Photonic generation of rectified cosinusoidal and sinusoidal shaped microwave waveforms with tunable duty cycle

We propose a photonics scheme to generate rectified cosinusoidal shaped (RCS) and rectified sinusoidal shaped (RSS) microwave waveforms and the duty cycle of the generated waveforms can be freely tunable. In this proposed method, two cascaded Mach-Zehnder modulators (MZMs) with polarization sensitive characteristics are employed. By setting the rotation angle of polarization controller, phase shift of the phase shifters and modulation index of the front MZM’s (modulation index of the rear MZM is unfixed) properly, the obtained RCS and RSS microwave waveforms with arbitrary duty cycle by the superposition of beating signals, can be seen as an approximation of the first three terms of the Fourier series expansion of the ideal waveforms. The detailed theoretical analysis and simulations are given. In the simulations, the duty cycle of 100%, 80% and 50% of the RCS and RSS microwave waveforms are successfully obtained. Also, fitting errors are introduced to measure the similarity between the generated waveforms and the ideal waveforms. Different from previous works, the RCS and RSS microwave waveforms can be both generated by our scheme and the duty cycle is freely tunable. Moreover, the modulation index of the rear MZM is unfixed, thus increasing the flexibility of the scheme.