the present invention relates to a type of optical fiber grating having an azimuthal refractive - index perturbation . the optical fiber includes a fiber grating that has a plurality of grating elements formed therein . at least one of the grating elements has a spatially varying index of refraction that varies azimuthally about the centerline of the optical fiber . the fiber grating acts as a band - stop optical spectral filter . in addition , since fiber - cladding modes are weakly - guided modes , their power can be easily dissipated by scattering , bending , stretching , and / or rotating the optical fiber . multiple configurations of these gratings within an optical fiber are given . methodologies are given for the fabrication of these gratings . devices are presented which can dynamically attenuate , tune , switch , or modulate the wavelength spectral characteristics of an optical signal .