A spectrometer including: a photodiode having a depleted region and generating an electrical detection signal indicating instants of detection of optical pulses; a converter generating an electrical delay signal, indicating delays between the instants of detection and corresponding instants of emission of the optical pulses; a memory, storing a theoretical function corresponding to the probability of triggering an avalanche by a charge carrier generated in the depleted region; and a computing stage which determines a statistical distribution of the delays between the instants of detection and the corresponding instants of emission; selects a Gaussian portion of the statistical distribution; calculates the ratio between the sum of the number of delays of the Gaussian portion and the sum of the number of delays of the statistical distribution; and determines an estimate of the wavelength of the optical pulses on the basis of the theoretical function and of the sample value.