Integrated NV Center-Based Temperature Sensor for Internal Thermal Monitoring in Optical Waveguides

At a Glance

Metadata	Details
Publication Date	2025-07-02
Journal	Sensors
Authors	Yifan Zhao, Shi‐You Ding, Shuo Wang, Yiming Hu, Hongliang Liu
Institutions	Ocean University of China, Wuhan Ship Development & Design Institute
Citations	1
Analysis	Full AI Review Included

Integrated NV Center-Based Temperature Sensor for Internal Thermal Monitoring in Optical Waveguides

Executive Summary

Core Achievement: Successful integration of nitrogen-vacancy (NV) centers into a diamond optical waveguide to enable internal, non-contact thermal monitoring.
Fabrication Method: A surface-cladding waveguide was fabricated in a Type IIa CVD diamond wafer using femtosecond laser direct writing (FsLDW).
Sensing Principle: Temperature was measured by analyzing the shift in the zero-field splitting (ZFS) resonance peaks of the NV centers using Optically Detected Magnetic Resonance (ODMR).
High Sensitivity: The sensor achieved a temperature monitoring sensitivity of 1.1 mK/√Hz, demonstrating suitability for precise micro-scale thermal management.
Thermal Quantification: The pump laser (532 nm) was confirmed as the source of internal heating, with the temperature rise quantified at a fitted ratio of 0.38 K/mW.
Calibration: The temperature coefficient (dD/dT) for the NV centers in this specific diamond sample was accurately calibrated to be 75.74 kHz/K.
Broad Applicability: The methodology is extensible to other color centers in various solid-state materials, broadening its potential use in integrated photonic systems.

Technical Specifications

Parameter	Value	Unit	Context
Temperature Sensitivity (η)	1.1	mK/√Hz	CW-ODMR measurement
ZFS Temperature Coefficient (dD/dT)	75.74	kHz/K	Calibrated NV center response
Waveguide Material	Type IIa CVD Diamond	N/A	Product model Q-DNV-S
Nitrogen Concentration	~0.5	ppm	Diamond wafer bulk
NV Center Concentration	~6 x 10^-3	ppb	Diamond wafer bulk
Waveguide Geometry	Half-circle surface-cladding	N/A	Fabricated structure
Waveguide Dimensions	50 µm (width), 3 mm (length)	µm, mm	Structure size
Waveguide Loss (532 nm)	8.44	dB	Includes propagation and coupling losses
FsLDW Wavelength	800	nm	Femtosecond laser direct writing
FsLDW Pulse Energy	33	nJ	Single pulse energy used for writing
Pump/Excitation Wavelength	532	nm	CW laser for heating and NV excitation
Maximum Measured Temperature	~60	°C	Observed at 100 mW pump power
Heating Ratio	0.38	K/mW	Temperature rise induced by pump laser
Zero-Field Splitting (D)	2.78	GHz	Unbiased NV ground state
ODMR Contrast (C)	4.5	%	Measured from ODMR spectrum
ODMR FWHM (Δν)	~10	MHz	Measured from ODMR spectrum

Key Methodologies

Diamond Selection and Preparation: A polished Type IIa CVD diamond wafer (3 x 3 x 0.3 mm³) with intrinsic NV centers (N concentration ~0.5 ppm) was used.
Waveguide Fabrication (FsLDW): A surface-cladding waveguide (50 µm width) was created using femtosecond laser direct writing. The laser parameters included 800 nm wavelength, 100 fs pulse width, 1 kHz repetition rate, 33 nJ single pulse energy, and a scanning speed of 0.1 m/s.
Structural Verification (Raman Mapping): Raman spectroscopy confirmed that structural damage and refractive index reduction were confined to the laser-irradiated cladding tracks, ensuring the guiding core remained largely pristine.
NV Center Confirmation (PL): Photoluminescence (PL) spectra confirmed the presence of NV centers (Zero-Phonon Line at 637 nm) within the waveguide core, verifying the material quality was maintained post-fabrication.
ODMR Setup: The diamond sample was mounted on a self-made microwave antenna. Microwave signals (0-3 GHz) were applied, and a weak bias magnetic field (1 mT) was used to minimize resonance peak broadening.
Thermometer Calibration: The temperature dependence of the ZFS (D) was measured using an external heating sheet. The linear relationship between D and temperature (T) yielded a coefficient (dD/dT) of 75.74 kHz/K.
Internal Temperature Measurement: A continuous 532 nm laser (up to 100 mW) was coupled into the waveguide, acting as both the NV excitation source and the heating element. Fluorescence was collected via end-face coupling, and shifts in the ODMR peak positions (v^- and v⁺) were recorded to determine the internal temperature rise.
Sensitivity Calculation: The sensitivity (η) was calculated based on the ODMR contrast, FWHM, photon count rate, and the calibrated dD/dT value, resulting in 1.1 mK/√Hz.

Commercial Applications

Integrated Optoelectronic Devices: Essential for thermal management in compact, high-density integrated circuits, preventing performance degradation caused by localized heating (e.g., in array waveguide gratings (AWGs) where temperature causes spectral drift).
Quantum Photonic Systems: Provides a high-resolution, non-invasive method for monitoring and stabilizing the temperature of quantum emitters (like NV centers) embedded in photonic structures, critical for maintaining spin coherence.
High-Power Fiber Optics: Monitoring internal temperature increases in optical fibers and waveguides transmitting high photon densities, which can lead to material aging and reduced lifespan.
Micro-scale Thermal Microscopy: Enables non-contact, high spatial resolution temperature mapping within solid-state materials, useful for characterizing thermal behavior in novel micro- and nano-devices.
Advanced Sensing Platforms: Applicable to developing multi-functional sensors leveraging other color centers in solids (beyond diamond NV centers) for simultaneous measurement of temperature, magnetic fields, and strain within integrated platforms.

View Original Abstract

Color centers in solids, such as nitrogen-vacancy (NV) centers in diamonds, have gained significant attention in recent years due to their exceptional properties for quantum sensing. In this work, we demonstrate an NV center-based temperature sensor integrated into an optical waveguide to enable internal temperature sensing. A surface-cladding optical waveguide was fabricated in a diamond wafer containing NV centers using femtosecond laser direct writing. By analyzing the resonant peaks of optically detected magnetic resonance (ODMR) spectra, we established a precise correlation between temperature changes induced by the pump laser and shifts in the ODMR peak positions. This approach enabled temperature monitoring with a sensitivity of 1.1 mK/Hz. These results highlight the significant potential of color centers in solids for non-contact, micro-scale temperature monitoring.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s25134123

References

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Integrated NV Center-Based Temperature Sensor for Internal Thermal Monitoring in Optical Waveguides

At a Glance