A simple photonic method to generate square and triangular microwave waveforms

We report a simple photonic method to generate square and triangular microwave waveforms. Previous works normally need complicated processing of optical signals for the generation of these waveforms. Actually we find that the simplest microwave photonic link can do the same thing without any optical signal processing which is the key advantage of our method compared with previous works. The proposed signal generator only consists of a sinusoidal radio-frequency (RF) source, a conventional Mach-Zehnder modulator (MZM), and a photodetector (PD). The intensity modulated optical signal is directly coupled to a PD for square-law detection without any signal processing. By properly setting the modulation index of the MZM to 1.15 rad, a square waveform can be easily obtained. For triangular waveform generation, a 90° hybrid coupler is attached after PD to compensate the phase mismatch. Besides, neither optical nor electrical filters are needed in our link which can ensure a wide frequency range. The proposed scheme is theoretically analyzed and experimentally verified. Square and triangular waveforms at repetition rates of 3, 4, and 5 GHz are successfully generated.