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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 x-direction 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
- Reflection And Refraction