A mircrostructured optical fiber that guides light in a core region, where the fiber has a cladding region that includes a background material and a number of cladding features or elements that are elongated in the longitudinal direction of the fiber and have a higher refractive index than the cladding background material. The core region has a lower effective refractive index than the cladding, and the fiber may guide light in the core by photonic bandgap effects.