Photonic Crystal Waveguide for One-Sided AR Light Out-Coupling
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Solution Overview
Problem
Conventional augmented reality waveguides suffer from inefficiencies due to unwanted out-coupling of light in opposite directions, leading to reduced optical efficiency and potential privacy concerns from external visibility of displayed content.
Innovation Solution
A waveguide design with optical structures in a photonic crystal that have varying profiles perpendicular to the plane, preferentially diffracting light towards a viewer from one major surface, suppressing unwanted out-coupling orders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional diffraction gratings are used in waveguides, then light can be coupled into and out of the waveguide, but unwanted diffraction orders extend in opposite directions causing light waste and privacy concerns
Solution Approach 1:
The patent applies local quality by varying the profile of optical structures at different locations within the photonic crystal. Specifically, optical structures have different heights or shapes at different positions to preferentially direct light in desired directions while suppressing unwanted diffraction orders, thereby improving optical efficiency and eliminating privacy concerns.
Solution Approach 2:
The patent employs asymmetry by designing optical structures with non-uniform profiles where structures at different locations have different geometries. This asymmetric arrangement ensures that light is preferentially coupled out in the intended viewing direction while minimizing unwanted out-coupling in opposite directions, resolving the contradiction between energy efficiency and harmful radiation.
2Adaptability or versatility
If multiple diffraction orders are produced, then light can be expanded in multiple directions, but efficiency decreases as light is wasted in unwanted directions
Solution Approach 1:
The patent uses local quality by assigning different profile characteristics to optical structures at different locations within the photonic crystal. This allows the structure to expand light in multiple directions where needed while suppressing unwanted diffraction orders in specific directions, maintaining versatility without energy waste.
Solution Approach 2:
The patent converts the potentially harmful effect of multiple diffraction orders into a benefit by using the varying profiles to direct unwanted orders away from the viewing zone. The structures that would normally create privacy concerns are instead designed to redirect light constructively, turning a harmful factor into a useful feature for controlled light distribution.
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
Enhances optical efficiency by preferentially directing light in a single direction, improving battery life in wearable devices and reducing power demands while minimizing privacy risks.
Implementation Method 1
an output diffractive element comprising a plurality of optical structures in a photonic crystal... diffract the light into a plurality of orders, some of the orders being diffracted in the plane of the waveguide at an angle to the input direction to provide 2D expansion
Implementation Method 2
The projected light is totally internally reflected within the waveguide
Data Source
AI summary
A waveguide (1) for use in an augmented reality or virtual reality display, comprising: an output diffractive element comprising a plurality of optical structures (22, 28, 26) in a photonic crystal; a first major surface of the waveguide, and a second major surface of the waveguide, the first major surface separated in a direction perpendicular to a plane of the waveguide from the second major surface, wherein light propagates along the waveguide towards the output diffractive element by undergoing total internal reflection between the first and second major surfaces wherein the plurality of optical structures (22, 28, 26) are arranged in a plane of the waveguide in an array which is configured to receive light from an input direction and diffract the light into a plurality of orders, some of the orders being diffracted in the plane of the waveguide at an angle to the input direction to provide 2D expansion across the plane of the waveguide, and other orders being out-coupled in a direction perpendicular to the plane of the waveguide towards a viewer; wherein at least one of the optical structures (22, 28, 26) of the plurality of optical structures (22, 28, 26) has a profile in a direction that is perpendicular to the plane of the waveguide, wherein the profile varies along one or more directions parallel to the plane of the waveguide, such that the out-coupled orders are provided preferentially from the first major surface of the waveguide compared to the second major surface of the waveguide.