Modelling evanescent field components in metal-oxide core waveguides for nonlinear applications

•The path of the evanescent field for input soliton solution was plotted.•Four oxide-cores viz. ZnO, MgO, ZnO:Ag and TiO2 were considered.•For TiO2, the evanescent field took the form of a solitonic pulse at 600 nm.•A decrease in the evanescent amplitude with increase in input wavelength was seen.

In a thin film planar geometry, the guiding effect due to the linear index results in light confinement in the thin film layer, at the same time causing evanescent waves to decay into the outer substrate or cladding layers. The magnitude of the field in the cladding is dependent on the characteristics of the waveguide and the wavelength of the wave. In this paper, we have modelled four metal-oxide core waveguides with prime focus on the evanescent field as light propagates through these optical structures. ZnO waveguide structure is taken as the benchmark. The evanescent path resembles a soliton consistent with the input soliton solution. A comparison is also carried out with a lower metal oxide core, MgO and a higher index TiO2. The variation in refractive index with input wavelength induces second order nonlinearity in these waveguide structures. For the simulated structures, mode field distributions are plotted against the refractive index. The magnitude of evanescent field also reduces with an increase in the input wavelength for the structures. The nature of the soliton path is insightful for the development of evanescent field based sensors. Optical waveguides with metal-oxide cores can act as a cheaper substitution to nanophotonic devices and integrated optics applications. With the study of evanescent phenomena in such structures, a minimally invasive manufacturing method without disturbance to the core may be made beneficial.

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