Magnetic-field tunable transmittance in a ferrofluid-filled silicon nitride photonic crystal slab

A numerical simulation was performed to demonstrate the active manipulation of the transmittance spectra in a ferrofluid-filled silicon nitride (SiN) photonic crystal slab (PCS) with magnetic field applied perpendicularly to the plane. Many sharp transmittance resonances were found to be correlated with the modes extracted from band structure calculations, where they show red-shift and mutual approach as the external magnetic field increases. By changing the angle of the incident light, we found strong coupling modes because of their asymmetric electric field distributions. This in situ control of transmittance properties of ferrofluid-filled SiN PCS should open up new applications for designing filters, mirrors and displacement sensors in compact optical devices.