Optical EngineeringHigh-power monomode fiber lasers
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The output power of cw monomode fiber lasers, commonly operated far below 1 W, can be enhanced using a double-clad fiber structure. Double-clad fibers can be excited with powerful multimode laserdiode arrays. An output power of several watts has already been demonstrated in a Nd3+-doped double-clad fiber. A further enhancement of the laser power can be achieved by side pumping the fiber. An upper limit of the order of 100 W given by the damage threshold of the fiber can be estimated for a multi-side-pumped system. As for the case of crystal lasers, even more output power in the fundamental mode can be obtained by coherent combination of several lasers. This procedure can be performed by active phase adjustment between identical lasers: The adjustment of the phase can be realized rather elegantly in fibers by squeezing or stretching the fibers with a piezoelectric element. Even if we are still far from the practical realization of a 100-W monomode fiber laser, all the different steps leading to high output power have been demonstrated to work.