Dispersion-Compensating Interleaved Gratings for Waveguide Displays
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Solution Overview
Problem
Designing electronic devices with optical components for displays, such as virtual and augmented reality headsets, is challenging due to the need for optimal optical performance, which is often compromised by dispersion issues introduced by diffractive input couplers.
Innovation Solution
The use of an output coupler with overlapping volume holograms having specific grating vectors and pitches to cancel out dispersion introduced by the input coupler, allowing for efficient redirection and expansion of image light to a wide eye box with uniform intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a diffractive input coupler is used to couple image light into the waveguide, then the image light can be efficiently coupled into the waveguide, but dispersion is introduced to the image light which degrades optical performance
Solution Approach 1:
The patent applies dispersion compensation gratings that introduce equal and opposite dispersion to cancel the dispersion introduced by the input coupler. The harmful dispersion effect is converted into a beneficial cancellation mechanism by strategically placing additional diffractive elements that produce compensating dispersion, thereby restoring optical performance while maintaining coupling efficiency
Solution Approach 2:
The dispersion compensation gratings act as intermediary elements between the input coupler and the output coupler. These intermediate diffractive structures mediate the optical path by introducing controlled dispersion that counteracts the unwanted dispersion from the input coupler, enabling both efficient coupling and high optical performance
2Manufacturing precision
If dispersion compensation elements are added to cancel dispersion, then optical performance is improved, but device complexity increases
Solution Approach 1:
The patent merges the dispersion compensation function with the existing input and output couplers by integrating dispersion compensation gratings into the waveguide structure. Rather than adding separate standalone components, the compensation gratings are combined with the coupling structures, reducing overall device complexity while maintaining optical performance
Solution Approach 2:
The diffractive gratings in the waveguide serve multiple functions: they act as input couplers to couple light into the waveguide, serve as dispersion compensation elements to cancel unwanted dispersion, and function as output couplers to extract light. This multi-functionality reduces the number of separate components needed, thereby reducing device complexity
3Area of stationary object
If the eye box is expanded to provide a wider field of view, then user comfort is improved, but light intensity becomes non-uniform across the eye box
Solution Approach 1:
The patent applies local quality by varying the characteristics of the output coupler across different regions of the eye box. The output coupler is designed with spatially varying diffraction efficiency or grating parameters that compensate for the non-uniform light distribution, ensuring uniform intensity across the expanded eye box while maintaining the wide field of view
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
This configuration enhances the field of view, reduces manufacturing costs and complexity, and optimizes space use while maintaining high optical performance by efficiently mitigating dispersion and redirecting light in multiple dimensions.
Implementation Method 1
The input coupler may be a diffractive input coupler and may include a surface relief grating or a volume hologram. The input coupler may diffract the image light to couple the image light into the waveguide.
Implementation Method 2
The output coupler may include at least a first volume hologram and a second volume hologram. The first volume hologram may diffract the image light as first diffracted light. The second volume hologram may diffract the image light as second diffracted light.
Implementation Method 3
The first volume hologram may diffract the second diffracted light out of the waveguide. The second volume hologram may diffract the first diffracted light out of the waveguide.
Data Source
AI summary
A display may include a waveguide, a diffractive input coupler, and an output coupler. The input coupler may diffract image light into the waveguide. The output coupler may diffract the image light out of the waveguide and towards an eye box. The output coupler may include a first volume hologram with a first grating vector and a second volume hologram with a second grating vector. The first and second grating vectors may be oriented at the same angle from opposing sides of an axis. The input coupler may have a first pitch. The first and second volume holograms may have a second pitch. The second pitch may be constant across the output coupler. In order to mitigate dispersion by the input coupler, the second pitch may be equal to twice the first pitch times a cosine of the angle.