Quadratic-soliton-enhanced mid-IR molecular sensing

TL;DR

This paper demonstrates that quadratic cavity solitons can significantly enhance mid-IR molecular sensing, achieving high sensitivity and path length enhancement for CO₂ detection beyond traditional linear cavity methods.

Contribution

It introduces the use of mid-IR quadratic cavity solitons for molecular sensing, showing substantial sensitivity improvements and new sensing capabilities.

Findings

Achieved an equivalent path length enhancement of 6000 for CO₂ sensing.

Demonstrated large sensitivity at high CO₂ concentrations beyond linear cavity limits.

Showed quadratic solitons can be effectively used for molecular sensing beyond broadband frequency comb generation.

Abstract

Optical solitons have long been of interest both from a fundamental perspective and because of their application potential. Both cubic (Kerr) and quadratic nonlinearities can lead to soliton formation, but quadratic solitons can practically benefit from stronger nonlinearity and achieve substantial wavelength conversion. However, despite their rich physics, quadratic cavity solitons have been used only for broadband frequency comb generation, especially in the mid-IR. Here, we show that the formation dynamics of mid-IR quadratic cavity solitons can be effectively leveraged to enhance molecular sensing. We demonstrate significant sensitivity enhancement while circumventing constraints of traditional cavity enhancement mechanisms. We perform experiments sensing CO$_2$ using quadratic cavity solitons around 4 $\mu$m and achieve an equivalent path length enhancement of 6000. Additionally, we demonstrate large sensitivity at high concentrations of CO$_2$, beyond what can be achieved using an equivalent high-finesse linear cavity by orders of magnitude. Our results highlight a path for utilizing quadratic cavity nonlinear dynamics and solitons for molecular sensing beyond what can be achieved using linear methods.