Although optical fiber dispersion does not weaken the signal, it shortens the distance that signal travels inside optical fibers and blurs the signal. For example, a pulse of 1 nanosecond at the transmitter will be spread out to 10 nanoseconds at the receiver, resulting in signals not properly received and decoded. Therefore, it is important to reduce optical fiber dispersion or make dispersion compensation in long-haul transmission like DWDM systems. Here, we will introduce three compensation strategies or techniques to compensate for the fiber dispersion.
Dispersion Compensation With DCF
In DCF (Dispersion Compensating Fiber) technique, one can use a fiber having large negative dispersion alongside a typical fiber. The number of light distributed by a traditional fiber is reduced or maybe nullified by using a dispersion compensating fiber having a really giant value of dispersion of opposite sign as compared to that of normal fiber. There are primarily 3 schemes (fiber-pre, post or symmetrical) which will be used for dispersion compensation. And the dispersion compensating fibers are used extensively for upgrading the installed 1310nm optimized optical fiber links for operation at 1550nm.
Dispersion Compensation With FBG
Fiber Bragg Grating (FBG) is a reflective device composed of an optical fiber that contains a modulation of its core refractive index over a definite length. By applying FBGs, the dispersion effects can be dramatically decreased in long transmission systems like 100 km. The fiber grating reflects light-weight propagating through the fiber once its wavelength corresponds to the modulation regularity. Using FBGs for dispersion compensation may be a promising approach since FBGs are passive optical element fiber compatible, having low insertion losses and prices. The FBGs can not only be used as filters for dispersion compensation, but also be used as sensors, wavelength stabilizers for pump lasers, in narrow band WDM add drop filters.
Dispersion Compensation With EDC
Electronic Dispersion Compensation (EDC) is a method using electronic filtering (also known as equalization) to compensate for dispersion in an optical communications link. The filtering can be included in a communications channel to compensate for signal degradation caused by the medium. EDC is typically implemented with a transversal filter, the output of which is the weighted sum of a number of time-delayed inputs. EDC solution has the ability to automatically adjust the filter weights according to the characteristics of the received signal, which is known as adaptation. EDC can be used both in single mode fiber systems and multimode fiber systems. Furthermore, it can be combined with other functions on 10-Gbit/s receiver ICs. It can get significantly reduced transmitter cost for single mode fiber systems or increased transmission distance for multi-mode systems at a small receiver cost penalty.