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 signals f0-f1 and f0+f1. The frequency interval of the optical signals is 2f1. 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 2f1, 2f1-2fm, and 2f1+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 2f1+2fm(max) and has the capacity of self-calibration to eliminate the influence caused by the modulator frequency response on the measurement results.