Characterization of laser-written dielectric-loaded surface plasmon polariton waveguides by leakage radiation microscopy

Abstract

We study the guiding properties of laser-written dielectric-loaded surface plasmon polariton waveguides (DLSPPWs). The guiding structures such as straight waveguides, S-bends, Y-splitter, resonant filters, and Mach- Zehnder interferometers are realized by two-photon induced polymerization of commercial photolithographic resists. The height of the components can be adjusted by spin-coating of the material. Minimum widths of 400 nm of the DLSPPWs fabricated directly on thin metal films can be achieved. Replica molding of polymer surface structures allows a further reduction of the DLSPPW width down to 200 nm. The DLSPPWs are characterized by leakage radiation microscopy in the visible and near infrared spectral region. We demonstrate the possibility to selectively excite different modes in the waveguides. Fourier-plane imaging allows a direct observation of the excited modes of the DLSPPWs. The simultaneous excitation of fundamental and higherorder modes results in a mode-beating, providing the possibility to control the splitting ratio of guided SPPs in Y-splitters. The experimental results are supported by theoretical modelling using the finite-difference time domain method.