Hi, i had same problem i concluded this.you can see good info about transfer function mach-zehnder here :opticsystem_component_library.pdf
https://drive.google.com/open?id=0Bxkt-d32S34gblFOVnNUSlF4TUE
phi0 is 0 radians for a conventional modulator and π radians for
phase-shift modulator
so i test modulation type with bit sequence 01:
when bit sequence is 0 in phase shift modulation amplitude is high and when bit sequence is 0 amplitude is negative or low.
https://drive.google.com/open?id=0Bxkt-d32S34gaEJsVW8tRkxOOHc
but for conventional is vice versa phase shift