Guide to Fiber Optic Cable Splicing

In the technological age, fiber optic cables are an essential component in data networking and communications. Our world relies on extensive cable networks to function, and the companies that maintain these cables are responsible for various precision processes — including fiber optic cable splicing. Understanding this process, approaches and best practices can help integrators achieve accurate and functional splices in a range of scenarios.

What Is Fiber Optic Cable Splicing?

In short, fiber optic cable splicing is the act of joining two fiber optic cables. In instances where a single cable is not long enough for an application, splicing allows technicians to extend it for the required run. Splicing can also be helpful when fiber optic cables need restoration, or they've broken during an installation.

Cable splicing exists across industries. If a sector uses fiber optic cable, splicing likely makes an appearance. Some of these industries include:

• Automotive: Fiber optic cables quickly transmit signals, making them ideal for vehicle safety features like airbags. These cables are also used in exterior and interior lighting.
• Medical: Many advanced medical tools allow surgeons and doctors to perform advanced procedures and care for patients more effectively. Technology like endoscopes, X-ray systems and more rely on fiber optic cables to function. 
• Telecommunications: Optical cables form a vast network around the world to connect people to one another. Phone calls, video and data can move through fiber optic cables, making mass communication possible. Splicing is a necessity to maintain telecom networks.
• Computer networking: A Local Area Network (LAN) relies on fiber optic cables to connect computers in a defined location. These networks are common in office buildings, universities, laboratories and residential areas.

How to Safely Handle Optic Cable Splicing

Fiber optic cable splicing comes with risks, so it's essential to maintain proper safety practices to protect yourself and those around you.

When you handle cable splicing, you should:

• Wear personal protective equipment (PPE): When splicing cables, small fibers can attach to your clothes and skin. While these fibers are hard to see with the human eye, they can cause damage. Wearing PPE like aprons, gloves and goggles will prevent any major damage as you work.
• Keep food away from the workspace: Fiber particles and small glass fragments can collect in food and beverages and can damage your throat and disrupt your digestive system. Keep anything edible away from the workspace and save it for your lunch break.
• Work in a well-ventilated area: A well-ventilated work area will create space for fiber particles to flow away from you and other people in the space.
• Practice fire safety: Fusion splicers can ignite flammable materials. Before you begin the splicing process, make sure the area is clear of any flammable gases and other materials.
• Ensure proper cleanup: Once your splicing project is complete, properly dispose of fiber pieces. Mark your trash to alert others to the glass debris.

Two Methods of Fiber Optic Cable Splicing

As fiber optic cable splicing becomes a more common practice, accurately performing the process becomes more accessible. As of now, you have two process approaches to choose from — mechanical splicing and fusion splicing.

Before approaching your installation, you should have a clear understanding of both methods. Understanding their steps and characteristics will help you determine which process is appropriate for your performance needs and pricing constraints.

Mechanical Splicing

In mechanical splicing, integrators create a junction of two or more optical fibers with a self-contained assembly. This self-contained assembly requires an alignment device and an index matching gel that fills in the air gaps between fibers. This gel needs to have a similar refractive index to the fibers to improve light transmission across the joint with low back reflection. 

There are four key steps to mechanical splicing:

1. Fiber preparation: Before splicing your fibers, you must strip them of all protective coatings, tubes, jackets and other external protectants. This first step makes it possible to access the fibers and join them. You'll know you've stripped your fibers when you can see nothing but bare fiber. For the splicing process to work smoothly, you should ensure your fibers are clean following the stripping process.
2. Cleaving: Using a fiber cleaver, you need to create a clean cut on your fibers. The cut should be perfectly perpendicular to the fiber axis, and you should perform this cut on each end you intend on splicing. 
3. Mechanical joining: The joining process does not require heat, which is why it's called mechanical splicing. In this step, you have to position the fiber ends together in your splicing unit. Your index matching gel will link the light in the ends of your cable. In older splicing units, you may need to use epoxy instead. Precision is essential in this step.
4. Securing: Once you've joined your fiber ends, you can place your fibers in a splice tray and closure to keep them secure. While the mechanical splice housing acts as its own protective barrier, you should also seal your cables to prevent moisture from entering the splice.

Fusion Splicing

Fusion splicing uses an electric arc or specialized machine to fuse glass fiber ends together. When the ends are fused precisely, you create a reliable joint with near-zero back reflection and minimal insertion loss. 

This process starts similarly to mechanical splicing with fiber preparation and cleaving. Fibers must be free of any protective coatings and cleanly cut before fusion splicing can begin. Using an isopropyl alcohol wipe will provide the cleanliness needed for smooth splicing. After these steps, you can work through the fusion process.

A fusion splice is typically performed with a fusion splicing machine. These machines have a space to place each cable and an electrode mechanism in the center that fuses the fibers together. Alignment is critical in these machines to ensure the weld is precise. Some machines will have an automatic alignment feature, while others require manual adjustments. 

