Backscattering in antiresonant hollow-core fibers: over 40 dB lower than in standard optical fibers

V Michaud-Belleau,F Poletti,E Numkam Fokoua,Y Chen,R Slavík,J R Hayes,D J Richardson,J Genest,T D Bradley

doi:10.1364/optica.403087

Abstract

The elastic backscattering of light in optical fiber is a fundamental phenomenon that sets the ultimate performance of several fiber systems such as gyroscopes and bidirectional transfer links. Until now, efforts to reduce the backscattering coefficient have yielded limited results, with the lowest value sitting at around − 76 d B / m in Ge-free silica-core fiber at 1.55 µm. Here, we present what we believe to be the first measurement of backscattering from a low-loss antiresonant hollow-core fiber and show that it is more than 40 dB below reported values in silica-core fiber and hollow-core photonic bandgap fiber. The record-low level of − 118 d B / m measured with our custom-built optical frequency-domain reflectometer is in good agreement with simulations in which we assume the scattering to originate from the intrinsic surface roughness. Our demonstration also shows that a tailored instrument can localize and quantify weak faults within a hollow-core fiber, enabling its detailed characterization.

Highlights

Lowering the backscattering coefficient (BSC) of a standard single-mode fiber (SMF) requires the diminution of either the recapture fraction η or the scattering loss αs (BSC = ηαs)
This is associated with a BSC of −76 dB/m assuming η = 1.2×10-3, about 4 dB below what is usually quoted for SMF at 1.55 μm [13]
Reported measurements in commercial 7-cell hollow-core photonic bandgap fiber (HC-PBGF) have shown a BSC of −60 dB/m or higher [13, 17, 18]. Such unexpectedly high BSC has been tentatively attributed to surface scattering from glass interfaces, which in those early fibers may have been oscillating along the entire length [19]

Summary

Introduction

The overlap of the mode field with the glass microstructure is typically 0.1 to 1% [15] which, given similar acceptance angles, should lead at least to a commensurate 20 to 30 dB reduction in volumetric Rayleigh backscattering when compared to standard SMF [16]. The demonstration in [22] confirms the theoretical prediction of a scattering loss below 0.1 dB/km in NANF (below the value in SMF) [21].

Results

Conclusion