Optical surge preventing method and system for use with or in a rare

Abstract

Optical surge preventing systems and methods for rare earth-doped optical fiber amplifiers are disclosed. The systems are so arranged as to cause any signal existing in a doped fiber section so as not to over excite the rare earth elements in the doped fiber section. In one embodiment, a background signal light with such a wavelength as to cause induced emission in the doped fiber section is always coupled into the doped fiber section regardless of whether a message signal light exists or not. The background signal light may be generated by any suitable light source or a light spontaneously emitted from either end of the doped fiber section. In another embodiment, a dummy signal light is coupled into the doped fiber section if the level of the message signal light becomes less than a predetermined value. Coupling of the background signal light or the dummy signal light into the doped fiber section may be done from either of the message signal input and output sides.