The difference between mechanical splicing and fusion splicing and how optical fibers are spliced. Fusion splicing works by melting and joining two optical fibers together. The result is an almost seamless/lossless connection. The following article provides more details on the fusion splicing procedure, especially fiber "preparation".
The foundation of a good splice is fiber preparation for splicing
Fusion splices are used for connecting optical fibers during network installation projects, repairing optical fibers, installing pre-polished fusion splices, and many applications in the factory for fabricating fiber optic assemblies and subsystems. For both field and factory splicing, the process requires the following consumables and equipment:
Aramid scissors and other tools to separate out a single fiber for splicing;
Stripping tool with hole size for removing fiber buffer coating;
Alcohol and rags to clean bare fibers before splicing;
Cleaver for terminating fiber to the proper length with a high-quality end face;
Optical fiber fusion splicer;
Protective tubes or ferrules, or optical fiber recoating equipment;
Test instruments such as loss testers or OTDRs.
Optical fiber fusion splicer
Some tools and equipment used for field splicing differ from versions used for factory or bench splicing. For example, in the case of fiber optic fusion splicers, there are portable portable units for field splicing, some available in kits, including batteries.
From start to finish, the fusion splicing process consists of four main steps: (1) Preparing the fiber terminations; (2) Fusing the fiber terminations together; (3) Adding splice protection or recoating the fiber splices, and (4) Testing the splices .
Step (1) is the main focus of this article and we will provide tips on cutting and cleaning. For step (2) the fiber fusion splicer creates the fusion splices. The operator is responsible for properly loading the fiber tip, checking the settings (including the fiber type program), and clicking a button to start the fusion process. We will also protect step (3) as it is critical to the long-term performance of the joint. Step (4) of the test is mainly done using the OTDR or loss test set, the details of the test will be covered in other articles.
Welding Basics
Welding Fundamentals: Welding Tips from Croft's Technical Experts
In the field or in the factory, the goal of all fusion splices is a low-loss joint that meets tensile strength requirements. Strength testing is important to ensure longevity. Experience has shown that many joint failures are due to fractures, often not directly at the joint, but nearby. The key steps to avoiding such breaks are good cleaning, cutting, and splice protection.
1. Fiber cleaning is a top priority. Dirt, dust, and other contaminants on the fiber can interfere with the splicing process, resulting in poor splice loss and strength issues. The fiber must also be completely clean in the area to be recoated or covered with a protective jacket.
2. Remember to keep tools and fixtures clean. Even in a controlled environment such as a tent, van, trailer or factory, dust is inevitable. For example, the process of stripping optical fibers produces tiny particles. This means it is necessary to clean cleavers, fiber fusion splicers and other tools so as not to contaminate the fiber and thus not affect the delicate V-grooves and surfaces.
3. Have multiple stripping tools on hand. Mechanical strippers sometimes wear hundreds of times and sometimes wear out. Keep the tool clean and replace it if necessary. Make sure to remove any acrylate buffer coating without scratching the fiber.
4. Use the correct solvent. Many fiber designs incorporate hydroblocking gels, which must all be completely removed from the bare fiber before splicing and covering the splice. Isopropyl alcohol (IPA) is considered by many companies to be suitable for cleaning fibers prior to splicing. If using IPA, high concentrations (very low water percentages) are best. Some companies offer special solvents for cleaning fiber optic adhesives.
5. Do not use compressed air for cleaning. Compressed air creates moisture, which attracts dust and interferes with good joints. The best way to do this is to use an optical-grade lint-free wipe and solvent. Croft offers a wide selection of dry or pre-moistened wipes specifically packaged for fiber optic applications.
6. Want good conditions for on-site repairs? Sorry, there are no easy-to-follow suggestions here. Field splicing must be performed under less than ideal conditions. Probably much less - bad weather, manholes, sewers, aerial installations, etc. Many field workers have trucks, tents and other facilities, and network operators have attempted to install fiber with slack coils in the system to allow for such repairs. The goal is to try to work in the most stable and protected environment possible.
