In a base element of a waveguide for a detector system at least a portion of radiation passing via the front side and incident on the diffractive element in a selection region is deflected via the diffractive element such that the deflected portion is propagated as coupled-in radiation in the base element by reflection to the out-coupling region and is incident on the associated out-coupling section of the out-coupling region. The out-coupling region couples at least a portion of the radiation out of the base element such that it is incident on the associated sensor section of the sensor unit, which continuously measures the intensity of the incident radiation and supplies the control unit. The control unit determines the distance of the object from the front side of the base element according to the measured intensity.