Fiber Optic Cleaning Practices

Fiber Optic Cleaning Practices

Introduction to Fiber Inspection and Cleaning

Fiber optics are the backbone of today's high-speed telecommunication networks. Ensuring clean fiber optic connections is one of the most basic and critical procedures for maintaining error-free communication in these optical systems.

The fiber core of a single mode fiber is a mere 9 micrometers in diameter. This is too small to see with the naked eye. In comparison, a human hair is typically 50 to 75 micrometers in diameter! Dust particles as small as 1 micrometer can actually cause a significant loss of signal if covering the fiber core. Even if the dust particle is not covering the core, it can cause an air gap or a misalignment between the cores of the mating surfaces resulting in significant attenuation or back-reflection.

CAUTION (1-1) Lasers used in telecommunication systems are powerful enough to burn contaminants into the fiber end face. Always ensure the laser is turned off while performing the cleaning procedure.

The three critical steps to ensuring high quality optical connections are:

Inspection

Cleaning

Re-inspection

General Warnings and Reminders

Please read and heed these reminders and warnings prior to inspecting and cleaning fiber optic connections.

Reminders

Grasp only the connector housing when plugging or unplugging connectors

Install dust caps on unplugged connectors

Store unused dust caps in a re-sealable container to prevent dust on the caps from being transferred to the fiber end

Do not re-use swabs or cleaning tissues. Dispose of properly.

Warnings

Do not look into a fiber while the system laser is on.

Do not connect a fiberscope while the system laser is on.

Do not use alcohol or other wet cleaner without a way to ensure that all residues are removed.

Do not clean bulkhead receptacles without a means of inspection following the cleaning. The attempted cleaning could easily make the condition worse.

Do not touch the end face of the fiber connector.

Do not use isopropyl alcohol around open flames or sparks.

Inspection and Cleaning Procedure

The following are general steps that should be performed for cleaning fiber ends. Details on dry and wet cleaning methods as well as recommended inspection tools will be discussed in the next sections.

Inspect the fiber end with a fiberscope of at least 200x magnification.

If the fiber end is contaminated, clean using a dry cleaning method.

Inspect the connector again using the fiberscope.

If the fiber end is still contaminated, attempt the dry cleaning method again.

Inspect the connector again using the fiberscope.

If the connector is still contaminated, clean using a wet cleaning method immediately followed by a dry cleaning method to remove all residue.

Inspect the connector again using the fiberscope.

Repeat this process until the end face is clean.

If the fiber end cleaning is unsuccessful, the contamination may be due to scratching, improper polishing, or other damage. If possible, this fiber should not be used.

Inspection Methods

Inspection of fiber end faces for contamination is impossible with the naked eye. It is recommended to use a microscope with at least 200x magnification.

Figure 1-1 shows a clean single mode fiber end face at 200x magnification.

Figure 1-1. Single mode fiber optic end face at 200x magnification.
During inspection it is important to ensure the entire end face is free of contamination. Although the signal only passes through the core, dirt or debris around the cladding can cause misalignment of the cores or an air gap resulting in attenuation or excessive back reflections. Note the textured white area surrounding the cladding. On a newly made connection, there should be no visible texturing. The image in Figure 1-1 is from a fiber loopback used in production testing. This connector end face is scratched from years of cleaning and repeated insertions. Such a surface feature cannot be corrected by cleaning.

Below are some examples of different types of dirty and damaged fiber connectors.

Figure 1-2. Debris Covered Fiber and Ringed Cladding
The picture in Figure 1-2 shows debris covering the fiber as well as a ring surrounding the cladding. The mating surface of the fiber end is convex, so only a section of the connector surfaces are in direct contact. This ring is from accumulation of dirt around the edges of the connection surface and could result in core misalignment or an air gap.

Figure 1-3. Excessive Scratching and Dirt Deposit Damage
The connector in Figure 1-3 is damaged excessively by scratching and dirt deposits. Multiple and repeated cleaning techniques would need to be used to clean this fiber end.

Figure 1-4. Ring Around the Cladding
Again we see in Figure 1-4 the ring formed around the cladding. This can also be made when the connector is not dried thoroughly following a wet cleaning technique.

