Abstract

It has been understood for over twenty years that multi-photon absorption can lead to photon-number squeezed states of light, where the photon statistics are sub-Poissonian.^1-2 We present the first observation of this effect using an AlGaAs waveguide within which high intensities can be maintained over a long interact ion length (~2 mm). In this system, we investigate two-photon absorption by using ultrashort laser pulses with photon energies above the half-bandgap, and three-photon absorption by using photon energies below the half-bandgap.³ This enables us to compare the squeezing from these two mechanisms and we find that our results relate well to theory that predicts stronger squeezing by three-photon absorption than by two-photon absorption for a given nonlinear absorption. The figure shows squeezing data from the AlGaAs waveguide for photon energies (a) above half-bandgap (two-photon) and (b) below half-bandgap (three-photon).

© 1999 Optical Society of America