Hologram Calculation for Compact Head-Up Display Ghost Image Reduction
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Solution Overview
Problem
Conventional waveguide-based pupil expansion systems in head-up displays suffer from ghost images due to non-infinite virtual image distances, leading to reduced image quality and blurring effects.
Innovation Solution
A method for calculating a hologram using a point cloud hologram technique that determines sub-holograms for each virtual image point, considering the optical path within a waveguide to eliminate ghost images and enhance image quality, involving a system with a display device and a waveguide that replicates the hologram, expanding the exit pupil in two dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a waveguide-based pupil expansion system is used in a head-up display, then the exit pupil is expanded and the eye-box area is increased, but ghost images are generated due to non-infinite virtual image distances, causing blurring effects and reduced image quality
Solution Approach 1:
The patent divides the hologram calculation into separate sub-holograms for different virtual image points. Each sub-hologram is calculated independently for a specific virtual image point, allowing the system to manage the complexity of multiple optical paths through systematic segmentation. This enables the waveguide to expand the exit pupil while calculating and managing ghost images as separate computational elements rather than trying to eliminate them entirely.
Solution Approach 2:
The patent changes the calculation parameters by introducing virtual image points at different distances along the optical path. By calculating sub-holograms for multiple virtual image points rather than a single point, the system can account for the finite virtual image distance effect. This parameter change allows the system to maintain accurate hologram calculation while using waveguide-based pupil expansion, effectively managing the ghost image problem through computational rather than purely optical means.
2Ease of manufacture
If conventional hologram calculation methods are used without accounting for waveguide optical paths, then the calculation process is simpler, but image quality deteriorates due to uncorrected ghost images and blurring
Solution Approach 1:
The patent performs preliminary calculations by pre-calculating sub-holograms for multiple virtual image points before final hologram assembly. This preliminary action allows the system to prepare and manage the optical path information in advance, making the overall calculation process more manageable despite the increased complexity. The pre-calculated sub-holograms can then be systematically combined to produce the final hologram with improved image quality.
Solution Approach 2:
The patent implements feedback by calculating sub-holograms for different virtual image points and using this information to adjust and refine the final hologram calculation. The system considers the optical paths through the waveguide and uses this feedback information to correct for ghost images and blurring effects. This iterative feedback process improves image quality while maintaining a structured calculation approach that remains manageable.
3Object-affected harmful factors
If the virtual image distance is made infinite to eliminate ghost images, then image quality improves, but the system cannot accommodate waveguide-based pupil expansion with finite optical paths
Solution Approach 1:
The patent adds the dimension of virtual image points at different distances along the optical path. Instead of working with a single virtual image plane at infinite distance, the system creates multiple virtual image points distributed along the optical axis. This dimensional change allows the system to accommodate the finite optical paths of waveguide-based pupil expansion while still calculating holograms that minimize ghost images. The additional dimension provides the flexibility needed to reconcile waveguide compatibility with image quality.
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 method effectively reduces ghost images, improving the quality of the perceived virtual image by accounting for different optical paths and allowing for a larger eye-box area, enabling viewer movement while maintaining a clear image.
Implementation Method 1
a first waveguide pupil expander arranged to provide replication or expansion of the diffracted light field in a first direction by internal reflection between a first pair of opposing surfaces
Implementation Method 2
A computer-generated hologram may be encoded on a spatial light modulator arranged to modulate the amplitude and/or phase of incident light
Data Source
AI summary
An optical system and a method of calculating a hologram of a virtual image for the optical system is described. The optical system comprises a display device arranged to display the hologram and a waveguide arranged to replicate the hologram. The method comprises determining a sub-hologram of a virtual image point within an area defined by straight line paths from the virtual image point to the perimeter of an entrance pupil of a viewer. The area comprises at least part of a virtual replica of the display device formed by the waveguide.