ApplicationNotesenko.com

The Importance of Proper Cleaving
for Fiber Optic Connectors
FEBRUARY 2022
Rev. 01

Issued by:EngineeringDepartment

Created by:Andrei Vankov

Application Engineering Note

1.0

Introduction

Cleaving is part of the fiber optic connector termination process that follows the epoxy heat cureof the connector (or ferrules) and precedes the polishing process. After injecting the epoxy andinserting the fiber into the connector’s ferrule, the epoxy will permanently cure withapproximately 5 - 10 mm of fiber protruding out of the epoxy bead that has formed on theferrule’s surface. This surface is commonly referred to as the end-face. Since the exposed fiber
is not encapsulated by the epoxy, it is prone to uncontrolled breakage that can propagate down
below the ferrule end-face. When mating ferrules, the applied force between fibers can reach
45,000 psi. Thus, it is imperative that fibers are cleaved and polished flush with the ceramic
ferrule end-face to ensure proper physical contact, without damaging the polished interfaces.
Cleaving is a controlled cut of the optical fiber that protrudes through the epoxy bead on theferrule end-face. The process begins by scoring or scratching the side of the fiber with a sharp
blade made of diamond, tungsten carbide, or sapphire. Tensile force is then applied to the fiberwith the operators’ fingers, which induces a controlled break that propagates rapidly from thefracture point across the entire fiber cross section. Executed properly, cleaving will yield arelatively flat surface perpendicular to the length of the fiber and only a miniscule protrusion ofglass remaining.
Fibers are cleaved and end-faces are air polished to equalize epoxy beads that are uniform insize and consistency. These steps are necessary to produce connectors with satisfactory visualand geometrical end-face parameters.

Good Cleave
Smooth, Flat Surface

Poor Cleave
Chips and Lips

Figure 1: Example of a good cleave (left) vs a poor cleave (right)

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Application Engineering Note

2.0

Overview

Tools for fiber cleaving are typically called fiber cleavers or scribes. There are a variety ofcleaving hand tool designs available, but they all rely on the same basic principles to cleanly cut
fibers just above the epoxy bead. Simple and inexpensive cleavers typically look like penshaped scribes (Figure 2) and are sufficient for achieving the desired result with proper training.
These are typically equipped with sapphire or tungsten carbide blades. Tungsten is usedbecause it is one of the strongest materials with an 8.5 to 9 rating on the hardness scale. For
comparison, the hardness rating for titanium is only 6.

Figure 1:2: Manual
Manual fiber
fiber optic
optic cleaving
cleaving tool,tool, SENKO
SENKO P/NPN AFT-T-CT
Figure
AFT-T-CTManual cleaving (or scribing) relies on a trained operator scoring the fiber with a scribe and thenbreaking the fiber away from the ferrule with tension. SENKO’s recommendation for a manualcleave is the following process, which can also be found in relevant SENKO Engineering
Termination Procedures (ETPs):
After epoxy curing, the end-face needs to be cleaved and air polished. Cleaving and polishing
are necessary to satisfy the required specifications for optical connectors. Incorrectly following
these steps may cause a yield problem and/or contribute to problems further along in thetermination process. When cleaving is done improperly and the fiber breaks, the resulting crackoften causes the terminated assembly to fail. After cleaving, a manual air polish process isrecommended to trim the fiber stub down to the epoxy level – this helps avoid fiber cracking
during the epoxy removal step on the polisher.
Caution: Please handle the exposed fiber carefully to avoid breakage.
1.

After the ferrules have cooled to room temperature, remove the excess fiber protrudingfrom the tip using a suitable cleaving tool (recommendation: SENKO P/N AFT-T-CT).

2.

Hold the ferrule with the fiber pointing upwards.

3.

Set the blade of the cleaving tool against the fiber just above the epoxy bead on thesurface of the ferrule.

2Application Engineering Note
4.

Gently run the full length of the blade along one side of the fiber. Be careful not to breakthe fiber with the cleaving tool.

5.

Lift the fiber up with your fingertips.

6.

Properly dispose of the cleaved fiber into a scrap bin.

7.

When all the fiber has been removed, check the sides of the ferrule for excess epoxy
that may have cured. Use a scalpel or Stanley blade to remove any excess.

Figure 2: Scribing

The manual aspect of fiber cleaving exposes the process to human variability and error. The
best way to eliminate this is to use automated cleavers (please contact your SENKO AccountRepresentative for more details). Automated cleavers are marketed as long-term cost-saving
solutions, with benefits that include:
••••
•
•

Consistency and precision, with a significant reduction in process variation stemmingfrom fiber damage
Critical time savings for the overall manufacturing process
Uniform starting point requiring less polishing time/consumables
Consistent epoxy removal
Improved geometry
Improved safety by minimizing the handling of scrap fiber

There are two main variations of automated cleavers, laser-based and mechanical. Both arecapable of cutting the fiber through the epoxy bead, thus cleaving closer to the ferrule surface
and reducing the amount of epoxy that needs to be removed during the polishing process. In aCO2 laser-based cutting system, a CO2 laser (typically 9.3 – 10.6 μm) cleaves fibers at specified
angles. The mechanism by which the cut is performed is absorptive, with strong thermal
heating. The laser beam emitted by the automated cleaver is reflected by metal mirrors before
being focused on the target area. Average laser power is below 50 watts with high output
stability (< 5%). The less expensive automated alternative, the mechanical cleaver, uses twocontrolled precision tungsten carbide blades to cut the fiber from both sides.

