LIGHTING DEVICE FOR MICROSCOPE

Abstract

A lighting device for an imaging system with an imaging objective lens, including: a sleeve configured to be positioned around the imaging objective lens; at least one optical fibre integral with the sleeve and arranged to guide a light originating from at least one light source; and a directing component configured to orient a light beam emitted by the at least one optical fibre so as to illuminate a field of view of the imaging system along a lighting axis forming an angle with respect to the optical axis of the objective lens larger than the numerical aperture of the imaging system.

Claims

1. A lighting device for an imaging system with an imaging objective lens, comprising: a sleeve configured to be positioned around said imaging objective lens; at least one optical fibre integral with said sleeve and arranged to guide a light originating from at least one light source; and a directing means configured to orient a light beam emitted by said at least one optical fibre so as to illuminate a field of view of said imaging system along a lighting axis forming an angle with respect to the optical axis of said objective lens larger than the numerical aperture of the imaging system.

2. The device according to claim 1, characterized in that it comprises a plurality of optical fibres, the optical fibres being arranged around the perimeter of the sleeve, either evenly in an individual manner or grouped in a plurality of groups of optical fibres, the groups being arranged evenly.

3. The device according to claim 1, characterized in that the directing means comprises a mirror.

4. The device according to claim 1, characterized in that the directing means comprises a guide element arranged to bend the end of the at least one optical fibre.

5. The device according to claim 1, characterized in that it moreover comprises a lens arranged facing or at the output of the at least one optical fibre.

6. The device according to claim 5, characterized in that the lens is produced by polishing the output end of the optical fibre.

7. The device according to claim 1, characterized in that the at least one optical fibre is a multi-mode fibre.

8. The device according to claim 1, characterized in that it moreover comprises translation means configured to move the sleeve relative to an imaging objective lens, in a direction parallel to the optical axis of said objective lens.

9. The device according to claim 1, characterized in that it moreover comprises attachment means capable of fixing the sleeve on an imaging objective lens.

10. The device according to claim 1, characterized in that it moreover comprises at least one light source configured to emit at least one light beam, and injection control means for injecting said at least one light beam into said at least one optical fibre.

11. The device according to claim 10, characterized in that the injection control means comprise at least one fibre coupler for injecting a light beam emitted by a light source into at least two optical fibres.

12. The device according to claim 10, characterized in that the injection control means comprise at least one switch configured to inject a light beam into at least two different optical fibres sequentially.

13. The device according to claim 10, characterized in that it moreover comprises means for modifying the numerical aperture of the light emitted by said at least one optical fibre.

14. The device according to claim 13, characterized in that the means for modifying the numerical aperture are arranged between the at least one light source and an input of the at least one optical fibre.

15. The device according to claim 14, characterized in that the means for modifying the numerical aperture comprise at least one of the following elements: a system of lenses; and a fibre component with a gradual variation in the cross-sectional diameter guiding the light along the propagation axis.

16. The device according to claim 1, characterized in that it comprises at least two light sources configured to emit light beams having different polarizations and/or wavelengths.

17. An imaging system, comprising an imaging objective lens, characterized in that it comprises a lighting device according to claim 1 for producing a darkfield illumination.

Description

DESCRIPTION OF THE FIGURES AND EMBODIMENTS

[0066] Other advantages and characteristics of the invention will become apparent on reading the detailed description of implementations and embodiments that are in no way limitative, and from the attached figures, in which:

[0067] FIG. 1 is a diagrammatic representation of a non-limitative embodiment of a device according to the invention, set up on two different types of microscope objective lens;

[0068] FIG. 2A illustrates a cross-section view of a device according to the invention;

[0069] FIG. 2B shows a detail from FIG. 2A;

[0070] FIG. 3 shows a detail of a device according to an embodiment of the invention;

[0071] FIG. 4 shows a detail of a device according to another embodiment;

[0072] FIGS. 5A to 5D diagrammatically represent embodiments of a system according to the invention; and

[0073] FIGS. 6A and 6B diagrammatically illustrate means for controlling the numerical aperture at the output of the fibres.

[0074] It is well understood that the embodiments that will be described hereinafter are in no way limitative. Variants of the invention can be considered in particular comprising only a selection of the characteristics described hereinafter, in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art. This selection comprises at least one, preferably functional, characteristic without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art.

