide and the outside is incident on the observer's eyes, causing visual interference.
Innovation Solution
A display device configuration featuring a first light guide with a reflective surface and a second light guide with a sawtooth surface, where the beam splitter at their interface transmits part of the light and reflects the remainder, preventing external light from entering the light guide and reducing stray light incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a flat plate light guide with beam splitters is used to enlarge the luminous flux, then the visible range of the observer is enlarged, but stray light from the interface is incident on the observer's eyes causing visual interference
Solution Approach 1:
The light guide is divided into two separate light guides: a first light guide for guiding the luminous flux from the collimator, and a second light guide with a sawtooth surface for extracting and enlarging the luminous flux. This segmentation allows the harmful interface between the flat plate and outside to be eliminated, as the second light guide's sawtooth surface directly interfaces with the outside without causing total reflection of external light.
Solution Approach 2:
The second light guide is designed with an asymmetric sawtooth surface rather than a symmetric flat surface. The sawtooth structure has inclined surfaces that are angled to allow external light to pass through without undergoing total internal reflection, thereby preventing stray light generation while still enabling effective light extraction for image display.
2Area of stationary object
If multiple beam splitters are used to enlarge the luminous flux, then the visible range is improved, but the device complexity increases
Solution Approach 1:
The patent replaces the conventional approach of using multiple beam splitters with a single beam splitter combined with a second light guide having a sawtooth surface. The sawtooth structure provides the light extraction and enlargement function that would otherwise require multiple beam splitters, thereby reducing device complexity while maintaining or improving the visible range.
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 the observer's visual range by enlarging the image while suppressing stray light, preventing partial shadows and improving the display device's efficiency by using a single beam splitter instead of multiple ones.
Implementation Method 1
a beam splitter formed at an interface between the first light guide and the flat surface of the second light guide, the beam splitter being configured to transmit a part of the light and reflect the remainder of the light
Implementation Method 2
the first surface being non-parallel to a propagating direction of the light propagating through the second light guide after passing through the interface and being configured to transmit the light
Implementation Method 3
a collimator configured to convert light emitted from each point on the image displayed on the image display element into collimated light
Implementation Method 4
The light guide is provided, in a flat glass plate, with a reflective surface that reflects the light incident from the collimator in a predetermined direction
Data Source
AI summary
A display device includes an image display element, a collimator, a first light guide formed of a flat plate transparent to light, a second light guide formed of a plate member transparent to the light and having one surface that is a flat surface in contact with one of surfaces of the first light guide and the other surface that is a sawtooth surface, and a beam splitter formed on an interface between the first and second light guides to transmit a part of the light and reflect the remainder thereof. The sawtooth surface is configured by alternately combining a first surface non-parallel to a propagating direction of the light propagating through the second light guide after passing through the interface and configured to transmit the light and a second surface substantially parallel to the propagating direction.