Abstract

Strong absorption saturation has been observed in single-mode channel waveguides fabricated in CdS_xSe_1-x semiconductor-doped glass by K⁺–Na⁺ ion exchange. At wavelengths below and close to the band gap of the semiconductor the transmission of the waveguide can be increased to several times the small-signal value. However, the waveguide never exhibits unity transmission. The saturable absorption properties of the waveguide are effectively modeled by a four-level system. Hercher has given equations describing the steady-state transmission of an optically thick sample of such a system.¹ Unity transmission cannot be attained in the four-level system even at high intensities due to absorptive transitions between the upper levels (i.e., free-carrier absorption). Typical transmission curves for different values of the waveguide small-signal transmission have been calculated using the model. Good qualitative agreement is observed between the features of the experimental and theoretical curves. An important consequence of these results is that all-optical guided-wave devices fabricated in these glasses will exhibit considerable losses even in the high-intensity regime due to free-carrier absorption.

© 1988 Optical Society of America