Chapter 4: Advanced Optical Technology

Chapter 4: Advanced Optical Technology

?I don?t think we?re in Kansas anymore.?

? The Wizard of Oz

Overview

There are a number of recent developments and advanced concepts that may have a significant effect on the future of optical access networks, and even on the structure of the entire telecommunications network. Optical amplifiers are likely to have a key role in the long term, and so may coherent optical systems. The concepts of optical ether and distributed switching could revolutionize the structure of the entire telecommunications network. Overcoming the limiting factors of optical-fiber transmission leads to the possibility of soliton transmission within access networks, and the ultimate form of secure data transmission is offered by the technique of quantum cryptography.

4.1 Optical Amplifiers

An erbium-doped fiber amplifier (EDFA) is a short length of optical fiber containing a small proportion of erbium ions with a separate pump laser, which excites these ions so that their decay can be used to amplify a suitable optical signal. An optical amplifier differs from a traditional optoelectronic amplifier in that it does not require the conversion of the optical signal into an electronic signal and back again. The pump laser can travel in the same direction as the signal being amplified (copropagating) or in the opposite direction (counterpropagating), although noise and gain performance can be improved if the doped fiber is pumped in both directions at the same time. Typically, optical isolators are needed at either end of the amplifier section to prevent the...

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Chapter 4: Advanced Optical Technology

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