A multimode optical fiber for continuous transmission of electromagnetic radiation at high power, wherein the fiber defines a fiber axis and includes a core and a cladding surrounding the core, and wherein the multimode optical fiber is a multimode graded-index fiber, the refraction index profile in the fiber essentially following formula (1): n ⁡ ( r ) = { n 1 ⁡ [ 1 - 2 ⁢ ( r a ) g ⁢ Δ ] 1 ⁢ / ⁢ 2 , r a ( 1 ) Δ = n 1 2 - n 2 2 2 ⁢ n 1 2 ( A ) NA = n 1 2 - n 2 2 ( B ) where Δ is formula (A), r is the distance from the fiber axis, n(r) is the nominal refractive index as a function of distance from the fiber axis, n1 is the nominal refractive index on the axis of the fiber, n2 is the refractive index of the cladding, a is the core radius, and g is a parameter that defines the shape of the profile, where the core diameter 2a is between 90 UM and 190 μM, the parameter g is between 1.2 and 1.8, and the numerical aperture (NA) of the fiber, formula (B), is between 0.2 and 0.3.