Optical Communications Link Various components that make up an optical telecommunications link i) transmitter, i.e. a laser ii) fiber iii) repeater or amplifier iv) detector i) laser => semiconductor laser diode Advantages: 1) compact 2) extremely efficient (~40%) 3) can be modulated at very high rates (10’s og GHz) The modulator is more often external to the laser. ii) fibers absorption/scattering attenuation coef = γ ~0.5dB/km @ 1550 nm For a single mode fiber the core typically has a radius of a=3-5 μ m and the cladding has a radius of b=80 μ m. The index difference is typically of the order of ∆ n=n 1-n 2 =0.005. Along with the index difference, the other parameter used to characterize an optical fiber is the V# where V = 2 p a l 2 n 1 D n ( ) 1 2 If V<2.405 the fiber will support a single spatial mode. However, if the wavelength is decreased or the core radius is increased the fiber can become multimode. Step-Index vs. Gradient Index Fibers
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