Relative frequency response measurement of Mach-Zehnder modulators utilizing dual-carrier modulation and low-frequency detection

A self-calibrated approach is proposed to measure the relative frequency response of Mach-Zehnder modulators (MZMs) based on dual-carrier modulation and low-frequency detection. In this scheme, a dual-carrier is generated by combining a continuous-wave light from a distributed feedback laser diode with its frequency-shifted replica. Through modulating the dual-carrier by a frequency-scanned single-tone microwave signal via the MZM under test biased at its minimum transmission point, a fixed low-frequency heterodyne signal carrying the electro-optic modulation response information is generated after photodetection, from which the relative frequency response of the MZM can be obtained. In the experiment, the relative frequency response of a commercial MZM is measured by using the proposed method, where the result fits in with those obtained by using the conventional optical spectrum analysis method and the microwave network analysis method. The proposed method features self-calibration, high frequency resolution, low-frequency detection, and usage of only a single frequency-scanned microwave source, which is favorable for characterizing the microwave performance of MZMs in backbone optical communication and microwave photonic systems.