Models of mode-locked fiber lasers and soliton logic gates.

摘要

A passively mode-locked dual-core fiber ring laser, similar to that first proposed by Winful and Walton, is numerically simulated incorporating losses and higher-order effects. Stable, ultrashort hyperbolic secant-like pulses with negligible chirp are found in the simulations of this laser. The laser operation is robust against perturbations; lasing action is found even when strong intra-pulse Raman scattering and changes in the cavity length are included.; However, simulations show that the laser is not self-starting; it needs relatively high input power comparable to the switching power of the dual-core fiber used in this laser cavity in order to get appropriate lasing action. To reduce the switching power, a dual-core fiber composed of one core with gain and the other core with loss can be considered. It is observed that the switching power of the input soliton is effectively reduced through the gain and loss of this dual-core fiber. We also show that this dual-core fiber can be used as an amplifier that can eliminate the unwanted pedestal or small background radiation.; Next, we present, as an alternative that can be examined experimentally, another fiber laser system which consists of a erbium-doped fiber amplifier (EDFA) as a gain medium and a passive dual-core fiber. This laser is named a hybrid dual-core fiber ring laser by us. It is also shown that a stable, ultrashort, soliton-like pulse with negligible frequency chirp can be generated. But, it has a disadvantage that the lasing action is limited by the length of fibers and the value of gain in the cavity.; Finally, we examine the soliton interactions on a passive dual-core fiber for the application of soliton logic gates. We present numerical simulations of a logic gate based on the repulsive interaction in a dual-core fiber and call it a soliton-repulsion logic gate (SRLG). The operation of the SRLG is compared to the conventional soliton-dragging logic gate based on the cross-phase modulation. It is shown that the SRLG can operate at speed of 1 Tbit/s because it can potentially overcome the timing jitter problems which restrict the operation of conventional soliton-dragging logic gate.