N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Technologies                                                              Slide 10 of 76 _________________                                                                                  __________

                                  Optical Fiber Transmission Terminologies

                                        Refractive Index

                                        Critical Angle

                                        Light Wavelength

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These three factors are very important in optical transmission. A fiber Optic System designer keeps these tree factors in mind while designing a commercial system.

Refractive Index - A refractive index is the ratio of the velocity of propagation of an electromagnetic wave in a  vacuum to its velocity in the medium. Light travels faster in pure glass fiber than in a glass with impurities. The cladding is made of impure glass with a high refractive index so that when the light hits the cladding it is reflected back to the core.

Critical Angle - The angle at which light is injected into the fiber to keep it within the core. The diameter of the fiber core is normally a few times the wave length transmitted.

Light Wave length - The wavelength of the light transmitted through the glass fiber dictates the attenuation. As the wavelength increases the attenuation decreases - 6 dB/km at 600 nm to less than 1 dB/km at 1600 nm..