| All-dielectric metasurfaces are two-dimensional metamaterials based on dielectric materials.They have attracted great research of many scholars due to their planar structure and strong light–matter interaction at the nanoscale.Compared to plasmonic devices in which metal nanostructures are used to confine electromagnetic fields at the nanoscale,all-dielectric Mie resonators show several important differences,including compatibility with CMOS process,little Joule heating effect,low optical absorption loss and high transmittance or reflectivity.In particular,all-dielectric nanoresonance structures with high refractive contrast can achieve near-field enhancement of electromagnetic fields,excite dielectric resonance modes,and discover novel photonic phenomena that do not exist in nature.The all-dielectric magneto-optical metasurface is a new all-dielectric metasurface structure that can enhance or regulate the magneto-optical effect through the dielectric resonance modes.Several key scientific issues attract researcher’s attention to this structure:Firstly,what is the mechanism of the magneto-optical enhancement and regulation based on different dielectric resonance modes in the all-dielectric magneto-optical metasurfaces?Secondly,whether the dielectric resonant structures with strong magneto-optical effect could be developed to solve the problem of heaviness in magneto-optical materials and support the miniaturization of magneto-optical devices?Finally,whether new applications for non-reciprocal radiation control faced free space electromagnetic waves can be explored based on all-dielectric magneto-optical metasurfaces?Based on the above research status and issues,this dissertation proposed and fabricated an all-dielectric magneto-optical metasurface based on high refractive index dielectric materials and dielectric magneto-optical films and systematically studied the interaction mechanism between different Mie resonance modes and magneto-optical materials,and observed the simultaneous enhancement of Faraday rotation and magneto-optical merit,as well as the generation of new magneto-optical effects such as optical gyromagnetic material;Studied the enhancement effect of high-Q resonance modes on the magneto-optical effect and developed nano-structures with strong magneto-optical effect at the sub-wavelength scale;Explored the non-reciprocal heat absorption effect of all-dielectric magneto-optical metasurfaces in infrared band,experimentally realized single-frequency,dual-band,ultra-wideband and polarization-independent non-reciprocal heat absorption effects and discuss its potential applications in thermophotovoltaic field.The detailed research contents have following aspects:1.The mechanism of the interaction between Mie resonance mode and magneto-optical effect in an all-dielectric magneto-optical metasurface with large refractive index contrast is studied.The Si/Ce:YIG all-dielectric magneto-optical metasurface with large refractive index contrast was experimentally constructed through a magnetic oxide Ce:YIG film grown on a quartz substrate.Excitation of Mie resonance modes in disk arrays were verified based on theories such as angular dispersion spectroscopy and multipole decomposition.The characterization set-up to measure the optical spectrum of these nanostructures was built up,and the measurement results proved that the structure can achieve simultaneous enhancement of Faraday rotation and magneto-optical merit at near-infrared wavelengths.In addition,the circular displacement current induced by magnetic resonance can change the vector distribution of the local electric field,thereby producing a new magneto-optical phenomenon.Experimental results show that this structure has 6.4%s-polarized TMOKE effect,which even does not exist in planar films and bulk materials.Furthermore,we applied the transfer matrix method to retrieving the permeability tensor elements of the equivalent medium by fitting the transmission curve and magneto-optical spectrum.We found that its effective permeability tensor has non-diagonal element which reaches the order of 10-2 and this value has been improved by nearly three orders of magnitude compared with bare Ce:YIG film.This means that the structure has new properties of optical gyromagnetism,providing a new dimension for the effective manipulation of electromagnetic waves.2.The interaction between high-Q resonant modes and magneto-optical effects in all-dielectric magneto-optical metasurfaces is studied.The coupling between these multiple poles will lead to destructive far-field scattering interference,thereby reducing the scattering loss of the structure and exciting high-Q resonance mode.We proposed the Ce:YIG hole structure supporting anapole mode,which is formed by the destructive interference of the electric dipole and the toroidal dipole.It can greatly suppress far-field scattering and improve the quality factor Q value（Q～3523）.Thus,this structure can achieve a substantial enhancement of Faraday rotation while ensuring the transmittance of the structure.We also introduce the local resonance mode into the magneto-optical photonic crystal cavity and proposed a（Si O2/Ta2O5）n/Ce:YIG/Si-pillar/（Si O2/Ta2O5）nstructure,which has a high Q resonance（Q=104）and a super large Faraday rotation angle（FR=41°）.This value is 820 times higher than that of bare Ce:YIG film.This mode originates from the interaction of cavity mode,Mie resonance mode and waveguide mode.And this extreme enhancement of magneto-optical effect has made structure exhibit extremely strong non-reciprocal performance in optical frequency band.As the results,this structure can achieve an insertion loss of 2.24 d B and an isolation of 10.16 d B under circularly polarized incident light.3.The further applications of all-dielectric magneto-optical metasurfaces in non-reciprocal thermal radiation devices are studied.We built up the infrared magneto-optical Kerr effect measurement platform under large magnetic field and experimentally verify the ultra-broadband non-reciprocal thermal radiation effect for the first time based on the magnetic ENZ material InAs.The ENZ property of InAs can improve the magneto-optical effect,which will make the different between absorption under positive and negative magnetic fields achieve 0.63 under a 1.5T magnetic field.By introducing a dielectric grating structure,non-reciprocal absorption at dual frequency points can be also realized;By introducing multilayer InAs films with gradient doping concentration,ultra-broadband non-reciprocal absorption can be finally achieved.This structure can ensure strong non-reciprocal performance within a bandwidth of 10μm;By introducing the magnetic resonance mode and changing the vector distribution of local electromagnetic field,it is also feasible to break through the polarization limitation and achieve multi-polarization non-reciprocal absorption. |
