FR2675910A1 - MATRIX OF OPTICAL CONCENTRATORS, OPTICAL ASSEMBLY COMPRISING SUCH A MATRIX, AND METHOD OF MANUFACTURING THE MATRIX. - Google Patents

Abstract

A matrix of optical concentrators (1) characterized essentially in that the concentrators (1) are optically independent rotationally symmetrical reflectors filled with a light-transparent optical material (2) having a refractive index n close to that of the fibre cores. An optical emission or reception assembly, wherein the concentrator matrix provides the coupling between the emitter (or receiver) matrix and an optical fibre matrix, and a method for producing said concentrator matrix, are also provided. Applications: coupling optical fibres with end components.

Description

MATRIX OF OPTICAL CONCENTRATORS, SET
OPTICS COMPRISING SUCH A MATRIX AND
MATRIX MANUFACTURING PROCESS
DESCRIPTION
The invention relates to a linear or two-dimensional matrix of optical concentrators, to an optical transmission or reception assembly comprising such a matrix. The invention also relates to a method of manufacturing such a matrix.

It is known in the field of solar energy the use of large conical concentrators as a single element which can be found in the article entitled "The Optics of non Imaging Concentrators, Light and
Solar Energy ", WT Welford and R. Winston, Academic
Press, 1978.

 However, the use of these concentrators is reserved for this particular field by their dimensions and the technologies used.

 The Applicant has encountered, in a completely different field since it is the transmission of light by optical fibers, the coupling of optical fibers to the end components. The end components can be either light sources (emitters) or receivers.

 They are semiconductor electronic components generally of small dimensions.

The dimensions are all the smaller as one seeks to work at high frequencies.

 The coupling between an optical fiber and such components is a delicate operation which has not so far produced excellent results. These results are all the less satisfactory insofar as it is sought to couple the fibers to components having increasingly small contact surfaces.

 In addition, we seek to obtain the best possible coupling (optimum coupling) between transmitter (or receiver) and optical fiber when using clear, scintillating or fluorescent plastic optical fibers.

In addition, in addition to the need to have a very good quality coupling between the fiber and
The transmitter or the receiver corresponding to it, we are confronted more and more often in Most applications with the need to make a very large number of connections: some devices can include several thousands and up to several hundreds of thousands of fibers . It is therefore very important to have systems that allow these many connections to be made quickly and safely.

 When it is desired to read a set of fibers with a single receiver, the fibers gathered in strands and polished at their ends are placed in optical contact with the active surface of the receiver.

Things get more complex if we try to read these fibers individually.

 Consequently, to date there are few solutions allowing perfect coupling between the optical fibers of large diameter and the end components (transmitters, receivers). A solution generally adopted and giving a result considered to date as the least bad, consists in placing the component directly at the end of the fiber.

This supposes acceptance of optical losses, namely loss of digital aperture at the input, attenuation in the ratio of the surfaces at the output.

 Conventional dioptric systems are rarely used because they generally have digital apertures that are too small compared to those of optical fibers.

 A solution has sometimes been used in the case, for example, of fibers read by a multi-anode photomultiplier. As a spherical lens, a sapphire ball, a material with a high optical index, is interposed between the two systems to improve coupling.

 This ball, the diameter of which must be approximately 1.5 times the diameter of the fiber, imposes a large minimum pitch between the fibers and is no longer usable as soon as it is contemplated to read plies of contiguous fibers.

 On the other hand, it should be noted that in this case, an image is obtained which is smaller in size than that of the fiber on the receiver.

 Furthermore, this method assumes the individual placement of the beads between the fibers and the receptors, which becomes complex or tedious as soon as the number is large.

 Another possibility of coupling is to use a fiber optic reducer ("type" according to the English term). This device has, in addition to its cost, two drawbacks.

 The first is that the digital aperture is reduced. The second is that there are generally no such size elements corresponding to a single fiber.

