EP0968146A1

EP0968146A1 - Method and device for assembling optical components or an optical component and a substrate

Info

Publication number: EP0968146A1
Application number: EP98910732A
Authority: EP
Inventors: Ramiro Conde; Christian Depeursinge
Original assignee: Andromis SA
Current assignee: Andromis SA
Priority date: 1997-03-04
Filing date: 1998-03-02
Publication date: 2000-01-05
Also published as: WO1998039265A1; US6453090B1; US20020118908A1; JP2000509853A; US7302142B2

Abstract

The invention concerns an optical component (30) and a substrate (32) assembly comprising: the optical component, the substrate, a glass coating (34) located between at the interface between the optical component and the substrate. The invention also concerns an assembly between two optical components, particularly well adapted for being used in the field of imaging, in particular for endoscopy.

Description

METHOD AND DEVICE FOR ASSEMBLING OPTICAL COMPONENTS OR AN OPTICAL COMPONENT AND A SUBSTRATE

DESCRIPTION

Technical field and prior art

The invention relates to the field of assembly between two optical components, in particular an optical fiber and another optical component, the latter possibly being, for example, another optical fiber.

(in particular a multicore fiber), or a lens, or microlens (in particular a gradient index lens). Likewise, the optical fiber can be a multicore fiber. Another example of an optical element that can be assembled using the invention is a lens-prism assembly.

The invention also relates to the assembly of an optical component with a substrate, for example a metallic or semiconductor substrate. The component can be for example an optical fiber or a lens.

The article by K. Kinoshita entitled "End preparation and fusion splicing of an optical fiber array with a C0 ₂ laser" published in Applied Optics, vol. 18, n ° 19, pages 3256-3260, 1979 describes the welding of optical fibers using a C0 ₂ laser. The article by K. Egashira entitled "Analysis of thermal conditions in C0 ₂ laser splicing of optical fibers" published in Applied Optics, vol. 16, n ° 10, pages 2743-2746, 1977 also relates to a fiber-fiber coupling produced using a C0 ₂ laser.

The article by K. Nakatate et al. "Silica based rod lens for the medical fiberscope" released in Proceedings SPIE, 1994 concerns a fiber-lens link. It uses a technology identical to that of fiber-fiber welding carried out using an electric arc. It implies a fusion of the surfaces to be brought into contact.

This technique only applies to optical elements of small diameter (less than 200 μ). Microlenses are produced there by the same techniques as those used to make optical fibers: the glasses thus obtained for the lenses therefore melt at temperatures comparable to the melting temperatures of the fibers. Consequently, this technique cannot be applied, in general, to the production of an assembly of any two optical components.

In general, all of these techniques cause deformation of the contact surfaces by heating. In the case of a fiber-fiber coupling, the welding results in a deformation of the end of the fibers welded together. In addition, in general, the optical fibers are previously prepared by cleavage, but the perpendicularity of the interface relative to the axis of the fiber is not guaranteed by this technique. Welding therefore requires plastic deformation obtained by exerting axial pressure.

A known technique for assembling any two optical components, for example a lens and a prism, consists in making a bonding. But bonding is chemically sensitive to certain solvents, and ensures poor mechanical strength for small areas. In addition, it requires the introduction of a material (glue) which reduces the optical quality of the path that a beam can follow. Bonding is used, in particular, for the production of multi-core lens-fiber assemblies for the preparation of microendoscopes. Endoscopy, and in particular microendoscopy, allows a medical practitioner to acquire information, or images, from parts inside the human body, such as the stomach, lungs, heart, blood vessels, or the eye. A device for implementing such a technique is shown diagrammatically in FIG. 1, where the reference 2 designates a light source which is focused by a lens 4 at the entry of a light guide 6. The latter is in fact most often connected to a plurality of optical fibers 8, 10 disposed at the periphery of a multicore fiber 12. An illumination beam 14 can thus be directed onto an area 16 of an organ to be observed, which reflects radiation 18 on a lens 20 connected to the input of a multicore fiber 12. The latter comprising a coherent beam of individual hearts, these therefore transmit the light in an orderly manner between them, and the image obtained at output 22 of the multicore fiber corresponds to the image formed at its entry. Means for storing, analyzing and / or representing the image can also be provided in combination with this device.

This imaging technique is described for example in the articles by A. Katzir: "Optical Fibers in Medicine", Scientific American, vol. 260 (5), p. 120-125, 1989 and "Optical Fiber Techniques (Medicine)", Encyclopedia of Physical Science and Technology, vol. 9, p. 630-646, 1987. The current embodiment of the multi-core lens-fiber assembly is illustrated in FIG. 2. A metal tube or a sleeve 24 holds the lens 20 in front of the multi-core fiber 12, and an adhesive 26 makes it possible to ensure optical continuity and prevent the lens from coming out of the tube 24. This technique gives good results, but has the drawback of requiring delicate handling, of reducing the optical quality by introducing an additional medium 26 between the lens and the multicore fiber, and of make the endoscope very vulnerable to the sterilization steps required by heating.

In addition, bonding is done blind, in the tube 24, without precise control. Due to the tolerances of the sleeve or the tube, necessary to introduce the glue, this results in a random and very variable bonding.

