A detection unit configured to detect a symbol from a received digital signal, wherein the digital signal has been derived from an optical signal transmitted over a first optical transmitted channel, and submitted to noise, the detection unit comprising: - a characteristics reception unit configured to receive information on characteristics of the first optical transmitted channel; on characteristics of a lower adjacent optical transmitted channel, using a wavelength lower than a wavelength of the optical transmitted channel; and on characteristics of a higher adjacent optical transmitted channel, using a wavelength higher than the wavelength of the optical transmitted channel; wherein the characteristics are one or more of: baud rate, bandwidth, modulation scheme of a transmitted channel; - a filter library comprising a plurality of noise whitening filters associated with a plurality of estimates of the power spectral density of the noise, respectively; wherein the filter library is a look up table allowing the look up of a particular noise whitening filter in dependence of combinations of characteristics of the first optical transmitted channel, the lower adjacent optical transmitted channel, and the higher adjacent optical transmitted channel; wherein a particular noise whitening filter which is associated with a particular estimate of the power spectral density is configured to whiten noise having the particular estimate of the power spectral density; - a filter selection unit configured to select a noise whitening filter from the filter library in dependency of the combination of the received characteristics; - a noise whitening filter unit, configured to filter the received digital signal using the selected noise whitening filter; and - a maximum likelihood sequence detector, referred to as MLSE detector, downstream of the noise whitening filter unit; wherein the MLSE detector is configured to detect the symbol from the filtered digital signal at a given time instant, while taking into account one or more symbols of one or more previous time instants. - a characteristics reception unit configured to receive information on characteristics of the first optical transmitted channel; on characteristics of a lower adjacent optical transmitted channel, using a wavelength lower than a wavelength of the optical transmitted channel; and on characteristics of a higher adjacent optical transmitted channel, using a wavelength higher than the wavelength of the optical transmitted channel; wherein the characteristics are one or more of: baud rate, bandwidth, modulation scheme of a transmitted channel; - a filter library comprising a plurality of noise whitening filters associated with a plurality of estimates of the power spectral density of the noise, respectively; wherein the filter library is a look up table allowing the look up of a particular noise whitening filter in dependence of combinations of characteristics of the first optical transmitted channel, the lower adjacent optical transmitted channel, and the higher adjacent optical transmitted channel; wherein a particular noise whitening filter which is associated with a particular estimate of the power spectral density is configured to whiten noise having the particular estimate of the power spectral density; - a filter selection unit configured to select a noise whitening filter from the filter library in dependency of the combination of the received characteristics; - a noise whitening filter unit, configured to filter the received digital signal using the selected noise whitening filter; and - a maximum likelihood sequence detector, referred to as MLSE detector, downstream of the noise whitening filter unit; wherein the MLSE detector is configured to detect the symbol from the filtered digital signal at a given time instant, while taking into account one or more symbols of one or more previous time instants.