Power Dither Technique for Measuring the RF Half-wave Voltage of a Silicon Mach–Zehnder Modulator

A novel method to measure the radio frequency(RF) half-wave voltage of the silicon Mach–Zehnder modulator (SMZM) is presented based on a low-frequency power dither signal. In our method, the power dither is applied to the thermo-optic phase shifter built into the SMZM, and an RF modulation signal applied to the SMZM is produced by a pulse-code generator. Then, a low-frequency monitor photodiode is used to detect the output signal of the SMZM, and a pair of orthogonal trigonometric functions with the same frequency as the power dither signal is constructed. This performs the cross-correlation integral operations with the output signal of the SMZM. The aforementioned integral results versus different amplitude RF modulation signals are plotted as two third-order polynomial functions, and the intersection point of the third-order polynomial functions corresponding to the RF voltage is the half-wave modulation voltage. Compared with the conventional methods, this new method not only removes the electrical absorption effect and nonlinear electro-optic effect of the SMZM-induced measurement error but also improves measurement accuracy and reduces measurement complexity.