Waveguide Pixel Extraction Layout for Low-Loss AR Microdisplays
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Solution Overview
Problem
Existing microdisplays for augmented reality systems suffer from high power consumption and optical losses due to inefficient light extraction and diffraction gratings, which affect compactness and image definition.
Innovation Solution
A display device with a substrate, addressing waveguides, and a matrix of extraction structures, utilizing liquid crystal and high index regions for evanescent coupling and total internal reflection to enhance light extraction efficiency and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If diffraction gratings are used to extract light at emission points, then light extraction is achieved, but optical losses occur due to unnecessary diffraction orders and parasitic images
Solution Approach 1:
The patent extracts only the necessary diffraction order from the diffraction grating, eliminating unnecessary diffraction orders that cause optical losses and parasitic images. The extraction structure is designed to selectively couple out only the desired light while maintaining efficient light extraction at emission points.
Solution Approach 2:
The patent applies different properties to different parts of the system by designing extraction structures with specific local characteristics. The extraction structures have varying coupling coefficients and geometries optimized for their specific positions, allowing efficient light extraction while minimizing optical losses in different regions of the waveguide array.
2Loss of energy
If a large length of diffraction grating is used to extract light efficiently, then energy loss is minimized, but compactness and definition of the microdisplay are impaired
Solution Approach 1:
The patent divides the light extraction function into multiple discrete extraction structures distributed along the waveguide array. Each extraction structure handles a specific portion of the light extraction task, allowing efficient energy extraction without requiring a single long diffraction grating, thus maintaining compactness.
Solution Approach 2:
The patent transitions from using a long one-dimensional diffraction grating to using multiple distributed extraction structures in both longitudinal and transverse dimensions. This dimensional redistribution allows efficient light extraction through multiple points simultaneously, reducing the required length in any single dimension and improving overall compactness.
3Use of energy by moving object
If directivity of light extracted at each emission point is increased to reduce power consumption, then light flux loss between microdisplay and user's eye is reduced, but device complexity increases
Solution Approach 1:
The patent implements dynamic control of light extraction by using electro-optic or acousto-optic modulators at each emission point. These dynamic elements can adjust the extraction characteristics in real-time to optimize directivity toward the user's eye, reducing power consumption while maintaining manageable device complexity through programmable control.
Solution Approach 2:
The patent changes key parameters of the extraction structures, such as refractive index, coupling coefficient, or grating period, to optimize light directivity. By adjusting these parameters, the system achieves improved light flux delivery to the user's eye while reducing power consumption, balancing performance gains against device complexity.
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 achieves a compact and energy-efficient image display with improved light extraction, reducing optical losses and enhancing image definition.
Implementation Method 1
comprises an intermediate waveguide in a liquid crystal extending in parallel to an upper face of the substrate from an input face of the intermediate waveguide to an output face of the intermediate waveguide, the intermediate waveguide being arranged between the addressing electrode and the common electrode so as to switch a refractive index of the liquid crystal along a direction of polarization, from a first level to a second level strictly greater than the first level, when a variation in an electric potential difference is applied between the addressing electrode and the common electrode
Implementation Method 2
a high index region extending from the output face of the intermediate waveguide, to the input face of an adjacent extraction structure of the matrix of extraction structures, the high index region having a refractive index np strictly greater than the first level
Data Source
AI summary
The invention relates to a device for displaying an image comprising a matrix of extraction structures and sets of waveguides and addressing electrodes extending respectively along axes xi and ya, ya forming an angle β with an axis yi orthogonal to xi. Each extraction structure comprises an intermediate waveguide of a liquid crystal arranged between an addressing electrode and a common electrode so as to switch its index from a first level to a second level. An input face of the intermediate waveguide forms an angle γ greater than 30 degrees with the substrate and an angle equal to β with the axis yi. In operation, a mode of the addressing waveguide is coupled to the intermediate waveguide only when the liquid crystal index is equal to the second level to extract a beam corresponding to the display of a pixel, after total reflection on the input face of the adjacent extraction structure.