 Applied to a matrix of fibers, a "tap" reduces not only the image of the end of a fiber, but also the whole of the pitch of the image of the fibers, and therefore imposes a very small pitch on the components of 'end.

 Another example shows a coupling effort between optical fiber and avalanche photodiode.

The commercially available component uses a fiber optic element of 300 / in diameter to make the connection between the photodiode of the same diameter and the front face of the case which contains it.

 Compared to the simple positioning of the fiber against the window of the shoemaker, this device allows better coupling with the fiber of which one would like to measure the output signal, but remains penalizing due to a weak numerical aperture and a low ratio between the surfaces of the two fibers (9% for a 1 mm fiber).

 The present invention overcomes these problems. It firstly relates to a linear or two-dimensional matrix of concentrators capable of being connected to optical fibers, comprising a set of optical concentrators and mainly characterized in that the concentrators are optically independent reflectors, with symmetry of revolution, filled with an optical material transparent to light with a refractive index n close to that of the core of the fibers.

 According to a second characteristic of the invention, the transparent optical material is chosen so that the refractive index n is greater than 1.56.

 According to another characteristic of the invention, the concentrators are joined together to form the matrix, by a retaining material.

 According to another characteristic of the invention, the holding material is a polymerized resin.

 According to another characteristic, the concentrators further comprise a reflective material which coats the internal wall of said concentrators and which forms an optical separation between the retaining material and the transparent optical material.

 According to another characteristic of the invention, the reflective material consists of a metal layer.

 According to another characteristic, the concentrators have a shape with symmetry of revolution generated by a straight or curvilinear generator.

 The subject of the invention is also an optical transmission or detection assembly comprising a matrix of optical fibers, a matrix of transmitters or receivers, mainly characterized in that it further comprises means of optical coupling between the matrix of optical fibers and the matrix of transmitters or receivers, and in that these coupling means comprise a matrix of concentrators formed of optically independent retro-reflectors with symmetry of revolution, filled with an optical material transparent to Light, of index of refraction close to that of the core of optical fibers.

 According to another characteristic of the invention, the optical assembly further comprises an optical contact material of optical index suitable for reducing Fresnel reflections and avoiding total reflections on the outlet face of the concentrators, this material being placed so as to ensure contact between the matrix of transmitters or receivers and the matrix of concentrators, and between the matrix of concentrators and the matrix of optical fibers.

 In this optical assembly, the concentrators are joined together by a retaining material to form the matrix.

 The holding material is a polymerized resin. The concentrators further include a reflective material which coats the interior wall and which forms a separation between the retaining material and the transparent optical material.

The invention also relates to a method for manufacturing a linear or two-dimensional matrix of optical concentrators intended to be coupled to a matrix of optical fibers, mainly characterized in that it comprises the following steps
- make a base mold comprising a matrix arrangement of male elements with symmetry of revolution,
- make a counter-mold of the base mold to obtain a matrix arrangement of female elements of shape complementary to that of the male elements,
- pour a material in the pure counter mold to obtain a new mold made up of male elements,
- pouring a retaining material over the male elements making it possible to ensure mechanical cohesion between the different optical elements which will be obtained subsequently and demold, after hardening, the matrix obtained,
optionally depositing a material in a thin layer inside the hollow shapes obtained after demolding, a layer which will serve to ensure the optical separation between the different elements,
- pouring a transparent optical material with a refractive index n close to that of the core of the fibers above the thin separation layer, so as to fill the hollow shapes of the matrix after demolding and to obtain an extra thickness,
- Machining the upper and lower faces of the matrix so as to remove the excess thickness of optical material of index n.

