Easier Fiber End Face Inspections: Key Changes to IEC 61300-3-35

30 de abril de 2025 / General, instalación y comprobación, actualización y resolución de problemas

It's crucial to inspect, clean, and reinspect fiber end faces before mating connectors — whether on patch cords and trunks within the network or on the test reference cord you connect to your tester. Contaminated fiber end faces can cause signal loss and reflections that degrade network performance. They can also transfer dirt to clean ports, including those on expensive network equipment. The International Electrotechnical Commission (IEC) developed the 61300-3-35 standard to guide consistent fiber end face inspection — the latest edition has some significant changes that can simplify your inspection and cleaning workflow.

Woman in green shirt using an FI-3000 FiberInspector Pro to inspect a recently cleaned fiber cable lying on a gray tabletop

What Is the IEC 61300-3-35 Standard?

The IEC 61300-3-35 standard focuses on observing and classifying debris, scratches, and defects during visual inspection of fiber end faces. It defines criteria for minimum microscope compliance, inspection procedures, and quantitative measures for analyzing end face images.

Like all standards, the 61300-3-35 standard undergoes revisions and updates. The 2009 (first) edition introduced methods for quantitatively assessing fiber end face quality and determining allowable surface defects (scratches, pits, and debris) that can impact optical performance. The second edition in 2015 (61300-3-35:2015) introduced specific criteria for grading cleanliness based on the quality and size of scratches (permanent surface features) and defects (particles and debris) within four different zones (regions) of a fiber end face: Zone A (core), Zone B (cladding), Zone C (adhesive), and Zone D (contact/ferrule). The fiber's core, where the signal travels, has the most stringent requirements.

Diagram showing the various zones of a fiber end face.

^{IEC 61300-3-35:2015 graded fiber cleanliness based on the quality and size of scratches and defects in four different zones of the end face.}

The cleanliness criteria outlined in IEC 61300-3-35:2015 varied based on the connector type and fiber size. For single-mode fiber end faces with smaller cores, the standard prohibited any scratch or defect within the core zone. Multimode fiber end faces with larger cores could have scratches less than or equal to 3 microns (mm) and up to four defects less than or equal to 5 mm.

While these criteria provided consistency in assessing fiber cleanliness, manually counting and measuring scratches and defects in each zone using a microscope is time-consuming and prone to human error. Automated solutions like the Fluke Networks FI-3000 / FI2-7300 FiberInspector™ Ultra Camera and FI-7000 FiberInspector™ Pro use an algorithmic process that grades and certifies fiber end faces based on the IEC 61300-3-35 criteria, providing automatic PASS/FAIL results.

What Changed with the IEC 61300-3-35 Third Edition?

Key changes in the third and latest edition of the standard, IEC 61300-3-35:2022, include the removal of Zone C (adhesive) and Zone D (contact) from the PASS/FAIL criteria. This is a logical adjustment, as contamination in these areas generally does not impede transmission of the light signal through the core of the connector. The standard now recommends initially inspecting the entire Zone D (contact area) and attempting to remove loose particles that can migrate to the more critical Zones A and B (core and cladding). If several attempts to clean the contact zone are unsuccessful, the particles are considered embedded defects and deemed acceptable. Inspection can then proceed to Zone A and Zone B, which still have PASS/FAIL criteria based on the size and number of scratches and defects.

For rectangular array connectors (like multi-fiber push on connectors or MPOs), IEC 61300-3-35:2022 recommends inspecting the entire ferrule and attempting to remove loose particles before inspecting Zone A and Zone B on individual end faces. MPOs feature a much larger surface, and loose particles anywhere on the ferrule can migrate to individual fiber end faces, causing air gaps that can increase insertion loss and return loss. If several attempts to clean the ferrule are unsuccessful, those particles are also considered embedded defects and acceptable.

To inspect the entire ferrule for MPOs, IEC 61300-3-35 permits microscopes with a large field of view (LFOV) of at least 6.4X2.5 mm and the capability to detect debris of 10 mm in diameter. Microscopes with a small field of view (SFOV) of at least 250 μm and the ability to detect defects of 2 μm in diameter and scratches 3 μm wide are still required for inspecting the contact zone on single-fiber connectors and the core and cladding zones for all end faces.

