Dispersion in optical fibers
Pulse Dispersion: The broadening or spreading of the output pulse with the time is called pulse dispersion. This can happen due to the different reasons. Let us discuss them one by one:
1. Inter-modal dispersion: The term “Inter-modal” consists of two terms “inter” and “modal”. “inter” means “within different” and “modal” term comes from mode (mode means path followed by the light). Therefore, intermodal dispersion means the dispersion between the different modes of the fiber. Therefore this dispersion can not occur in mono-mode fibers. Thus it can only occur in multi-mode fibers.
Reason: This dispersion arises due to the different time taken by different modes of the fiber. This dispersion depends on the angle at which light ray strikes the core-clad interface. As there are more than one path (mode) through which the rays are propagating therefore each group of rays has its different characteristics group velocity. As the velocity will be different thus the rays will not reach the output at the same time. Therefore, the intermodal dispersion occurs.
2. Intra-modal dispersion: The term “Intra-modal” consists of two terms “intra” and “modal”. “intra” means “within same” and “modal” term comes from mode (mode means path followed by the light). Therefore, intramodal dispersion means the dispersion between the same modes of the fiber. Therefore this dispersion can occur both in mono-mode fibers as well as in multi-mode fibers.
This dispersion is of two types:
a) Material dispersion
b) Waveguide dispersion