The invention also relates to a method for manufacturing a linear or two-dimensional matrix of optical concentrators intended to be coupled to a matrix of optical fibers, mainly characterized in that it comprises the following steps
- produce a basic mold comprising a matrix arrangement of male elements, with symmetry of revolution,
- make a counter-mold of the base mold to obtain a matrix arrangement of female elements of shape complementary to that of the male elements,
- pouring a transparent optical material with a refractive index n close to that of the core of the fibers in the counter-mold, leaving an additional thickness to obtain a matrix of optical elements,
- after hardening of the optical material and demolding, possibly depositing a material in a thin layer to ensure optical separation between the different elements,
- pouring a retaining material on the matrix obtained to ensure mechanical cohesion between the different optical elements,
- machine the upper and lower faces of the matrix so as to remove the extra thicknesses of optical material of index n to obtain the matrix of concentrators.

 According to another characteristic of this manufacturing process, the material of refractive index n is a polymerized optical resin whose index n is greater than 1.56.

 According to another characteristic, the retaining material is a polymerized resin.

 According to another characteristic, the deposition in a thin layer consists in producing a metallization.

Other advantages and characteristics of the invention will appear on reading the description which is given by way of illustration and not
Limiting, with reference to the appended drawings in which
FIG. 1 represents the diagram of a two-dimensional matrix of optical concentrators according to the invention,
FIG. 2 represents diagrams corresponding to the different stages of the process for manufacturing a matrix in accordance with a first embodiment,
FIG. 3 represents diagrams corresponding to the different stages of production of a second embodiment of the method of manufacturing the matrix according to the invention,
FIG. 4 represents the diagram of an optical reception assembly in accordance with the invention,
- Figure 5 shows the diagram of an optical transmission assembly according to the invention.

 FIG. 1 shows the diagram of a matrix of concentrators according to the invention.

This diagram represents a two-dimensional matrix provided with a set of optical concentrators 1.

 These concentrators are, in accordance with the invention, optically independent reflectors, with symmetry of revolution.

 Preferably, these reflectors have a shape such that they are generated by a straight or curvilinear generator. They can therefore have a conical or paraboloid shape.

 According to the invention, the retro-reflectors are filled with an optical material 2 transparent to light, with a refractive index n close to that of the core of the optical fibers with which the matrix produced can be coupled.

 To produce such a matrix, the concentrators are joined together by a retaining material 3.

 The retaining material used 3 consists for example of a polymerized resin which may, depending on the case, be rigid or not.

 Thus, the matrix represented in FIG. 1 comprises a set of optically independent systems, these systems being Concentrators 1, the size, number and pitch of which may be any, but will generally be chosen identical to those imposed by the matrix of components d end or matrix of optical fibers between which it will perform a coupling, as will be explained below.

 According to an improvement of the invention, the internal wall of the concentrators producing the separation between the retaining material 3 and the transparent optical material 2 is coated with a reflective layer protected by the optical material filling the concentrators.

 This protection is similar to the protection provided by the low-index coating constituted by the sheath of an optical fiber on which the total reflections of the light propagated for the core of the fiber occur, the medium in which the Light propagates.

 The hub matrix is an extension of the optical fiber.

 Conventionally, optical fibers have a core with a relatively high refractive index in which the Light propagates and a sheath surrounding this core with a lower refractive index, serving as a guide to the Light and protecting the core of the fibers. .

 In the case of conventional optical fibers, the core of which is constituted by transparent materials of amorphous type, such as for example polymethyl methacrylate known by the abbreviation of PMMA, the refractive index is relatively low and is in the range of 1.48 to 1.50. In this case therefore, it is usual to produce the sheath with a low index polymer which is the 2,2,2 trifluorethyl polymethacrylate whose refractive index is 1.41. According to the invention, the filling material of the concentrators can therefore be, according to this embodiment of the optical fibers, polymethyl methacrylate.

 In the case of optical fibers comprising a core consisting of a polymer of a compound such as styrene whose refractive index is relatively high and of a sheath consisting for example of PMMA, of an acetate polymer vinyl or a fluorinated derivative of vinyl acetate whose refractive index is relatively low, we generally take as filling material polystyrene whose refractive index is 1.58-1.62.

