Photonic Generation and Transmission of Frequency-Doubled Triangular and Square Waveforms Based on Two Mach–Zehnder Modulators and a Sagnac Loop

In this paper, a new photonic approach for frequency-doubled triangular and square waveforms generation is proposed and experimentally demonstrated. The scheme is based on two single-drive Mach-Zehnder modulators (MZMs) and one of them is located in a Sagnac loop. By properly setting the working points of the two MZMs and the polarization angle of the light injected into the Sagnac loop, two orthogonal-polarization optical signals with tunable amplitudes can be obtained. One of them is the carrier-suppressed first-order optical sidebands and the other is the carrier-suppressed third-order optical sidebands. After the photoelectric conversion, we can get frequency-doubled and frequency-sextupled microwave harmonics with tunable amplitudes and the desired waveforms can be obtained. In addition, the phase relationship and the amplitude of the generated second- and sixth-order electrical harmonics will remain unchanged during fiber transmission. Thus, the scheme is suitable for fiber transmission in future centralized radio-over-fiber systems.