Pancake Lens Beamsplitter Layout for Higher Optical Throughput
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Solution Overview
Problem
Folded optic configurations in head-mounted displays (HMDs) suffer from lower efficiency compared to non-folded configurations, leading to increased power consumption and discomfort due to higher temperatures, which reduces the usability of augmented and virtual reality devices.
Innovation Solution
Implement a beamsplitter with varying reflectance regions, where the edges have a higher reflectance than the central region, combined with a reflective polarizer to enhance optical throughput and image uniformity, using a pancake lens configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a folded optic configuration including a pancake lens is used, then the device becomes compact with wide field-of-view and higher resolution, but the system efficiency decreases leading to increased power consumption and heat generation
Solution Approach 1:
The beamsplitter is designed with spatially varying reflectance properties: the central region has lower reflectance to transmit light from the display, while the peripheral region has higher reflectance to redirect light toward the user's eye. This local differentiation of optical properties optimizes light throughput efficiency while maintaining the compact folded optic configuration.
Solution Approach 2:
The beamsplitter surface is segmented into distinct functional zones with different reflectance characteristics. The central portion and peripheral portion are treated differently to optimize their respective roles in light transmission and redirection, improving overall system efficiency without compromising the compact form factor.
2Device complexity
If a folded optic configuration with uniform beamsplitter reflectance is used, then the device structure is simplified, but image uniformity and optical throughput are reduced
Solution Approach 1:
The beamsplitter incorporates non-uniform reflectance distribution across its surface, with the central region having lower reflectance and the peripheral region having higher reflectance. This local quality variation compensates for optical path differences and improves image uniformity across the user's field of view.
Solution Approach 2:
The reflectance parameter of the beamsplitter is deliberately varied across different spatial locations rather than kept uniform. This parameter change from constant to spatially varying reflectance optimizes light distribution and image uniformity while maintaining relatively simple device structure.
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 increases lens efficiency, reduces power consumption, and decreases heat generation, thereby improving the usability and battery life of AR/VR devices.
Implementation Method 1
the first region of the beamsplitter has a first reflectance; the second region of the beamsplitter has a second reflectance
Implementation Method 2
a light ray emitted by the display is transmitted through the first region of the beamsplitter, reflects from the reflective polarizer, reflects from the second region of the beamsplitter, and is transmitted through the reflective polarizer
Implementation Method 3
a reflective polarizer; the apparatus is configured so that a light ray emitted by the display is transmitted through the first region of the beamsplitter, reflects from the reflective polarizer
Data Source
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AI summary
An example apparatus may include a display, a beamsplitter having a first region and a second region, and a reflective polarizer. The reflectance of the second region of the beamsplitter may be appreciably greater than the reflectance of the first region; for example, at least approximately 20% greater. In some examples, the second region may be a peripheral region surrounding a generally centrally located first region. An example apparatus may be configured so that at least some light emitted by the display is transmitted through the first region of the beamsplitter, reflects from the reflective polarizer, reflects from the second region of the beamsplitter, and is then directed through the reflective polarizer to an eye of a user when the user wears the apparatus. Other devices, methods, systems, and computer-readable media are also disclosed.