Abstract: The invention relates to an external cavity, continuously tunable monomode laser source, comprising, in a resonant cavity, resonating at the emission wavelength &lgr;e, a retroreflecting wavelength dispersing device, arranged to produce a selectivity curve with a peak 80 s. According to the invention, additional fine-control means, enable, from the approximate continuous tunability position, to monitor the deviation &lgr;e-&lgr;s during the variation of the emission wavelength ke while preventing this deviation from reaching one of the limits causing mode hopping. Such a configuration enables to avoid imperfections usually associated with mechanical adjustment and to guarantee continuity of the wavelength variation and to compensate for the latter as long as its fluctuations remain smaller than approx. &Dgr;&lgr;e/2 where &Dgr;&lgr;e is the distance between two successive resonance modes of the cavity.

Abstract: The invention relates to an optical spectrum analyzer of an incident light beam (101) and a process for analyzing the corresponding spectrum. The spectrum analyzer comprises addressing means (1), a diffraction grating (2), a reflecting dihedron (3), a device (4) for adjusting the rotation of the reflecting dihedron and reception means (5). A polarization separator (11) divides the incident beam (101) into a first and second parallel secondary beam (102, 104), of linearly polarized light along the directions parallel to and perpendicular to the grooves in the grating respectively, and a .lambda./2 plate (12) placed on the path of the first secondary beam (102) applies a perpendicular polarization direction to this beam. The grating diffracts the secondary beams (103, 104) a first time, the reflecting dihedron exchanges their directions, the grating diffracts them a second time, the .lambda./2 plate applies a 90.degree.