Engineering Made Easy: Meridional and Skew Rays (Optical Fiber Communication)

24 Dec 2018

Meridional and Skew Rays (Optical Fiber Communication)

There are two types of light rays on the basis of propagation inside the optical fiber-
#Meridional Rays and
#Skew Rays (Helical Rays)

Here we will discuss propagation of both types of rays-

Meridional Rays

*Meridional rays enter into the optical fiber through it's axis.
*These rays cross the fiber axis at each reflection.

Meridional Rays Propagation Inside Optical Fiber

The two diagrams given above show the propagation of meridional rays inside the optical fiber. The first diagram provides the ray path view along the fiber axis. It is clear from the diagram that the light ray is crossing the fiber axis at each reflection. These reflections are marked as 1, 2 and 3.

Meridional and Skew Rays Video

Another diagram is also of meridional ray propagation but with a different view. It is ray path view along the plane normal to the fiber axis.

Now let's discuss another kind of light ray propagation inside optical fibers i.e. Skew rays.

Skew Rays (Helical Rays)

*Skew rays are also known as helical rays as they move on helical path inside the optical fiber.
*Skew rays do not cross the fibre axis and propagate around the optical fiber axis on zigzag path.
*Skew rays greatly outnumber the meridional rays. *Skew rays enter the optical fiber off the fiber axis.
It should be noted here that, in case of skew rays, the point of emergence from the fiber in air depends upon the number of reflections inside the optical fibre. It does not depend upon the input conditions to the fiber.

This concept is made clear with the help of two diagrams given below.

Skew Rays (Helical Rays) Propagation Inside Optical Fiber

The first diagram of skew ray shows the ray path view along the fiber axis and the second diagram shows the ray path view along the plane normal to the fiber axis.
It is clear from the second diagram that the skew ray (helical ray) is not crossing the optical fiber axis and propagating around the axis.