Abstract: A high power fiber laser is configured with a multimode active fiber and input and output single mode passive fibers butt-spliced to respective opposite ends of the active fiber. If the input passive and active fibers do not have substantially matched diameters, a SM radiation coupled into the active fiber may excite fundamental and high order modes which, while interfering with one another, create a non-uniform distribution of refractive index in each of forward and backward light propagation directions along the resonator of the laser. The variable longitudinal perturbation components of the refractive index in respective forward and backward directions along an optical path in the active fiber are distributed in accordance with respective cosine functions.

Abstract: A high power fiber laser is configured with a multimode active fiber and input and output single mode passive fibers butt-spliced to respective opposite ends of the active fiber. If the input passive and active fibers do not have substantially matched diameters, a SM radiation coupled into the active fiber may excite fundamental and high order modes which, while interfering with one another, create a non-uniform distribution of refractive index in each of forward and backward light propagation directions along the resonator of the laser. The variable longitudinal perturbation components of the refractive index in respective forward and backward directions along an optical path in the active fiber are distributed in accordance with respective cosine functions.

Abstract: A powerful fiber laser system is configured with at least one gain block. The gain block includes an input fiber guiding a pump light, a multiclad active fiber receiving the pump light so that a major portion is absorbed in the core of the active fiber while a minor portion of the pump light propagates in the inner cladding of the active fiber, and a multiclad output fiber. The multiclad output fiber is configured with a core, guiding a signal lased by the core of the active fiber upon absorption of the major portion of the pump light, an inner cladding receiving the minor portion of the pump light and an outer cladding. The inner and outer claddings of the multiclad output fiber have respective refractive indexes which are selected so that the refractive index of the outer cladding is higher than that one of the inner cladding.

Abstract: A powerful fiber laser system is configured with at least one gain block. The gain block includes an input fiber guiding a pump light, a multiclad active fiber receiving the pump light so that a major portion is absorbed in the core of the active fiber while a minor portion of the pump light propagates in the inner cladding of the active fiber, and a multiclad output fiber. The multiclad output fiber is configured with a core, guiding a signal lased by the core of the active fiber upon absorption of the major portion of the pump light, an inner cladding receiving the minor portion of the pump light and an outer cladding. The inner and outer claddings of the multiclad output fiber have respective refractive indexes which are selected so that the refractive index of the outer cladding is higher than that one of the inner cladding.