We propose a photonic approach to generate triangular waveforms based on nonlinear polarization rotation (NPR) effect in a highly nonlinear fiber. A continuous wave probe light is polarization rotated by an intensity-modulated control light through the NPR effect. By tuning the cascaded polarization controller, the undesired second-order harmonic is well suppressed after photodetection. A 90-deg hybrid coupler is used to compensate the phase mismatch between the fundamental and third-order harmonic components, so that triangular waveforms are generated successfully. The proposed approach is theoretically analyzed and experimentally verified. Triangular waveforms at repetition rates of 3, 4, and 5 GHz with full-duty cycle are experimentally generated.

We propose a photonic approach to generating frequency-doubled triangular waveforms using a dual-parallel Mach–Zehnder modulator (DPMZM). Most previous modulator-based schemes require additional processing of optical sidebands using filters or a dispersive element. In our work, optical processing of optical components is no longer necessary. The triangular waveforms with a repetition rate twice the frequency of the applied microwave signal can be directly generated by properly setting the bias and driven signal of the DPMZM. Since there is no additional optical processing, the proposed structure is cost effective. The repetition rate of the generated waveform is freely tunable over a wide bandwidth since there is no optical or electrical filter involved. The proposed approach is theoretically analyzed and experimentally demonstrated. Triangular waveforms with the repetition rates of 6, 8, and 10 GHz are successfully generated.