As when in case of machzender-modulator a voltage is applied across one of the arms, a phase shift is induced for the wave passing through that arm. When the two arms are recombined, the phase difference between the two waves is converted to an amplitude modulation. I think You must have problem with your design because we don’t have any problem in using machzender-modulator in optisystem 13 or 14 version.
The attachments by AAsif sir works successfully and will clear your doubt