An ultrafast saturable absorber was demonstrated experimentally in AlG
aAs, operated with a photon energy below half the band gap, near 1555
nm. Both the saturation intensity and the linear transmission can be i
ndependently designed in the structure. The device is based on spatial
soliton emission from a tapered channel waveguide with a correspondin
g increase in transmission of 50%. The experimental data compare favor
ably with numerically simulated results.