Wet-to-dry fiber cleaning: A good way to ensure network reliability

By Jay Tourigny, MicroCare LLC

Expert opinions vary, but many agree that up to 75% of all fiber network problems are caused by contamination of patch cords, adapters, alignment sleeves or transceivers. Dirty endface connectors in particular are a real hazard to modern fiber-optic networks. The higher the light frequency in a network, the greater its sensitivity to contamination. This means that faster 5G networks, which need every milliwatt of power to function flawlessly, are more vulnerable to contamination. Although endface contamination is typically just microns in size, and only visible when magnified with an inspection scope, it can still cause serious performance and reliability problems for a network.

Two common contaminants

Two main types of endface contamination are dust and oil residue. Dust comes from various environmental sources. These can include things like skin flakes and stray hair from installers or dirt from dusty work sites. It also comes from other, less obvious sources. For instance, dust often generates through the contact friction between plastic connectors as they are mated. Dust can even come from the fiber cleaning tools themselves. Examples include lint from paper-type wipes and foam particles from foam-tipped cleaning sticks.

Static often makes dust contamination worse. An electrostatic charge on a connector attracts airborne particulate and locks it onto the connector endface. The condition is worsened in dry, low-humidity conditions such as winter cold or desert heat. Electrostatically charged particles are often created by test equipment, cooling fans on network gear or by an internal HVAC system. These charges, also known as triboelectric effect, remain on the ferrule surface and turns the contact area of the endface into a magnet, attracting dust right to the center of the endface where it will do the most damage.

Any dust residing on the sleeve gets pushed into the contact zone as the connector pair is mated. The dust breaks apart and grinds into the ceramic and glass ferrules with an approximately 15,000-psi force in the contact zone. This can cause permanent scratches and pits in the center core, or contact zone, of both termini endfaces. If the damage is severe enough, it may require reterminating or replacing the cables altogether.

Oil and other residues

Oil-based contamination and other residues come from many sources. The most common are fingerprints and skin oil. However, other residues also contribute to endface contamination. These include things like plasticizer off-gassing from PVC plastic connector endcaps, coastal salt for and isopropyl alcohol (IPA). IPA is commonly used for fiber cleaning; however, IPA is hygroscopic. It absorbs water and minerals from the atmosphere, which redeposit onto the fiber endfaces.

Signal interference

A microscopic dust particle, a residue from an accidental finger touch, or even the outgassing from the removal of a dustcap can interfere with the network’s light path as it passes between two mated fibers. When the light is blocked, or the direction of the light changes, a phenomenon known as chromatic aberration exists.

Contamination blocking the light signal’s path can cause absorption loss. Or it may change the light’s index of refraction, or disperse the signal’s wavelength unpredictably, causing insertion loss. Dust or oil contamination could also cause light to be directed back into the fiber to its original source, also known as back reflection. In all of these instances, the light signal weakens, slows down the network speed or results in unacceptable data transmission losses—especially for those networks with angled-polish connectors. And if the refraction angle is altered enough, the network signal may be lost altogether, requiring an expensive and disruptive emergency rollback to troubleshoot and repair the problem. So, cleaning all connection points becomes vitally important; and wet-to-dry cleaning is an effective way to get that done.

How wet-to-dry cleaning works

One of the most common ways contaminate draws to a fiber endface is from wiping the endface with a dry wipe, dry clicker tool or a dry stick. The wiping action creates a triboelectric charge that attracts unwanted airborne contaminants to the connector face. This static buildup is especially intensified in low-humidity environments.

Dust clings to both the outer regions of the connector and at the ferrule apex in the contact zone. Most fiber endfaces are made of nonconductive materials such as plastic, ceramic, glass and epoxies so the static charge doesn’t have a path to ground and the charge cannot discharge. The dust particles stay electrically bonded to a cable endface until the static charge finds a conductive path for it to dissipate.

Wet-to-dry cleaning using a fiber-optic cleaning fluid provides a solution. The wet cleaning fluid serves as a dissipative medium. It adds humidity to the endfaces, breaks the static bond and allows the fiber cleaning tools to do a better job. The fluid temporarily creates a conductive path for the static to disperse, making it easier to physically remove the contaminant with a wipe, cleaning stick or mechanical clicker tool.

Wet-to-dry cleaning with a wipe

Always use a high-quality optical-grade wipe for wet-to-dry cleaning. Use one that will not lint, shred or leave debris behind. During the wet-to-dry cleaning process, an installer uses a section of an optical-grade cleaning wipe, dampened with a static-dissipative cleaning fluid. The installer then wipes the connector endface starting at the damp area of the wipe and moving in one direction toward the dry area of the cleaning wipe. This removes the contamination and minimizes the static charge in one step.

Some suppliers offer wipes in special packaging engineered to minimize static charges as individual wipes are dispensed. Also, leaving the wipes in the packaging until ready to use ensures they stay clean, preventing waste. Wipes should be used only once and then thrown away to prevent cross-contamination on other network endfaces.

Wet-to-dry cleaning with a cleaning stick

For best results use a polymer-tipped cleaning stick. Avoid those with a paper or foam tip. They typically fall apart, leaving lint and foam particles behind. Cleaning sticks are ideal for use on heavily soiled connectors or for cleaning in hard-to-reach alignment sleeves. For wet-to-dry cleaning with a stick, the installer moistens the cleaning stick with a cleaning fluid first, being careful not to oversaturate the tip. After inserting the stick into the connector, they rotate the stick about six times in the same direction. They avoid extreme force and do not excessively scrub the endface to prevent scratching, pitting or scarring the endfaces.