 According to this embodiment of the optical fibers, the filling material of the concentrators may in this case be polystyrene.

 In general, the filling material will be chosen such that its refractive index is close to that of the core of the fibers and preferably, a material will be chosen whose refractive index will be greater than 1.56.

 FIG. 2 schematically represents the different stages of a process for manufacturing such a matrix, in accordance with the invention.

 These steps correspond to a first embodiment of the method according to the invention.

 Step a of the process consists in making a basic mold. This mold comprises a matrix arrangement of male elements 11, with symmetry of revolution, which can end, for example, by a stud 12.

 The conical shape of these elements 11 is generated by a straight or curvilinear generator.

In practice, these male forms of the concentrators can be produced in a metallic material or not with an optical quality of the surface. These shapes can be obtained by machining, polishing and duplicating.

 The shapes thus obtained are produced in sufficient number to then be the subject of a precise matrix placement on a support 10, as can be seen in this figure 1. The assembly 10 and It constitutes the basic mold.

 Step b then consists in producing a counter-mold 13 of the base mold, for example using a fluid resin, flexible after hardening and perfectly reproducing the shapes and the states of the surface of the mold. This resin can be a silicone resin, for example an RTV.

 The use of a flexible mold makes it possible to ensure easy demoulding of the matrix, even if it is large, and to maintain very good flatness of this matrix.

 This counter-mold will be used for duplicating the dies but, by its very nature, will have a lifetime limited by possible deterioration during work.

 Thus, after having produced the counter mold 13 which constitutes a matrix arrangement of female elements of hollow shape complementary to that of the male elements of the base mold 10, the method consists in carrying out Step c.

 This step c consists of pouring a material into the counter mold to obtain a new male mold.

 Step d of the method then consists in pouring between the male elements 20 a retaining material making it possible to ensure mechanical cohesion thereafter between the different optical elements that the concentrators will constitute.

 This step d further comprises a demoulding after hardening of the material, so as to obtain a matrix 21 of female elements of hollow shape.

 Optionally, we then proceed to Step e, which consists in depositing a material inside the hollow forms of the matrix 21, this deposit making it possible to obtain a thin layer coating of the internal surface of the hollow forms obtained. after demolding and will subsequently serve to ensure the optical separation between the different optical elements constituting the matrix of concentrators.

 Step f of the method consists in pouring a transparent optical material of index n, chosen so as to be close to that of the core of the optical fibers with which the matrix of concentrators obtained will be coupled.

 This step f therefore consists in pouring this material of index n over the thin separation layer, so as to fill the hollow shapes of the matrix obtained after demolding and to obtain an additional thickness 24.

 Step i of the method consists in machining the upper and lower faces of the matrix obtained in step f so as to remove the pins 12 and the excess thickness 24 of the optical material of index n.

 This step g results in the production of a matrix of concentrators as shown for example in FIG. 1.

 Figure 3 illustrates the different steps of a manufacturing process according to the invention, according to a second embodiment.

 In this second embodiment, the first two steps a and b are identical to the previous steps shown in FIG. 2.

 In fact, according to this embodiment, a base mold is first produced in step comprising a support 10 and male elements 11 which can end, for example, with a stud 12.

 Step b consists in producing a counter-mold 13 made up of a set of female elements of hollow shape but complementary to the male elements.

 Step c, in accordance with this embodiment, consists in pouring into the counter-mold obtained at the end of step b a transparent optical material of index n close to that of the core of the fibers with which the matrix of concentrators to be carried out will be coupled.

 According to a preferred embodiment, use will be made, for example, of a transparent optical resin with a high optical index which is greater than 1.56.

 An extra thickness 31 of this resin is obtained so as to maintain between them the different male elements of conical shape, obtained after demolding of this material of refractive index n.

