The Yokogawa AQ6370D is an optical spectrum analyzer for characterizing telecom transmitters, optical components, and fiber-based systems. Its 600–1700 nm wavelength range supports both single-mode and multimode fiber measurements. A 0.02 nm resolution setting helps separate closely spaced spectral features, while the listed power range extends from +20 to −90 dBm under applicable measurement conditions. Standard and High Performance versions have different wavelength-accuracy specifications, so the performance grade remains part of the instrument configuration.