N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Technologies                                                                Slide 3 of 76 _________________                                                                                  __________

                                            What is an Optical Fiber?

                                        Transmission Fiber Types

                                        Optical Fiber

                                        Transmitted Light Staying Within Core

                                        Fiber Applications

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Transmission of data using light as the carrier has changed the world of the communications industry. It was hardly four decades ago when optical communications became commercially viable with the development of a reliable laser as a light source. The glass fiber with cladding was proposed in 1966 to transmit data using a laser light source. In 1970, industry developed glass fibers with losses of 20 decibels per kilometer (dB/km).   By the late 70s optical fiber, with losses of 0.2 dB/km, was refined to carry 400 M bps over 100 kilometers without repeaters and amplifiers. Optical fiber communications has come of age as a major innovation in the communications industry. Optical fiber has taken over from copper wire, the work horse of the communications industry, to carry data at extremely high bandwidths, free from external interference, immune from interception from external means, and inexpensive (extracted from silicon, an abundant material on earth).

Transmission Fiber Types - Optical fibers are made of glass and fiber.

Optical Fiber - is made of a pure glass core (Silica - SiO2) and a cladding, a glass mixed with specific elements to adjust their refractive indices to keep the transmitted light within the core.

Transmitted Light Staying Within Core - The difference between the refractive indices of the two materials keeps the transmitted light within the core.

Fiber Applications - Glass optical fibers are used for data transmission, inter-building applications and buried cable. Large core Silica Fiber is typically used in applications involving high power lasers and sensors, such as medical laser-surgery. The plastic fibers are used for short data links within equipment as it can be used with relatively inexpensive Light Emitting Diodes (LED), a light source. Plaster fibers have also found a use in an isolation system for a high voltage power supply.