The WaveAnalyzer 100S from Finisar is a compact optical spectrum analyzer that operates from 1528.6 to 1567.5 nm covering the C-band of optical communications. It has been designed in particular to measure key parameters of DWDM systems like channel power, channel center frequency and optical signal to noise ratio (OSNR). The instrument uses a coherent measurement technique which provides two measurements per second across the entire C-band of optical communications with a measurement resolution of 1.75 GHz. The WaveAnalyzer 100S is based on a coherent measurement principle which allows operation without any moving part inside the instrument. It is available in a module that measures 108 x 164 x 28 mm3 and is ideal for spectral analysis in system test, gain equalization, optical Signal to Noise Ratio (OSNR) measurement and WDM analysis. The analyzer is operated using Finisar's WaveAnalyzer Graphical User Interface (GUI). A full programming interface is provided for integration into automated test systems.