7. Scratching or cleaving is critical. The sharp edge of the scribing tool scribes the fiber before the technician manually breaks the fiber. The cleaving tool similarly scores the surface of the fiber and then applies mechanically controlled pressure to break the fiber. The difference between a scriber and a cutter is price, technician skill, replacement part cost, and consistency of scribes and breaks.
8. The goal of fiber splicing preparation is to cleave each fiber at a 90° end face and minimize cracks and spots. The key to repeatable, strong splices: clean, flat cuts. Any cracks and spots will only degrade the quality of the splice (although most modern splice equipment can tolerate less than ideal fiber cleavage to some extent). The fusion process may "fuse" or eliminate the protuberances. However, the large bumps can prevent the fiber ends from being placed close enough together to make a good splice.
Notes:
A protrusion that can appear on the end face of an optical fiber after scratches and breaks.
"Roughness" refers to surface defects, also known as "fog," that can lead to splice loss after fusing.
Clean fiber, clean split! Do this and you'll have a 90% chance of a strong split.
Fiber hand cords and cleaning for field connections are the same as for lab connectors - the same principles apply. Do not damage the fiber during stripping, make sure the bare/stripped fiber does not touch any surface that could damage the fiber, etc.
9. The fusion process – the machine does the job. A fiber fusion splicer precisely positions the ends of the fibers and heats them to fuse them. Positioning relies on tiny digital cameras. Although some fusion splicers are equipped with lasers or filaments, the heat source is usually an electric arc from carefully controlled electrodes. Many splicers also have subsystems for performing tensile strength testing and software to estimate splicing loss using an internal camera. Many products also have fixtures and heat sources to protect the sleeves, as well as trays or fixtures to protect protected joints while cooling.
10. Select the correct connector protection tube. The splice protection tube or sleeve is made of heat shrinkable polymer and microrod strength members to prevent buckling. Some sleeves have a special coating or adhesive (hot melt) on the inner wall, and there are options for the material, color, and other characteristics of the strength parts. The preferred outside diameter and length depends on the application – whether the fittings are included in enclosures for external equipment, diverter equipment trays, compact assemblies or other subsystems, etc. Note that the tube specifications include reduced outer diameter after heating. It is critical that the heat shrink protection tube is fully shrunk to eliminate any chance of air bubbles or the like being trapped in it.
11. Estimated splice loss is an estimate only. Most common fusion splicers have a function to calculate estimated splice loss for the finished splice. This loss is calculated by comparing the alignment of the connected fiber cores. While this estimated loss may be accurate, it is not a true validation of the joint performance. Typically, such an "estimated splice loss" uses a "coarse filter" to help ensure that performance tolerances are met and that you are identifying the main problem splice. However, the best way to understand the true performance of a connector is to perform a separate power meter/detector insertion loss test.
12. Additional note on splice protection: Recoating is an alternative to pipe, but is primarily used for factory splices. The recoating process uses UV-cured acrylates such as the buffer coating that was initially applied to the fiber during the drawing process. Recoat systems have fixtures or molds that hold the paint and cure it. This may take longer than the heat shrink process, but the outer diameter is the same as the original fiber, 250 µm. This approach relies on benchtop equipment and is usually done in factories that manufacture pigtail components and other equipment.
Optical fiber fusion splicer
Splicer Options
As mentioned earlier, there are multiple field and factory fiber fusion splicers on the market with different features and price ranges. Must include the following: built-in cleaver, system for estimating splice loss, integrated tensile strength testing, heat shrink tube oven, procedures for different fiber sizes and types, splice polarization capability - maintains the fiber, and has a "quality fusion" ” function, up to 12 fibers can be spliced at one time. Field devices are designed for portability and battery-powered operation, but still have many advanced features for testing and using different types of fiber.
Last but not least, our fusion stitching technology has been developed for decades. The latest generation of digital alignment and control features deliver outstanding results, and vendors continue to develop new features and enhancements. Another benefit of the long history is that there is a lot of information about fusion splicing: training courses, instructional videos, white papers, technical articles, standards and manufacturer support. ZR Fiber is happy to answer questions and provide more references on this topic.
