An optical spectrum analyzer (OSA) measures and displays the optical power distribution over a wavelength range. Yokogawa OSAs are recognized for leadership in wavelength resolution, close-in dynamic range, and stray-light suppression ratio (measurement dynamic range). For over 45 years, Yokogawa. Grating-based instruments for the spectral testing of optical sources, amplifiers, transceivers, and passive optical components. It measures parameters such as wavelength (in nanometers or nanometers), optical power (in dBm), and signal-to-noise ratio (SNR), providing a. This page covers an application note on the Optical Spectrum Analyzer (OSA).