A sensor, apparatus and method for non-invasively monitoring blood characteristics of a subject are disclosed. The sensor comprises an emitter unit configured to emit radiation through the tissue of the subject at a plurality of measurement wavelengths and a detector unit that comprises photo detectors. To achieve a simple sensor assembly, the photo detectors are together adapted to receive the radiation at the plurality of wavelengths and to produce in-vivo measurement signals corresponding to the plurality of measurement wavelengths, the in-vivo measurement signals being indicative of absorption caused by blood of the subject. Furthermore, the photo detectors are mounted so that optical paths from the emitter unit to the photo detectors are different, and the plurality of wavelengths are divided between the photo detectors so that two spectrally adjacent photo detectors have at least one common wavelength. The apparatus comprises a path normalization unit configured to normalize the in-vivo measurement signals to an optical path specific to one of the photo detectors.
