Ultrafast nonlinearities and gain dynamics in high-power semiconductor amplifiers

The limits imposed by two-photon absorption and free-carrier absorption on the gain and output powers of an InGaAsP∕InP slab-coupled optical waveguide amplifier with a confinement factor of Γ=0.5% were studied. The two-photon absorption coefficient and the induced free-carrier absorption cross section were measured to be 65cm∕GW and 7×10−17cm2, respectively. The effects of two-photon absorption begin to limit the gain significantly for pulses shorter than 40ps. The carrier recovery times were observed to vary between 390 and 160ps for 1–4A bias currents, and the short-pulse saturation fluence of the gain was determined to be 1.4mJ∕cm2.