Abstract: An optical wavelength control system for an optical source, includes: a beam splitter arrangement for propagating radiation from the source over two paths, first and second photodetectors, each arranged at a respective one of the two propagation paths, a wavelength selective optical filter affecting propagation of said radiation over the propagation path to the first photodetector, whereby the first and second photodetectors are adapted to generate photocurrents indicative of the possible displacement of the actual wavelength of the radiation from the source with respect to a reference wavelength and the power emitted by the optical source, respectively. The wavelength selective optical filter is e.g. an interference filter or an etalon filter arranged to receive reflected radiation from the beam splitter arrangement.