Femtosecond laser writing of integrated photonic circuits in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | EPJ Web of Conferences |
| Authors | Giulio Coccia, Argyro N. Giakoumaki, Vibhav Bharadwaj, Ottavia Jedrkiewicz, Roberta Ramponi |
| Institutions | University of Insubria, Istituto di Fotonica e Nanotecnologie |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Integrated Diamond Photonic Circuits
Section titled âTechnical Documentation & Analysis: Integrated Diamond Photonic CircuitsâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a robust, scalable method for fabricating integrated quantum sensing devices using femtosecond laser writing in synthetic diamond. 6CCVDâs expertise in high-purity MPCVD diamond is essential for commercializing and advancing this technology.
- Core Achievement: Successful integration of optical waveguides (WGs) and high-density Nitrogen Vacancy (NV) color center ensembles in the bulk of synthetic diamond.
- Methodology: Femtosecond laser writing (300 fs, 515 nm, 100 nJ) was used to create Type II WGs and vacancy defects, followed by 1000 °C annealing to form NV- centers.
- Material Requirement: High-quality, low-strain synthetic diamond (HPHT grade used in the study) is required to maintain the coherence time (T2*) necessary for high-sensitivity sensing.
- Performance Metrics: The proof-of-concept device achieved estimated sensitivities of 1.5 nT Hz-1/2 for magnetic fields and 2.4 V cm-1 Hz-1/2 for electric fields, exceeding many state-of-the-art systems.
- Density Control: NV- ensemble densities up to 1.4 x 1015 cm-3 (8 ppb) were achieved, demonstrating control over the active sensing volume.
- Future Potential: The technique is versatile and non-invasive, paving the way for complex 3D quantum photonic circuits, including integrated Bragg reflectors and on-chip electrodes for bias control.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper detailing the fabrication parameters and performance estimates.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Laser Pulse Duration | 300 | fs | Yb Laser System |
| Laser Repetition Rate | 500 | kHz | Yb Laser System |
| Central Wavelength | 515 | nm | Laser Writing |
| Pulse Energy (WG/Static Exposure) | 100 | nJ | Laser Writing Intensity |
| Post-Fabrication Annealing | 1000 | °C | NV Center Formation Treatment |
| Waveguide Separation (Type II) | 13 | ”m | Distance between modification lines |
| Waveguide Mode Field Diameter | 10 | ”m | Estimated at 532 nm |
| Fabrication Depth | 18 | ”m | Below diamond surface |
| NV- Ensemble Density (Max) | 1.4 x 1015 | cm-3 (8 ppb) | Achieved in âstatic exposureâ WGs |
| Estimated Magnetic Sensitivity | 1.5 | nT Hz-1/2 | Proof-of-concept device performance |
| Estimated Electric Sensitivity | 2.4 | V cm-1 Hz-1/2 | Proof-of-concept device performance |
| NV- Zero Phonon Line (ZPL) | 637 | nm | Confirmed NV- presence |
Key Methodologies
Section titled âKey MethodologiesâThe integration of optical waveguides and NV ensembles relies on precise control over the laser parameters and post-growth thermal processing.
- Material Preparation: Use of synthetic diamond (HPHT sample mentioned) as the host material, selected for its transparency and inherent nitrogen impurities necessary for NV formation.
- Waveguide Writing: Focused femtosecond laser pulses (300 fs, 515 nm, 100 nJ) were used to create two parallel tracks in the bulk of the diamond, forming a Type II waveguide structure. This process locally decreases density and refractive index in the tracks, resulting in light guiding between them.
- Vacancy Creation: Single, low-intensity static laser exposures (100 nJ) were focused within the waveguide region to create ensembles of vacancy defects.
- Thermal Annealing: A post-fabrication high-temperature annealing treatment (1000 °C) was applied. This mobilizes the created vacancies, allowing them to recombine with nitrogen impurities present in the diamond lattice, thus forming the desired NV- color centers.
- Optical Readout: Photoluminescence (PL) spectroscopy and confocal mapping were used to confirm the presence of NV- centers (ZPL at 637 nm) and estimate the ensemble density by comparing saturation measurements to a known single NV- source.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD provides the foundational MPCVD diamond materials and advanced processing required to replicate, optimize, and scale the integrated quantum sensing devices demonstrated in this research.
Applicable Materials for Quantum Sensing
Section titled âApplicable Materials for Quantum Sensingâ| Material Grade | Description | Relevance to Research |
|---|---|---|
| Quantum Grade Single Crystal Diamond (SCD) | Ultra-low strain, high purity, controlled nitrogen doping. | Essential for maximizing the NV center coherence time (T2*) and achieving the record sensitivities demonstrated. |
| Custom Doped SCD | SCD grown with specific, tailored nitrogen concentrations (e.g., 1-10 ppm). | Allows researchers to deterministically control the resulting NV ensemble density (up to 1.4 x 1015 cm-3) after annealing. |
| Optical Grade SCD | High transparency across the visible and NIR spectrum (515 nm excitation, 637 nm ZPL emission). | Ensures minimal absorption and scattering losses for efficient light coupling and readout through the laser-written WGs. |
Customization Potential & Engineering Support
Section titled âCustomization Potential & Engineering SupportâThe successful transition of this technology from proof-of-concept to a robust commercial device requires highly customized diamond substrates and advanced integration features, all available through 6CCVDâs in-house capabilities.
- Precision Polishing: The research relies on efficient light coupling and low scattering. 6CCVD guarantees Ra < 1 nm polishing for SCD substrates, ensuring optimal surface quality for end-fire coupling and minimizing losses in the integrated photonic circuits.
- Custom Dimensions: We provide SCD plates in custom thicknesses (0.1 ”m to 500 ”m) and large-area Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, supporting scaling and high-throughput fabrication of integrated devices.
- Advanced Metalization: The paper notes that applying a constant bias electric field (Stark effect) is crucial for improving sensitivity to weak electric fields. 6CCVD offers in-house metalization services, including Ti/Pt/Au, W, and Cu stacks, for fabricating on-chip electrodes directly onto the diamond surface.
- Complex Structuring: Future optimization involves integrating Bragg reflectors [13] within the waveguides. Our precision laser cutting and structuring services enable the creation of the complex 3D features required for these integrated optical components.
- Engineering Support: 6CCVDâs in-house PhD team specializes in diamond growth and defect engineering. We offer consultation services to assist researchers in selecting the optimal material specifications (e.g., nitrogen concentration, substrate orientation, and thickness) for similar quantum sensing and integrated photonics projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Integrated photonic circuits pave the way for next generation technologies for quantum information and sensing applications. Femtosecond laser writing has emerged as a valuable technique for fabricating such devices when combined with diamondâs properties and its nitrogen vacancy color center. Such color centers are fundamental for sensing applications, being possible to excite them and read them out optically through the fabrication of optical waveguides in the bulk of diamond. We show how to integrate these building blocks in diamond, to develop proof-of-concept devices with unprecedented electric and magnetic field sensitivities.