Bandgap-confined large-mode waveguides for surface plasmon-polaritons

摘要

The optical properties of a novel type of open waveguiding structure for surface plasmon-polaritons (SPPs) are experimentally investigated. The waveguide consists of a strip-like region of a gold surface confined by a periodic sequence of dielectric ridges forming a Bragg-type reflector. This bandgap structure resembles the plasmonic analogue of an antiresonant reflecting optical waveguide (ARROW) for SPPs, providing direct access to the guided plasmonic field. The main structural parameters are evaluated by numerical modeling using the finite element and finite-difference time-domain methods. We investigate field distributions of the plasmonic modes in the antiresonant Bragg-reflector waveguides with varied numbers of dielectric ridges and demonstrate a large mode-area single-mode performance at a telecom wavelength of 1550 nm. Furthermore, for an excitation wavelength of 974 nm, it is shown that different low-order modes can be selectively excited using multiple laser beams with variable phase relation. Selective excitation of single longitudinal and transversal modes of the waveguide is realized by coherent two-beam excitation. Possible sensing applications of these large-mode open waveguides are discussed.