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