In general, the assembly of two optical components or an optical component and a substrate, by bonding, also suffers from a certain brittleness and is not compatible with uses at high or very high temperature. , especially if sterilization is necessary.

Document US-5208885 describes a method for making a connection between a waveguide produced on a substrate and an optical fiber. A glass paste, the melting temperature of which is lower than a temperature at which the waveguide can be heated, is applied to the optical fiber and / or to the waveguide. The glass paste is heated to make the connection between the fiber and the waveguide.

More specifically, the glass may consist of a borosilicate-aluminum-lead mixture, and the heating

5 can be produced with a laser, for example a CO ₂ laser or an excimer laser.

The technique described in this document does not solve the optical problems, that is to say of optical disturbance and alteration of the beam.

K ⁾ when the latter must pass through the glass connection. The use of this technique with a view to producing an imaging device, for example an endoscope, is therefore excluded. In addition, the application presented concerns a weld between materials (in

15 glass) of similar compositions (Si0 ₂ / Si substrate with a weakly doped Si0 ₂ fiber) which melt at high temperatures, which leaves the choice, for welding, of multiple glass compositions melting at lower temperatures as well as different

20 production techniques.

The material used in this document, for welding (glass paste), is difficult to dose due to the evaporation of the binder which considerably modifies its volume.

In addition, the dough can undergo chemical alterations making it unsuitable for use in optics. In addition, the homogenization necessary to reduce the diffusion implies a temperature rise up to 1000 ° C, which is not acceptable

3o when certain optical components are to be brought into contact or welded together.

Finally, using glasses that melt at low temperatures is not necessarily an advantage if their optical (refractive index) and thermal (expansion) properties are too different from those of optical elements. For example, the respective expansion coefficients of a multicore fiber and a

5 lens are 5.10 ^"7 and 100.10 ^{" 7 respectively} .

Finally, the implementation described in this document (immersing the end of a fiber in a glass bath) does not allow precise control of the quantity of glass deposited, nor of

K ⁾ alignment of the elements to be welded before the layer is fused.

This technique also implies good wettability

EP-678 486 (Gould Electronics) describes a method for making a bond, or a side coating between glass-based components.

The assembly is carried out using a glass-based composition, which is heated, by

2o example using a C0 ₂ laser or by electric arc. The wettability properties of surfaces are essential for assembly.

Again, this document does not address the issue of optical transmission of the materials used. of the

25 degradations of the optical properties can occur, due for example:

- when a fiber is put under stress, which can induce variations in the refractive index and thus disturb the propagation of the signal, 0 - at optical absorption by lead glasses, which can produce an attenuation or a signal coloring, especially under the influence due to X-rays (for example when using an endoscope),

- the presence of binder residues in the case of glass pastes, or inhomogeneities, which can produce diffusion.

The link described in this document is therefore unsuitable for producing an imaging device, in particular an endoscope. In addition, here again, the application presented relates to the joining of elements made of materials close in terms of their compositions and which melt at high temperatures, which leaves the choice for multiple glasses melting at low temperatures. Finally, the technique used in this document does not make it possible either to carry out precise control of the quantity of glass deposited, or of the alignment of the elements to be welded.

None of the techniques set out above is, moreover, suitable for producing assemblies of very different materials, for example an optical component and a metallic or semiconductor or plastic or shape memory substrate. .

However, a lens-metal tube assembly is used, for example in rigid endoscopes. Another example of such an assembly is that of a shape memory material and an optical component, for example an optical fiber.

The only known technique for making such assemblies is, here again, the bonding technique, which has the drawbacks already explained above (instability of certain solvents, poor mechanical strength for small surfaces, introduction of a material (the glue) who disrupts the optical beams, or else decreases the optical quality of the path that a beam can follow).

It is therefore desirable to find an assembly technique making it possible to reduce the optical disturbance between the two elements to be assembled.

In addition, known techniques do not allow a precise adjustment of the surfaces to be brought into contact.

Finally, in the case of glass-to-metal welding, conventional welding techniques do not make it possible to eliminate the deformations of the glass.

Statement of the invention

The invention firstly relates to a method of assembling an optical component and a substrate, making it possible to avoid the drawbacks exposed above.

The invention therefore firstly relates to a method of assembling an optical component on a substrate, comprising:

a first step of depositing a layer of glass on at least one of the two faces, or surfaces, to be brought into contact,

a second step of bringing the two faces, or surfaces, into contact,

- A third step of heating the glass, making it possible to produce a weld between the optical component and the substrate.

The subject of the invention is also a method of assembling two optical components making it possible to avoid the drawbacks set out above, and can in particular be applied to the production of imaging devices, for example endoscopes.

The invention therefore also relates to a method of assembling first and second optical components, comprising:

a first step of depositing a thin layer of glass on one of the two faces, or surfaces, to be brought into contact,

- a second step of bringing the two faces, K) or surfaces into contact,

- a third step of heating the glass making it possible to produce a weld between the optical components.

In both cases, the weld, or solder, obtained has great mechanical strength and good thermal resistance.

In addition, in both cases, the glass layer is deposited on the active face (s) of the optical component (s), (2) i.e. on the or the face (s) intended to be crossed by radiation.

Furthermore, the glass layer is deposited

"in situ", without the need for subsequent spreading during assembly. The wettability of the surfaces to be contacted is therefore not essential to the process according to

1 invention.

