Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J4/00—Measuring polarisation of light
  • G01J4/04—Polarimeters using electric detection means
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
  • A61B5/0062—Arrangements for scanning
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
  • A61B5/0062—Arrangements for scanning
  • A61B5/0064—Body surface scanning
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/44—Detecting, measuring or recording for evaluating the integumentary system, e.g. skin, hair or nails
  • A61B5/441—Skin evaluation, e.g. for skin disorder diagnosis
  • A61B5/442—Evaluating skin mechanical properties, e.g. elasticity, hardness, texture, wrinkle assessment
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/8422—Investigating thin films, e.g. matrix isolation method
  • G01N2021/8438—Mutilayers

Definitions

• the present invention relates to a device and a method for determining a polarization information at a point of a target sample, as well as a polarimetric imager.
• the invention relates to a type determination device comprising:
• a light source capable of emitting a linearly polarized light beam in a predefined direction, the light beam being intended to be reflected by the measurement point of the target sample;
• the waveguide being a polarization maintaining optical fiber having an optical axis of its own parallel to the predefined direction.
• a polarization information determining device makes it possible to obtain information on the micro or nanostructuration of target samples, on their texture on the surface or at shallow depth below the surface.
• This polarization information may be, for example, the degree of polarization of the beam returned by the target sample.
• This information is mainly used in the medical field for the diagnosis of diseases, and in the field of microelectronics to characterize thin films monolayer, multilayer or to analyze complex surfaces.
• the polarization information is obtained by reflection of a polarized light beam on a target sample. The analysis of the polarization of the reflected beam makes it possible to determine polarization information of the target sample.
• the object of the invention is in particular to overcome this drawback and to propose a device for determining polarization information that makes it possible, among other things, to analyze non-accessible target samples by a direct-aiming light beam.
• the subject of the invention is a device for determining the aforementioned type, characterized in that it comprises: polarization rotation means capable of rotating two orthogonal polarimetric components Ey 1 , Ei 1 of the incident beam after passing through the waveguide, and two orthogonal polarimetric components Ey R, E.
• the rotation means comprise at least one optical axis orientable about an axis of rotation, said axis of rotation being perpendicular to the optical proper axis and the predefined direction;
• the calculating means being suitable for calculating a polarization information from the reflected beam measured for at least three different orientations of the optical axis of the rotation means; said polarization information being the orientation of the proper axes and the phase shift induced by the birefringence of the target sample.
• This invention makes it possible to analyze biological tissue structures such as collagen, in vivo, in situ and without the need for a biopsy.
• the subject of the invention is also a polarimetric imager capable of generating a polarimetric image of a target sample, the imager comprising: a device for determining a polarization information according to one of the embodiments described above, said device being able to determine a plurality of polarization information;
• the subject of the invention is also a method for determining a polarization information, the method comprising the following steps: a) emission of an incident light beam polarized rectilinearly in a predefined direction; b) guiding the incident beam to the measurement point of the target sample using a waveguide, the waveguide being a polarization maintaining optical fiber having an optical axis parallel to the direction predefined; c) rotation of two orthogonal polarimetric components Ey 1 , Ei 1 of the incident beam after passing through the waveguide, the polarimetric component Ei 1 of the incident beam perpendicular to the predefined direction being zero; d) reflection of the incident beam on the measurement point of the target sample; e) rotation of two orthogonal polarimetric components Ey R ; E_ ⁇ _ R of
• FIG. 1 is a schematic view of the determination device according to the invention
• FIG. 2 is a schematic representation of the orientations of the proper axes of the rotation means, the proper axes of the waveguide and the proper axes of the target sample;
• FIG. 3 is a schematic view of a polarimetric imager according to a second embodiment of the invention.
• FIG. 4 is a diagram illustrating the steps of the method according to the invention.
• the determination device 2 comprises a monochromatic light source 4 capable of emitting an incident light beam, a waveguide 6 adapted to be traversed by an incident beam and by a beam reflected by the target sample. 8, and means 9 for calculating the polarization information from the reflected beam recovered at the output of the waveguide 6.
• the light beam is called “incident beam” over the entire path from source 4 to the target sample 8, and “reflected beam” over the entire path of the target sample 8 to the calculation means 9.
