Fig. 1. (Color online) Schematic diagram of the proposed method based on low-speed photonic sampling. MLLD: passively mode-locked laser diode, PC: polarization controller. MZM: electro-optic Mach-Zehnder modulator. DUT: device under test. MS: microwave source. PD: photodetector. ESA: electrical spectrum analyzer.

Fig. 2. (Color online) Measured electrical spectra of photonic sampling signals at different symmetric modulation frequencies for extracting the uneven response of the MLLD.

Fig. 3. (Color online) Measured uneven response p_n/p₁ induced by the comb lines from the MLLD.

Fig. 4. (Color online) Measured typical electrical spectra of the MZM under test at different modulation frequencies.

Fig. 5. Measured modulation depth and microwave driving power applied on the MZM.

Fig. 6. (Color online) Measured half-wave voltage and relative frequency response of the MZM under test with our method (red open circles) and the electro-optic heterodyne mixing method (blue solid circles).

Fig. 7. Measured electrical spectra of the repetition frequencies nf_r when the MZM works with null modulation, in the case of the PD under test.

Fig. 8. (Color online) Measured frequency response of PD under test with our method (red line) and the electro-optic heterodyne mixing method (open circles).

Fig. 9. Error transfer factor as a function of modulation depth.