Exciting the optical response of nanowire metamaterial films on the tip of optical fibres

The coupling between light and sur-face plasmon-polaritons (SPPs) in thin metallic films is very sensitive to variations of the optical properties of the surrounding medium [1, 2] and is extensively used as the sensing principle for a wide range of detecting and meas-uring devices, including optical fibre based sensors [3, 4]. Only light modes with electric field components perpen-dicular to the surface of the metal can excite SPPs and therefore most of the fibre based sensors are adaptations of the Kretschmann configuration [5] consisting of a thin me-tallic film deposited in a side-polished or tapered fibre [6, 7]. The challenge in developing plasmonic sensors using metallic films deposited on the tip of a cleaved fibre is that the electric field of the guided modes in the fibre is mostly parallel to the surface of the metal, and therefore unable to excite SPPs. To circumvent this difficulty, other proposals have replaced the thin film with metallic nanostructures with geometries capable of supporting SPPs, or rely on other sensing principles [8]. The majority of these devices is fabricated directly on the fibre tip, requiring complex and expensive/high-cost techniques such as electron beam/UV lithography and focused ion beam [9]. Such structures include metallic metamaterials (MMs), such as nanorods or nanostripes [10–13].