Fiber Optic Cable Assembly Process: Why it’s not Like the Traditional Cable Assembly Process?

It’s no secret that today’s digital economy is built on optical fiber. These thin fibers of glass are responsible for sending large streams of data every second, which makes the use of the internet possible. However, fiber needs to be handled carefully. Since the optic cables are small, you need to align the fiber with great precision and small shifts. To better understand the fiber optic cable assembly process, we’ll thoroughly discuss them in this blog.

Fiber optic cable assembly understanding

Cable assemblies combine several wires and connectors with doing what is needed. But it’s hard to put fiber optic components together. Fiber is different to work with than aluminum or copper wire because of the nature of the material it’s made from and how flexible it is.

Common materials for strands in Optical cables

You can often see two types of fibers in life.

Silica

SiO2, a chemical formula for “silicon dioxide,” is the main ingredient in many optic cables. This is the same substance you find in the sand. Optic fibers are made by heating silica to a very high temperature until it turns into glass. The result is a pliable optical fiber, which can hold up to about 20 lbs. of pressure in a certain area of the fiber.

Plastic

Some fiber optics are made up of plastic components instead of glass. It’s a 96% mix of materials that make up the core of the optic fiber. Even though the loss might occur due to the use of different materials, still lower in cost, making it the preferred choice for consumers.

Plastic fiber is best for short ranges, and you can use them in homes and cars. Glass fiber, on the other hand, is ideal for greater distances and faster speeds. Thus, you can find them in offices and factories.

How Are Fiber Optic Cable Assemblies Designed?

It doesn’t matter whether you use plastic or glass as the material for your optical fiber; however, what matters is the way you have designed your cable assembly and how you plan to use it.

• Single Mode: Single-mode cables only bend the optical signal in one direction. They can’t send a signal back and forth. Because their diameter is only 9 micrometers, they have much control over how they send information. Thus, manufacturers always make single-mode fiber optics in the glass.
• Multimode Fiber Optic: Multimode optical fibers have an average size of 125 microns, which is bigger than single-mode fiber and enables the light to bend in more than one direction. The companies use glass or plastic to make multimode fiber optic cables.

Another factor that changes the design decisions is the type of cladding you plan to use. For example, in Step index cladding, you use the same material through the cable. However, in gradual index cladding, you need different materials at every layer, giving a specific refractive index. The latter ensures that the signals are refracting with little to no loss.

Grade index cladding is harder to make. Which means it costs more than the step-index cladding. In the end, the type of fiber optics material you want to use depends on what you want to do with your optical assembly or harness.

Caption: Fiber optics in Telecommunication cables

Fiber Optic Cable Assembly Process: Fiber Optic Connector Types

• ST: Bayonet mount, long cylindrical ferrule that ties up all the fibers. It’s popular in multimode networks, like university campuses and building networks. 
• FC/PC: Also popular for single-mode connectors for decades. It fixes on the cable properly if you carefully align the fibers with the slot.
• SC: A snap-in connector popular for its excellent performance in single-mode cables. It snaps onto the cable with a simple push-and-pull motion. Also, it is available in duplex mode as well.
• LC: A standard, ceramic ferrule connector that is half of the size of ST. You can easily terminate with any adhesive, making it a high recommendation for single-mode cables.
• MT-RJ: A duplex connector having two fibers in one polymer ferrule. It is put together with pins, both male and female versions.
• Opti-Jack: A neat, tough duplex connector that develops around two ST-type ferrules in a bundle the size of an RJ-45. It comes in both plug and jack (male and female) forms.
• Volition: A nice-looking, low-cost duplex connector with no ferrule. It puts the fibers in a V-shaped groove, just like a splice. Here, you can only perform field termination on jacks. 
• E2000/LX-5: Like an LC, but the end of the fiber has a shutter on it.
• MU: Looks like a small SC with a ferrule of 1.25 mm and is common in Japanese products
• MT: A connector for a cable system with 12 fibers. Its main application is for cable assemblies that are already put together.

Fiber Optic Cable Assembly Process: Connector Ferrule Shapes & Polishes

Since the fibers are extremely vulnerable to handle, the strands had air gaps to prevent friction between them. However, it has greater insertion loss, usually 0.5dB or more. So, engineers came up with other solutions like physical contact or PC connectors and Angled-PC connectors that reduced insertion loss to 0.3 dB or even better.

Caption: Fiber strands inside optical cable

Fiber optic cable assembly manufacturing 

Typical Fiber Preparation

1. Measure the cable to the required length and mark it.
2. Place the jacket remover on the spot and gently press on it.
3. Now, take the cut part of the jacket off the cable with the tool.
4. Label Kevlar at the specified length
5. Using scissors, trim the extra Kevlar at the measured mark.
6. Place a transparent heat-shrinking sleeve over the buffer and use it to fold the Kevlar back over the cable jacket.
7. After measurement, insert the buffer stripper on the buffer jacket and gently press until the cutter closes.
8. Strip the buffer in multiple phases to avoid harming the fiber.
9. Thoroughly clean the fiber with a lint-free, alcohol-soaked tissue.

Termination by Connectors

A mini-pigtail enclosed in a connector encase is a rapid termination fiber connector. The manufacturer bonds a fiber stub into the ferrule and polishes its ends to a PC finish.

A mechanical clamp method holds the fiber in place and forms the junction without needing polish or epoxy. Moreover, after removing the strain from the fiber to the connector, you are ready to mate it inside an adapter.

Applications for quick termination connectors

The quick termination method is best when

• There is less number of connectors.
• The tests, modifications, and updates are readily happening.
• In LAN areas where the range is smaller.
• You require maintenance and restoration of the active system.

Applications for traditional polishing connectors

Traditional polish and epoxy methods are best when

• There is a large number of connectors to fix
• Fiber retention is necessary
• The use of buffer coatings is happening
• Gel-filled cables are in use
• Environmental conditions do not conform to TIA 568-B.3

Termination by Splicing

Mechanical splicing

Mechanical splicing is best when two fibers line up with each other perfectly and hold in place by a machine. Also, it lines up the ends of two fibers to have the same centerline. This lets light move from one fiber to the other.

For applications that use multimode fiber, mechanical splices work best. For single-mode fibers, some mechanical splices can work. However, they might cause higher insertion loss.

Fusion splicing

Fusion splicing is joining two optical fibers using an electronic arc. For such splicing, get each fiber end ready for fusion. In addition, you must inspect the ends of each fiber for any protective coatings. Then, you will cut the fiber with fiber cleavers that are very sharp. Moreover, the splice loss in fusion splice directly relates to the strands and their angles.

Caption: Fiber Optic cable splicing

Challenge Faced When Assembling Fiber Optic Cable 

Requirements for fiber optic assembly can be as small as 10 microns or as small as 1 micron, so precise alignment is essential for getting consistent and accurate results. When joining fibers, the biggest problem is making sure that the faces of each strand line up equally with each other. It is very important to boost light signals.

Any change in alignment will cause the signal to be lost. Some things, like how curved the fiber tip is and where you hold a fiber pigtail, make the alignment process even more variable. Optical fiber also has a layer on the outside that is of a shielded cladding and a buffer. Also, it is better to remove the jacketing before using the optic cable.

Also, fiber optic parts have been hard to handle and put together automatically. Because optical fiber is flexible, it is harder to work with than parts that are not flexible, like aluminum or copper wire.

Conclusion

Even though optic fibers are becoming more popular, cutting, stripping, and putting them together is still hard. Engineers have to deal with things like alignment and placement, clarity, preparing the strands, and thermal gradients.