In the rapidly evolving landscape of industrial IoT networks, understanding the intricacies of fiber optic cables is essential for IT technicians and plant management alike.

Although fiber has been deployed for more than four decades, several misconceptions remain. At the top of the list is that installing fiber optics is more expensive than copper due to its networking devices, terminations, and cables. Another is that fiber is harder to install and terminate than copper. Last, there’s the fallacy that fiber cables are fragile since they're “made of glass”. We’ll dispel those lingering myths here.

Fiber optic cables are now the fastest-growing transmission medium for both new network builds and expansions, especially in applications that require high bandwidth, long distances, and immunity to electrical interference. Network backbones transmitting huge amounts of bandwidth-consuming data files almost exclusively rely on fiber.

So, is fiber right for your industrial network? Let’s find out.

Construction

As the name implies, fiber optic cables carry optical signals using fast-traveling pulses of light instead of electricity over long distances. At the cable’s core are extremely pure glass fibers the same width as human hair that transmit light photons down the length of cable.

A 125µm layer of glass cladding surrounds the core to guarantee that light is reflected, rather than leaking out at the edges, therefore enabling the signal to travel longer distances without attenuation. Over the cladding is a buffer that keeps the cable's internal glass structure safe from damage and discourages excessive bending. An additional layer of reinforcing fibers shields the core, followed by a rugged plastic jacket.

Durability

Fiber is far from fragile. The strength members of fiber cables provide protection against crushing blows, bending forces and, of course, the pulling tension encountered during installation. Reinforcing around the core keeps the cable stiff to maintain the allowable cable-bend radius and prevent kinking when pulling around corners. Once installed, fiber optic cables are sturdier than copper with fewer parts. In fact, a fiber optic cable can last up to 50 years, withstanding extreme temperatures, high shock, moisture and vibration without degrading.

All this doesn’t mean careless installation won’t damage fiber optic cables. Exceeding bending radius limits or kinking the cable will lead to micro-cracks that increase the potential for degradation. Poorly spliced cable will give rise to fiber movement if splice materials have different characteristics than the cable, such as different thermal expansion coefficients. Malfunctions in fiber optic networks are virtually always due to poor installation, misaligned fusions, or accidental cuts.

Despite the built-in mechanical protection in modern fiber optic cables, some industrial or outdoor plant installations require more protection. In these instances, armored cables are recommended.

Armored fiber optic cables are manufactured to handle abrasion, impact, UV damage and are designed for underground direct burial out of the box. Armored cables can be a cost-effective alternative to running the cable through protective conduit. Conduit installation costs are incurred twice: first, when installing the conduit and second, when installing the cables, hence doubling labor and material costs. Armored cables cost more than standard fiber cables, but the labor to install them is considerably less.

Single mode fiber

Fiber optic cables are broken down into two main product categories — single-mode (SM) and multimode (MM).

Single-mode cable has a small diametral core of 9µm that permits only one mode of light to propagate. SM decreases the number of reflections created as light passes through its core, resulting in lowered attenuation and creating the ability for a signal to travel several miles before needing to be enhanced. SM is the preferred choice for long-haul networks, telcos, campus backbone and large enterprises spread over extended areas.

SM is available in two classifications:

• OS1: for use in indoor locations over shorter distances and where electrical interference may be greater.
• OS2: targeted at outdoor installations with a maximum range of 125 miles. OS2 cables support bandwidth speeds of up to 400 gigabits per second (Gbit/s) over distances up to 80km or further using off-the-shelf optical modules. OS2 is generally more tolerant to flexing and stretching than OS1. Not surprisingly, OS2 cables also tend to be more expensive than their OS1 counterparts.

Multimode

Multimode (MM) fiber optic cables feature multiple strands, ranging in number from 2 to several hundred, resulting in a wider core (50µm to 62.5µm) that accommodates the transmission of numerous data streams over one cable. However, the larger core has its limitations. Due to higher signal attenuation, MM cables are unable to handle the same long distances as SM fiber cables, typically 2km or less, so they are used to connect in short range applications. MM developed with a plastic core may be used in place of glass for certain industries, such as mining or sensing applications, while bigger core diameter fiber (called MM200) is necessary in other applications.

