Evolution of surface plasmon resonance with slab thickness in hybrid nano-structures of Au/InGaAs slab waveguide

We report on the evolution of the surface plasmon (SP) and waveguide mode (WM) as the core thickness is varied in InGaAs slab waveguides covered by metallic sub-wavelength slit arrays. By comparing transmission spectrum in the near-infrared region with numerical simulations, transmission dips were assigned to resonant excitations of either SPs or WMs. As the core thickness was smaller than the SP penetration depth, the resonance energy exhibits a blue shift, which scales with the field intrusion into the substrate region. For the core thickness of 400 nm supporting both the WM and SP, effective refractive index of the SP is almost constant due to the field decay within the InGaAs region, which is different to the case of the WM.