Hi All
Shanmuga srinivasan i would still suggest u to upload ur .osd file so that we could see what exactly the problem is. And may be by switching to the latest versions of optisystem u could get the results u require. As rightly mentioned by Naazira Fayiqa Aabid and Aasif they gave u the underlying logic behind but i believe if u upload the file the help could be more precise rather than beating around the bushes and discussing Machzender Modulator as a whole. still i would attach a link for ur reference.
https://www.comsol.co.in/model/mach-zehnder-modulator-15061
Best Regards
Burhan