 Optionally, step d is carried out, which consists of depositing a material in a thin layer over the hollow shapes obtained after demolding, so as to ensure optical separation between the various elements 30. The deposition of this layer can be carried out by deposition techniques used in integrated optics.

 Step e consists in pouring a retaining material 33 onto the matrix obtained after deposition of the thin layer 32. This retaining material will make it possible to ensure mechanical cohesion between the different optical elements which the concentrators obtained will constitute.

 Stage f finally consists in machining the upper and lower faces of the matrix obtained at the end of Stage e so as to remove the pins 12 and the additional thickness 31. This stage f thus makes it possible to obtain a matrix of concentrators 34 as shown in FIG. 1.

 Step d in fact consists in carrying out surface treatments allowing the optical reflections on the internal surface of the concentrators.

 We have therefore described in this step the production of a thin layer deposition which will preferably be a metallic deposition, a low index deposition, and which may further comprise multi-electric treatments or a combination of these various treatments.

 In addition to the role of reflector, these deposits provide optical separation between the different elements, that is to say between the different concentrators, and make these concentrators optically independent.

 In the case where a very low optical index bonding resin is used in step e, these various surface treatments can be eliminated. The objective to be achieved, however, is to obtain a total reflection inside these different concentrators in order to avoid any risk of crosstalk between the different channels thus formed.

 We can use the first embodiment of the method which has been described in the case where an optical resin is used (bearing the reference 30 in FIG. 3 and 23 in FIG. 2) which would not withstand the following stages of the method. of Figure 3, or in the case where there are difficulties in hanging the metallization on this resin.

 The base molds may for example be metallic. The counter-mold could for example be an RTV resin in the case of the second embodiment and teflon in the case of the first embodiment.

 FIG. 4 illustrates the simplified diagram of an optical reflection assembly. In order to simplify the representation, this assembly only illustrates an optical fiber of a matrix assembly, not shown, coupled to a concentrator 40 of a matrix, as described with reference to FIG. 1, and of a receiver 60 belonging to a reception matrix not shown.

 The optical assembly therefore includes the optical coupling means between an optical fiber matrix represented by the optical fiber 50 and a reception matrix represented by the receiver 60.

 According to the invention, these coupling means comprise a matrix of concentrators represented by the concentrator 40, this concentrator being a reflector with symmetry of revolution generated by a straight or curvilinear generator and filled with an optical material transparent to light, d refractive index close to that of the core 52 of the fiber 50.

 The sheath of this fiber is also shown, which bears the reference 51.

 The filling material of the concentrator 40 bears the reference 41.

 The optical assembly also comprises an optical contact material 70 with an optical index suitable for reducing Fresnel reflections and avoiding total reflections from the exit surface of the concentrators. This material 70 is placed so as to ensure contact between the receptor matrix and the concentrator matrix. As can be seen in this figure, this material 70 is placed between the receiver 60 and a face which is the face of the smallest diameter of the cone of the concentrator 40.

 In accordance with the invention, the optical assembly represented in this FIG. 4 further comprises an optical contact material 80 of suitable optical index of the same kind as the material bearing the reference 70 and ensuring the same function. This material 80 makes contact between the larger diameter face of the cone 40 and the end of the fiber 50.

 In Figure 5 there is shown an optical transmission assembly according to the invention. This diagram is a simplified diagram such as that which has been represented in FIG. 4. In fact, only a transmitter 90, a concentrator 40 and an optical fiber 50 have been represented. Of course, the transmitter 90 belongs to a matrix d emission, just as the concentrator 40 belongs to a matrix of concentrators as shown in FIG. 1 and the fiber 50 can belong to a matrix of optical fibers.

 This diagram in fact makes it possible to show that the matrix of concentrators can be used in a completely symmetrical manner, either in reception as shown in FIG. 4, or in emission as shown in FIG. 5 in an optical assembly.

