Abstract

Wavelength division multiplexing (WDM) systems can utilize the full capacity of a single optical fiber and thereby keep up with the increasing demand for higher bandwidths within datacenters. A single mode-locked laser diode emits a comb of wavelengths and can thus, in principle, be used to generate all the channels of a WDM system. However, achieving a large channel spacing of much more than 20–30 GHz can be troublesome, since this depends directly on making the cavity smaller. To circumvent this, harmonic mode-locking can be utilized, as this increases the channel spacing while keeping the cavity size fixed. In this work, we show that a monolithically integrated 45-GHz harmonically mode-locked ring laser based on an intra-cavity Mach–Zehnder filter is feasible on a generic integration platform. True harmonic mode-locking was achieved with no measurable RF peak at the fundamental frequency. The pulse train exhibits an autocorrelation trace width of ${\sim}2.5 \;{\rm{ps}}$ FWHM, RF linewidth of ${\sim}0.44 \;{\rm{MHz}}$, and 3-dB comb bandwidth of ${\sim}240 \;{\rm{GHz}}$.

© 2021 Optical Society of America

Optical frequency comb generator based on a monolithically integrated passive mode-locked ring laser with a Mach–Zehnder interferometer

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