Abstract: An optical wavelength control system for an optical source (LD) such as a laser diode in a DWDM transmitter module includes a beamsplitter arrangement (9, 10; 12) for propagating radiation from the source (LD) over two paths. A first (1) and a second (2) photodetector are arranged each in a respective one of said two propagation paths, while a wavelength selective optical filter (3) is interposed in the propagation path from the source (LD) to the first photodetector (1). The first (1) and second (2) photodetectors are thus adapted to generate photocurrents indicative of the possible displacement of the actual wavelength of the radiation from said source (LD) with respect to a reference wavelength and the power emitted by the optical source, respectively.