Magnetic field sensor based on coupled photonic crystal nanobeam cavities

We report the design, fabrication, and characterization of a resonant Lorentz force magnetic field sensor based on dual-coupled photonic crystal nanobeam cavities. Compared with microelectromechanical systems (MEMS) Lorentz force magnetometers, the proposed magnetic field sensor has an ultra-small footprint (less than 70 μm × 40 μm) and a wider operation bandwidth (of 160 Hz). The sensing mechanism is based on the resonance wavelength shift of a selected supermode of the coupled cavities, which is caused by the Lorentz force-induced relative displacement of the cavity nanobeams, and thus the optical transmission variation. The sensitivity and resolution of the device demonstrated experimentally are 22.9 mV/T and 48.1 μT/Hz1/2, respectively. The results can be further improved by optimizing the initial offset of the two nanobeams.