Efficient photon coupling from a diamond nitrogen vacancy center by integration with silica fiber

At a Glance

Metadata	Details
Publication Date	2016-02-12
Journal	Light Science & Applications
Authors	Rishi N. Patel, Tim Schröder, Noël Wan, Luozhou Li, Sara L. Mouradian
Institutions	Stanford University, Massachusetts Institute of Technology
Citations	79
Analysis	Full AI Review Included

Technical Documentation & Analysis: Fiber-Integrated NV Center Coupling

Research Paper Analyzed: Efficient photon coupling from a diamond nitrogen vacancy center by integration with silica fiber (Patel et al., Light: Science & Applications, 2016)

Executive Summary

This paper presents a robust, alignment-free approach for coupling single photons emitted by a Nitrogen Vacancy (NV) center in diamond directly into a single-mode silica optical fiber, a critical advance for quantum networking and single-photon source applications.

Core Achievement: Demonstration of a compact, highly efficient interface using adiabatic power transfer between a high-quality, MPCVD-grown diamond micro-waveguide and a tapered silica fiber.
Material Basis: Requires 200 nm thick, [100] electronic grade Single Crystal Diamond (SCD) thin films for lithographic patterning into micro-waveguides.
Performance Metrics: Achieved high raw single photon detection rates exceeding 600,000 cps (estimated saturation rate > 700 kHz).
Quantum Purity: Demonstrated exceptionally low raw anti-bunching signals, g⁽²⁾(0) < 0.2, confirming single NV operation without relying on background subtraction.
Efficiency: Overall photon collection efficiency ranged between 16% and 37%, representing a roughly fourfold improvement over previous fiber-coupled approaches utilizing diamond point emitters.
Methodology: Integration achieved via a deterministic pick-and-place technique, utilizing van der Waals forces for reliable adhesion between the tapered structures.
Future Impact: This geometry enables efficient optical access for coherent spin manipulation and extends potential to evanescently integrate diamond nano-cavities for enhanced quantum communication.

Technical Specifications

Extraction of key physical and performance parameters from the study.

Parameter	Value	Unit	Context
Diamond Material Type	Synthetic [100] SCD	Dimensionless	Electronic Grade, High-Quality CVD
Diamond Film Thickness	200	nm	Required for micro-waveguide fabrication
Waveguide Total Length	12	µm	Includes both taper sections
Waveguide Center Width	2	µm	Constant width section
Taper Length (Individual)	5	µm	Triangular taper on each side
Integrated Fiber Diameter	≈500	nm	Tapered silica fiber waist
NV Zero Phonon Line (ZPL)	≈637	nm	Characteristic emission peak
NV Center Lifetime (τ_NV)	15.7 ± 1.1	ns	Measured lifetime (inverse time constant 1/τ₁)
Saturation Photon Count Rate (I_sat)	(712 ± 24) * 10³	cps	Combined collection from both fiber ends
Anti-Bunching (g⁽²⁾(0))	< 0.2	Dimensionless	Raw measurement (no background subtraction)
Maximum Incident Pump Power	2.25	mW	Limit before g⁽²⁾(0) > 0.5 due to background emission
Overall Collection Efficiency (η_C)	16 to 37	%	Range of estimated lower and upper bounds

Key Methodologies

A concise sequence detailing the fabrication and integration of the diamond/fiber system.

Fiber Tapering: Standard heat-and-pull technique applied to single-mode optical fiber (Thorlabs 630HP). The pull was monitored using 630 nm laser transmission and halted when transmission dropped, yielding a fiber waist diameter of approximately 500 nm.
Diamond Micro-Waveguide Definition: Micro-waveguides (12 µm long, 2 µm wide center section, 5 µm tapers) were fabricated from a 200 nm thick film of [100] electronic grade synthetic CVD diamond. This utilized transferred hard mask lithography.
NV Center Selection: Individual micro-waveguides were optically characterized to select those containing exactly one high-quality NV memory center.
Deterministic Integration: A tungsten micro-manipulator tip was used to detach and precisely position the selected diamond micro-waveguide onto the waist of the tapered fiber, adhering via van der Waals forces.
Optical Excitation: The NV center was pumped using a 532 nm laser focused through a high Numerical Aperture (NA = 0.75) objective.
Photon Collection and Filtering: The NV fluorescence signal was collected directly through both the left and right fiber ends and filtered using two 550 nm long-pass filters before detection by Avalanche Photo-Diodes (APDs).
Characterization: Photon count rates, saturation behavior, and second-order autocorrelation measurements (Hanbury Brown-Twiss setup) were performed to confirm single-photon emission and efficiency.

6CCVD Solutions & Capabilities

6CCVD provides the specialized MPCVD diamond materials and engineering services required to replicate, scale, and advance the fiber-integrated NV system demonstrated in this research. Our capabilities directly address the material constraints and scalability challenges cited by the authors (e.g., improving low fabrication yield and reducing optical losses).

Applicable Materials

To replicate and enhance the performance of the NV-fiber coupler, 6CCVD recommends:

Optical Grade Single Crystal Diamond (SCD): Required for maximizing NV coherence times and minimizing internal scattering losses. We specifically offer high-purity, electronic grade [100]-oriented SCD wafers, matching the required crystal direction for optimal NV alignment.
Custom Thin Film Thickness: We provide SCD membranes grown and processed to precise thicknesses from 0.1 µm up to 500 µm. This is critical for meeting the 200 nm requirement for ideal mode-matching and adiabatic coupling optimization.
High-Surface Quality Substrates: SCD polished surfaces with Ra < 1 nm are available, essential for minimizing surface scattering, which is a limiting factor for coupling efficiency and broadband adiabatic power transfer (Figure 2e).

Customization Potential

The success of this method hinges on highly precise dimensions and integration features.

Custom Service	Relevance to Research Requirements	6CCVD Advantage
Custom Wafer Dimensions	Supports upscaling the fabrication process, addressing the low 5%-10% yield cited by the authors.	Plates/wafers available up to 125 mm (PCD/SCD integration support), facilitating larger-scale lithographic patterning.
High-Precision Laser Cutting	Required for creating the complex tapered micro-waveguide geometries (12 µm length, 2 µm width, 5 µm tapers) and specialized separation features for the pick-and-place method.	In-house precision cutting allows the production of transfer-ready membranes and specialized substrate geometries with micron-level tolerance.
Advanced Metalization	Essential for future implementations, such as creating fiber-integrated Bragg filters for pump rejection, or integrating electrical contacts for coherent Electron Spin Resonance (ESR) control (Figure 4f inset).	Internal capability for depositing common contact materials including Au, Pt, Pd, Ti, W, and Cu, suitable for subsequent cleanroom processes.

Engineering Support

6CCVD’s in-house PhD team provides specialized consultation to accelerate research in diamond nanophotonics. We can assist with:

Material Selection and Orientation: Optimizing SCD purity and crystal orientation for maximum NV center creation yield and spin coherence in demanding quantum networking projects.
Interface Optimization: Consulting on ideal film thickness and surface treatment required for successful adiabatic coupling to various optical fibers and photonic integrated circuits.
Post-Processing Integration: Providing guidance on metalization stacks compatible with subsequent micro-manipulation and low-temperature (cryogenic) operation.

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/lsa.2016.32