Optical fiber is classified based on material used, mode & refractive index.
Step Index Optical Fiber:
- In the step index fiber, the refractive index of the core is uniform throughout.
- Different light modes in a step-index multimode fiber follow different lengths along the fiber in zigzag way
- The arrival of different modes of the light at different times causes Inter Modal Dispersion.
- 50 mm core for step index.
Graded Index Optical Fiber:
Single Mode Fiber:
- In a single mode fiber only one mode can propagate through the fiber.
- Core of SM fiber is smaller (8.3 to 10 microns). Common size is 9um.
- Laser is used as light source for single mode fiber.
- Used in long distance communication upto100 Gbit/s data in DWDM.
- 1310 or 1550 nm wavelength is used in SM fiber with higher data rate.
Practically used Optical Fibers:
- MM Step index: 62.5/125 µm
- MM Graded index: 50/125 µm
- SM Step index: 9/125 µm
- Single mode graded index is not practically used