Abstract
Si3N4 waveguides, pumped at 1550 nm, can provide spectrally smooth, broadband light for gas spectroscopy in the important 2 μm to 2.5 μm atmospheric water window, which is only partially accessible with silica-fiber based systems. By combining Er+ fiber frequency combs and supercontinuum generation in tailored Si3N4 waveguides, high signal-to-noise dual-comb spectroscopy spanning 2 μm to 2.5 μm is demonstrated. Acquired broadband dual-comb spectra of CO and CO2 agree well with database line shape models and have a spectral-signal-to-noise as high as 48/√s, showing that the high coherence between the two combs is retained in the Si3N4 supercontinuum generation. The dual-comb spectroscopy figure of merit is 6 × 106/√s, equivalent to that of all-fiber dual-comb spectroscopy systems in the 1.6 μm band. based on these results, future dual-comb spectroscopy can combine fiber comb technology with Si3N4 waveguides to access new spectral windows in a robust non-laboratory platform.
Highlights
Frequency-comb spectroscopy can rival and exceed the signal-to-noise, speed, resolution and precision of traditional broadband spectroscopy [1,2,3,4,5]
Comb spectroscopy has been shown with bandwidths over ~4700 cm−1 (~140 THz) in several spectral regions [6,7,8], frequency-comb sources still lag behind traditional broadband thermal sources in spectral coverage
One attractive solution for generating broadband light in many spectral regions is spectral broadening in nanophotonic waveguides [9,10,11,12,13,14,15,16,17,18,19]
Summary
Frequency-comb spectroscopy can rival and exceed the signal-to-noise, speed, resolution and precision of traditional broadband spectroscopy [1,2,3,4,5]. Previous dual-comb spectroscopy results using chromium-based solid-state lasers and thulium fiber based combs partially accessed this region but at the cost of complexity relative to mature erbium technology as well as a narrower spectral coverage [28,29,30]. Accessing this spectral region through the combination of highly reliable Er+:fiber combs [31,32,33] and SiN waveguides is an attractive option
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