hi sahil singh…
Double-clad fibers is indeed a very important technology in the area of active fiber optics, particularly for amplifiers and high-power fiber lasers.It allows cladding pumping of fiber devices. Here, the laser light propagates in a single-mode (or multimode) core, which is surrounded by an inner cladding in which the pump light propagates. Only the core (or sometimes a ring around the core) is rare-earth-doped. The pump light is restricted to the inner cladding by an outer cladding with lower refractive index, and also partly propagates in the single-mode core, where it can be absorbed by the laser-active ions. The inner cladding has a significantly larger area (compared with that of the core) and typically a much higher numerical aperture, so that it can support a large number of propagation modes, allowing the efficient launch of the output, e.g. of high-power laser diodes (e.g. beam-shaped high-power diode bars), despite their poor beam quality.
with regards