Last Updated: September 23, 2020
A growing trend in the fiber optic industry is the increasing use of specialty fibers. Clearly, telecommunications and data communications applications are the high-volume users of fiber optics, yet other areas are burgeoning. In fact, many specialty fiber optic products have moved out of the experimental stage and into commercial markets.
Today, some specialty fiber optic products are embedded in concrete to sense stress in bridges and buildings, some are used purely for optical power transmission, and others offer a unique emitter or detector for highly specific applications.
Wherever there is growth, there are growing pains.
If you’re a cable assembly house, splitter or DWDM manufacturer, sensor manufacturer, umbilical cable assembler, or specialty cable assembly house – and you’re looking to work with specialty fiber, cables, and furcation tubes – there are many considerations to think about.
As you know, specialty fibers are generally made by specialty fiber manufacturers, which then need to be cabled or furcated. Let’s look at an example: Let’s say a specialty fiber manufacturer has invested considerable resources into producing 808 meters of fiber optic cable – and they need 800 meters cabled. When they knock on the door of large cable assembly houses, these cablers may bristle at the low production quantity and high yield. They often turn down the opportunity simply because it’s not in their wheelhouse. Since they don’t have the specific engineering expertise in-house, they reason that a specialty fiber optic cabling project might not be successful and profitable.
Small cablers, on the other hand, may be more open to the business opportunity of working with specialty fiber. However, they may not have a thorough understanding of the uniqueness – and the distinct challenges – inherent in working with specialty fiber.
I believe it’s well worth the effort to take on specialty fiber projects.
Clearly, cabling specialty fiber is not a high-volume activity. While quantities are much smaller, profit can be much higher for a specialized cabling operation. In some cases, the volume may suddenly increase. (An example is new applications for sensor fibers.) Starting with a good process – and being able to reproduce that process – is important.
When it comes to specialty fiber, each application is unique, and there are an extraordinary number of variables. A one-size-fits-all approach doesn’t work. That’s why it’s imperative to start with a solid foundation. You need to understand the specific properties required when cabling or furcating specialty fiber, make the right choices, and set up the process for success. The key is asking a lot of questions; the trick is knowing which questions to ask.
When you take on a project involving specialty fiber, you quickly come to a decision point…
When working with specialty fiber, the first question to answer will be: “Do I cable it or put it into a furcation tube?” This is a critical decision. For an example, let’s look at laser power fiber, which takes 1,000 watts of laser power. It has a 1mm core and about 1,100 microns of glass altogether. This specialty fiber typically costs $30 to $50 per meter to manufacture, while some cost hundreds of dollars per meter. As a cabler, if your experience is limited to working with 125-micron acrylate clad communications fiber, the fiber manufacturer (or the end user purchasing this specialty fiber) may not trust you to take on this project – unless you can prove that you have the necessary internal or external technical expertise.
If you use a furcation tube with a pulling string, you now have a capable way to pull that expensive fiber into a tube and make it a simplex or duplex cable. In this process, you typically lose a couple of centimeters of fiber (not meters), a critically important factor for this expensive fiber. Alternatively, the project may require one 800-meter length of fiber – too long for a furcation tube. In this case, you will cable the specialty fiber. Either way, you must fully understand the fiber’s properties, all specifications, and the application to ensure ultimate project success and acceptance by the end user. Again, this decision point – this fork in the road – is critical.
Some considerations for specialty cabling
As a cable house, you need to understand the ins-and-outs of the specialty fiber. Keep in mind, every specialty fiber has a very different set of characteristics and specifications for use. It’s critically important that an internal or external expert asks questions to clearly understand the required properties, so you can make the right cabling choices.
For example, it’s important to recognize that bend radius is a key consideration for a large-core, power-delivery fiber. The glass is more rigid, the bend radius is much larger, and it has more sensitivity to stress. Plus, it must withstand tremendous heat. Further, let’s say your equipment uses 4” sheaves (to change fiber direction in the cabling process), which is fine for telecommunications and data communications fiber, yet is problematic for large-diameter fiber. The equipment can cause small flaws that, over time, would grow. This is similar to a crack in a car windshield growing due to hot/cold temperature cycles. The same thing happens on a microscopic scale across the face of an optical fiber when a small crack or flaw is induced by a bend radius that is too tight. Therefore, a large-core, power-delivery fiber may need a cabling process that uses extra-large sheaves to control the diameter over which the optical fiber is bent. And separately when you consider the design of the cable, you will need to add a design feature such that it has some type of “armor” or other bending radius limiter aid that restricts bending, so it doesn’t exceed the radius and cause flaws in the glass.
