A device for measuring optical signal-to-noise ratio (OSNR) of a wavelength division multiplexing (WDM) optical signal including multiple wavelength channels may include a tunable optical filter to select an optical wavelength channel of the plurality of optical wavelength channels. The device may also include a polarization controller to adjust a polarization state of the selected optical wavelength channel, and a control unit to compute the OSNR of the selected wavelength channel based on a target control point.