The use of a thin layer of glass

(layer thickness between 0.1 μm and 10 μm) for welding makes it possible to reduce or avoid the problems of parallelism between the faces or surfaces to be brought into contact, and to avoid deformation of these faces or surfaces. In addition, a thin layer of glass does not not reduce the optical quality of the components, unlike a layer of glue or a drop of glass paste. In particular, the thin layer does not disturb, or only slightly, an optical beam passing through it: this is the case when it is located, for example, at the junction of two optical fibers.

Such a layer of glass can be used to bond or weld very different materials. In particular, the method according to the invention applies particularly well to the production of assemblies of optical components, or of an optical component and of a substrate, having different or very different coefficients of thermal expansion. A composition is then chosen for the glass of the thin layer having a coefficient of expansion intermediate between those of the components.

In the case of an optical component-substrate connection, the latter may be metallic or plastic or semiconductor or with shape memory or else a metallic layer deposited on a shape memory substrate, the optical component being for example a single core optical fiber, or multi-core optical fiber. Finally, the substrate may or may not be planar. Thus, it is possible to produce a lens-metal tube assembly, of the type of those used in conventional endoscopy. The invention also relates to an endoscope implementing such an assembly.

In the case of two optical components, one of the two components can be an optical fiber, with a single core or else a multicore fiber, the second optical component being for example or else an optical fiber (again with a single core, or multi-core), or well a microlens (for example with index gradient). Likewise, the first and / or the second optical components can both be a lens or a prism. In addition, the method according to the invention makes it possible to weld optical components of any size or diameter, less than or greater than 200 μm.

Another advantage of the glass layer is that, due to its ductility, it absorbs part of the mechanical stresses linked to possible respective expansions of the components. Thus, the final assembly suffers very little, or not at all, from the mechanical stresses from which components, for example, directly assembled by laser fusion can suffer.

We can therefore achieve, thanks to the glass layer, a precise adjustment of the surfaces to be contacted.

Furthermore, in the case of two optical components, an adjustment of the positioning of an element with respect to the other can first be made before heating, and this thanks to the use of the thin layer: 'use of a drop of glue, as in document US-5208885, does not allow any adjustment to be made before the intermediate glass liquefies.

Adjustment of the positioning can also be carried out during heating, using optical control means. In particular, when one of the optical components is a multicore fiber, it is possible to carry out a check by an interferometric device. The image of the fringes is transmitted by the multicore fiber. It will be noted that the glass layer is produced on the optically active part of the system. Furthermore, preferably, it does not contain lead, which can oxidize.

The use of a thin layer of glass also has the following advantage. A thin layer has a glass transition point lower than the melting temperature of the same material taken as a macroscopic volume. So we have a low font

K) temperature, which is already advantageous compared to the optical component (s) to be assembled, which can be affected by a rise in temperature too high.

The thinness of the layer makes it possible to decouple the

15 welding properties of the fusion properties. A gradual softening of the layer occurs during heating, which allows an adjustment of the surfaces. The temperature is increased to perform the actual welding which is linked to the energies

20 of activation at the interfaces between the elements present. Preferably, therefore, heating is carried out in two stages. A first step makes it possible to reach the softening temperature of the thin layer. In a second step, the temperature is brought to one

25 sufficient value to perform the actual welding. This second step can be brief (for example: on the order of a few minutes or less).

The heating step can for example be carried out by electric arc or by filament

3o (operating by Joule effect) or by laser. Heating by laser is better controlled in temperature. In the case of the laser, and for an optical fiber-optical component or optical fiber-substrate assembly, it it may be advantageous to arrange the laser beam and the fiber-component or fiber-substrate assembly so that, at the point of impact of the laser beam, the latter is offset on the side of the optical fiber. In this way, the absorption of the laser beam and the conductivity of the fiber are combined. Thus, the heated volume is moved to the side of the latter, and the heating does not affect, or little, the substrate or the component. Depending on the nature of the latter, an offset of a distance, measured between the center of the beam and the end of the fiber, of between ^{• a} few tens and a few hundred micrometers (for example between 50 μm and 200 μm or 300 μm , or between 90 μm and 170 μm) is appropriate. Heating by laser has, compared to other methods (electric arc, filaments), the advantage of offering great adaptability. The focus and the beam size are adaptable to the type of surface or object to be welded. A step of preheating the thin layer is possible, in order to increase its adhesion, without deforming it. This step can be carried out before the substrate and the optical element or component or the optical elements or components are brought into contact with each other. It strengthens the bond (combination of covalent and ionic bonds) between the glass layer and the surface on which it is deposited, which then promotes the actual welding.

Preferably, the glass used is an evaporable glass which, during its evaporation, retains the same chemical composition and the same physical properties as the original material. It is possible to choose, for the glass layer, a glass having a glass transition temperature of between 400 ° and 600 ° C, or between 400 and 500 ° C, for example a glass comprising a silica matrix doped with sodium and boron, for example also a silica matrix doped with a mixture B ₂ 0 ₃ -Al ₂ 0 ₃ -Na ₂ 0- K ₂ 0. Glasses doped with germanium also have a low glass transition temperature. Thus, the glass transition takes place at relatively low temperatures compared to the critical temperatures of most optical components, for example of optical fibers with one core or with several cores. In the case of optical components having a certain brittleness to thermal shocks or a risk of thermal deformation of the index profile (for example lens with index gradient used in endoscopy) this aspect may prove to be important.

