As one of the most effective approaches today for reliable and long-distance communications, fiber optic cable has attracted network designers’ notice while they take on cabling installation and upgrade projects. Undoubtedly, compared with copper, fiber optic cable delivers more bandwidth, and allows for more reliable data transmission over longer distance, say 10km distance is possible in GbE applications when used in combination with 1000BASE-LX SFP transceivers (EX-SFP-1GE-LX). To put it simply, fiber is able to carry more information with greater fidelity since finer is immune to many environmental factors that affect copper wire. However, there are many aspects that may influence the performance of fiber, such as light loss, a key issue. And such fiber light loss seems to be a top priority for network designers to consider while handling fiber optic cable. This article mainly discusses problems that cause loss and methods to fix it.

Before talking about fiber light loss, it’s imperative to have the basic knowledge about light loss.

Fiber optic signal is made of light, and when fiber optic cable carries these pulses of light between transmitters and receivers, signal loss occurs during transmission. In order to ensure the smooth data transmission, the light must arrive at the far end of the cable with enough power to be measured. Light loss between the ends of a fiber link results from multiple sources, such as the attenuation of the fiber itself, fusion splices, macro bends, and loss through adapter couplings where end-faces meet. Among these important sources that can bring a network down, dirty and damaged end-faces are the most underestimated threat. Dirty end-faces are a leading cause of fiber link failure for both installers and private network owners. Contaminated end-faces are likely to cause fault in fiber links. It’s easy to prevent, but there continues to be a lack of appreciation for this crucial issue and lots of misinformation about proper techniques.

In this passage, two sources that cause loss as light leaves one end-face and enters another inside an adapter are introduced: contamination and damage.

• Contamination

Contamination falls in many forms, from dust to oils to buffer gel. Simply touching the ferrule will immediately deposit an unacceptable amount of body oil on the end-face. Dust and small static-charged particles float through the air and can land on any exposed termination. This can be true in facilities which are under construction or renovation. In new installations, buffer gel and pulling lube can easily find its way onto an end-face.

As for such contamination, protective caps, also called "dust caps”, are one of the most common contributors. These caps are made in rapid production processes during which a mold release compound is used. Such compound is likely to contaminate end-faces on contact. What’s more, as the time goes by, the plastic cap becomes "old”, and then plasticizers would deteriorate and result in an outgas residue. Last, airborne dust itself would find its way into the protective cap and move to the end-face when the cap is pushed onto a ferrule. It’s a very common mistake to assume that end-faces are clean when patch cords or preterminated pigtails are removed from a sealed bag with protective caps in place.

• How to Avoid Such Contamination?

To avoid this problem, it’s recommended to follow the following steps. Inspection of the end-face is necessary to verify that no containments are within the field of view. The most crucial area to clean is the core of the fiber, followed by the cladding. Yet contamination on the ferrule—outside of the end face—could slide towards to core as the fiber is mated or handled. Therefore, all visible contamination should be removed if possible.

• Damage

It’s ill-advised to mate every connection first and then inspect only those that fail, as the physical contact of mated contaminants can cause permanent damage. This permanent damage would lead to more costly and time-consuming determination or replacement of preterminated links.

Scratches, pits, cracks or chips all "belong to” damage. These end-face surface short comings could attribute to the poor termination or mated contamination. Regardless of the cause, damage must be evaluated to determine if action is required, as some of it can be ignored or remedied. Up to 5% of the outer edge of fiber cladding generally may be chipped; this is a common result of the polishing process. Any chips on the core are unacceptable. If scratches or excess epoxy bleed are found, re-polishing with fine lapping paper can eliminate the problem. If the end-face is cracked or shattered, the fiber must always be re-terminated.

• How to Prevent Such Damage?

In every step taken, all end-faces should be inspected before insertion. If a connector is being mated to a port, then the port should be inspected as well. Be aware that contamination inside a port can not only cause damage but also migrate to the connector being inserted. Too often equipment ports are overlooked not only as contaminated themselves but also as a source of contamination for test cords. So, it’s a wise approach to check every equipment port before they are safe and clean to be inserted.

It’s known that fiber light loss can affect the data transmission speed and distance. This distance further depends on wavelength, and cable types, ranging from 550m with multi-mode cable with GbE modules (eg. MA-SFP-1GB-SX) and up to 40km for single-mode cable 40GbE modules (ie. QSFP-40G-ER4).

To reduce fiber light loss as much as possible, it’s of great importance to keep fiber from being contaminated or damaged. Certainly, fiber light loss sources are not limited to above-mentioned two, the intrinsic fiber core attenuation also included. Hope this text is helpful for you to avoid possible external fiber contamination and damage, so as to improve fiber performance.

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