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Unformatted text preview: Photonic Network By Dr. M H Zaidi Optical Fiber Technology Photonic Network By Dr. M H Zaidi Numerical Aperture (NA) What is numerical aperture (NA)? Numerical aperture is the measure of the light gathering ability of optical fiber The higher the NA, the larger the core of light acceptance of the fiber and the easier it is to couple the light signal into the fiber At the same time, the higher the numerical aperture, the lower the bandwidth The two specifications must be balanced for optimum performance Photonic Network By Dr. M H Zaidi Specifying numerical aperture 62.5/125 –– 0.275 + 0.015 Numerical Aperture Photonic Network By Dr. M H Zaidi Index of Refraction C= 3 10 8 meters per second, but it is reduced when it passes through matter. The index of refraction n : c n speed of light in a vacuum, 3 10 8 m/s speed of light in the given material f 1 n n c f wavelength of light in a vacuum wavelength of light in the given material c Photonic Network By Dr. M H Zaidi Index of refraction and speed of light for various materials. Index of Refraction Speed of Light Free space (vacuum) 1.0 3 10 8 m/s Air at sea level 1.003 2.99 10 8 m/s Ice 1.31 2.29 10 8 m/s Water 1.33 2.26 10 8 m/s Glass (minimum) 1.45 2.07 10 8 m/s Glass (maximum) 1.80 1.67 10 8 m/s Diamond 2.42 1.24 10 8 m/s Photonic Network By Dr. M H Zaidi 1 : The incident angle (from the surface normal) 2 : The angle of refracted light (from the surface normal) n 1 : index of refraction in the incident medium n 2 : index of refraction in the refracting medium Light that is not absorbed or refracted will be reflected. The incident ray , the reflected ray , the refracted ray , and the normal to the surface will all lie in the same plane. 2 2 1 1 sin sin n n Refraction with Snell's Law Photonic Network By Dr. M H Zaidi Critical Angle We want to find the critical case of total internal reflection at the core cladding boundary. Using Snell’s Law with 2 = 90º, we can find the critical angle CR : 1 2 1 2 arcsin or , sin n n n n CR CR φ φ Incident ray Reflected ray Cladding n 2 Air n Core n 1 Cladding Unguided ray θ r ´ θ r φ´ φ 2 ´ θ i ´ θ i φ 2 = 90º if φ = φ CR Photonic Network By Dr. M H Zaidi Since we can relate r, CR to angle CR by simple geometry, and we can make the approximate n = 1, this equation can be simplified: The negated and shifted sine function is identical to the cosine, and we can relate this cosine to the sine by the trigonometric identity: this sine is replaced in terms of n 1 and n 2 : CR 1 CR , 1 CR , 2 sin sin sin n n r i 2 CR 1 CR 1 CR 1 CR , sin 1 cos 2 sin sin n n n i NA n n n n n i ...
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This note was uploaded on 06/03/2011 for the course IT ISE808 taught by Professor Mr.tayyab during the Spring '11 term at College of E&ME, NUST.
 Spring '11
 Mr.Tayyab

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