Magnetically sensitive nanodiamond-doped tellurite glass fibers

At a Glance

Metadata	Details
Publication Date	2018-01-15
Journal	Scientific Reports
Authors	Yinlan Ruan, David Simpson, Jan Jeske, Heike Ebendorff‐Heidepriem, Desmond W. M. Lau
Institutions	University of South Australia, The University of Melbourne
Citations	55
Analysis	Full AI Review Included

Analysis of Magnetically Sensitive Nanodiamond-Doped Tellurite Glass Fibers

This documentation analyzes the key findings and methodologies of the research paper “Magnetically sensitive nanodiamond-doped tellurite glass fibers,” and connects the stringent material requirements to 6CCVD’s expertise in specialized MPCVD diamond fabrication for advanced quantum sensing applications.

Executive Summary

This research successfully developed a robust, intrinsically magneto-sensitive optical fiber by embedding Nitrogen-Vacancy (NV) center nanodiamonds (NDs) into a tellurite glass fiber matrix. This work represents a significant step toward integrated, remote solid-state magnetometry using diamond spin physics.

Integrated Sensing Platform: The methodology successfully fixed NV center nanodiamonds (40-50 nm average size) within a 160 µm diameter tellurite glass fiber, resolving issues associated with external magnetic sensing materials.
NV Generation Protocol: NV centers were generated in the high-purity nanodiamonds via 2 MeV electron irradiation (10¹⁸ cm^-2 dose) followed by a dual-stage annealing process (800 °C vacuum, 475 °C air).
Optically Detected Magnetic Resonance (ODMR): Measurements verified the magnetic sensitivity, detecting Zeeman splitting of the NV ground state sublevels (D = 2.87 GHz).
Performance Metrics: A projected DC magnetic sensitivity of approximately ~11 µT/√Hz was calculated, limited primarily by the broad ODMR linewidth (28.8 MHz) caused by inhomogeneous broadening and strain within the glass matrix.
Optical Coupling Demonstrated: The characteristic NV emission (Zero-Phonon Line, ZPL, at 637 nm) was efficiently coupled from the localized NDs into the guided modes of the optical fiber, enabling remote longitudinal collection from side excitation.
Application Potential: This hybrid material approach paves the way for miniature, robust fiber-based magnetometers for fields like medical magneto-endoscopy and remote geophysical sensing.

Technical Specifications

The following hard data points were extracted from the analysis of the material synthesis and measurement results.

Parameter	Value	Unit	Context
ND Source Purity	>99.95	%	Non-detonation synthesis
ND Average Particle Size	40 - 50	nm	Initial diamond material
NV Creation Irradiation Dose	10¹⁸	cm^-2	2 MeV Electron Irradiation
High-Temp Annealing	800	°C	Vacuum stage for vacancy mobilization (2 h)
Fiber Outer Diameter (OD)	160	µm	Final drawn ND-doped tellurite fiber
ND Concentration (Melt)	12	ppm (wt)	Initial concentration doped into glass melt
ND Concentration (Final Fiber)	Approx. 0.7	ppm (wt)	Loss due to oxidation during dwelling time
Optical Loss (500-800 nm)	9 - 14	dB/m	Loss profile of the final tellurite fiber
NV Zero Field Splitting (D)	2.87	GHz	Intrinsic diamond crystal field splitting
Measured ODMR Resonance (B=0)	2.876	GHz	Measured single degenerate dip
ODMR Linewidth ($\delta$)	28.8 ± 0.8	MHz	Full Width at Half Maximum (FWHM)
Max ODMR Contrast (R)	10	%	Measured at zero magnetic field
Projected Magnetic Sensitivity ($n_{dc}$)	~11	µT/√Hz	Calculated sensitivity for DC fields
Excitation Wavelength	532	nm	CW Green Laser used for optical pumping
Excitation Power Density	~600	W/cm²	Power density used for side excitation
Detected Photon Count (N)	4 x 10⁶	s^-1	Photons collected longitudinally from endface

Key Methodologies

The experiment relies on three primary technical stages: NV center preparation, tellurite fiber synthesis, and advanced optical characterization using ODMR.

