TECHNICAL
Is there a standard for hollow-core fibre (HCF) testing?
What is the goal of OTDR testing in the context of hollow-core fibre (HCF)? The objective of OTDR testing for hollow-core fibre remains consistent with traditional fibre: verify continuity, measure loss, locate events, and characterise splices. What changes is the level of performance required from the OTDR. HCF exhibits back scattering levels approximately 15dB lower than standard SMF. As a result, OTDRs designed solely for conventional fibre may struggle to deliver usable traces—especially over long distances. EXFO’s hollow-core fibre– optimised OTDR test kit addresses this with exceptionally high dynamic range, enabling reliable characterisation even on links exceeding 100km. Another key challenge unique to HCF is splice interpretation. Hollow-core splices introduce gas filling events (GFEs) that can extend for kilometres and distort traditional OTDR measurements. EXFO developed a patent-pending method that decouples the GFE signature from the fibre trace, allowing accurate splice loss and reflectivity measurements—
At present, there is no dedicated industry standard written specifically for hollow-core fibre testing. However, reliable hollow-core fibre characterisation can be achieved today by applying established fibre test principles through instrumentation and analysis tools adapted to its unique physical properties. In practice, HCF characterisation follows the same fundamental testing principles used for conventional single-mode fibre (SMF), adapted to account for the unique physical properties of hollow-core designs —such as lower Rayleigh backscatter (RBS) and surface scattering as the dominant scattering mechanisms arising from nanoscale surface imperfections in the micro structured silica walls. Standards bodies are actively evaluating HCF, but until formal specifications are published, validated test methods and field-proven instrumentation are what matter most. This is where practical experience becomes critical. EXFO solutions have been validated on Band- Gap and various NANF-based hollow- core fibre in both laboratory and field trials, ensuring accurate and repeatable results under real-world conditions.
something not achievable with conventional analysis alone.
Volume 48 No.2 MAY 2026
97
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