• upstream and downstream are defined according to the direction of the light beam.
• angles of rotation are defined algebraically in this description with respect to a trigono-metric direction illustrated by an arrow F in FIG.
• the light source 4 is able to emit an incident light beam polarized rectilinearly in a predefined direction e x .
• This light source 4 is, for example, constituted by a laser diode 10, a polarizer 12 and a half-wave plate 14.
• the polarizer 12 and the half-wave plate 14 are arranged downstream of the laser diode, considering the direction of the incident beam. They are adapted to be traversed by the beam emitted by the laser diode 10.
• the light source may include a device for protecting it from external reflections.
• the determination device 2 comprises between the light source 4 and the waveguide 6, a cube 16 beam splitter and a system 18 for focusing the incident beam in the waveguide 6.
• the cube 16 is neutral to the polarization. It affects only the intensity of the beam of the light source and going towards the waveguide 6. It is adapted to modify the direction of the reflected beam to direct it towards the calculation means 9.
• the focusing system 18 is constituted for example by a microscope objective or a convergent lens whose focal plane is located at the entrance of the waveguide 6.
• the waveguide 6 is adapted to guide the incident beam on the target sample 8, in particular when the latter is positioned in a cavity or a recess, or even in the human body, so that it can not be achieved by transmission of a light beam in direct sight. It has an end 6a called said proximal end, located near the light source 4 and calculation means 9, and a distal end 6b said end intended to be disposed near the target sample 8.
• the waveguide 6 is constituted by a monomode optical fiber at the wavelength of the beam emitted by the light source 4.
• This optical fiber is for example a polarization-maintaining optical fiber having one of its own axes parallel to the direction of polarization e x of the light source 4.
• the polarimetric component Ey 1 of the incident beam is therefore not disturbed when its passage in the waveguide 6.
• the determining device 2 comprises, considering the direction of the incident beam, means 21 for polarization rotation, a first system optical 20 whose focal plane is located at the opening of the distal end of the waveguide 6, and a second optical system 24 whose focal plane is located at the target sample 8.
• the means of rotation 21 comprise a phase plate having two optical eigenfaces referenced e X ⁇ and e n .
• the determining device 2 further comprises means 22 for driving in rotation the own axes e x , e about an axis of rotation A; the axis A being
• the drive means 22 consist for example of an actuator. They are controlled by the calculation means 9 in order to rotate the proper axes e x ,
• the drive means 22 are connected to the calculation means 9 by an electric wire 23.
• the rotation means 21 and the drive means 22 are mounted between the distal end 6b and the target sample 8. In particular, they can be attached to the distal end 6b of the waveguide.
• the calculation means 9 are able to determine polarization information from the reflected beam for at least three different orientations of the proper axes e X ⁇ , e n of the rotation means 21.
• FIG. 2 illustrates an example of orientation of the optical eigenfunctions e x , e y of the waveguide (the vector e x also representing the orientation of the polarization of the light source 4 ), an example of orientation of the proper axes e x0 , e yO of the target sample, as well as three examples of orientation of the proper axes e x , e y of rotation means 21.
• FIG. 2 also represents the angle ⁇ defined between an own axis e x 0 of the target sample and the direction of the polarization e x , and the angles O 1 , ⁇ 2 , ⁇ 3 defined between the proper axis e x of rotation means 21 and the direction of the polarization e x for three
• the rotation means 21 are capable of rotating two polarimetric components E 1 , E 1 of the incident beam in the direction of rotation F by an angle ⁇ 1 to make a first measurement of the reflected beam at an angle ⁇ 2 to realize a second measurement of the reflected beam, and an angle 2O 3 for performing a third measurement of the reflected beam.
• the polarimetric component E_ ⁇ _ F perpendicular to the predefined direction e x is nothing.
• the first optical system 20 is able to collimate the incident beam.
• the second optical system 24 is able to focus the incident beam on the measurement point of the target sample.
• the incident beam is able to be reflected by the measurement point of the target sample 8.
• One of the polarization components of the incident beam is out of phase with a value ⁇ during this reflection.
• the phase shift ⁇ is characteristic of the birefringence of the target sample 8.
• the reflected beam is collimated by the second optical system 24, and is focused by the first optical system 20 at the input of the distal portion 6b of the waveguide.
