Hello Zulkarnain…
As clearly explained by aaabid baba the difference between the two, i would like suggest you to go through one of the previous post here i am attaching the link of that where Reflective Semiconductor Optical Amplifiers are already discussed…
Reflective Semiconductor Optical Amplifiers [Optical System]
More allistu had briefly explained Mach-Zehnder Modulator in the previous posts…..link of that is
Hope it helps
best regards