Wavelength-selective directional coupling with dielectric-loaded plasmonic waveguides

Abstract

We consider wavelength-selective splitting of radiation using directional couplers (DCs) formed by dielectric-loaded surface-plasmon-polariton waveguides (DLSPPWs). The DCs were fabricated by depositing sub-wavelength-sized polymer ridges on a gold film using large-scale UV photolithography and characterized at telecommunications wavelengths with near-field microscopy. We demonstrate a DLSPPW-based $45\text{-}\mu \mathrm{m}$-long DC comprising $3\mu \mathrm{m}$ offset S bends and $25\text{-}\mu \mathrm{m}$-long parallel waveguides that changes from the “through” state at $1500\mathrm{nm}\text{to}3\mathrm{dB}$ splitting at $1600\mathrm{nm}$, and show that a $50.5\text{-}\mu \mathrm{m}$-long DC should enable complete separation of the radiation channels at 1400 and $1620\mathrm{nm}$. The DC performance is found to be in good agreement with full vectorial three-dimensional finite-element simulations.