• the rotation means 21 are then adapted to rotate the two orthogonal polarimetric components E
• the angles 2 (/ + S 1) and the ⁇ - ( ⁇ + ⁇ ⁇ ) are defined with a polarimetric component Ey R parallel to the own axis e xQ à.Q the target sample 8 and a polarimetric component perpendicular E_ ⁇ _ R to this proper axis e x0 .
• the waveguide 6 is adapted to guide the reflected beam towards the focusing system 18. Since the waveguide is polarization maintaining, the power ratio of the polarimetric components Ey R and Ei R of the reflected beam is not changed during the crossing of the waveguide.
• the determination device 2 further comprises a polarization separator cube 26 and two photodetectors 28, 30 connected to the calculation means 9.
• the cube 26 is shaped to separate a polarimetric component Ey F oriented in the direction of polarization e x of the source 4, and a polarimetric component E_ ⁇ _ F perpendicular thereto.
• the parallel polarimetric component Ey F and the perpendicular polarimetric component E_ ⁇ _ F of the reflected beam are able to be directed respectively towards the photodetector 28, and toward the photodetector 30.
• the photodetectors 28, 30 are shaped to each deliver a photocurrent, hereinafter called electric signal, to computing means 9.
• the calculation means 9 are able to calculate the angle ⁇ between the e xO axis of the target sample and the polarization direction e x , as well as the phase shift ⁇ induced by the target sample.
• the calculation means 9 are suitable for calculating the following ratios:
• - W 1 is the i th angle defined between the own axis x e of the rotation means 21 and the direction of polarization E x;
• P 11 is representative of the normalized power polarimetric component E.
• L F perpendicular to the polarization direction x e, measured when the own e X ⁇ axis rotating means 21 has an i th angle O1 with respect to the polarization direction e x ;
• ⁇ is the angle defined between the proper axis e x ⁇ of the target sample and the polarization direction e x ;
• P ⁇ 1 is the power measured by the photodetector 30 and P ⁇ 1 is the power measured by the photodetector 28.
• the calculation means 9 are able to calculate the angle ⁇ from the normalized powers P 11 , P 12 , P 13 representative of the perpendicular polarimetric components E_ ⁇ _ F measured for the orientations O 1 , ⁇ 2 , ⁇ 3 of the proper axes. rotation means.
• this angle ⁇ can also be calculated from the ratio between the normalized powers P 1n , P 111 P / n representative of the parallel polarimetric components E
• the calculation means 9 are able to calculate the phase shift ⁇ from the following equation:
• ⁇ is the angle defined between the eigen axis g xO of the target sample and the polarization direction e x .
• Equation (la), (Ib) and (2) were obtained from the expressions of the normalized power P 11 , of the polarimetric component E
• the polarimetric imager 32 is formed from a device 2 for determining a polarization information, as described above, equipped with a unit 34 for the construction of a polarimetric image and a scanning system 36.
• the waveguide 6 of the determination device 2 is replaced by several waveguides 40, or by a multicore optical fiber whose axes are parallel to each other .
• the building unit 34 is adapted to receive beam polarization information from a plurality of measurement points of the target sample 8 and to construct a polarimetric image therefrom. Each gray level or chrominance of a pixel in the image represents the information associated with a measurement point of the target sample.
• the image building unit 34 is synchronized with the scanning system 36.
• the scanning system 36 is capable of directing the incident beam towards several measurement points of the target sample 8.
• the scanning system 36 is arranged upstream of the waveguides by considering the direction of the incident beam. It is adapted to direct the incident beam in turn towards each waveguide so that the beam sequentially illuminates several measurement points of the target sample 8.
• the scanning system sequentially processes the reflected beam.
• the building unit 34 is synchronized with the scanning system 36 so as to be able to assign to each polarization information calculated by the calculation unit 9 a corresponding position on the target sample 8.
• It is for example constituted by two oscillating mirrors, one along a vertical axis, and the other along a horizontal axis, at a frequency corresponding to the frequency of construction of an image by the unit 34. It is connected to the building unit 34.
• the construction unit 34 is able to generate a polarimetric image representative of the orientation ⁇ of the proper axis 0 0 of the target sample 8, a polarimetric image representative of the phase shift ⁇ or an image showing both the phase shift ⁇ and the orientation ⁇ of an own axis of the target sample.
