Abstract

Recent investigations into the origin of the nonresonant nonlinearity, n₂, have shown that the magnitude of the effect has a resonance close to the two-photon absorption, TPA, edge [1]. Earlier experimental investigations into ultrafast all-optical switching in semiconductor waveguides have shown that the two-photon absorption TPA imposes severe limitations on the practical operation of a device [2]. Therefore, to avoid the TPA at optical communication wavelengths of around, λ =1.55 μm, semiconductors are selected with a half band-gap energy slightly above the optical communication spectral region. We have already demonstrated ultrafast all-optical switching in waveguide geometries at photon energies below half the band gap of Al_0.18 Ga_0.82As [3-5]. The previously published results have shown that the switching performance was hampered by the multi-photon absorption MPA effect, primarily the three photon absorption 3PA [4]. We have shown that the nonlinear absorption can be avoided by reducing the switching power which is achieved by employing a longer interaction length to obtain the required phase change for the NLDC to switch [6].

© 1993 Optical Society of America