Tapered ultra-high numerical aperture optical fiber tip for nitrogen vacancy ensembles based endoscope in a fluidic environment
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-03-16 |
| Journal | Applied Physics Letters |
| Authors | Dewen Duan, Vinaya Kumar Kavatamane, Sri Ranjini Arumugam, Yan-Kai Tzeng, Huan-Cheng Chang |
| Institutions | Max Planck Institute for Biophysical Chemistry, Stanford University |
| Citations | 13 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation: NV Endoscope Diamond Integration
Section titled âTechnical Analysis and Documentation: NV Endoscope Diamond IntegrationâCompany: 6CCVD (6ccvd.com) - Expert in MPCVD Diamond Solutions
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a robust method for fabricating high-performance Nitrogen-Vacancy (NV) center diamond endoscopes optimized for fluidic environments, overcoming the severe Fluorescence (FL) collection efficiency losses typical of high-Refractive Index (RI) liquids.
- Core Challenge Addressed: Traditional Multi-Mode Fiber (MMF) tips suffer nearly 100% FL collection loss when immersed in high-RI liquids (e.g., immersion oil, RI = 1.51), limiting their application in biological and chemical sensing.
- Engineering Solution: A high-density NV diamond crystal (~8 ”m diameter) was grafted onto an end-sealed, tapered Ultra-High Numerical Aperture (NA) Microstructured Optical Fiber (MOF-taper).
- Performance Improvement: The sealing technique isolated the core from the liquid, allowing the MOF-taper to maintain relative FL collection efficiency, demonstrating only 71.5% FL loss in immersion oil compared to the MMF-taperâs near 100% loss.
- Sensing Output: The endoscope demonstrated stable magnetic sensing performance via Optically Detected Magnetic Resonance (ODMR) in oil, achieving a calculated sensitivity of approximately 10.7 ”T.
- Material Specification: Success relies on sub-14 ”m diameter, NV-rich diamond crystals, requiring extreme precision in cutting, polishing, and quality control of the Single Crystal Diamond (SCD).
- 6CCVD Value: This application mandates custom-sized, highly polished, NV-enabled SCD. 6CCVD is uniquely positioned to supply these required micro-diamonds with guaranteed surface roughness (Ra < 1 nm).
Technical Specifications
Section titled âTechnical SpecificationsâThe following table extracts key material, performance, and dimensional parameters essential for replicating and optimizing this quantum sensing device.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Dimensions (Test) | 8.0 to 13.7 | ”m | Varying sizes used on different fiber tips |
| Final Endoscope Diamond Size | ~8.6 | ”m | Size used for magnetic sensing (ODMR) |
| Silica RI ($n_{s}$) | â 1.456 | N/A | Refractive index of standard fiber material |
| Ultra-High NA MOF (Nominal) | > 0.6 | N/A | Measured at 880 nm |
| MOF Core Diameter (Used) | 35 ± 2 | ”m | MM-HNA-35 |
| Surrounding RI (Water) | 1.33 | N/A | Liquid environment test 1 |
| Surrounding RI (Oil) | 1.51 | N/A | Liquid environment test 2 (high RI) |
| MMF-Taper FL Loss in Oil | â 100 | % | Baseline performance (failure point) |
| Sealed MOF-Taper FL Loss in Oil | 71.5 | % | Demonstrated performance in high RI liquid |
| Target Critical Sealing Length ($t$) | < 2.4 | ”m | Required length for MOF-taper (13.2 ”m core, 8 ”m diamond) to prevent FL loss |
| Magnetic Field Sensitivity | ~10.7 | ”T | Derived from 0.3 MHz ODMR stability in 2.7 mT field |
| Excitation Laser Power (CW Green) | ~5.86 | mW | Used for FL and excitation measurements |
Key Methodologies
Section titled âKey MethodologiesâThe NV endoscope was fabricated through highly precise mechanical and fusion splicing techniques, leveraging the geometry of Microstructured Optical Fiber (MOF).
- Diamond Preparation: NV-rich diamond crystals (ensemble-grade SCD) are selected, sized, and polished to micrometer dimensions (typically 8-14 ”m diameter).
- MOF Tapering: Ultra-high NA MOF (35 ”m core, 125 ”m cladding) is stretched while heated on a flame, and subsequently cleaved at the taper waist to achieve the desired tip core diameter (e.g., 5.2 ”m shown in results).
- Capillary End-Sealing (Fusion Splicing): The MOF-taper tip is fusion spliced to a section of MMF (or MMF-taper).