The invention also relates to an assembly of an optical component and a substrate comprising, in addition to the component and the substrate, a layer of glass located at the component-substrate interface.

The invention also relates to an assembly of two optical components comprising, in addition to the two components, a thin layer of glass located at the interface between these two components.

As already explained above, the substrate can be metallic or of semiconductor type, or plastic or with shape memory, and the optical component (s) can be one, or , optical fiber (s) (single core, or multi-core) or a microlens (gradient index) or a lens, or a prism. The glass can be an evaporable glass, as defined above.

The invention also relates to an endoscopic device comprising a multicore fiber and a lens fixed to the end of the fiber by means of a layer of glass located at the lens-fiber interface.

Finally, the invention also relates to an endoscopic device comprising a multicore fiber, a lens connected to this multicore fiber, means for lighting an area to be observed, the connection between the lens and the fiber being made of a material. supporting the sterilization temperature and the humid heat of an autoclave.

The lens-fiber connection is for example produced by a thin layer of glass according to one or other of the embodiments already described above.

Brief description of the figures

In any case, the characteristics and advantages of the invention will appear better in the light of the description which follows. This description relates to the exemplary embodiments, given by way of explanation and without limitation, with reference to the appended drawings in which:

FIG. 1 diagrammatically represents an endoscopic device,

FIG. 2 shows more precisely the fiber-to-lens connection of an endoscopic device according to the prior art, FIG. 3 represents a fiber and a substrate to be assembled,

FIGS. 4A-4C represent steps of a fiber-substrate assembly method according to the invention,

FIG. 5 is an example of assembly of an optical component with a metal layer deposited on a shape memory material,

FIG. 6 represents two fibers intended to be assembled by a method according to the invention,

FIGS. 7A-7C represent steps for assembling two fibers, according to the invention,

FIG. 8 represents a fiber and a lens intended to be assembled by a method according to the invention,

FIGS. 9A-9D represent steps for assembling a fiber and a lens, according to the invention,

FIGS. 10A and 10B respectively represent a device for producing a weld according to the invention, and a device for controlling the end of a fiber,

- Figure 11 shows another device for making a weld according to the invention, - Figures 12A and 12B show cross-sectional views of a multi-core optical fiber.

Detailed description of embodiments of the invention FIG. 3 represents an optical fiber, for example with a single core, or even a multicore fiber. This fiber 30 is intended to be connected to an optical component (for example: a lens or a prism) or else to a substrate 32, for example a metallic substrate or a semiconductor type substrate (for example made of silicon, or GaAs, or ....). To this end, a layer 34 of glass is first deposited on the end of the fiber 30 (FIG. 4A). We preferably choose an evaporable glass. The glass layer can be deposited by plasma (pulse). It can also be carried out by evaporation, for example from a glass target bombarded by electron beam: the control of the evaporation time makes it possible to control the thickness of the layer. A thin layer, of thickness less than or equal to a few micrometers or 10 μm, for example equal to or substantially equal to 1 or 2 μm, or 3 μm or 5 μm, or to a few tenths of micrometers, for example 0.1 μm, can suit. The layer obtained is therefore evaporated in molecular form.

To deposit the glass layer, it is also possible to use the "spin-on-glass" techniques known and mastered in the field of microelectronics. The silica glass is generally mixed with organic solvents and then, after heating to typical temperatures of the order of 500 ° C. for typical times of a few hours, an extremely resistant glass layer is obtained. One can then deposit a layer on the surfaces, then centrifuge to obtain a layer of defined thickness (the thickness values are those given above) and planar. Cooking then creates the layer of glass with the right characteristics. The layer obtained does not contain a binder which should then be removed in a subsequent step. The fiber, provided with its glass layer, is then brought into contact with the surface 32 (FIG. 4B). Precise positioning can be achieved due to the thinness of the glass layer and the absence of binder to be removed. This is, upon filing, in almost final form.

Then, a heating step is carried out (FIG. 4C): this heating can be carried out by laser, or by electric arc, or by filaments wound in turns on a cylinder with a diameter greater than the diameter of the elements to be assembled, or else by any another known heating method enabling the glass transition temperature of the glass to be reached. After cooling, the fiber-substrate assembly is securely assembled. The laser heating method is the most adaptable for each particular case.

According to a variant, the elements are heated, and in particular the fiber 30 and the glass layer 34, prior to the assembly proper. This promotes ion exchange before assembly.

The invention also relates to the assembly of any optical component and of a substrate itself which is not necessarily planar. For example, the invention can be applied to a lens to be fixed in a metal tube. Such an assembly is used in rigid endoscopes for medical or industrial use. The invention then makes it possible to locate the lens in any position relative to the substrate. The assembly takes place as indicated above: a layer of evaporable glass is deposited on one of the surfaces to be assembled, then the two surfaces are brought into contact with one another, the layer of glass being located at the interface. The heating is carried out by laser or by electric arc, or by filaments wound in turns on a cylinder with a diameter greater than the diameter of the elements to be assembled, or else by any other known heating method making it possible to reach the glass transition temperature of the glass.

