Hybrid integrated mode-locked laser diodes with a silicon nitride extended cavity

TL;DR

This paper demonstrates a high-performance, externally extended cavity mode-locked laser using silicon nitride waveguides, achieving significantly narrower RF linewidths than monolithic InP platforms, enhancing laser performance.

Contribution

First demonstration of a chip-scale silicon nitride extended cavity for integrated mode-locked lasers with superior RF linewidth performance.

Findings

Achieved mode-locked lasers at 2.18 GHz and 15.5 GHz.

RF linewidth of 31 Hz at 2.18 GHz.

Significantly narrower linewidths than monolithic InP lasers.

Abstract

Integrated semiconductor mode-locked lasers have shown promise in many applications and are readily fabricated using generic InP photonic integration platforms. However, the passive waveguides offered in such platforms have relatively high linear and nonlinear losses that limit the performance of these lasers. By extending such lasers with, for example, an external cavity the performance can be increased considerably. In this paper, we demonstrate for the first time that a high-performance mode-locked laser can be achieved with a butt-coupling integration technique using chip scale silicon nitride waveguides. A platform-independent SiN/SU8 coupler design is used to couple between the silicon nitride external cavity and the III/V active chip. Mode-locked lasers at 2.18 GHz and 15.5 GHz repetition rates are demonstrated with Lorentzian RF linewidths several orders of magnitude smaller than what has been demonstrated on monolithic InP platforms. The RF linewidth was 31 Hz for the 2.18 GHz laser.