The method for attaching fiber optic connectors to optical fibers varies among connector types. While not intended to be a definitive guide, the following steps are given as a reference for the basics of optical fiber interconnection.
1. Cut the cable one inch longer than the required finished length.
2. Carefully strip the outer jacket of the fiber with “no nick” fiber strippers. Cut the exposed strength members, and remove the fiber coating. The fiber coating may be removed two ways: by soaking the fiber for two minutes in paint thinner and wiping the fiber clean with a soft, lint-free cloth, or by carefully stripping the fiber with a fiber stripper. Be sure to use strippers made specifically for use with fiber rather than metal wire strippers as damage can occur, weakening the fiber.
3. Thoroughly clean the bared fiber with isopropyl alcohol poured onto a soft, lint-free cloth such as Kimwipes®. NEVER clean the fiber with a dry tissue. Note: Use only industrial grade 99% pure isopropyl alcohol. Commercially available isopropyl alcohol is for medicinal use and is diluted with water and a light mineral oil. Industrial grade isopropyl alcohol should be used exclusively.
4. The connector may be connected by applying epoxy or by crimping. If using epoxy, fill the connector with enough epoxy to allow a small bead of epoxy to form at the tip of the connector. Insert the clean, stripped fiber into the connector. Cure the epoxy according to the instructions provided by the epoxy manufacturer.
5. Anchor the cable strength members to the connector body. This prevents direct stress on the fiber. Slide the back end of the connector into place (where applicable).
6. Prepare the fiber face to achieve a good optical finish by cleaving and polishing the fiber end. Before the connection is made, the end of each fiber must have a smooth finish that is free of defects such as hackles, lips, and fractures. These defects, as well as other impurities and dirt change the geometrical propagation patterns of light and cause scattering.
Figure 2 - Fiber End Face Defects: Hackle (left), Lip (right)
Cleaving
Cleaving involves cutting the fiber end flush with the end of the ferrule. Cleaving, also called the scribe-and-break method of fiber end face preparation, takes some skill to achieve optimum results. Properly done, the cleave produces a perpendicular, mirror-like finish. Incorrect cleaving will result in lips and hackles as seen in Figure 2. While cleaving may be done by hand, a cleaver tool, available from such manufacturers as Fujikura, allows for a more consistent finish and reduces the overall skill required. The steps listed below outline one procedure for producing good, consistent cleaves such as the one shown in Figure 3.
1. Place the blade of the cleaver tool at the tip of the ferrule.
2. Gently score the fiber across the cladding region in one direction. If the scoring is not done lightly, the fiber may break, making it necessary to reterminate the fiber.
3. Pull the excess, cleaved fiber up and away from the ferrule.
4. Carefully dress the nub of the fiber with a piece of 12-micron alumina-oxide paper.
5. Do the final polishing. (See Figure 4.)
Figure 3 - A Well-cleaved Multimode Fiber
Polishing
After a clean cleave has been achieved, the fiber end face is attached to a polishing brush, and the fiber is ground and polished. The proper finish is achieved by rubbing the connectorized fiber end against polishing paper in a figure-eight pattern approximately sixty times.
Figure 4 - Polishing Technique
To increase the ease and repeatability of connector installation, some companies offer connector kits. Some kits are specific to the type of connector to be installed while others supply the user with general tools and information for connecting different types of connectors. Some connectors require the use of an alignment sleeve, also called an interconnection sleeve. This sleeve serves to increase repeatability from connection to connection.
Care and Handling of Fiber Optic Connectors
A number of events can damage fiber optic connectors. Unprotected connector ends can experience damage by impact, airborne dust particles, or excess humidity or moisture. The increased optical output power of modern lasers also have the potential to damage a connector, an often overlooked factor in discussions about handling and caring for optical fibers and connectors. Most designers tend to think of the power levels in optical fibers as relatively insignificant. However, a few milliwatts at 850 nm will do permanent damage to a retina. Today, optical amplifiers can generate optical powers of 1 Watt of more into a single-mode fiber. This becomes quite significant when one considers that the optical power is confined in the optical core only a few microns in diameter. Power densities in a single-mode fiber carrying an optical power of 1 Watt (+30 dBm) can reach 3 megawatts/cm2 or 30 gigawatts/m2! To put it in everyday terms, sunl