Another example of assembly concerned by the invention is an assembly of an optical component with a shape memory material or with a material deposited on a shape memory material. Thus, as illustrated in FIG. 5, it is possible to deposit a metallic layer 35 on an element 37 (having the shape indicated in solid lines or that, more curved, in broken lines) in a material with shape memory (for example an alloy NiTi or CuZnAl or NiTiCu).

An optical fiber 30 is welded to the metal layer by the technique described above: first, on the end of the fiber 30, a layer of glass 34 is deposited (evaporable glass, deposited by evaporation from '' an electron beam bombarded target). The fiber, provided with its glass layer is then brought into contact with the metal, then heating is carried out (laser, electric arc, etc.) to reach the glass transition temperature of the glass.

After cooling the fiber-metal substrate assembly, and therefore the fiber-substrate-element assembly made of shape memory material, are securely assembled. The fiber can convey light energy necessary for heating, and therefore for controlling, the shape memory material. FIG. 6 represents two optical fibers 36, 38 each having an end surface 37, 39, these two surfaces being intended to be brought into contact. These fibers can be fibers with a single core, for example monomode or multimode fibers. Multicore fibers, or multifibers, which can be used in microendoscopy are also concerned. At the end of one of the two fibers, a deposit of glass 40 is made (FIG. 7A), for example by the technique mentioned above (evaporation by bombardment by electron beam). The two fibers are then positioned relative to each other (FIG. 7B) and brought into contact, the glass layer 40 being at the interface between the surfaces 37, 39. The assembly is then heated (FIG. 7C ), for example by laser beam, or by electric arc, or by any other method making it possible to provide the heat necessary to reach the glass transition temperature of the glass layer 40. After cooling, a solid bond is established between the two fibers without deformation thereof. Again, laser heating has, compared to other methods, the advantage of adaptability to the various possible configurations. In arc welding a gap lets the spark through and the system cannot be assembled beforehand.

Another example concerns the assembly of an optical fiber 42 and a lens 44 (FIG. 8). The lens may in particular be a gradient index lens (GRIN lens). The two elements are intended to be brought into contact via their end surfaces 43, 45. On one of these surfaces, a layer of glass 46 is deposited, for example by the technique already described above (FIG. 9A). Then, the two elements are brought opposite one another (Figure 9B). They are then brought into contact with each other, the layer 46 being located at the interface of the surfaces 43, 45, and the assembly is heated (FIG. 9C) using one of the techniques already mentioned. above with their advantages and disadvantages. After cooling, a very solid lens-fiber bond is obtained, and practically without any deformation of the lens or the fiber.

This technique is particularly advantageous in the case of lenses having characteristics very different from the characteristics of the fibers. This is the case for lenses used in endoscopy, at the end of a multi-core fiber: the glass transition point of these lenses is much lower than that of multi-core fibers and, therefore, the lenses soften much more faster than fibers. In addition, the lenses do not withstand long-term heating which would modify the distribution of thallium ions, therefore the optical properties of the lens. Direct welding of the two elements, for example by laser C0 ₂ or by electric arc therefore causes deformations of the lens. This results in a degradation of the quality of the images. In addition, certain lenses are produced by diffusion of cations into the material (such lenses and their composition are for example described in document FR-2 004 043) and excessive temperatures modify the refractive indices, and therefore the optical properties of the lenses. lenses. Such excessive temperatures are reached when direct welding of the lens with the fiber is carried out. Consequently, in certain cases, it proves appropriate to locate and move the heating zone, on the side of, and in the direction of the element least sensitive to the heat supply, for example on the side of the fiber in in the case of a lens-fiber assembly or in the case of a substrate-fiber assembly. Thus, in FIG. 9D, the arrows 48, 50 show diagrammatically a localized heat supply on the side of the fiber 42, at a distance d from the fiber-lens or fiber-substrate interface, and being for example between 90 μm and 170 μm . The fiber conducts heat towards the glass layer, until it reaches its glass transition temperature. Thus, the supply of heat to the lens 44, or to the substrate, is extremely limited. In such a case, the use of the glass layer makes it possible to limit the deformation of the elements; indirect heating of the glass layer, via the fiber 42, makes it possible not to affect the optical properties of the lens 44, or not to affect the substrate.

In general, it is preferable to use a glass layer with a glass transition point of, for example, between 400 ° C and 600 ° C or between 400 ° C and 500 ° C (for example of the order of 500 ° C). Such a range of temperatures, which can be considered to be low for carrying out a glass transition of the glass, makes it possible to limit the supply of heat to the optical component (s). A glass having this property can consist of silica doped with sodium and boron. This is for example a silica matrix doped with a mixture B ₂ 0 ₃ -A1 ₂ 0 ₃ - Na ₂ 0-K ₂ 0 (for example: Si0 ₂ : 78-83%; B ₂ 0 ₃ : 11-13%; A1 ₂ 0 ₃ : 2-4%; Na ₂ 0: 1-3%; K ₂ 0: traces; an evaporated layer may differ from this composition, because the different compounds do not evaporate with the same ease).

A glass of this composition has an expansion coefficient of 27,5.10 ^{~ 7} (intermediate between that of a multicore fiber (5.10 ^-7) and that of a lens (10 ^{~ 5)),} a glass transition temperature intermediate between 560 ° C and 580 ° C (for the lens), an optical attenuation of 4.10 ^{~ 2} % over the visible radiation range and for thicknesses of a few micrometers, and a refractive index (1.4689) very close to that of 'an optical fiber.

