An adaptive filter being configured to filter an input signal, wherein the input signal comprises a first input signal portion in time domain representing an optical signal according to a first optical polarization, and a second input signal portion in time domain representing an optical signal according to a second optical polarization, comprising: fourier transforming means (101; 201) being configured to transform the first input signal portion into a first frequency domain signal, and to transform the second input signal portion into a second frequency domain signal upon the basis of the Fourier transform; weighting means (103; 207, 209) being configured to weight at least a portion of the first frequency domain signal with the filter coefficient to obtain a first filtered signal in frequency domain, and to weight at least a portion of the second frequency domain signal with a further filter coefficient to obtain a second filtered signal in frequency domain; correlating means (107; 211) being configured to cross-correlate the first filtered signal and the second signal in frequency domain to obtain a correlation value; and adaptation means (109, 111; 213, 215) being configured to select another filter coefficient from a plurality of predetermined filter coefficients, and to select another further filter coefficient from a plurality of predetermined filter coefficients for further weighting, the other filter coefficient replacing the filter coefficient, the other further filter coefficient replacing the further filter coefficient, and wherein the adaptation means (109, 111; 213, 215) is further configured to select the other filter coefficients upon the basis of the correlation value or a mean value of the correlation value or a mean value of an absolute value of the correlation value. fourier transforming means (101; 201) being configured to transform the first input signal portion into a first frequency domain signal, and to transform the second input signal portion into a second frequency domain signal upon the basis of the Fourier transform; weighting means (103; 207, 209) being configured to weight at least a portion of the first frequency domain signal with the filter coefficient to obtain a first filtered signal in frequency domain, and to weight at least a portion of the second frequency domain signal with a further filter coefficient to obtain a second filtered signal in frequency domain; correlating means (107; 211) being configured to cross-correlate the first filtered signal and the second signal in frequency domain to obtain a correlation value; and adaptation means (109, 111; 213, 215) being configured to select another filter coefficient from a plurality of predetermined filter coefficients, and to select another further filter coefficient from a plurality of predetermined filter coefficients for further weighting, the other filter coefficient replacing the filter coefficient, the other further filter coefficient replacing the further filter coefficient, and wherein the adaptation means (109, 111; 213, 215) is further configured to select the other filter coefficients upon the basis of the correlation value or a mean value of the correlation value or a mean value of an absolute value of the correlation value.