Adjoint-optimized nanoscale light extractor for nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-11-16 |
| Journal | Nanophotonics |
| Authors | Raymond Wambold, Zhaoning Yu, Yuzhe Xiao, Benjamin F. Bachman, Gabriel R. Jaffe |
| Institutions | University of WisconsinâMadison |
| Citations | 18 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Adjoint-Optimized Nanoscale Light Extractor for NV Centers
Section titled âTechnical Documentation & Analysis: Adjoint-Optimized Nanoscale Light Extractor for NV CentersâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a highly effective, fabrication-robust Nanoscale Light Extractor (NLE) designed to maximize photon collection from shallow Nitrogen-Vacancy (NV) centers in diamond.
- Core Achievement: Achieved a broadband optical power extraction enhancement factor greater than 35x compared to unpatterned bulk diamond.
- Collection Efficiency: The NLE successfully shapes the emitted light into a narrow ±30° cone in the far field, enabling efficient collection using low-Numerical Aperture (NA) optical systems.
- Material System: The design utilizes a patterned crystalline silicon (Si) layer placed directly on a flat diamond surface, crucially avoiding the complex and damaging etching of the diamond substrate itself.
- Quantum Preservation: By avoiding diamond etching near the NV center (positioned 10 nm below the surface), the technique minimizes surface damage and preserves the spin coherence and quantum properties of the emitter.
- Robustness: The adjoint optimization method yielded a structure highly tolerant to fabrication errors (e.g., ±20 nm edge deviation) and NV positioning uncertainty (up to 40 nm lateral offset).
- Broadband Performance: Optimization was performed across the entire NV emission spectrum (635-800 nm), making the device highly suitable for quantum sensing applications where total collected photon count is critical.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper detailing the performance and geometry of the optimized NLE.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optical Power Enhancement | >35 | Factor | For NV depth of 10 nm, compared to bulk diamond |
| Figure of Merit (FoM) | ~35 | N/A | Spectrum-averaged extraction efficiency |
| Purcell Enhancement | ~3 | Factor | Averaged across the emission spectrum |
| NV Center Depth (Optimized) | 10 | nm | Below the diamond/air interface |
| NLE Structure Material | Crystalline Silicon (Si) | N/A | Patterned layer on diamond substrate |
| NLE Structure Height | 300 | nm | Optimal thickness for 3D optimization |
| Minimum Feature Size (R) | 40 | nm | Controlled by conical blurring function |
| Emission Wavelength Range | 635-800 | nm | Covering the NV zero-phonon line (~637 nm) |
| Beaming Cone Angle | ±30 | ° | Angle containing the bulk of the beamed power |
| Fabrication Tolerance (Edge Deviation) | ±20 | nm | Maintains high FoM under erosion/dilation |
| Fabrication Tolerance (Lateral Offset) | ±30 (X), ±40 (Y) | nm | FoM remains >25 for these offsets |
Key Methodologies
Section titled âKey MethodologiesâThe NLE design relies on advanced computational techniques and specific material constraints to ensure manufacturability and high performance.
- Material System Definition: The structure consists of a patterned Si layer placed on a flat, unpatterned diamond substrate. This approach is compatible with Si membrane transfer techniques or direct CVD growth of Si on diamond.
- Simulation Environment: Finite-Difference Time-Domain (FDTD) simulations (Lumerical FDTD) were used to model the electromagnetic fields across the entire broadband spectrum (635-800 nm).
- Optimization Algorithm: Adjoint optimization was employed, maximizing the overlap between the forward simulation field (sourced by the NV dipole) and the adjoint simulation field (sourced by a Gaussian beam injected into a ±30° cone).
- Emitter Modeling: The negatively charged NV center (NV-) in [100] diamond was modeled as an incoherent sum of emitted intensities from two orthogonal linear dipoles positioned 10 nm below the surface.
