Photonic versatile waveform generation based on phase modulation in Sagnac loop

A photonic versatile waveform generator based on phase modulation in a Sagnac loop is proposed and experimentally verified. A continuous-wave light is modulated by a sinusoidal signal in a phase modulator to generate optical sidebands. Combined with a polariser, the Sagnac loop is used to manipulate the carrier of the modulated signal. Then, a fibre Bragg grating is applied to attenuate one of the first-order sidebands. By properly choosing the modulation index and the polarisation state of the light wave output from the Sagnac loop, versatile waveform sequences can be generated. In the demonstrating experiment, full-duty-cycle sawtooth, triangular and square waveform sequences are successfully generated. The proposed photonic microwave waveform generator features the advantages of a simple structure, low cost, being free from bias drift and tunability in repetition rate.