AR Light Projector Absorptive Exit Pupil Ghost Image Reduction
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Solution Overview
Problem
Existing light projectors for augmented or virtual reality applications often generate unwanted 'ghost images' that obscure and reduce the clarity of the main image intended for the user.
Innovation Solution
A light projector design featuring an emissive display with an absorptive structure positioned off-center, which couples the main image light into a specific region of the exit pupil and uses absorptive slats to absorb partial reflections, preventing them from entering the waveguide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light is coupled into the waveguide using a conventional exit pupil design, then the main image is displayed, but ghost images are generated that reduce image clarity
Solution Approach 1:
The exit pupil is divided into multiple regions: a first region for coupling the main image light into the waveguide, and a second region for absorbing ghost image light. This spatial segmentation allows differential treatment of different light paths, enabling the main image to be transmitted while ghost images are absorbed by the absorptive structure positioned at the second region.
Solution Approach 2:
Different regions of the exit pupil are assigned different optical properties. The first region is designed to transmit light for the main image, while the second region incorporates an absorptive structure with specific optical absorption properties. This local differentiation of optical characteristics enables selective transmission and absorption of light paths.
2Measurement precision
If an absorptive structure is added to eliminate ghost images, then image clarity improves, but device complexity increases
Solution Approach 1:
The absorptive structure is integrated directly into the exit pupil assembly, merging the ghost image absorption function with the existing light coupling structure. This integration approach avoids adding separate, independent components and reduces overall device complexity compared to implementing ghost image elimination as a separate subsystem.
Solution Approach 2:
The exit pupil structure serves multiple functions: it couples light into the waveguide, defines the exit pupil position, and absorbs ghost image light through the integrated absorptive structure. By making the exit pupil assembly multi-functional, the design avoids adding dedicated components for each function, thereby reducing device complexity.
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 solution effectively separates and absorbs unwanted partial reflections, mitigating ghost image effects and improving the clarity and quality of the main image displayed to the user.
Implementation Method 1
an absorptive structure at the emissive display arranged to absorb visible light reflected towards the emissive display from the exit pupil
Implementation Method 2
Light then propagates within the waveguide by total internal reflection and an output diffraction grating couples light out of the waveguide
Implementation Method 3
an optical arrangement configured to couple the first supplied light from the emissive display towards the exit pupil
Data Source
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AI summary
A projector (10) for an augmented reality or mixed reality headset is disclosed, comprising: an emissive display (20) defining an optical axis (9), configured to provide first supplied light (40); an exit pupil (80) configured to couple the first supplied light into a waveguide for an augmented reality or mixed reality headset, the exit pupil comprising a first region (82); an optical arrangement (60) configured to couple the first supplied light from the emissive display towards the exit pupil; and an absorptive structure (70) at the emissive display arranged to absorb visible light reflected towards the emissive display from the exit pupil; wherein the emissive display is configured to provide the first supplied light to the optical arrangement off-centre with respect to the optical axis so that a first partial reflection (50) of the supplied light is coupled towards and absorbed by the absorptive structure.