One of the most important limiting factors in linear optical transmission systems is chromatic dispersion. The research topic of this paper is the effect of second order dispersion on the output of the optical system for different input pulse shapes. This paper also studies the effect of coherent interference on device efficiency. We consider the worst-case scenario, in which there is an interference phase shift. Since different spectral components of the pulse scatter and do not arrive at the fibre output synchronously during propagation, a significant value of the propagation velocity contributes to pulse expansion; the shorter portion of an optical pulse transmits faster than its larger part, resulting in progressive joint expansion of the pulse.