Fiber Optic Communications: Fundamentals and Applications

Chapter 3Lasers

3.1 Introduction

LASER is an acronym for light amplification by stimulated emission of radiation. In 1917, Einstein postulated that an atom in the excited level is stimulated to emit radiation that has the same frequency and phase as the radiation [1]. This is known as stimulated emission, which remained a theoretical curiosity until Schewlow and Townes in the USA [2], and Basov and Prokhorov in the USSR, proposed that stimulated emission can be used in the construction of lasers. Townes, Gordon, and Zeiger built the first ammonia MASER (microwave amplification by stimulated emission of radiation) at Columbia University in 1953. This device used stimulated emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of about 24 GHz. In 1960, Maiman demonstrated the ruby laser, which is considered to be the first successful optical laser [3]. In 1962, the first semiconductor laser diode was demonstrated by a group led by Hall [4]. The first diode lasers were homojunction lasers. The efficiency of light generation can be significantly enhanced using double heterojunction lasers, as demonstrated in 1970 by Alferov and his collaborators [5].

Fiber-optic communications would not have progressed without lasers. Lasers have not only revolutionized fiber-optic communications, but also found diverse applications in laser printers, barcode readers, optical data recording, combustion ignition, laser surgery, industrial machining, ...