Claims (14)

 1. Linear or two-dimensional matrix of concentrators capable of being connected to optical fibers, comprising a set of optical concentrators (1), characterized in that the concentrators are optically independent reflectors, with symmetry of revolution, filled with a material (2) optical transparent to light with a refractive index n close to that of the core of the fibers.  2. Concentrator matrix according to claim 1, characterized in that the optical material (2) is chosen so that its refractive index n is greater than 1.56.  3. Concentrator matrix according to claim 1 or 2, characterized in that the concentrators (1) are joined together by a retaining material (3) to form the matrix.  4. Concentrator matrix according to claim 3, characterized in that the holding material (3) is a resin.  5. concentrator matrix according to any one of claims 1 to 4, characterized in that the concentrators further comprise a reflective material (4) which coats the inner wall of said concentrators and which forms an optical separation between the retaining material and The transparent optical material.  6. Concentrator matrix according to any one of the preceding claims, characterized in that the reflective material (4) consists of a metallic layer.  7. Concentrator matrix according to any one of the preceding claims, characterized in that the concentrators (1) have a conical shape with symmetry of revolution generated by a straight or curvilinear generator.  8. Optical transmission or reception assembly comprising a matrix of optical fibers, a transmission or reception matrix, characterized in that it also comprises means of optical coupling between the matrix of optical fibers and the matrix d transmitting or receiving, and in that these coupling means comprise a matrix of concentrators according to at least one of claims 1 to 7.  9. Optical assembly according to claim 8, characterized in that it further comprises an optical contact material (70, 80) of optical index adapted to reduce Fresnel reflections and avoid total reflections on the output face of concentrators, this material being placed so as to ensure contact between the matrix of transmitters or receivers and the matrix of concentrators and between the matrix of concentrators (1) and the matrix of optical fibers.  10. A method of manufacturing a linear or two-dimensional matrix of optical concentrators intended to be coupled to a matrix of optical fibers, characterized in that it comprises the following steps  - make a base mold comprising a matrix arrangement of male elements with symmetry of revolution,  - make a counter-mold of the base mold to obtain a matrix arrangement of female elements of shape complementary to that of the male elements,  - pour a material into the counter mold to obtain a new mold made up of male elements,  - pouring a retaining material over the male elements making it possible to ensure mechanical cohesion between the different optical elements which will be obtained subsequently and demold after hardening,  - possibly depositing a material in a thin layer inside the hollow forms obtained after demolding, a layer which will serve to ensure the optical separation between the different elements,  pouring a transparent optical material of index n close to that of the core of the fibers over the thin separation layer so as to fill the hollow shapes of the matrix obtained after demolding and to obtain an extra thickness,  - Machining the upper and lower faces of the matrix so as to remove the extra thicknesses of optical material of index n.  11. Method for manufacturing a matrix of linear or bidirectional optical concentrators intended to be coupled to a matrix of optical fibers, characterized in that it comprises the following steps  - make a base mold comprising a matrix arrangement of male elements with symmetry of revolution,  - make a counter-mold of the base mold to obtain a matrix arrangement of female elements of shape complementary to that of the male elements,  - pour a transparent optical material of index n close to that of the core of the fibers in the counter-mold, leaving an additional thickness to obtain a matrix of optical elements,  - after hardening of the optical material and demolding, possibly deposit a material in a thin layer to ensure optical separation between the different elements,  - pouring a holding material on the matrix obtained to ensure mechanical cohesion between the different optical elements,  - machine the upper and lower faces of the matrix so as to remove the extra thicknesses of optical material of index n to obtain the matrix of concentrators.  12. The manufacturing method according to claims 10 and 11, characterized in that the material of refractive index n is a polymerized optical resin whose index n is greater than 1.56.  13. The manufacturing method according to claims 10, 11 and 12, characterized in that The holding material is a polymerized resin.  14. The manufacturing method according to any one of claims 10 to 13, characterized in that the deposition in a thin layer consists in carrying out metallization.