Which wavelength(s) of light are used for fiber-optic transmission? Do
> single-mode and multimode fibers require different wavelengths?
Its different for different technologies.
SONET (ie. OC-x) uses 1550nm.
CWDM/DWDM is popular ways to use more capacity on fiber, and those frequencies are centered around 1550nm, and branch out either direction. (ie. 8-band CWDM is 1470nm to 1610nm)
Ethernet over single-mode fiber is 1310nm. Ethernet over multi-mode fiber is 850nm.
There are a few obscolecent ones (ie. 1300nm multimode).