b2) Step Index Single Mode Fiber:-
- Only the fundamental mode will travel through it. hence, the diameter of the core s very small.
- single mode step index fiber have Zero inter-model dispersion but they exhibit Chromatic or Source based or Intramodal dispersion because the source has finite spectral width i.e. the wavelength equivalent of bandwidth. Hence, they exhibits Chromatic dispersion because all component travel with different wavelength and velocity.
- LED exhibits maximum chromatic dispersion because its spectral width is broad.
- LED is also not preferred for step index single mode fibers because they are not directional.Hence, there is difficulty in coupling of light.
- To avoid chromatic dispersion and coupling difficulties LASERS are preferred.
- Step index single mode fiber does not have intramodal dispersion and due to the use of LASER intramodal dispersion is also reduced. Hence, the overall dispersion is less So, preferred for long distance communication.
NOTE:-
- The index number of any fiber is defined with the help of Bessel’s Function.
- The range of the index number for step index single mode fiber,
- 0,<=v<=2.405; for step index single mode(SISM)
- v>2.405; for step index multi-mode fiber(SIMM)
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