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Fibre Optic Cable Assemblies

An optical fibre connector terminates the end of an optical fibre, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibres so light can pass. Better connectors lose very little light due to reflection or misalignment of the fibres. In all, about 100 fibre optic connectors have been introduced to the market.

Application

Optical fibre connectors are used to join optical fibres where a connect/disconnect capability is required. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are generally assembled onto optical fibre in a supplier’s manufacturing facility. However, the assembly and polishing operations involved can be performed in the field, for example, to make cross-connect jumpers to size.

Optical fibre connectors are used in Telephone Company central offices, at installations on customer premises, and in outside plant applications to connect equipment and cables, or to cross-connect cables.

Most optical fibre connectors are spring-loaded, so the fibre faces are pressed together when the connectors are mated. The resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibres.

Every fibre connection has two values:

Attenuation or insertion loss

Reflection or return loss.

Measurements of these parameters are now defined in IEC standard 61753-1. The standard gives five grades for insertion loss from A (best) to D (worst), and M for multimode. The other parameter is return loss, with grades from 1 (best) to 5 (worst).

A variety of optical fibre connectors are available, but SC and LC connectors are the most common types of connectors on the market.[citation needed] Typical connectors are rated for 500–1,000 mating cycles.[2] The main differences among types of connectors are dimensions and methods of mechanical coupling. Generally, organizations will standardize on one kind of connector, depending on what equipment they commonly use. Different connectors are required for multimode, and for single-mode fibres.

In many data centre applications, small (e.g., LC) and multi-fibre (e.g., MTP) connectors are replacing larger, older styles (e.g., SC), allowing more fibre ports per unit of rack space.

Features of good connector design:

Low insertion loss

High return loss (low amounts of reflection at the interface)

Ease of installation

Low cost

Reliability

Low environmental sensitivity

Ease of use

Outside plant applications may require connectors be located underground, or on outdoor walls or utility poles. In such settings, protective enclosures are often used, and fall into two broad categories: hermetic (sealed) and free-breathing. Hermetic cases prevent entry of moisture and air but, lacking ventilation, can become hot if exposed to sunlight or other sources of heat. Free-breathing enclosures, on the other hand, allow ventilation, but can also admit moisture, insects and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location, and environmental factors. Careful assembly is required to ensure good protection against the elements.

Depending on user requirements, housings for outside plant applications may be tested by the manufacturer under various environmental simulations, which could include physical shock and vibration, water spray, water immersion, dust, etc. to ensure the integrity of optical fibre connections and housing seals.