Guided Light Source Using Segmented Mirrors for Single Photon Emission
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Solution Overview
Problem
Existing single photon sources face challenges in directional emission and precise control due to the divergence of photon beams and sensitivity to etching roughness, making them inefficient for applications like quantum cryptography.
Innovation Solution
A guided light source is proposed, comprising a quantum box associated with a discoid waveguide and an annular waveguide with a coupling grating, ensuring cylindrical propagation and normal incidence of the wavefront, along with an output waveguide and a mirror to enhance directional emission and reduce divergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a Fabry-Pérot cavity with Bragg mirrors is used to increase emission probability, then the emission directivity is improved, but the photon beam diverges and becomes sensitive to etching roughness
Solution Approach 1:
The cavity is segmented into multiple sections with varying mirror reflectivities along the propagation direction. The first mirror has high reflectivity to confine photons, while subsequent mirrors have decreasing reflectivity to gradually couple photons into the waveguide, reducing divergence and sensitivity to roughness.
Solution Approach 2:
Different sections of the cavity have locally optimized properties: the first mirror region has high reflectivity for strong confinement, while later mirror regions have progressively lower reflectivity for controlled coupling. This local variation in quality resolves the contradiction between strong resonance and divergence.
2Productivity
If precise alignment of quantum dot in pillar is required, then emission efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
A micropillar structure serves as an intermediary that guides and confines photons, making the system less sensitive to precise quantum dot positioning. The pillar's optical confinement compensates for alignment tolerances while maintaining high emission efficiency.
Solution Approach 2:
The device is segmented into the micropillar cavity region and the waveguide region, with each having optimized functions. This segmentation allows the quantum dot to be positioned within the pillar's confinement region without requiring sub-wavelength precision, easing manufacturing while maintaining efficiency.
3Productivity
If strong resonance is used to increase emission probability, then photon lifetime in cavity is extended, but diffraction by rough edges increases
Solution Approach 1:
The cavity resonance is segmented into multiple weaker resonances across different mirror sections rather than one strong resonance. This distributes the emission probability across multiple modes with shorter lifetimes, reducing the impact of roughness-induced diffraction while maintaining overall high emission efficiency.
Solution Approach 2:
The mirror reflectivity parameter is changed progressively along the cavity length, creating a gradient that reduces the quality factor Q of individual resonances. This parameter variation decreases photon lifetime in each section, reducing sensitivity to roughness while maintaining total emission probability through cumulative coupling.
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 guided light source achieves efficient and directional emission of single photons, improving the collimation and directivity of the photon beam, thereby enhancing its usability in quantum cryptography and other applications.
Implementation Method 1
ensure cylindrical propagation of a wavefront emitted by at least one quantum dot in the discoidal waveguide
Implementation Method 2
an annular waveguide surrounding the discoidal waveguide and having a coupling grating (T) formed on its inner periphery to receive said wavefront at normal incidence
Implementation Method 3
along with an output waveguide and a mirror to enhance directional emission
Data Source
Figure 1~2
Figure 3a~3g
Figure 4a~4h
AI summary
The invention relates to a guided light source (1) comprising: - at least one quantum dot (2) associated with a discoidal waveguide (3) so as to ensure cylindrical propagation of a wavefront emitted by the at least one quantum dot in the discoidal waveguide; - an annular waveguide (5) surrounding the discoidal waveguide and having a coupling grating (T) formed on its inner periphery to receive said wavefront at normal incidence; - an output waveguide (6) optically coupled to the annular waveguide, in which said wavefront is guided. The invention extends to the method of manufacturing such a source and to its use for the emission of a sequence of single photons.