1. OPTICAL FIBER COMMUNICATION
RAMESH BHARTI

2. Major elements of an optical fiber link

4. The Nature of Light • Quantum Theory – Light consists of
small particles (photons)
• Wave Theory – Light travels as a
transverse electromagnetic wave
• Ray Theory – Light travels along a
straight line and obeys laws of
geometrical optics. Ray theory is valid
when the objects are much larger than
the wavelength (multimode fibers)

5. Refraction and reflection

6. Step Index Fiber

7. The step index optical fiber
The step index optical fiber. The central region, the core, has greater refractiv
index than the outer region, the cladding. The fiber has cylindrical symmetry
use the coordinates r, φ, z
to represent any point in the fiber. Cladding is
normally much thicker than shown.

8. Meridian Ray Representation

9. Total Internal Reflection Cladding

10. Graded Index Fiber

11. Single Mode Step Index Fiber

12. Fiber Key Parameters

13. Comparison of fiber structures

14. Fiber Key Parameters

15. Step and Graded Index Fibers

16. Total Internal Reflection

17. Skew Rays

18. Skew rays

19. Major Dispersions in Fiber
Modal Dispersion: Different modes travel at
different velocities, exist only in multimodal
conditions
• Waveguide Dispersion: Signal in the cladding
travel with a different velocity than the signal
in the core, significant in single mode
• Material Dispersion: Refractive index n is a
function of wavelength, exists in all fibers,
function of the source line width

20. Effects of Dispersion and Attenuation

21. Dispersion for Digital Signals

22. Modal Dispersion

23. The Nature of Light
Quantum Theory – Light consists of small particles (photons)
Wave Theory – Light travels as a transverse electromagnetic wave
Ray Theory – Light travels along a straight line and obeys laws of geometrical optics. Ray theory is valid when the objects are much larger than the wavelength (multimode fibers)

24. Refraction and reflection
Critical Angle:
Sin Φc=n2/n1
Snell’s Law: n1 Sin Φ1 = n2 Sin Φ2 6

25. Step Index Fiber n1 n2
n1>n2
Core and Cladding are glass with appropriate optical properties while buffer is plastic for mechanical protection

26. Step Index Fiber

27. Single Mode Step Index Fiber

28. Meridian Ray Representation

29. Total Internal Reflection

30. Comparison of fiber structures

31. Graded Index Fiber

32. Step and Graded Index Fibers

33. Total Internal Reflection

34. Skew Rays

35. Skew rays
Skew rays circulate around the core and increase the dispersion

36. Fiber Key Parameters

37. Fiber Key Parameters

38. Polarizations of fundamental mode
Two polarization states exist in the fundamental mode in a single mode fiber

39. Polarization Mode Dispersion (PMD)
Each polarization state has a different velocity  PMD 8

40. Major Dispersions in Fiber
Modal Dispersion: Different modes travel at different velocities, exist only in multimodal conditions
Waveguide Dispersion: Signal in the cladding travel with a different velocity than the signal in the core, significant in single mode conditions
Material Dispersion: Refractive index n is a function of wavelength, exists in all fibers, function of the source line width

41. Effects of Dispersion and Attenuation7

42. Dispersion for Digital Signals

43. Modal Dispersion

44. Field Distribution in the Fiber

45. Higher order modes  Larger MFD

46. Mode-field Diameter (2W0)
In a Single Mode Fiber,
At r = wo,
E(Wo)=Eo/e
Typically Wo > a

47. Power in the cladding
Lower order modes have higher power in the cladding.

48. Higher the Wavelength  More the Evanescent Field