Non linear effects in monomode ytterbium doped silica fibers : cooperative luminescence Y. OUERDANE, S. MAGNE, M. DRUETTA, A. BOUKENTER, J.P. GOURE and B. JACQUIER J. Phys. IV France, 04 C4 (1994) C4-545-C4-548 DOI: 10.1051/jp4:19944131