Fusion splicing equipment may stop the process if certain characteristics are not correct. Poor alignment, dirty fibers and cuts outside of 90 degrees may cause the splicer to stop. Once a fusion is successful, the splicing machine will report the estimated attenuation of your fused fibers.

Mechanical Splicing vs. Fusion Splicing: Which Is Better?

Knowing that you have two different options to handle fiber optic cable splicing, you may want to know which one is the better option. When comparing the two processes, there are three factors to consider — performance, price and environment.

Performance

One of the most notable differences between mechanical and fusion splicing is their performance. Fusion splicing is a higher quality method that results in minimal loss and a permanent joint. Loss values are typically less than 0.05 dB. When a fusion splice is well-executed, it may not even register on an optical time domain reflector (OTDR), which is an ideal splice result.

Mechanical splicing doesn't physically join fibers together as the fusion method does. The closeness of the fibers allows them to function, but it often results in higher loss values. In an application where several splices are needed, these losses add up. The one performance factor that mechanical splicing has over fusion splicing is its compatibility with multi-mode fibers.

Price

Another notable difference between the two methods is how much it costs to complete them. Since fusion splicing requires a specialized machine, the required costs can be much higher than a mechanical splice. While the stripping and cleaver tools will cost about the same for both approaches, the machines for fusion splicing can cost thousands of dollars to yield the best results.

Mechanical splicing offers far lower short-term costs, but many operations view fusion splicers as long-term investments. The precision creates a permanent bond between fibers, and once you've purchased the machine, you won't have to buy new components for every splice as you do with the mechanical method.

Environment and Time

For most applications, fusion splicing is the method of choice because it's permanent. In scenarios where you need a reliable, long-lasting cable connection, fusion splicing provides that secure connection with minimal insertion loss and back reflection. In telecommunication networks and LANs, companies are willing to invest in fusion splicing for the necessary stability in these scenarios.

Depending on the circumstances, fusion splicing may not be the most accessible method. Mechanical splicing is preferred in moments where a quick or temporary fix is needed. In telecommunications, mechanical splicing may be the only option given the environment. If a broken cable is hard to access or in severe environmental conditions, technicians will use a mechanical splice to fix the network temporarily and perform a fusion splice when the time and environment allow it. 

As fusion splicing technology improves, these machines become more compact and easy to use in more challenging circumstances. Fusion splicing will continue to become more widely accessible, but mechanical splicing is always an option when the situation demands it.

You should apply the “which is better?” question on a case-by-case basis to reap the benefits of both methods. Being prepared for either method can make your fiber optic cable repairs and extensions more flexible.

Best Practices for Optic Splicing

Now that you understand the basic steps in mechanical and fusion splicing, you can learn about some of the best practices to apply to the process. Fiber optic cable splicing requires the utmost precision. Applying a precise approach to every aspect of the procedure will support strong results every time. 

1. Know the Signs of a Bad Splice

The quality of your splice will affect how your cable performs in your application. Are there visual differences between a good splice and a bad one? Looking for the signs of a bad splice can tell you when you need to try again or work on your strategy. Signs of a bad splice include:

• Bubbles
• Bulges
• Black shadow
• A thick black line at the splice

All of these signs can point to fibers that are poorly joined and unprepared to function. If you see any of these in your splice, redo the process. It's essential to note that splices should not be performed more than twice to protect the integrity of the fibers.

While these signs can signify undesirable performance, there are other physical features that are acceptable following a splice. After splicing, you may notice:

• A blurred, thin line
• A white line
• Diameter difference
• Dirt on fibers
• A slight offset

These physical characteristics may make you believe the splice was not precise enough, but they are all acceptable. Your splice is ready to perform, even with these features.

2. Keep Your Splicing Tools Clean

Fiber optics are microscopic, and many particles can disrupt performance even when they're not visible. Keeping all of your tools clean is vital for keeping unwanted particles out of the splicing process. Taking the time to meticulously clean your tools before and after a splice will make a huge difference in splice quality. 

This cleanliness rule also applies to the stripping process before your splice. While you should clean your tools meticulously, cleaning your fibers closely will also support a secure and functional splice. There is no such thing as being too careful in the splicing process.

3. Maintain Your Cleaver and Use it Correctly

The cut you make to your fibers is a significant determinant of how well your splice will work. Mechanical splicing requires proper angles at end faces to prevent air gaps and excess light from escaping. A precise cut also helps you achieve high attenuation in a fusion splice. Maintaining and using your cleaver correctly will ensure a smooth process from start to finish.

Your cleaver manufacturer will include care instructions for your equipment, including how to sharpen and clean it. Follow through with this guide to make precise cuts for every splice.

4. Modify Fusion Parameters Methodically

In regard to fusion splicing, you need to handle your parameters with care. When using a fusion splicer, fusion time and current are the two parameters you'll adjust to join fibers. Finding the right parameters requires methodical adjustment. Change only one parameter at a time, and approach it with a strategy to reach the ideal figures for your fiber type.