Abstract

Ultrafast all-optical switching has been demonstrated in a number of silica fibre interferometric devices. In particular, the nonlinear optical loop mirror (NOLM), first fabricated by us, has been successfully used to demonstrate stable ultrafast multiplexing/de-multiplexing for high bit-rate optical fibre communication systems and for pulse shaping and pedestal supression. The switching power tends to be generally high due to the small nonlinearity of fused silica. However, the signal switching powers can now be reduced to the order of microwatts with the use of fibre amplifiers due to demonstrably stable operation of NOLMs with very long loop lengths (> 5 km). The NOLM exhibits a sinusoidal CW transmittance as a function of the input power. The development of an ultrafast digital optical switch for all-optical signal processing is attractive [1], requiring that the switching characteristics be sharper than sinusoidal. One approach to synthesizing a digital switching characteristic is to concatenate nonlinear fibre interferometric switching devices. In this paper we present the results of the first switching experiment involving two concatenated NOLMs. Digital switching characteristics are obtained. The device can also be used for generating nearly square pulses.

© 1991 Optical Society of America