A two-wave extra-flat Fourier-transformed static spectrometer comprising an optical detection plane and a device placed between a light source and said optical detection plane, said device making it possible to obtain a location plane of an interference pattern of the light source, the light of which passes through the device, coinciding with the optical detection plane, said device being characterized in that it includes: - a single phase-shifting layer made from a first material with optical index n A, transparent at least at one wavelength of the light source, the phase-shifting layer including a first face and a second face opposite it, said first face including at least one element or surface not parallel to said second face; - a support layer made from a second material, with optical index nB different from optical index nA, transparent at least at one wavelength of the light source, the support layer including a first face across from and parallel to a second face; - the second face of the phase-shifting layer and the second face of the support layer being joined by molecular adhesion or by gluing or via maintaining layer or by means of a mechanical part, so as to form a monolithic interferometric plate, the angle formed between the optical detection plane and the first or the second face of the phase-shifting layer being adaptable, based on the incidence angle of the light beam on said face (A1, A2), so that the location plane is combined with said optical detection plane, so as to maximize the contrast, the phase-shifting layer forming at least one partially resonant full cavity (C, Ci) delimited by a first diopter comprising the first face of the phase-shifting layer and by a second diopter comprising the second face of the phase-shifting layer and/or the second face of the support layer, the average reflection coefficient R of the partially resonant full cavity (C, Ci) being less than 70%, or preferably less than 50%, the spectrometer further comprising maintaining means between said plate and the detection plane, the maintaining means being configured so as to be able to pivot the plate relative to the optical detection plane. - a single phase-shifting layer made from a first material with optical index n A, transparent at least at one wavelength of the light source, the phase-shifting layer including a first face and a second face opposite it, said first face including at least one element or surface not parallel to said second face; - a support layer made from a second material, with optical index nB different from optical index nA, transparent at least at one wavelength of the light source, the support layer including a first face across from and parallel to a second face; - the second face of the phase-shifting layer and the second face of the support layer being joined by molecular adhesion or by gluing or via maintaining layer or by means of a mechanical part, so as to form a monolithic interferometric plate, the angle formed between the optical detection plane and the first or the second face of the phase-shifting layer being adaptable, based on the incidence angle of the light beam on said face (A1, A2), so that the location plane is combined with said optical detection plane, so as to maximize the contrast, the phase-shifting layer forming at least one partially resonant full cavity (C, Ci) delimited by a first diopter comprising the first face of the phase-shifting layer and by a second diopter comprising the second face of the phase-shifting layer and/or the second face of the support layer, the average reflection coefficient R of the partially resonant full cavity (C, Ci) being less than 70%, or preferably less than 50%,