Abstract
We present a theoretical analysis into the fundamental physical mechanisms contributing to backscattering in hollow-core antiresonant fibers. We consider Rayleigh scattering originating from the hollow regions of the fiber, which may be filled with gases, Rayleigh scattering from within the glass membranes, as well as the contribution from scattering at the glass surfaces. We derive expressions for the backscattering coefficient into any specified guided mode for an arbitrary excitation. These lead to general scaling relations with the core size and wavelength, which are found to be the key parameters for backscattering, regardless of the exact antiresonant geometry. For a nested antiresonant hollow-core fiber with a core diameter of 35 µm, the only antiresonant fiber geometry for which the experimental data are available in the literature, we find that the surface-scattering limited backscattering coefficient of the fundamental mode into itself is nearly 40 dB below that of a single mode fiber, in good agreement with recently published measurements.
Highlights
Over the past few years, hollow-core optical fiber (HCF) research has gained renewed interest, driven primarily by the sustained and rapid improvement in their performance
For a nested antiresonant hollowcore fiber with a core diameter of 35 μm, the only antiresonant fiber geometry for which the experimental data are available in the literature, we find that the surface-scattering limited backscattering coefficient of the fundamental mode into itself is nearly 40 dB below that of a single mode fiber, in good agreement with recently published measurements
For hollow-core fibers based on antiresonance guidance, there are further advantages, such as low chromatic dispersion and, as recently shown, high polarization purity and very low levels of backscattering.[5,6]. Such low levels of backscattering, measured to be more than 40 dB lower than in single mode fibers (SMFs), are especially beneficial for applications relying on bidirectional propagation, for example, in fiber optic gyroscopes,[7] remote fiber sensors interrogated in reflection,[8] or bidirectional fiber links used in time and frequency transfer.[9]
Summary
Over the past few years, hollow-core optical fiber (HCF) research has gained renewed interest, driven primarily by the sustained and rapid improvement in their performance. For hollow-core fibers based on antiresonance guidance, there are further advantages, such as low chromatic dispersion and, as recently shown, high polarization purity and very low levels of backscattering.[5,6]. The rapid pace of development of hollow-core antiresonant fibers has not permitted a thorough understanding of some of their most striking properties.[1,10,11] Backscattering is one such example where practical demonstration of ultralow backscattering levels has preceded a detailed understanding of the physical mechanisms that contribute to it.[6]. Such an understanding is necessary for at least two reasons. When filled with a gas at a sufficient pressure level (e.g., air at atmospheric pressure), Rayleigh scattering from within the hollow regions can become the dominant contribution to the backscattering signal
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