Advances in Mid-Infrared Low-Loss Hollow-Core Anti-Resonant Fibers

In a step forward in hollow-core fiber technology, our research has yielded two anti-resonant fibers that demonstrate record-low optical losses in the mid-infrared wavelength range. The first has a loss of $0.05 \mathrm{~dB} / \mathrm{m}$ between 3.4-3.6 $\mu \mathrm{m}$ and $0.24 \mathrm{~dB} / \mathrm{m}$ between $4.5-4.6 \mu \mathrm{m}$, setting a new benchmark for low loss in this spectral region. The second fiber has a transmission window at longer wavelength, 4.1-6 $\mu \mathrm{m}$, also with a notably low loss, measured as $\sim 7 \mathrm{~dB} / \mathrm{m}$ at $6 \mu \mathrm{m}$, but potentially with lower fundamental mode loss. These fibers are also capable of transmitting laser light, with the first efficiently transmitting the near-diffraction-limited light generated by a tunable optical parametric oscillator and delivering a peak power of 1.1 kW through 108 meters, with a coupling efficiency of $\sim 70 \%$. The second fiber facilitated the delivery of light from a quantum cascade laser, achieving a maximum delivered power of 3.4 mW at $6.045 \mu \mathrm{m}$ over a 0.9 -meter length. These advances represent a substantial improvement in reducing transmission loss, enhancing the overall efficiency and usability of MIR fiber systems, and demonstrates their potential for practical applications. (©2024 The Author(s)