MASAYUKI MURAKAMI OPTICAL CONNECTOR CLEANING
THE IMPORTANCE OF END FACE CLEANING FOR OPTICAL CONNECTORS IN THE DATA CENTRE ERA Optical networks have expanded rapidly in response to growing internet traffic, cloud computing, and the increasing scale of AI‑driven data centres. Optical connectors are indispensable in these networks because they enable flexible and repeatable fibre connections between equipment, patch panels, and optical transceivers. However, connector interfaces can also become a source of network trouble when they are not handled appropriately, writes NTT AT Application Engineer Masayuki Murakami . Contamination at the connector end
PERFORMANCE CHARACTERISTICS Optical connector performance is primarily characterised by insertion loss and return loss. Insertion loss quantifies the amount of optical power lost at the interface, while return loss represents the amount of reflected light. These parameters are influenced by connector geometry, alignment accuracy, polishing quality, and external contamination. IEC standards define how these values are measured and provide common criteria for evaluating commercial connectors. In practical high‑speed systems, low insertion loss and high return loss are both essential to ensure reliable transmission margins. IMPACT OF CONTAMINATION Contamination on connector end faces is one of the most significant causes of degraded optical performance. Typical contaminants include dust, skin oils, and hard particles such as sand or plastic debris. Soft contaminants may not immediately create large loss if they do not cover the core region, but they can be transferred from one connector to another and may move during repeated mating cycles. As a result, a connection that appears acceptable initially may later become unstable. Hard particles are particularly dangerous because they may create a physical gap between fibre end faces, causing a substantial increase in reflection and a sharp reduction in return loss. In high‑power optical systems, contamination becomes even more critical. Absorption of optical power at the end face can generate local heating, which may melt the fibre end face or trigger fibre fuse phenomena. Such events can damage not only the connector but also upstream fibre and associated optical equipment. Accordingly, contamination control is not merely a matter of good
zirconia ceramic – a strong material for holding an optical fibre - ferrule manufactured with sub‑micron precision. The ferrules are aligned using a precision split sleeve, which suppresses axial offset. The ferrules are also allowed a slight floating movement so that angular misalignment is reduced when the connectors are mated. Most importantly, the ferrule end faces are polished to a slightly spherical geometry, and springs apply pressure from behind so that the ferrules and fibres elastically deform and establish stable physical contact. This physical‑contact mechanism is the essential basis of low loss and low reflection in optical connectors. In multi‑fibre connectors such as MPO, the alignment structure is different, because guide pins and guide holes are used instead of a split sleeve. This enables simultaneous connection of multiple fibres within a compact interface suited to high‑density transmission. However, the fundamental optical principle does not change. Even in MPO and other high‑density interfaces, stable physical contact at the fibre end faces is still required to preserve optical characteristics. In other words, although the connector form factor, lane count, and mounting density may evolve with the advance of high‑speed optical interconnection, the optical mechanism that guarantees performance remains the same. If the physical‑contact region is contaminated, proper end‑face contact may be prevented, leading to increased insertion loss, reduced return loss, unstable transmission, and, in high‑power environments, even permanent fibre damage. Therefore, understanding connection principles is directly linked to understanding why cleaning is indispensable. Cleaning is not an auxiliary maintenance activity added after the fact; it is a basic requirement for preserving the intended optical function of the connector.
face is one of the most important causes of degraded optical performance, and this makes a proper understanding of connection principles, interface design, and maintenance practices essential for reliable network operation.
OPTICAL CONNECTOR TECHNOLOGIES AND MAINTENANCE
Optical connectors provide a detachable alternative to fusion splicing. Whereas fusion splicing permanently joins fibres with low loss, optical connectors allow repeated mating and unmating by bonding fibres into precision ferrules and polishing the end face. IEC standardisation ensures mechanical and optical interoperability. Among the mainstream connector types, SC (Subscriber Connector) are widely used in carrier and access networks, LC (Lucent Connector) are dominant in data centres because of their compact size and duplex implementation, and MPO (Multi-Fibre Push-On) connectors support high‑density multi‑fibre interconnection for parallel optics. Regardless of connector used, its end face remains a decisive optical interface whose quality must be preserved.
OPTICAL CONNECTION PRINCIPLES The most fundamental principle
underlying the performance of optical connectors is physical contact between the mating fibre end faces. Optical losses at a connector interface arise mainly from axial misalignment, angular misalignment, and the presence of a gap between the fibres. Reflection at the boundary between fibres can also affect system performance. For this reason, optical connectors are not merely mechanical joining parts; they are precision optical interfaces designed to minimise both insertion loss and return loss. In single‑fibre connectors such as SC and LC, the fibre is held in a
maintenance practice; it is directly related to the preservation of the physical‑contact mechanism that
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| ISSUE 44 | Q3 2026
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