Calibration-free scheme for frequency response measurement of a Mach–Zehnder modulator with low-frequency detection

This paper presents a novel, to the best of our knowledge, calibration-free scheme for measuring the frequency response of Mach–Zehnder modulation (MZM) using low-frequency detection. An auxiliary MZM1 modulated by a MHz-level electrical signal f 1 is utilized to generate a double-sideband optical signal, which is subsequently directed into the device under test (MZM2). The MZM2 is biased at its minimum point and driven by a frequency-swept microwave signal f m . After photoelectric converting, a fixed low-frequency electrical signal f L carrying the frequency response information of the MZM2 is generated. By sweeping f m while extracting the amplitude of f L , the frequency response of the MZM2 free from the response of the photodetector (PD) is thus determined. In the experiment, the frequency response of a commercial MZM is characterized in the frequency range from 0.1 GHz to 20 GHz with a resolution of 50 MHz. The measurement result is consistent with the vector network analyzer swept method. In addition, the new method eliminates errors introduced by the PD and reduces the requirement for a high-bandwidth PD.