Pancake Lens Ghosting Mitigation via Air Gap Defocusing
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Solution Overview
Problem
Near-eye displays face challenges with compact optics, such as distortions, non-uniformity, ghost image formation, and residual coloring, which hinder their use in wearable display systems due to the bulkiness and weight of optics components.
Innovation Solution
The implementation of a pancake lens with a quarter-wave waveplate spaced apart from the electronic display and pancake lens, along with a circular polarizer having an air gap and anti-reflective coatings, to mitigate ghost images by defocusing and attenuating secondary beam paths, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If compact optics (pancake lens) are used to reduce size and weight, then the size and weight of the optics block are reduced, but ghost image formation and image quality degradation occur
Solution Approach 1:
A circular polarizer is introduced as an intermediary component between the electronic display and the pancake lens. This polarizer includes a quarter-wave waveplate spaced apart from the display by a first air gap and spaced from the lens by a second air gap. The circular polarizer converts linearly polarized light from the display into circularly polarized light, which then reflects off the partial reflector in the pancake lens and returns through the waveplate, effectively managing the light path to reduce ghost images while maintaining compact form factor.
Solution Approach 2:
The patent introduces spatial separation in the optical path by creating air gaps between components (display to waveplate, waveplate to lens). This dimensional separation allows the light to travel different path lengths, causing ghost images to be defocused and spatially separated from the main image plane, thereby reducing their visual impact on image quality.
2Volume of moving object
If compact optics are used to reduce size, then the volume of the optics block is reduced, but distortions and non-uniformity increase
Solution Approach 1:
The patent modifies the optical parameters of the system by introducing a circular polarizer with specific spacing (air gaps) between components. The quarter-wave waveplate is positioned at specific distances from both the display and the lens, creating controlled optical path differences. This parameter optimization allows the compact pancake lens design to achieve acceptable image uniformity by defocusing ghost images and managing polarization effects throughout the optical path.
3Length of moving object
If the circular polarizer is placed close to the display to reduce size, then the overall size is reduced, but ghost images become more prominent
Solution Approach 1:
The patent utilizes the spatial dimension by introducing air gaps between the display and the quarter-wave waveplate, and between the waveplate and the pancake lens. This spatial separation creates different optical path lengths for the main image and ghost image trajectories. The ghost images, which undergo additional reflections, travel longer effective paths and become defocused, appearing dimmer and less prominent despite the compact overall size of the optical assembly.
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 effectively reduces the impact of ghost images on the main image, enhancing image contrast, color fidelity, and sharpness, making the display more comfortable and effective for users by minimizing distracting artifacts.
Implementation Method 1
a circular polarizer comprising a quarter-wave waveplate spaced apart from the electronic display to circularly polarize the image light
Implementation Method 2
with an anti-reflective coating on a surface of the quarter-wave waveplate facing the pancake lens
Implementation Method 3
The quarter-wave waveplate is spaced apart from both the electronic display and the pancake lens, with an anti-reflective coating on a surface of the quarter-wave waveplate facing the pancake lens
Data Source
AI summary
A near-eye display assembly includes an electronic display for providing image light, a circular polarizer disposed downstream of the electronic display for circularly polarizing the image light, and a pancake lens disposed downstream of the circular polarizer for conveying the image light to an eyebox of the near-eye display. The circular polarizer includes a quarter-wave waveplate disposed between the electronic display and the pancake lens, and spaced apart from the electronic display and the pancake lens, to additionally defocus ghost image artifacts at the eyebox.