Olson Technology OT-DCM-F - Manual (Page 4)

025-000566 Rev. X3 www.olsontech.com 3
THEORY OF OPERATION
The most commonly used fiber in the world today is NDSF (non-dispersion shifted fiber) such as Corning SMF-28 ® . For
long distance applications, a wavelength near 1550nm is usually used resulting in dispersion of about 17ps/nm/km as
shown in Figure 1 below. Dispersion causes the bit error rate (BER) to increase in digital systems and the analog
distortion, primarily CSO and 2 nd order distortion, to increase sharply with increasing fiber distance. The DCM offers a
way to nullify most of this dispersion allowing very long fiber links to be achieved.
Figure 1 - Dispersion Characteristics of NDSF
A DCM is a device that has negative dispersion. The Olson OT-DCM-F series module contains a special fiber that has a
very high negative dispersion equivalent to “xx” km (ranging from 10 to 100 in 10’s) of Corning SMF-28 ® fiber. It
operates over a wide wavelength range. Figure 2 below shows the benefit of using a DCM.
Figure 2 - The Effect of a DCM on a Long Fiber Run