Stokes dual-soliton spectroscopy in a graphene functionalized over-modal microresonator

Abstract

Dual comb spectroscopy enables fast and accurate measurements over broad spectral ranges, offering a powerful tool to identify chemical species with unprecedented spectral resolution. Co-generation of soliton combs in one single microresonator can be used to improve the compactness of multi-comb sources and bridge the lab-to-fab gap. However, the robustness of pristine microresonators to environmental changes limits their potential in broader applications such as biochemical sensing. Here, we realize for the first time a two-dimensional-material functionalized dual-comb spectrometer by asymmetrically depositing graphene in an over-modal microsphere. Spectrally trapped Stokes solitons belonging to distinct transverse mode families are co-generated in one single device. A soliton mode in the graphene-functionalized region is highly sensitive to environmental changes while a second soliton mode in the pristine region serves as reference, thus producing dual-comb ultrasensitive beat notes in the electrical domain. Taking advantage of an advanced optoelectronic heterodyne detection scheme, we trace the frequency shift of the dual-soliton beat-note with uncertainty < 0.2 Hz and we achieve real-time individual gas molecule detection in vacuum. This combination of atomically thin materials and microcombs shows the potential for integrated spectroscopy with unprecedented performances and offers new insights toward the design of versatile functionalized microcavity photonic devices.