Splice World: Inside fusion-splicing

Single-mode fiber needs many more splices than multimode. Outside plant (OSP) single-mode fiber links often require splicing shorter lengths of cable or drops off of a backbone cable. These OSP cables are usually fusion-spliced. Indoors, connectors are usually spliced onto single-mode fiber for termination.

Fusion-splicing is the best way to join fibers for the lowest loss and greatest reliability, and it may be the least expensive method. The splicing machine is expensive, but it can be used for many splices. Each splice only costs a small amount—mostly the cost of the labor and an inexpensive splice protector.

The image most people have of fusion-splicing is of a technician using a splicing machine to strip fibers and fuse them. That’s only a small part of the process. Long before a technician sits down to do the splicing, he or she spends a lot of time setting up and preparing the cable. The time at the splicer is short compared to the time to finish the process, placing each fiber into a splice closure as the splice is made.

Let’s look at what a typical technician will do when assigned to splice two cables somewhere in the field.

First, the technician has to go to the location where the cables are to be joined. For OSP cables, that means driving a truck and splicing trailer or van equipped as a field-splicing lab to the site. It’s rare that you splice out in the open.

Splices need to be made in a clean environment at comfortable temperatures, so most crews have a splice trailer or van equipped with a work surface and tool storage. It also will be heated and air conditioned. Indoors, a technician only needs a clean workspace.

The cables to be spliced need to be long enough to reach into the trailer from where they come up from the ground or down from a utility pole. Add to that the extra length needed to prep the cable for splicing, typically 2 meters (6 feet) or more. After the technician finishes, he or she will need a plan for where to store that excess cable in storage loops.

Inside the trailer, the technician must first set up equipment, including the fusion-splicing machine, cable-prep tools and a splice closure. The splice closure will probably take up the most space, and it needs to be positioned conveniently to allow the technician to go straight from the splicing machine to the splice tray in the closure without getting the fibers tangled in other equipment.

The cables must be prepared for splicing. If dealing with the usual loose-tube cable, the technician must first strip off the cable jacket for about 2 meters to expose the buffer tubes. Then the technician will cut off the buffer tubes to expose about 1 meter (3 feet) of the fibers. If the technician is lucky, the cable will use dry water blocking, which is easy to clean. However, if it’s gel-filled, the technician will need to budget for a good amount of time to clean each fiber, using proper cleaning solutions and wipes.

Once the cable is prepared, the splicing begins. The process is simple—slide the splice protector on the first fiber, clean then cleave the fiber, place it in the splicer groove, clean and cleave the second fiber, and put it in the splicer.

Technicians will need to remember that fibers are color-coded. If they are splicing two cables that are the same type, convention is to splice fibers to like colored fibers following the usual sequence (blue, orange, green, brown, etc.). The buffer tubes are also color-coded, so technicians must splice like fibers with like colored buffer tubes.

Once the fibers are in the splicing machine, it’s just a matter of pushing the start button and waiting while the machine does its thing. If the splice is successful, the machine will give the technician a loss estimate, which generally indicates a good or bad splice. If it looks good, the technician will slide the splice protector over the splice and seal it, usually with a heater on the machine.

Now comes the hard part: delicately placing the splice and the fibers neatly in the splice tray. It takes patience and experience, but eventually, it becomes second nature and goes quickly.

The technician repeats this process until all fibers in each tube are finished. That usually fills a splice tray, and the next tube gets a new tray. The technician will continue until all the fibers are spliced, the trays are filled and the closure is sealed.

Next month, I’ll discuss some secrets of successful splicing.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor

Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.

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