Field-Terminated Fiber Examined

By Brian Rhodes, Published Nov 25, 2012, 12:00am EST

Getting into fiber optics can be costly. Many security integrators simply lack sufficient fiber runs to justify the special tools, training, and materials needed to terminate fiber optics cables. Despite being a good solution, fiber is either avoided or subcontracted to a specialist. However, an alternative solution exists: field terminated fiber connectors. In this note, we examine these connectors, compare their costs to alternatives and recommend where they should be used.

Fiber Termination: Delicate Operation

Terminating fiber optics takes an entirely different level of skill, attention, and tooling than ethernet and coax cable. Unlike copper strand terminations that use a simple 'clip and crimp' process, glass fiber terminations require very precise cutting, end polishing, and connector matching.

When electrical impulses are transmitted in ethernet cables, the surface area of the conductor inside the terminator is critical. However, the optical impulses transmitted by glass fiber are subject to many other types of problems. The picture below illustrates several of the aspects that must be controlled to guarantee successful fiber terminations:

A good quality fiber termination is similar to splicing a piece of water pipe - the mating surfaces between the sections of pipe must be precisely matched to each other, or else leaks will occur. With fiber, this 'leaking' translates into signal loss and degradation, and even slight flaws will significantly affect signal quality.

Outrageous Costs

Because the connections must be so exacting, traditional fiber terminations have required specialized and costly equipment like:

The capital investment required to terminate cable is measured in tens of thousands of dollars, even before considering the cost of operator training and upkeep.

For the typical integrator faced with a small number of fiber terminations each year, the economics to 'get into' fiber is often prohibitive.

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Field Terminated Connectors

For those ocassionally termianting fiber, field terminated connectors provide better overall value. While the cost of a single 'field terminated' connector (~$15 - $35 USD) might be several times more costly than a 'traditional' spliced connector (~$2 - $10 USD), the overall cost of the solution is significantly lower than traditional termination tools or subcontracting a few terminations.

Many options of 'field terminated' connectors exist, from a number of major wire/cable/fiber manufacturers, including:

  • Belden FiberExpress Brilliance
  • AFL Telecommunication FAST [link no longer available]
  • 3M NPC [link no longer available]
  • Panduit OPTICAM [link no longer available]

In general, these connectors are engineered with some form of 'pre-polished' fiber end that is encapsulated in a index matching optical conductivity gel within the connector. The promotional video from Belkin below gives an example of how 'field terminated connectors' typically are installed:

No Special Training Required

While the exact process varies between products, it typically employs a few steps that an inexperienced technician can follow and quickly master:

a) Strip the jacket away from the fiber core

b) Clean the fiber core using a mild solvent

c) Use a hand cleaver to score and part the fiber end

d) Insert prepared fiber end into the connector, such that a 'butt joint' is achieved inside the connector

e) Verify quality of connection (often Empirical or visual)

f) Affix connector to fiber by some mechanical locking method, often by twisting, compressing, or snapping the connector in place.

A full catalog of single and multimodal connectors are available, including common LC, ST, and SC formats for the standard fiber diameters.

Installation Kits

Use of field-terminated connectors often requires buying a few specialized hand tools. While the contents of the kit depend on how the respective connector works, the kits typically contain cleavers, assembly cradles, cleaning supplies, and jacket stripping tools. While none of these kits are required to use field terminated connectors, the hand cleaver is essential and cannot be substituted for other options.

The cost of these kits range between ~$300 - ~$1000 each, and typically are good for installing thousands of connectors before needing to be replaced. Unlike traditional installation equipment costing tens of thousands, these installation kits are a fraction of the cost.

Cost Comparison

The cost of terminating a fiber cable using 'field terminations' will be between $30 - $70 per cable. Fiber Installers will often subcontract the same connections for $75 - $125 per cable.

The ability for the integrator to self-perform these terminations has significant scheduling value. Instead of being forced to schedule a subcontractor for just a few terminations, the integrator can apply these terminations themselves without waiting in several minutes.

Not only can applying field terminations cost less in total that 'traditional' terminations, the work can be performed without the costs of using a specialty subcontractor.

Environmental Risks of Field Terminated Fiber

In adverse environments, field terminated fiber connectors may have problems. This is because they are filled with 'index matching gel', used to mitigate surface imperfections/reflections in the fiber cleave and bridge tiny gaps between the butt-jointed connector and cable. Over time, the gel can dry out and harden. 

For many fiber applications, this impact is minimal, but for environments that are subject to continuous vibrations and wide swings in temperature, field terminated connectors can break down due gel decay. While determining when/where a field terminated connector may have an issue is subjective, avoiding the use of these easy installing connectors in harsh environments is prudent."

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