Hello zulkarnian,
First of all i would like to mention that RSOA and MZ modulator are two different things. One is amplifier and the other is modulator that modulated the optical signal with the information signal. No doubt , both can be put into various applications and differently like MZ can be used to design a switch etc but it is primarily used as modulator. However, RSOA can be used as a modulator but i have not heard of MZ being used as an amplifier.
Regards