Although most fiber SFP are relatively low power they can still cause damage if care is not taken.
The power is similar to laser pointers but since it is infrared it does not evoke the immediate reaction that a pointer shined in your eye does so it is possible to get a minor retinal burm
Note: Some fiber transmitters are much higher power such as those used for 'fiber to the home' applications where the outbound (only) path is split 32 or even 64 ways.
A while back I was in a meeting where I made the comment that one way to tell if the TX diode was working was to look at the fibre; if you did not see anything it was working
Four out of the other 5 people in the room responded with a blank stare, the exception being a grizzled manufacturing engineer with an equally dark sense of humor.