An optical measuring device measures a wavelength of a response from a sensing device. The optical measuring device contains a light path coupled to an interface for coupling the light path to the sensing device. A periodic optical filter has an input coupled to the light path, to sample light that is supplied to or received from the sensing device. A continuous output optical filter has an input coupled the light path to sample light that is supplied to or received from the sensing device. A computation circuit is coupled to detectors at the periodic optical filter and the continuous output optical filter. The computation circuit is programmed to process output signals from the detectors obtained during a wavelength scan. The processing involves quantization of data derived from the continuous filter wavelengths associated with respective time points at which the wavelength scan reaches corresponding positions in respective periods of the periodic optical filter. The processing computes a wavelength associated with the response of the sensing device from the identified wavelengths on the basis of a temporal relation between said respective time points and a time point of the response of the sensing device.