1. Mode coupling in optic fibers

2. Mode is the path for light rays through an optical fiber.
If an optic fiber supports only one mode, it is called as single mode fiber. Multimode fiber supports more than one mode.

3. The electric field distribution of various modes yields similar distributions of light intensity within the fiber core.
These patterns are called mode patterns which gives an idea of different modes propagating in the fiber.
Propagation characteristics of a fiber are very sensitive to the
deviations of the fiber axis from straightness
variations in the core diameter
irregularities in the core-cladding interface
refractive index variations.

4. Individual modes do not normally propagate throughout the length of the fiber. This result in a mode conversion which is known as mode coupling.
Coupled mode equations obtained from Maxwell’s equations can be used for the analysis of mode coupling.
Mode coupling affects the transmission properties of fiber which is a serious cause for concern when used for long distance communication.

5. Mode coupling leads to intramodal dispersion like material dispersion and waveguide dispersion and also intermodal dispersion.