Device and method for determining a piece of polarization information and polarimetric imaging device

A method for determining at least one piece of polarisation information for a measurement point of a target sample, said method comprising the following steps:

• a) emitting a rectilinearly polarised incident light beam in a predefined direction,
• b) guiding the incident light beam towards the measurement point of the target sample with the aid of a waveguide and outputting two orthogonal polarimetric components of the incident light beam,
• c) rotating two orthogonal polarimetric components of the incident light beam after passage through the waveguide,
• d) reflecting the incident light beam at the measurement point of the target sample as a reflected light beam;
• e) rotating two orthogonal polarimetric components of the reflected light beam before passage through the waveguide, the steps c) and e) compensating for the effect of the birefringence of the waveguide;
• f) guiding the reflected light beam towards photodetectors by the same waveguide;
• g) measuring the reflected light beam and delivering to a calculation unit an electric signal representative of the polarimetric component of the reflected light beam oriented in the predefined direction, called a parallel signal, and an electric signal representative of the polarimetric component perpendicular to the polarimetric component of the reflected light beam oriented in the predefined direction, called an orthogonal signal;
• h) selecting a value of the parallel signal, the parallel signal varying over time or as a function of the wavelength;
• and
• i) calculating a degree of polarization (DOP), based on the following formula:
• DOP=1−2K where K=P∥s/(P⊥s+P∥s)
• in which:
• DOP is the degree of polarization of the measurement point of the target sample,
• P∥s is the power representative of the parallel signal,
• P⊥s is the power representative of the orthogonal signal,
• (P⊥s+P∥s) is the total power collected by the photodetectors.

A device for determining at least one piece of polarisation information for a measurement point of a target sample, said device comprising:

• a light source emitting a rectilinearly polarised incident light beam in a predefined direction, the incident light beam being intended to be reflected by the measurement point of the target sample as a reflected light beam,
• at least one waveguide guiding the incident light beam towards the target sample, and the reflected light beam towards photodetectors,
• a polarisation rotation means rotating two orthogonal polarimetric components of the incident light beam after passage through the waveguide and two orthogonal polarimetric components of the reflected light beam before passage through the waveguide, to compensate for the effect of the birefringence of the waveguide,
• photodetectors measuring the reflected light beam and delivering to a calculation unit an electric signal representative of the polarimetric component of the reflected light beam oriented in the predefined direction, called a parallel signal, and an electric signal representative of the polarimetric component perpendicular to the polarimetric component of the reflected light beam oriented in the predefined direction, called an orthogonal signal;
• the calculation unit selecting a value of the parallel signal, the parallel signal varying over time or as a function of the wavelength, the calculation unit calculating a phase shift θ introduced between main axes of the target sample based on the following formula:
• sin
• 2
• ⁡
• (
• θ
• 2
• )
• =
• (
• 1
• -
• K
• )
• ·
• P
• //
• s
• -
• K
• ·
• P
• ⊥
• s
• (
• 1
• -
• 2
• ⁢
• K
• )
• ⁢
• (
• P
• //
• s
• +
• P
• ⊥
• s
• )
• where K=P∥s/(P⊥s+P∥s)
• in which:
• θ is the phase shift θ introduced between the main axes of the target sample,
• P∥s is the power representative of the parallel signal,
• P⊥s is the power representative of the orthogonal signal.

A device for determining at least one piece of polarisation information for a measurement point of a target sample, said device comprising:

• a light source emitting a rectilinearly polarised incident light beam in a predefined direction, the incident light beam being intended to be reflected by the measurement point of the target sample as a reflected light beam,
• at least one waveguide guiding the incident light beam towards the target sample, and the reflected light beam towards photodetectors,
• a polarisation rotation means rotating two orthogonal polarimetric components of the incident light beam after passage through the waveguide and two orthogonal polarimetric components of the reflected light beam before passage through the waveguide, to compensate for the effect of the birefringence of the waveguide,
• photodetectors measuring the reflected light beam and delivering to a calculation unit an electric signal representative of the polarimetric component of the reflected light beam oriented in the predefined direction, called a parallel signal, and an electric signal representative of the polarimetric component perpendicular to the polarimetric component of the reflected light beam oriented in the predefined direction, called an orthogonal signal,
• the calculation unit selecting a mean value of the parallel signal and a corresponding value of the orthogonal signal measured at the same moment, the calculating unit calculating a phase shift θ at the measurement point of the target sample, based on the following formula:
• θ=f(x) where x=P∥mean/(P⊥mean+P∥mean)
• in which:
• θ is the phase shift θ introduced between main axes of the target sample,
• f is a continuously increasing function between 0 and 180° when x varies from 0 to 1,
• P∥mean is the mean power obtained based on the mean of several measurements of the parallel signal, and
• (P⊥mean+P∥mean) is the mean power collected by the photodetectors during a predefined period of time.