LMA fibers for suppression of thermal mode instability

An optical fiber comprising a core configured to guide light propagating in a fundamental mode and at least one higher order mode, wherein:

• the higher order mode or modes have physical mode areas that are at least 60% larger than a physical mode area of the fundamental mode, to reduce thermal mode instability between the fundamental mode and the at least one higher order mode;
• a refractive index profile of the optical fiber comprises a graded-index portion and a step at a core-cladding interface of the optical fiber;
• and
• an index difference between a center of the core and a cladding is equal to or greater than 0.00141.