PHASE CONTROL BY ACTIVE THERMAL ADJUSTMENTS IN AN EXTERNAL CAVITY LASER

摘要

The present invention relates to a wavelength tuneable extemal-cavity laser module, the laser being tuneable across a predetermined wavelength range and comprising: a thermally stabilised substrate; a gain medium for emitting an optical beam passing through the external cavity along an optical axis, said gain medium being placed in thermal contact with the thermally stabilised substrate; an end mirror for receiving and reflecting the optical beam within the external cavity, and a phase element for controlling the phase of the optical beam and being positioned within the external cavity between the gain medium and the end mirror, wherein said phase element comprises a material having a refractive index that varies in response to changes in temperature and has a transmissivity substantially independent of wavelength across said predetermined wavelength range. The thermally-controllable phase element in the laser external cavity is configured so as to induce a phase variation that compensates the drop in the output power due to ageing or to external temperature variation. According to a preferred embodiment, a heating element is placed in thermal contact to the phase element. The temperature of the phase element can be increased to "bring back" the output power to a value very close to the initial value. Preferably, the phase element is a silicon plate. By thermally controlling an intra-cavity phase element it is possible to vary continuously the output power as a function of the injection current. Therefore, the solution has the advantage that it is possible to configure the ECL to laser at a desired value of the output power selected along a mono tonic function of the injection current.