Photonic scheme for broadband frequency response measurement of PDs

Abstract

We report a scheme to measure the broadband frequency response of photodetectors (PDs) with the capacity of self-calibration. The optical carrier at f 0 is modulated through one modulator, and this modulator is driven by a microwave signal with a fixed frequency f 1 to produce the carrier-suppressed double sideband optical signals f 0 − f 1 and f 0 + f 1 . The frequency interval of the optical signals is 2 f 1 . Subsequently, the two optical signals are sent to another modulator driven by a swept microwave signal f m . Two pairs of carrier-suppressed double sideband signals with a high signal-to-noise ratio are generated. The frequencies of these signals are f 0 − f 1 − f m , f 0 − f 1 + f m , f 0 + f 1 − f m , and f 0 + f 1 + f m . After the PD under test, the frequency response can be extracted from the amplitude of the microwave signals at 2 f 1 , 2 f 1 − 2 f m , and 2 f 1 + 2 f m . 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 f m ( max ) to 2 f 1 + 2 f m ( max ) and has the capacity of self-calibration to eliminate the influence caused by the modulator frequency response on the measurement results.