An active optical fibre, including: a core comprised of at least a first material with at least a first refractive index; an inner cladding comprised of at least a second material with at least a second refractive index substantially surrounding the core, whereby the core and the inner cladding form an area configured to propagate pump radiation from a pump laser coupled to the optical fibre when in use; an outer cladding comprised of at least a third material with at least a third refractive index substantially surrounding the inner cladding, the third refractive index being smaller than the second refractive index, whereby the outer cladding confines pump radiation from the pump laser to the core and the inner cladding; and a coating comprised of a thermally conductive metal, graphite or other thermally conductive material substantially surrounding the outer cladding, wherein the inner cladding has a symmetry breaking shape configured to reduce impact of spatial hole-burning on absorption of the pump radiation as the pump radiation propagates through a length of the active optical fibre as compared to a circular cladding, and wherein the thermally conductive metal, graphite or other thermally conductive material of the coating supports a reduced temperature increase between the area and an outer surface of the coating via the coating and the outer cladding as compared to conventional polymer coatings and supports an increased operating temperature of the area configured to propagate pump radiation and wherein thickness of the coating is determined by desired function of the active optical fibre. a core comprised of at least a first material with at least a first refractive index; an inner cladding comprised of at least a second material with at least a second refractive index substantially surrounding the core, whereby the core and the inner cladding form an area configured to propagate pump radiation from a pump laser coupled to the optical fibre when in use; an outer cladding comprised of at least a third material with at least a third refractive index substantially surrounding the inner cladding, the third refractive index being smaller than the second refractive index, whereby the outer cladding confines pump radiation from the pump laser to the core and the inner cladding; and a coating comprised of a thermally conductive metal, graphite or other thermally conductive material substantially surrounding the outer cladding, wherein the inner cladding has a symmetry breaking shape configured to reduce impact of spatial hole-burning on absorption of the pump radiation as the pump radiation propagates through a length of the active optical fibre as compared to a circular cladding, and wherein the thermally conductive metal, graphite or other thermally conductive material of the coating supports a reduced temperature increase between the area and an outer surface of the coating via the coating and the outer cladding as compared to conventional polymer coatings and supports an increased operating temperature of the area configured to propagate pump radiation and wherein thickness of the coating is determined by desired function of the active optical fibre. <EOS>