Aperture Multiplier with Depolarizer for Compact Near-Eye Displays
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Solution Overview
Problem
Existing optical aperture multipliers for near-eye and head-up displays face challenges in achieving a compact design due to the requirements for a large aperture, which adds bulk and weight, especially in the first stage of aperture multiplication.
Innovation Solution
The optical arrangement includes an image projector with a polarizing element, an optical aperture expansion arrangement with a waveguide having parallel external faces for internal reflection, and a depolarizer deployed in the path of the image illumination to ensure uniform polarization management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large aperture is used to cover the observer's eye location area, then the display coverage and field of view are improved, but the device bulk and weight increase
Solution Approach 1:
The aperture multiplication is divided into two stages: first stage using a rectangular waveguide with width much smaller than the image wavefront to provide initial aperture expansion, and second stage using a slab waveguide to achieve final aperture multiplication. This segmentation allows each stage to be optimized independently, reducing overall device bulk and weight while achieving the required large aperture coverage
Solution Approach 2:
The patent transitions from traditional single-dimension slab waveguide approach to a two-dimensional rectangular waveguide approach for the first stage of aperture multiplication. This dimensional change allows the waveguide width to be much smaller than the image wavefront width, achieving compact design while maintaining effective aperture expansion through internal reflection in multiple dimensions
2Area of stationary object
If a large aperture is used to cover the observer's eye location area, then the display coverage and field of view are improved, but the device bulk and weight increase
Solution Approach 1:
The aperture multiplication process is segmented into two distinct stages performed by separate waveguide components. The first stage rectangular waveguide provides initial aperture expansion with compact dimensions, while the second stage slab waveguide completes the aperture multiplication. This segmentation enables the device to achieve large aperture coverage without requiring a single large bulky component, thus reducing overall device length
Solution Approach 2:
The patent employs a rectangular waveguide geometry for the first stage where the waveguide width is much smaller than the image wavefront width, representing a dimensional optimization. This allows the system to achieve aperture multiplication in a compact form factor by utilizing internal reflection across multiple dimensions rather than requiring a large single-dimension slab
3Manufacturing precision
If polarization management is implemented using polarizing elements, then image quality and uniformity are improved, but the device complexity increases
Solution Approach 1:
The patent extracts and addresses the polarization issue at a specific location in the optical path by deploying a depolarizer after the polarizing element in the image projector. This targeted approach removes polarization effects only where necessary (after image generation but before waveguide entry) without requiring complex polarization management throughout the entire optical system, thus improving image quality while limiting the increase in 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 expands the optical aperture while maintaining image quality and reducing the bulk and weight of the device, making it suitable for compact near-eye and head-up display applications.
Implementation Method 1
the image illumination propagating within the at least one waveguide by internal reflection at the at least one pair of external faces
Implementation Method 2
the image projector comprising at least one polarizing element such that the image illumination is polarized
Implementation Method 3
a depolarizer deployed in a path of the image illumination after the at least one polarizing element of the image projector and before the at least one waveguide
Data Source
AI summary
An optical aperture multiplier includes a first optical waveguide (10) having a rectangular cross-section and including partially reflecting surfaces (40) at an oblique angle to a direction of elongation of the waveguide. A second optical waveguide (20), also including partially reflecting surfaces (45) at an oblique angle, is optically coupled with the first optical waveguide (10). An image coupled into the first optical waveguide with an initial direction of propagation at an oblique coupling angle advances by four-fold internal reflection along the first optical waveguide, with a proportion of intensity of the image reflected at the partially reflecting surfaces so as to be coupled into the second optical waveguide, and then propagates through two-fold reflection within the second optical waveguide, with a proportion of intensity of the image reflected at the partially reflecting surfaces so as to be directed outwards from one of the parallel faces as a visible image.