An Introductory Guide to Fiber Optic Link Simulation

Posted by Kevin Miller on Fri, Mar 18, 2022 @ 16:03 PM

An Introductory Guide to Fiber Optic Link Simulation

Fiber optic technology has revolutionized modern communications, now taking only fractions of a second for data to be transmitted globally compared to the old days of the Pony Express, telegrams, and regular postal mail. Using optical fiber as the primary medium, vast amounts of information flow continuously every second of every day, supporting virtually everything humans do from an information perspective.  Whether talking on a mobile device, executing a crypto trade, watching the latest video on TikTok, participating in a eGaming tournament, or uploading a document to the cloud, fiber optic technology is the supporting architecture.

For entities tasked with designing, installing, and maintaining fiber optic devices and networks, a major and necessary challenge is replicating these fiber links and spans in the lab for testing and validation purposes and ensuring everything operates as required. However, doing this in an efficient, accurate, and effective way that produces consistent results isn’t always simple, considering every network is different and there are a number of variables and options to sort through. Fortunately, there are proven solution approaches available that can help engineering teams do this the right way.

In this article, we will address the importance of accurately simulating fiber optic links, some challenges that arise, and finally some best practices for effective fiber optic link simulation. The specific focus today will be on the optical fiber infrastructure itself, as it is very difficult to accurately simulate a fiber network without this component.

Why Is Fiber Optic Link Simulation Important?

As a whole, a fiber optic communications network is an expensive undertaking, especially when one considers all of the necessary infrastructure, devices, and labor that are required for a network to function at an acceptable performance level on a continued basis. From architecting the physical fiber routes, to designing the devices that will be used, and certifying which devices best meet the network’s goals, a lot of effort and testing is required at all stages. 

A common thread in all of these areas is that one must simulate these physical fiber links, otherwise there is a major risk that something will not go as planned or intended. If this happens, significant amounts of money can be lost, networks can perform poorly, and so on. Similar to an auto manufacturer that performs track and road tests to ensure performance expectations of a vehicle, fiber optic link simulation allows those designing and deploying fiber-based gear to accomplish the same objectives.     

Who Benefits from Fiber Optic Link Simulation?

As noted above, anyone designing, manufacturing, deploying, or certifying fiber optic networks can benefit from effective link simulation testing. A few examples include:

  • Network Equipment & Device manufacturers
  • Telecom, ISP, and Cable TV service providers
  • Dark & Lit fiber infrastructure providers
  • Data Centers
  • Web & Cloud service providers
  • Banking and Financial trading entities
  • Electric and Energy utility companies
  • Government, Aerospace, & Defense entities
  • Education and University campuses
  • Communications system integrators
  • Telecom Training entities

How To Accurately Simulate A Fiber Optic Link

The most accurate way to simulate or replicate a fiber optic link in a test environment is using real spools of bare optical fiber since that is the same exact medium that is being used in the network environment. In effect, using spools of fiber not only enable a person to simulate the link but actually emulate it because they are able to use that exact same type and distance just in a spooled format as opposed to cable.

It’s important to note that with optical fiber being made of glass, while of extremely high quality, each strand has natural impurities. Additionally, there are a number of major fiber manufacturers that produce a variety of fiber types that while adhering to industry standards, can produce slightly different performance characteristics. In fact, no two spools even of the same fiber type and manufacturer are exactly the same. One spool may have a loss/attenuation spec of 0.185db/km, while the next may be 0.189db/km. While not a huge difference, still different nonetheless.  Thus, the best way to replicate any fiber’s performance in the field is to ideally use that exact same fiber type in the lab or test environment.

Other approaches have been attempted in the past, like using an attenuator to reduce the optical power of a signal to simulate a similar power loss over that target distance. However, as no real fiber is being used, no other optical characteristics of the fiber are replicated like chromatic dispersion or even the latency/delay of the signal across that distance, both extremely important factors to account for.

Additionally, while some software exists that may note it can simulate a given fiber performance value, it often doesn’t take into account many of these fiber-specific variables. Lastly, since performance changes slightly from fiber to fiber of the same type, the software doesn’t take that into account either. Using our vehicle example again from above, using a driving simulator is beneficial to a degree, but nothing replaces the actual driving experience. 

Challenges That Arise When Simulating Fiber Links

Now that using spooled lengths of bare optical fiber is proven to simulate the physical fiber infrastructure in the most accurate manner, what types of challenges can arise when seeking to acquire and manage fiber spools?

