Mechanical cover technology seals fiber fusion splices without tools

June 1, 1995

Mechanical cover technology seals fiber fusion splices without tools

An elementary sleeve method bonds a fused fiber splice from environmental and moisture contamination



Fusing and protecting fiber-optic splices can prove difficult for users who have limited service budgets. Moreover, maintaining a fiber cabling plant generally dictates costly repair parts, tools, fixtures, fusion splicing machines, splicing vans and other specialty instruments, as well as installer training. The latest fusion splice protection technologies, however, have helped installers reduce repair time, cost and effort.

The two main fiber splice protection technologies are the heat shrink and mechanical sleeve methods. Both methods help installers safeguard a fused fiber-optic cable splice, but each has limitations. In applying splice protection technologies, installers are interested in a variety of parameters, including cost, process time, tools, training and field conformity.

An inexpensive but dependable fiber splicing protection process implements a V-groove alignment guide, for example. Although this guide blocks viewing of the fibers, the installer can use a tool to accurately align the fibers. In this process, the parts are reusable. Custom parts are also available to handle a fiber buffer combination ranging from 250 to 900 microns.

In another approach, some fiber-optic cable installers prefer to save costs by purchasing an emergency fiber restoration kit. After applying a temporary splice and protection, they call an outside service agency to permanently fuse and protect the fiber.

Available mechanical splice and protection parts and their associated tools aid in the quick restoration of a fiber break--at minimal cost. For example, a quality cleaver costs approximately $550. Such fiber preparation tools as the buffer stripper, stripper and cutter cost approximately $30, $40 and $20, respectively. Many suppliers offer all the splicing tools required for fiber preparation, including fiber cleaning items, a lighted magnifier and holder and alignment guides for almost $1000.

Heat shrinking

A common way to mechanically protect a fused fiber joint is the heat shrink method. This method generally involves a fusion splice machine--usually battery-operated for field use--and a battery-powered heat shrink oven that weighs an average of 10 to 12 pounds. The rechargeable battery lasts approximately two to three hours.

Of course, battery life depends mainly on the installer`s ability to fuse the fibers and quickly install the heat shrink protector cover. In practice, the protector cover can be installed in two to three minutes, depending on the heating characteristics of the oven and the installer`s skill.

A mini-fusion splice machine costs approximately $7000. The heat shrink oven could add an additional $1500. Several manufacturers include a built-in oven in the fusion machine--at a cost of $10,000.

Several steps are needed to operate a fusion machine: These steps must be performed in correct order, and each step proves crucial in obtaining the desired splice protection. Consequently, training is essential.

While installing a heat shrink protector cover, even an experienced installer is prone to an occasional mistake. The heat shrink protector comprises inner and outer tubes and a metal (or rigid plastic) rod, which keeps the fused fiber joints straight and sturdy. The inner tube of the protector is first melted onto the fiber. Then, the outer tube is shrunk to enclose the inner tube and the rod or strength member.

Before performing the fusing process, the installer must slide the heat shrink protector onto the fiber cable. Unfortunately, in practice, this step is sometimes overlooked--even by experts. In that case, the installer has to cut the newly fused fiber, slide the heat shrink protector onto the fiber and redo the protection process.

The heat shrink process includes the time needed by the installer to cleave both fibers--an average of one to two minutes. Add to that the fusing time (including alignment), which takes 30 to 60 seconds. Although the total time is relatively short, the installation process must be effectively accomplished. An improperly performed fused fiber joint protection process could produce high and costly transmission system losses.

To ensure reliable results, an installer using the heat shrink process should assess:

The entire installation time--usually five to six minutes on average per fiber (assuming no errors)

The battery life of the fusion machine, typically two to three hours. In some machines, the oven consumes more battery power than the fusion splicer, itself.

Network downtime because of the inactivity of the fiber being spliced

Materials needed in stock to redo mistakes.

The initial investment for the heat shrinking method is of utmost concern. Some installers opt to avoid the cost of a heat oven and do not include it in the purchase of a mini-fusion splicing machine. The installer must, therefore, use a heat gun, which is economically feasible but demands careful use.

An installer who uses a heat gun must ensure even shrinking of the splice protector cover. If uneven shrinkage occurs, air gaps could evolve under the protector sleeve. The gaps could cause condensation, which, in turn, would degrade the fused fiber joints.

In addition, during normal hot and cold temperature cycling of the fiber application environment, the heat shrink protector cover could eventually exhibit cracks, leading to fiber joint deterioration.

Because some telephone companies reported heat shrink protector problems, Bell Communications Research developed Generic Requirement GR-001380 in May 1994. This document details the procedure required to ensure proper installation and quality of heat shrink protector covers. The requirements deal mostly with such environmental conditions as temperature cycling, humidity, field conditions, water immersion and pull strength.

In the water immersion test, the protector cover is placed in distilled water for 30 days. This trial reveals whether the protector can properly secure the fibers and prevent water and moisture degradation. The pull-strength test demonstrates whether the protector cover can hold the buffer and partially hold the fiber, so they cannot be easily separated.

A fusion splice machine, without the heating oven, weighs approximately five to six pounds and comes in a smaller size. The machine`s battery life depends on usage. Extra rechargeable batteries can be purchased, but during charging, the fusion machine cannot be used.

Mechanical heat shrinking

To address the fusion machine`s expense, training and field usage burdens, a fusion splice protection cover or sleeve has been developed. This sleeve eliminates the need for tools, fixtures, heat guns and heat ovens, thereby saving costs and accommodating field use.

Made of a liquid-crystal polymer plastic housing, the sleeve comprises two hinged halves, either 40 or 60 millimeters long, that form an open "U" shape. Neither half of the sleeve needs grooves or fixed alignment guides. The sleeve accepts a single fiber, any combination of 250- to 900-micron buffers or multifiber fused joints up to a 4-fiber ribbon.

The installer does not need to thread the sleeve onto the fibers before fusing, as called for in the heat shrinking approach. After the fibers are fused, the installer places them into the fold of the sleeve`s two hinged halves, removes the sealing tape guard and snaps the two halves together. The snapping action simultaneously closes and bonds the sleeve to the fibers. No alignment tools or fixtures are needed.

Installation time is usually 15 seconds after fiber preparation. This time is less than the few minutes needed to install a heat shrink cover. Time savings, ease of use and no mounting fixtures all contribute to fast implementation by a relatively untrained installer.

Compression of the double-coated acrylic foam closed-cell tape mounted on the sleeve`s hinged halves forms a hermetic seal that protects the fused fiber joints from environmental and liquid hazards. No heating, curing, gluing or crimping is necessary. But, because the sleeve forms a permanent lock, it cannot be reopened or reused.

The sleeve fits into standard fusion splice trays, and has been tested by the Inchcape Testing Facility (Testmark Laboratories), an outside testing agency, for conformance to Bellcore GR-001380 requirements.

The heat shrink cover and the mechanical sleeve incur the same average product cost of 95 cents each (in small quantities). But process savings accrue with the mechanical sleeve because tools, ovens and batteries are not needed, and it takes just seconds to install. u

Attila Huebscher is marketing director at Advanced Custom Applications Inc. in Belle Mead, NJ.

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