Waveguide index contrast: implications for passive integrated optical components

The index contrast increase of integrated optical waveguides permits to move towards very large scale of integration of photonic integrated circuits, mainly because of the very small bending radius achievable. Furthermore, high index contrast waveguides allow to access new devices, such as ring resonators, more compact and with better spectral characteristics. These two invaluable advantages push to consider new technologies, new materials and new solutions to exploit the integrated optic world. Trying to see the index contrast as a free parameter in the design of a dielectric waveguide, we discuss the general properties and the main impairments of high index contrast waveguides. Not always an increase of the index contrast corresponds to an increase of the waveguide and circuit criticity.