Large Raman gain and nonlinear phase shifts in high-purity As_2Se_3 chalcogenide fibers

Third-order Kerr nonlinearities and Raman gain are studied experimentally in high-purity ${\mathrm{As}}_2{\mathrm{Se}}_3$ optical fibers for wavelengths near 1.55 µm. Kerr nonlinear coefficients are measured to be nearly 1000 times higher than those for silica fibers. In pulsed mode, nonlinear phase shifts near 1.2-π rad are measured in fibers only 85 cm long with peak pulse powers near 3 W. However, there are nonlinear losses near 20% for nonlinear phase shifts near π. By use of a cw optical pump, large Raman gains nearly 800 times that of silica were measured. In the cw case there were losses in the form of index gratings formed from standing waves at the exit face of the fiber. Discrete Raman amplifiers and optical regenerators are discussed as possible applications.