hi khadija
https://www.osapublishing.org/view_article.cfm?gotourl=https%3A%2F%2Fwww%2Eosapublishing%2Eorg%2FDirectPDFAccess%2F95D53BA6-A072-823B-F75B9D46A19C06A6_320226%2Foe-23-12-16177%2Epdf%3Fda%3D1%26id%3D320226%26seq%3D0%26mobile%3Dno&org=
https://www.researchgate.net/post/How_can_I_simulate_the_PM-QPSK-WDM_system_in_Matlab
http://www.diva-portal.org/smash/get/diva2:463292/FULLTEXT01.pdf
http://www.mathworks.com/matlabcentral/answers/86096-dsp-for-dispersion-compensation-by-fft-overlap-add-method
http://arxiv.org/abs/1407.1671
hop ypu might get some help from these links
with regards