Symmetric Cladding Thin Film Waveguides: From Lossy Media to Disordered Nanostructures

Abstract

Intrinsic absorption in a waveguiding material is often considered an undesirable effect that severely limits wave propagation. However, with appropriate design of the cladding, waveguides can be made from highly absorbing materials, to the degree that stronger absorption actually increases the propagation length. Here, we discuss the permittivity landscape showing accessible optical properties of lossy materials together with their fitness for symmetric cladding thin film waveguides. The concept of Zenneck wave-like propagation in absorbing materials is extended to thin films of disordered nanocomposites. In an experimental demonstration, we show that despite intrinsic absorption and disorder, a metal–polymer composite itself can support long-range propagation of light. We have used a nanoparticle filled poly­(N-isopropylacrylamide) (PNIPAM) polymer brush that can serve as a functionalized surface. The material supports bounded optical modes with superior propagation length, exceeding its bulk absorption length by far. Waveguiding on lossy nanocomposite surfaces may bring new optical devices that combine the versatility of metal-based nanostructures with the well-defined propagation of thin film waveguides.