Abstract

All-optical switches have attracted much attention due to their potential application in high speed optical communication systems. Among the many concepts that have been studied are pump/probe nonlinear etalon devices, both in InGaAs/InP¹ in the wavelength range of 1.5μm and in GaAs-based structures²at 0.85μm. In general, the excite (pump) and probe wavelengths have to be different, to avoid probe absorption. The use of a single wavelength but different states of polarisation in the pump and probe beams to produce switching has been investigated in CdS.³ In this case, the device relies on the natural dichroism of a CdS crystal platelet, to absorb only light of a specific polarisation, which is chosen to be the pump. InGaAs/InP quantum wells exhibit much larger dichroism for TE/TM polarisations and we have observed large refractive index changes at wavelengths away from the bandedge.⁴ Reported below are experiments where a single wavelength was used, together with the large splitting between the heavy and light hole absorption bandedges in InGaAs/InP quantum well waveguides, to demonstrate a two- polarisation switch with signal gain. The waveguide, with uncoated facets, is a nonlinear Fabry-Perot etalon, whose refractive index can be changed by the absorption of the pump beam which in turn changes the cavity transmission characteristics sensed by the probe beam. This type of device could have important applications, as it uses a single wavelength and offers cascadability and compatibility of all-optical switching with optical fibre communications.

© 1995 Optical Society of America