Because this is a networking forum Im going to assume that the
application your speaking of is digital data transmission (ie ethernet),
so in that context the answer is "both"
LEDs and LASER LEDs are kissing cousins and are both used to drive
fiberoptic transmission systems. In general terms "regular" LEDs are
typically used in multimode, low bandwidth, low distance systems. In
contrast, LASER LEDs are more often (but not always) used in
single-mode, high bandwidth, long reach applications.
Dick Dastardly is correct.
1550nm Single mode is driven with a laser.
Multi-Mode can be driven with either, depending on temperature...
850nm MM is driven with an LED.
1300nm MM is driven with a laser
can someone confirm?