Development of Swept Frequency Method for Measuring Frequency Response of Photodetectors Based on Harmonic Analysis

We develop a swept frequency method for measuring the frequency response of photodetectors (PDs) based on harmonic analysis. In this technique, a lightwave from a laser source is modulated by a radio-frequency (RF) signal via a Mach-Zehnder LiNbO₃ modulator, and detected by a PD under test. The measured second-order harmonic of the RF signal contains information of the frequency responses and nonlinearities of the RF source, modulator, and PD. The frequency response of the PD alone is obtained by deducting the known frequency responses and nonlinearities of the RF source and modulator. Compared with the conventional swept frequency method, the measurement frequency range can be doubled using the proposed method. Experiment results show a good agreement between the measured results and those obtained using other techniques.