Step-like structure and assisted tunneling in two coupled modulated waveguides

The propagation of an initially-localized optical beam along two coupled modulated waveguides is investigated. A universal step-like structure emerges in the propagation process once |d|delta v/v₀|v_0| ~ 1 and T = 2 π/m v₀m v_0, both for the linear and nonlinear optical waveguides. The reason is that the coupling between the two waveguides can be completely suppressed at z = m T or (2 m+1)T/2. When the nonlinearity is strong, assisted tunneling can be found for the initially-localized optical beam by slightly increasing the strength of the modulation.