The invention proposes a method for feedback control, in which a portion of a data signal is split and rectified and the signal intensity is detected with slow speed electronics for improving the control of a delay line interferometer (DLI) used in optical data transmission. A control signal is generated and fed back to the DLI based on the detected signal intensity. The invention further proposes a device provided with a DLI, a first and second optoelectronic component, and a differential amplifier.