Measurement of α-parameter for push-pull operation of π phase-shift MQW Mach-Zehnder modulator

Two swept signals (2-20 GHz) with a phase difference of 180° are required in order to use the fibre frequency response measurement technique to determine the α-parameter of a Mach-Zehnder modulator for the push-pull modulation format. It is shown that the mismatch in the magnitude and phase responses of a microwave assembly used to obtain these signals permits accurate determination of the α-parameter. Good agreement is obtained between experimental and theoretical results for the dependence of the α-parameter on the voltages applied to the two arms of a π phase-shift MQW Mach-Zehnder modulator with asymmetric Y-branch waveguides