Consequently, if the fibre is propagating substantial energy in affected modes, the modal distribution will be changed.
If the launch fibre is underfilled, for example as a consequence of being energized by a laser diode or edge-emitting LED, there will be no effect on the mode power distribution or loss measurements.
Ultimately, the effect of mandrel wrapping on optical measurements depends on the propagating mode power distribution.
The practical effect of mandrel wrapping is to attenuate optical power propagating in the highest-order modes.
This reveals step-like reductions in transmitted power as the diameter decreases, where each step is the point at which the mandrel is beginning to affect the next-lower mode group.