An optical fibre that use index-guidance formed with a low index cladding or a microstructured cladding using voids/holes or low index features (404) together with multiple high index resonant cladding features (1205, 1206). One to three resonant cross sectional extending structure act as a filter by resonantly coupling light out to part of the cladding (1202) or other structures (fx. a high index outer cladding ring) that acts as light sink(s) at one to three wavelength when using one to three materials or features with different size, shape, refractive index profile or normalized frequency parameter. The fibre can be asymmetrical. The fibre can be adapted for suppression of higher order modes (HOM) and/or guiding light in a narrow spectral wavelength range and act as a band pass filter. For enhancing out-coupling the high index features can be arranged along two intersecting lines tangentially positioned in relation to the core and along a line that extends from the core and intersects the tangentially positioned lines. Light absorbing material such as samarium can be used in the light sink. The fibre can be used in a fibre amplifier or fiber laser.