Bare Optical Fiber Is Easily Damaged

Optical fiber in its raw manufactured form off the draw tower consists of the glass core, glass cladding, and a thin protective coating that typically has a total diameter of 250µm, just slightly larger than a human hair. As a result, it is very easy to break this fiber when not handling it carefully. All it takes is bending too sharply, sitting or dropping something on it, or other mishandling and you have a damaged fiber.

Fiber Spools Take Up Significant Physical Space

When the fiber manufacturers spool bare optical fiber onto factory-sized reels, the reels are designed to accommodate adequate shipping of the fiber, since 99%+ of fiber manufactured is delivered to cable manufacturers who then add protective jacketing and other materials necessary for withstanding installation and environmental elements in a network environment. Thus, these shipping reels were not designed to provide the most space-efficient format for desktop or rack use, or add further protection for someone that may be manually using it for these types of testing applications in a lab.

Standard-sized bare fiber reels can be as large as 9.25 inches in diameter x 4~6 inches in width. Additionally, a standard 50.4km spool of fiber on a reel can weigh as much as 9 or 10 pounds. When you consider that large test laboratories may require tens or hundreds of spools over time, this is a tremendous amount of physical space being occupied, not to mention difficult to manage and organize.

Shown Below: Fiber Lab Flex rack chassis with multiple spools maximizes space efficiency

Optical Fiber Network Link Simulation Modules in a Rack

Easily Identifying Fiber Types Can Be Difficult

Most bare optical fiber spools include a small label on the flange that includes the fiber type as well as some values like the total distance and attenuation specification. These are generally in very small fonts, so one must inspect each spool closely by hand to determine the fiber type and length. Adding to this, to support automated, mass production of fiber, most manufacturers standardize on just a few types of reels for the majority of their fibers. Unless you can closely inspect the labels on two spools, you might otherwise just see two identical-looking spools, when in fact they could have two completely different fiber types.

Fiber Can Be A Challenge To Acquire

Bare optical fiber is not something fiber manufacturers seek to market as an off-the-shelf item or available in many places like other more prevalent fiber components and commodities that are acquired easily in the marketplace. Since bare fiber is consumed primarily by cable manufacturers, some fiber manufacturers do not sell spools to the general market at all, while others have only specific distribution partners or entities that add value to the fiber with whom they have established relationships.

Additionally, since manufacturers are set up to produce fiber at mass scale, bare optical fiber is often spooled to a few standard lengths, leaving limited options for those that require more accurate lengths when simulating their known network spans and links.

Technical Note: It’s also important to note that bare optical fiber is always manufactured and spooled as a single (simplex) strand of fiber. Most people think of fiber as a jacketed cable which often includes more than one fiber. So, when needing to simulate a true fiber “link” which typically consists of a Transmit fiber (Tx) and a Receive (Rx) pair, ie. two individual fibers, it requires the use of two fiber spools.

Best Practices for Simulating Fiber Links

Despite the challenges noted above, there are some steps you can now take to improve the way you acquire, use, and manage optical fibers for link simulation testing.

Invest In A Quality Fiber Link Simulation Solution

When acquiring spools of optical fiber for link simulation testing, the most sensible decision for improving the use and management of the spools is to invest in a quality, professional link simulation platform, sometimes also referred to in the industry as a network simulator. In short, these are fiber enclosure platforms that contain the spools of optical fiber that don’t just solve a number of challenges noted previously, but also deliver benefits.

Consistent Performance Results

Protecting the fiber in a secure and stable platform helps to ensure long-term testing consistency and reliability. Since the ultimate goal of network simulation testing is to accurately replicate optical performance and latency of field network links on a repeatable basis, it is vital to trust that the results are accurate each and every time.

Highly Accurate Simulation of Field Network / Links

The best link simulator solution vendors offer a wide array of customization options in terms of available fiber types via relationships with fiber manufacturers, precision lengths, setup configurations, and related special services that result in a setup that mirrors the intended network.

Professional & Efficient Organization

Whether you require a rack-mount chassis with multiple fibers or a portable solution for benchtop use, a quality platform will organize all test fibers in the most professional and space-efficient manner. In addition to enhancing the look and space-efficiency of the lab, these solutions offer easier handling and usage, resulting in achieving maximum value from the fiber.

Select A Proven Vendor Partner

In addition to selecting a quality link simulator style that will meet your unique testing requirements, it is equally important to select a vendor with a proven track record and capabilities that will serve as a true partner.

Since a significant level of technical expertise and customization is required when manufacturing these solutions to match a user’s specific setup needs, the partner chosen should use a consultative approach that helps to identify the exact needs and determine the most appropriate solution.

