Continuous-wave two-photon absorption in a Watt-class semiconductor optical amplifier.

We report the observation of photoluminescence produced by the recombination of free carriers generated via continuous-wave (CW) two-photon absorption (TPA) in a packaged, low-confinement (Gamma approximately 0.5%) InGaAsP/InP quantum-well slab-coupled optical waveguide amplifier (SCOWA) having a saturation output power of 0.8 W and 1/e-mode-field diameters of 5 x 7 microm. Photoluminescence power measured at the wavelength corresponding to the bandgap wavelength of the SCOWA's InGaAsP waveguide (lambda(G) approximately 1040 nm) exhibits a quadratic dependence on the amplifier's 1540-nm output power. Comparison between measured and simulated CW gain saturation data reveals that the combination of TPA and TPA-generated free-carrier absorption (FCA) limits the CW output intensity of high-power, low-confinement semiconductor optical amplifiers and semiconductor lasers.