Display Lightguide Coupling for Uniform Illumination in Thin Optics
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Solution Overview
Problem
Existing lightguide-based displays face challenges in achieving optimal image uniformity while minimizing system size and weight, as they require large projectors and coupling configurations that are at odds with practical objectives.
Innovation Solution
An optical system comprising an aperture-expanding lightguide optical element (LOE) with redirecting configurations and a coupling-in arrangement using a coupling lightguide element (CLE) with a beam splitter coating and input coupler, allowing for progressive light redirection and uniform illumination across the lightguide thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a large projector and coupling configuration is used to achieve optimal image uniformity by filling the lightguide thickness, then image uniformity is improved, but system size and weight increase
Solution Approach 1:
The coupling lightguide element (CLE) is nested within or coupled to the main lightguide optical element (LOE), creating a compact integrated structure. The CLE acts as a smaller auxiliary lightguide that couples light into the larger LOE, enabling efficient light injection without requiring a large external projector system.
Solution Approach 2:
The patent introduces a third dimension by using a separate coupling lightguide element (CLE) with thickness in the z-direction that is optically coupled to the main LOE. This vertical stacking approach allows light to be coupled into the LOE from the bottom surface, enabling compact integration without increasing the horizontal footprint.
2Illumination intensity
If a large projector and coupling configuration is used to achieve optimal image uniformity, then image uniformity is improved, but device complexity increases
Solution Approach 1:
The CLE and LOE are optically combined at their interface through direct bonding or optical adhesive, merging two lightguide functions into a single integrated optical path. This reduces the number of separate components and simplifies the overall coupling configuration while maintaining effective light injection.
Solution Approach 2:
The CLE serves multiple functions: it acts as both a light injection interface and an aperture expansion element. By making the CLE thickness可调 (adjustable) and optimizing its optical properties, it can control both the amount of light coupled in and the angular distribution, simplifying the need for separate control elements.
3Area of stationary object
If the coupling lightguide element has a small area relative to the lightguide optical element, then system size is reduced, but coupling efficiency decreases
Solution Approach 1:
The patent optimizes the reflectivity parameter of the beam splitter coating at the CLE-LOE interface, setting it to at least 50% to maximize light coupling efficiency. It also optimizes the thickness ratio (T2/T1 ≤ 0.5) and area ratio (A2/A1 ≤ 0.1) to achieve the best balance between compact size and coupling performance.
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 solution enables efficient aperture expansion and uniform illumination, reducing the size of the projector and ease of manufacture, while maintaining image quality and minimizing system size and weight.
Implementation Method 1
at least part of the interface provided with a beam splitter coating having a reflectivity of at least 50%
Implementation Method 2
the LOE supporting propagation of light by internal reflection at the major surfaces
Implementation Method 3
Progressive redirection of the light is typically performed either by a set of embedded partial reflectors or by diffractive optical elements
Data Source
AI summary
An optical system (100, 111, 125, 126, 127, 128) includes an aperture-expanding lightguide optical element (LOE) (106) with major surfaces (103a, 103b) separated by a first thickness T1. The LOE (106) includes redirecting configurations for progressively redirecting light within the LOE and coupling it out towards a viewer. A coupling-in arrangement includes a coupling lightguide element (CLE) (104) with mutually parallel surfaces separated by a second thickness T2 that is no more than half of the first thickness T1. CLE (104) is bonded to major surface (103a) at an interface (105) provided with a beam splitter coating having a reflectivity of at least 50%. The coupling-in arrangement also includes an input coupler deployed to couple light corresponding to a collimated image into the CLE.