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. 2 (Color online) Parabolic-shaped dark-dark soliton via Solutions (11) with the same parameters as those in Fig. 1 except that $b(z)=2z$.