High-precision three-dimension microwave magnetic field measurements using fiber-integrated diamond nitrogen-vacancy center scanning probe.

Accurate characterization of the three-dimensional (3D) spatial radiation characteristics of microwave fields, especially the out-of-plane intensity distribution, remains a critical challenge in advanced microwave technology and diamond nitrogen-vacancy (NV) center-based quantum sensing. In this work, a high-precision three-dimensional microwave magnetic field measurement system based on a fiber-integrated NV center scanning probe is developed. The system enables high-spatial-resolution characterization of electromagnetic fields on the surface of miniaturized microwave antennas. The core of the system is a mechanically polished tapered optical fiber with a 26.5° taper angle, integrated with a diamond nanopillar containing ensemble NV centers at the fiber tip. This tapered structure conforms more closely to the diamond nanopillars, thereby enabling high-sensitivity electromagnetic imaging on the chip surface. We perform microwave magnetic field measurements on a standard Ω-ring radiating structure: in-plane measurements at 100 and 500 μm from the ring edge verify excellent field uniformity in the central region of the Ω-ring radiating structure, while out-of-plane characterization from 0 to 500 μm above the ring center identifies an effective radiation distance of 500 μm for the structure. This system realizes non-destructive, high-precision on-chip electromagnetic field characterization and can be extended to diverse quantum magnetometry applications requiring 3D measurement capability.