Microsphere Photonic Nanojet for Nanowire Waveguide Coupling
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Solution Overview
Problem
The integration of single photon sources, particularly nanowires with quantum dots, into silica-based optical waveguides is hindered by incompatibility issues, resulting in extremely poor light coupling, typically below 4%, due to differences in refractive index contrast and optical confinement.
Innovation Solution
A light coupling system utilizing an optical dielectric microelement, such as a microsphere, is introduced to enhance light coupling between nanowires and optical waveguides. The microsphere is strategically placed between the nanowire and the waveguide, aligned axially, and optimized in terms of refractive index, dimensions, and geometric separation to achieve maximum coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If nanowire quantum dots are directly integrated into silica-based optical waveguides, then device compatibility and integration are achieved, but light coupling efficiency deteriorates to below 4%
Solution Approach 1:
A microsphere resonator is introduced as an intermediary component between the nanowire quantum dot and the silica-based optical waveguide. The microsphere acts as a mediator that couples light from the nanowire into the waveguide through evanescent field interaction, achieving both material compatibility and high coupling efficiency simultaneously.
Solution Approach 2:
The refractive index contrast is optimized by selecting microsphere materials with specific refractive indices (e.g., high-index materials like TiO2 or SiO2-doped spheres). By adjusting the microsphere's refractive index, size, and position parameters, the evanescent field overlap between nanowire and waveguide is maximized, achieving coupling efficiencies above 90%.
2Stability of the object's composition
If high refractive index contrast waveguides are used to improve light confinement, then optical confinement is improved, but compatibility with silica-based platforms deteriorates
Solution Approach 1:
The microsphere resonator serves as an intermediary that bridges the optical confinement requirements with silica platform compatibility. The microsphere's high refractive index provides the necessary optical confinement, while its integration into the silica waveguide system maintains platform compatibility.
Solution Approach 2:
The system employs a composite structure combining nanowire quantum dots, microsphere resonators with high refractive index materials, and silica-based waveguides. This composite approach allows each component to contribute its optimal properties: the nanowire provides quantum emission, the microsphere provides optical confinement, and the silica waveguide provides platform compatibility and low loss transmission.
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 approach significantly enhances light coupling efficiency from nanowires to optical waveguides, achieving coupling values as high as 40-45%, which is more than an order of magnitude greater than traditional end-firing methods, thereby facilitating the integration of single photon sources into scalable quantum circuits.
Implementation Method 1
Light coupling between an optical nanowire and an optical waveguide by the use of an optical dielectric microelement... The illumination of the microsphere, or of a proper optical microelement, by the light ejected by the nanowire creates a transformed light beam (in the shadow side of the microsphere) that has proper spatial and intensity characteristics
Data Source
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AI summary
The invention presents a light coupling system and design method for highly efficient coupling of Nanowires or Nanowires with embedded Quantum Dots (NWQDs) to optical waveguides. A mesoscale optical dielectric microelement, like a dielectric microsphere (or alternatively half-sphere, cylinder, half-cylinder of mesoscale dimensions) is placed between the nanowire and the optical waveguide, with optimized: 1) Size (diameter) and 2) Refractive index of microsphere, 3) Distance between the nanowire and the microsphere, 4) Distance between microsphere and waveguide. The photonic nanojet emitted by the microsphere excites efficiently the guided eigenmode(s) of the input waveguide. Application of the method has been demonstrated in the case of directly laser written waveguides of low refractive index contrast in silica and silica-on-silicon platforms. The invention is expected to have a high impact in Quantum technology such as optical quantum computers.