An optoelectronic module includes a light guide arranged to receive light, such as ambient light or light reflected by an object. The light guide has a diffractive grating that includes multiple sections, each of which is tuned to a respective wavelength or narrow band of wavelengths. The module further includes multiple photosensitive elements, each of which is arranged to receive light diffracted by a respective one of the sections of the diffractive grating. The module can be integrated, for example, as part of a spectrometer or other apparatus for optically determining characteristics of an object.