Like SM, MM cables are split into several classifications:

• OM1: maximum bandwidth of 10 Gbit/s, 100 feet distance (obsolete in ISO/IEC 11801 and TIA 568 standards)
• OM2: maximum bandwidth of 10 Gbit/s, 260 feet distance (obsolete in ISO/IEC 11801 and TIA 568 standards)
• OM3 maximum bandwidth of 10 Gbit/s, 1000 feet distance
• OM4: capable of reaching 1300 ft at 10 Gbit/s and 40 Gbit/s up to 500 feet
• OM5: like OM4 but uses different colors of laser light to increase support for greater bandwidth up to 200 Gbit/s or even 400 Gbit/s.

MM should not be confused with “breakout” fiber optic cables. Breakout cables are essentially a group of SM or MM jacketed fibers bound together within an outer jacket. A single connector is shared at one end of the breakout cable with individual connectors on the other. Color-coded cables are "broken out” and therefore enable several connections between network devices with different speed ports, while fully utilizing port bandwidth. Consider, for instance, a switch with a 100G port connected to ten 10G ports. Ideal for patching, breakout cables simplify installation, reduce cable congestion, and improve overall cable management.

Single vs. multimode

In the past, the general rule was MM for short indoor/same building applications while SM was for long distance links and just about everywhere else. That is changing.

Recently, there’s been a big decrease in cost-per-foot for SM cables. Also, the price of SM transceivers has come down considerably, while their designs have become more resilient; in the past, an attenuator was required, or you’d risk burning out the receiver if the cable was too short for the laser used.

Both these factors have made SM more cost-efficient for indoor/ same building applications. With 40- and 100-Gbit/s connections becoming commonplace, SM increasingly makes business sense for new installations and network expansions. Single mode electronics are still about 30% more expensive than conventional electronics because they require more complex optical processors to create powerful light sources. However, when factoring in the lower costs of SM cables, the overall expense is similar — yet SM’s performance benefit is dramatically better. SM supports brighter, more powerful light sources with lower attenuation. Its bandwidth is unlimited, at least in theory. Although MM comes in five different cable grades, none of them can match SM’s limitless bandwidth over short or long distances.

Fiber vs. copper

In general, fiber remains more expensive than copper in the near term. However, fiber ends up costing less in the long run after factoring in copper’s overlooked costs, maintenance, interference, risk of tampering and replacement expense.

There is no question that installation prices for fiber are higher than those for copper due to the skill required for terminations. But as we said earlier, the cost of fiber cable, hardware, and components is declining. In addition, fiber usually requires less than half the networking hardware, has significantly less downtime, and is less expensive to scale and maintain.

Another big plus is that fiber optic cables are immune to electrical noise. Produced by motors, relays, welders, and other industrial equipment, electrical noise can seriously interfere with copper cabling. The more distance that copper cabling travels between two points, the more noise it absorbs and the more the signal deteriorates. Data is also more secure with fiber since it does not radiate signals and is nearly impossible to tap, thwarting a potentially expensive cyber-attack. Importantly, fiber makes upgrading unnecessary as network speeds and requirements escalate.

Installed “first costs” have long been the driving force behind selecting a cabling medium. Frequently, these costs become the reason users choose to deploy copper instead of fiber. But with the price of industrial fiber networks rapidly dropping due to the factors described above, there are now both short- and long-term benefits that make fiber a more compelling choice.

Fiber termination 

Many technicians fear that installing fiber connectors on bulk fiber requires a high level of skill to be done correctly. Several years ago, this was true, but today it is not always the case. The old school way involved solvent glue, lots of small pieces, and hand polishing the tip. Besides being difficult and time-consuming, the precision required by this method led to unacceptable levels of light loss and back reflection when performed by a less experienced technician.

Today there are better ways to terminate bulk fiber like using pre-polished connectors, fusion or mechanical splicing, and fiber optic pigtails allowing successful implementation even for beginners. Network technicians can choose the best termination option for their needs by weighing the benefits of each technique. Of course, they can also order factory pre-terminated fiber optic cables in the lengths needed that have already been tested for plug-and-play deployment. That said, field termination or “on-site” termination requires a trained technician adhering to industry standards and using specialized tools. The same goes for splicing broken or severed fiber cables to maintain network integrity.

Like any network technology, fiber terminations are not immune to problems even when performed by a professional. Once a termination is complete, the optical signal must be tested to ensure proper connectivity. Routine troubleshooting will help identify any underlying issues without interrupting network service. Contamination of connector end-faces by dust, dirt and oil is one of the primary causes for signal loss and failure. Poor polishing or incorrect alignment of fibers can also result in signal loss, as can exposure to excessive humidity or caustic chemicals.