Another thing to keep in mind when selecting a vendor partner is that it takes time for a vendor to build the finished, customized solution. Given that most engineers have testing plans and project deadlines, it is important to select a vendor with an excellent track record of delivering solutions on time. Do not hesitate to ask for the expected lead time when specifying a solution, but also inquiring about customer references, capabilities, and the level of timely responses you receive can also be a good indicator of the credibility of the vendor.

The vendor chosen should have extensive fiber expertise and established relationships for acquiring fiber in a timely manner, along with offering a wide range of customization, spooling, and packaging capabilities. As a result, products aside, they can serve as an excellent resource of information about various fiber types, solutions utilized for specific applications, and more.

Similar to most products and services, it is always important to select a reputable partner that will provide maximum value - both high-quality solutions that deliver maximum benefits along with outstanding service.

Intend To Use The Same Fiber As Installed In The Field

When seeking to replicate a known field link fiber, one should always try to match or specify the same fiber in the link simulator that is deployed in the field to achieve the most accurate performance comparison.

Industry organizations such as the ITU have established standards that ensure optical fibers meet certain specifications, in order to allow various types of equipment and networks to operate seamlessly around the world. While ITU G.652D single-mode fiber, for example, requires that manufacturers adhere to a degree of shared standards resulting in a level of performance equivalence, it’s important to remember that each manufacturer produces it using their own proprietary recipe, processes, and equipment.

As noted earlier in this article, fibers often have slightly different degrees of performance specifications in various areas. This is not to say that any one is “better” than another but may produce slightly different results. As an example, while all offer great performance, one fiber may have a slight advantage in a loss specification, while another in chromatic dispersion, and all may vary for latency due to differing Indices of Refraction (IOR) of the glass.

If only the general spec (ex: G.652D) of a fiber in the field is known but not the exact manufacturer/brand, then just be certain to choose a G.652D fiber from a reputable manufacturer in general. While possibly not a perfect match, it will still typically yield similar and acceptable results for most testing applications. 

Asking your vendor for suggestions can be helpful, as they should be able to provide suitable fibers along with other insights on popularity, the potential cost and availability differences, and more.


Always Use A New or Quality Owned Fiber

Found an old, unmarked fiber spool in the lab that hasn’t been used in a while? Located “used” fiber online for a really low price? While it is commendable to try and minimize costs for the organization and budget constraints are a reality for any engineer, it is not a best practice to use a fiber if you are uncertain of the exact type or quality.

Unless purchasing new fiber from a reputable source or using existing spools on-site that were previously acquired, it is never a guarantee of what you might receive when purchasing a used or low-cost fiber from a 3rd party source. Not only might it not be the exact type you require or that is listed, but it may have bends, crimps, or degradations that can negatively affect performance. Some companies in the market are also known to manufacture or sell lower-priced fibers considered “B grade”, which did not meet the quality manufacturer specifications. Lastly, as with most products and services, there are some sellers that will attempt to market fibers as being produced by a leading manufacturer when in fact they are not.

With so much riding on the results of these critical simulation testing procedures, it simply makes the most sense to invest or to always utilize the highest quality fibers available, either purchased new through a reputable vendor partner or known fibers already in possession

Lastly, if already owning unsecured spools and seeking to enhance or make an existing test setup more efficient, it would be wise to contact the vendor partner, as they may offer services and suggestions for how they can help you package fiber that you already own in an improved manner.


Clean Connectors Frequently 

This is a common theme across all fiber optic communications systems, but it is very important to keep connectors and interface adapters clean, as dirt on a connector will have a negative impact on signal transmission. As commonly known, one of the first steps when troubleshooting devices and systems that are not performing optimally is to check to make sure all connections are secure and clean – the same thinking applies when utilizing optical fibers in network and link simulation solutions in the lab.

Remember to clean connectors prior to testing, ideally before each use, but especially during times of increased handling, frequent use, or after long periods of minimal use.

There are a variety of useful connector and adapter interface cleaning devices on the market - inquire with your network simulation vendor partner, as they may provide them or in some cases include them for use with this equipment.

Learn More About Fiber Link Simulators

Since 2001, M2 Optics has specialized in designing and manufacturing customized, efficient fiber optic link simulation solutions for leading entities around the world. By helping engineering teams significantly improve the way they use and manage optical fiber, M2’s trusted team of fiber experts and Fiber Lab solutions consistently support advanced testing initiatives across multiple markets.

If you'd have questions and would like to communicate with one of our experts about link simulation, require further technical information about optical fibers, or have an upcoming fiber requirement, the M2 Optics team or a local authorized partner is available at your convenience.

Topics: fiber optic training, network simulation