Topologically optimized periodic resonant nanostructures for extraordinary optical transmission [Invited]

Extraordinary optical transmission (EOT) is the phenomenon of greatly enhanced transmission of light through a subwavelength aperture in an otherwise opaque metallic film which has been patterned with a regularly repeating periodic structure. It was firstly described by Ebbesen et al. in 1998 [1]. In EOT, the regularly repeating structures enable much higher transmissivity to occur, up to several orders of magnitude greater than that predicted by classical aperture theory. The mechanism of EOT is attributed to the scattering of surface plasmon polaritons (SPPs) [2,3]. EOT offers one key advantage over a surface plasmonic resonance (SPR) device, which is a nanometer-micrometer scale device, and it is particularly amenable to miniaturization. This paper presents the inverse design of resonant nanostructures for extraordinary optical transmission of periodic metallic slits, where the topology optimization approach is utilized to implement the inverse design procedure and find the geometrical configurations of the nanostructures. By using the inverse design method, the subwavelength-sized resonant nanostructures, localized at the inlet and outlet sides of the periodic metallic slits, are derived with transmission peaks at the prescribed incident wavelengths. The transmissivity is enhanced by effective excitation and guidance of surface plasmon polariton at the inlet side of the slits, the coherent resonance of surface plasmon polariton inside the slits, and radiation of the photonic energy at the outlet side of the slits. The transmission peaks of the periodic metallic slits, with inversely designed resonant nanostructures, are raised along with the red shift of the incident wavelength. The position of the transmission peak of periodic metallic slits can be controlled and localized at the desired frequency, by specifying the incident wave with the wavelength corresponding to the desired frequency preset in the inverse design procedure. By maximizing the minimum transmissivity of the periodic metallic slits with incident wavelengths in a prescribed wavelength range, the extraordinary optical transmission bandwidth can be enlarged, and the sensitivity of transmissivity to wavelength can be decreased equivalently. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Extraordinary optical transmission (EOT) is the greatly enhanced transmission of light through a subwavelength aperture in an opaque metallic film patterned with a periodic structure, attributed to the scattering of surface plasmon polaritons (SPPs). The inverse design method can be used to enhance the transmissivity and control the frequency of periodic metallic slits.