HELLO..
Double-clad fibers are an important technology in the area of active fiber optics, particularly for high-power fiber lasers and
amplifiers.There are a variety of different designs of double-clad fibers.The simplest kind of design has a circular pump cladding and
a centered core . This is relatively easy to make and use, but in this kind of fibers there are propagation modes of the inner cladding
(related to helical rays) which have hardly any overlap with the core, so that some significant part of the pump light exhibits incomplete absorption. As a result, the gain and power efficiency are compromised
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