NV Precursor Material Preparation:
- 40-50 nm nanodiamonds were selected for their high purity (>99.95%).
- NV vacancies were created by high-energy electron irradiation (2 MeV) at a dose of 10¹⁸ cm^-2.
- Vacancies were mobilized and graphitic layers removed via two-stage annealing: 800 °C under vacuum (2 h) followed by 475 °C in air (2 h).
ND-Doped Tellurite Glass Fiber Fabrication:
- Melt Quench Billet: Crystalline raw tellurite materials were melted at 690 °C.
- Doping: The melt temperature was reduced to 610 °C, and 12 ppm (wt) ND powder was added, mixed, and dwelled for 10 minutes to ensure dispersion.
- Extrusion and Drawdown: The resulting doped billet was cast, extruded into a rod, and finally drawn down to an optical fiber with a 160 µm outer diameter.
ODMR and Fluorescence Characterization:
- Excitation Geometry: The fiber was excited transversely (side excitation) using a 532 nm CW laser (power density ~600 W/cm²) focused by a high NA objective (0.9 NA).
- Collection Geometry: Fluorescence was collected remotely/longitudinally from the fiber endface using a multimode fiber coupled to a spectrometer or APD.
- ODMR Implementation: A 2 mm microwave antenna delivered RF power (1-4 W) in close proximity to the optical excitation spot to drive the NV spin transitions.
- Magnetic Field Application: External DC magnetic fields (B-fields) up to 3.7 mT were applied to observe Zeeman splitting and the resulting reduction in fluorescence contrast.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials required to replicate, optimize, and scale the quantum sensing platform demonstrated in this research, particularly by mitigating the material limitations identified (strain, background fluorescence, and coupling efficiency).

Applicable Materials

To achieve optimal NV sensitivity, researchers require high-purity, low-strain diamond with tightly controlled geometry. 6CCVD recommends the following materials to advance NV-based fiber magnetometry:

Requirement	6CCVD Recommended Material	Rationale for Application
High-Purity NV Host (Bulk)	Optical Grade SCD (Single Crystal Diamond)	Offers superior intrinsic low-strain environment (Ra < 1 nm polished face) critical for minimizing the 28.8 MHz ODMR linewidth observed in the paper, leading to higher intrinsic magnetic sensitivity.
High-Density Doping (Scaling)	High-Purity MPCVD PCD	Provides a scalable material platform for generating high concentrations of NV centers required for increasing the detected photon count (N) and improving the overall sensitivity ($n_{dc}$).
Micro/Nano-Geometries	Custom Thin SCD/PCD Films (0.1 µm - 500 µm)	Essential for creating micro-wafers or ultra-thin substrates suitable for direct bonding/integration onto fiber endfaces or within waveguide structures, bypassing the oxidation and dispersion challenges of NDs in a glass melt.
Advanced Devices (All-Optical)	Heavy Boron-Doped (BDD) Diamond	For replication of all-optical magnetometry protocols (microwave-free detection), BDD films offer excellent electrical conductivity while maintaining necessary optical properties.

Customization Potential

The research highlights the need to couple NV fluorescence into guided modes efficiently. 6CCVD’s custom fabrication services directly support advanced integration strategies:

Custom Dimensions and Geometries: We offer laser cutting and shaping of SCD and PCD plates up to 125 mm (PCD) to create specific micro-waveguide structures, tapered tips, or geometric inclusions designed to maximize the numerical aperture for fluorescence collection, overcoming limitations noted in conventional detection.
Precision Thickness Control: We supply films in the critical range of 0.1 µm to 500 µm (SCD/PCD) with strict thickness uniformity necessary for precise optical mode matching and coupling to external wave guides.
High-End Polishing: Achieving high efficiency relies on minimal scattering losses. 6CCVD provides industry-leading polishing, guaranteeing Ra < 1 nm for SCD surfaces, which is critical for minimizing optical loss when integrating diamond directly with optical elements.
Integrated Metalization Schemes: The ability to integrate microwave drive structures (like the antenna used in the paper) directly onto or adjacent to the diamond element is key for miniaturization. 6CCVD provides in-house metalization services, including Ti/Pt/Au, Ti/W, and Cu layers, for the reliable fabrication of integrated coplanar waveguides (CPWs) necessary for efficient RF delivery and localized ODMR.

Engineering Support

The successful implementation of this research requires deep expertise in diamond material science, NV creation protocols, and integration engineering.

6CCVD’s in-house PhD team provides specialized consultation to ensure optimal material performance:

Material Selection Optimization: Assistance in selecting the ideal balance between low-strain SCD and high-NV-concentration PCD for specific remote magnetometry projects.
NV Protocol Development: Consultation on electron irradiation doses (10¹⁷ cm^-2 to 10¹⁹ cm^-2) and custom annealing recipes necessary to maximize NV creation yield and optimize the m_s=0 spin polarization contrast in new material geometries.
Integration Strategy: Support in developing robust bonding and packaging techniques to utilize custom metalized diamond substrates as integrated quantum sensors.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-018-19400-3