cleaning of fiber ends (original) (raw)

Definition: removing dust, films or polymer residues from fiber endfaces

Category: fiber optics and waveguides

• cleaning of fiber ends
  • dry cleaning
  • wet cleaning

Related: fibersfiber endface inspectionfiber jointsfusion splicing of fiberscleaning of optics

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

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Contents

Introduction

Fiber optics is generally quite sensitive to contamination of fiber endfaces — be it bare fiber ends or fiber connectors. For example:

• The efficiency of launching light into a fiber can be substantially degraded by dust particles, which may also be burned in by intense laser radiation.
• A beam emerging from a fiber end may not only lose optical power but also be deteriorated in terms of beam quality.
• Fusion splicing of fibers can suffer from dirt on endfaces.
• Fiber connectors will exhibit increased insertion loss and possibly increased reflection (reduced return loss). In addition, hard particles may damage fiber endfaces when mating connectors.

Therefore, refined methods of fiber endface inspection as well as cleaning methods have been developed. As improper methods can cause various problems themselves — for example, scratching the endface, leaving solvent residue, or creating static charges — it is important to understand common risks and use optimized methods and tools. Further, various kinds of safety precautions should be observed, depending on the cleaning method applied, to avoid injuries. Typical aspects are proper solvent handling, ventilation, eye protection, and disposal of contaminated materials and fiber shards.

Typical Types of Contamination of Fiber Ends

• Dust particles are ubiquitous and can easily be deposited on fiber ends, particularly as a result of static electricity. They may not directly matter on an isolated bare fiber end as long as they are located well outside the fiber core, but they may later be moved to that critical area. Particularly hard dust particles are problematic when mating connectors or splicing fibers.
• Films formed by oils, solvent residues or fingerprints may be transparent but have an optical effect according to their refractive index and spatially varying thickness. They often raise reflectance and can visually (under a microscope) appear as a rainbow sheen or fog.
• Residues from buffer coating may remain on glass after stripping fiber coatings. They cause poor cleaves and weak splices.

When to Perform Fiber Cleaning

Typically, cleaning is performed when there is concrete evidence for contamination, provided by careful inspection or inferred from degraded optical performance that suggests a contamination problem.

Cleaning should not be performed right after a careful inspection has confirmed high quality of an endface, because unnecessary cleaning attempts can make things worse. For example, cleaning may create static electricity that then attracts dust to the fiber end.

Cleaning should always be followed by thorough inspection; see the article on fiber endface inspection. If a problem is noticed, clean again and re-inspect.

Cleaning is typically part of a workflow like inspect → clean (if needed) → inspect again → connect for connectors, or strip → clean → cleave → inspect → splice for bare fiber ends.

Different types of tools can be used, which may be usable for bare fiber ends and/or connectors. Each has specific advantages and limitations:

Dry “Click” Cleaners

These handheld dry cleaning tools for fiber connectors are the first choice for loose particles and light films because they avoid liquids and work quickly with consistent pressure and stroke length. They present a fresh section of woven or microfiber tape with each click, so debris is captured and not redeposited to the next fiber. They are sized for specific connector types, typically for 2.5 mm ferrules (SC/FC/ST), 1.25 mm ferrules (LC/E-2000), or MPO/MTP ferrules. There are also versions for bulkheads as well as fiber patch cords.

Such cleaners should be discarded when the tape is spent or visibly soiled; trying to “stretch” a reel is risky as it increases re-contamination.

Lint-free Wipes

High-quality nonwoven polyester or microfiber wipes/cards provide a flat, clean surface for controlled one-direction drags. They are ideal at the bench for single-pass dry cleaning and for the wet-to-dry technique when a solvent is needed.

Wipes should be kept sealed until use and handled only by the edges to avoid transferring skin oils. Use a fresh area of wipe for every pass.

Air Sources

Dry gas and manual blow bulbs can remove loose dust before contact cleaning, which is often advantageous.

The cleanest options are oil-free, moisture-free filtered dry gas (e.g., nitrogen) delivered through a clean nozzle, or a manual blow bulb when gas is not available. Simple “canned air” should be avoided, as it can expel propellant or moisture.

The jet should be directed across the surface at a shallow angle such that particles leave the area rather than being driven into the ferrule bore. One should not blast at close range, where the jet could embed particles.

