fiber endface inspection (original) (raw)

Definition: inspection of the quality of fiber endfaces, e.g. before splicing

Alternative term: fiber inspection probes

Category: article belongs to category fiber optics and waveguides fiber optics and waveguides

Related: fiberscleaning of fiber endsfiber opticsfiber connectorsfiber-optic adapterscleaving of fibersfusion splicing of fibers

DOI: 10.61835/7w3 Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn

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📦 For purchasing fiber endface inspection, use the RP Photonics Buyer's Guide — an expert-curated directory for finding all relevant suppliers, which also offers advanced purchasing assistance.

Contents

Introduction

Fiber optics is generally quite sensitive; tiny defects and even low levels of contamination on fiber endfaces can substantially degrade device and system performance. In fiber connectors, for example, particles or defects at the contact point can raise insertion loss, increase reflectance (reduce return loss), and permanently scratch the opposing fiber in a connector. Fusion splicing suffers when cleave angles are excessive. Therefore, effective inspection tools and practices are vital in this technology.

It is common to use various types of fiber endface inspection instruments which are specifically developed to analyze cleaved or polished endfaces of optical fibers or fiber connectors. One can verify that a fiber endface is clean, undamaged and overall within quality limits, e.g. before splicing fibers or mating connectors. While recognized contamination can usually be removed by cleaning, other defects often require new cleaving, i.e., preparing a new fiber end.

Some of these devices are made only for inspecting fiber connectors of certain types, others only for bare fiber ends, and some are suitable in both cases. V-grooves with clamps are common holders for bare fibers, while connectors need other fixing tools. Some probes can scan multi-fiber arrays.

All-purpose benchtop microscopes can in principle also be used, but specialized fiber inspection devices can be more convenient in various respects — beginning with mounting and also with specific inspection types, particularly for advanced instruments. They also yield more consistent (repeatable) results across different operators.

Advanced inspection instruments not only allow viewing, but perform automatic assessment with pass/fail tests and export detailed logs with serial numbers and job IDs.

Aspects of Inspection

Clean, undamaged fiber endfaces are often essential for optical performance. In detail, different aspects can be relevant, depending on the context.

Connectorized Fibers

Depending on the application, different details can be relevant. Some standards have been developed for connectorized fibers in order to produce more objective results:

Note that the cleanliness thresholds in IEC 61300-3-35 depend on connector type (PC vs. APC) and selected criteria set (e.g., single-mode vs multimode).

Bare Fiber Ends

For bare fiber ends, various aspects can be investigated:

There is no IEC bare-fiber visual inspection standard equivalent to IEC 61300-3-35 for connectors. Instead, non-standardized bare fiber inspection criteria are usually built into devices like fusion splicers (cleave angle tolerances, chip/mist detection). Industry guidelines (from ITU, Telcordia, training manuals) describe typical limits such as ≤1° cleave angle for single-mode, but these are recommendations, not global IEC requirements.

Applications of Fiber Inspection Devices

Fiber endface inspection devices are used both in manufacturing and in the field. Examples:

Some devices have integrated fiber inspection devices — for example, many fusion splicers.

Main Categories of Fiber Inspection Devices

Microscopes

Optical microscopes (eyepiece scopes) are compact, low-cost microscopes used for checking cleanliness and finding defects. Typically, they have a tube shape, allowing direct inspection of the endfaces, but often not of endfaces inside equipment or through bulkheads.

Fiber microscopes illuminate the properly fixed endface (often with an LED) and show a magnified image through an eyepiece. They are simple and can reveal very fine detail, but results are operator-dependent and not automatically aligned to pass/fail criteria.

Also note that viewing a fiber directly can be risky if it may carry substantial optical power — often in the infrared, so that it stays unnoticed. Therefore, many organizations prefer video scopes to avoid any risk of viewing live fibers directly.

Video Inspection Probes

These are usually handheld instruments used for the same purposes as fiber microscopes. Instead of an eyepiece, they have an image sensor and a display. That architecture has several implications:

There are also benchtop instruments, possibly using an external monitor.

Common video probes have a field of view around 250 µm for single-fiber connectors, which comfortably covers the inspection zones. This in combination with the pixel count determines the limit of resolution, provided that the optics are of high quality. The absolute optical resolving power is often well below a good benchtop microscope, but handling, automation, and consistent grading typically make fiber video probes better for field work.

Different illumination types (coaxial or oblique) may be offered for focusing on different aspects of fiber endface quality.

