Bragg Gratings in Waveguides for Reflective WHUDs
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Solution Overview
Problem
Wearable heads-up displays (WHUDs) suffer from see-through artifacts due to remaining light in exit pupil expanders and outcouplers, which obstructs user views and distracts both users and onlookers, caused by inefficient light reflection and diffraction from gratings in these components.
Innovation Solution
The implementation of Bragg gratings in waveguides within WHUDs, which are dispersion-free and increase the efficiency of exit pupil expanders and outcouplers, reducing the number of see-through artifacts by effectively directing light without separating polychromatic light into constituent wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional gratings are used in exit pupil expanders and outcouplers, then light can be reflected and diffracted to guide light through the waveguide, but some light remains in the components causing see-through artifacts that obstruct user views and distract users
Solution Approach 1:
The patent changes the grating parameters by using volume holographic gratings with specific refractive index modulations and spatial frequencies. These gratings are designed with optimized duty cycles and depths to achieve near-complete light coupling into the waveguide mode, minimizing residual light that causes see-through artifacts while maintaining efficient light guidance.
Solution Approach 2:
The patent employs composite grating structures combining different materials with complementary optical properties. The volume holographic gratings are formed within the waveguide substrate using photopolymerization, creating a composite structure that enhances light coupling efficiency while reducing unwanted reflections and see-through artifacts through material property optimization.
2Reliability
If gratings with high reflection efficiency are used, then light can be effectively directed through the waveguide, but remaining light interacts with outside sources through undesired reflections or diffraction
Solution Approach 1:
The patent optimizes grating parameters including spatial frequency, refractive index modulation depth, and duty cycle to achieve selective wavelength and angle coupling. These parameter adjustments ensure that light is efficiently coupled into the desired waveguide mode while minimizing coupling into unwanted modes that would cause undesired reflections and diffraction interactions with external light sources.
Solution Approach 2:
The volume holographic gratings act as intermediary elements that mediate between the incoming light and the waveguide mode. The gratings provide a controlled interaction mechanism that selectively couples light into the waveguide while rejecting unwanted wavelengths and angles, thereby preventing undesired reflections and diffraction effects.
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 use of Bragg gratings in waveguides enhances the efficiency of light transmission, minimizing remaining light in exit pupil expanders and outcouplers, thereby reducing see-through artifacts and improving user experience by minimizing obstructions and distractions.
Implementation Method 1
The implementation of Bragg gratings in waveguides within WHUDs, which are dispersion-free and increase the efficiency of exit pupil expanders and outcouplers
Implementation Method 2
Each exit pupil expander and outcoupler includes gratings that are configured to reflect or diffract light as it travels through the exit pupil expander or outcoupler
Implementation Method 3
Each exit pupil expander and outcoupler includes gratings that are configured to reflect or diffract light as it travels through the exit pupil expander or outcoupler
Data Source
AI summary
A waveguide including first and second sections has a first molded optic material forming a portion of the geometry of one or more Bragg gratings disposed on one surface of the first section of the waveguide. Similarly, a second molded optic material forming another portion of the geometry of one or more Bragg gratings is disposed on one surface of the second section of the waveguide. Further, a photopolymer material is deposited on the first molded optic material. As the first and second sections are coupled, a waveguide is formed with a layer of photopolymer material disposed in the waveguide with the layer of photopolymer material having a geometry defined by the first and second molded optic materials. Bragg grating holograms are then recorded in the layer of photopolymer material, resulting in a waveguide with a plurality of Bragg gratings.