Fibre Optic Connector Termination Methods

There are several different ways in which fibre optic cable can be attached to fibre optic connectors. All require specific procedures and tools plus a good deal of care as the fibres are delicate and easily damaged. Not all will be offered by every manufacturer of fibre optic cabling solutions and each technique has its own relative pros and cons, summarised at the end of this section.

Epoxy & Polish Connectors

This type of connector requires the application of some form of epoxy (glue) between the fibre and the connector ferrule that firmly bonds the two elements together once the epoxy has dried. There are a number of different types of epoxy available:

Heat Cured Epoxy - uses some form of ‘oven’ to cure the epoxy, which can be selected for the optimum performance within pre-determined temperature ranges. The epoxy may either need to be injected in to the ferrule by the technician or the connectors may be supplied with the epoxy already injected by the connector manufacturer.

Ambient Temperature Epoxy - cures at room temperature without the need for any power, making it suitable for on-site terminations.

UV Adhesive - utilises Ultra Violet (UV) light to cure the epoxy but requires special connectors with a glass capillary around the fibre that allows the introduction of the UV light.

Fast Acting (Anaerobic) Adhesive - use an accelerant to speed the curing time. Can cause problems if the technician is unable to complete the insertion of the fibre into the ferrule before the epoxy cures.

Acrylic Adhesive - a new material that works in a similar way to anaerobic epoxy but with a longer curing time that offers more time to insert the fibre into the ferrule.

Crimp - This kind of connector eliminates the use of epoxy/adhesive altogether. These connectors utilise a method to mechanically grip the fibre and other cable components.
 

When the fibre has been installed into the ferrule and the epoxy has cured or the crimp completed, it is then necessary to complete a number of addition processes:

  1. Cleave the excess length of fibre that protrudes beyond the ferrule end face. The excess fibre must be disposed of in a safe manner, ideally by placing it in a ‘sharps’ disposal bin.
  2. Polish the fibre and ferrule end face until they are flush with each other and scratch free. This will require the use of several different grades of lapping (polishing) paper, a polishing puck to hold the ferrule and a ‘figure of eight’ polishing motion that ensures an even polish.
  3. Clean the ferrule end face with an alcohol impregnated, lint-free wipe.
  4. Inspect the ferrule end face using an inspection microscope to ensure that the fibre end face is clear of any scratches, cracks or chips.

                 Fibre End Face Images

Pre-polished Connectors

This type of connector has a short length of fibre already installed into the ferrule by the manufacturer of the connector. The ferrule end face will also have been polished by the manufacturer, removing the need to carry out this operation on-site. The fibre to be terminated must be prepared using a specialist cleave tool and inserted into the rear of the connector where an index matching gel is often used to bridge the gap between the two fibres. The terminated fibre is held in place using some form of crimp or locking mechanism on the rear of the connector.

 

Pigtails

A pigtail is a short length (typically 1 metre) of 900 micron buffered fibre that has been factory terminated with a fibre optic connector, thus eliminating the need for any on-site termination or polishing of the connector. The pigtail is attached to the cable fibre by splicing the end of the fibre of the pigtail to the end of the fibre of the cable. The preferred method of splicing is Fusion Splicing, where the two fibres are melted together using a high powered electric arc to effectively create one, single, continuous strand of glass. The joint between the two fibres is then protected using a splice protection sleeve that usually comprises a heat shrink polymer tube with an embedded stainless steel rod.

Pigtails and Splice Protectors

Fusion splicing requires the use of precision fibre cleaving tools and a fusion splicing machine. Modern fusion splice machines automatically align the two fibre end faces and fuse the two together to create a very low loss joint. The fusion splicing machines often also have an integral oven that is used to heat shrink the splice protector around the fibre joint.

Precision Cleaver and Fusion Splicer

Pre-Terminated Cable Assemblies

Many manufacturers now offer one or more options of factory terminated fibre optic cable assemblies. The fibre optic cables are cut to the customer’s defined length and connectors are terminated on to one or both ends of the fibre optic cable. The connectors may be presented ready to be attached to couplers or they may be presented in a cassette that can be simply loaded into a suitable chassis.

MPO or MTP® multi-fibre connectors are always factory terminated due to the precision polishing that is required.

Pre-terminated cable assemblies are quick and easy to install, require relatively low levels of skill and need no special termination equipment on-site. They do, however, require accurate surveys of the cable routes, advanced planning and allowance for the factory termination and delivery times.

 

Termination Methods Comparison

Termination Method

Typical Field Termination Time (minutes)

Typical Time Available to Insert Fibre

Curing Method

Heat Cured Epoxy

10 + 30 Curing Time

2 Hours

Oven

Ambient Temperature Epoxy

10 + 120 Curing Time

15 Minutes

Air Temperature

UV Adhesive

5

30 Seconds

UV Light

Anaerobic Adhesive

3

5 Seconds

Accelerant

Acrylic Adhesive

2.5

30 Seconds

Activator

Crimp

2

No Limit

Not Applicable

Pre-polished Connector

3

No Limit

Not Applicable

Pigtail

5

No Limit

Not Applicable

Pre-terminated Cable Assemblies

0

Not Applicable

Not Applicable

 

Termination Method

Relative Connector Cost

Special Tools Required

Relative Skill Level

Heat Cured Epoxy

Low

Curing Oven

High

Ambient Temperature Epoxy

Low

None

High

UV Adhesive

Medium

UV Curing Light

High

Anaerobic Adhesive

Low

None

High

Acrylic Adhesive

Low

None

High

Crimp

High

Specific Crimp Tools

High

Pre-polished Connector

High

Precision Cleaver & Specific Termination Tools

Medium

Pigtail

Medium

Precision Cleaver & Fusion Splicer

Medium

Pre-terminated Cable Assemblies

High

None

Low