Stimulated Raman scattering in all-fiber optical switching

Stimulated Raman scattering is analyzed as a potential mechanism for ultrafast switching and amplification in a nonlinear loop mirror (NOLM). The control pulse power requirements for the Raman switch are calculated to be practically the same as for the Kerr switch. The real and imaginary parts of the Raman susceptibility in a germanium-doped fiber for different GeO2 concentrations are derived. The stimulated Raman scattering is shown to dominate over the nonlinear Kerr effect with an increase of germanium concentration, resulting in the linear (at low Raman gain) and exponential (at greater Raman gain) transfer functions of the NOLM. An important advantage of this optical transistor is a possibility to obtain ah-optical switching and amplification in a single device. We have demonstrated experimentally an optical switch with the amplification factor of 10 using 120 ps pulses in 20 mol.% germanium-doped fiber.