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Application Engineering Note

Figure 3: Mechanical blade cleave (left) vs manual cleave (right)

3.0

Manual vs. Automated Cleaving

Automated cleaving has a much higher upfront tooling cost, which is justified when production
volumes are consistently high based on Return on Investment (ROI) calculations. The
investment for an automated cleaving system is significant, but the financial calculations need toconsider the increased processing speed and overall improvements in quality. An automatedcleave can save up to 30 seconds per connector versus the manual alternative. Unlike theautomated process, the ferrule is not ready for fiber polishing after manual scribing. The manualcleave removes protruding fibers from the tip of the epoxy bead, resulting in a stub that requires
removal with additional air polishing (refer to SENKO Application Note “Polishing Fiber OpticConnectors with Ceramic Ferrules” for more information on air polishing and the polishingprocess). In short, additional manufacturing time is required to manually remove the fiber stub
before the epoxy can be polished off using an automated polishing machine. Therefore,automated cleaving leads to increased performance and production yields.
The latest generation of automated single fiber cleavers use a bi-directional laser beam, whichallows for ultra-low profile cleaves at 30 – 35 µm above the ferrule tip, reshaping the fiber andremoving most of the epoxy. Equipment manufacturers claim that cleaved ceramic connectors(from single fiber pre-domed connectors) can be forwarded straight to a 1 μm diamond polishing
step when using a high quality polisher. This reduces the polishing process from 4 - 5 steps,
down to just 2. However, from SENKO trials and experiments, this statement was found to bemostly true for multimode connectors because the final end-face allows for more imperfections
when compared to a single-mode finish; per IEC document 61300-3-35 “Visual Inspection ofFiber Optic Connectors”. The requirements for IEC 61300-3-35 are very detailed, with specificacceptance criteria for single-mode and multimode connectors in both single fiber (i.e. LC, SC,FC, etc.) and multi-fiber (i.e. MPO) connectors. The criteria are based on several factors,including size, count, and location of the defects/scratches.
Automated cleavers are particularly advantageous when cleaving mechanical transfer (MT)ferrules by achieving a uniform fiber height across all fibers (Figure 4). After the epoxy has4

Application Engineering Notecured in an MT ferrule, the protruding fibers at the edges (typically fibers 1 - 2 and 11 - 12) areencapsulated by less epoxy and are thus considered unsupported at the sides. These fibers areprone to uncontrolled breakage if mishandled. A typical manual operation entails a curved
scribing just above the epoxy bead. A careful, manual, and time consuming cleave followed by aflattening of the curve of individual fibers. This is all required before polishing to avoid fiber
breakage below the ferrule surface. In contrast, the laser from an automated cleaver cuts wider
and results in a flat surface with a more uniform fiber protrusion. Alternatively, automatedmechanical cleavers are equipped with precision adapters to ensure accurate and reproducible
positioning of the ferrules during cleaving, resulting in very consistent fiber heights. The lack offiber nubs and a flat planar surface reduces the potential for fiber breakage and its
accompanying rework.

Figure 4: Automated cleaves (flat) provide a consistent final fiber cut height in MT ferrules. Compared is the manualalternative (concave).

5Application Engineering Note
Table 1. Comparison between manual and automated (mechanical and laser-based) cleavers.

Main Points
Operation
Equipment Cost
High Volume
Production Cost
Ease of Use
MaintenancePrecision
Consumables
Portability
ReproducibilityLife Span (# ofcleaves)
SoftwareSet Up Time
SafetyManualCleaver Type
Mechanical

Laser

Operator dependent$$$$$

Automated$$$$

Automated$$$$$$$

Skilled labor/training
requiredNoneLow
Requires air polish
Pocket sizeLowUp to 1000

Single button
operationMinimal
High
Optional
Small box
High~ 750000

Requires software
knowledge
ExtensiveHigh
Optional
Large station
High~ 1000000

None
None
Requires carefulmanual shards
disposal

None
ShortShards collected
automatically in abinYes
Long
Shards vacuumed
automatically into thedisposal compartment

