Sensing of Magnetic-Field Gradients with Nanodiamonds on Optical Glass-Fiber Facets

We demonstrate a photonic sensor of the magnetic fieldand itsgradients with remote readout. The sensor is based on optically detectedmagnetic resonance (ODMR) in nanodiamonds with nitrogen-vacancy colorcenters that are covalently attached as a thin film on one facet ofan optical fiber bundle. By measuring ODMR signals from a group ofindividual fibers in an & SIM;0.5-mm-wide imaging bundle, differencesof local magnetic field strengths and magnetic field gradients aredetermined across the plane of the bundle facet. The measured gradientsare created by direct electric currents flowing in a wire placed nearthe nanodiamond film. The measurement enabled the determination ofthe net magnetic field corresponding to various current directionsand their corresponding magnetic field gradients. This demonstrationopens up a perspective for compact fiber-based endoscopy, with additionalavenues for remote and sensitive magnetic field detection with submicrometerspatial resolution under ambient conditions.