The method according to the invention is well suited for assembling elements of fairly different refractive index. This minimizes Fresnel losses, the index of the intermediate glass layer lying between the indices of the two elements to be welded. For example, for a fiber composed of silica, the index of pure silica being approximately 1.46, and for a lens with gradient of radial index obtained by diffusion of thallium ions, of index greater than or equal to 1.6, the layer may have an index of approximately 1.47.

The use of an evaporable glass, instead of a glass paste, makes it possible to overcome the problems associated with the use of this latter material. Glass paste is difficult to dose due to the evaporation of the binder which considerably changes its volume. In addition, this evaporation produces bubbles which can be incorporated into the material. A paste glass can also undergo chemical alterations which can make it unfit for use with an optical component. Finally, the homogenization necessary to reduce the diffusion involves a temperature rise up to 1000 ° C., which is unacceptable for a system using an optical component.

The invention is not limited to the assembly examples given above: any two optical components can be assembled by the technique according to the present invention. In particular, prism-lens assemblies can be produced, a layer of glass being deposited at the interface of the surfaces intended to be in contact. Two optical components being assembled, they can be assembled with a third component. An assembly of N components can thus be produced in which intermediate components (portholes, or spatial or spectral or interferometric filters, or polarizing layers) are included between two end components. For example, one or more portholes can be used to adjust the distance between an optical fiber and a lens. In addition, a layer of glass can be deposited on the two surfaces intended to be in contact. This can be particularly interesting if the materials to be assembled are very different: with a layer of glass on each of the materials, the welding is easier and of better quality.

Finally, the surfaces intended to be in contact can be flat or not. The fact of using, in accordance with the invention, a thin layer to make the connection between two optical components, or between an optical component and a substrate, has the following advantages: - precise presetting between the elements is allowed,

- the fusion is carried out at low temperature (indeed, a thin layer melts at a lower temperature than the material in macroscopic volume), - the deposit is controllable with very high precision, in terms of its optical quality, its composition, its thickness and its adhesion, the optical importance of this intermediate layer is reduced: the thin layer can therefore be crossed by an optical beam without disturbing it in a notable manner, stress overloads on the interfaces are avoided, because the thin material is more elastic.

An example of a device for carrying out the welding of two optical components, for example a fiber 42 and a lens 44, will be described in connection with FIG. 10A. This device uses a laser C0 ₂ 50. The laser beam is divided in two by a semi-transparent mirror 52. A part of the beam is taken beforehand in the direction of a detector 54, in order to control the output power of the laser. A set of mirrors and lenses 56, 58 makes it possible to focus the two beams on the welding site, in order to obtain a local and homogeneous heating zone. A mechanical xyz displacement system allows the position between the lens and the multicore fiber. Once the system is assembled, the lens-fiber contact area is placed in the laser beam. A thin layer of evaporable glass, which has been previously deposited on one of the surfaces to be brought into contact, ensures the weld between the two elements.

Optical control means or systems 60, 62 can be used to achieve relative optical positioning of the components during the assembly step, in particular to control the parallelism between the facing surfaces of the lens and the fiber (system 60) and / or the relative positioning (laser diode 62) between the fiber and the lens (centering) and / or between the fiber-lens system and the focused beams (along an axis). The optical control means therefore allow a possible correction of the relative position of the components during the actual welding step. A helium-neon laser 64 also makes it possible to control the positioning of the fiber-lens system relative to the focused beams (along the other two axes).

Such an optical control, during welding, is impossible to achieve with either of the techniques of the prior art, the latter requiring positioning before the welding step, therefore less precise positioning.

The system 60 is shown more precisely in FIG. 10B. Part of the beam of a laser diode 70 is injected into the fiber 42. The beam introduced into the fiber is reflected at the output interface of the latter and at the input interface of the lens. These two reflected signals interfere to form an interference figure, with interference lines, detected by a CCD 72 camera. The distance between the lines and the orientation of these lines makes it possible to control the relative orientation of the two faces to be

5 contact. The interference pattern can be viewed on a display device 74. This approach can be generalized to all surface shapes, since this system simply measures the distance between these two surfaces. This procedure also makes it possible to evaluate

10 quickly if the interfaces are flat or if they have faults. Finally, it also makes it possible to follow the progress of the weld in real time.

The laser beam emitted by the laser diode 62 forms a point of light on the rear face of the

15 lens, by simple focusing. This light point can be centered by direct observation through the multi-core fiber 42, the camera 72 and the display device 74.

An example of a device for performing the

20 welding of an optical component, for example a fiber 49, and a substrate 47, will be described in connection with FIG. 11 in which reference numerals identical to those of FIG. 10A designate identical or corresponding elements therein. The beam of

^{• j} -s laser C0 ₂ 50 is divided in two by a semi-transparent mirror 52. A part of the beam is taken beforehand in the direction of the detector 54, in order to control the output power of the laser. A set of mirrors and lenses 56, 58 makes it possible to focus the

3o two bundles on the welding site, in order to obtain a local and homogeneous heating zone. A mechanical xyz displacement system allows the position between the fiber and the substrate to be adjusted. Once the assembled system, the substrate-fiber contact area is placed in the laser beam. A thin layer of glass, which has been previously deposited on one of the surfaces to be brought into contact, ensures the welding between the two elements.

