Nonlinear effects in rare-earth-doped fibers and waveguides

The purpose of the present paper is to report on the activities carried out in our laboratory in the pursuit of a rare-earth element that provides large nonlinearity and fast speed of response. Along the way, we also developed many useful devices based on this nonlinearity. Obviously, the nonlinearity is proportional to the concentration of the rare-earth in the fibre. However, the concentration is limited by the clustering effect. Our experience shows that the concentration for the onset of clustering increases in the following order: Sm, Nd, Yb and then Er. Finally, this paper also reports on the generation of second harmonics (SHG) in germanium/phosphorous/samarium doped planar waveguides.