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Unformatted text preview: Lecture 9 7.7 TIR cont. 7.8 Metals 8 Geometric Optics The evanescent wave Without a transmitted wave we have problem The boundary condition cannot be fulFlled We need a transmitted wave which does not carry energy across the boundary (on average) E t = E ot e " # y e i k t x n i n t sin $ i " % t & ( ( ) * + + " = k t # n i n t $ % & ( ) 2 sin * i + 1 Lets go back to the reection and refraction problem What happens if a the gap is very small such that the eveanescent wave reaches another medium ? rustrated total internal refection Prism Coupler As we have seen in both descriptions for the waveguide only certain modes will be guided effectively The modes have different wave vectors in xdirection If we want to couple light into a waveguide using the evanescent wave only certain angle of incidence will work Coupling light into a waveguide (light ray picture) Waveguide (fber) Can we couple light directly From the top ? No, because eFFective incoupling can only be achieved For directions which result in total internal reection in the fber. This means the angle in air is larger than 90 o !...
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This note was uploaded on 08/06/2008 for the course PHYS 352 taught by Professor Dierolf during the Fall '04 term at Lehigh University .
 Fall '04
 DIEROLF
 Reflection And Refraction

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