Patent ID: 8643942

Claim:
An optical fiber configured to compensate for thermal lensing caused by light absorption and/or amplification within the optical fiber, the optical fiber comprising: a fiber core configured to guide and amplify light along the longitudinal dimension of the fiber core, the amplification and/or absorption of the guided light causing thermal lensing in the fiber core that is induced by a change in a refractive index as a function of position along one or more dimensions perpendicular to the longitudinal dimension of the fiber core, wherein the fiber core includes a designed-in effective refractive index profile such that the designed-in effective refractive index of the fiber core changes as a function of the position along the one or more dimensions perpendicular to the longitudinal dimension of the fiber core, the designed-in effective refractive index profile being selected to at least partially offset thermal lensing in at least one dimension perpendicular to the longitudinal dimension of the fiber core when light is guided by the fiber core, wherein the designed-in effective refractive index profile is provided by a predetermined cross-sectional shape of the fiber core, wherein the predetermined cross-sectional shape is selected such that a first core dimension perpendicular to the longitudinal dimension of the fiber core is greater than a second core dimension perpendicular to the longitudinal dimension of the fiber core, and wherein at least one side of the predetermined cross-sectional shape is concave toward a central longitudinal axis of the fiber core.