Table Summary:Operation
Manual cleaving relies on a trained operator scoring the fiber with a scribe and then breaking
the fiber away from the ferrule in hopes of achieving the proper scribe/break combination.
Automated cleaving is very consistent and precise from ferrule to ferrule, with no humanvariable present to affect the scribe/break combination.
Equipment Cost
Manual Scribe $15 - $50; Automated Mechanical Cleaver $10K - $15K; Automated Laser
Cleaver $40K - $70K.
High Volume Production Cost
Manual cleaving leaves fiber stubs protruding over variously sized epoxy beads. It is imperative
to manually air polish the individual ferrules to bring the epoxy beads to the same level before
using a mass polisher. Both automated cleaving solutions cleave fibers in a highly reproduciblemanner with a very low profile cut. After automated cleaving, the fibers remain sufficiently
protected for the initial polishing stage, making an additional air polish optional, or evenunnecessary.
Ease of Use
Manual cleaving requires training and experience. Mechanical cleavers are the easiest to use
with a simple setup and single button operation. Laser cleavers often require an operator that isproficient in the software for proper operation.

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Application Engineering NoteMaintenance
Manual cleaving requires an operator’s judgment to determine whether a blade is dull andneeds a replacement. Disposable cleavers are discarded. Some cleavers come withreplaceable blades that are changed in a manner similar to that of a utility knife. Mechanicalcleavers require less frequent blade changes and cleaning as the blades are large in size. Lasercleavers require more extensive maintenance, as depicted in the following maintenanceschedule (Table 2).
Table 2. Example of a maintenance schedule for an automated laser cleaver.

Operator
Replacement Frequency
Task

Description

Frequency

Adapter and hard stop

Daily

Clean

As necessary

Vacuum drawer
Vacuum filter

Daily
WeeklyEmptyClean

As necessary

Lens

WeeklyClean

Annual ServiceYearly

Check

Request manufacturer to perform

Precision and Reproducibility
Manual cleaving relies on manual labor, resulting in poor consistency. Automated versions
cleave in a highly reproducible manner. When the ferrules are subsequently mounted on apolishing fixture, all automatically cleaved epoxy beads will protrude by the same amount,leading to a much more consistent polish.
Consumables
After manual cleaving, additional polishing material is required to air polish inconsistent fiber
ends and epoxy beads.
Portability
The Manual Cleaver is the size of a pocket-sized pen. The Mechanical Cleaver is half the sizeof a shoe box. The Laser Cleaver is a small operating unit the size of a work bench that shouldbe placed in a fixed location. It is considered to be an advantage of mechanical cleavers thatthey are portable, sometimes battery operated, and easily carried from station to station. Incontrast, a laser cleaver is typically quite large and requires a new setup when transporting.
Life Span
Manual cleavers typically last for up to 1000 cleaves, while automated units are rated for up to amillion cleaves.
Software7

Application Engineering Note
Laser cleavers are driven by software that requires knowledge/training and could haveupgrades, glitches, etc. Mechanical cleavers typically only have two buttons for power and blade
operation.
Set Up Time
Laser cleavers typically require engineering support to set up and calibrate between fixturechanges, but are easy to operate via a pedal or a button once installed. Mechanical cleavers
have their cut length limited by their blade size, while lasers can cleave across wider surfaces.
However, mechanical cleavers can easily accommodate different connector types with a quick
adapter change and calibration. In comparison, an adapter change on a laser cleaver requires
fine tuning with a few terminated connectors that represent an actual product to ensure proper
fiber cleaving height. Too high of a cleave leaves too much fiber nub, while too low of a cleaveburns the ferrule material by singeing it with the heat of the laser, leaving it discolored andunusable.
SafetyProduction safety levels are easier to manage with automation. Manual scribing results inoperators handling the tiny fiber shards themselves. It is very easy for an operator to
accidentally break a fiber tip off during scribing, and that broken tip can end up anywhere in theproduction area and/or on the operator’s skin. Automated cleavers have removable trays thatallow for the periodic disposal of all fiber shards in a safe and controlled manner. Laser cleavers
vacuum the fiber shards into a disposal container automatically.

4.0

Conclusion

Cleaving is an important part of the termination production process, which can improve quality,yields, and efficiency. Improper cleaving could lead to process rework and costly delays. Even aseemingly straightforward step such as cleaving requires good manufacturing support,procedures, proper tools, and well trained operators. While the manual process can produce
similar results, it takes extra effort to ensure that an operator has the right skills, good eyesight,and dexterity. Considerations must also be made for proper fiber scrap management, and theadditional time and technique required to air polish the epoxy beads down to the same level
before using a mass polisher. Both automated cleaving solutions, whether mechanical or laser
based, cleave in a highly reproducible manner with a very low profile cut. After cleaving, thefibers remain encapsulated in a greatly reduced, consistent, and supportive epoxy bead and aresufficiently protected for the initial polishing stage; making an additional air polish optional, oreven unnecessary. This results in increased process speed and higher output. Automation
should be considered whenever production volumes justify hefty upfront investments throughROI calculations. Nevertheless, with proper training and experience, a $20 manual cleaver cando just as good a job as a laser cleaving station for $40K.
Please contact a SENKO representative if you have any additional questions.

8Application Engineering Note9