- Manufacturability Constraints: The optimization enforced a constant refractive index profile in the vertical (Z) direction and utilized a conical blurring function (R = 40 nm) and a binary push function to ensure the final structure was composed purely of air and silicon with features large enough for electron-beam lithography.
- Robustness Integration: The inherent broadband nature of the FDTD optimization automatically built in robustness against fabrication defects and alignment errors, confirmed by simulating eroded and dilated structures (±20 nm edge deviation).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the foundational materials and custom engineering required to replicate, extend, and commercialize this high-performance light extraction technology for quantum applications.
Applicable Materials
Section titled âApplicable MaterialsâThe success of this NLE relies entirely on a high-quality, ultra-flat diamond substrate suitable for shallow NV implantation.
| Research Requirement | 6CCVD Solution & Material Grade | Customization & Value Proposition |
|---|---|---|
| High-Purity Substrate | Electronic Grade Single Crystal Diamond (SCD) | Low nitrogen content (< 1 ppb) is essential for maximizing NV spin coherence time (T2) and ensuring optimal quantum performance. |
| Ultra-Flat Surface | Optical Grade SCD Polishing | Required for reliable Si layer deposition/transfer and minimizing scattering losses. 6CCVD guarantees surface roughness Ra < 1 nm on SCD plates. |
| Bulk Diamond Platform | SCD Substrates (up to 10 mm thick) | We provide custom-thickness SCD substrates, allowing researchers to choose the optimal bulk material depth for implantation and thermal management. |
| Alternative Emitters | Boron-Doped Diamond (BDD) | While the paper focuses on NV-, 6CCVD offers BDD for electrochemical or sensing applications requiring conductive diamond platforms. |
Customization Potential for NLE Fabrication
Section titled âCustomization Potential for NLE FabricationâThe NLE design is a patterned Si structure, but related quantum photonic devices often require metal contacts or plasmonic elements. 6CCVD offers comprehensive services to support the full fabrication workflow.
- Custom Dimensions: We supply SCD plates and wafers up to 125 mm in diameter (PCD) and custom-cut SCD plates, ensuring the substrate dimensions perfectly match the researcherâs lithography tools and experimental setup.
- Advanced Metalization: If future research extends this concept to resonant metal-dielectric structures (as referenced in the paper, Ref. [52]), 6CCVD offers in-house metalization capabilities, including:
- Metals: Au, Pt, Pd, Ti, W, Cu.
- Service: Custom deposition of adhesion layers (e.g., Ti) and bulk metal layers (e.g., Au) directly onto the polished diamond surface.
- Precision Processing: We offer high-precision laser cutting and shaping services to define the final device geometry, ensuring compatibility with subsequent Si transfer or lithography steps.
Engineering Support
Section titled âEngineering SupportâThe optimization process described in this paper is highly complex, requiring expertise in material properties (refractive index, crystal orientation) and advanced simulation.
- NV Center Expertise: 6CCVDâs in-house PhD team specializes in MPCVD diamond growth and material science, offering consultation on material selection, crystal orientation ([100] vs. [111]), and surface preparation necessary for optimal shallow NV implantation and NLE integration.
- Application Extension: Our team can assist engineers and scientists in adapting the core material requirements for similar quantum sensing and communication projects, including those targeting other solid-state color centers (e.g., SiV, GeV) or alternative high-index materials (SiC, hBN).
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract We designed a nanoscale light extractor (NLE) for the efficient outcoupling and beaming of broadband light emitted by shallow, negatively charged nitrogen-vacancy (NV) centers in bulk diamond. The NLE consists of a patterned silicon layer on diamond and requires no etching of the diamond surface. Our design process is based on adjoint optimization using broadband time-domain simulations and yields structures that are inherently robust to positioning and fabrication errors. Our NLE functions like a transmission antenna for the NV center, enhancing the optical power extracted from an NV center positioned 10 nm below the diamond surface by a factor of more than 35, and beaming the light into a ±30° cone in the far field. This approach to light extraction can be readily adapted to other solid-state color centers.