Integrated frequency comb laser with narrow intrinsic optical linewidth based on a dielectric waveguide feedback circuit

TL;DR

This paper demonstrates an integrated hybrid semiconductor-dielectric waveguide laser that produces highly coherent frequency combs with an ultra-narrow linewidth of 34 kHz, achieved by extending the cavity photon lifetime on-chip.

Contribution

It introduces a novel integrated hybrid laser design with extended cavity photon lifetime using low-loss dielectric waveguides, achieving record-low linewidths for on-chip frequency combs.

Findings

Record-low intrinsic linewidth of 34 kHz achieved.

Effective optical path length extended to 6 cm on-chip.

High potential for highly coherent, electrically pumped frequency combs.

Abstract

We present an integrated hybrid semiconductor-dielectric (InP-Si$_3$N$_4$) waveguide laser that generates frequency combs at a wavelength around 1.5 $\mu$m with a record-low intrinsic optical linewidth of 34 kHz. This is achieved by extending the cavity photon lifetime using a low-loss dielectric waveguide circuit. In our experimental demonstration, the on-chip, effective optical path length of the laser cavity is extended to 6 cm. The resulting linewidth narrowing shows the high potential of on-chip, highly coherent frequency combs with direct electrical pumping, based on hybrid and heterogeneous integrated circuits making use of low-loss dielectric waveguides.