超短光脉冲在有源三芯非线性光纤耦合器中开关和传输特性的数值分析

Numerical Study of Ultrashort Optical Pulse Propagation and Switching in Active Three-Core Nonlinear Fiber Couplers

基于耦合非线性薛定谔方程(CNLSEs),利用分裂步长傅里叶方法(SSFM),研究了超短光脉冲在有源三芯非线性光纤耦合器中的传输和开关特性。重点分析了在一阶色散耦合系数和二阶色散耦合系数的影响下,线性增益系数和有限增益带宽对脉冲传输和开关特性的影响。研究表明,线性增益系数能增大开关陡峭性、降低开关临界能量、提高开关效率;虽然有限增益带宽使耦合器开关特性变差,但是它不仅能显著抑制由线性增益系数引起的脉冲压缩和放大,而且还能有效抑制由一阶色散耦合系数引起的脉冲展宽和分离以及由二阶色散耦合系数引起脉冲高频振荡,使光脉冲在三纤芯间呈现出类似无源光纤耦合器那样的周期性耦合传输特性。

Based on coupled nonlinear Schrodinger equations （CNLSEs） and the split-step Fourier method （SSFM）, the ultrashort optical pulse propagation and switching in active three-core nonlinear fiber couplers are numerically investigated. The effects of linear gain coefficient and finite gain bandwidth on pulse propagation and switching have been highlighted, considering the influences of the first and second order coupling coefficient dispersion. It is demonstrated that the linear gain coefficient can sharpen the switching characteristic, lower considerably the switching critical energy, and increase significantly the switching efficiency. Though the finite gain bandwidth of the linear gain degrades the switching characteristics, it not only can suppress significantly the pulse compression and amplification induced by linear gain, but also can suppress effectively the pulse distortion even pulse breakup due to the first order coupling coefficient dispersion as well as the pulse high-frequency fluctuation caused by the second order coupling coefficient dispersion. Because of the effects of the finite gain bandwidth of the linear gain, optical pulses tend to restore periodical coupling propagation in active three-core nonlinear fiber couplers as in the case of the passive fiber couplers.