Figure 1-5. Results of Cloth Cleaning of the Surface
The connector end in Figure 1-5 was cleaned by wiping the surface on a piece of clothing. Only approved dry cleaning methods and materials should be used to clean fiber ends.

There are many brands of fiberscopes available allowing for at least 200x magnification including benchtop as well as portable models. The benchtop models offer superior magnification at a modest price. But they are limited, as they do not offer an adapter to view the fiber face inside a bulkhead connector of an assembled module.

Avici recommends using the Ferrule Cam made by AEFOS (part number AFXM-VD.) This is a portable 200x fiberscope capable of looking at fiber ends inside bulkhead connectors. See Figure 1-6.

Figure 1-6. AEFOS Ferrule Cam

Operation of the Ferrule Cam

Turn on by pressing the red button.

Perform battery check by depressing the green button. The four LEDs above the green button indicate battery status. Four LEDs lit indicates full charge.

For Gen II route modules, insert the probe end into the faceplate SC connector port as shown in Figure 1-7.

For Gen I route modules, disconnect the fiber from the upper connector in the drawer and view using a spare SC connector as shown in Figure 1-8.

Focus using the thumbwheel on the probe body.

Contrast and brightness controls are located under the green and red buttons.

Refer to the operational manual for detailed instructions on charging the battery and operation of the Fiber Scope.

Figure 1-7. Operation of the Ferrule Cam on Gen II module

Figure 1-8. Operation of the Ferrule Cam on Gen I module

NOTE Inspections should be performed before and after each cleaning.

Dry Cleaning Methods

For Gen I modules and loose fiber patchcord, the recommended dry cleaning method is using the Cle-top cleaner. Refer to Figure 1-9.

Move the thumb lever to expose the cleaning cloth. Each time the lever is pressed, a clean section of cloth is exposed.

Holding the fiber end perpendicular to the cleaning cloth, twist 90 degrees and then drag down across the exposed cleaning cloth applying a small amount of pressure.

Do not re-use the same section of cleaning cloth once a fiber end has been cleaned. To expose a new section of cleaning cloth, release the thumb lever, then actuate the lever again.

Inspect with fiberscope.

Figure 1-9. Using the Cle-top Cleaner
For Gen II route modules, or any bulkhead fiber connector, the current industry practice has been to use swabs inserted into the ferrule of the connector to clean the internal fiber face. This method can be done effectively by experienced personnel, but can be difficult to master.

Avici recommends the use of the AFC-3000 Automated Ferrule Cleaner for this application. See Figure 1-10.

Insert the end of the cleaner into the connector. The adapter is keyed to ensure proper alignment. Please refer to Figure 1-11.

Press the Ferrule Cleaner into the connector to actuate the automatic cleaner. Maintain pressure until the cleaning process is completed (approximately 3 seconds.)

Remove the cleaner and inspect the fiber end using the Ferrule Cam.

Details on the operation of the AFC-3000 can be found in the operator's manual.

Figure 1-10. AFC-3000 Automated Ferrule Cleaner

Figure 1-11. Using the Automated Ferrule Cleaner on a Gen 1 route module

Wet Cleaning Methods

If the dry cleaning method does not adequately clean the connector, use an optical quality cleaning cloth and fluid. Isopropyl alcohol is frequently used as the cleaning fluid, but alcohol is not very quick drying and leaves residue.

The recommended cleaning cloth and fluid are Opticwipes by Chemtronics (pn - C920) and Microcare's Fiber Preparation Fluid (pn - FPF1).

Dampen the cleaning cloth with the cleaning fluid. Do not saturate the cloth.

Holding the fiber connector perpendicular to the cloth, twist and wipe the end face in the damp area of the cloth several times.

Repeat the twist and clean on a clean, dry area of the cleaning cloth.

Inspect the end face.

Relevant Documents

AFC-3000 Automated Ferrule Cleaner for Fiber Optics User's Manual

AFXM-VD Ferrule Cam User's Manual

	CAUTION (1-1) Lasers used in telecommunication systems are powerful enough to burn contaminants into the fiber end face. Always ensure the laser is turned off while performing the cleaning procedure.