The role of index contrast in dielectric optical waveguides

The refractive index contrast plays a fundamental role in determining the characteristics of an optical dielectric waveguide and a higher index contrast permits to move towards larger scales of integration and to access new devices and functionalities. In this paper, the impact of the index contrast on the characteristics of dielectric waveguides such as single mode regime, losses, fibre to waveguide coupling efficiency, minimum bending radius, mode hybridness, birefringence, polarisation effects, repeatability and stability, scale of integration, realisable circuits, technological constraints and available materials are investigated. Both classical step index waveguides and multilayer structures that engineers the contrast are considered.