Experimental study of second-harmonic-generation saturation in fibers by phase modulation between the fundamental and second-harmonic writing beams

We study saturation of photoinduced second-harmonic generation in a Ge-doped silica fiber by modulating the relative phase between the fundamental and second-harmonic writing beams. We shift the phase by pi and present measurements that identify saturation that is due to site depletion and saturation that is due to a backfield.