FR2815139A1 - Fibre optic connector or photon detector/emitter for telecommunications optics alignment, using component with auxiliary holes in outer component placed against fibre optic connector with alignment pegs - Google Patents

Abstract

The passive alignment method uses a connector (2) having fibre optic (4) ends (10) connecting to optical components (14,16). An auxiliary zone (22) in the optical component has guide holes (24) for guidance elements. The auxiliary hole provides alignment to the fibre optic connector which has alignment pegs (12).

Description

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METHOD AND DEVICE FOR PASSIVE ALIGNMENT OF A MULTI-FIBER OPTIC CONNECTOR AND A COMPONENT
OPTICAL DESCRIPTION TECHNICAL AREA
The present invention relates to a method and a device for passively and precisely aligning an optical fiber connector and an optical component.

 The invention applies in particular to the field of optical telecommunications.

 The optical component can be of the photo-detector type or of the photo-emitter type (or both).

 The invention applies more particularly to the assembly of a standard multifiber connector and a strip of transmitting or receiving optical circuits.

 The invention also applies to the connection of optical fiber arrays mounted in connectors, and of VCSEL, that is to say of lasers with surface emission and vertical cavity (vertical cavity surface emitting laser).

 The invention also applies to the assembly of optoelectronic components and high speed optical links as well as to the assembly of parallel optical fibers and juxtaposed optoelectronic components.

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STATE OF THE PRIOR ART
The coupling of an optical fiber and a laser beam emitter requires a precise alignment of this component and the fiber, in general an alignment to within 10 µm, the precision required being even higher for single-mode optical fibers.

 The same precision is required for the coupling of a fiber with a detector circuit.

 If we consider the example of the coupling of an optical fiber and an iaser transmitter, a commonly used alignment technique is the active alignment of the fiber and this laser transmitter, the latter being powered up to emit a laser beam. When alignment is obtained, the fiber is fixed to the laser transmitter by welding or gluing.

 This active alignment technique leads to a high cost for the assembly obtained.

 This is why a passive alignment technique has been studied. In this case, the relative positioning and then the fixing of the fiber to the emitting or receiving component are carried out without tension (for the component) or light flux: the fiber and the component are mechanically calibrated relative to each other and then fixed precisely.

 A technique is known for example for passive assembly of an optical fiber and a laser rod (laser rod) whose emission is lateral. According to this technique, the fiber is stuck in a V groove formed on a support and the

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 The laser bar is precisely hybridized on this support, facing the fiber. This technique achieves precision of the order of 1 µm to 5 µm.

 This known technique makes it possible to assemble an optical fiber and a side emission laser but does not allow the assembly of a fiber and a laser of the VCSEL type which emits light from one side.

 However, this technique has been modified to allow such assembly. In this case, optical or mechanical means are used to set the VCSEL to 900 of the optical fiber.

 However, this modified passive alignment technique requires the use of complex means, in particular auxiliary alignment means.

 A problem therefore arises, namely the problem of coupling, in a simple and precise manner, optical fibers and a planar optoelectronic component (emitter and / or detector), which is active by its larger face, this coupling being passive. that is to say performed in the absence of operation of the component.

 Consider for example the particular problem of precision assembly of VCSEL and optical fibers.

 There is a known assembly technique of VCSEL emitting from the rear face, this technique making it possible in particular to bring these VCSELs onto a silicon control circuit by the flip chip technique. This technique is known from the following document:

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[1] LA Coldren et al., Flip-chip bonded, back-emitting, microlensed arrays of monolithic vertical cavity lasers and resonant photodetectors, IEEE 1999
Electronic components and technology conference, pp. 733-740.

 It follows in particular from this document [1] that, to passively couple a strip of VCSEL (transmitters or detectors) to optical fibers, it is necessary to use a complex alignment support.

By way of example, a technique is known for connecting optical fiber ribbons, respectively mounted on a male connector and a female connector, using mechanical means and with alignment tolerances sufficient for correct fiber- fiber. This technique is known from the following document: [2] T. Satake et al., MT multifiber connectors and new applications, Proceedings of 44th ECTC, Volume 1,
1994, pp. 994-996.

 This document [2] also shows how to couple, with the same optical and mechanical means, a ribbon of optical fibers to a strip of VCSEL.

To do this, the VCSEL bar is actively aligned and glued to a mechanical support comprising guide pins (guide pins). This alignment requires an optical alignment and bonding system.

 Thus, the known techniques for precisely aligning optical components with optical fibers require the implementation

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 active alignments or complex optical positioning methods.

STATEMENT OF THE INVENTION
The object of the present invention is to remedy the above drawbacks.

 The invention solves the problem of aligning optical fibers and zones of an optical component, this alignment being passive, that is to say performed in the absence of operation of the component, and obtained more simply. . but just as precise as the known techniques of passive alignments. The invention does not use any optical alignment of the component and the fiber connector.

