Nonlinear phase changes at 1310 nm and 1545 nm observed far from resonance in diode pumped ytterbium doped fiber

Resonant nonlinearities at 1310 mm and 1545 nm have been observed in diode pumped ytterbium doped fiber, with greater than /spl pi/ phase changes observed with 18 mW launched pump power. These signal wavelengths lie far from the ytterbium absorption peak centred at 980 nn, and can be explained by considering the effect of strong absorptions in the UV. It has been confirmed that these phase changes are not due to thermal effects in the optically pumped fiber.