Optical Frequency-Detuned Heterodyne for Self-Referenced Measurement of Photodetectors

A self-referenced frequency response measurement of high-speed photodetectors (PDs) is proposed and demonstrated based on optical frequency-detuned heterodyne method. Our method provides a narrow linewidth and wide-bandwidth optical stimulus consisting of acoustooptic frequency shifting and two-tone phase modulation in a Mach-Zehnder interferometer, and achieves the self-referenced frequency response measurement of high-speed PDs without the need for correcting the power variation of optical stimulus. Moreover, it allows multiplied measuring frequency range and avoids any bias drifting problem. Frequency responses are experimentally measured for a commercial PD, which agree well with the results obtained by the conventional methods.