MASAYUKI MURAKAMI OPTICAL CONNECTOR CLEANING
Figure 1: Example of the effect on optical characteristics when contamination adheres to the connector end face
defines connector performance. As line rates rise and loss budgets become tighter, sensitivity to end‑face condition increases. The importance of cleaning should therefore be understood not as a legacy habit associated only with conventional connectors, but as a fundamental and future‑oriented requirement for all optical interconnection systems, including next‑generation AI data‑centre networks. CLEANING, INSPECTION, AND POLISHING Effective maintenance begins with cleaning. Dedicated cleaning tools are selected according to the location and connector form. Reel‑type cleaners are commonly used for plug end faces, while stick‑type and pen‑type cleaners are used for ports inside equipment. Many newer pen‑type cleaners are designed to apply a consistent cleaning force, reducing operator dependence. Dry cleaning is generally the standard method, while wet cleaning with alcohol or purified water may be used for persistent contamination. When wet cleaning is employed, a final dry cleaning step is necessary to remove residual liquid or streaking. Cleaning must be combined with inspection. End‑face inspection instruments provide objective evaluation of contamination and defects, and many systems support pass/fail judgement based on IEC 61300‑3‑35. This is especially valuable because visual judgement by operators alone is subjective and may miss contamination
that is invisible to the naked eye but still optically harmful. A recommended workflow is to inspect first, clean if necessary, and then inspect again before connection. For critical links and high‑power systems, this process is especially important. Polishing quality also affects long‑term connector behaviour. Older PC‑polished connectors often exhibit numerous fine scratches and lower return loss, whereas modern polishing process provides smoother end faces and better optical performance. Re‑polishing tools can be used to restore certain degraded connectors and remove minor defects generated through repeated mating. Even so, polishing cannot substitute for everyday cleanliness; the maintenance priority remains to keep the physical‑contact region clean and intact. FUTURE-READY NETWORKS STILL DEPEND ON CLEAN, STABLE FIBRE CONNECTIONS Optical connector technologies are continuing to evolve in response to higher transmission rates, greater packaging density, and the rapid growth of AI‑driven data centre infrastructure. New interconnection technologies, including MPO and various VSFF (Very Small Form Factor) connector formats, are increasingly being introduced to support higher port density and next‑generation optical interfaces. However, despite these structural and architectural changes, the fundamental mechanism required to preserve optical performance remains unchanged: stable physical contact at the mating fibre end faces.
This is the most important point for future network construction and operation. Regardless of whether the connector is a conventional SC or LC type, a multi‑fibre MPO type, or a newly introduced high‑density interface, optical characteristics such as insertion loss and return loss ultimately depend on whether the physical‑contact region is maintained in an appropriate and clean condition. For that reason, the significance of connector cleaning should be emphasised more strongly than ever. Cleaning is not simply a routine maintenance task carried out after contamination is suspected. Rather, it is an essential practice for preserving the very optical mechanism on which connector performance is based. As network speeds increase and interconnect density rises, degradation caused by contamination can have an even greater impact on transmission stability, reliability, and system availability. Accordingly, understanding and practising proper end‑face cleaning is indispensable not only for maintaining existing optical networks but also for ensuring the successful deployment of future high‑speed optical interconnection systems. In this sense, connector cleaning should be regarded as one of the most fundamental technologies for sustaining the long‑term reliability and quality of optical networks.
Masayuki Murakami, Application Engineer, NTT Advanced Technology Corporation
Figure 2: Differences in end‑face condition by polishing grade
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ISSUE 44 | Q3 2026
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