Numerical study of short pulse propagation and switching in active two-core nonlinear fiber couplers

The propagation and switching of short pulses in an active two-core fiber nonlinear directional coupler have been investigated theoretically by using the numerical simulation method. The analysis highlight the effects of the second order coupling coefficient dispersion, the linear gain coefficient and the finite gain bandwidth on the propagation and switching of short pulses. We demonstrate that with the influences of the second order coupling coefficient dispersion, the linear gain can sharpen the switching characteristic, lower considerably the switching threshold power, as well as increase significantly the switching efficiency. On the contrary, both the second order coupling coefficient dispersion and the finite gain bandwidth, degrade the switching characteristics. The interplay between the second order coupling coefficient dispersion and the linear gain coefficient on pulse propagation can cause pulse periodic fluctuation associated with pulse compression and amplification. Additionally, pulse compression and amplification induced by linear gain can be significantly suppressed by the interplay between the second order coupling coefficient dispersion and the finite gain bandwidth on pulse propagation, consequently, as in the case of the passive fiber coupler, optical pulses tend to restore periodical coupling propagation in active two-core fiber coupler.