Wet Cleaning

Although dry cleaning should usually be tried first, wet cleaning may be needed for more persistent contamination such as oily substances.

Solvents

Typical solvents used for fiber cleaning are:

• High-purity isopropyl alcohol (at ≥99 %) is widely used because it evaporates quickly and leaves little non-volatile residue when it is sufficiently pure.
• Fiber-safe engineered cleaners (marketed for optics) can work well on oily films and fast-dry with very low residue. They should be used only if they are plastic-safe and documented as low-residue.

Denatured alcohols and household alcohol are not suitable, because denaturants can leave film or damage parts. Acetone is also problematic when used near plastics, as dissolved plasticizers have similar effects.

Rules for handling solvents:

• Apply solvent with a dropper or pump-top dispenser onto the wipe/swab, never directly onto the connector or into the adapter, to avoid flooding and capillary wicking.
• Use very small volumes; the goal is to soften films so that the final dry contact removes them, not to soak the part.
• Keep bottles tightly capped. Alcohol is hygroscopic and will absorb water from air, slowing evaporation and increasing residue over time. Decant small amounts into clean, labeled working bottles.

Additional Materials

• Lint-free polyester or microfiber-tipped swabs are available, sized for 2.5 mm or 1.25 mm sleeves. (Foam and cotton tips are not suitable, as they can shed small tissue fibers or leave a film formed by binders or lotions.)
• For MPO/MTP connectors, there are cleaners designed for wider MT ferrules; their contact patch covers the full fiber array and avoids snagging on guide pins. The correct variant for pinned vs. unpinned connectors and for bulkhead vs. patch-cord access must be used, because geometry matters for full coverage.
• For cleaning transceiver ports, there are ESD-safe, optics-rated port swabs or specialty tools designed for SFP/QSFP/CFP cages.

Wet-to-dry Technique

It is common to use the wet-to-dry technique:

• Touch the fiber end down on a small wet zone of a fresh wipe, then drag once into a dry zone so the last point of contact is dry and residue is removed with it.
• Wait a few seconds for complete evaporation and inspect immediately, because dissolved contaminants can redeposit as a faint ring while drying. If that occurs, clean again with fresh media.

Wet Cleaning of Fiber Connectors

• For cleaning bulkhead adapters, rotate a lightly moistened swab once with gentle pressure, then follow with a fresh dry swab. Dispose of swabs after one use, as re-use moves debris deeper into sleeves.
• For MPO/MTP connectors, apply a suitable cleaner with light, even pressure in a single pass; back-and-forth “scrubbing” drags particles across many fibers.
• For cleaning transceiver ports, use suitable port swabs or specialty tools. Avoid any free solvent that could wick into the module. Cleaning should be done with optical power removed when possible. A wet swab should never be inserted into a port.

Wet Cleaning of Bare Fibers and Fixtures

After stripping and before cleaving, wipe the bare glass once with a slightly moistened lint-free wipe, then wipe dry to remove buffer residue and avoid mist or hackle in the cleave. Do not touch the glass after this step; proceed directly to cleaving and inspection.

Residue in fixtures seeds recurring contamination. V-grooves, clamps and cleavers can be cleaned with a dry swab first, then, if needed, a lightly moistened swab followed by a dry one.

Keep the cleaver anvil and blade area free of shards; use a soft brush or an air bulb and collect waste in a sharps container to avoid injuring skin or eyes.

Storage, Contamination Control and Lifecycle

• Store wipes, swabs, and cleaner reels in sealed packaging and closed cases; open only what you need for the current job.
• Keep separate kits for endfaces and adapters/ports to prevent cross-contamination.
• Work on a clean mat with controlled airflow, and keep dust caps in a clean container rather than loose on a bench.
• Wear powder-free, low-lint gloves or finger cots for production work to prevent skin oils from reaching optics.
• Replace reel tapes and swab stock before they are exhausted or past shelf life, and record lot numbers if your process requires traceability.
• Inspect and clean probe tips and cleaner nozzles; a dirty tool can contaminate every part it touches.

Automated Fiber Cleaning Systems

Automated fiber cleaning systems are used in manufacturing and high-volume fiber-optic assembly to ensure consistent, contamination-free connector endfaces. Unlike manual cleaning with wipes or reels, these systems use robotic or mechanized processes to clean multiple connectors rapidly and uniformly.

