Abstract
We study the mid-infrared attenuation of antiresonant hollow-core fiber made of fused silica glass. The role of absorptive losses increases with wavelength but can be minimized by reducing the overlap of the trapped light with the silica. We show that this overlap is least at the lowest-order antiresonance condition, corresponding to the thinnest core wall, and for higher resonances scales with the core wall thickness. A record-low minimum attenuation of 18 dB/km measured in our fiber at 3.1 µm wavelength is not limited by silica absorption. We measured 40 dB/km attenuation at 4 µm wavelength, where the attenuation of bulk silica is 860 dB/m. We show that this corresponds to a modal overlap of 2.81 × 10−5 which is in good agreement with simulations, suggesting that at this wavelength, attenuation is limited by silica absorption. This enables us to predict the achievable attenuation at longer wavelengths as well. Extrinsic losses due to gaseous molecular absorption may make demonstration of such losses difficult in some spectral bands. In contrast to shorter wavelengths, where leakage loss is the primary attenuation mechanism, introducing additional elements into the cladding design is unlikely to reduce the attenuation further, and further loss reduction would require a larger core size.
Highlights
Hollow-core (HC) waveguides were originally developed for electromagnetic wave transmission at long wavelengths from the microwave1 to the far/mid-infrared2 where material absorption is dominant
We study the mid-infrared attenuation of antiresonant hollow-core fiber made of fused silica glass
This paper reports on the design and demonstration of a silicabased Antiresonant hollow-core fibers (AR-HCFs) for the mid-IR spectra region
Summary
Hollow-core (HC) waveguides were originally developed for electromagnetic wave transmission at long wavelengths from the microwave to the far/mid-infrared where material absorption is dominant. The attenuation of PBG-PCF in the mid-infrared has been shown to be around 1% of the bulk material absorption, which is only possible because of the low overlap of the guided light with the glass. By filling an AR-HCF with molecular gases, novel light sources have been demonstrated at mid-IR wavelengths based on optically pumped gas lasing and stimulated Raman scattering.. By filling an AR-HCF with molecular gases, novel light sources have been demonstrated at mid-IR wavelengths based on optically pumped gas lasing and stimulated Raman scattering.23,27–30 These systems offer the merits of fiber lasers such as excellent laser beam quality, high power conversion efficiency, stability, and compactness. Our simulations show that using current designs, the material absorption of the silica glass plays a limiting role in the attainable attenuation of AR-HCF at 4 μm wavelength and beyond. We demonstrate an attenuation of 40 dB/km at 4 μm wavelength where the material absorption of bulk fused silica is 860 dB/m
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