FIELD: physics.
SUBSTANCE: fibre has a core which contains a rare-earth element, inner cladding surrounding the core and outer cladding which surrounds the inner cladding. The outer cladding is a polymer cladding. The inner cladding has a polygonal cross-section which does not have second order rotational symmetry so that the form of the boundary between the inner cladding and the outer cladding is polygonal and does not have second order rotational symmetry. The difference between the maximum outer diameter and the minimum outer diameter of the polygonal cross-section of the inner cladding is 6% or less of the average outer diameter. The polygonal cross-section of the inner cladding has 15 or less sides. Fibre may be used as a radiation-amplifying medium in the fibre laser or amplifier.
EFFECT: low level of the twisted mode.
7 cl, 10 dwg
