Optical Wedge Waveguide for Uniform Pupil Expansion
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Solution Overview
Problem
Waveguide pupil expanders suffer from inconsistent light intensity among replicas due to continuous division of light with each bounce, leading to uneven illumination.
Innovation Solution
The optical wedge's curved surface design compensates for the decreasing intensity of light replicas by varying the angle and refractive index along the waveguide, ensuring consistent light transmission and expansion of the exit pupil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If light is continuously divided with each bounce in the waveguide, then the exit pupil is expanded, but the light intensity becomes inconsistent among replicas
Solution Approach 1:
The waveguide is designed with non-uniform properties along its length, specifically varying refractive index or reflective properties at different positions. This local variation compensates for the continuous light division, ensuring that replicas at different positions maintain consistent intensity while still achieving pupil expansion.
Solution Approach 2:
The refractive index or reflective characteristics of the waveguide are changed along its length to counteract the intensity loss from continuous light division. By dynamically adjusting these optical parameters, the system maintains uniform light intensity across multiple replicas while preserving the expanded exit pupil area.
2Illumination intensity
If a curved surface design is used in the optical wedge, then light intensity consistency is improved, but the device complexity increases
Solution Approach 1:
Instead of using a flat surface in the optical wedge, a curved surface is employed to vary the angle and refractive index along the waveguide. This curvature enables continuous compensation of light intensity while maintaining a compact structure, balancing the improvement in uniformity against the increase in geometric complexity.
3Area of stationary object
If the optical wedge is designed to expand the exit pupil, then the viewing window is increased, but unwanted reflections are generated
Solution Approach 1:
The optical wedge is designed to convert unwanted reflections into beneficial effects. By carefully controlling the wedge angle and refractive index, reflections that would normally be harmful are redirected to serve the pupil expansion function or are minimized, turning a potential harm into a useful contribution to the display 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 achieves uniform light intensity across multiple replicas, enhancing the quality of holographic projections and reducing unwanted reflections, while also serving as a glare trap for head-up displays.
Implementation Method 1
The first surface is not parallel to the second surface at the input (port). The optical wedge has one relatively thick end and one relatively thin end. A first surface of the optical wedge abuts the second surface of the optical slab—and is substantially parallel to the second surface of the optical slab—to form an interface that allows partial transmission of light guided by the optical slab into the optical wedge
Implementation Method 2
A first surface of the optical wedge abuts the second surface of the optical slab—and is substantially parallel to the second surface of the optical slab—to form an interface that allows partial transmission of light guided by the optical slab into the optical wedge at a plurality of points along the interface such that the light is divided a plurality of times
Data Source
AI summary
There is disclosed herein a waveguide including an optical slab and an optical wedge. The optical slab has a first refractive index, n1>1. The optical slab includes: a pair of opposing surfaces and an input port. The pair of opposing surfaces are arranged in a parallel configuration. The input port is arranged to receive light into the optical slab at an angle such that the light is guided between the first and second opposing surfaces. The optical wedge has a second refractive index, n2, wherein 1<n2<n1. The optical wedge includes a pair of opposing surfaces arranged in a wedge configuration. A first surface of the optical wedge abuts the second surface of the optical slab to form an interface. The angle of the wedge allows light received at the interface to escape through the second surface of the optical wedge such that the exit pupil of the waveguide is expanded.