Kramers Kronig Dispersion Relations and MZ Modulator

Wavelength detuning in MZ modulator is important parameter as the change in Index of Refraction depend on absorption coefficient change alpha. The larger detuning leads to larger loss due to alpha change from Kramers Kronig Relation. If the absorption peak is situated further away from operating wavelength, the change of refractive index is small and hence need larger voltage for sufficient pi phase shift. We can use absorption measurements and Reflectance measurements to calculate the real part of refractive index and the phase. this will enable us to find optimum parameters for the devices.Refractive Index change is highly polarised due to its dependence on change in Alpha which is the transition between electron state E1 and heavy holes state HH1 tends to be TE polarised. The change in refractive index is due both QCSE and Pockels effect even though Pockels effect is in the order of magnitude smaller compared to QCSE effect nonetheless not negligible when the detuning is much larger than 160nm.