The ever-growing demand for more bandwidth is creating a breakneck pace in the development and implementation of new optical telecommunications technologies. And when we compare transport capacity developed in the laboratory with installed capacity, it is clear that the time between development and implementation is getting shorter every day. The impact on the test and measurement industry is an increasing demand for instruments designed to yield laboratory-quality results in a sometimes rough outside-plant environment. Among these new optical technologies is dense wavelength division multiplexing (DWDM), a key strategy for telecommunications service providers. This technology provides scalable bandwidth and overcomes most fiber exhaust scenarios. It can handle different data formats and bit rates. Further, it can be integrated easily into existing network architectures at a reasonable cost. DWDM brings with it the need for new testing instruments. These systems must be tested and maintained as any other telecommunications system. One device that plays an important role in ensuring proper system operation is the optical spectrum analyzer, which can measure most of the parameters in a DWDM system as well as its individual components. It also can be used during the development, manufacture, installation, commissioning and maintenance of the optical transmission systems and components. . . .