In this work, we studied MMI and Y-junction based Mach-Zehnder modulators on both silicon-on-insulator and polymer based on thermo-optic effect. Both Pπ values and frequency response of the devices were measured and found to be consistent with those observed in the literature as well as results obtained from finite element simulations. We feel that our BCB based Y-junction modulators have the highest reported 3 -dB cut-off frequency to date. We also observe that all of our devices are polarization independent, an important feature for applications in optical communications.