PHOTONICS NETWORKS2Photonic networksQuestion 1λ0=1.55μm,v=2, Core radius a=4μm, Index contrast ∆=0.003, and refractive of claddingn2=1.45, Parameter v=2V=2πλ0a√n12−n22But we know that sin(θa)=√n12−n22Therefore, V=2πλ0asin(θa)sin(θa)=Vλ02πa=2×1.552π×4=0.123345Thus, the acceptance angle, θa=sin−10.123345=7.085°Question 2LEDs are used in fiber optic communication networks. However, they are not the best choice because: LEDs emit incoherent light characterized by a broad spectrum since they generate light through spontaneous emission. As a result, the signal will be bound by chromatic dispersion thuslimiting the distance over which LEDs based transmitters can transmit data.Also, LED transmitters can only be coupled into multimode fiber because the light emitted by the LED is non-directional. Moreover, the LEDs are less efficient as a small percentage of the light can be useful to the fiber optic cable.
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