They are two different modulator formats, in the first the second MZ is used to carve the optical power, but really the information is encoded into the phase. In the second pulses are not carved because it is NRZ.
They are two different modulator formats, in the first the second MZ is used to carve the optical power, but really the information is encoded into the phase. In the second pulses are not carved because it is NRZ.