Research on photonic generation of quadrupling triangular-shaped waveform using external modulation

We propose an improved approach to generate frequency-quadrupled triangular-shaped waveform signals based on two cascaded modulators. A dual-parallel Mach-Zehnder modulator (DP-MZM) is employed to provide the quadrupling RF modulation, after which two primary optical sidebands (±2nd) are generated in spectrum. Then a dual-drive Mach-Zehnder modulator (DD-MZM) is followed to perform the optical double sideband (ODSB) modulation and signal with four sidebands (±2nd and ±6th) is obtained. By adjusting modulation index carefully, the power ratio of ±2nd and ±6th sidebands can be tuned to 9.5 dB. A piece of single mode fiber (SMF) is applied to remove the undesired harmonic. The expression of optical intensity is approximately equal to the Fourier expansion of ideal triangular-shaped waveform. The principle is illustrated by theory, simulation, and experiment. Finally, triangular-shaped waveform signals with repetition rate of 8 GHz, 12 GHz, 16 GHz and 20 GHz are generated.