An assembly between a gradient index lens and a multicore fiber can be used in a microendoscopy device. The principle of

K) operation of such a device has already been described in the introduction to the present application, in connection with FIG. 1: such a device essentially comprises a multicore fiber 12, a lens 20 connected to this fiber, and means 2 , 8, 10 for

15 illuminate an area 16 to be observed; means for storing, analyzing and / or representing an image of the area 16 can also be provided in combination with this device. The operating principles of this device are also described in the articles

20 by A. Katzir already mentioned above. A multi-core lens-fiber assembly obtained by a method according to the invention makes it possible to produce endoscopic images of better quality, due, in particular, to the absence of deformation of the lenses and of the fiber.

25 multi-core.

We will recall in connection with Figures 12A and 12B the structure of a multicore fiber.

A multicore fiber is a bundle of fibers, melted and stretched, which therefore forms a continuous whole. The

3o coat of each individual fiber is melted with the coats of neighboring hearts. Inside a multi-core fiber one can only distinguish individual hearts, the mantle of fibers having become somewhat collective.

FIG. 12A represents a cross-sectional view of a multi-core fiber, the hearts 84 and the coats 86 being grouped inside a first sheath 88, for example made of silica, and a second sheath 90, called sheath external or "black" coating. The outside diameter Dι_ of the assembly can for example be of the order of 200 to 500 μm.

FIG. 12B is an enlarged view of the portion 92 of the bundle of hearts. In this FIG. 12B, it appears that the hearts have cross sections of variable shape, more or less homogeneous. In particular, the diameter d of each heart, that is to say the greatest distance separating two points from the same heart, varies from one heart to another. Typically d can, for example, vary between 3 and 4 μm for the same multicore fiber. Likewise, the average distance from one core to another is not uniform and can, for example, vary, for the same multicore fiber, from 3 to 3.5 μm.

Since the thickness of the glass layer is less than or of the same order of magnitude as the characteristic diameter or dimensions of the cores of a multicore fiber, this results in a reduction in the problems of light diffraction at the multicore fiber interface. optical component.

In the case of application to an imaging device, and in particular to an endoscope, this makes it possible to maintain a high spatial resolution.

In the case of a multi-core fiber, possible deformations due to direct welding between the fiber and another element, in particular a lens, are not compatible with the use of fiber in the field of imaging. In addition, the deformations mainly affect the peripheral hearts, and they are therefore inhomogeneous on all the hearts. This aspect relating to deformations is therefore even more troublesome in this type of fiber than in fibers with a single core. In fibers with a single core, only the central portion of the core, which represents only a tiny portion of the lateral surface, must be little or not deformed with conventional methods.

Furthermore, the intermediate glass layer is much less sensitive to water vapor and to sterilization pressures and temperatures (approximately 134 ° C., to the humid heat of the autoclave) than the adhesives usually used. This better resistance to sterilization and to water vapor leads to a longer lifespan of the endoscope and therefore a reduction in costs corresponding to the use of this type of material.

The use of lead-free glass to make the connection between two optical components makes it possible, in the case of a multi-core fiber-to-lens link, to avoid any problem of coloration of the optical signal passing through the glass layer. Indeed, positioning of the endoscope in the body is often carried out using X-rays, simultaneously with the endoscopic visualization itself. Finally, the weld produced in accordance with the invention, that is to say using a thin layer, has the following property. The thin layer reacts mainly, during the formation of the bond with the fibers, with the hearts present in the multicore fiber and which are doped with germanium. This element makes it possible to lower the glass transition point as a direct function of the concentration. As the hearts have an index gradient, the attachments are created at the center of the hearts and then spread to the periphery, the connection being less strong with the inter-heart areas, which are not or only slightly doped with favorable elements. welding, germanium type.

This property remains valid for many optical components into which germanium doping is introduced. This is particularly the case for single, single-mode or multimode optical fibers. The invention thus applies to fibers having various compositions, for example based on fused silica with a core doped with Ge, and optionally with fluorine, or based on fluorinated glass or based on silver chalcogenide, or sapphire, or "Tex" glass. In the case of a connection between a multi-core fiber and a Selfoc or GRIN lens, the alkaline ions contained in the glass layer (silica) diffuse on both sides, towards the fiber and towards the lens. The cores of the fibers of the multicore fiber have a lower melting point than that of silica, and there is a diffusion towards the hearts of the multicore fiber. On the lens side, there is in fact an interdiffusion phenomenon: thallium ions from the lens diffuse towards the glass layer and alkaline ions diffuse from the glass layer towards the lens.

The bond established is therefore a bond by ion exchange, and the wettability of the surfaces by the material constituting the glass layer is therefore not necessary.

The invention therefore makes it possible to produce the lens-fiber connection of an endoscope. This bond has properties, already given above, of resistance to humidity, and to sterilization pressures and temperatures. In general, the invention also covers any lens-fiber link compatible both with use in endoscopy and having this resistance to humidity and sterilization temperatures.

