ALL-OPTICAL POLARIZATION MODULATOR BASED ON SPATIAL SOLITON COUPLING

The possibility of realizing an all-optical polarization modulator is theoretically demonstrated. Basic device exploits the cross-phase modu lation effect involving spatial solitons in a Kerr-like nonlinear mate rial. It is shown that a weak wave (modulating signal) can be used to control a stronger wave (pump signal), in such a way to obtain a polar ization switch, if their input phase difference is exactly equal to 90 degrees and the two waves exhibit mutual orthogonal polarizations. Si nce the required relative phase may be difficult and sometimes impossi ble to maintain, an improved solution Is then proposed which eliminate s any effect due to random phase difference between the colliding soli tons. It is based on the adoption of a suitable control device employi ng two additional nonlinear blocks excited by solitons with equal ampl itude and linear polarization. The resulting field is then subjected t o self-phase modulation. The structure is completed by a cascade of li near and nonlinear waveguides acting as proper soliton filters. This w ay, the behavior as an all-optical polarization modulator is ensured, even in the most critical input conditions, corresponding to a phase d ifference of 12.5 degrees for our choice of the physical and geometric al parameters.