[0075] In particular, all the variants and all the embodiments described can be combined together, if there is no objection to this combination from a technical point of view.

[0076] In the figures, elements common to several figures retain the same reference sign.

[0077] The embodiments presented illustrate, without loss of generality, embodiments of the lighting device according to the invention in an imaging system of the microscope type, provided with an imaging objective lens of the microscope objective lens type. Such a device makes it possible for example to produce an image of an object to be inspected in a field of view on an imaging sensor (for example of the CCD camera or sensor type).

[0078] Similarly, hereinafter, the terms “lower” and “upper” are used to denote the location of elements when the device according to the invention is used with a microscope, i.e. fixed on an objective lens, without being limitative. In particular, the term “lower” can denote the end of the (microscope) objective lens facing the field of view.

[0079] In the embodiments presented, an object to be inspected or observed can be, in particular, any substrate or any plate intended to be used in the field of electronics, optics or optoelectronics.

[0080] FIG. 1 diagrammatically illustrates an example of a lighting device 1 according to an embodiment of the invention. The lighting device 1 is illustrated mounted on a microscope objective lens 2. The device 1 comprises a cylindrical element in the form of a sleeve 10. The sleeve 10 can be attached to the objective lens 2 in different known ways, for example by means of a screw or a clamping collar (not represented). Preferably, the inner diameter of the cylindrical sleeve 10 is adapted in order that the sleeve 10 can be attached to several types of objective lens. For example, the same sleeve can be fixed on objective lenses 32 to 34 mm in diameter.

[0081] The cylindrical sleeve 10 comprises at least one, or in the embodiment illustrated a plurality of, optical fibres 14. Each optical fibre 14 is arranged in the wall of the sleeve 10 parallel to the axis of revolution of the sleeve 10.

[0082] Each optical fibre 14 is configured to guide the light in order to illuminate a substrate 3 to be inspected at an angle with respect to the axis of the sleeve 10, so as to obtain a darkfield illumination of the substrate 3. The illumination beam is indicated by the reference 16 in FIG. 1. The specular reflection on the substrate 3 due to the illumination beam 16 is indicated by the reference 18.

[0083] FIG. 2A shows a cross-section view of the cylindrical sleeve 10 in the plane perpendicular to its axis, and FIG. 2B shows a detail from FIG. 2A. The sleeve 10 is constituted by an inner ring 11 and an outer ring 12. The outer diameter of the inner ring 11 corresponds substantially to the inner diameter of the outer ring 12.

[0084] The inner ring 11 has grooves 13 in the shape of a V arranged along the axis and over the whole length of the sleeve 10. The grooves 13 serve to receive optical fibres 14. The optical fibres 14 are held in the grooves when the inner ring 11 and the outer ring 12 are assembled together.

[0085] According to variants, the grooves 13 can have other shapes suitable for holding the optical fibres 14, such as a U shape for example.

[0086] According to another embodiment, the cylindrical sleeve 10 is produced in a single piece. In this case, channels in the wall of the sleeve can receive the optical fibres, possibly inserted into a ferrule and stuck there at their end. In this case, the insertion of the ferrules into channels with a suitable diameter ensures a precise and easy positioning of the optical fibres 14. The channels can extend only to the lower end of the sleeve 10 facing the field of view in order to ensure the hold of the end of the optical fibres 14 in the ferrules, and to lead into wider openings or recesses in the wall of the sleeve towards its upper end making it easy to pass the optical fibres through it.

[0087] According to the embodiment illustrated in FIG. 2, the device 1 comprises 64 optical fibres 14, distributed homogeneously over the whole perimeter of the sleeve 10. According to other examples, the device according to the invention can comprise a single optical fibre, or between two and approximately a hundred optical fibres. The number of fibres depends in particular on the illumination configurations that it is desired to produce.

[0088] The optical fibres 14 are, preferably, multi-mode fibres. Their diameter is, for example, of the order of 400 μm.

[0089] FIG. 3 represents a detail view of the lower part of the device 1 according to the embodiment in FIG. 1.

