Optical coherence tomography apparatus and method using line confocal filtering

1. An optical tomography apparatus comprising:

a polychromatic light source;

a one-dimensional optical sensor;

an interferometric microscope comprising: a reference arm, at the end of which is arranged a reference mirror; an object arm; a beam splitter coupling said reference arm and said object arm to said polychromatic light source and to said sensor, and a first objective situated in the reference arm, said reference mirror being arranged in a focusing plane, situated in the reference arm, of said first objective,

a one-dimensional confocal spatial filter, cooperating with said polychromatic light source to illuminate an object to be observed, arranged in said object arm, with an observation line,

wherein said observation line comprises a line of light that lies in a focusing plane of a second objective, situated in the object arm, and extends perpendicular to an optical axis of said second objective,

wherein a one-dimensional image of said observation line is formed on said sensor,

wherein the apparatus further comprises:

at least one actuator configured to displace said observation line in a depth wise direction and parallel to the optical axis of said second objective, extending along the object arm, so as to perform a depth scan of said object, while maintaining a zero optical path difference between, on the one hand, a first trajectory going from said beam splitter to said reference mirror and back by traveling along said reference arm and, on the other hand, a second trajectory going from said beam splitter to said observation line and back by traveling along said object arm; and

a processor programmed or configured to reconstruct a two-dimensional image of a section of said object to be observed, oriented parallel to said optical axis of said second objective, extending along the object arm, from a plurality of one-dimensional interferometric images acquired by said sensor corresponding to different positions of said observation line during said depth scan.

2. The apparatus of claim 1 , wherein said one-dimensional confocal spatial filter is also arranged to select the light backscattered by said object and originating from said observation line.

3. The apparatus of claim 1 , wherein said at least one actuator is configured to provoke a relative displacement, parallel to said optical axis of said second objective placed in the object arm, of said object to be observed relative to said interferometric microscope, without modifying the optical lengths of said reference arm and of said object arm.

4. The apparatus of claim 1 , wherein said at least one actuator is configured to displace the second objective in the focusing plane of which said observation line is located and to modify the optical length of said reference arm so as to maintain the zero optical path difference between said first trajectory and said second trajectory.

5. The apparatus of claim 1 , also comprising a dispersion compensator arranged on at least one out of said object arm and said reference arm, said at least one actuator being configured to act also on said dispersion compensation device during said depth scan.

6. The apparatus of claim 1 , wherein said interferometric microscope is a Linnik interferometric microscope, said first objective is arranged on said reference arm and said second objective is arranged on said object arm, said reference and object arms being separate.

7. The apparatus of claim 6 , wherein said first and second objectives are immersion objectives, and in which said at least one actuator is configured to provoke a relative displacement, parallel to said optical axis of said second objective placed in the object arm, of said object to be observed relative to said interferometric microscope, without modifying the optical lengths of said reference arm and of said object arm.

8. The apparatus of claim 1 , wherein said polychromatic light source is spatially coherent and said confocal filter comprises an astigmatic optical system arranged between said polychromatic light source and the beam splitter, a lens arranged in front of said one-dimensional optical sensor and the one-dimensional optical sensor itself arranged in a focusing plane of said lens.

9. An optical tomography method comprising the following steps:

a) providing a polychromatic light source;

b) using a beam splitter to direct a first fraction of light emitted by said source along a first trajectory, called reference trajectory, and a second fraction of light emitted by said source along a second trajectory, called object trajectory;

c) using an objective cooperating with a one-dimensional confocal spatial filter to focus said second fraction of light so as to illuminate a semi-transparent object to be observed with an observation line, wherein said observation line comprises a line of light that lies in a focusing plane of said objective, situated in an object arm, and extends perpendicular to said optical axis of said objective, and to collect the light backscattered by said illuminated object;

d) using said objective, or another objective, to focus said first fraction of light on a reference mirror arranged on said reference trajectory, and to collect the light reflected by said reference mirror;

e) using said beam splitter to combine the light backscattered by said object with the light reflected by said reference mirror and direct it to a one-dimensional optical sensor;

f) forming a one-dimensional image of said observation line on said sensor;

g) using at least one actuator to displace said observation line in a depth wise direction and parallel to an optical axis of said objective so as to perform a depth scan of said object to be observed on said object trajectory, while maintaining a zero optical path difference between said reference trajectory and said object trajectory; and

h) using a processor to reconstruct a two-dimensional image of a section of said object to be observed, oriented parallel to said optical axis, from a plurality of one-dimensional interferometric images acquired by said sensor corresponding to different positions of said observation line during said depth scan.

10. The method of claim 9 , wherein step f) also comprises selecting the light originating from said observation line.

11. The method of claim 9 , wherein said step g) is implemented by provoking a relative displacement, parallel to said optical axis, of said object to be observed relative to said interferometric microscope without modifying the optical lengths of said reference trajectory and of said object trajectory.

12. The method of claim 9 , wherein said step g) is implemented by displacing the objective in a focusing plane of which said observation line is located and by modifying the optical length of said reference trajectory so as to maintain the zero optical path difference between said first trajectory and said second trajectory.

13. The method of claim 9 , also comprising a step i) of compensation of the modifications of the dispersion induced by the displacement of the observation line inside said object to be observed during said depth scan.

14. The method of claim 9 , wherein said object to be observed is a biological tissue.

15. An optical tomography apparatus comprising:

a polychromatic light source;

a one-dimensional optical sensor;

an interferometric microscope comprising: a reference arm, at the end of which is arranged a reference mirror; an object arm; a beam splitter coupling said reference arm and said object arm to said polychromatic light source and to said sensor, and a single objective, said reference mirror being arranged in a first focusing plane, situated in the reference arm, of said objective;

a one-dimensional confocal spatial filter, cooperating with said polychromatic light source to illuminate an object to be observed, arranged in said object arm, with an observation line;

at least one actuator configured to displace said observation line in a depth wise direction and parallel to the optical axis of said objective, extending along the object arm, so as to perform a depth scan of said object, while maintaining a zero optical path difference between, on the one hand, a first trajectory going from said beam splitter to said reference mirror and back by traveling along said reference arm and, on the other hand, a second trajectory going from said beam splitter to said observation line and back by traveling along said object arm; and

a processor programmed or configured to reconstruct a two-dimensional image of a section of said object to be observed, oriented parallel to said optical axis of said objective, extending along the object arm, from a plurality of one-dimensional interferometric images acquired by said sensor corresponding to different positions of said observation line during said depth scan,

wherein said observation line comprises a line of light that lies in a second focusing plane, situated in the object arm, of said objective and extends perpendicular to an optical axis of said objective,

wherein a one-dimensional image of said observation line is formed on said sensor, and

wherein said interferometric microscope is chosen from a Michelson interferometric microscope and a Mirau interferometric microscope.

16. The apparatus of claim 15 , wherein said interferometric microscope is a Mirau interferometric microscope comprising the single objective, and the reference mirror and the beam splitter are secured to said single objective and aligned along its optical axis, said at least one actuator is configured to provoke a relative displacement, parallel to said optical axis, of said interferometric microscope relative to the object to be observed, an immersion medium is arranged, on the one hand, between said beam splitter and the object to be observed and, on the other hand, between said beam splitter and the reference mirror.