Bullseye dielectric cavities for photon collection from a surface-mounted quantum-light-emitter
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-03-31 |
| Journal | Scientific Reports |
| Authors | Reza Hekmati, John P. Hadden, Annie Mathew, Samuel G. Bishop, Stephen A. Lynch |
| Institutions | Cardiff University |
| Citations | 10 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Bullseye Dielectric Cavities for Quantum Emitters
Section titled âTechnical Documentation & Analysis: Bullseye Dielectric Cavities for Quantum EmittersâThis document analyzes the research paper âBullseye dielectric cavities for photon collection from a surface-mounted quantum-light-emitterâ to highlight key technical achievements and demonstrate how 6CCVDâs advanced MPCVD diamond materials and fabrication services can accelerate the commercialization and extension of this quantum technology.
Executive Summary
Section titled âExecutive SummaryâThis research successfully designs and simulates a high-performance dielectric bullseye cavity structure optimized for efficient photon collection from surface-mounted quantum emitters (QEs), such as nano-diamonds and 2D materials.
- High Performance: Achieved a peak Purcell Factor (F) of 22.5 and a Collection Efficiency (CE) of 80% into a high Numerical Aperture (NA=0.68) lens.
- Target Application: Structure is explicitly designed for integration with key quantum materials, including nano-diamonds and diamond defect centers (e.g., NV, SiV).
- Structure: Utilizes a circular Bragg grating etched into a Titanium Dioxide (TiOâ) layer, supported by a Silicon Dioxide (SiOâ) spacer and a 150 nm Gold (Au) reflective mirror.
- Resonance: Optimized performance occurs at a resonance wavelength of approximately 750 nm, suitable for many common QEs.
- Advanced Coupling: Demonstrated iterative apodization techniques to optimize coupling into low NA single-mode optical fibers, achieving a CE of 21.4% for a 5-ring structure.
- 6CCVD Relevance: The integration of diamond-based QEs requires ultra-high purity, low-roughness Single Crystal Diamond (SCD) substrates, which 6CCVD specializes in providing, along with custom metalization capabilities (e.g., Au mirror deposition).
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the optimized periodic bullseye cavity design:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Peak Purcell Factor (F) | 22.5 | Dimensionless | Periodic Bragg Grating Design |
| Peak Collection Efficiency (CE) | 80 | % | NA = 0.68, Periodic Design |
| Resonance Wavelength | 750 - 752.5 | nm | Optimized performance window |
| Grating Period (Î) | 420 | nm | Ideal periodic circular Bragg grating |
| TiOâ Layer Thickness (hTiOâ) | 200 | nm | Dielectric grating layer |
| SiOâ Layer Thickness (hSiOâ) | 435 | nm | Low refractive index spacer |
| Gold Mirror Thickness | 150 | nm | Reflective layer |
| Optimized Central Disk Diameter (RTiOâ) | 1.67 | ”m | For 750 nm resonance, Duty Cycle 0.66 |
| Effective Mode Volume (Veff) | 0.076 | ”m3 | Calculated for optimized cavity |
| Apodized CE (5 Rings) | 21.4 | % | Optimized for low NA fiber coupling (NA=0.13) |
| CE Bandwidth (60% efficiency) | 25.4 | nm | Bandwidth around resonance |
Key Methodologies
Section titled âKey MethodologiesâThe experimental design relied heavily on computational modeling and iterative optimization of the dielectric stack and grating geometry.
- Structure Definition: A multi-layer stack was defined, starting with a Silicon (Si) substrate, followed by a 150 nm Gold (Au) reflective layer, a 435 nm Silicon Dioxide (SiOâ) spacer, and a 200 nm Titanium Dioxide (TiOâ) layer.
- Grating Geometry: A circular Bragg grating, consisting of concentric rings of alternating TiOâ and air (WTiOâ and WAir), was etched into the TiOâ layer.
