Figure 2

Schematic of possible working situations, corresponding to waveguides with infinitely large cladding as illumination sources. Environmental illumination is achieved via radiation losses due to sinusoidal modulation of the core radius. (a) Application in air or a medium with significantly lower refractive index than the core. (b) Application in a working medium whose refractive index is a bit lower than that of the core. In the latter case, the medium itself acts as an effective cladding, forming a step-index waveguide.