Optical magnetic field sensor based on guided-mode resonance with Ni subwavelength grating/waveguide structure

Highly sensitive optical sensor for magnetic field detection was experimentally demonstrated using a guided-mode resonance in waveguide with Ni nano-grating. The electromagnetic field distribution was calculated by finite-difference time-domain method in order to estimate the sensing performance of our device. The calculation results indicated that the optical characteristics of our sensor considerably varied with applying magnetic field. We fabricated the Ni-subwavelength grating/ Si₃N₄ waveguide structure on the optical glass substrate using electron beam lithography technique. The reflection peak resulting from the guided-mode in the waveguide was obtained with normal incident geometry. The peak intensity depended on static magnetic field applied to the structure, and the intensity changed by about 5 % for the magnetic field intensity of 39.4 mT. These experimental results suggest our sensor can sensitively detect magnetic field while avoiding use of the complex and expensive system, and our device is pretty suitable for the integration devices in internet of things society.