- Cleaving for Sealing Region: The fiber is cleaved near the spliced joint to ensure a short section of the capillaries collapsed region remains on the MOF-taper, thereby sealing the air capillaries.
- Note: The researchers observed that the fabricated sealing length ($t$) was longer than the critical condition ($t$ < 2.4 ”m), suggesting that optimization via advanced sealing techniques is necessary to minimize residual FL loss.
- Grafting: The micro-diamond is fixed onto the end-sealed MOF-taper apex using UV-curing glue.
- Testing Environment: Performance validation includes measuring FL collection and NV excitation efficiencies in air, water (RI = 1.33), and immersion oil (RI = 1.51). ODMR stability is measured in a 2.7 mT magnetic field environment.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is an experienced supplier of engineered CVD diamond necessary to meet the demanding material specifications of high-resolution quantum sensing and endoscope development.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this specialized NV quantum sensing research, customers require diamond with high purity, predictable NV ensemble density, and highly precise geometry.
| Requirement | 6CCVD Recommended Material | Rationale |
|---|---|---|
| High Density NV Centers | High-Purity SCD (Single Crystal Diamond) | Essential for stable quantum sensing signals (ODMR/FL) and maximum photon yield required in low-light collection applications. |
| Geometry and Size | Customized SCD Plates/Wafers | The application demands precise cutting and polishing of diamond crystals in the 8 ”m to 14 ”m diameter range for optimal coupling to the tapered fiber core. |
| Substrates (if needed) | High-Quality SCD Substrates | Available up to 10 mm thickness for bulk sensing or substrate growth refinement. |
Customization Potential
Section titled âCustomization PotentialâThe success of this endoscope hinges entirely on the quality and dimensional control of the micro-diamond particle and its interface with the fiber optic tip. 6CCVD provides the necessary micro-fabrication support:
- Precision Sizing and Dicing: We offer custom dicing and laser cutting services to produce diamond structures in complex geometries and ultra-small dimensions (down to micrometer scale) required for grafting onto fiber tips.
- Ultra-Smooth Polishing: The diamond surface must minimize light scattering and maximize coupling into the MOF core. 6CCVD guarantees Ra < 1 nm polishing for SCD materials, crucial for high-efficiency optical interfaces.
- Custom Metalization Support: Although the paper utilized UV glue, future device architectures often require metallic layers (e.g., Ti/Pt/Au/W) for enhanced thermal management, electrical contacts (for applied E-fields), or micro-reflector fabrication. 6CCVD offers internal metalization capabilities for Au, Pt, Pd, Ti, W, and Cu layers.
Engineering Support and Shipping
Section titled âEngineering Support and Shippingâ- Engineering Consultation: 6CCVDâs in-house PhD engineering team specializes in the physical and quantum properties of CVD diamond. We assist researchers in optimizing material selection (SCD vs. PCD, specific NV density creation) and dimensional specifications for complex NV endoscope and micro-sensor projects.
- Global Logistics: We provide reliable global delivery with DDU (Delivery Duty Unpaid) as the standard, and DDP (Delivery Duty Paid) options available upon request, ensuring timely acquisition of critical research materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Fixing a diamond containing a high density of Nitrogen-Vacancy (NV) center ensembles on the apex of a multimode optical fiber (MMF) extends the applications of NV-based endoscope sensors. Replacing the normal MMF with a tapered MMF (MMF-taper) has enhanced the fluorescence (FL) collection efficiency from the diamond and achieved a high spatial resolution NV-based endoscope. The MMF-taperâs high FL collection efficiency is the direct result of multiple internal reflections in the tapered region caused by silica, which has a higher refractive index (RI) than the surrounding air. However, for applications involving fluidic environments whose RI is close to or higher than that of the silica, the MMF-taper loses its FL collection significantly. Here, to overcome this challenge and achieve a high spatial resolution NV-based endoscope in a fluidic environment, we conceptually proposed a tapered ultra-high numerical aperture microstructured optical fiber (MOF) whose air capillaries at the tapered end are sealed. Since the end-sealed air capillaries along the tapered MOF (MOF-taper) have isolated the MOF core from the surrounding medium, the core retains its high FL collection and NV excitation efficiency in liquids regardless of their RI values. Replacing the MMF-taper with the MOF-taper will achieve a versatile NV-based endoscope that could potentially find widespread applications in fluidic environments where many biological processes and chemical reactions occur.