Nanophotonic supercontinuum-based mid-infrared dual-comb spectroscopy

Abstract

High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical processes, and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for ultra-broadband and flat-envelope mid-IR frequency combs. Our mid-IR dual-comb spectrometer has an instantaneous bandwidth covering the functional group region from 2800-3600 cm −1 , comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, sub-Doppler spectral resolution, and a high speed. In addition to the traditional functional groups, their isotopologues are also resolved in this supercontinuum-based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signaling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment.

Architecture for microcomb-based GHz-mid-infrared dual-comb spectroscopy

“…3 a, c and 100 ms for Fig. 3 b are shorter than fibre-comb-based mid-IR DCS systems, which generally require an acquisition time longer than tens of seconds 8 , 11 , 12 (usually those systems have a much larger comb line number). Even shorter acquisition times should be possible that are comparable to EO-comb-based systems, where mid-IR DCS has also been demonstrated 15 .…”

ADVANCED PROGRESS ON Χ<SUP>(3)</SUP> NONLINEARITY IN CHIP-SCALE PHOTONIC PLATFORMS (INVITED REVIEW)

“…However, it is a little regretful that the conversion efficiency was only around 1%. In 2020, the same group experimentally obtained MIR dual-comb spectroscopy based on dispersive wave generation in dual-core Si 3 N 4 nanowires [112]. Figure 8 shows the schematic diagram of the MIR dual-comb spectroscopy, the microscopic and SEM pictures of the dual-core Si 3 N 4 waveguide, and the experimental results of the MIR dispersive wave.…”

Single-cycle all-fiber frequency comb

“…The greenhouse gases and atmospheric pollutants have absorption peaks between 2 µm to 2.6 µm, making this an important spectroscopic region [46][47][48]. To extend fiber laser spectrum beyond the silica window, people have invested significant effort in soft-glass optical fibers [49][50][51] and planar waveguides [52][53][54]. When pumped at 1.5 µm, Si 4 N 3 (SiN) is a promising waveguide platform for this purpose, and dual-comb spectroscopy at 2 µm to 3 µm has been demonstrated [45,54].…”

“…To extend fiber laser spectrum beyond the silica window, people have invested significant effort in soft-glass optical fibers [49][50][51] and planar waveguides [52][53][54]. When pumped at 1.5 µm, Si 4 N 3 (SiN) is a promising waveguide platform for this purpose, and dual-comb spectroscopy at 2 µm to 3 µm has been demonstrated [45,54]. Still, an all-fiber source providing flat and bright spectrum in this range can be a more integrated, accessible, and robust solution for frequency comb spectroscopy.…”