Polarization Mirror HMD Brightness Efficiency
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Solution Overview
Problem
Conventional pancake lens designs for Head-Mounted Displays (HMDs) suffer from low brightness efficiency, with only about 25% of light passing through the optics, leading to dim output and user discomfort due to increased thickness or heat from brighter displays.
Innovation Solution
Incorporating two polarization sensitive mirrors between the half mirror and the display, with a quarter-wave plate between each mirror, to create two light paths that enhance brightness efficiency to up to 50% without significantly increasing the device's thickness or causing discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If conventional pancake lens designs are used to reduce device thickness, then device compactness is improved, but brightness efficiency deteriorates to only 25%
Solution Approach 1:
The optical path is divided into two separate polarization channels using two polarization selective mirrors. Each mirror handles a specific polarization state (one for s-polarized light, one for p-polarized light), allowing both channels to contribute to the final image brightness. This segmentation enables the system to achieve up to 50% brightness efficiency while maintaining the compact pancake form factor.
2Illumination intensity
If display brightness is increased to compensate for low efficiency, then visual performance is improved, but heat generation increases causing user discomfort
Solution Approach 1:
The patent converts the normally wasted light (which would be absorbed and converted to heat) into a useful resource. By using polarization selective mirrors to redirect both s-polarized and p-polarized light paths to contribute to the image, the system utilizes what would otherwise be lost energy, achieving higher brightness efficiency without requiring increased display power and thus avoiding excessive heat generation.
3Device complexity
If a single polarization selective mirror is used in pancake optics, then device complexity is reduced, but brightness efficiency is limited to 25%
Solution Approach 1:
Different regions of the optical system are assigned different functions based on their polarization characteristics. The first polarization selective mirror is optimized for one polarization state while the second mirror handles the orthogonal polarization state. This local optimization allows each mirror to efficiently handle its designated polarization channel, collectively achieving up to 50% brightness 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 doubles the brightness efficiency of conventional pancake lens designs while maintaining a compact form factor, ensuring user comfort and improved visual performance.
Implementation Method 1
a first quarter wave plate between the first linear polarization selective mirror and the partial mirror and a second quarter wave plate between the partial mirror and the second linear polarization selective mirror
Implementation Method 2
a first polarization selective mirror configured to transmit a first polarization component of the emitted light and a second polarization selective mirror configured to transmit a second polarization component of the emitted light
Data Source
AI summary
An optical system and, specifically an HMD, is disclosed for increasing brightness efficiency of light transmitted from a display. By including one polarization selective mirror between a half mirror and a display and another polarization selective mirror between the half mirror and a lens, brightness efficiency is increased without a substantial increase in thickness.