Waveguide Incoupling Polarization Scheme for Etendue Limits
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Solution Overview
Problem
Head-mounted display systems face inefficiencies due to the conservation of etendue, leading to limited coupling efficiency and increased weight or decreased light engine efficiency, which are undesirable in augmented and mixed reality displays.
Innovation Solution
Implementing a configuration with a first optical element to convert polarization state, a second optical element to selectively reflect or transmit based on polarization, and an incoupler to direct light into a waveguide, minimizing the 'multibounce' effect and optimizing polarization states for improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the waveguide thickness is increased to improve coupling efficiency, then the coupling efficiency is improved, but the weight of the device increases
Solution Approach 1:
The patent changes the polarization state parameter of light to resolve the contradiction. By using a quarter-wave plate to convert linearly polarized light to circularly polarized light, the system achieves high coupling efficiency without increasing waveguide thickness, thus avoiding weight increase while maintaining productivity.
Solution Approach 2:
The patent introduces a quarter-wave plate as an intermediary optical element between the light source and waveguide. This intermediary converts the polarization state of light, enabling efficient coupling into the waveguide without requiring increased thickness, thereby resolving the contradiction between coupling efficiency and device weight.
2Productivity
If the exit pupil size is reduced to improve coupling efficiency, then the coupling efficiency is improved, but the light engine efficiency decreases
Solution Approach 1:
The patent changes the polarization state parameter of light to resolve the contradiction. By converting to circularly polarized light, the system can maintain a large exit pupil size for high light engine efficiency while achieving high coupling efficiency through the polarization-sensitive waveguide coupling mechanism.
3Device complexity
If a traditional grating in-coupler is used, then the device complexity is reduced, but the coupling efficiency is limited due to etendue conservation
Solution Approach 1:
The patent changes the polarization state parameter of light using a quarter-wave plate, which enables high coupling efficiency while maintaining a relatively simple optical system. The added complexity of the wave plate is minimal compared to the significant improvement in coupling efficiency achieved.
4Productivity
If the waveguide thickness is increased to improve coupling efficiency, then the coupling efficiency is improved, but the duration of action decreases due to increased power consumption
Solution Approach 1:
The patent changes the polarization state parameter of light to achieve high coupling efficiency without increasing waveguide thickness. This avoids increased power consumption and heat generation, thereby maintaining longer battery life and duration of action while achieving the desired coupling efficiency.
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 significantly enhances system efficiency, allowing for lighter and longer-lasting head-mounted displays by reducing power constraints and enabling smaller battery sizes.
Implementation Method 1
a first optical element configured to convert a polarization state of light from the light source
Implementation Method 2
a second optical element configured to selectively reflect or transmit light transmitted by the first optical element based on a polarization state of the light transmitted by the first optical element
Implementation Method 3
a first incoupler configured to direct light transmitted by the second optical element into a waveguide
Implementation Method 4
direct light transmitted by the second optical element into a waveguide
Implementation Method 5
the first optical element is further configured to convert a polarization state of light directed into the waveguide by the first incoupler such that the light directed into the waveguide by the first incoupler is selectively reflected by the second optical element
Data Source
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AI summary
Embodiments disclosed variously address the etendue limit on incoupling, e.g., in an augmented or mixed reality display waveguide combiner, by trading polarization state purity for reduced space-bandwidth product using a combination of optical elements, thereby improving system efficiency, reducing power constraints, and thus enabling longer battery life and/or smaller battery size. Efficiency of optical systems such as head mounted display devices can thus be increased to allow for lighter weight devices and/or devices that require fewer charges between uses.