Multimode Fiber Optic Wavelength Division Multiplexing

Optical wavelength division multiplexing (WDM) systems, with signals transmitted on different wavelengths through a single optical fiber, can have increased bandwidth and fault isolation properties over single wavelength optical systems. This paper considers two WDMsystem designs that might be used with multimode fibers and gives a general descripton of the components which could be used to implement the system. The components described are sources, multiplexers, demultiplexers, and detectors. Emphasis is given to the demultiplexer technique which is the major developmental component in the WDMsystem. INTRODUCTION Optical wavelength division multiplexing (WDM)involves the simultaneous transmittal of information via different wavelengths of light. The various wavelengths after generation by separate optical sources are mixed by a multiplexer and transmitted over an optical communication link. At the receiving end of the link_ the distinct wavelengths of light are separated by a demultiplexer and converted to electrical signals by a photo detector. By using WDMa single optical fiber will provide multiple transmission paths. WDMincreases the information capacity of a single optical fiber and also provides a means for two-way simultaneous transmission (full duplex). For a given data transmission requirement a WDMsystem would require less optical fibers, repeaters, splices and/or connectors than a single wavelength system. The WDMsystems also have the standard advantages of single wavelength optical systems such as reduced weight and cost and immunity to lightning-induced transients. An additional attribute of WDMis that a faulty or failed transmitter will be confined to a single communication path and will not disturb the information transmitted on the same fiber at different wavelengths. This fault containment attribute makes WDMa prime candidate for application in NASA-Langley's research program in flight crucial fault tolerant systems for advanced aerospace vehicles. GENERALSYSTEMDESCRIPTIONS Asdiscussed in the introduction, there are two general system design advantages using WDMtechniques. The one for increasing the capacity of the transmission system and the second pertains to fault containment in the system. An N channel WDMsystem block diagram of the increased capacity type is shown in figure I. Each input channel has an optical source transmitting light at a given wavelength. The output of these sources are combined onto a single transmission fiber using a passive multiplexer.