Oblique Reflective Polarizer Optical Stack for AR HMD Brightness
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Solution Overview
Problem
Existing optical see-through augmented reality head-mounted display (AR HMD) systems face challenges in maintaining high brightness and resolution when integrating virtual images with the real world.
Innovation Solution
The optical system incorporates a reflective polarizer oriented obliquely between a second display and the viewer, along with an optical stack including a partial reflector and a retarder layer, to enhance image brightness and maintain high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective polarizer is used to display virtual images, then brightness is improved, but resolution and contrast deteriorate
Solution Approach 1:
The optical system is divided into separate optical stacks for different displays (first display and second display). Each optical stack contains specific components (reflective polarizer, partial reflector, retarder layer) configured to handle light from its associated display independently, allowing optimization of brightness for virtual images without compromising the quality of real world view
Solution Approach 2:
The reflective polarizer is oriented obliquely relative to the first display, creating different optical paths and properties for different regions of the system. The partial reflector is positioned specifically between the reflective polarizer and the second display to manage light distribution locally, ensuring high resolution and contrast are maintained in critical areas
2Illumination intensity
If a reflective polarizer is used to display virtual images, then brightness is improved, but contrast deteriorates
Solution Approach 1:
A retarder layer is introduced as an intermediary component between the reflective polarizer and the partial reflector. This retarder layer modifies the polarization state of light, enabling the system to maintain high contrast by controlling the interaction between virtual and real image light paths while preserving the brightness enhancement provided by the reflective polarizer
3Adaptability or versatility
If multiple displays are integrated in an AR HMD, then functionality is improved, but device complexity increases
Solution Approach 1:
The optical stacks are designed to serve multiple functions: they guide light from both the first display (virtual images) and the second display (additional visual information) to the viewer's eye. The reflective polarizer and partial reflector work together to manage light from multiple sources, reducing the need for separate optical paths and simplifying the overall system architecture while maintaining versatility
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 achieves increased brightness of the displayed images while maintaining high resolution and contrast, thereby improving the overall augmented reality experience.
Implementation Method 1
the reflective polarizer reflects at least 70% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state
Implementation Method 2
the reflective polarizer reflects at least 70% of the incident light having a first polarization state
Implementation Method 3
the reflective polarizer transmits at least 60% of the incident light having an orthogonal second polarization state
Implementation Method 4
the partial reflector reflects at least 70% of the incident light for each of the first and second polarization states
Implementation Method 5
the partial reflector transmits at least 60% of the incident light
Implementation Method 6
The retarder layer is substantially a quarter wave retarder at at least one of the blue, green and red wavelengths for at least one of the first and second polarization states
Data Source
AI summary
An optical system for displaying first and second images to a viewer is provided. A reflective polarizer is disposed between the second display and the viewer and is oriented obliquely relative to the first display. An optical stack including a partial reflector and a retarder layer is disposed between the reflective polarizer and the second display. The reflective polarizer reflects at least 70% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state. The partial reflector reflects at least 70% of the incident light for each of the polarization states. For each of the first and second polarization states and for each of a blue-green wavelength and a green-red wavelength the reflective polarizer transmits at east 70% of the incident light and the partial reflector transmits at least 60% of the incident light.