In this article, we employ the nonlinear complex conformable Kundu–Eckhaus model which represents the propagation of the ultra-short femtosecond pulses and the rogue wave in an optical fiber. The exact and solitary wave solutions of this model are obtained for the first time in the framework of the modified extended tanh-function method. The obtained results give a good interpretation for the propagation of ultra-short femtosecond pulses and the rogue wave in an optical fiber. A comparison between our result and that obtained in previous work is listed. The constructed method can be applied to many other nonlinear evolution equations.