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chapter 8

chapter 8 - Dr Joseph C Palais 8.1 Dr Joseph C Palais 8.1...

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Unformatted text preview: Dr. Joseph C. Palais 8.1 Dr. Joseph C. Palais 8.1 11 THE FIBER FORUM Fiber Optic Communications • PRESENTED BY • Dr. JOSEPH C. PALAIS Click to edit Master subtitle style 5/13/10 Dr. Joseph C. 8.1 22 Chapter 8 Couplers and Connectors 5/13/10 Dr. Joseph C. 8.1 33 Section 8.1 Connector Principles 5/13/10 Dr. Joseph C. 8.1 44 2a d Core Four major loss mechanisms are: 1) Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 55 2) Angular Misalignment θ 3) Non-Contacting Ends x 5/13/10 Dr. Joseph C. 8.1 66 4) Rough Ends 5/13/10 Dr. Joseph C. 8.1 77 Connecto r Pi n Po ut η = Coupling Efficiency L = - 10 Log η (dB) out in P η= P 5/13/10 Dr. Joseph C. 8.1 88-- =-- 2 1 1 2 d d d η cos 1 π 2a 2a 2a d cos 2a is in radians (8-1) 8.1.1 Lateral Misalignment The lateral misalignment loss for a multimode step-index (SI) fiber is given by: 5/13/10 Dr. Joseph C. 8.1 99 Assume the fiber end illumination distribution is uniform. The coupling efficiency is equal to the fractional overlap of the transmitting and receiving fiber cores, as illustrated on the next slide. Derivation Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1010 y a d/2 d A = Overlap Area θ m θ x r 5/13/10 Dr. Joseph C. 8.1 1111 2 4 m a d r C O S A r d r d θ θ θ = = Radius = r Area element = rdrd θ dr d rd θ θ θ Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1212 θ r d/2 θ = d cos 2r θ = d r 2cos Determining m θ θ a d/2 m = m d/2 cosθ a- = 1 m d θ cos 2a Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1313 Now, ( 29 2-- = =- =- = =-- =- D D D D m m m m m 2 a d 2cos 2 2 2 2 2 2 2 2 1 2 2 2 1 r A 4 d 2 d 2 a d 2cos d d 2 a 4 cos d tan cos d d A 2 a cos tan 2a 4 a d/2 d d A 2 a cos 2a 4 d/2 θ θ θ θ θ θ θ θ θ θ θ θ θ θ Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1414 The functional overlap is :- = = - - = - 2 2 1 A η a 2 d d d η cos 1 2a 2a 2a L 10logη π π 0.2 0.4 1 2 3 4 5 Fractional Lateral Offset Loss(dB) 10 log 2 π acos x ( ) x ( ) 1 x ( ) 2- ⋅- ⋅ ⋅ - x x = d/2a Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1515 Solution: From the figure, = d 2a 0.02 d = 0.02(50) = 1 μ m Lateral offset losses for single mode fibers ( / ) 10log d w L e- = - 2 (dB) (8-3) Ex. Core diameter = 5 0 μ m Requirement: Compute the maximum lateral displacement allowed. 0.1 Loss dB a Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1616- = 2 2 2r w I I e x = r/w Ex. If V = 2.4 , then w/a = 1.1, a = core radius w = spot size of the Gaussian propagating beam Lateral Misalignment 5/13/10 Dr. Joseph C. 8.1 1717- = - 2 d w 1 10 log e d/w = 0.48 d = 1. 9 μ m Ex. Let and w = 4 μ m. Compute the maximum lateral displacement allowed....
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chapter 8 - Dr Joseph C Palais 8.1 Dr Joseph C Palais 8.1...

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