How to Verify Fiber Cables

Fiber optics cables, although composed of glass fibers, are durable and resilient.   But to ensure optimal performance, you should maintain their integrity by testing them regularly.  That process, thankfully, is a simple one.

What Are you Checking For?

Simply stated, you test a cable to determine it’s working properly and to verify the quality of the system connection.  Doing so will reduce factors that may lead to failure over time.

Why Do Cables Typically Fail?

  • Stress or excessive bending can cause fibers to break, leading to malfunctions;
  • A cable span that’s too long can result in excessive signal loss but using the wrong length cable is often an installation issue;
  • A contaminated connector can cause excessive signal loss;
  • Faulty splices or connectors can result in signal loss.

Techniques for Verifying Cables

Visual Test

Inspect the cable, looking for obvious breaks in the fiber. Look for cracks, crimps, rips, scratches, dirt, tears, or other defects.

Disadvantage:  This method cannot identify where the fiber optic patch cord has failed nor can it quantitatively measure the degree of weakening or signal loss.

Use of Precision Testing Equipment

There are several precision instrument measuring tools on the market.

  • Optical Time Domain Reflectometers (OTDR)

The OTDR, a popular tool recommended by many engineers, can analyze the causes of cable failure in optical fiber networks and give precise and accurate measurements to guide you to the location of the fiber breaking point.  It also provides technicians with a permanent visual record of the cable’s attributes.

Other tools include:

  • fiber optic light source and/or visual fault locator: This popular tool is often used by data centers, in high-performance computing LAN or WAN installations, by wireless and other telecommunications companies.  When testing fiber optic cable networks, a visible laser source connected to one end of the cable is used to verify the transmission to the opposite end. This instrument is only intended to detect gross fiber defects.  You can also test fiber optic cable continuity to determine whether the right fiber optic cable is connected to the right patch panel location. There are safety precautions that you need to follow to avoid injury to your eyes (see best practices);
  • fiber identifier (FI) is a small handheld fiber test tool that can detect optical signals from the outside at any point along the fiber link. Widely used in the tech industry to identify the cable you want to test without having to disconnect it, fiber identifiers can be used to confirm the presence of traffic on a fiber;
  • optical power meters, typically used with a light source, are an inexpensive way to certify optical fiber. Used by data centers, in high-performance computing, LAN or WAN IT installations, or by wireless or other telecommunications companies, optical power meters can measure fiber optic light continuity, loss, and the strength of the optical signal;
  • fiber multimeter is a handheld measurement tool that combines features of many tools and is used to troubleshoot potential issues. It is a popular tool used for technology cable installations;
  • fiber fault locator, also called visual fault identifier (VFI), is a visible laser that injects light energy into an optical fiber. This instrument, typically used when cables are installed, is a cost-effective way to spot defects of fiber glass such as sharp bends, breaks, faulty connectors and other faults which, if present, will “leak” red or green light;
  • digital fiber optic microscopes can verify the cleanliness of the core and connecting ferrules and identify scratches on the cable and other defects used primarily by companies that manufacture and inspect fiber or in research and development test labs.

Best Practices

100G Form Factors
  • Testing: Cables should be tested regularly. Do a quick visual inspection when you receive the cable.  Before, during and after installation, cables should be verified.  It’s an essential part of the installation process as well as integral to ongoing maintenance of the network.
  • Safety considerations: When using a Visual Fault Locator or other fiber tester for fault location, eye safety is extremely important. Since this device uses a high-intensity laser light source which can cause serious injuries to the eye, neither the source nor the fiber core illuminated should be viewed directly with the naked eye.
  • Cleaning: The importance of cleanliness in fiber installation and testing cannot be overstated.  These are procedures for cleaning a fiber optics cable.  For a more detailed explanation of how to clean fiber optics cables, read this article on how to clean fiber optic connectors

Performance Standards

The Telecommunications Industry Association (TIA) maintains and updates engineering specifications and standards. (See TIA Online) and  These are highly recommended by engineers and telecommunications professionals.

Other industry associations maintain inspection standards including:

  • The Fiber Optic Association
  • The International Electrotechnical Commission (IEC). Standard IEC 61300-3-35 specifies pass/fail requirements for compliance with standards at each stage of the fiber optic cycle.  Compliance requires use of analytical software programmed to specified pass/fail criteria for connector quality;
  • The Institute of Electrical and Electronics Engineers (IEEE) maintains standards to ensure single-mode and multi-mode fiber used commercially in products are flame-resistant and resistant to water, sunlight, and extreme temperatures, as well as to ensure compatibility with other equipment.

Vitex, based in northern New Jersey, is a leading supplier of fiber optics components in the U.S.  We carry a wide variety of fiber optics cables in different lengths and can customize them to meet your needs.  For more information about products, contact

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