Fiber Optic Testing


Fiber Optic Testing

Fiber optic testing is essential for certifying installed links and for necessary troubleshooting. Knowing testing procedures and how to develop a link loss budget is key to installation and testing success.

Cleerline offers two testing kits, the SSF-TKITP-400 Pro Testing Kit and the SSF-TKITE-100 Basic Testing Kit. The SSF-TKITP-400 Pro Fiber Testing Kit is intended for network certification to TIA-568-C standards.

The following videos use the SSF-TKITP-400 Pro Kit. Access all testing kit demos on our instructional video page.

For a full, in-depth overview of testing, including the difference between absolute vs relative measurements, full details on testing procedures, and more, please refer to the Fiber Optic Association Guidelines. We include these instructions with all kits. The below is a basic overview based on those guidelines.

Demo Videos

Multimode LC Testing with SSF-TKITP-400
Multimode SC Testing with SSF-TKITP-400
Single Mode LC Testing with SSF-TKITP-400
Single Mode SC Testing with SSF-TKITP-400

Testing Procedure: What am I measuring?

Insertion loss is the measurement in decibels (dB) of optical power lost in transmission over a cable and any attached connectors or splices.

What do I need in order to test?

  1. Most importantly, you need a testing kit. Cleerline testing kits include an Optical Light Source and Optical Power Meter. The light source has two laser light outputs: one at 850/1300 nanometers (nm) for multimode fibers, and one at 1310/1550 nm for single mode.
  2. Note that the laser does not operate at visible wavelengths. To avoid eye damage, do not look into optical light sources at any time. The power meter measures output power and provides the loss measurement in dB.
  3. Reference cables must match the cable type under test. If testing a single mode cable, use a single mode reference cable. For multimode fiber, utilize a multimode reference cable. Reference cables link the light source to the power meter and are used to reference the power meter to 0 dB. Without this calibration, tests will not be valid. The reference cable is also required during testing for all loss measurements.
  4. Feedthrough adapters – Feedthrough adapter(s) connect cable under test to reference cable.
  5. Fiber optic cleaning supplies: As we discussed in our cleaning video, a small amount of contaminate on a connector can invalidate test results. The industry invalidates testing records if proper cleaning methods are not employed. Always clean connectors under test! We recommend having 1-Click Type cleaners on hand and using them in advance of mating any connector.
  6. Finally, you must have access to the cable you wish to test.

Single-Ended Testing vs Double-Ended Testing: How many reference cables?

Reference Cables
Multimode Reference Cable

Depending on installation and configuration, one or more reference cables may be required.

Single-ended testing uses one reference cable connected to the cable under test. Note that single-ended testing only includes connector loss for the connector attached to the reference cable. This can be a good way to find faulty connectors, as the connectors on each end of the cable can be tested separately.

Double-ended testing places the cable under test between two reference cables. This allows immediate measurement of the loss of both connectors on the cable under test, plus all cable loss, and any included splices. Double-ended testing is the recommended procedure for in-plant testing.

How do I test?

For the full steps, please refer to the videos.

Key points

  1. Set light source output to match the type of cable under test. 850 nm = multimode. 1310 nm = single mode.
  2. Select reference cables. Reference cables must match the type of fiber under test.
  3. Connect reference cable(s) and set reference value by pushing the reference button on the power meter.
  4. Using feedthrough adapters, connect cable under test to reference cable(s).
    • Remember, if using single-ended reference testing, the reference cable stays connected to the light source for the duration of the test.
    • For double-ended reference testing, connect the cable under test to the reference cables without disconnecting the reference cables from the optical power meter and light source.
  5. Remember to clean in advance of any mating of connectors during testing.

Link Loss Budgets

In order to determine test success, a link loss budget is necessary. The loss budget is the calculation of estimated loss of all connectors, cables, and splices within a link.

The Fiber Optic Association sets out some basic guidelines, which are listed below.

  • Mechanical Splice Connectors (such as Cleerline SSF™): up to 0.75 dB each
  • Single Mode Fiber: 1.0 dB per kilometer (0.1 dB per 600 feet) for 1310 nm sources
  • Multimode Fiber: 3.0 dB per km (0.1 dB per 100 feet) for 850 nm sources
  • Splices: 0.2 dB each

The FOA has also released a convenient Loss Budget Calculator, available at

Always, however, review your system design and requirements when creating your link loss budget.

Fiber Optic Testing
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