9.1 Introduction

The history of the laser dates back to at least 1951 and an idea of Townes. He wanted to use ammonia molecules to amplify microwave radiation. Townes and two students completed a prototype device in late 1953 and gave it the name maser or microwave amplification by stimulated emission of radiation. ^[1.] In 1958 Townes and Schawlow published results of a study showing that a similar device could be made to amplify light. ^[2.] The device was named a laser which is an acronym for light amplification by stimulated emission of radiation. In principle, a large flux of essentially single-wavelength electromagnetic radiation could be produced by a laser. Independently, Prokhorov and Basov proposed related ideas. The first laser used a rod of ruby and was constructed in 1960 by Maiman.

In late 1962 lasing action in a current-driven GaAs p- n diode maintained at liquid nitrogen temperature (77 K) was reported. ^[3.] Room-temperature operation and other improvements followed.

Soon, telephone companies recognized the potential of such components for use in communication systems. However, it took some time before useful devices and suitable glass-fiber transmission media became available. The first fiber-optic telephone installation was put in place in 1977 and consisted of a 2.4 km-long link under downtown Chicago.

Another type of laser diode suitable for use in data communication applications was inspired by the work of Iga published in 1977. ^[4.] By the late 1990s, these vertical-cavity surface-emitting...