Optical balance

White Paper : optical balance or optical loss management



Preamble: Most active devices on a network are now interconnected with optical fiber. The inclusion of an active or passive equipment within an optical link network is different from within a copper network. Within an optical infrastructure, each element consumes a part of the energy transmitted by the transmitter and must therefore ensure that the receiving equipment will have sufficient light energy for its operation. It is then necessary to first calculate the optical balance . This document describes the development of an optical balance


Mathematical review:


Optical energy is measured in dBm or in mW depending on the recommendations of the equipment suppliers. The usefulness of Decibels (dB) as a measure lies in the fact that they allow one to compare very disparate values more clearly than when using values expressed to five or six decimal places.


The mathematical formula for the conversion of power into dBm is as follows:

dBm = 10 log (Power measured in mW/ 1mW)

Such that:

1mW=0 dBm

4mW= 6dBm

0,01mW= -20dBm

0,001mW= -30dBm


When one doubles the power one increases by 3dB. When the power rises tenfold one increases by 10 dB. When the power is halved there is a reduction of 3dB ; when it is divided by 10, a reduction of 10 dB.

A difference in power is given in dB and not dBm. For example, 3dBm-20 dBm = -17dB.


A Case Study of an Optic Assessment:


The issue: a user wishes to insert an optic tap to make a replica of the port allowing the analysis of application traffic with an APM probe. The user wants to position the tap between a switch and a server as shown in the diagram below:.

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