Although the primary emphasis of this book is on light-emitting diodes (LEDs), this author would be remiss if he did not address the laser diode. In this chapter, we will describe and discuss the meaning of the term laser diode, including its fabrication and operation. Because the generation of coherent light is one of the key characteristics of lasers, we will also examine what this term means, which will serve as a refresher for some readers. Once this is accomplished, we will turn our attention to several types of laser diodes and how they supplement the use of LEDs in certain applications as well as enable other applications that cannot be supported by the LED.

As we describe and discuss the laser diode, we will periodically compare and contrast it with the LED. Because both devices are based on the use of similar semiconductor materials but operate differently, in the second section of this chapter, we will compare and contrast their operation. In doing so, we will describe and discuss several key differences between the laser diode and the LED, which include but are not limited to areas such as their focus, wavelength, power, safety, and other parameters, to make readers aware of the major differences between the two devices. This in turn will provide readers with knowledge concerning some of the applications each device is well suited to perform.