Investigation of multilayer microstrip electrode for an asymmetric Mach-Zehnder modulator

In the condition of velocity matching and impedance matching, Mach-Zehnder modulator can obtain large bandwidth and low driving voltage. Based on Wheeler's transformation of multilayer microstrip line, effective permittivity of microwave has been analyzed. Both the microwave index and characteristic impedance are affected by the thickness and the width of microstrip electrode. In order to achieve velocity matching and impedance matching simultaneously, a compensation layer is placed on the electrode. The optimal thicknesses of the electrode and the compensation layer as well as the width of electrode have been obtained. Based on single-mode condition, an asymmetric Mach-Zehnder modulator (AMZM) has been designed and simulated by effective index method and finite-difference beam propagation method (FD-BPM). The initial phase difference between the two arms of the modulator has been achieved 0.522 pi in the linear region. Comparing with the typical MZM, AMZM can get a larger value of f (3dB) , increased by 67.32%.