N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Technologies                                                             Slide 20 of 76 _________________                                                                                  __________

                                                        Optical Fiber

                                                Fiber Types (Silicon, Plastics)

                                                Single- Mode

                                                Multi-Mode

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Optical fibers come from silicon and plastics. The glass fibers are used for data transmission by carriers as buried cable and for inter-building applications. The large core silica fibers are typically used in applications involving high power lasers and sensors such as medical laser surgery. The plastic fibers are used for very short data links within equipment and as an isolation system of a high voltage power supply. The data transmission fibers are available in two flavours: Single-Mode, Multi-Mode. The modes of a fiber are related to its diameter. The larger diameter allows rays to enter into the fiber at different angles. These rays are refracted many times through the fiber before reaching the destination and do not arrive at the destination with the same phase relationship as when they entered the fiber. The fibers with larger diameters are known as Multi-Mode fibers. Fibers with small diameters are known as Single-Mode fibers. 

Single-Mode Fiber - The diameter of the fiber is normally three times the diameter of the wavelength of the transmitted wave.  

Multi-Mode Fiber - A multi-mode fiber carries wavelengths. The diameter of the fiber is many times the wavelength of the light transmitted.