Patent ID: 7573919

Claim:
A method for selecting the emission wavelength of a tuneable laser having an external-cavity defining a plurality of cavity modes, wherein selecting occurs by means of a tuneable mirror that comprises a diffraction grating and a planar waveguide optically interacting with said diffraction grating, the diffraction grating and the planar waveguide forming a resonant structure, the tuneable mirror further comprising a light transmissive material having an index of refraction that varies in response to an electric field applied to the light transmissive material, making the tuneable mirror electrically tuneable, comprising the steps of: emitting a light beam by a gain medium to the external cavity; applying an alternating voltage of an amplitude to the light transmissive material of the tuneable mirror at a frequency f A , thereby selecting a resonance wavelength of the resonance structure and thereby modulating in amplitude the light beam reflected or transmitted by the tuneable mirror; and aligning the resonance wavelength of the tuneable mirror to at least one of the cavity modes by analysing the modulated component of the light beam reflected or transmitted by the tuneable mirror, wherein the step of aligning the resonance wavelength is carried out by changing the amplitude of the voltage applied to the tuneable mirror so as to minimise the amplitude of the modulated component of the light beam either reflected by the tuneable mirror or transmitted through the tuneable mirror.