Tapered Nanowire Single Photon Source
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Solution Overview
Problem
Current single photon sources, particularly electrically driven ones, face limitations in efficiency due to sensitive far-field emission patterns and optical losses, resulting in low efficiency values around 14% and being effective only over narrow bandwidths at cryogenic temperatures.
Innovation Solution
A single photon source is designed using a nanowire with a tapered end to enclose a photon emitter, allowing for controlled emission of a single photon with high efficiency, utilizing semiconductor materials like GaAs and InAs, and incorporating optical elements for improved light coupling and reduced reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-Q optical microcavity is used to enhance spontaneous emission into a resonant mode, then the coupling efficiency beta is improved, but the far-field emission pattern becomes very sensitive to fabrication imperfections and the overall source efficiency remains limited to around 40%
Solution Approach 1:
The patent extracts the quantum dot emitter from the conventional high-Q microcavity structure and places it directly in contact with the nanowire surface. This removes the problematic intermediate cavity structure that causes sensitivity to fabrication imperfections while maintaining efficient coupling through direct waveguide coupling between the quantum dot and nanowire mode.
Solution Approach 2:
The nanowire acts as an intermediary structure that couples the quantum dot emitter to the optical fiber. Instead of using a high-Q cavity as the intermediary, the nanowire's guided modes provide a robust coupling pathway that is less sensitive to fabrication variations while achieving high coupling efficiency.
2Ease of operation
If a conventional microcavity design is used, then directional emission can be achieved, but the source efficiency is limited to around 14% in electrically driven devices due to optical losses from cavity doping
Solution Approach 1:
The patent removes the doped cavity structure entirely and replaces it with a nanowire waveguide. This extraction eliminates the source of optical losses associated with cavity doping while maintaining the ability to achieve directional emission through the nanowire's guided mode propagation.
Solution Approach 2:
The patent uses a composite structure combining undoped semiconductor nanowire material with a quantum dot emitter. This composite approach avoids the need for doped cavity materials, eliminating the associated optical losses while maintaining efficient light guiding and directional emission capabilities.
3Measurement precision
If a high-Q cavity resonance is used to achieve monochromatic emission, then the emission is confined to a narrow bandwidth, but the device can only operate at cryogenic temperatures
Solution Approach 1:
The patent changes the operating temperature parameter from cryogenic to room temperature by replacing the high-Q cavity system with a nanowire waveguide system. The nanowire's guided mode coupling mechanism remains effective at room temperature, and the monochromatic emission is maintained through the quantum dot's inherent narrow linewidth at room temperature.
4Quantity of substance
If conventional optical coupling methods are used with quantum dots, then the collection efficiency eta is limited, but the overall source efficiency epsilon = beta*eta remains below unity
Solution Approach 1:
The patent transitions from three-dimensional bulk cavity modes to one-dimensional nanowire guided modes. This dimensional change enables efficient coupling between the quantum dot and the nanowire mode, and the nanowire can be directly coupled to optical fibers, significantly improving the overall photon collection efficiency and source 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 design achieves a significant increase in efficiency, potentially exceeding 90%, with robustness against fabrication imperfections and the ability to operate at room temperature, enabling reliable single photon generation for various applications.
Implementation Method 1
The nanowire is tapered so as to adiabatically expand an optical mode from the quantum dot
Implementation Method 2
The intrinsic layer is configured to emit a single photon upon radiative recombination of an electron-hole pair
Implementation Method 3
emit a single photon upon radiative recombination of an electron-hole pair
Implementation Method 4
The nanowire is tapered so as to adiabatically expand an optical mode from the quantum dot
Data Source
AI summary
The present invention relates to a single photon source 1800 comprising a tapered nanowire 1802, where the nanowire 1802 is made of a semiconductor material, a first electrode 1828 and second electrode 1814, where the electrodes are electrically coupled to a photon emitter 1804 embedded in the nanowire 1802 and wherein the photon emitter 1804 is capable of emitting a single photon when an activation voltage is applied between the electrodes. In advantageous embodiments of the invention, the nanowire is encircled by air or vacuum, such that advantage can be taken of the resultant large ratio between a refractive index of the nanowire and the encircling material, air. Another advantageous feature might be that the first and second electrodes are optically transparent, such that they can be used as part of a reflective element or anti-reflective element.