A chromatic dispersion estimator for estimating a chromatic dispersion in an input signal block comprises a transformer for transforming the input signal block into a transformed signal block in frequency domain, a chromatic dispersion compensator for compensating a certain chromatic dispersion in the transformed signal block to obtain a compensated transformed signal block, an inverse transformer for inversely transforming the compensated transformed signal block into time domain to obtain an output signal, an adaptive filter for filtering the output signal to obtain a filtered signal, and a determiner for determining upon the basis of the filtered signal whether the certain chromatic dispersion corresponds to the chromatic dispersion in the input signal block.