Calculating loss budget (2)

Hello, everyone!

Today, I will finish explaining the loss budget. This is the second and last article about this topic. The first article was an introduction for calculating the loss budget. Now, I will show you how you can calculate the loss budget for every optical network. Let’s get started.

1. Type of optical fiber and wavelength

The attenuation of optical fiber depends on the type of optical fiber and the wavelength used by the system. MM optical fibers have a higher attenuation than SM optical fibers. At higher wavelengths, the attenuation is smaller. In the next table, we can see typical values for MM and SM optical fibers for typical wavelengths 850 nm, 1300 nm, 1310 nm and 1550 nm.

For indoor applications, for SM optical fibers, the max attenuation is assumed to be about 1 dB/km.

2. Splice loss

Fusion splicing is the most common way to connect optical fibers in outdoor applications. SM optical fiber is usually flattened. On the other side, MM optical fibers use mechanical splices. Values for multimode splices are 0.1 to 0.5 dB. The attenuation value of the fusion splice for SM optical fiber is about 0.05 dB. 0.3 dB can be taken as the max value.

3. Connector pair

The typical attenuation of MM optical connectors is 0.2 to 0.5 dB. In SM optical fibers, where the optical connectors are factory made, the attenuation is up to 0.1 to 0.2 dB. Typically, 0.3 dB for adhesive/polish optical connectors and 0.75 dB for prepolished/splice optical connectors are taken for losses on optical connectors. For all optical connectors, the maximum acceptable value is 0.75 dB.

4. Optical splitters and WDM modules

Certain optical networks also have optical splitters and WDM modules, such as PON and OLAN networks. These are the elements that bring the greatest attenuation. Typically, the WDM module introduces attenuation from 0.7 to 1 dB. Typical optical splitters and their values are shown in the next table.

The attenuation of optical splitters can also be calculated using the following formula:

a_s(dB) = 10*log(1/N), N = 2, 4, 8, 16, 32 and 64.

Calculating the loss budget

Finally, the formula for calculating the loss budget is as follows:

A_u= α * L + a_ss* N_s+ a_cs* N_c + a_s+ a_m,

• α - attenuation coefficient of optical fiber (about 0.35 dB/km for 1310 nm and 0.2 dB/km for 1550 nm or 1490 nm),

• L - length of optical fiber,

• a_ss - average attenuation of fusion splice (about 0.1 dB/km),

• N_s - total number of fusion splices on the optical trace,

• a_cs - average attenuation of connector pair (about 0.5 dB/km),

• N_c - total number of connector pairs on the optical trace,

• a_s - all attenuation of optical splitters in this trace, and

• a_m - margine of the optical trace (1 dB for 0 - 5 dB, 2 dB for 5 - 10 km, 3 dB for distance bigger than 10 km).

This is the end of this article and topic. I hope that you learned something new!

Thank you!