- Emitter Placement: The quantum light emitter was modeled as a dipole positioned either 1 nm above the TiOâ surface or embedded at the center (z = 100 nm) of the TiOâ disk.
- Simulation: Finite Difference Time Domain (FDTD) simulations (Lumerical) were used to calculate the Purcell factor (F) and collection efficiency (CE) as functions of wavelength, dipole orientation, and displacement.
- Bragg Condition: The periodic grating was designed to satisfy the second-order Bragg scattering condition (Π= mλ / 2nTE) for efficient vertical light extraction.
- Apodization: An iterative optimization procedure was employed to vary the period and duty cycle of successive rings (apodization) to maximize coupling efficiency into a specific low Numerical Aperture (NA=0.13) single-mode optical fiber.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful implementation of high-performance bullseye cavities for quantum emitters, particularly those based on diamond defect centers (NV, SiV), requires specialized material science and precision fabrication capabilities. 6CCVD is uniquely positioned to supply the foundational diamond materials and integrated services necessary to transition this research from simulation to robust, scalable devices.
| Research Requirement / Application | 6CCVD Solution & Value Proposition |
|---|---|
| Host Material for Quantum Emitters (Nano-diamonds, NV/SiV centers) | Optical Grade Single Crystal Diamond (SCD): 6CCVD provides ultra-high purity, low-strain SCD plates (up to 500 ”m thick). Our MPCVD growth process ensures the crystalline quality necessary for creating high-coherence NV or SiV defect centers, minimizing non-radiative decay paths. |
| Ultra-Smooth Surface Quality (Required for surface-mounted QEs) | Precision Polishing (Ra < 1 nm): The paper emphasizes surface-mounted emitters. Our SCD polishing capability achieves surface roughness (Ra) consistently below 1 nm. This ultra-smooth surface is critical for minimizing scattering losses and ensuring optimal dipole-cavity coupling, which is highly sensitive to emitter positioning. |
| Reflective Mirror Layer (150 nm Au) | Custom Metalization Services: 6CCVD offers precise, in-house deposition of various metals, including Au, Ti, Pt, Pd, W, and Cu. We can deposit the required 150 nm Au mirror layer directly onto the diamond substrate or intermediate layers, ensuring excellent adhesion and high reflectivity for the back-reflector. |
| Integration into Complex Stacks (Thin film deposition, etching) | Custom Thickness SCD Membranes: We supply thin SCD membranes (0.1 ”m - 500 ”m) and substrates (up to 10 mm) that can be integrated into complex dielectric stacks (like the simulated Au/SiOâ/TiOâ structure) or used as the primary material for the grating itself. |
| Scalability and Manufacturing (Moving beyond lab prototypes) | Large Area PCD/SCD Wafers: 6CCVD offers Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, and inch-size SCD wafers. This capability supports the scalable manufacturing and commercialization of high-efficiency quantum light sources. |
| Design Optimization & Fabrication Support | Expert Engineering Support: 6CCVDâs in-house PhD team specializes in material selection and optimization for quantum photonics and solid-state lighting projects. We can assist researchers in selecting the optimal diamond grade (e.g., low nitrogen, high-purity) and orientation for similar Bullseye Cavity Quantum Emitter projects. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Coupling light from a point source to a propagating mode is an important problem in nano-photonics and is essential for many applications in quantum optics. Circular âbullseyeâ cavities, consisting of concentric rings of alternating refractive index, are a promising technology that can achieve near-unity coupling into a first lens. Here we design a bullseye structure suitable for enhancing the emission from dye molecules, 2D materials and nano-diamonds positioned on the surface of these cavities. A periodic design of cavity, meeting the Bragg scattering condition, achieves a Purcell factor of 22.5 and collection efficiency of 80%. We also tackle the more challenging task of designing a cavity for coupling to a low numerical aperture fibre in the near field. Finally, using an iterative procedure, we study how the collection efficiency varies with apodised (non-periodic) rings.