They typically employ rotating cleaning reels, air jets, or ultrasonic mechanisms that remove dust, oil, and residue without physical damage. Many systems integrate inspection cameras that verify cleanliness according to IEC 61300-3-35 before and after cleaning, enabling a closed-loop “clean–inspect–verify” workflow.

Automation can not only be faster and more reliable, but also reduces operator variability. It is ideal for mass termination, transceiver assembly, and cable harness production environments where thousands of connectors must meet strict cleanliness standards.

Special Fiber Cleaning Techniques

The cleaning methods explained above are commonly used in fiber optics. There are other techniques applied under special circumstances — for example, before applying dielectric or metal coatings on fiber endfaces under high vacuum. Here, one has especially stringent requirements on cleanliness which are not met by standard techniques. The fiber end must be completely free of particles, organics, and ionic contamination. One also must ensure that the surface is chemically active enough for strong adhesion of the coating materials. Introducing any new contamination during handling or transfer into the coating system must be avoided.

Typical cleaning techniques before applying coatings involve precision mechanical cleaning, solvent sequences, ultrasonic cleaning, plasma or UV/ozone cleaning, and bake-out / vacuum pre-cleaning. Such operations are performed in cleanrooms under special precautions.

Industry Standards for Fiber Cleanliness

As cleanliness of optical fiber connectors is essential for maintaining low signal loss and preventing damage, international standards have been developed which define how to inspect and assess fiber cleanliness.

The key reference is IEC 61300-3-35, “Fibre optic interconnecting devices and passive components — Examination and measurement of fibre optic connector endface visual inspection.” It specifies inspection methods, cleanliness zones, and pass/fail criteria for defects and contamination on connector endfaces.

The standard divides the endface into concentric zones:

• Zone A (core): Most critical; no contamination or scratches are permitted here.
• Zone B (cladding): Small, limited contamination is allowed if it does not intrude into the core.
• Zones C and D (epoxy and ferrule): Less critical; more contamination is tolerated.

Automated inspection tools commonly apply these IEC criteria to classify connectors as “Pass” or “Fail”. The standard underpins the industry's “inspect before you connect” practice.

Related documents include Telcordia GR-326-CORE (connector reliability), IPC-8497-1 (cleaning procedures), and ISO 14644 (cleanroom environments). Together, they form the foundation for maintaining fiber-optic system integrity through standardized inspection and cleaning.

Frequently Asked Questions

Why is it important to clean fiber optic endfaces?

Contamination on fiber endfaces can degrade light transmission efficiency and beam quality, increase insertion loss in connectors, cause physical damage when mating, and lead to poor quality fusion splices.

What are the most common types of contaminants on fiber ends?

Common contaminants include ubiquitous dust particles, films from oils or fingerprints that cause reflections, and residues from the fiber's buffer coating that can interfere with cleaving and splicing.

What are typical safety precautions in fiber cleaning?

Typical aspects are solvent handling, ventilation, eye protection, and disposal of contaminated materials and fiber shards.

What is the recommended workflow when dealing with fiber connectors?

The best practice is to inspect the endface first, clean it only if contamination is confirmed, and then inspect it again to verify cleanliness before making a connection. Unnecessary cleaning can introduce new problems.

When should you use wet cleaning instead of dry cleaning for fiber optics?

Dry cleaning is the first choice for loose particles and light films. Wet cleaning, using a suitable solvent, should be reserved for more persistent contamination, such as oily substances, that dry methods cannot remove.

What is the wet-to-dry cleaning technique?

This technique involves touching the fiber end to a small wet spot on a lint-free wipe and then dragging it once into a dry area. This method effectively softens and removes contamination while minimizing solvent residue.

Which solvents are suitable for cleaning fiber optics?

High-purity isopropyl alcohol (99% or higher) is widely used as it evaporates quickly with little residue. Specially formulated, fiber-safe engineered cleaners are also very effective, particularly for oily films.

Is canned air suitable for cleaning fiber ends?

Standard 'canned air' products should be avoided because they can expel liquid propellant or moisture, which will contaminate the fiber endface. A filtered, oil-free dry gas source is a much safer alternative.

How should one clean a bare fiber before cleaving or splicing?

After stripping the coating, wipe the bare glass once with a slightly moistened lint-free wipe, then immediately wipe it dry with a clean section of the wipe. This removes buffer residue and ensures a high-quality cleave.

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