Angularly Reflective Optical Coating for Display Waveguides
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Solution Overview
Problem
Optical waveguides for display devices face limitations in field of view and color bandwidth due to the dispersive nature of diffraction gratings, which restrict the ability to efficiently inject and propagate full-color images, with substantial portions of red and blue light failing to diffract correctly.
Innovation Solution
An optical component featuring a prism with an angularly reflective optical coating, comprising a multi-layer stack of dielectric layers, that allows for partial reflection and transmission of light at varying angles, enabling efficient internal reflection and propagation within the waveguide while maintaining high transmission for light that undergoes an angular change, thereby expanding the field of view and color bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If diffraction gratings are used to inject and output light in the waveguide, then light can be diffracted to enable total internal reflection and guided propagation, but the dispersive nature of the gratings limits the field of view and color bandwidth
Solution Approach 1:
The waveguide surface is divided into multiple discrete coupling regions, each equipped with its own diffraction grating optimized for specific wavelength ranges. This segmentation allows different parts of the spectrum (red, green, blue) to be handled by specialized gratings, thereby expanding the overall color bandwidth while maintaining efficient diffraction for each color channel.
Solution Approach 2:
The patent transitions from a single-plane diffraction grating to a multi-layer stacked configuration where gratings are arranged at different depths and orientations within the waveguide. This three-dimensional arrangement enables simultaneous optimization for multiple wavelengths and angles, expanding both field of view and color bandwidth without sacrificing diffraction efficiency.
2Measurement precision
If a diffraction grating is optimised for one particular colour, then that colour can be diffracted correctly, but other colours fail to diffract as desired or diffract to incorrect angles
Solution Approach 1:
Each diffraction grating in the stacked configuration is locally optimized for specific wavelength ranges. The first grating stack is tuned for blue wavelengths, the second for green, and the third for red. This local optimization ensures that each color is diffracted at the precise angle required for total internal reflection, while the collective system handles the full color bandwidth.
Solution Approach 2:
The patent varies key parameters of the diffraction gratings across the stack, including grating period, orientation, and depth within the waveguide. By changing these parameters systematically across different grating layers, the system achieves wavelength-selective diffraction optimization, allowing each color to be precisely controlled while expanding the overall color bandwidth.
3Productivity
If light is guided through successive total internal reflection at opposing surfaces, then light can be propagated along the waveguide, but the angle of incidence must be sufficiently oblique which restricts the field of view
Solution Approach 1:
The patent employs multiple diffraction grating stacks with different orientations and positions, creating a dynamic light coupling system. By distributing coupling regions throughout the waveguide and using gratings oriented at various angles, the system can efficiently couple light across a broader range of incident angles, thereby expanding the field of view while maintaining effective light propagation through total internal reflection.
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 enhances the field of view and color bandwidth by optimizing light transmission and reflection within the waveguide, ensuring that a broader range of light is directed correctly for viewing, including red, green, and blue light, resulting in improved image quality and uniform brightness across the display.
Implementation Method 1
An input diffraction grating 5 is positioned upon a surface of the waveguide to receive the input light and to diffract the received ray in a direction forming an angle of incidence to the opposite surfaces of the waveguide internally which permits TIR. Guiding of the light ray 8 ensues until the guided light is incident upon an output diffraction grating 6
Implementation Method 2
The output part may include a prism in optical contact with the said transmissive angularly reflective optical coating part arranged to receive light from the said waveguide part and to direct the received light out of the optical waveguide part
Implementation Method 3
Optical waveguides for display devices of this type typically release guided light from an output part by a process of diffraction for viewing, whereby guided light is diffracted within the waveguide to a direction which prohibits total internal reflection
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An optical component for a display apparatus comprises an optical waveguide part (11) arranged to guide light therealong between surface parts thereof by internal reflection, an input part (13) arranged to receive light and direct the received light into the optical waveguide part, and an output part comprising a partially transmissive angularly reflective optical coating (19; 25) arranged upon a surface part of the optical waveguide part. The output part is optically coupled to the input part by the optical waveguide part to receive guided light and to transmit some but not all of said guided light out from the optical waveguide part. The angularly reflective optical coating extends along a dimension of the optical waveguide part to expand the guided light in said dimension along the output part by repeated partial transmission thereof for output.