Editing Mandrel wrapping (section)

==Principle of operation==

The effect of physically bending an optical fibre around a cylindrical form is to slightly modify the effective refractive index in the curved region, which locally reduces the effective mode volume of the fibre.  This causes optical power in the highest order modes to become unguided, or so weakly guided as to be released into an unbound state, absorbed by the fibre coating or completely ejected from the fibre.   The practical effect of mandrel wrapping is to attenuate optical power propagating in the highest-order modes.  Lower-order modes are unaffected, experiencing neither increased loss nor conversion into other modes (mode mixing).