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Fiber Cabling / Fiber Testers & Tools / Optical Power Meter (OPM): A Must for Fiber Cable Testing

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

Posted on By FS.COM

Fiber optic cable is seeing broad adoption in telecom industry to feed insatiable demand for bandwidth. Test these massive fiber cables thus becomes the most frequent yet laborious task. However, some test-and-tried tools will help to make your testing work much easier. Optical power meter (OPM) is such a powerful tool made purposely for fiber cable testing, installation and maintenance, making it the perfect choice for a wide range of field applications. What is optical power meter and how does it facilitate fiber testing? All of your confusions will be clarified right here.

What Is an Optical Power Meter?

An optical power meter (OPM) is a testing instrument working to accurately measure the power of fiber optic equipment, or the power of an optical signal passed through the fiber cable. An optical power meter is made up of a calibrated sensor that measures amplifier circuit and a display. Optical power meter is newly developed portable to fit the hand, while with enhanced stability and reliability. It can be used for installation, debugging, and maintenance of any fiber network. An optical power meter can be widely used in a variety of fields such as cable construction and maintenance, optical fiber transmission/communication, and CATV.

Generally, there are four buttons on the optical power meter: power button, dBm/w button, light button and λ button.

optical power meter

Applications of Optical Power Meter

Optical power meter has changed much and is made easier to operate and more efficient through the addition of new features. It is widely used in LAN, WAN, metropolitan network, CATV or long-distance optical network for the following purposes:

Attenuation Measurements. Optical attenuation should be measured to determine the quality of the fiber installation. Compared to a pre-calculated link budget, a simple calculation of link attenuation indicates if the link will perform as installed.

Fiber Continuity Testing. Continuity can be measured by placing a calibrated light source on one end of the fiber and the optical power meter on the other end. A power reading on the display of OPM shows the presence of optical power.

Active Equipment Power Measurements. Active equipment should be monitored on a regularly basis to test its power levels and stability. Optical power meter can be directly attached to this equipment via a patch cord to check whether the transmitter is stable and within the manufacturer’s specified power range.

Length Measurement. Generic cabling standards such as the TIA-568 use the actual length of the cable under test to calculate loss budgets. Spool testing can verify that the amount of fiber delivered on the spool is accurate.

Patch Cord Testing. An invalid fiber link may result from bad fiber patch cables. Optical power meter can be used to test the attenuation of a patch cable to see how it performs.

How to Test Fiber With an Optical Power Meter?

To test the end-to-end performance of a fiber optic system, two pieces of handheld equipment are needed – an optical power meter and a light source. The light source sends a wavelength of light down the fiber. At the other end of the cable, the power meter reads that light, or optical power level, and determines the amount of signal loss. Since optical fiber loss varies with wavelength, optical power meter should use the same wavelength as the one used by the light source. For example, if the light source operates at the 1310nm wavelength, the optical power meter should also be set to 1310nm testing.

optical power meter and light source for fiber testing

Power meter and light source testing, also known as the one jumper method, is the most accurate way to measure end-to-end signal loss of the fiber, referred to as attenuation. Listed below are TIA/EIA- 568 insertion loss limits for the various components. Specific installations or protocols may impose stricter limits.

Loss budget (TIA/EIA specification limits)

Insertion Loss
< 0.3 dB at all wavelengths
Connector Pair
< 0.75 dB at all wavelengths

Test results should be compared to the link attenuation allowance calculated as follows:

Link Attenuation Allowance (dB) = Cable Attenuation Allowance (dB) + Connector Insertion Loss Allowance (dB) + Splice Insertion Loss Allowance (dB)

optical power meter (OPM) fiber optic cable test

When testing optical fiber cable with power meter and light source, perform the following steps.

Step 1. Disconnect active equipment.

Step 2. Acquire suitable light source for the single mode (generally 1310 nm or 1550 nm), multimode (850 nm or 1300 nm), and power meter.

Step 3. Verify proper wavelength to set source and meter. (Note: Calibration of the equipment is required before each test. Follow the equipment manufacturer’s procedures.)

Step 4. Acquire accurate test jumpers and couplers, which should be part of the light source and power meter kit.

Step 5. Connect the jumper (containing the same fiber size as the system fiber) to the optical source and the optical power meter. Turn unit on. Record the reference power reading (Pref), displayed in dBm.

Step 6. By applying an adapter, insert a second jumper (Test jumper 2) between the jumper used in Step 5 and the optical power meter. Verify the attenuation added by the second jumper is not greater than 0.75 dB: Pref-Pcheck ≤ 0.75 dB.

Step 7. Attach the jumpers to the optical source and optical power meter. Disconnect the two jumpers at the adapter. Connect the optical source/Test jumper 1 to one end of the system fiber to be tested. Connect the optical power meter/Test jumper 2 to the other end of the system fiber. Document the test power (Ptest). Subtract the test power (Ptest) from the reference power (Pref), recorded in Step 5, to conclude the end-to-end attenuation: Attenuation (dB) = Pref-Ptest.

Step 8. Document the test results.


Compact in size while easy to use in often confined working environments, optical power meter is widely use to efficiently conduct an end-to-end performance. Fully understand the value of qualified fibers and standards-compliant test equipment to a sound optical network. FS.COM’s optical power meters are designed with cabling standards, and are available with various connector type and wavelength options. For more details, please contact us via sales@fs.com.





IT enthusiast, networking specialist & consultant.

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