For some of Ciscos SFP modules Cisco implemented some DOM (Digital optical monitoring) capabilities. This means, that you can debug fibre-links to a certain grade with thos DOM-enabeld fibre modules. For example the GLC-LH-SMD is such a modules.
With DOM-capbale modules the command
can be executed on the switch and the RX & TX power on the modules links are displayed. It’s a cool feature to quickly debug a fibre link and check the attenuation on a link.
Further infos and an example can be found at: