The Mach-Zehnder modulators, Mach-Zehnder modulator (MZM), are external modulators Mach-Zehnder interferometer-based, which uses the principle of constructive and destructive interference between the phases of the signals that propagate by each arm of the modulator.The MZM consists of two parallel waves guides and of same length, usually manufactured by an alloy of lithium Niobate (LiNO3), which exposes properties that cause the variation of the refractive index as a function of electric field applied. Each of the waveguides is inserted inside of a pair of electrodes which allow the application of an electric field on the same.The MZMs have an important phase modulation parameter that can be printed to the modulated signal. You can obtain a free modulation chirp, which is often desired. The two arms of the modulator are controlled by the same voltage amplitude, but with opposite signs. This way, the phase term becomes null. This condition is known as control balanced or push-pull operation. And due to the possibility of working with high rates of transmission, being independent of them, with the possibility of modulate the intensity and phase of the optical field independently, the MZMs are part of most advanced optical modulation formats displayed, i.e. its use is necessary to obtain these formats of desired modulations:
ACRZ: Alternative-chirp return-to-zero
AMI: Alternate mark inversion
AP: Alternate-phase
CAPS: Combined amplitude phase shift
C-NRZ: Chirped non-return-to-zero
CRZ: Chirped return-to-zero
CSRZ: Carrier-supressed return-to-zero
DB: Duobinary
DCs: Duobinary carrier suppressed
DST: Dispersion-supporterd transmission
M-ASK: Multilevel amplitude shift keying
Pass: Phase amplitude shift keying
PSBT: Phase-shaped binary transmission
SSB: Single side band
VSB Vestigial side band.