Connecting Optical Modules on short distance links
Testing is an important part before actual deployments, as it can save a lot of time in case there are some issues. Therefore, there are many situations in which, before actual deployment, customers would like to make local tests in their lab. Such of test is also important to make sure optical transceivers contain correct coding and links can be made between two sites. If the coding is wrong, the transceiver will not be recognized, and links will not go UP. This is not a good situation if you are located at the remote site and hope to launch the link by plug and play.
It is not necessary to utilize the full site-to-site fibre infrastructure to test transceivers, one rack-to-rack setup is enough. Mostly because optical fibre can be simulated with attenuators (in this kind of setup, non-linear effects are not taken into account).
For example, if we take:
An 80km 10G SFP+ optical transceivers, EDGE Part number: 10G-SFP-80, (Technical specification), then, from the datasheet, we see the following parameters:
The transceiver has a maximum transmit power of +5dBm. Receiver overload starts at -7dBm, which means we cannot connect one 80km transceiver directly with a short patch cord to another transceiver. There is a high chance that the receiver side element might get burned from such a strong Tx signal.
In this situation, if we do lab tests with a short patch cable, it is strongly recommended to use at least 15dB optical attenuators. They look as in the picture below (the particular one is for use in modules which has LC connectors), and we plug them inside the optical module and then attach a patch cable to it:
Why in this mentioned example we need to use 15dB attenuators?
– Maximum Tx is 0dB, and if we add 15dB loss to it, then the signal will be 0-15dB=-15 dB. Rx side receiver overload is -7dB, so with the help of 15dB attenuators, our Tx side will be below this signal and will not cause Rx overload. Attenuators add attenuation [dB] in the connection between transceivers. The increase in attenuation simulates optical fibre distance. The bigger the attenuation, the longer the optical fibre path can be simulated.
If you have any doubts about whether you can connect the modules you have on hand for short-distance connections, please feel free to write: sales@edgeoptic.com, and we will do our best to give our suggestions!