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 | Politecnico di Milano, Istituto di Fotonica e Nanotecnologie |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the fabrication and integration of integrated photonic circuits and Nitrogen Vacancy (NV-) color centers within the bulk of synthetic diamond using femtosecond laser writing (FLW).
- Core Value Proposition: FLW enables the systematic, non-invasive, and 3D fabrication of optical waveguides (WGs) and quantum emitters (NV- centers) in diamond, creating a robust platform for room-temperature quantum sensing.
- Fabrication Method: Type II WGs and high-density NV- ensembles are created using a 515 nm, 300 fs Yb laser, followed by a 1000 °C annealing step to mobilize vacancies and form the color centers.
- Integration Achievement: NV- ensembles were successfully integrated between the laser-written WG tracks with a spatial accuracy of approximately 500 nm.
- Density Achieved: The process yielded high NV- densities, reaching up to 1.4 x 1015 cm-3 (8 ppb) in the âstatic exposureâ regions.
- Sensing Performance (Estimated): The proof-of-concept device demonstrates competitive estimated sensitivities: 1.5 nT Hz-1/2 for magnetic fields and 2.4 V cm-1 Hz-1/2 for electric fields.
- Future Optimization: Future work includes integrating Bragg reflectors to increase the effective light-NV- interaction length and exploiting strain-induced electric bias fields to enhance sensitivity to weak external fields.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Laser Type | Yb Femtosecond | N/A | Fabrication source |
| Pulse Duration | 300 | fs | Laser writing parameters |
| Repetition Rate | 500 | kHz | Laser writing parameters |
| Central Wavelength | 515 | nm | Laser writing parameters |
| Pulse Energy | 100 | nJ | Used for writing WGs and static exposures |
| Post-Fabrication Annealing | 1000 | °C | Required for vacancy migration and NV- formation |
| Waveguide Type | Type II | N/A | Guiding achieved between two written tracks |
| Waveguide Sidewall Separation | 13 | ”m | âEmptyâ waveguide design |
| Waveguide Mode Field Diameter | 10 | ”m | Estimated at 532 nm |
| NV- Density (Static Exposure) | 1.4 x 1015 | cm-3 | Highest density achieved (8 ppb) |
| Estimated Magnetic Sensitivity (ηm) | 1.5 | nT Hz-1/2 | Proof-of-concept device estimate |
| Estimated Electric Sensitivity (ηe) | 2.4 | V cm-1 Hz-1/2 | Proof-of-concept device estimate |
| NV- Spin Transition Shift (Magnetic) | 28 | GHz T-1 | Fundamental NV- property (km) |
| NV- Spin Transition Shift (Electric) | 17 | Hz cm V-1 | Fundamental NV- property (ke) |
| Spatial Accuracy (NV placement) | ~500 | nm | Accuracy of NV creation relative to WG tracks |
Key Methodologies
Section titled âKey MethodologiesâThe integration of photonic circuits and NV- centers relies on a multi-step femtosecond laser writing and thermal processing recipe:
- Material Selection: High-Pressure/High-Temperature (HPHT) synthetic diamond is used as the substrate, providing the necessary nitrogen impurities for NV- formation.
- Femtosecond Laser Writing (FLW): A focused Yb femtosecond laser (300 fs, 515 nm, 100 nJ) is used to induce localized structural changes in the bulk diamond, creating vacancies (lattice disorder).
- Waveguide (WG) Fabrication: Type II WGs are formed by writing two parallel tracks (13 ”m separation). The lattice disorder in the tracks decreases the refractive index, confining light in the unmodified region between them.
- NV- Ensemble Creation: High-density NV- ensembles are created by applying single âstatic exposuresâ (100 nJ pulses) between the WG tracks, generating a high concentration of vacancies in the desired sensing volume.
- Thermal Annealing: The diamond sample undergoes a post-fabrication high-temperature annealing treatment (1000 °C). This step is critical as it mobilizes the laser-created vacancies, allowing them to migrate and combine with existing nitrogen impurities to form the stable NV- color centers.
- Optical Readout and Characterization: Photoluminescence (PL) spectroscopy is used to confirm the presence of NV- centers (Zero Phonon Line at 637 nm). Power-dependent PL saturation measurements are used to quantify the resulting NV- ensemble density.
- Sensing Device Operation: Excitation and detection are performed by coupling a green laser into the written WG, allowing the light to interact with the integrated NV- ensemble for Optically Detected Magnetic Resonance (ODMR) measurements.
Commercial Applications
Section titled âCommercial ApplicationsâThe integration of robust quantum emitters and photonic circuits in diamond enables next-generation technologies across several high-value sectors:
- Quantum Sensing and Metrology:
- High-Resolution Magnetometry: Used for detecting extremely weak magnetic fields in medical diagnostics (e.g., non-invasive brain imaging), materials science, and geological surveys.
- Electric Field Sensing: Detection of weak electric fields for characterizing microelectronic devices, particularly in harsh environments, or for biological measurements.
- Room-Temperature Operation: NV- centers allow quantum sensing without the need for cryogenic cooling, simplifying device deployment.
- Quantum Information Processing:
- Integrated Quantum Circuits: Diamond serves as a stable host for quantum memory and logic gates, paving the way for scalable quantum computers and repeaters.
- Quantum Communication: Fabrication of 3D photonic structures (like integrated Bragg reflectors) to enhance light-matter interaction for efficient quantum state transfer.
- Harsh Environment Photonics:
- High-Power Optics: Utilizing diamondâs superior thermal and mechanical properties for integrated optical components (WGs) that must withstand extreme temperatures or chemical exposure.
- Fundamental Physics Research:
- Strain Engineering: Exploiting the strain created by the WG writing process to introduce a constant electric bias field, which can decouple the NV- centers from stray magnetic noise, improving measurement fidelity.
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.