Single-Photon Generating Device Back-Side Extraction
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Solution Overview
Problem
Current single-photon generating devices face challenges in achieving high extraction efficiency and coupling efficiency to optical fibers due to light expansion and quality degradation issues, particularly when using quantum dots in semiconductor substrates for quantum cryptography communication.
Innovation Solution
A single-photon generating device with a solid substrate having a base portion and a pillar portion, where the pillar portion has a larger cross-section at the base than at the tip, allowing light to be reflected and output from the back face of the base, enhancing extraction and coupling efficiency without degrading the quantum dot quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If light is extracted from the surface side of a quantum dot in a semiconductor substrate, then the device structure is simple, but the extraction efficiency is low due to light reflection at the substrate surface
Solution Approach 1:
The patent inverts the light extraction direction from the conventional surface side to the back side of the substrate. By forming a light extraction structure on the back surface, the device extracts light that has propagated through the substrate, avoiding the reflection problem at the front surface and achieving high extraction efficiency while maintaining structural simplicity
Solution Approach 2:
The patent transitions from two-dimensional surface extraction to three-dimensional volume utilization by extracting light from the back side of the substrate. This dimensional change allows light to be collected from a larger effective area and at different angles, significantly improving extraction efficiency
2Loss of energy
If a DBR micropost cavity structure is used to improve extraction efficiency, then light extraction is improved, but the manufacturing complexity increases due to precise etching requirements
Solution Approach 1:
The patent extracts only the essential light extraction function from the complex DBR micropost cavity structure. By forming simple protrusions or patterns on the back surface without requiring DBR mirrors or precise micropost fabrication, the device achieves adequate light extraction efficiency while dramatically simplifying the manufacturing process
Solution Approach 2:
The patent applies partial action by implementing light extraction structures only on the back surface rather than the entire device. This selective approach achieves sufficient light extraction improvement without the need for complex structures throughout the device, balancing performance and manufacturing simplicity
3Ease of manufacture
If the cross-section of the pillar portion is uniform, then the manufacturing process is simpler, but the light extraction efficiency is reduced due to insufficient internal reflection
Solution Approach 1:
The patent introduces asymmetry in the pillar cross-section, making it larger at the base and smaller at the top. This asymmetric geometry creates optimal conditions for internal light reflection and extraction, where the wider base provides a larger interaction area for light-matter interaction and the tapered shape enhances light confinement and extraction efficiency
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 configuration increases the extraction and coupling efficiency of single photons, improving communication speed and reliability in quantum cryptography, especially for telecommunication band applications, while maintaining the quality of the quantum dots.
Implementation Method 1
the light generated from the localized level is reflected on the surface, propagated internally, and output from the back face side of the base portion
Data Source
AI summary
A single-photon generating device is configured to have a solid substrate including abase portion, and a pillar portion which is formed on the surface side of the base portion with a localized level existent in the vicinity of the tip of the base portion. The above pillar portion is formed to have a larger cross section on the base portion side than the cross section on the tip side, so that the light generated from the localized level is reflected on the surface, propagated inside the pillar portion, and output from the back face side of the base portion.