Interferometric Endface Analyzers

These are particularly sensitive interferometric instruments for quality control during connector manufacturing and high-end termination work. They measure geometry very sensitively, but do not perform cleanliness grading.

The instrument reflects light from the polished surface and superimposes it with a reference beam to obtain interference fringes, which allow the generation of a 3D height map. From this map it computes key parameters such as the radius of curvature, apex offset (how far the highest point is from the fiber center), and fiber height (protrusion/undercut). These parameters strongly influence contact pressure, return loss, and long-term reliability.

For multi-fiber MT ferrules, specialized fixtures and algorithms evaluate fiber-to-fiber height differences and coplanarity across the array.

Integrated Analyzers

Some fiber end analyzers are integrated into other instruments. In particular, some modern splicers use their built-in microscopes to check the cleave quality just before splicing. They estimate cleave angle and flag chips, lip/step, or bad endface texture. It can save substantial time to discover such a problem before a splicing attempt which would fail or at least bring non-ideal results.

Inspection of Fiber Adapters

Fiber-optic adapters are pure mechanical parts, not containing fibers themselves. Nevertheless, their inspection can be vital, as contaminated or defective adapters can cause substantial problems:

Many video inspection probes have bulkhead tips that insert into the adapter to look at the connector endface while it is in place. This also lets one notice if contamination seems to come back after cleaning connectors, pointing to a dirty adapter sleeve.

Technicians may shine a flashlight or use a loupe to check the sleeve bore for cracks, dirt, or shards.

Standard practice is to clean the adapter with a specially designed cleaning stick or swab, then re-inspect the connector endface after reinserting it. If the connector keeps failing cleanliness checks, the adapter may be at fault.

In data centers and telecom sites, a common rule is “inspect, clean, inspect” for both connectors and adapters. In case of doubt, an adapter is exchanged, as adapters are cheap compared to the cost of downtime.

Good Practices

Some generally advisable good practices in the context of fiber inspection:

Frequently Asked Questions

What is fiber endface inspection?

It is the process of using specialized instruments, like microscopes or video probes, to analyze the endfaces of optical fibers for cleanliness, defects, and correct geometry to ensure optimal performance of connections.

Why is inspecting fiber endfaces so important?

It is crucial because even microscopic contamination or tiny defects on a fiber endface can substantially degrade performance by increasing insertion loss and reflectance, and can even cause permanent damage to mating connectors.

What are the main types of fiber inspection devices?

The main categories are optical microscopes for direct visual checks, video inspection probes which offer safer viewing and automated analysis, and interferometric analyzers for highly precise 3D geometry measurements.

What is the IEC 61300-3-35 standard for?

It is an international standard that defines microscope requirements, inspection procedures, and quantitative pass/fail criteria for debris, scratches, and defects on the endfaces of fiber optic connectors.

What are common defects on a cleaved bare fiber end?

Common defects include an incorrect cleave angle, hackle (a rough texture), micro-cracks, edge chips, a ledge at the fiber edge, and contamination from residues or dust particles.

What is the difference between a fiber microscope and a video inspection probe?

A fiber microscope has an eyepiece for direct viewing, posing a potential laser safety risk. A video probe uses an image sensor and a display, which is safer and often includes software for automated pass/fail analysis based on industry standards.

Why is it necessary to inspect fiber optic adapters?

Adapters must be inspected because they can be a source of contamination that is repeatedly transferred to clean connectors. A damaged or worn adapter sleeve can also cause poor ferrule alignment, leading to high loss and scratches.

Suppliers

Sponsored content: The RP Photonics Buyer's Guide contains 14 suppliers for fiber endface inspection. Among them:

NYFORS

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fiber endface inspection

Nyfors offers high precision interferometers for checking the end face quality of cleaved optical fibers and for cleave process optimization. They show crisp and clear fringe patterns and come with software for advanced measurement functionality. Ideal for use in production settings and when working with difficult to cleave fibers in laboratory environments.

Fiber holder adapters available for use with cleavers and splicers from the major splicer manufacturers. This facilitates easy transfer of the fiber from cleaver to interferometer and then onto the splicer with no need for reclamping.

AMS Technologies

âš™ hardware

fiber endface inspection

Particles con­tami­nating the end face of optical fibers are typically only 2 to 20 µm in size, but substantially degrade the performance. Inspecting a fiber connection with a microscope that illuminates and magnifies the fiber tip is the only way to ensure that this connection is free of contamination and defects. Our extensive range of fiber optic microscopes for every application and budget provides intuitive and reliable inspection solutions for certification of new installations or troubleshooting of existing networks, avoiding subjective evaluations and estimates:

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