A ‘DOMZM–Filter–BPD’-Based Microwave Photonic Link for Eliminating Even Harmonics Distortion

The ‘Mach-Zehnder modulator (MZM)–wavelength division demultiplexer (WDM)–photodetector (PD)’ structure in photonic analog-to-digital converters (PADCs) may result in residual even harmonics after photodetection. In this paper, we build the model for the ‘Dual-output MZM (DOMZM)–filter–balanced PD (BPD)’-based microwave photonic link, where the amplitude and the phase responses of the filter can be arbitrary. It is proved that this link can eliminate the aforementioned even harmonics. Theoretical analysis is verified by the simulation and experimental results. By using this structure, the spur-free dynamic range (SFDR) limited by the even harmonics can be improved and the sampling frequency range can be expanded for the PADCs. As the spectrum contains only odd harmonics, the inverse cosine transform for calibrating the nonlinearity of the MZM can be applied to further improve the SFDR.