[0090] According to this embodiment, the inner ring 11 comprises a mask 15 on one of its ends. The mask 15 has, for example, the shape of a ring. Preferably, the mask 15 forms an integral part of the inner ring 11. The mask 15 can alternatively be fixed on the inner ring 11 by known means. The mask 15 makes it possible to mask the light coming from the optical fibres 14 and being reflected by the object inspected 3 in the field of view of the microscope, in order to prevent this reflected light from re-entering the inside of the sleeve and being reflected by the inner wall thereof to constitute parasitic light sources. Thus, only the light directly originating from the optical fibres 14 and diffused by faults or structures of the substrate is collected by the objective lens and thus detected by a detection system.

[0091] The outer ring 12 comprises a mirror 17 at its lower end. The mirror 17 is arranged such that the light emitted by each optical fibre 14 is oriented by the mirror 17 at an angle with respect to the axis of the cylindrical sleeve 10 in order to illuminate the substrate to be inspected which is located in the field of view of the microscope, or more precisely in the acceptance cone of the objective lens of the microscope, with darkfield illumination. The angle of illumination is adjusted such that the specular reflections are outside the acceptance cone of the objective lens of the microscope.

[0092] The mirror 17 can have an annular shape. It can in particular be produced in the form of a polished metallic ring. The mirror 17 can also comprise a plurality of plane mirror elements such that one mirror element is arranged in the axis of each optical fibre 14.

[0093] The optical fibres 14 arranged in the sleeve 10 each have a lower end (facing the mirror 17) without termination, polished or cleaved at a right angle, and an upper end coupled to a light source, a coupler or another optical component, for example via connectors or splices.

[0094] FIG. 4 represents a detail of another embodiment of the device according to the invention. A lens 19 is arranged close to the output of an optical fibre 14. The lens 19 controls the opening angle of the light beam illuminating the substrate to be inspected. According to an example, the lens 19 can be configured to obtain a collimated or focused beam. In this embodiment, the end of the optical fibre can be held, as previously, by a groove (V-groove) or, as illustrated in FIG. 4, inserted in a ferrule 40. The lens 19 can be a microlens, or a gradient-index (GRIN) lens. In the latter case, it can also be integrated in the ferrule 40.

[0095] Alternatively, the output end of the optical fibre 14 can be processed directly, for example by polishing, in order to modify the characteristics of the beam emitted by the fibre 14. It can in particular be processed so as to form a lens at its end, and/or angle-polished in order to generate an illumination beam deflected from the axis of the fibre 14.

[0096] According to another aspect, the invention also relates to a darkfield lighting system for an imaging system with a microscope objective lens.

[0097] FIGS. 5A to 5D diagrammatically represent embodiments of the lighting system 100. The system 100 comprises the device described previously and at least one light source 20 as well as the means 21, 22 for controlling the injection of the beams into the optical fibres 14, such as switches 22 and/or couplers 21.

[0098] The light source 20 is placed at a distance from the objective lens of the microscope. The optical fibres 14 are coupled directly or indirectly, for example via couplers 21, to the light source 20. The source 20 can be, for example, a light-emitting diode (LED) source, a heat source or a laser. The source 20 is, preferably, provided with an optical fibre connector. If the device according to the invention comprises several optical fibres 14, the light beam 23 exiting the light source 20 can be divided into several beams 24 with the aid of a coupler 21. The coupler 21 can be produced by a component with optical fibres, an integrated optical circuit or a bulk optical component. Each beam 24 exiting the coupler 21 is injected into one of the optical fibres 14.

[0099] The different examples of the system, illustrated diagrammatically in FIGS. 5A to 5D, make it possible to obtain different illumination configurations. The individual control of the illumination of each fibre 14 is produced by means of different combinations of couplers 21 and/or switches 22. In FIGS. 5A to 5D, only one of the bases 10a of the sleeve 10, corresponding to the input face of the optical fibres 14, is represented diagrammatically.

[0100] FIG. 5A illustrates an embodiment of the lighting system in which a light beam 24 is injected into each optical fibre 14 at the same time, the fibres 14 being distributed evenly in the wall of the sleeve, around its perimeter. In order to do this, the light beam 23 emitted by the source 20 is divided into as many beams 24 as there are optical fibres 14 by a coupler 21. This embodiment thus makes a uniform and continuous illumination possible.

[0101] FIG. 5B shows another embodiment of the lighting system. A switch 22 is placed between the source 20 and two couplers 21a, 21b. Depending on the state of the switch 22, one or other of the couplers 21a, 21b receives the light from the source 20 sequentially. The optical fibres 14 at the output of the couplers 21a, 21b are arranged in the sleeve 10 in order to ensure an illumination at two different azimuth angles. According to variants, more than two couplers can be used in order to obtain more than two azimuth angles of illumination.

