Bias-Independent and Self-Calibrated Electrical Method for Microwave Characterization of Dual-Parallel Mach–Zehnder Modulators Based on Two-Tone and Bias-Swing Modulation

A bias-independent and self-calibrated measurement is proposed for the high-frequency response of dual-parallel Mach–Zehnder modulators (DPMZMs) based on two-tone and bias-swing modulation. The two-tone and bias-swing sidebands beat with each other and generate the desired low-frequency beat notes, which allows to extracting the modulation depths and half-wave voltages of DPMZMs from the sub-MHz electrical spectrum analysis. Our measurement is bias-independent due to the insensitivity to the bias voltages of the DPMZM, and it avoids any correction for the roll-off responsivity of photodetection through the specific two-tone and bias-swing modulation. Our method is experimentally demonstrated and is compared with the traditional ones for the accuracy. The proposed electrical method features bias-independence and self-calibration, providing a low-frequency photodetection and spectrum analysis for measuring high-speed DPMZMs.