Apparatus for characterizing a chromatic dispersion of an optical receive signal, the apparatus comprising: a delay means for delaying the optical receive signal by a predetermined time delay to obtain a delayed signal, the delayed signal being delayed with respect to the optical receive signal; a phase detecting means for determining a first value indicating a phase delay of the optical receive signal, and for determining a second value indicating a phase delay of the delayed signal; and a processor for determining a chromatic dispersion indicator upon the basis of the first value and the second value, the chromatic dispersion indicator characterizing the chromatic dispersion wherein the optical receive signal comprises communication symbols, and wherein the delay means is configured to delay the optical receive signal by a fraction, in particular by 1/4 th, of a communication symbol time; wherein the phase detecting means is configured to recover a sampling phase of the optical receive signal or of the delayed signal to determine the first value or the second value; wherein the phase detecting means is configured to determine the first value or the second value according to the following equation: y = real x n * x n + 1 − x n − 1 wherein x denotes the optical receive signal or the delayed signal in time domain, n denotes a sample index, (*) denotes complex conjugate, real(·) denotes the real part of a complex number, and y denotes the first value or the second value; wherein the processor is configured to determine the chromatic dispersion indicator according to the following equation: W = W 1 2 + W 2 2 wherein W 1 denotes the first value, W 2 denotes the second value, and W denotes the chromatic dispersion indicator. a delay means for delaying the optical receive signal by a predetermined time delay to obtain a delayed signal, the delayed signal being delayed with respect to the optical receive signal; a phase detecting means for determining a first value indicating a phase delay of the optical receive signal, and for determining a second value indicating a phase delay of the delayed signal; and a processor for determining a chromatic dispersion indicator upon the basis of the first value and the second value, the chromatic dispersion indicator characterizing the chromatic dispersion wherein the optical receive signal comprises communication symbols, and wherein the delay means is configured to delay the optical receive signal by a fraction, in particular by 1/4 th, of a communication symbol time; wherein the phase detecting means is configured to recover a sampling phase of the optical receive signal or of the delayed signal to determine the first value or the second value; wherein the phase detecting means is configured to determine the first value or the second value according to the following equation: y = real x n * x n + 1 − x n − 1 wherein x denotes the optical receive signal or the delayed signal in time domain, n denotes a sample index, (*) denotes complex conjugate, real(·) denotes the real part of a complex number, and y denotes the first value or the second value; wherein the processor is configured to determine the chromatic dispersion indicator according to the following equation: W = W 1 2 + W 2 2 wherein W 1 denotes the first value, W 2 denotes the second value, and W denotes the chromatic dispersion indicator.