Bimetallic Fe–Ag Nanopyramid Arrays for Optical\nCommunication Applications

Abstract

There\nis a pressing need to discover optical and magneto-optical\nmaterials with better performance and lower cost that operate at telecommunication\nwavelengths. Here, we report the discovery of giant negative nonlinear\nrefraction and nonlinear (photoinduced) Faraday rotation at 1550 nm\nusing an array of bimetallic Fe–Ag nanopyramids. This system\nexhibited a very large third-order nonlinear refractive index (<i>n</i>₂ = −2.32 cm²/GW) and nonlinear\nfigure of merit (<i>F</i> = 2.3). The same system also exhibited\nan extraordinarily large magneto-optical susceptibility (χ_i⁴ = 6.5 × 10^–12 esu) and nonlinear Faraday rotation up to 2.5 radian/μm\nat a magnetic field of 0.5 T. The nonlinear response was dependent\non the degree of overlap of the Fe nanopyramid on the Ag nanopyramid,\nwhich influences the strength of plasmon-induced dipoles on the Ag\nnanopyramid. This nanoscale system opens up a rich set of possibilities\nin utilizing magnetoplasmonic materials to miniaturize future multifunctional\ndevices such as frequency converters and Faraday rotators at telecommunication\nwavelengths.