Fiber Optics PDF

Fiber Optics  Introduction Optical fiber is a long thin transparent dielectric material which carries EM waves of visible and IR frequencies from one end to the other end of the fiber by means of Total Internal Reflection. Glass or Plastic is used as Dielectric material. Optica...

Fiber Optics  Introduction Optical fiber is a long thin transparent dielectric material which carries EM waves of visible and IR frequencies from one end to the other end of the fiber by means of Total Internal Reflection. Glass or Plastic is used as Dielectric material. Optical fibers works as Wave guides in optical television signals, digital data to transmit voice television signals, digital data to any desired distance from one end to the other end of the fiber.  What are Fiber Optics? Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair. They are arranged in bundles called optical cables and used to transmit light signals over long distances. Fiber Optics are cables that are made of optical fibers that can transmit large amounts of information at the speed of light.  Optical fiber consists of three sections 1. Core 2. Cladding 3. Protective Jacket Core: It is an inner cylindrical material made up of glass or plastic. Cladding: It is a cylindrical shell of glass or plastic material in which Core is inserted. Protective Jacket: The Cladding is enclosed in polyurethane jacket and it protects the fiber from surroundings. The RI of core is slightly greater than the RI of Cladding. The normal standard values are 1.48 and 1.46 respectively.  Structure of an Optical fiber Poly urethane protective jacket Cladding Core glass or plastic plastic jacket fiber core cladding Fiber Optic Cables SOURCE: SURFNET.NL  How Does Optical Fiber Transmit Light?? Principle: Optical fiber works on the principle of TIR. Once light ray enters into core ,it propagates by means of multiple TIR’ s at core-cladding interface. The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances. However, some of the light signal degrades within the fiber, mostly due to impurities in the glass. The extent that the signal degrades depends on the purity of the glass and the wavelength of the transmitted light How Does an Optical Fiber Transmit Light? Total Internal Reflection Physical Media Total Internal Reflection according to law of refraction n1 sin   n2 sin r    c r  90 0 n2 sin  c  sin 900 n1 n2 sin  c  n1  Acceptance angle Numerical Aperture  Acceptance Angle The maximum angle of incidence at the end face of an Optical fiber for which the light ray can be propagated along Core-Cladding interface is known as Acceptance angle.  Core-Cladding interface B θr θ Core n1 θr θi A C Fiber axis Cladding n2 Incident light ray Applying Snell’ s law for Air-Core media n0 sin  i  n1 sin  r..............(1) from the right angle triangle ABC  r    90 0  r  90   0 n0 sin  i  n1 sin(900   ) n0 sin  i  n1 cos n1 sin  i  cos.........( 2) n0 when   critical angle( c )  i   m n1 sin  m  cos c................( 3) n0 according to law of refraction n1 sin i  n2 sin r i   c r  900 n2 sin  c  sin 900 n1 n2 sin  c  n1 n2 2 cos c  1  sin  c  1  ( ) 2 n1 n1  n2 2 2 cos c ............( 4) n1  substitute equation (4) in (3) n1  n2 2 2 n1 sin  m  n0 n1 if the medium surrounding the fiber is air, then n0  1 sin  m  n1  n2 2 2  max  sin 1 n1  n2 2 2 Which is required expression for Acceptance Angle in optical fibers.  Numerical Aperture The light gathering capacity of an optical fiber is known as Numerical Aperture and it is proportional to Acceptance Angle. It is numerically equal to sine of Acceptance Angle.  Numerical Aperture It is the measure of the amount of light that can be accepted by a fiber. It depends only on Refractive indices of core and cladding and not on fiber dimensions. It is always