Mechanism of optical losses in bismuth-doped silica fibers. - Alexander S. Zlenko; Valery M. Mashinsky; Ludmila D. Iskhakova; Sergey L. Semjonov; Vasiliy V. Koltashev; Nikita M. Karatun; Evgeny M. Dianov (OFC/NFOEC, 2013)