A method for producing a quality of transmission estimator for optical transmissions, the method comprising: - defining a local dispersion value, - defining a dispersion increment having a sign identical to the local dispersion value, - for each of a plurality of integer numbers, wherein the integer numbers range from 0 to an upper bound greater than or equal to 0, performing a propagation calculation by a propagation model and/or experiment, each propagation calculation and/or experiment dealing with the propagation of an optical signal along an elementary section, wherein the elementary section is a propagation medium characterized by the local dispersion value, an elementary section length corresponding to the dispersion increment and wherein the optical signal which is incoming in the elementary section is previously affected by a cumulative dispersion value (D 1 to D 6) equal to the sum of a predefined pre-compensation dispersion and the integer number times the dispersion increment, - for each elementary section, determining a variance of noise, the noise representing a distortion due to Kerr nonlinear field contributions in the elementary section, - for each couple of elementary sections, determining a covariance of noise between the couple of elementary sections, - storing in a data repository a look-up table (Σ 1) comprising each determined variance of noise in association with the corresponding local dispersion value and cumulative dispersion value and each covariance of noise, in association with a first couple of local dispersion value and cumulative dispersion value and a second couple of local dispersion value and cumulative dispersion value. - defining a local dispersion value, - defining a dispersion increment having a sign identical to the local dispersion value, - for each of a plurality of integer numbers, wherein the integer numbers range from 0 to an upper bound greater than or equal to 0, performing a propagation calculation by a propagation model and/or experiment, each propagation calculation and/or experiment dealing with the propagation of an optical signal along an elementary section, wherein the elementary section is a propagation medium characterized by the local dispersion value, an elementary section length corresponding to the dispersion increment and wherein the optical signal which is incoming in the elementary section is previously affected by a cumulative dispersion value (D 1 to D 6) equal to the sum of a predefined pre-compensation dispersion and the integer number times the dispersion increment, - for each elementary section, determining a variance of noise, the noise representing a distortion due to Kerr nonlinear field contributions in the elementary section, - for each couple of elementary sections, determining a covariance of noise between the couple of elementary sections, - storing in a data repository a look-up table (Σ 1) comprising each determined variance of noise in association with the corresponding local dispersion value and cumulative dispersion value and each covariance of noise, in association with a first couple of local dispersion value and cumulative dispersion value and a second couple of local dispersion value and cumulative dispersion value.