Low-Loss Coupling of Quantum Cascade Lasers into Hollow-Core Waveguides with Single-Mode Output in the 3.7–7.6 μm Spectral Range
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Dipartimento Interateneo di Fisica, Università degli studi di Bari Aldo Moro e Politecnico di Bari, Via Amendola 173, Bari I-70126, Italy
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Department of Electrical and Computer Engineering, Rice University, 6100 Main Street, Houston, TX 77005, USA
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National Institute for Laser, Plasma and Radiation Physics Laser Metrology and Standardization Laboratory 409 Atomistilor, 077125 Magurele-Bucharest, Romania
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Opto-Knowledge Systems, Inc. (OKSI), 19805 Hamilton Ave., Torrance, CA 90502-1341, USA
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Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Sensors 2016, 16(4), 533; https://doi.org/10.3390/s16040533
Received: 28 January 2016 / Revised: 29 March 2016 / Accepted: 11 April 2016 / Published: 13 April 2016
(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)
We demonstrated low-loss and single-mode laser beam delivery through hollow-core waveguides (HCWs) operating in the 3.7–7.6 μm spectral range. The employed HCWs have a circular cross section with a bore diameter of 200 μm and metallic/dielectric internal coatings deposited inside a glass capillary tube. The internal coatings have been produced to enhance the spectral response of the HCWs in the range 3.5–12 µm. We demonstrated Gaussian-like outputs throughout the 4.5–7.6 µm spectral range. A quasi single-mode output beam with only small beam distortions was achieved when the wavelength was reduced to 3.7 μm. With a 15-cm-long HCW and optimized coupling conditions, we measured coupling efficiencies of >88% and transmission losses of <1 dB in the investigated infrared spectral range.