Shinji Hayashi
Kobe University
Shinji Hayashi is an emeritus professor of Kobe University, Japan and currently a senior researcher at Moroccan Foundation for Science, Innovation and Research (MAScIR), Rabat, Morocco. He has been an associate professor at Kobe University from 1986 to 1996 and professor at Kobe University from 1996 to 2013. He has been working in the fields of optical properties of nanomaterials (metal, semiconductor, carbon) and plasmonics, and currently working on Fano resonances in multilayer systems. In 2012, he received the Fellow Award from the Japan Society of Applied Physics (JSAP).
Over the past decade, a great effort has been made to realize the Fano resonance in optical spectra of plasmonic nanostructures and metamaterials. High-Q Fano resonances have potential applications such as optical sensors and switches. However, the fabrication of desired nanostructures is time consuming and high cost, preventing real applications. Very recently, we have demonstrated both theoretically [1] and experimentally [2] the feasibility of realizing sharp Fano resonances in metal-dielectric multilayer structures, which can be fabricated without nanofabrication. The Fano resonance is a consequence of coupling between a surface plasmon polariton (SPP) mode acting as a bright mode and a planar waveguide (PWG) mode acting as a dark mode. Sharp Fano resonances were clearly observed in the attenuated total reflection (ATR) spectra of Kretschmann configurations consisting of Ag and organic dielectric layers [2].
To widen the applicability of our Fano structure, in particular to the UV light region, we prepared Al-based multilayer structures with inorganic dielectrics and studied experimentally and theoretically their Fano characteristics. Figure 1 shows schematically the sample attached to a prism (Kretschmann configuration). Figure 2 shows a typical angle-scan ATR spectrum obtained for the present sample. Without the Al2O3 waveguide layer, we observe only a broad dip corresponding to the excitation of SPP mode. However, in the presence of Al2O3 waveguide layer, we observe a sharp Fano resonance (TM0F). The experimental spectrum (dots) is in good agreement with a theoretical curve (solid line) obtained by an electromagnetic calculation. One of the advantages of utilizing Al is its broad SPP resonance, to which the waveguide mode can easily be tuned. The present Fano structures exhibit Q factors an order of magnitude larger than those reported recently for plasmonic nanostructures, demonstrating high potentiality for a variety of applications.
[1] S. Hayashi et al., APEX, 8, 022201 (2015), J. Phys. D : Appl. Phys., 48, 325303 (2015).
[2] S.Hayashi et al, APL, 108, 051101 (2016) .
