Low-Loss Coupling of Quantum Cascade Lasers into Hollow-Core Waveguides with Single-Mode Output in the 3.7–7.6 μm Spectral Range

• Main Authors: Pietro Patimisco, Angelo Sampaolo, Laura Mihai, Marilena Giglio, Jason Kriesel, Dan Sporea, Gaetano Scamarcio, Frank K. Tittel, Vincenzo Spagnolo
• Format: Article
• Language: English
• Published: MDPI AG 2016-04-01
• Series: Sensors
• Subjects: single-mode output; hollow-core waveguide; quantum cascade laser; optical coupling
• Online Access: http://www.mdpi.com/1424-8220/16/4/533
• ISSN: 1424-8220

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.