Microdisplay Pixel Catadioptric Light Extraction for Narrow Exit Angles
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Solution Overview
Problem
Conventional microdisplay technologies face challenges in achieving high forward-directed light emission and efficient light extraction due to broad emission angles and high power consumption, particularly in augmented/virtual-reality applications, and existing solutions like sapphire lenses suffer from reduced light extraction efficiency and potential separation issues.
Innovation Solution
A microdisplay pixel structure featuring a light extractor with a hemispherical protrusion and a concave reflector with a center aperture, made of GaN material, which serves as a base for growing a light-emitting body, enhancing light emission in a specific wavelength and direction through total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a planar light-emitting surface is used in a vertical stacking structure, then the manufacturing process is simplified by removing the pixel-transfer process, but the light emission angle becomes broad which is unsuitable for waveguide coupling
Solution Approach 1:
The patent introduces a hemispherical protrusion structure on the light-emitting surface that modifies the emission pattern. The curved surface of the hemisphere focuses light into a narrower angular range while maintaining the planar substrate structure for simple manufacturing. This resolves the contradiction by achieving narrow emission angles through geometric curvature without complicating the base manufacturing process.
Solution Approach 2:
The invention applies a localized hemispherical structure only at specific regions of the light-emitting surface rather than changing the entire planar structure. This allows the majority of the device to maintain simple planar geometry for easy manufacturing, while the local hemispherical region provides the necessary light focusing capability for waveguide coupling.
2Loss of energy
If a sapphire lens is bonded to the back surface of the substrate to improve light extraction, then light extraction efficiency is enhanced, but adhesive interfaces reduce efficiency and the lens may separate due to heat and environmental factors
Solution Approach 1:
The patent integrates the light extraction function directly into the light-emitting body structure by forming a hemispherical protrusion from the same GaN material. This eliminates the need for separate sapphire lenses and adhesive bonding interfaces, combining the light-emitting and light-extraction functions into a single monolithic structure that is thermally and mechanically stable.
Solution Approach 2:
The hemispherical protrusion acts as an intermediary structure that provides the refractive index transition needed for improved light extraction without requiring external lenses or adhesives. The GaN material itself serves as the optical element, eliminating the adhesive interface that causes efficiency loss and reliability issues.
3Loss of energy
If a sapphire lens with refractive index 1.77 is used, then light extraction is improved, but insufficient light is emitted in the perpendicular direction due to the refractive index mismatch
Solution Approach 1:
The patent changes the geometric parameters of the light-emitting structure by introducing a hemispherical protrusion with a specific radius of curvature. This geometric modification optimizes the light emission pattern to achieve both high extraction efficiency and strong perpendicular emission, overcoming the limitations of flat surfaces and standard lens configurations.
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 proposed structure significantly increases the intensity of forward-directed light emission, improving light extraction efficiency and reducing power consumption by focusing light within a narrow angular range, suitable for applications like augmented/virtual-reality glasses.
Implementation Method 1
a reflector with a center aperture formed on a surface of the protrusion... based on internal total reflection on an upper portion of a light emitting body
Data Source
AI summary
Disclosed is a unit pixel of a microdisplay having a concave reflector with a center aperture. The light extractor has a protrusion and a bulk portion formed using the same epitaxial growth process. The concave reflector with a center aperture is formed on the protrusion, and epitaxial growth of the light-emitting body is made through the aperture concave reflector. In addition, the light rays reflected by the concave reflector with a center aperture has exit angles that are nearly perpendicular to the exit surface and are thus easily emitted to the outside.