Coupling of single NV center to adiabatically tapered optical single mode fiber

At a Glance

Metadata	Details
Publication Date	2016-12-01
Journal	The European Physical Journal D
Authors	Vadim Vorobyov, Vladimir V. Soshenko, Stepan V. Bolshedvorskii, Javid Javadzade, Н. Г. Лебедев
Institutions	Skolkovo Foundation, Moscow Institute of Physics and Technology
Citations	27
Analysis	Full AI Review Included

Technical Documentation & Analysis: Efficient NV Center Coupling via Tapered Optical Fiber

This document analyzes the research detailing the robust coupling of single Nitrogen-Vacancy (NV) centers within nanodiamonds to tapered optical fibers, highlighting 6CCVD’s capability to supply the advanced diamond materials required for replicating and advancing this quantum technology.

Executive Summary

This research successfully demonstrates a reliable, high-efficiency technique for integrating single diamond NV centers (key solid-state quantum emitters) with optical fibers, achieving significant gains in photon collection.

Core Achievement: Efficient, high-yield transfer (85% success rate) of single nanodiamonds containing NV centers onto adiabatically tapered single mode fibers.
Collection Enhancement: Achieved up to 3X improvement in single photon emission collection compared to a standard high numerical aperture (NA 0.95) confocal microscope setup.
Calculated Efficiency: Estimated total photon collection efficiency (two sides) reaches 3% from the NV center, demonstrating strong coupling potential between diamond and fiber optics.
Robust Quantum Statistics: Confirmed single photon statistics (g⁽²⁾(0) < 0.5) and stable NV lifetime (~21 ns) before and after mechanical transfer, validating the technique’s integrity.
Material Implication: The study underscores the critical role of diamond as a foundation for scalable solid-state quantum computing and communication systems.
6CCVD Value: 6CCVD specializes in the high-purity single crystal diamond (SCD) necessary for engineering highly stable, narrow-emission NV centers required for future integrated photonics devices.

Technical Specifications

The following table summarizes the key experimental parameters and performance metrics extracted from the research paper.

Parameter	Value	Unit	Context
Excitation Wavelength	532	nm	Continuous Wave (CW) Laser
Fiber Taper Waist Diameter	~450	nm	Optimized coupling diameter
Tapered Waist Length	5	mm	Achieved up to 90% transmission
Confocal Objective NA	0.95	N/A	Nikon 60X PLAN APO
Initial Confocal Collection Efficiency	~0.5	%	Baseline measurement
Fiber Collection Enhancement	Up to 3X	N/A	Ratio over confocal setup
Calculated Total Fiber Collection	3	%	Estimated efficiency for two sides
NV Center Lifetime	~21	ns	Consistent before and after transfer
Fiber Background Lifetime	30	µs	Long-lifetime fluorescence (silica oxygen centers)
Nanodiamond Transfer Success Rate	85	%	17 successful transfers out of 20
Functionalization Temperature (Acid)	75	°C	HNO₃ + H₂SO₄ mixture
Functionalization Temperature (Base)	90	°C	NaOH and HCl mixtures

Key Methodologies

The experiment involved careful fiber fabrication, chemical functionalization of nanodiamonds, and precise mechanical alignment and transfer under confocal visualization.

Fiber Tapering System: Silica-fused optical fibers were pulled using two Newport M462 translational stages, heated by a home-built hydrogen-oxygen (H₂+O₂) flame torch.
Taper Optimization: The tapering process was carefully controlled (balancing time/speed) to minimize contamination and achieve high transmission (up to 90%), resulting in a 450 nm diameter waist.
Nanodiamond Functionalization (Surface Charge): Nanodiamonds (100 ct/kg) were subjected to a multi-step acid/base treatment (conc. HNO₃, H₂SO₄ at 75°C, followed by NaOH and HCl at 90°C) to clean the surface and render it negatively charged.
Donor Fiber Preparation: A tapered fiber (donor) was coated with Poly-L-Lysine (PLL) solution (30000-70000 M_w) for 15 minutes, then immersed in a methanol/functionalized diamond mixture (1:1) for 5 minutes, resulting in a dense coating of nanodiamonds.
NV Center Selection: Single NV centers on the donor fiber were identified via lifetime measurements and confirmed via second-order correlation function g⁽²⁾(t) measurement using a PicoHarp 300 system.
Mechanical Transfer: The donor fiber (perpendicular) and acceptor fiber (horizontal) were brought into contact under the confocal microscope, and the acceptor fiber was moved until a mechanical ‘jump’ indicated successful transfer of the targeted single nanodiamond.
Background Suppression: Fiber fluorescence (long lifetime, 30 µs) was minimized by optimizing the polarization of the 532 nm excitation light (up to factor of 2 suppression) and using temporary photo bleaching (factor of 2 drop after 60 seconds of 30 µW exposure).

6CCVD Solutions & Capabilities

This research demonstrates a successful pathway for single photon source integration, an area critically dependent on the quality and form factor of the source diamond. 6CCVD provides the high-specification MPCVD diamond substrates necessary for engineers and scientists to move beyond relying on functionalized nanodiamond powder toward wafer-scale integrated photonic solutions.

Applicable Materials for Quantum Emitter Projects

The long-term success and scalability of integrated quantum photonics require engineered SCD platforms, offering superior coherence and emission stability compared to fragmented nanodiamonds.

6CCVD Material Recommendation	Specification & Value Proposition	Application in Research Advancement
Optical Grade Single Crystal Diamond (SCD)	Ultra-high purity, low birefringence SCD plates (up to 500 µm thick). Essential for creating high-coherence NV centers via controlled implantation/annealing.	Ideal substrate for fabricating on-chip devices like diamond nanobeams or solid immersion lenses (SILs), circumventing the stability issues of transferred nanodiamonds.
Custom PCD Plates	Polycrystalline Diamond (PCD) substrates up to 125 mm diameter, polished to Ra < 5 nm.	Serves as robust, large-area sacrificial or carrier substrates for complex micro- or nanofabrication steps preceding fiber integration.

Advanced Customization Potential for Integrated Photonics

Moving toward scalable quantum devices, researchers often require custom geometries and coupling elements. 6CCVD’s in-house capabilities directly support the advanced requirements needed to extend this coupling mechanism to integrated platforms.

Custom Dimensions and Etching: While this paper used commercial fiber, 6CCVD provides SCD wafers up to 125 mm and specialized SCD thickness control (0.1 µm to 500 µm). This enables fabrication of large-scale diamond photonic circuits (e.g., waveguides or resonators) designed for optimal fiber coupling geometry.
Precision Polishing: To interface efficiently with tapered fibers (or fabricated on-chip waveguides), 6CCVD offers atomic-scale surface polishing (SCD: Ra < 1 nm), crucial for minimizing light scattering losses when interfacing high-refractive index diamond with fiber structures.
Custom Metalization Schemes: The paper’s introduction mentions plasmonic structures [14-16] as an alternative approach for Purcell enhancement. 6CCVD provides in-house metalization services (Au, Pt, Pd, Ti, W, Cu), allowing researchers to deposit customized metal patterns directly onto polished SCD wafers for engineering highly efficient plasmonic NV interfaces or electro-optical control elements.

Engineering Support

6CCVD’s commitment extends beyond material supply. Our in-house PhD team can assist researchers in selecting the optimal diamond substrate specifications (purity, orientation, and surface termination) for implementing quantum projects, particularly those involving NV center creation and light extraction methodologies. We provide global shipping (DDU default, DDP available) to ensure timely delivery of custom materials worldwide.

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

Tech Support

Original Source

DOI: https://doi.org/10.1140/epjd/e2016-70099-3