Coating options further complicate the cabling choices related to specialty fiber. Instead of having a nice, smooth, conformal soft coating, specialty fibers may have a polyimide coating, which is a hard, high-temperature coating. This provides no cushioning in the cabling process and makes the fiber more sensitive to microbends. In some cases, specialty fibers have a carbon-shield coating that’s only 2 microns thick. Or they may have a super-soft silicon coating; it’s so soft, it comes apart as you peel the fiber off the spool. (I faced these issues when I worked on a wide variety of specialty fiber cabling projects for several specialty fiber manufacturers.)
Another key consideration: How do you need to protect the specialty fiber? Are you simply looking for a protective carrier with basic tensile strength? Or do you need to protect the specialty fiber from moisture and hot/cold environments. Or does it need impact resistance? Each of these parameters changes how you would specify your cabling performance.
Prior to cabling a specialty fiber, it’s important to quiz the specialty fiber manufacturer and, if possible, the end user. Here’s an example: Perhaps a scientific laboratory requires a specialty fiber. When we play the game of “20 questions,” the lab reveals that they plan to integrate the specialty sensor fiber, once cabled, into a robotic arm. It must have certain flex and tension controls, with specific connectors. You’d be surprised how often end users’ basic requirements are not communicated to the fiber manufacturer or to the cabler. The key is for an experienced technical expert (internal or external) to ask the right questions to illicit answers with telling information.
Some considerations for specialty furcation tubing
Furcation tubes come in all sizes, shapes, and qualities. With some furcation tubes, you can push through just a few centimeters or up to a meter of fiber. Others are precision engineered, so you can push through (or use vacuum suction) for as much as 5 to 10 meters of fiber.
When it comes to furcation tubes, there are a number of pitfalls to watch out for. As an example, let’s say you’re furcating a 288-fiber cable. If you’re using furcation tubes that are not super-smooth on the interior, you’ll break some of the fibers and have to reterminate all the others already done because there is a length-uniformity requirement. You may need to reprocess the entire assembly.
The most significant issues related to furcation tubes are dimensional stability, thermal stability, and final use. Again, it’s critical to thoroughly evaluate how the optical fiber (either standard or specialty), once furcated, will be used in its application. For example, will the final product be exposed to a temperature range of only 0 to 50 degrees C? If so, the performance of your furcation tubes must match that. However, if the furcation tube is attached to an optical switch in a non-environmentally controlled space, you may need to meet specs that mandate performance of -40 to +70 degrees C. In this case, the thermal properties of your furcation tubes are critical.
It’s important to ask questions of the furcation tube manufacturers, understand their quality systems, and closely review their performance specifications. As noted above, it’s also extremely helpful for an experienced technical expert (internal or external) to quiz the specialty fiber manufacturer and the end user. This can ensure ultimate product acceptance by the end user.
A little homework up front can save a lot of pain later.
While specialty fibers and their applications are unique, I believe there is a basic set of issues to address. You must gain clarity on the final application, understand the specialty fiber’s characteristics, ensure you know the exact performance requirements and how to test for them, understand regulatory requirements, and confirm the properties required for the assembly.
The key to gaining this clarity is for an experienced technical expert (internal or external) to ask questions. And there is almost any number of questions to be asked! When I sit down with clients and end users, I pepper them with a long list of queries to learn more about the application, clarify critical values, and fine-tune performance requirements. In addition, clients often ask me to:
- Provide specification details and troubleshoot tight buffer and furcation tubing issues
- Help develop custom requirements and incoming inspection processes
- Develop a design concept and/or manage it through to a finished product or component
- Work with cablers who toll the specialty fiber through the buffering or cabling process
Whether the technical expert is internal or external, he or she must have in-depth knowledge of the fiber optic industry, specifications, materials, process, and applications. Above and beyond this is the ability to ask questions that will tease out critical information to ensure the cabler enjoys a successful specialty fiber project – and the end user gets the right product for their application.