Numerical simulation of a passive twin-core fibre coupler ring laser based on nonlinear optical switching

We have described a comprehensive numerical model of a passive nonlinear fibre coupler laser. The effect of Raman self-frequency shift and gain saturation are both included. It is shown that the Raman effect generally limits the steady-state operation of a passive nonlinear coupler laser, and can be well controlled by employing two wideband bandpass filters. The modelocking threshold has been investigated. It is found that solitonic modelocking in such a laser can not always be realised. Gain saturation and longer nonlinear coupling length are most favourable for soliton formation in this laser