Optical Fiber Basics (MM) 多模光纤基础.pdf

Chapter 3 Chapter 3 Optical Fibers – (Multimode) Optical Fibers – (Multimode) Basics Basics How to conduct light ? Attenuation (衰减) ? Dispersion (色散) ? Bandwidth (带宽) ? 2013-03-27 1 History Although glass fibers were made in the 1920s, their use became practical in the 1950s when the cladding layer was used. In 1966, 高錕suggested to reduce the loss of optical fiber for fiber- optic communications. In 1970, Corning Ltd. fabricated the step-index optical fiber. In 1972, the attenuation of optical fiber was improved from 20dB/km to 4 dB/km with the improvement of material and fabication procedure. Further progress resulted by 1979, the loss of fiber was reduced to be only 0.2dB/km near the 1.55-um spectral region. 2013-03-27 2 3.1 How optical fibers conduct light Daniel Colladon first described this light fountain or light pipe in an 1842 article titled On the reflections of a ray of light inside a parabolic liquid stream . This particular illustration comes from a later article by Colladon, in 1884. 2013-03-27 3  Step-Index Fiber (阶跃光纤） Step-Index Fiber Bare Fiber ：Fiber Core + Cladding + Coating Bare Fiber ： Core: Doped silica - n1 Cladding: Pure SiO2 - n2 Coating：Plastic or carbon To achieve TIR: n n 1 2