N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Technologies                                                                Slide 6 of 76 _________________                                                                                  __________

                              Snell's Law For Light Transmission

                                            Light Ray Escaping

                                            Light Ray Absorbing

                                            Light Ray Reflecting

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How light traveling from one material into another material will behave depends on the angle (Incident Angle) it is entering into the second material and the refractive index of the two materials. The refractive index is the ratio of the propagation of waves in a vacuum over the propagation of waves in the material. The refractive index of pure glass (pure Silicon) is higher than the optical fiber cladding (glass with impurities). This allows the total reflection of light back into the optical fiber core. Think of material #1 as the pure silicon core and material #2 as Cladding. 

Light Ray Escaping - If the angle of incidence is less than the Critical angle the light escapes into the second material#2. 

Light ray Absorbing - If the Incidence angle is such that refractive light will be traveling parallel to two materials.

Light Ray Reflected - This is desirable when the light ray is reflected back into material #1.