Hi.
The In-Phase Quadrature-Phase (IQ) optical modulator is a critical platform used in transmitter architectures designed to address these problems.
Today three types of commercial coherent IQ modulators are based on parallel inner and outer traveling-wave Mach-Zehnder interferometers (MZI). Each material system uses a different physical property to modulate the light intensity in such a traveling-wave Mach-Zehnder IQ modulator. LiNbO3 modulators are based on the electro-optic effect, InP modulators are based mainly on the quantum-confined Stark effect, and silicon modulators are based on carrier depletion. Despite the differences in the principles of operation, all three types of modulators have a fundamental limit which can be expressed as Vπ x L = constant, where Vπ is the switching voltage (voltage required to change the modulator output from its maximum to minimum) and L is the active electrode length. A low Vπ, which requires a large L and therefore a higher optical loss, can offer a lower drive voltage and thus a lower electrical power consumption. Conversely, a high Vπ gives a lower optical loss but a higher power consumption. An example is shown in Fig.1 below, where we can see that the higher the optical loss, i.e., a longer interaction between the driving signal voltage and the traveling-wave electrodes, the higher the extinction ratio is. Also, a higher driving voltage can enable a lower optical loss.
I am attaching a link you may go through it.
http://blog.neophotonics.com/coherent-iq-modulator-performance/
Thanks