Table 1.

Features of index guiding waveguides with high or low refractive index contrast (λ refers to the wavelength of the guided light).

Properties	High refractive index contrast	Low refractive index contrast
Radius of curvature	short	large
Propagation loss	high	low
Mode field	small	large
Coupling with optical fiber	bad	good
Evanescent field in air	large	small
Waveguide width	λ and sub-λ	several λ