22.1 Introduction: Fiber-Optic Communications Systems

Fiber-optic communications developed very rapidly in the past two decades. Many systems have been installed and many others are planned in the United States, Europe, and Japan. These systems clearly compete very well with the traditional communications systems as a cost-effective means for information exchange. Fiber-optic systems typically operate at hundreds of megabits per second, and new systems operating at 2.4 Gbit/s are now being installed. At the same time, research laboratories around the world are developing multi-Gbit/s components and systems with potential for terabit per second communications links in the late 1990s.

In addition to the increase in the data rates over fiber-optic networks, the performance of the devices, components, and subsystems used in such networks is improving at a very high rate. For example, a semiconductor laser needed in an optical amplifier system must have a mean time between failures (MTBF) of more than 100,000 h. If the amplifier is used in the submarine cable (transatlantic or transpacific), the laser must be reliable to withstand severe operating conditions (temperature, humidity, pressure, etc.). In addition to developing high-performance components, the trend continues toward lowering the effective cost per bit and mile of information. As a result, the designers of lightwave devices, components, and subsystems are faced with a challenge. They need to maximize the performance of each system building block, minimize the adverse interactions between these blocks, and at the same time design for manufacturability and cost-effectiveness.