Enhanced Magneto-Optical Effect in Ce:YIG Based All Dielectric Metasurfaces

Abstract

Magneto-optical (MO) devices based on the Faraday effect are widely used for optical communication and optical sensing. Due to their weak MO effect in the optical frequency range, the size of MO devices is typically in the range of 10~1000 wavelengths, limiting their application in integrated photonic systems. Currently, most studies for enhancing the Faraday effect are based on surface plasmon resonance.1, 2 However, due to the Ohmic loss of metals, these structures are optically lossy. Therefore, all dielectric nanostructures provide an alternative route to achieve high Faraday rotation and high transparency simultaneously.3,4 Here, we report theoretical and experimental study on enhanced Faraday effect in all dielectric MO metasurfaces based on Si/Ce:YIG nanostructures. The device is composed of a 2D periodic array of amorphous Si nanodisks patterned on Ce:YIG/YIG oxide thin film stacks grown on silica. By adjusting the geometric parameters, magnetic dipole and electric dipole Mie resonance modes can be excited in the Si disks. Thanks to the high refractive index of Ce:YIG/YIG, the modes are also strongly confined in the Ce:YIG/YIG layers. The transmission spectrum is simulated using the finite element time-domain difference method, which agrees excellently with experimental results. The Faraday rotation spectrum of the sample was measured using a home-made microscale Faraday rotation characterization set-up, which shows obvious enhancement peaks in the vicinity of each resonance. The MO response of the Ce:YIG thin film deposited on the same silica substrate is also presented as a reference. With the transmission close to 40%, we achieved 2.3-fold Faraday rotation enhancement compared to bare Ce:YIG thin films. Our device shows effective MO enhancement in the sub-wavelength scale, which is promising for applications such as free space non-reciprocal photonic devices and MO imaging.