Meta-material Coated Waveguide for Wide Field of View Displays
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Solution Overview
Problem
Optical waveguides for display devices have limited field of view due to angular limitations in total internal reflection (TIR), which restricts the acceptance of light at extreme angles, especially for different wavelengths, leading to reduced viewing angles and color variations.
Innovation Solution
Coating the external surfaces of the waveguide with a meta-material having a refractive index of 1.0 or less, comprising a spatially periodically repeating array of unit cells with magnetic resonators and conductive meshes or wires, reduces the critical internal angle for TIR, allowing wider acceptance angles and improved light guidance across various wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a Bragg grating is used to diffract light into the waveguide for propagation by total internal reflection, then light guidance is achieved, but the field of view is limited by the angular range required for TIR
Solution Approach 1:
The patent changes the refractive index parameter of the external medium by applying a meta-material coating with refractive index less than 1.0. This parameter change modifies the TIR condition, allowing a wider angular range of light to be reflected and propagated within the waveguide, thereby expanding the field of view while maintaining effective light guidance
Solution Approach 2:
The patent uses a composite structure combining the waveguide material with a meta-material coating layer. This composite material system creates the necessary refractive index contrast to enhance TIR performance across a broader angular range, resolving the contradiction between maintaining guidance efficiency and expanding viewing angles
2Reliability
If the waveguide relies on total internal reflection for light propagation, then light retention is achieved, but light at extreme angles escapes the waveguide
Solution Approach 1:
By changing the refractive index parameter of the external medium through meta-material coating, the patent expands the angular range over which TIR occurs. This allows the waveguide to reliably retain light while accepting a broader range of incident angles, improving both light retention and angular adaptability
3Manufacturing precision
If a Bragg grating is tuned to a specific wavelength, then efficient diffraction is achieved for that wavelength, but the field of view varies for different wavelengths
Solution Approach 1:
The meta-material coating modifies the refractive index parameter to compensate for wavelength-dependent angular variations. By optimizing the coating properties, the patent achieves improved wavelength independence, where light of different wavelengths maintains more consistent field of view characteristics while preserving diffraction efficiency for the tuned wavelength
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 meta-material coating enhances the field of view by reducing the critical angle for TIR, enabling the retention and guidance of light outside the original viewing range, thus expanding the field of view and improving color consistency across different wavelengths.
Implementation Method 1
light is injected into the waveguide and is subsequently released from the waveguide for viewing... the waveguide to retain light injected into it for propagation along the waveguide by total internal reflection (TIR)... reduces the critical internal angle for TIR
Implementation Method 2
a Bragg grating (2A) arranged to receive light (3A) input through an opposite surface of the waveguide so as to be incident upon a facing surface of the Bragg grating... the received light is diffracted into a diffraction order (usually the first order) to redirect the input light into light (6A) for propagation along the body of the waveguide
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2~3
AI summary
An apparatus is disclosed for producing an optical display comprising an optical waveguide including a first diffractive part arranged to receive display light and to diffract the display light into an angle for guided propagation along the optical waveguide. A second diffractive part of the waveguide is optically coupled to the first diffractive part by the optical waveguide and is arranged to receive and to diffract light from the first diffractive part to an angle for output from the optical waveguide. Those external surfaces of the waveguide against which guided light reflects internally are coated with a meta-material having a refractive index of value less than 1.0 (one).