Vectorial magnetic field sensing with a dual-core photonic-crystal fiber: Toward fiber-optic stereomagnetometry

A monolithic, ultra-compact fiber probe integrating a nitrogen-vacancy diamond microcrystal, a dual-core photonic-crystal fiber (PCF), and a microwave transmission line is shown to enable a highly sensitive dual-channel vectorial magnetic field measurements by means of simultaneous optical detection of magnetic resonances through the two fiber cores. A reliable detection of microscale magnetic-field variations as low as ∼10 µT/(Hz)1/2 is demonstrated using a dual-core PCF with a core-to-core separation of 6 µm. Such a fiber probe is shown to provide a unique tool for a vectorial three-dimensional mapping of weak magnetic fields induced by microscale objects.