PIETRO BERNASCONI FIBRE CONNECTION LOSSES
The capillary’s inner diameter is intentionally sized to accept standard manufacturing tolerances, removing the need for tight matching between fibre and ferrule. The core centring process starts with a circular wedge-shaped crimping tool pressed onto the front of the ferrule to plastically deform the titanium and to collapse the capillary wall uniformly around the fibre cladding. Any remaining offset is then precisely measured, before a second arc-shaped crimping tool selectively deforms the metal to nudge the fibre core toward the exact ferrule centre. The adjustment is repeatable and finely controlled, reducing the remaining eccentricity below 0.125 µm. With this technique pioneered and developed by Diamond SA and known as active core alignment (ACA), coupling losses between mated ferrules can be reduced by nearly an order of magnitude. Of course, when mated, two ferrules must be held in position very accurately. This is achieved by inserting them into a snug fit sleeve that suppresses any additional, lateral and/or angular misalignment. NEARLY AS GOOD AS SPLICES By applying ACA techniques to a variety of fibres, it has been possible to reliably and reproducibly demonstrate coupling losses well below the values specified by the international standards IEC 61753-1. As prescribed therein, connectors from a sufficiently large production lot assembled on standard telecom fibres (1310-1550 nm wavelength) and mated to each other generate a loss distribution characterised by average value ILavg ≤ 0.12 dB and a value at the 97% of the cumulative distribution IL97% ≤ 0.25 dB, so-called Grade B connectors. Since these loss values are still not suitable for many applications, higher- grade connectors have been offered based upon top-quality ferrules and fibres with tighter tolerances to achieve losses approximately halved, i.e. ILavg ≤ 0.05 dB and IL97% ≤ 0.15 dB. With ACA technologies and metal- ceramic ferrules, these values can be lowered even further to set new limits: ILavg ≤ 0.02 dB and IL97% ≤ 0.05 dB. Note
that the use of distributions to characterise the loss performance of connections is not simply dictated by the need of a realistic representation of what could be expected in the field, but it is now necessary to obtain a correct assessment of values very close to the accuracy of the measurement system. To verify the correctness of the characterisation method, the stability and accuracy of these results have been independently confirmed by the U.S. National Institute of Standards and Technology (NIST) using instrumentation specifically developed to resolve extremely low insertion losses while still following IEC 61300-3-34 test methodology. These values eventually show that mating two fibres by means of connectors can compete closely with permanent fibre splices in terms of power attenuations. FROM NIR TO UV Driven by many applications in the sensing and quantum photonics fields, the ultra- low loss performances demonstrated with SM fibres at 1550 nm have been extended to shorter wavelengths with fibres with much smaller MFDs and thus intrinsically more sensitive to fibre core misalignments. Since the residual core-to-ferrule eccentricity remains < 0.125 um after ACA regardless of the fibre’s MFD, exceptionally low loss values can be achieved through the visible and down to the near-UV spectral range. For example, ILavg ≤ 0.05 dB and ILavg ≤ 0.10 dB are available at 800 nm and 450 nm, respectively. Moreover, the advantages deriving from a better
centring extends beyond standard fibres and can encompass other specialty fibres such as polarisation maintaining (PM) or photonic crystal fibres (PCF). THE FUNDAMENTAL ENABLER OF FUTURE OPTICAL INFRASTRUCTURES: ULTRA-LOW- LOSS CONNECTIVITY As optical technologies continue to advance, the tolerance for power loss is shrinking across a broader range of applications. Even small connection losses can turn into higher costs, increased power consumption, reduced measurement sensitivity, or compromised system performance. This trend is particularly evident at shorter wavelengths, where conventional connector technologies often struggle to deliver the required levels of efficiency. ACA addresses this issue by dramatically reducing fibre core eccentricity and the resulting coupling losses at the fibre connector interfaces. By enabling connector losses that approach those of permanent splices while retaining the flexibility and serviceability of a connectorized interface, ACA technology removes a long-standing compromise in optical network design. As performance requirements continue to tighten and photonic systems expand into new application areas, ultra-low-loss connectivity is poised to become not just a desirable feature, but a fundamental enabler of next-generation optical infrastructures.
Pietro Bernasconi Technical Key Account Manager, Diamond SA
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ISSUE 44 | Q3 2026
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