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

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


OPM is the abbreviation of Optical Power Meter. If this technology sounds alien to you then don't worry, we will be providing you a complete information regarding an optical power meter, what is it and why is it used.

Let's start with the first question that pops up in our minds when we hear the term optical power meter

What is meant by Optical Power Meter?

It is a testing instrument for accurately measuring the power of any fiber optic equipment or in other words, it measures the power of an optical signal that passes through a fiber cable.

Moreover, it also helps us to determine the power loss that occurs when the signal passes through optical media.

Optical power meter is used to install, debug and maintain any fiber network. It adapts variety of connector styles like ST, SC, FC etc.

What is it made of?

Optical Power meter is made up of a display and a calibrated sensor used for measuring amplifier circuit.

The sensor consists of a semiconductor. This semiconductor can be germanium (Ge), silicon (Si) or indium-gallium arsenide (InGaAs). The measurement of optical power and the wavelength of the optical signal is shown on the display.

Setting the wavelength for an OPM:

For novice users, measuring the accuracy can be problematic. The power meter has to be set according to the correct wavelength otherwise we will get wrong values of power level. Experienced users find this process to be easy and most of them will be aware of the wavelength already. If we don't set accurate values of wavelength then it will result in wrong values of power. It can be disastrous because some applications demand to have an exact measurement.

A broad light of spectrum can be tested with optical power meter. However, if it is not calibrated correctly then there will be fluctuations in the readings ( it can be both high and low).

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Is OPM compatible with all cable types?

Optical power meter works fine with fiber optics only and cannot read accurate energies from other types of cables.

OPM for Continuity Testing:

These meters are also helpful in continuity testing. Operators use these meters for testing the complete length of cable to ensure that there is a continuous flow of power and there are no drops or spikes anywhere in the cable.

A special function named as test tone detections is used by optical power meters to produce best results in the continuity testing.

An optical power meter isn't the only type to check such cables. There are some other meters such as lux meters, light meters and photometers that can be used for this purpose. However, the functionality of optical power meter is different from all the other types.

Average power output is read by this unit and it normally doesn't capture the power that it finds to be deviating from the average.

These units are best for those users who are interested in having a snapshot of the power reading. Not for those who want to have a record of power levels for a longer timespan.

Design of OPM

A standard optical meter consists of 5 buttons.

  • Power Button
  • Light Button
  • dB button
  • Zero Button
  • Button

Functionalities of buttons on OPM:

Their functionalities are defined below:

Power Button

It is used to turn the optical power meter ON of OFF

Light Button

It is used to turn the LCD backlight on or off.

dB Button

It is used to select the unit in which the value will be display.

Zero Button

If you press this button thrice, then you will enter into zero calibration procedure.

Lambda Button

This button is used for selecting different wavelength

Measurement unit of OPM

The reading of optical power meter expressed in dBm is a significant unit for measuring power of the signal.

The "m" in the dBm unit is used to refer the reference power. The reference power is 1 milliwatt.

If the source has a power level of 0 dBm then it possesses a power of 1milliwatt. Similarly, -10 dBm equals 0.1 milliwatts and +10 dBm equals 10 milliwatts.

The higher the negativity of the number, the higher the loss. If the reading of OPM is -5.0 dBm then the loss is 5.0 dBm.

Types of Optical Power Meter:

We have various number of OPM testers because of the different resolutions that vary from 0.001dB to 0.1dB. The selection of appropriate resolution to measure depends on the type of test needed. The resolution of OPM required for laboratory networks is 0.01dB

However, some specialized OPMs provide 0.001dB resolution.

All OPMs have a same measurement uncertainty. Most of the meters have uncertainty level of +/-5% or 0.2dB approximately despite of what the resolution of display is.

Testing Procedure of OPM:

We need a light source and an OPM tester for testing the end-to-end performance of any fiber optic system. A wavelength of light is send down the fiber by a light source. This light is read at the other end by the power meter to determine the amount of signal lost.

Since the loss of optical fiber is dependent on the wavelength, the OPMs should use the same wavelength that is being used by the source of light.

Light source and power meter testing is also called one jumper method. It is one of the key methods to accurately measure the end-to-end signal loss of any optical fiber network.  This is called attenuation.

Below, we will be listing some insertion loss limits for different components.

The results of the test should be compared to the attenuation allowance.

The attenuation allowance can be calculated as follows:


VFL stands for Visual Fault Locator. It is also called VFI (Visual Fault Identifier). The VFL is designed to inject visible light in an optical fiber. An OPM deals with measuring the power loss in the light signal whereas VFL is used for detecting faults in the optical fiber such as breaks, bends or faulty connectors. Such faults may lead to leakage of red or green light visually