If you're installing fibre cable in a permanent installation, it pays to install single-mode fibre instead of multimode fibre. Why? The higher bandwidth and signal-carrying capacity of single-mode fibre is something you'll certainly want to use in the future. Multimode fibre may be adequate for today's needs, but single-mode fibre is for the future and due to higher usage now tends to be cheaper.

Check out the following suggested RRP prices supplied as a point of reference from Fibre supplier, Amphenol.

• Single fibre, Single Mode = A$0.60/mt + GST
• Single fibre, Multi Mode = A$1.80/mt + GST
• Dual Fibre, Single Mode = A$1.40/mt + GST
• Dual Fibre, Multi Mode = A$3.00/mt + GST

• ST and SC Connectors = A$7 + GST ea.

• ST and SC Connector including factory termination / test = A$22 + GST ea.
  

IDT makes available a Dow Corning Termination kit for use with the Cornings’ Uni-Cam connectors. These connectors are available as ST

FC.       Insertion Loss 0.50-1.00 dB, SM, MM

LC. Insertion Loss 15 db (SM) 0.10 dB (MM) SM, MM

SC. Insertion Loss 20-0.45 dB SM, MM

SC Duplex.  Insertion Loss 0.20-0.45 dB SM, MM

ST

Insertion Loss Typ. 0.40 dB (SM) Typ. (SM)
Insertion Loss Typ. 0.50 dB (MM) Typ. (MM)

The Ferrule: The fibre is mounted in a long, thin cylinder, the ferrule, which acts as a fibre alignment mechanism. The ferrule is bored through the center at a diameter that is slightly larger than the diameter of the fibre cladding. The end of the fibre is located at the end of the ferrule. Ferrules are typically made of metal or ceramic, but they may also be constructed of plastic.

The Connector Body: Also called the connector housing, the connector body holds the ferrule. It is usually constructed of metal or plastic and includes one or more assembled pieces which hold the fibre in place. The details of these connector body assemblies vary among connectors, but bonding and/or crimping is commonly used to attach strength members and cable jackets to the connector body. The ferrule extends past the connector body to slip into the coupling device.

The Cable: The cable is attached to the connector body. It acts as the point of entry for the fibre. Typically, a strain-relief boot is added over the junction between the cable and the connector body, providing extra strength to the junction.

A number of events can damage fibre optic connectors. Unprotected connector ends can experience damage by impact, airborne dust particles, or excess humidity or moisture. Most designers tend to think of the power levels in optical fibres as relatively insignificant. However, a few milliwatts at 850 nm will do permanent damage to a retina.

 Never clean an optical connector attached to a fibre that is carrying light. Optical power levels as low as +15 dBm, or 32 milliwatts, may cause an explosive ignition of the cleaning material when it contacts the end of the optical connector, destroying the connector. Typical cleaning materials, such as tissues saturated with alcohol, will combust almost instantaneously when exposed to optical power levels of +15 dBm or higher. The micro-explosions at the tip of the connector can leave pits in the end of the connector and crack the connectors surface, destroying its ability to carry light with low loss. Figure 5 shows an optical connector that has been heavily damaged by high optical power levels. Usually the damage is limited to less severe pitting.

Figure 5 - Connector Damaged by High Optical Power (Photo courtesy of Dr. D.D. Davis.)

Another important thing to remember in handling fibre optic connectors is that the fibre end face and ferrule must be absolutely clean before it is inserted into a transmitter or receiver. Dust, lint, oil (from touching the fiber end face), or other foreign particles obscure the end face, compromising the integrity of the optical signal being sent over the fiber. From the optical signals point-of-view, dirty connections are like dirty windows. Less light gets through a dirty window than a clean one.

It is hard to conceive of the size of a fibre optic connector core. Single-mode fibres have cores that are only 8-9 µm in diameter. A typical human hair is 50-75 µm in diameter, approximately 6-9 times larger! Dust particles can be 20 µm or larger in diameter. Dust particles smaller than 1 µm can be suspended almost indefinitely in the air. A 1 µm dust particle landing on the core of a single-mode fiber can cause up to 1 dB of loss. Larger dust particles (9 µm or larger) can completely obscure the core of a single-mode fibre. Fibre optic connectors need to be cleaned every time they are mated and unmated; it is essential that fibre optics users develop the necessary discipline to always clean the connectors before they are mated.

It is also important to cover a fiber optic connector when it is not in use. Unprotected connector ends are most often damaged by impact, such as hitting the floor. Most connector manufacturers provide some sort of protection boot. The best protectors cover the entire connector end, but they are generally simple closed-end plastic tubes that fit snugly over the ferrule only. These boots will protect the connectors polished ferrule end from impact damage that might crack or chip the polished surface.