Claims

1. Method for assembling an optical component (30) on a substrate (32), comprising:

a first step of depositing a thin layer (34) 5 of glass on at least one of the two surfaces to be brought into contact,

- a second step of bringing the two surfaces into contact,

a third step of heating the glass, allowing K) to produce a solder between the optical component and the substrate.

2. Method according to claim 1, the substrate (32) being glass or metallic or plastic or shape memory or semiconductor.

3. Method according to claim 1, the substrate (32) being a metallic layer deposited on an element made of a shape memory material.

4. Method according to one of claims 1 to 3, the optical component (30) being an optical fiber to

20 a single core or a multicore optical fiber.

5. Method for assembling a first (36, 42) and a second (38, 44) optical components, comprising:

a first step of depositing a thin layer (40) 25 of glass on at least one of the two surfaces (37, 39,

43, 45) to put in contact,

- a second step of bringing the two surfaces into contact,

a third step of heating the glass allowing a solder to be produced between the optical components.

6. Method according to claim 5, the first optical component being an optical fiber (12, 36, 42).

7. The method of claim 6, the optical fiber being a multicore fiber.

8. The method of claim 7, a control of the positioning of the multicore fiber and the second optical component being carried out during the third step, using an interferometric device.

9. Method according to one of claims 6 to 8, the second optical component being an optical fiber (38).

10. The method of claim 6 to 8, the second optical component being a multicore fiber.

11. Method according to one of claims 5 to 8, the second optical component being a microlens ^ (20, 44).

12. The method of claim 11, the microlens being a gradient index lens.

13. The method of claim 5, the first and / or the second optical component being a lens or a prism.

14. Method according to one of claims 3, or according to one of claims 6 to 12, the heating being carried out by laser beam (48, 50), the laser beam and the optical fiber assembly (42) - optical component. (44) or optical fiber (42) -substrate, being arranged so that, at the point of impact on the fiber-component or fiber-substrate assembly, the beam is offset on the side of the optical fiber.

15. The method of claim 14, the beam o being offset by a distance (d) between

90 μm and 170 μm, measured between the center of the beam and the end of the fiber.

16. Method according to one of claims 1 to 13, the heating step being carried out by electric arc.

17. Method according to one of claims 1 to 13, the heating step being carried out by laser beam.

18. Method according to one of claims 1 to

17, the step of heating the glass comprising two sub-steps: a first sub-step during which a softening temperature of the glass is reached,

- A second sub-step during which the temperature is brought to a value sufficient to perform the actual welding.

19. Method according to one of claims 1 to

18, the glass being an evaporable glass.

20. Method according to one of the preceding claims, the glass (34, 40, 46) having a glass transition temperature between 400 and 500 ° C.

21. Method according to one of claims 1 to 20, the glass comprising a silica matrix doped with a mixture B ₂ 0 ₃ -Al ₂ θ ₃ -Na ₂ θ-K ₂ 0.

22. Method according to one of the preceding claims, further comprising a step of preheating the thin layer.

23. The method of claim 22, the preheating taking place after deposition of the thin layer on one of the two surfaces to be contacted but before contacting the two surfaces.

24. Assembly of an optical component (30) and a substrate (32) comprising: - the optical component,

- the substrate,

- a thin layer of glass (34) located at the interface between the optical component and the substrate.

25. The assembly of claim 24, the substrate (32) being metallic or semiconductor or plastic or shape memory, or else being a metal layer deposited on an element made of a shape memory material.

26. Assembly according to one of claims

24 or 25, the optical component (30) being a single-core optical fiber or else a multi-core optical fiber.

27. The assembly of claim 24, the optical component being a lens and the substrate being a metal tube.

28. Endoscopic device comprising at least one metal tube and a lens forming an assembly according to claim 27.

29. Assembly of a first (36, 42) and a second (38, 44) optical components, comprising the first and second optical components, as well as a thin layer of glass (10, 46) located at the interface between optical components.

30. The assembly of claim 29, the first optical component being an optical fiber or a lens or a prism.

31. An assembly according to claim 29, the first component being an optical fiber (38, 44) with a single core or else a multicore fiber.

32. An assembly according to one of claims 29 to 31, the second optical component being a single-core optical fiber or else a multi-core fiber.

33. Assembly according to one of claims 29 to 31, the second optical component being a lens or a prism.

34. An assembly according to claim 29 to 31, the second optical component being a microlens.

35. An assembly according to claim 34, the microlens being with index gradient.

36. Assembly according to one of claims 24 to 35, the glass having a transition temperature

K) glassy between 400 and 500 ° C.

37. Assembly according to one of claims 24 to 35, the glass having a silica matrix doped with a mixture of B ₂ θ ₃ -Al ₂ θ ₃ -Na ₂ θ-K ₂ 0.

38. Assembly according to one of claims 15 24 to 37, the glass being an evaporable glass.

39. Endoscopic device comprising a multi-core fiber and a lens constituting an assembly according to one of claims 29 to 38.

40. Endoscopic device comprising a multicore fiber (12), a lens (20) connected to this multicore fiber, means (8, 10) for lighting an area to be observed, the connection between the lens (20) and the fiber (8) being made of a material supporting the sterilization temperature, the pressure and the humid heat of an autoclave.

41. Endoscopic device according to claim 40, the connection between the lens (20) and the fiber (8) comprising a thin layer of glass located at the interface between the fiber and the lens.

30