Spectrometers can be classified into several types, including prism, grating, Fourier transform (such as Michelson, Mach–Zehnder, and Sagnac interferometers), tunable filter (such as Fabry–Pérot, acousto-optic and liquid crystal tunable filters) spectrometers, as. Spectrometers can be classified into several types, including prism, grating, Fourier transform (such as Michelson, Mach–Zehnder, and Sagnac interferometers), tunable filter (such as Fabry–Pérot, acousto-optic and liquid crystal tunable filters) spectrometers, as. A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that most common spectrum analyzers measure is electrical;. Optical spectrum analyzers (OSA) are precision instruments which are used for measuring optical spectra, based on which a further analysis is often possible. Some typical applications are: testing of optical systems, for example wavelength division multiplexing systems in optical fiber. On an optical spectrum analyzer, incoming light passes through a wavelength-tunable optical filter (monochromator or interferometer) which resolves individual spectral components.