Optical fiber filter of wideband deleterious light and uses thereof

Optical fiber filters and uses thereof are presented. In typical implementations, there is provided a FBG taking deleterious light out of a fiber core without reflecting it into the fiber core. It also allows the unhindered transmission of useful light at a wavelength outside of the spectral band covered by the deleterious light. The filter couples the incoming deleterious light to cladding modes propagating in the opposite direction without coupling the incoming useful light to core or cladding modes propagating in the opposite direction. The filter may for example be useful as a Raman or ASE filter in a laser cavity of other optical devices.