Reflective Polarizer Optical System for HMD Brightness
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Solution Overview
Problem
Existing optical systems in head-mounted displays face challenges in achieving high brightness and efficiency due to the use of absorptive linear polarizers, which reduce image brightness by absorbing light that could be recycled.
Innovation Solution
A folded optical system is implemented using a single reflective polarizer and a partial reflector, which recycles unpolarized image light to increase brightness by reflecting and transmitting light in specific polarization states, eliminating the need for an absorptive linear polarizer and enhancing the optical path length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an absorptive linear polarizer is used in the optical system, then the polarization state of light can be controlled, but the image brightness is reduced due to light absorption
Solution Approach 1:
The patent replaces the conventional absorptive polarizer with a reflective polarizer that redirects unpolarized light back toward the display panel instead of absorbing it. This inversion of the light interaction mechanism (from absorption to reflection/recycling) resolves the contradiction by maintaining brightness while achieving polarization control.
Solution Approach 2:
The reflective polarizer recycles unpolarized light that would otherwise be lost, reflecting it back through the display panel where it can be converted to polarized light. This recovery mechanism eliminates the energy loss associated with absorptive polarizers while maintaining the necessary polarization function.
2Adaptability or versatility
If the optical path is extended to improve image quality, then the field of view is enhanced, but the device size increases
Solution Approach 1:
The patent uses a folded optical path design that extends the optical trajectory in three-dimensional space without proportionally increasing the device footprint. By folding the optical path rather than extending it linearly, the system achieves enhanced field of view while maintaining a compact form factor suitable for head-mounted displays.
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 significantly increases the brightness of the pixelated image by recycling light within the display system, providing a higher field of view and improved efficiency without the drawbacks of absorptive polarizers, while maintaining a compact optical path.
Implementation Method 1
The reflective polarizer substantially reflects light having a first polarization state and substantially transmitting light having an orthogonal second polarization state in the predetermined wavelength range
Implementation Method 2
The reflective polarizer is adapted to receive an image ray reflected by the partial reflector and reflect the received image ray toward the viewer
Implementation Method 3
a partial reflector disposed on and conforming to a major surface of the first optical lens; The partial reflector has an average optical reflectance of at least 30% in a predetermined wavelength range
Implementation Method 4
a first optical lens comprising a curved first major surface; a folded optical system disposed between the pixelated display system and the viewer and adapted to receive the emitted pixelated image and form the pixelated virtual image
Data Source
AI summary
An optical system for displaying an image to a viewer includes a pixelated display including a plurality of pixels emitting unpolarized image light; a partial reflector having an average optical reflectance of at least 30% in a predetermined wavelength range; a first retarder layer disposed between the pixelated display and the partial reflector; a second retarder layer disposed between the first retarder layer and the partial reflector; and a reflective polarizer disposed between the first and second retarder layers. The reflective polarizer is adapted to increase a brightness of a pixelated image emitted by the pixelated display and displayed to the viewer by recycling at least a portion of unpolarized image light emitted by the pixels; and receive an image ray reflected by the partial reflector and reflect the received image ray toward the viewer.