Design, Fabrication, and Characterization of Large Mode Area Inhibited-Coupling Guiding Hollow-Core Fibers

We report on the design, fabrication, and characterization of an 8-tube inhibited-coupling guiding hollow-core photonic crystal fiber (IC-HCPCF) with a large diameter of the core of about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$60{\bm{\ \mu}} \text{m }$</tex-math></inline-formula>and a record low bending-induced increase of the confinement loss to a value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$19.2{\text{ dB}}/{\text{km}}$</tex-math></inline-formula> at a bend radius of 0.16 m for an operational wavelength of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1{\bm{\ \mu}} \text{m}$</tex-math></inline-formula>. Compared to fibers with a similar core diameter, the increase of the confinement loss induced by the bending is more than four times lower than the one of state-of-the-art Kagomé IC-HCPCF. At a bending radius of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.5{\bm{\ m}}$</tex-math></inline-formula>, the produced fiber exhibits a confinement loss of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$7.4{\text{ dB}}/{\text{km}}$</tex-math></inline-formula> at a wavelength of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1032{\bm{\ nm}}$</tex-math></inline-formula>, which is comparable to the loss of state-of-the-art IC-HCPCFs with tubular cladding structures. The output beam emitted from the fiber exhibits a near to diffraction-limited beam quality with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\bm{M}}^2} &lt; 1.15$</tex-math></inline-formula>. The fiber shows a good polarization-maintaining property with a measured degree of linear polarization (DOLP) exceeding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$90{\bm{\% }}$</tex-math></inline-formula> after 5 m of fiber. The simulation indicates that the power overlap between the core-guided laser beam and the surrounding glass cladding is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${10^{ - 5}}$</tex-math></inline-formula>, which makes this fiber a promising candidate for the flexible delivery of ultrashort laser pulses at a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\bm{mJ}}$</tex-math></inline-formula> energy level.