Orthogonally-polarized soliton interactions for all-optical logic

Abstract

Spatial soliton interactions can be used for switching and logic. Logic gates must have gain, high contrast, three-terminal operation, and be logically complete. In addition, phase-insensitivity is a system requirement for an optical logic gate, therefore we will only consider the use of solitons of orthogonal polarizations, resulting in phase-insensitive attraction between the two beams. Consider the case of 1-D asymmetric spatial soliton dragging in a waveguide [1] as illustrated in Figure 1. In the absence of a weak signal, a strong pump soliton propagates the length of the gate without diffracting and passes through an output aperture. In the presence of a weak signal spatially overlapping the pump at the input to the nonlinear medium and propagating at an angle relative to the pump, the two solitons form a bound pair and propagate off to the side so that the pump no longer passes through the aperture, thus forming an inverter with gain and high contrast. If only the undragged pump soliton, in the absence of the signal, is passed on to subsequent stages, these inverter gates become true three-terminal devices, which restore signal level and position, and can be cascaded to form logically-complete NOR gates. Asymmetric spatial soliton dragging is the analog of temporal dragging in a fiber [2, 3]. Phase-dependent dragging of spatial solitons of the same polarization has been demonstrated [4], albeit without gain.