24.1 Introduction

As the technology of fiber-optic communication systems advances to meet the demand for higher data rates, the trend toward lowering the effective cost per bit per mile will continue. The component designer will strive for lower cost, and better design and testing tools will be crucial to achieving this goal. Therefore, optical component analyzers play a significant role in the testing and debugging of the key components utilized in communications systems.

There are three basic classes of component analyzers: First, modulation domain component analyzers are used to measure the response of optical components as a function of the frequency of modulation of the optical carrier. Second, wavelength domain component analyzers are used to measure the parameters of optical components as a function of the optical wavelength. Third, reflection domain analyzers are used to measure the amplitudes and locations of the reflections from various parts within the optical component under test. The three types complement each other, and in order to do a complete component analysis of all components within a communications system, the three types are needed by the design, manufacturing, and test engineers.

In modulation domain component analyzers, a light signal (from a laser source) is modulated at a rate controlled by the instrument and then applied to the device under test. The output is then received by the analyzer, demodulated, and processed to compute the scattering parameters ( S parameters). The modulation frequency is varied, the S