Abstract

It is well known that it is possible to obtain all-optical switching by using the nonlinear response of materials to laser light, but it is also well known that to excite nonlinear contributions high local-electric fields are necessary. This means that high-intensity laser beams must be used for having switching of photonic devices between different states. On the same time it has been largely demonstrated both theoretically and experimentally that in optical fibers only low intensity beams can propagate for communication purposes, even in the case of solitonic beams, where the average powers should not be larger than few tens of mW. Thus until now no real applications of the proposed photonic devices have been done in real fiber communication networks. In the present paper we present from both the theoretical and the experimental points of view an all-optical multiplexer-demultiplexer for low-intensity pulses. In particular the devices has been projected to work for high-repetition rate mode-locked pulses, 100 and 35 ps long, with average powers of the order of few tens of mW. The device is working at the wavelength of 1.064 μm because of testing possibility, but there are no obstacles to let it work at 1.3 or 1.5 μm. The device is based on a thin Fabry-Perot cavity filled by a second-order nonlinear material. In particular it has been chosen a BBO with type I cut for second harmonic generation of 1.064 μm pulses. The basis of operation are the generation-amplification of the second harmonic. In particular the Fabry-Perot cavity is set out-of-resonance for the fundamental frequency: because of its low intensity the fundamental is not able to produce a relevant second-harmonic field and for this reason does not modify its out-of-resonance regime. However if a high-intensity second-harmonic field is sent together, the fundamental beam can be amplified, experiencing a phase-modulation which depends on the group-velocity mismatching between the frequencies and their intensity ratio. This cross-phase-modulation can be high enough to let the fundamental frequency switch from the out-of-resonance to the resonance regimes. In fig.s 1 and 2 the out-of-resonance / resonance conditions are shown respectively.

© 1998 IEEE