Bilinear Forms and Dark-Dark Solitons for the Coupled Cubic-Quintic Nonlinear SchrÕdinger Equations with Variable Coefficients in a Twin-Core Optical Fiber or Non-Kerr Medium*

Mei-Xia Chu,Bo Tian,Yu-Qiang Yuan,Ze Zhang,and He-Yuan Tian

Fig. 5 (Color online) Overtaking interaction between the parabolic-shaped two dark-dark soltions via Solutions (13), with $p_1=1+{i}/{3}$, $p_2=1+i$, $c_1=1$, $c_2=-1$, $\mu_1=({\sqrt{13}}/{3})$, $\mu_2={5}/{3}$, $v=-1$, $R={3}/{10}$, $\xi_1^{(0)}=2$, $\xi_2^{(0)}=0$, and $b(z)={1}/{7}+({7}/{10})z$.