I have a problem about the optical modulator measured element in Lumerical Interconnect. I want to design an asymmetric mach-Zehnder Interferometer and use an optical modulator conncted to DC source to make length difference between two arms. Despite of voltage change in DC source, I never see any shift in optical transmission, and all transmission spectra Vs. frequency or free spectral range are the same. How can I solve this problem and make one phase controbale mach-zehnder circuit?

Thanks for your attention.