Ch5Sec1 - 100 m) All Plastic High loss. Short distances (up...

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THE FIBER FORUM Fiber Optic Communications JOSEPH C. PALAIS PRESENTED BY
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Joseph C. Palais 5.1 2 Chapter 5 OPTIC FIBER WAVEGUIDES
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Joseph C. Palais 5.1 3 Section 5.1 Step-Index Fiber Step Index Fiber (SI Fiber) θ n 1 n 2 Cladding index n 2 Core index n 1 n 1 > n 2 For total reflection we require θ > θ c sin 1 2 n n c = θ n 1 n 2
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Joseph C. Palais 5.1 4 Section 5.1 Step-Index Fiber 1 2 1 n n n - = As for the slab waveguide, we have the fractional refractive index change Typically is on the order of 0.01 for fibers.
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Joseph C. Palais 5.1 5 STEP-INDEX FIBER Both core and cladding must be very low loss. Evanescent waves travel in the cladding. If the cladding is thick (~ 20 μ m or more), very little light reaches the outer edge of the cladding. Common SI Waveguides 1.) Glass core Glass cladding 2.) Glass core Plastic cladding 3.) Plastic core Plastic cladding
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Joseph C. Palais 5.1 6 All Glass Lowest loss. Used for longest distances (up to about 100 km) Glass/Plastic Moderate loss. Moderate distances (up to about
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Unformatted text preview: 100 m) All Plastic High loss. Short distances (up to about 10 m) STEP-INDEX FIBER Joseph C. Palais 5.1 7 STEP-INDEX FIBER Fiber n 1 n 2 NA o All-glass 1.48 1.46 0.24 13.9 Plastic-Clad Silica 1.46 1.4 0.41 24.2 All-plastic 1.49 1.39 0.53 32 Typical fiber properties: Joseph C. Palais 5.1 8 STEP-INDEX FIBER Example: Compute NA and o for an all-glass fiber having NA = 0.24. From the slab waveguide analysis 2 2 2 1 sin n n n NA o o-= = 24 . sin = o If n o = 1 (air), we have that Joseph C. Palais 5.1 9 STEP-INDEX FIBER = 28 2 o 2 o Acceptance Cone Lost Light = 14 o cone. acceptance the of angle half the is o Joseph C. Palais 5.1 10 STEP-INDEX FIBER Cladding modes may also be trapped in the fiber by total reflection at the outer boundary of the cladding. The cladding modes are lossy and do not travel far. n 2 n 1 Total Reflection...
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This note was uploaded on 05/11/2010 for the course EEE EEE-448 taught by Professor Palais during the Fall '09 term at ASU.

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Ch5Sec1 - 100 m) All Plastic High loss. Short distances (up...

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