An analog-digital converter has an optical input stage configured to convert an analog input signal (S(t)) into a phase-modulated optical signal and to supply it to a hybrid coupler having a plurality of output waveguides, each being connected to at least one photodiode. The photodiodes are each connected to the input of an associated analog-digital converter via which an analog electrical input signal is convertible into a digital output signal. An output stage is configured to form the digital data stream at the output from the digital output signals of the analog-digital converter, and the output stage may be configured to select the output signal of the analog-digital converter which lies within a predefinable range of the amplitude and has a predefinable slope and/or is larger than a predefinable adjacent output signal.