ESSAY SIXTEEN - Light Amplifiers and Solitons

Abstract

This chapter describes light amplifiers and solitons. The light amplifier is one of the most remarkable inventions of recent years. In a light amplifier, the amplification depends on laser action, the word laser, it will be recalled, being an acronym for light amplification by stimulated emission of radiation. Surprisingly, special fiber is not essential. Regular fiber can provide the laser action. All that is necessary is to inject, at a point where the signal is weak, a strong input from a separate, continuously running semiconductor laser. Light amplifiers may be expected to find wide application. For example, they will greatly facilitate the use of optical fiber for cable television because, given the availability of an amplifier, the amount of energy it is necessary to bleed off for each subscriber or group of subscribers is very small. In telecommunications, it is now possible to contemplate the design of submarine cables using amplifiers instead of repeaters. For the more distant future, there is the interesting possibility of being able to treat nonlinearity as an ally rather than as an enemy. Russell realized that if an attempt were made to launch a solitary wave of small enough amplitude for the motion to be linear, dispersion would soon cause the wave to lose its form, and that the stability of the wave he had observed depended on nonlinearity. Solitary waves in a canal can be of any amplitude. The larger the amplitude, the smaller the width of the wave and the higher its speed.