The specific criteria for Zone A and Zone B are also slightly less stringent and better defined in IEC 61300-3-35:2022. As shown in the table below for multimode fiber end faces, the previous edition did not allow any scratches within Zone A greater than 3 mm, while the latest edition now allows four scratches equal or less than 4 mm and none greater than 5 mm. The overall size of the cladding zone is also slightly reduced in the latest edition since contaminants on the very edge of the cladding do not significantly impact the light signal.

IEC 61300-3 Multimode Fiber End Face Inspection Criteria
Zona	Defectos		Raspaduras
	Edition 2, 2015	Edition 3, 2022	Edition 2, 2015	Edition 3, 2022
R: Núcleo	4 ≤ 5 µm Ninguno > 5 µm	Sin límite < 2 µm 4 from 2 to 5 µm Ninguno > 5 µm	Sin límite ≤ 3 µm Ninguno > 3 µm	Sin límite < 3 µm 4 ≤ 4 µm Ninguno > 5 µm
B: Revestimiento	Sin límite < 2 µm 5 from 2 to 5 µm Ninguno > 5 µm	Sin límite ≤ 25 µm Ninguno > 25 µm	Sin límite ≤ 5 µm Ninguno > 5 µm	Sin límite
C: Adhesivo	Sin límite	Sin límite	Sin límite	Sin límite
D. Contact	None ≥ 10 µm µm	Sin límite	Sin límite	Sin límite

The most notable change in IEC 61300-3-35:2022 is language that allows a connector that has been cleaned of loose debris but failed inspection to still be used if it passes optical performance tests for insertion loss and return loss. In other words, the optical performance of a connector now takes precedence over a failed inspection.

Why Did IEC 61300-3-35 Change?

The changes in IEC 61300-3-35:2022 were implemented to provide a recommended inspection method for MPO connectors, streamline the inspection and cleaning workflow, and help avoid unnecessary and costly cable and/or equipment replacement.

One of the challenges with previous editions was that technicians could get trapped in a seemingly endless loop of inspect, clean, and inspect again — even if the contamination was only in the contact area. With a simplified workflow, technicians can inspect the entire ferrule or contact area, attempt to clean loose debris, and then proceed to inspect only the critical Zones A and B (core and cladding).

Furthermore, the presence of a defect or scratch on a fiber end face does not necessarily mean that it obstructs enough of the light signal to adversely impact performance. With less-stringent requirements and optical performance (insertion loss and return loss) now taking precedence, there is no need to replace cables and/or equipment if the link is functioning as expected. The changes also enhance the repeatability of inspection test equipment and help avoid false fails.

Flow diagram showing the IEC 61300-3-35 third edition inspection and cleaning process for fiber end faces.

^{IEC 61300-3-35:2022 simplifies the fiber end -face inspection and cleaning process. Fuente: International Electrotechnical Commission, from the IEC 61300-3-35:2022 standard.}

What Do Changes to IEC 61300-3-35 Mean for You?

These changes to the IEC 61300-3-35 should simplify your inspecting and cleaning process, helping you save time and money by avoiding a never-ending cycle of "inspect, clean, and inspect" — and reduce the need to replace connectors, patch cords, equipment, and other components with fiber end faces.

You also don't need to be overly concerned about these changes. Fluke Networks fiber inspection tools have all been updated to provide automated PASS/FAIL based on the latest edition of IEC 61300-3-35. Additionally, a passing performance test with your fiber certification tester will take precedence over any inspection results. However, a failed inspection will be indicated on your test results, which can aid in future troubleshooting.

While inspection has become easier and some of the requirements are less stringent, it remains crucial to inspect every fiber end face according to the recommended process and clean them if necessary. Fluke Networks Fiber Optic Cleaning Kits contain everything you need for optimal wet and dry cleaning, including Quick Clean™ tools for various connector types, fiber optic solvent pen with specially formulated fiber cleaning solution, and convenient cleaning cube/card.