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Designing silicon-core fiber tapers for efficient supercontinuum generation in the greenhouse gas absorption region

We propose a tapered silicon-core optical fiber design for extending the long-wavelength edge of supercontinuum generation to obtain a high spectral density source across the 3–4.5 µm regime. The taper works by generating sufficient spectral broadening of the driving laser pulse to produce a series of pumps for nondegenerate four-wave mixing, and then opening up new phase-matching conditions to transfer the power from these pumps to a target region of mid-infrared wavelengths. We show, by simulation, that this taper design works effectively when pumped with a conventional 2.1 µm femtosecond fiber laser, significantly improving the spectral coverage obtained with a fixed-diameter fiber. Thus, these tapered silicon-core fibers offer a potential platform for an efficient all-fiber spectroscopy solution to measure greenhouse gases.