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How To Test Optical Loss with Light Source and Power Meter?


In order to know how effectively your fiber optic cables are transmitting, you’ll need to test each one for optical loss. The term “optical loss” can also be called insertion loss, describes the difference between the amount of light sent into the transmitting end of a fiber optic cable, and the amount of light that successfully makes it to the cable’s receiving end. TIA-standards specify that you must measure optical loss using an optical power meter and the proper optical light source to certify an optical fiber cable. How to do that? This blog will tell you.

Introduction to Optical light source
A light source is a device that provides a continuous wave (CW) and stable source of energy for attenuation measurements. It includes a source, either an LED or laser, that is stabilized using an automatic gain control mechanism. LEDs are typically used for multimode fiber. On the other hand, lasers are used for singlemode fiber applications.

optical light source
The output of light from either an LED or laser source may also have the option of modulation (or chopping) at a given frequency. The power meter can then be set to detect this frequency. This method improves ambient light rejection. In this case, a 2 kHz modulated optical light source can be used with certain types of detectors to tone the fiber for fiber identification or for confirmation of continuity.

Introduction to power meter
The power meter is the standard tester in a typical fiber optic technician’s toolkit. It is an invaluable tool during installation and restoration. The power meter’s main function is to display the incident power on the photodiode.

Introduction to power meter
Transmitted and received optical power is only measured with an optical power meter. Optical loss must be measured with a optical light source. Connect one end of the fiber to the light source and the other end to the power meter. The light source sends a wavelength of light down the fiber. At the other end of the cable, the power meter reads that light, and determines the amount of signal loss.

Introduction to Testing Procedure

  • Connect the optical light source to the transmitting end of the test cable.
  • Connect the power meter to the receiving end of the test cable.
  • Turn on the source and select the wavelength you want for the loss test.
  • Turn on the meter, select the “dBm” or “dB” range and select the wavelength you want for the loss test.
  • Measure the power and loss at the meter.

Light Source and Power Meter

Cables with losses higher than 0.5 dB per end should be cleaned and retested. Dirt is always an issue. If any of the connectors are dirty, measurements will show higher loss and more variability. If the optical loss is still higher than 0.5 dB after cleaning, that means this cable is unqualified. Then you can discard it.

Related Article:

How to Test a Fiber Optic Transceiver?

Optical Power Meter (OPM): A Must for Fiber Cable Testing