Focusing an intense laser beam and its second harmonic into a glass fiber transforms the fiber into a frequency doubler. We measure the temporal evolution of both the amplitude and the phase of the second-harmonic light produced by a germanium-doped fiber and so determine the initial phase of the second-harmonic light to be Δθ = −71° ± 3°. We demonstrate that the fiber-produced green light can exceed the seeding green light even if these two beams are 90° out of phase. We also show that cross-phase modulation in the fiber can limit the maximum useful interaction length and consequently the ultimate efficiency of second-harmonic generation in fibers.
© 1996 Optical Society of America
Patrick Lambelet and Jack Feinberg, "Phase of second-harmonic light self-generated in a glass fiber," Opt. Lett. 21, 925-927 (1996)