Abstract

Compact and integrated optical pulse generation with a high repetition rate and a small duty cycle can benefit various applications such as integrated microwave photonics. In this work, a method to generate a repetition-frequency-doubled narrow optical pulse train based on two cascaded silicon Mach–Zehnder modulators is proposed and demonstrated. The generated frequency comb has even-order sidebands with linear phase and suppressed odd-order sidebands, which results in the transform-limited pulses in the time domain. The tunability of the repetition rate from 4.0 to 6.6 GHz and the duty cycle from 10.6% to 14.0% has been achieved. An analytic model that considers the non-ideal properties of the silicon modulators is also established and is able to reproduce the key features in the experiment. Our work shows the potential of an integrated silicon chip to generate high-speed optical pulse trains with tunable duty cycles demanded in integrated microwave photonics and integrated photonic signal processing.

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