Fiber optic transmission uses the same basic elements as copper-based transmission systems: A transmitter, a receiver, and a medium by which the signal is passed from one to the other, in this case, optical fiber. Figure 1 illustrates these elements. The transmitter uses an electrical interface to encode the use information through AM, FM or digital modulation. A laser diode or an LED do the encoding to allow an optical output of 850 nm,1310 nm, or 1550 nm (typically).
Figure 1 - Elements of a Fiber Optic Link
The optical fiber connects the transmitter and the receiver. This fiber may be either single-mode or multi-mode. The fiber consists of three main regions, as illustrated in Figure 2. The core, the center of the fiber, actually carries the light. The cladding surround the core in a glass with a different refractive index than the core, allowing the light to be confined in the fiber core. A coating or buffer, typically plastic, provides strength and protection to the optical fiber. The receiver uses either a PIN photodiode or an APD to receive the optical signal and convert it back into an electrical signal. A data demodulator converts the data back into its original electrical form. These elements comprise the simplest link, but other elements may also appear in a fiber optic transmission system. For example, the addition of WDM components allows two separate signals to be joined into a composite signal for transmission, and then can be separated into their original signals at the receive end. Other wavelength-division multiplexing techniques allow up to eight signals (CWDM) or more (DWDM) to be combined onto a single fiber. These are discussed in separate articles as linked in this paragraph. Long distance fiber optic transmission leads to further system complexity. Many long-haul fiber optic transmission systems require signal regenerators, signal repeaters, or optical amplifiers such as EDFAs in order to maintain signal quality. System drop/repeat/add requirements, such as those in multichannel broadcast networks, further add to the fiber optic system, incorporating add-drop multiplexers, couplers/splitters, signal fanouts, dispersion management equipment, remote monitoring interfaces, and error-correction components. See the linked articles for additional information on these components.
Figure 2 - Cross-section of an Optical Fiber
Related Fiber Optic Transmission Basics Links
• Analog vs Digital Fiber Optic Transmission Comparison
•Broadband Video Fiber Optic Transmission
•Baseband Video Fiber Optic Transmission
•Digital Fiber Optic Video/Audio/Data Transmission Systems
•Fiber Optic Network Topologies for ITS and Other Systems
•Digital Video & HDTV over Fiber Optics