Abstract
The trade-off between the spectral bandwidth and average output power from chalcogenide fiber-based mid-infrared supercontinuum sources is one of the major challenges towards practical application of the technology. In this paper we address this challenge through tapering of large-mode-area chalcogenide photonic crystal fibers. Compared to previously reported step-index fiber tapers the photonic crystal fiber structure ensures single-mode propagation, which improves the beam quality and reduces losses in the taper due to higher-order mode stripping. By pumping the tapered fibers at 4 μm using a MHz optical parametric generation source, and choosing an appropriate length of the untapered fiber segments, the output could be tailored for either the broadest bandwidth from 1 to 11.5 μm with 35.4 mW average output power, or the highest output power of 57.3 mW covering a spectrum from 1 to 8 μm.
Highlights
Chalcogenide glass fibers is an excellent medium for nonlinear applications in the midinfrared (MIR), and offers flexible delivery and collection of broadband MIR light for fiberbased sensing applications, such as: Fiber evanescent wave spectroscopy (FEWS) [1], bundled-fiber imaging [2], scanning fiber near-field spectroscopy [3], and fiber medical endoscopy [4]
The OPA pump generation efficiency was reduced at longer wavelengths due to absorption of the MgO:LiNbO3 crystal (MgO):PPLN crystal, so the best case for high average power was to pump at 4 μm
In order to optimize the taper design it was important to understand the underlying dynamics of supercontinuum generation (SCG) in the experiments. For this reason we modelled the nonlinear pulse propagation using a specific implementation of the generalized nonlinear Schrödinger equation (GNLSE) for including tapering and multiple propagation modes, derived from Maxwell’s equations using the approach of Lægsgaard [21,22] and Kolesik et al [23]
Summary
Chalcogenide glass fibers is an excellent medium for nonlinear applications in the midinfrared (MIR), and offers flexible delivery and collection of broadband MIR light for fiberbased sensing applications, such as: Fiber evanescent wave spectroscopy (FEWS) [1], bundled-fiber imaging [2], scanning fiber near-field spectroscopy [3], and fiber medical endoscopy [4]. Recent experimental work with SCG has demonstrated spectra spanning more than 11 μm [5,6], covering the entire functional group and a significant part of the fingerprint region of molecular vibrational resonances, revealing the true potential of the MIR SC technology. For this reason there has been a rapid development in the community with research groups pursuing both generation of longer wavelengths and higher average output power for enabling applications in the MIR. Achieving both a long wavelength range and high average power has proved challenging due to the relatively low damage threshold of chalcogenide glasses, and the trade-off between peak power and average power in most available MIR pump systems
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