A sensitive optical magnetic field sensor was experimentally demonstrated using Ni-subwavelength grating (SWG) combined with a SiO<sub>2</sub>/Ag plasmonic structure. We fabricated the Ni-SWG structure on the Ag/SiO<sub>2</sub> structure using electron beam lithography and a liftoff process. As a result, a dip in the reflection spectra with normal incidence was obtained at a wavelength of 530 nm. The reflectivity at the dip position significantly decreased with the intensity of the magnetic field applied to the structure. When a magnetic field of 43 mT was applied, the change in reflection reached approximately 4% of that without magnetic field. The experimental results indicate that our sensor achieves millitesla order of sensitivity for the magnetic field. The electromagnetic field distribution around the Ni-SWG/SiO<sub>2</sub>/Ag calculated using the finite-difference time-domain method clarified the reason for the high sensitivity of our sensor.
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/ Si<sub>3</sub>N<sub>4</sub> 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.
We analytically investigated the influence of grating shape on polarization characteristics of the emission from a GaN-based light-emitting diode with a low-contrast subwavelength grating (SWG), such as SiO2-SWG. The electromagnetic field distribution, calculated using the finite-difference time-domain method, predicted that the polarization characteristics strongly depend on the grating side slope. A trapezoid SiO2-SWG was fabricated on the GaN-based-LED using electron-beam lithography. The optical characteristics of the electroluminescence agreed with those theoretically predicted, and we succeeded in demonstrating the influence of grating shape on the polarization of LED emission.