Nonlinear fiber couplers: switches and polarization beam splitters.

Propagation in a nonlinear coupler at a specified input power is like that in a linear coupler with a specified but nonsinusoidal periodic refractive index. This suggests novel schemes for reducing the switching power and leads to simple analytical expressions for ideal switches and for power-sensitive polarization beam splitters. Most importantly, we show that the critical power is reduced significantly by "freezing" a nonsinusoidal refractive index into the basic linear structure that mimics the nonlinear index above the critical power, thus biasing the nonlinear coupler.