基于非线性偏振旋转的全正色散锁模光纤激光器偏振特性的研究

Study on Polarization Characteristics of All-Normal-Dispersion Fiber Laser Mode-Locked by Nonlinear Polarization Rotation

基于耦合的Ginzburg-Landau方程和各器件的琼斯矩阵,建立了全正色散锁模光纤激光器的数值模型,计算了腔内各点脉冲不同部分的偏振态。计算结果表明,当线性双折射较强时,光纤中脉冲的偏振态近似以拍长为周期变化,一个拍长内的演化过程为右旋椭圆偏振光-线偏振光-左旋椭圆偏振光-线偏振光-右旋椭圆偏振光。与一般的饱和吸收体不同,非线性偏振旋转等效饱和吸收体的调制深度随波片角度变化。计算了波片方位角改变时,调制深度的变化情况。相比于偏振分束器之前的1/2波片及1/4波片,偏振分束器之后的波片对调制深度的影响更大。

Based on the coupled Ginzburg-Landau equations and Jones matrix of all devices, a numerical model of an all-normal-dispersion mode-locked fiber laser by nonlinear polarization rotation is proposed. The polarization states of different points across the pulse are calculated along the cavity. It is found that when the linear birefringence of the fibers is strong, the evolution of polarization state in the fiber rounds a period of one beat length. Over one beat length, the state of polarization changes from right-handed elliptic to linear, left-handed elliptic, linear, and then back to right-handed elliptic. Different from a common saturable absorber, the modulation depth of the equivalent saturable absorber of the nonlinear polarization rotation varies with the wave plates angles. The dependence of modulation depth on wave plates angles is calculated. The results show that compared with the half wave plate and quarter wave plate before polarization beam splitter, the one after polarization beam splitter has a more obvious effect on modulation depth.