Difference Between Step Index Fiber And Graded Index Fiber (With Comparison Chart)

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What Is A Step Index Fiber?

In optical fiber, a step index fiber is a fiber characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface so that the cladding is of a lower refractive index. In a step index fiber, the light rays propagate in zig-zag manner inside the core. The rays travel in the fiber as meridional rays and they cross the fiber axis for every reflection.

It is important to note that, Step index fiber is found in two types, that is mono mode fiber and multi mode fiber. Signal distortion is more in case of high-angle rays in multimode step index fiber. In single mode step index fiber, there is no distortion. The Step index fiber has a lower bandwidth. The bandwidth is about 50 MHz km for multimode step index fiber whereas it is more than 100 MHz km in case of single mode step index fiber.

What You Need To Know About Step Index Fiber

  1. Step index fiber is a fiber in which the core is of a uniform refractive index and there is a sharp decrease in the index of refraction at the cladding.
  2. Step index fiber is found in two types, that is mono mode fiber and multi mode fiber.
  3. Index profiles are in the shape of step.
  4. The light rays propagate in zigzag manner inside the core. The rays travel in the fiber as meridional rays and they cross the fiber axis for every reflection.
  5. Signal distortion is more in case of high-angle rays in multimode step index fiber. In single mode step index fiber, there is no distortion.
  6. The fiber has lower bandwidth. The bandwidth is about 50 MHz km for multimode step index fiber whereas it is more than 100 MHz km in case of single mode step index fiber.
  7. The diameter of the core is between 50-200µm in the case of multimode fiber and 10µm in the case of single mode fiber.
  8. Used for short distance communication.
  9. Attenuation of light rays is more in multimode step index fibers but for single mode step index fibers, it is very less.
  10. Less expensive.
  11. NA  of multimode step index fiber is more whereas in single mode step index fibers, it is very less.
  12. Pulse broadening and inter modal dispersion is present.

What Is Graded Index Fiber?

Graded index fiber is a type of optical fiber where the refractive index of the core is uniform at the center core and then it decreases towards core-cladding interface. The uniformity is present because the refractive index is higher at the axis of the core and continuously reduces with the radial movement away from the axis. However, the refractive index of the cladding is constant in the case of graded index fiber; hence the nature of the refractive index is somehow parabolic.

The light rays in graded index fiber, propagate in the form of skew rays or helical rays. They will not cross the fiber axis. Also, it is important to note that inside the fiber, signal distortion is very low even though the rays travel with different speeds. The graded index fiber has a higher bandwidth. The bandwidth of the fiber lies in between 200 MHz Km to 600 MHz km even though theoretically it has an infinite bandwidth.

Advantages of Graded Index Fiber

  • It can transmit a large amount of information.
  • The distortion is comparatively small than step index fiber.

Disadvantages of Graded-index Fiber

  • These fibers possess low light coupling efficiency.
  • It is costly when compared to step index fiber.

What You Need To Know About Graded Index Fiber

  1. Graded index fiber is a type of fiber where the refractive index of the core is uniform at the center core and then it decreases towards core-cladding interface.
  2. Graded index fiber is of only one type, that is, multi mode fiber.
  3. Index profiles is in the shape of a parabolic curve (for α=2).
  4. The light rays propagate in the form of skew rays or helical rays. They will not cross the fiber axis.
  5. Signal distortion is very low even though the rays travel with different speeds inside the fiber.
  6. The fiber has higher bandwidth. The bandwidth of the fiber lies in between 200 MHz Km to 600 MHz km even though theoretically it has an infinite bandwidth.
  7. The diameter of the core is about 50µm in the case of multimode fiber.
  8. Used for long distance communication.
  9. Attenuation of light rays is less in graded index fibers.
  10. Highly expensive.
  11. NA of graded index fibers is less.
  12. No pulse broadening and inter modal dispersion due to periodic self focusing.

Also Read: Difference Between Single Mode And Multi-mode Optical Fibers

Difference Between Step Index Fiber And Graded Index Fiber In Tabular Form

BASIS OF COMPARISON STEP INDEX FIBER GRADED INDEX FIBER
Description Step index fiber is a fiber in which the core is of a uniform refractive index and there is a sharp decrease in the index of refraction at the cladding.     Graded index fiber is a type of fiber where the refractive index of the core is maximum at the center core and then it decreases towards core-cladding interface.  
Types Step index fiber is found in two types, that is mono mode fiber and multi mode fiber.   Graded index fiber is of only one type, that is, multi mode fiber.  
Index Profiles Index profiles are in the shape of step.   Index profiles is in the shape of a parabolic curve (for α=2).  
Light Rays Propagation The light rays propagate in zigzag manner inside the core. The light rays propagate in the form of skew rays or helical rays. They will not cross the fiber axis.  
Signal Distortion Signal distortion is more in case of high-angle rays in multimode step index fiber. In single mode step index fiber, there is no distortion.   Signal distortion is very low even though the rays travel with different speeds inside the fiber.  
Bandwidth Size The fiber has lower bandwidth. The fiber has higher bandwidth.  
Diameter Of The Core The diameter of the core is between 50-200µm in the case of multimode fiber and 10µm in the case of single mode fiber.   The diameter of the core is about 50µm in the case of multimode fiber.  
Application Used for short distance communication.   Used for long distance communication.  
Attenuation Of Light Rays Attenuation of light rays is more in multimode step index fibers but for single mode step index fibers, it is very less.   Attenuation of light rays is less in graded index fibers.  
Cost Less expensive   Highly expensive.  
NA NA  of multimode step index fiber is more whereas in single mode step index fibers, it is very less.   NA of graded index fibers is less.  
Pulse Broadening Pulse broadening and inter modal dispersion is present.   No pulse broadening and inter modal dispersion due to periodic self focusing.  

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