Photonic generation of frequency-doubled microwave waveform based on a PDM-MZM modulator

A novel and simple photonic approach for frequency-doubled microwave waveforms generation based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed and experimentally demonstrated. The PDM-MZM is driven by a local oscillation (LO) signal through a 90 degree hybrid coupler. One sub-modulator of the PDM-MZM is biased at the peak transmission point and the other sub-modulator is biased at the null transmission point. The optical signals from the two arms are polarization multiplexed at the output of the PDM-MZM and then injected into a photodetector (PD) for photoelectrical conversion. By properly controlling the amplitudes of the LO signal, the triangular and square waveforms with a repetition rate twice the frequency of the LO signal can be generated. This scheme has features of compact, low-cost structure and simple operation. Simultaneously, the frequency of the generated waveform can be tuned over a wide bandwidth since there is no optical or electrical filter involved.