Photonic scheme for broadband frequency response measurement of PDs

We report a scheme to measure the broadband frequency response of photodetectors (PDs) with the capacity of self-calibration. The optical carrier at f0 is modulated through one modulator, and this modulator is driven by a microwave signal with a fixed frequency f1 to produce the carrier-suppressed double sideband optical sig-nals f0 - f1 and f0 + f1. The frequency interval of the optical signals is 2 f1. Subsequently, the two optical signals are sent to another modulator driven by a swept microwave signal fm. Two pairs of carrier-suppressed double sideband signals with a high signal-to-noise ratio are generated. The frequencies of these signals are f0 - f1 - fm, f0 - f1 + fm, f0 + f1 - fm, and f0 + f1 + fm. After the PD under test, the frequency response can be extracted from the amplitude of the microwave signals at 2 f1, 2 f1 - 2 fm, and 2 f1 + 2fm. Two PDs in our laboratory are experimentally characterized from 0.1 to 40 GHz with a resolution of 100 MHz. Compared with the traditional vector network analyzer swept method, the proposed method extends the measurement range from fm(max) to 2 f1 + 2 fm(max) and has the capacity of self-calibration to eliminate the influence caused by the modulator frequency response on the measurement results. (c) 2022 Optica Publishing Group