Light Guide Plate Fresnel Reflection Suppression
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Solution Overview
Problem
Existing light guide plates for extended reality applications suffer from image degradation due to Fresnel reflection, which current techniques fail to adequately suppress.
Innovation Solution
A light guide plate design incorporating an incidence diffraction grating, a substrate for total internal reflection, and a function part that transmits or reflects light, with specific grating vector relationships and residual film thickness to minimize Fresnel reflection losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If materials with high refractive indexes are used to increase field angle, then field angle is improved, but Fresnel reflection increases causing image degradation
Solution Approach 1:
A function part with a specific grating structure is introduced as an intermediary element between the incident light and the high refractive index substrate. This function part acts as a mediator that diffracts light in a controlled manner, enabling the system to achieve both wide field angle and suppressed Fresnel reflection by decoupling these two functions.
Solution Approach 2:
The patent changes the optical parameters by introducing a diffraction grating with specific pitch and orientation. By adjusting the grating pitch to be equal to or less than half the wavelength of incident light, the system transforms the light interaction mechanism from direct refraction (which causes Fresnel reflection) to diffraction-based coupling, thereby reducing reflection losses while maintaining wide field angle coverage.
2Loss of energy
If conventional techniques are used to suppress Fresnel reflection, then some reflection loss is reduced, but image quality still degrades and further improvement is needed
Solution Approach 1:
The patent replaces conventional anti-reflection coating mechanisms with a diffraction-based light coupling mechanism. Instead of using thin film interference to reduce reflection, the system uses a sub-wavelength grating structure to diffract and couple light into the waveguide, fundamentally changing the approach from suppression to constructive redirection of light.
Solution Approach 2:
The patent introduces a third dimension by creating a three-dimensional grating structure on the substrate surface. This vertical dimension with controlled depth and pitch allows for advanced light manipulation that goes beyond conventional two-dimensional surface coatings, enabling simultaneous achievement of low reflection and wide field angle through volumetric diffraction effects.
3Loss of energy
If diffraction gratings are added to suppress Fresnel reflection, then reflection loss is reduced, but device complexity increases
Solution Approach 1:
The patent merges the anti-reflection function with the light coupling function into a single integrated grating structure. The same diffraction grating that couples light into the waveguide also serves to reduce Fresnel reflection, eliminating the need for separate anti-reflection coatings and simplifying the overall device architecture despite the advanced functionality.
Solution Approach 2:
The grating structure is designed to perform multiple functions simultaneously: it acts as both a light coupling element and an anti-reflection element. This multi-functional design reduces the total number of components needed and simplifies manufacturing by consolidating multiple optical functions into a single structural feature.
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 proposed solution effectively suppresses Fresnel reflection losses, improving image quality without increasing manufacturing complexity, and enhances light use efficiency, reducing power consumption and increasing luminance.
Implementation Method 1
an incidence diffraction grating that diffracts incident light into the light guide plate
Implementation Method 2
a substrate that internally and totally reflects the light diffracted into the light guide plate by the incidence diffraction grating and guides the light
Implementation Method 3
a function part that transmits or reflects the incident light or performs both of the transmission and the reflection
Data Source
AI summary
To improve image quality by suppressing a loss caused by Fresnel reflection. Provided is a light guide plate including at least an incidence diffraction grating that diffracts incident light into the light guide plate, a substrate that internally and totally reflects the light diffracted into the light guide plate by the incidence diffraction grating and guides the light, and a function part that transmits or reflects the incident light or performs both of the transmission and the reflection, wherein when the substrate has a refractive index of nb,a transmittance T0 of zeroth-order transmitted light of the function part substantially at the center of the field angle area for guiding light satisfies formula below:T0>1-(nb-1)2/(nb+1)2