A device for determining at least one piece of polarization information of a measurement point of a target sample, said device having: - a light source (4; 44) able to emit a rectilinearly polarized light beam in a predefined direction, the light beam being intended to be reflected by the measurement point of the target sample; - means for detecting (28, 30) and calculating the piece of polarization information of the measurement point from the beam reflected by the target sample; - at least one waveguide (6; 40) able to guide the incident beam towards the target sample and the reflected beam towards the calculation means; the waveguide (6; 40) being a single-mode optical fiber at the or at each wavelength of the beam emitted by the light source (4; 44) characterized in that it further comprises: - means of rotating the polarization comprising a Faraday rotator able to rotate two orthogonal polarimetric components (E I ∥, E I ⊥) of the incident beam after passage through the waveguide (6; 40) and two orthogonal polarimetric components (E R ∥, E R ⊥) of the reflected beam before passage through the waveguide (6; 40) to compensate for the effect of the birefringence of the waveguide (6; 40), and - means (19; 44) of varying the polarization of the incident beam and of the reflected beam, which are either in the form of means for varying the birefringence of the waveguide, which are mounted on the waveguide, for which the light source is monochromatic and which are adapted to modify, over time and in an identical manner, the orthogonal polarimetric components (E I ∥, E I ⊥) of the incident beam after passage through the waveguide and the orthogonal polarimetric components (E F ∥, E F ⊥) of the polarization of the reflected beam after passage through the waveguide, or are provided by the light source in the form of a polychromatic light source, the chromatic dependency of the birefringence of the waveguide thereby forming said means for varying the polarization of the incident beam and the reflected beam, the means (19; 44) for varying the polarization of the incident beam and of the reflected beam being such that they enable the calculation of the piece of polarization information for the measurement point from the measurements for each polarization of the incident beam. - a light source (4; 44) able to emit a rectilinearly polarized light beam in a predefined direction, the light beam being intended to be reflected by the measurement point of the target sample; - means for detecting (28, 30) and calculating the piece of polarization information of the measurement point from the beam reflected by the target sample; - at least one waveguide (6; 40) able to guide the incident beam towards the target sample and the reflected beam towards the calculation means; the waveguide (6; 40) being a single-mode optical fiber at the or at each wavelength of the beam emitted by the light source (4; 44) characterized in that it further comprises: - means of rotating the polarization comprising a Faraday rotator able to rotate two orthogonal polarimetric components (E I ∥, E I ⊥) of the incident beam after passage through the waveguide (6; 40) and two orthogonal polarimetric components (E R ∥, E R ⊥) of the reflected beam before passage through the waveguide (6; 40) to compensate for the effect of the birefringence of the waveguide (6; 40), and - means (19; 44) of varying the polarization of the incident beam and of the reflected beam, which are either in the form of means for varying the birefringence of the waveguide, which are mounted on the waveguide, for which the light source is monochromatic and which are adapted to modify, over time and in an identical manner, the orthogonal polarimetric components (E I ∥, E I ⊥) of the incident beam after passage through the waveguide and the orthogonal polarimetric components (E F ∥, E F ⊥) of the polarization of the reflected beam after passage through the waveguide, or are provided by the light source in the form of a polychromatic light source, the chromatic dependency of the birefringence of the waveguide thereby forming said means for varying the polarization of the incident beam and the reflected beam, the means (19; 44) for varying the polarization of the incident beam and of the reflected beam being such that they enable the calculation of the piece of polarization information for the measurement point from the measurements for each polarization of the incident beam.