Numerical finite-difference time-domain calculation for extreme enhancement of magneto-optical effect at ultraviolet wavelength using Ni-subwavelength grating on SiO2/Ni structure

An extreme enhancement of the polar Kerr magneto-optical (MO) effect was numerically demonstrated using surface plasmon polaritons (SPPs) at the SiO2/Ni interface combined with the Ni-subwavelength grating (SWG). Utilizing the ω–k dispersion relation for the SPP at the SiO2/Ni interface, the parameters of Ni-SWGs were designed to couple the SPP mode with the incident light. The electromagnetic field distribution was calculated using the finite-difference time-domain method to estimate and discuss the enhancement of MO effect in the designed structure. The results indicated that the reflectance of light for the designed structure dramatically decreased owing to SPP excitations. The field distributions revealed that the high electric field of the SPP was concentrated not only on the Ni substrate but also on Ni-SWG, yielding Kerr rotation angle 224 times higher than that without SPP. The results provide a new method for enhancing the MO effect; the extremely large MO enhancement achieved by our structure has a great potential for use in a wide range of applications.