• the waveguide comprises a single optical fiber and the scanning system 36 is disposed downstream of the waveguide considering the direction of travel of the incident beam. In particular, it is arranged between the distal end 6b of the waveguide and the target sample 8. In this case, the scanning system 36 is able to direct the incident beam towards several measurement points of the target sample. .
• the optical fiber or fibers used are polarization-maintaining multimode optical fibers.
• the monochromatic light source is replaced by a polychromatic source 44, constituted for example by a superluminescent diode.
• the polarimetric imager 32 is able to generate polarization and wavelength response information of the target sample.
• the invention also relates to a method for determining a polarization information.
• the method illustrated in FIG. 4 comprises a measurement phase 59 followed by a calculation phase 80.
• the measurement phase 59 begins with a step 60 of emission of an incident light beam E / polarized rectilinearly.
• the incident beam is guided towards the measurement point of the target sample using the waveguide 6.
• the polarimetric components E 1 , E 1 the incident beam are rotated by an angle of 2O 1 and ⁇ + 2 ⁇ i respectively, defined algebraically with respect to the direction of rotation F by the rotation means 21.
• the waveguide is an optical polarization-maintaining fiber having a clean optical axis parallel to the predetermined direction x e
• the polarimetric component Ej_ F perpendicular to the predetermined direction is an x nothing.
• the incident beam is reflected on the measurement point of the target sample.
• a step 68 two orthogonal polarimetric components E // F ; Ei F of the reflected beam are rotated one at an angle of 2 ( ⁇ - ⁇ ⁇ ), the other by an angle of ⁇ -2 ( ⁇ - ⁇ ⁇ ) in a direction opposite to the direction of rotation F. Then, the reflected beam is injected into the waveguide 6 by the optical system 20.
• the reflected beam is guided to the computing unit 9 by the same waveguide 6.
• the separator cube 26 separates a polarimetric component E / / oriented in the predefined direction e x towards the photodetector 28 and a polarimetric component E.
• L F oriented perpendicular to the predefined direction e x to the photodetector 30.
• Each photodetector 28, 30 delivers an electrical signal to the calculation means 9 which memorize this information.
• the drive means 22 rotate the own axis e x rotation means 21 about the axis A of rotation so that it forms an angle ⁇ 2 with respect to the direction of polarization e x .
• steps 62 to 70 are repeated for this new orientation ⁇ 2
• two polarimetric components of the incident beam are rotated by an angle of 2 ⁇ 2 defined algebraically with respect to the direction of rotation F by the rotation means 21.
• the waveguide is a polarization maintaining optical fiber having an optical self-axis parallel to the predefined direction e x
• the polarimetric component Ei F perpendicular to the predefined direction e x is zero.
• step 68 the orthogonal polarimetric E // F components, E. L F of the reflected beam are rotated through an angle 2 ( ⁇ - S 2) each other by an angle of ⁇ - 2 ⁇ - ⁇ 2 ) in a direction opposite to the direction of rotation F.
• the drive means 22 rotate the own axis e x rotation means 21 around the axis of rotation A so that it forms an angle ⁇ 3 with respect to the direction of polarization e x .
• steps 62 to 70 are repeated for this new orientation ⁇ 3 .
• the computing means 9 calculate the angle ⁇ defined between the eigen axis e x0 of the target sample and the direction of polarization e x , from the ratios (Ia) and (Ib), electrical signals delivered during steps 70 and angles Oi 1 O 2, and ⁇ 3 .
• the calculation unit 9 determines the phase shift ⁇ from equation (2).
• angles ⁇ ⁇ ⁇ 2j and ⁇ 3 are for example respectively equal to 0 degrees, - ⁇ degrees and + ⁇ degrees with ⁇ other than 45 degrees.
• the determinations of ⁇ and ⁇ via the measurements described above assume that the target sample has only a linear birefringence, that is, the target sample is not depolarizing, does not exhibit dichroism or circular birefringence.
• the reflected beam is guided towards the calculation means by another optical fiber having an own axis parallel to the own axis of the optical fiber supplying the incident beam.

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• 2009
  • 2009-01-15 FR FR0950236A patent/FR2941047A1/fr active Pending
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