Pancake Optics AR Headset Resolving Eyebox and Length Trade-offs
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Solution Overview
Problem
Existing VR/AR display systems face challenges in achieving a wide field of view and high resolution with a large eyebox while maintaining a compact and lightweight design, often resulting in dim images due to light loss through multiple optical components.
Innovation Solution
The proposed display system incorporates a first polarizer, a transparent display, a beam splitter, and a selective mirror to polarize and collimate light, allowing background light to pass through while maintaining image brightness and reducing the system's size and weight by using pancake optics with orthogonal polarizations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a simple magnifier with a long focal length lens or mirror is used to achieve a wide field of view and large eyebox, then the eyebox size and field of view are improved, but the device length and weight increase, creating an uncomfortable moment that pulls the head-mounted display downward
Solution Approach 1:
The patent employs pancake optics that fold the optical path into a compact configuration, transforming the linear optical path into a multi-dimensional folded structure. This allows the optical system to achieve the equivalent of a long focal length while maintaining a short physical device length, resolving the contradiction between eyebox size and device length.
Solution Approach 2:
The patent integrates multiple optical components (lens, polarizer, beam splitter, mirror) into a nested compact arrangement where components are positioned close together in a folded optical path. This nesting allows the system to achieve long optical path length effects within a short physical footprint, improving eyebox without increasing device length.
2Length of stationary object
If polarization elements are used to fold the optical path and reduce device size, then the device length is reduced, but image brightness decreases due to repeated reflection and transmission through optical components that remove light
Solution Approach 1:
The patent uses a polarizer in combination with a beam splitter and selective mirror to convert the potentially harmful light loss from multiple reflections into a beneficial system. By controlling polarization states, the system maintains high transmission efficiency for the desired light path while blocking unwanted reflections, thus preserving image brightness despite the folded optical path.
Solution Approach 2:
The patent changes the polarization parameter of light as it passes through different optical components. The polarizer creates polarized light, the beam splitter separates polarizations, and the selective mirror reflects or transmits based on polarization state. This parameter manipulation allows the system to guide light efficiently through the compact folded path while minimizing losses, maintaining image brightness.
3Manufacturing precision
If multiple optical components are used to achieve wide field of view and high resolution, then image quality is improved, but light loss increases causing dim images
Solution Approach 1:
The patent uses polarization state changes as a control parameter to manage light transmission through multiple optical components. By ensuring that each component is optimized for its specific polarization state, the system maintains high transmission efficiency and minimizes light loss while achieving wide field of view and high resolution through the multi-component optical 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
This configuration enhances image brightness and reduces the system's size and weight, providing a wider field of view and improved eye alignment, while maintaining image quality and comfort for users.
Implementation Method 1
a first polarizer element arranged to polarize background light received at the display system
Implementation Method 2
a selective mirror configured to permit a first polarization of light to pass therethrough but reflect a second polarization of light
Implementation Method 3
a beam splitter arranged to receive the emitted light and the background light, wherein the emitted light and the background light have orthogonal polarizations
Data Source
AI summary
Embodiments provide for a display system that overlays augmented reality (AR) content onto a view of an environment. The display includes a first polarizer that receives light providing a view of the environment (which can be natural light or light generated from another display). The polarized light then passes through a transparent display that emits light forming the AR content. The light emitted by the display and the polarized light of the environment pass through a beam splitter before reaching a selective mirror. The polarized light from the environment passes through the selective mirror while the light from the display is reflected back towards the beam splitter where it is collimated. Moreover, when collimating the light, the beam splitter also reflects the light back towards the selective mirror and changes its polarization so the light can pass through the selective mirror.