3.5 DIRECT NANOPARTICLE DEPOSITION
The Direct Nanoparticle Deposition (DND) technology, developed and com-
mercialized by Liekki Corporation (Finland), is a new fiber manufacturing
process, ideally suited for the demanding needs of advanced high-power fiber
laser applications. DND provides the flexibility to engineer the glass matrix into
which the rare-earth ions are dissolved [23]. This capability makes it possible to
increase the rare-earth (RE) concentration without sacrificing the fiber perform-
ance with effects resulting from too high local RE ion concentration [24, 25].
Furthermore, DND technology inherently provides radial control of dopants,
resulting in excellent flatness of the refractive index profile, a key attribute in
large, low numerical ...