A photonic-bandgap fiber includes a photonic crystal lattice with a material having a first refractive index and a pattern of regions formed therein. Each of the regions has a second refractive index lower than the first refractive index.
An optical fiber includes a cladding with a material having a first refractive index and a pattern of regions formed therein. Each of the regions has a second refractive index lower than the first refractive index.