A Quadrature Biasing Method Based on Slope Detection for Si Mach-Zehnder Modulators

We propose a novel quadrature biasing method for a silicon Mach-Zehnder Modulator (Si MZM) with an on-chip heater. The proposed technique determines the quadrature point by sweeping the heater voltage while modulating the RF signal to locate the point of maximum optical modulation efficiency. The quadrature bias point can be identified by sweeping the heater voltage only within the ${{V}_\pi }$ range, instead of the full ${{V}_{2\pi }}.$ Moreover, this method can determine the slope polarity simultaneously while detecting the optimal modulation point, enabling a more robust dithering mode operation. The proposed technique is successfully demonstrated for a custom-designed Si MZM using an FPGA along with a few commercial ICs.