Singlemode Fibers

In addition to the standard singlemode fibers, there is an entire
range of fibers whose cut-off wavelength is adapted to specific
wavelength ranges.

Polarisation-maintaining (PM) fibers are another group of singlemode
fibers. With PM fibers, the required polarisation behaviour
of the fibers is produced through a direction-dependent disparity
in the distribution of the refractive index.

If polarised light is launched into this type of fiber, this polarisation
alignment is maintained over the entire fiber length.