Hi San,
Mach-Zehnder modulator is a kind of modulator which has a structure like a mach-zehnder interferometer (MZI). MZI has two arms, and the same signal is being split between the two arm. Each arm induces a different phase shift than the other arm. By changing phase shift of the arms (by applying electrical voltage to them) you can modulate the input signal at the output. For example, if the phase shifts applied by the arms have a difference of 180 degrees, the output is zero and if no phase shift is applied, you can get the whole input in the output. So you can do amplitude modulation this way.
Regards
.
