Multilayer Waveplate Optical Structures for HMD Ghost Image Reduction
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Solution Overview
Problem
Existing waveguides in Head Mounted Displays (HMDs) suffer from undesirable ghost images due to light from unwanted spectrums bleeding into the waveguides, which is exacerbated by non-flat waveguide surfaces.
Innovation Solution
Incorporating a multilayer waveplate into the waveguides to outcouple unwanted light spectrums before they reach the eyebox, thereby reducing ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a waveguide is used to direct image light in an HMD, then the device can deliver images to the user within compact form factors, but ghost images appear due to unwanted light spectrums bleeding into the waveguide
Solution Approach 1:
The waveguide is divided into multiple functional layers including a first waveguide layer for directing blue light and a second waveguide layer for directing green light. This segmentation allows each layer to handle specific wavelengths independently, preventing spectral bleeding and ghost images while maintaining compact form factor.
Solution Approach 2:
A dichroic filter layer is introduced as an intermediary between the first and second waveguide layers. This filter selectively transmits green light to the second waveguide while reflecting blue light back into the first waveguide, thereby mediating the interaction between different spectral components and preventing unwanted light from entering the wrong waveguide layer.
2Use of energy by moving object
If the waveguide surface is made non-flat to improve certain optical properties, then light coupling may be enhanced, but ghost images are exacerbated due to increased light scattering
Solution Approach 1:
Different regions of the waveguide structure are assigned different surface characteristics. The input surface may have micro-structures for enhanced light coupling, while the output surface maintains appropriate flatness to minimize scattering-induced ghost images. This local differentiation allows optimization of light coupling without sacrificing image quality.
Solution Approach 2:
The problem of light coupling is solved by moving from surface-only modifications to volumetric control through multiple layered structures. Each layer can have optimized thickness and refractive index profiles that control light propagation in three dimensions, enabling effective coupling while maintaining surface quality for ghost image reduction.
3Manufacturing precision
If multiple waveguide layers are stacked to handle different color spectrums, then color accuracy is improved, but device complexity increases
Solution Approach 1:
Multiple waveguide functions are merged into a single stacked structure where the first and second waveguide layers are vertically integrated with a dichroic filter layer. This combined structure handles both blue and green light spectrums simultaneously through one compact assembly, achieving color accuracy without proportionally increasing device complexity.
Solution Approach 2:
The stacked waveguide structure serves multiple functions within a single integrated component: the first waveguide layer directs blue light, the dichroic filter separates spectra, and the second waveguide layer directs green light. This multi-functionality allows precise color control while minimizing the number of separate components needed.
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 multilayer waveplates effectively reduces ghost images by outcoupling unwanted light, improving the overall quality of the image delivered to the user.
Implementation Method 1
a first multilayer waveplate in the first stack is configured to act as a half-wave plate in reflection of the first spectrum of image light
Implementation Method 2
an input grating is configured to incouple a first spectrum of image light into the waveguide
Implementation Method 3
an input grating is configured to incouple a first spectrum of image light into the waveguide
Implementation Method 4
an output grating is configured to direct the first spectrum propagating in the waveguide to an eyebox area
Implementation Method 5
a waveguide is used to direct the image light to the eye
Data Source
AI summary
An optical structure includes an input grating and a multilayer waveplate. The input grating is configured to incouple a first spectrum of received image light. The multilayer waveplate is configured to reflect the first spectrum of the image light incoupled by the input grating in the second polarization orientation and reflect a second spectrum of the image light incoupled by the input grating by diffraction in the first polarization orientation.