Folded Viewing Optics with Quarter-Wave Plate for VR Headsets
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Solution Overview
Problem
Folded optics in virtual reality, augmented reality, and mixed reality systems face challenges in achieving compact designs with large field of view while maintaining optical quality and image contrast, often requiring performance trade-offs in terms of field of view, optical quality, and image contrast/ghosting.
Innovation Solution
A folded-lens system utilizing polarization of light and reflective optical power, with a focal length between 20-30 mm, a field of view greater than ±45 degrees, and a z-distance of up to 22 mm, incorporating a reflective polarizer on a compound curved surface, two identical quarter-wave plates clocked by 90 degrees, and an absorptive polarizer to reduce the Narcissus effect, while minimizing manufacturing complexity and stress-induced birefringence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If folded optics are used to achieve compact design, then the device size is reduced, but optical quality and image contrast deteriorate due to performance trade-offs
Solution Approach 1:
The optical system is divided into multiple discrete elements including a first lens element, second lens element, third lens element, and fourth lens element, each with specific optical powers and positions. This segmentation allows optimization of each element's contribution to overall optical quality while maintaining compact folded geometry
Solution Approach 2:
The patent employs composite optical structures combining refractive lens elements with reflective surfaces. The system integrates multiple materials with different optical properties (refractive indices, dispersions) to achieve superior image quality and contrast ratio while maintaining compact form factor through the folded configuration
2Volume of moving object
If folded optics are used to achieve compact design, then the device size is reduced, but field of view and image contrast suffer from ghosting effects
Solution Approach 1:
The patent converts potentially harmful ghosting effects into beneficial outcomes by using polarizing beam splitting surfaces that direct reflected light into useful optical paths. The ghosting that would normally degrade image contrast is redirected to contribute to the overall image formation, improving contrast ratio while maintaining compact design
Solution Approach 2:
The system utilizes changes in polarization state parameters as light interacts with different optical elements. By controlling polarization angles and using polarizing beam splitters at specific orientations, the system manages reflected light to minimize ghosting while maintaining compact folded geometry
3Volume of moving object
If reflective surfaces are used to achieve compact design, then the optical path is folded, but manufacturing complexity increases due to compound curved surfaces
Solution Approach 1:
The complex optical system is divided into multiple simpler lens elements (first, second, third, and fourth lens elements) with manageable curvatures and optical powers. Each element can be manufactured separately using standard optical manufacturing techniques, reducing overall manufacturing complexity while achieving the desired compact folded design
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 solution enables compact VR headset designs with improved optical quality and reduced ghosting, maintaining a large field of view and image contrast, while minimizing manufacturing complexity and stress-induced birefringence, thus addressing the trade-offs in existing folded optics systems.
Implementation Method 1
A lens system is designed to use polarization of light and reflective optical power
Implementation Method 2
two quarter-wave plates; two-quarter wave plates that are identical and clocked by 90 degrees
Implementation Method 3
reflective optical power; a reflective polarizer on a compound curved surface
Implementation Method 4
an absorptive polarizer (e.g., to reduce or eliminate Narcissus effect)
Data Source
AI summary
A folded-lens system is used in an artificial-reality headset. The folded-lens system has a first mirror, a second mirror, and a quarter-wave plate between the first mirror and the second mirror. The first mirror and the second mirror are not strongly curved, which enables the quarter-wave plate to be on a flat surface.