[0102] FIG. 5C presents an embodiment making it possible to illuminate the substrate from different directions or at different azimuth angles, with a plurality of sources. Preferably, the illumination is produced sequentially. The use of two or more light sources 20a, 20b moreover makes it possible to vary the characteristics of the light emitted. The sources 20a, 20b can, for example, emit light beams 23a, 23b with different wavelengths from each other. It is thus possible to choose a wavelength for which the substrate to be inspected is transparent in order to be able to penetrate the substrate, and another wavelength for which the substrate is opaque. The light from the two sources can also have different polarization states. Of course, according to variants, more than two light sources can be used.

[0103] Of course, the configurations described by FIGS. 5B and 5A can be combined with the configuration in FIG. 5C in order to be able to connect a fibre to several sources able to be switched sequentially. This makes it possible to modify the lighting conditions (such as for example the wavelength) coming from a fibre.

[0104] In the embodiment shown in FIG. 5D, two light sources 20a, 20b are each combined with a coupler 21a, 21b. The couplers 21a, 21b each have one input channel and several output channels. The optical fibres 14 of the lighting device are grouped in four groups 14′ of three fibres respectively. The groups 14′ are arranged evenly around the perimeter of the sleeve. This arrangement makes it possible to illuminate the substrate at favoured azimuth angles. As with the embodiment in FIG. 5C, the use of two light sources 20a, 20b makes it possible to have light beams 23a, 23b having different characteristics. Of course, other groupings of fibres 14 are also possible.

[0105] In addition to the azimuth angle or the direction of illumination, it is also important to be able to control the uniformity and the luminance of the illumination over a given area of the substrate to be inspected. The dimension of the area illuminated can be adjusted thanks to the position of the sleeve, and therefore of the optical fibres, with respect to the substrate.

[0106] It is moreover possible to control the numerical aperture at the output of the fibres by adjusting the numerical aperture at the input of the fibres.

[0107] FIGS. 6A and 6B diagrammatically illustrate means for controlling and adjusting the numerical aperture of the light beams at the output of the fibres.

[0108] FIG. 6A shows an optical fibre 14 with a numerical aperture converter 30 placed between the light source and the input 14a of the optical fibre 14 in order to control the conditions of injection of the light into the fibre. Thus, the converter 30 is configured to modify the numerical aperture NA.sub.in of an input beam in order to obtain a different numerical aperture NA.sub.out for the output beam. The input beam originates from the light source. The numerical aperture converter 30 can be produced, for example, by lenses or fibre components such as multi-mode fibre combiners with gradual changes of the guides along the propagation axis. The beam exiting the converter is injected into the optical fibre 14 and has a numerical aperture NA.sub.out. The numerical aperture NA.sub.out is preserved at the output 14b of the fibre 14.

[0109] FIG. 6B represents an example of a fibre component for producing a numerical aperture converter 30. The converter 30 is produced by a fibre coupler. Such a fibre coupler consists of a bundle of optical fibres on one side, which are merged into a single optical fibre on the other side (“tapered fibre bundle”). The merged part 31 has a conical shape (“taper”) defining a draw ratio d.sub.out/d.sub.in between the output diameter d.sub.out and the input diameter d.sub.in. The coupler 31 can be connected to a light source at the input 31a (single-fibre side) and on the optical fibres 14 of the lighting device on the bundle side 31b. The draw ratio of the fibre coupler 31 defines a ratio between the input numerical aperture NA.sub.in and the output numerical aperture NA.sub.out:

NA.sub.out=d.sub.in/d.sub.out NA.sub.in.

[0110] This relationship can be applied to the particular case of a single drawn optical fibre (“fibre taper”) with a guide core with a diameter d.sub.in at the start of the drawing and d.sub.out at the end of the drawing.

[0111] Advantageously, the numerical aperture conversion is produced at a distance from the microscope objective lens, thus making an adjustment flexibility possible without the bulk of additional elements. The optical fibre will emit a beam with a numerical aperture NA.sub.out controlled by the numerical aperture of the source and/or of the numerical aperture converter towards the substrate inspected.

[0112] Of course, the invention is not limited to the examples that have just been described, and numerous modifications may be made to these examples without exceeding the scope of the invention.