OPTICAL SOURCES AND FIBER OPTIC TRANSMITTERS

LEARNING OBJECTIVES

Upon completion of this chapter, you should be able to do the following:

• Explain the principal properties of an optical source and fiber optic transmitter.
• Discuss the optical emission properties of semiconductor light-emitting diodes (LEDs) and laser diodes (LDs).
• Describe the operational differences between surface-emitting LEDs (SLEDs), edge-emitting LEDs (ELEDs), superluminescent diodes (SLDs), and laser diodes.
• Describe typical fiber optic transmitter packages.

INTRODUCTION TO OPTICAL SOURCES AND FIBER OPTIC TRANSMITTERS

Chapter 1 taught you that a fiber optic data link has three basic functions.

One function is that a fiber optic data link must convert an electrical signal to an optical signal permitting the transfer of data along an optical fiber.

The fiber optic device responsible for that signal conversion is a fiber optic transmitter.

A fiber optic transmitter is a hybrid device.

It converts electrical signals into optical signals and launches the optical signals into an optical fiber. A fiber optic transmitter consists of an interface circuit, a source drive circuit, and an optical source. The interface circuit accepts the incoming electrical signal and processes it to make it compatible with the source drive circuit. The source drive circuit intensity modulates the optical source by varying the current through the source.

An optical source converts electrical energy (current) into optical energy (light). Light emitted by an optical source is launched, or coupled, into an optical fiber for transmission. Fiber optic data link performance depends on the amount of optical power (light) launched into the optical fiber. This chapter attempts to provide an understanding of light-generating mechanisms within the main types of optical sources used in fiber optics.

Q.1 What are the three parts of a fiber optic transmitter?
Q.2 Which part of a fiber optic transmitter converts the processed electrical signal to an optical signal?