Spatially-Varying Retarder for HMD Stray Light Control
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Solution Overview
Problem
Conventional near-eye display technologies in VR and AR systems suffer from undesirable visual effects such as flood illumination, ghosting, and glare due to the angularly broad light emissions from traditional displays, which are not properly imaged to the user's eyes when the light strikes the lenses at off-axis angles, resulting in stray light effects.
Innovation Solution
The implementation of a spatially-varying retarder (SVR) in the optical subsystem of head-mounted displays (HMDs), which modifies the phase of light by different amounts for different portions to provide appropriate retardation for varying angles of incidence, mitigating these visual effects by working in concert with other optical elements like polarizing beam splitters and quarter-wave plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional information displays with broad angular emission are used in HMD, then the display can be directly viewed with wide field of view, but off-axis light strikes lenses beyond imaging capability causing stray light effects and visual artifacts
Solution Approach 1:
The patent applies local quality by implementing a spatially-varying retarder (SVR) that provides different phase modifications for different portions of the display corresponding to different viewing angles. The SVR has a first region for modifying on-axis light and a second region for modifying off-axis light, allowing each region to be optimized for its specific angular range, thus resolving the contradiction between wide field of view and stray light reduction.
2Illumination intensity
If off-axis light is allowed to pass through the lens system, then the field of view is maintained, but the light exhibits elliptical polarization that cannot be properly imaged to the user's eyes
Solution Approach 1:
The patent employs parameter changes by modifying the phase of off-axis light using the spatially-varying retarder. The SVR changes the phase parameter of elliptically polarized off-axis light to convert it into linearly polarized light that can be properly imaged. This phase modification allows the system to maintain wide field of view while ensuring reliable imaging capability for all angular ranges.
3Object-affected harmful factors
If a spatially-varying retarder is implemented to correct polarization for different angles, then stray light effects are reduced, but the optical system complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the spatially-varying retarder into distinct regions: a first region for on-axis light modification and a second region for off-axis light modification. This segmented approach allows the SVR to be integrated into the existing optical system without requiring complete redesign, thus reducing the increase in system complexity while still achieving effective stray light reduction.
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
The SVR effectively reduces undesirable visual artifacts by ensuring that only properly polarized light reaches the user's eyes, enhancing the clarity and immersion of virtual or augmented reality experiences by minimizing stray light and improving the overall optical system performance.
Implementation Method 1
The SVR is configured to modify the phase of light passing through the SVR by amounts that are different for different portions of the SVR
Implementation Method 2
ensuring that only properly polarized light reaches the user's eyes
Implementation Method 3
working in concert with other optical elements like polarizing beam splitters and quarter-wave plates
Implementation Method 4
working in concert with other optical elements like polarizing beam splitters and quarter-wave plates
Data Source
AI summary
A head-mounted display, or other near-to-eye display, incorporates optics that include a spatially-varying retarder (SVR). The SVR may be manufactured with a correction factor applied thereto in order to compensate for one or more manufacturing errors that are exhibited in a molded lens and/or a polarizing beam splitter included in the optics of the system.