In this lecture, we are going to learn about the Difference between Step Index Fiber and Graded Index Fiber. Before starting the difference between them, first, learn about optical fiber and various types of optical fibers.
We have covered the full detail of Optical fiber communication, with its various types of optical fiber in the previous lectures. To know more about optical fiber click the below link.
Types Of Optical Fibers Based On refractive index (Index profile)
Difference between Step Index Fiber and Graded Index Fiber
| Step Index Fiber | Graded Index Fiber |
|---|---|
| The refractive index of the core cladding is uniform. | The refractive index of the core is not uniform. but, the refractive index of the cladding is uniform. |
| Since there is an abrupt change in the refractive index at the core and cladding interface, the refractive index profile takes the shape of a step. Hence called step-index fiber. | In this fiber, the refractive index of the core is maximum at the center and decreases gradually with distance toward the outer edge. Hence called graded index fiber. |
| Pulse dispersion is more in single-mode step-index fiber. | Pulse dispersion is reduced by a factor of 200 in comparison to step-index fiber. |
| Attenuation is less for single-mode step-index fiber and more for multimode step-index fiber. | Attenuation is less. |
| The light rays propagate through the fiber in the form of meridional rays. i.e., the rays follow a zig-zag path when they travel through fiber and, for every reflection it will cross the fiber axis. | The light rays propagate through the fiber in the form of skew rays. i.e., the rays follow a helical path around the fiber axis, and they would not cross the fiber axis at any time during their propagation. |
| SMSI fibers are expensive and difficult to manufacture. But MMSI is inexpensive and simple to manufacture. | Graded index fibers are easy to manufacture. |
| The bandwidth of single-mode step-index fiber is more than multimode step-index fiber. | Multimode graded-index fiber has a higher bandwidth. |
| The numerical aperture is very less for single-mode step-index fiber but is more for MMSI fiber. | The numerical aperture is high. |
| The number of modes of propagation for a multimode step index fiber is given by N_{step}=4.9 \left( \frac{d \times NA}{\lambda}\right )^2 where d is the diameter of the core, \lambda is optical wavelength and NA is Numerical aperture. | The number of modes of propagation for a multimode-graded index fiber is given by, N_{graded}=\frac{4.9 \times \left( \frac{d\times NA}{\lambda} \right )^2}{2} i.e., N_{graded}=\frac{N_{step}}{2}. Thus, the number of modes is half the number supported by an MMSI fiber. |
