Abstract: The present invention is a regulator circuit for combined regulation of the emitted wavelength from a laser diode, and its output. According to the invention, a fraction of the radiation from the laser diode (1) is caused to be transmitted, via a glass fibre (2) to a sensor unit (8). The sensor unit contains a dispersing device (3), possibly separate focussing devices, and a detector unit (4). The detector unit (4) contains one or more detector elements, whose electrical output signals are conducted to a signal decoding unit (5). The signal decoding unit (5) is connected (i) to a temperature generator (6), in turn connected by thermal means to the laser diode, (ii) to a power generator (7) which is electrically connected to the laser diode. By using a concave lattice as the dispersing device, the reflective radiation from the lattice (3) is focussed on to the detector elements in the detector unit.