Tunable narrow linewidth chip-scale mid-IR laser

TL;DR

This paper demonstrates a tunable, narrow-linewidth, chip-scale mid-IR laser at 3.4 μm using a high-Q silicon microring cavity with integrated heaters, enabling wide tuning and stable single-mode operation for portable sensing applications.

Contribution

The authors present the first on-chip, tunable, narrow-linewidth mid-IR laser at 3.4 μm with high Q-factor microresonator and self-injection locking, advancing portable mid-IR spectroscopy technology.

Findings

Achieved a 54 nm tuning range at 3.4 μm.

Demonstrated an effective linewidth of 9.1 MHz.

Produced a stable, single-mode laser with 0.4 mW output power.

Abstract

Portable mid-infrared (mid-IR) spectroscopy and sensing applications require widely tunable, narrow linewidth, chip-scale, single-mode sources without sacrificing significant output power. However, no such lasers have been demonstrated beyond 3 $\mu$m due to the challenge of building tunable, high quality-factor (Q) on-chip cavities. We demonstrate a tunable, single-mode mid-IR laser at 3.4 $\mu$m using a high-Q silicon microring cavity with integrated heaters and a multi-mode Interband Cascade Laser (ICL). We show that the multiple longitudinal modes of an ICL collapse into a single frequency via self-injection locking with an output power of 0.4 mW and achieve an oxide-clad high confinement waveguide microresonator with a loaded Q of $2.8\times 10^5$. Using integrated microheaters, our laser exhibits a wide tuning range of 54 nm at 3.4 $\mu$m with 3 dB output power variation. We further measure an upper-bound effective linewidth of 9.1 MHz from the locked laser using a scanning Fabry-Perot interferometer. Our design of a single-mode laser based on a tunable high-Q microresonator can be expanded to quantum-cascade lasers at higher wavelengths and lead to the development of compact, portable, high-performance mid-IR sensors for spectroscopic and sensing applications.