 Specifically, the subject of the present invention is a method of passive alignment of an optical fiber connector and an optical component, the connector comprising respective ends of optical fibers, the axes of which are parallel, these ends opening onto a face of the connector, and also comprising guide elements, the component comprising optical connection zones which are capable of being optically coupled respectively to the ends of the optical fibers, this method being characterized in that: - an auxiliary part is formed comprising guide holes, formed from one side of this auxiliary part and provided for inserting the guide elements therein respectively, and an auxiliary hole, formed from this face of the auxiliary piece and provided for inserting the

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 component, the relative positioning of the guide holes and the auxiliary hole on the auxiliary part allowing the alignment of the optical connection zones and the axes of the ends of the optical fibers, - this component is placed in the auxiliary hole and - the elements are placed guide in the guide holes.

 These guide elements may include guide pins whose axes are parallel to the axes of the ends of the optical fibers.

 In a particular embodiment of the invention, these guide pins are arranged on either side of all of the ends of the optical fibers and the axes of the guide pins and of the ends of the optical fibers are coplanar.

 The connector can be brought into contact with the component or it is possible to provide, between this connector and the assembly formed by the auxiliary part and the component, spacers capable of maintaining a predefined distance between this connector and this assembly.

 Means for fixing the connector to the auxiliary part can be provided.

 This auxiliary part can be manufactured by molding or machining or by photolithography (in several copies).

 The optical connection zones can be light emitting and / or receiving zones. The optical component may include surface emitting lasers with vertical cavities forming such areas.

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 In the invention, the optical component can comprise a substrate and an optoelectronic component which comprises the optical connection areas and which is hybridized to the substrate.

 The present invention also relates to a passive alignment device for an optical fiber connector and an optical component, the connector comprising respective ends of optical fibers, the axes of which are parallel, these ends opening onto one face of the connector, and also comprising guide elements, the component comprising optical connection zones which are capable of being optically coupled respectively to the ends of the optical fibers, this device being characterized in that it comprises an auxiliary part comprising holes for guide, formed from one face of this auxiliary part and provided for inserting the guide elements therein respectively, and an auxiliary hole, formed from this face of the auxiliary part and provided for inserting the component therein, the relative positioning guide holes and the auxiliary hole on the auxiliary part allowing the alignment of the connection zones n optics and axes of the ends of the optical fibers.

BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood on reading the description of exemplary embodiments given below, by way of purely indicative and in no way limiting, with reference to the appended drawings in which:

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* la figure 1 est une vue en coupe schématique d'un exemple de connecteur optique utilisable dans l'invention, 'la figure 2 est une vue en coupe schématique d'un exemple de composant optique que l'on veut coupler au connecteur de la figure 1 et qui comprend un ensemble de VCSEL hybridé sur un circuit de lecture, 'la figure 3 est une vue en coupe schématique d'une plaque auxiliaire permettant l'alignement du composant de la figure 2 et du connecteur de la figure 1, 'la figure 4 est une vue en coupe schématique du composant placé dans la plaque auxiliaire et du connecteur en cours d'assemblage avec cette plaque auxiliaire d'alignement et * la figure 5 est une vue de dessus schématique du composant comprenant l'ensemble de VCSEL logé dans cette plaque auxiliaire.

* Figure 1 is a schematic sectional view of an example of an optical connector used in the invention, 'Figure 2 is a schematic sectional view of an example of optical component that is to be coupled to the connector of the FIG. 1 and which comprises a set of VCSELs hybridized on a reading circuit, “FIG. 3 is a schematic sectional view of an auxiliary plate allowing the alignment of the component of FIG. 2 and of the connector of FIG. 1, Figure 4 is a schematic sectional view of the component placed in the auxiliary plate and of the connector being assembled with this auxiliary alignment plate and * Figure 5 is a schematic top view of the component comprising the VCSEL assembly housed in this auxiliary plate.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
Referring to Figures 1 to 3, there is a male optical connector 2 comprising several optical fibers 4. In the example, only four fibers have been shown, but there could be many more.

 The connector 2 comprises a connector body 6 provided with holes 8, each hole being intended to receive the end 10 of one of the optical fibers 4.

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The ends 10 of the fibers 4 thus open onto one face of the body 6.

 The holes 8 make it possible to precisely align the portions of the hearts (cores) of the fibers, which are contained in these ends 10, with respect to each other.

 The axes of these heart portions are coplanar and parallel.

 In addition, the connector body 6 comprises two guide pins 12. These two guide pins are respectively placed on either side of all of the ends 10 of the optical fibers and the axes of these guide pins are parallel. 'to each other and to the axes of the heart portions and are located in the same plane as the latter.

 All the ends 10 of the fibers (or, more precisely, all the core portions situated at these ends) are precisely aligned with respect to the two guide pins (or, more precisely, with respect to the axes of these pins) .

 This kind of male connector is known from document [2] in which such a connector is called an MT connector.

 We want to connect the set or network (array) of optical fibers 4 to a set or network 14 of optoelectronic elements (transmitters or receivers), for example VCSELs, without having to optically align the connector 2 and all of these optoelectronic elements with respect to each other.

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 In the example of FIG. 2, the network 14 of the VCSELs is thinned and hybridized on a substrate 16 forming for example a reading circuit (when the VCSELs are photodetectors). This circuit 16 is for example made of silicon while the network 14 is for example made of GaAs.

 The hybridization uses solder balls 18 which connect the network 14 to the circuit 16 by means of pads (not shown). The various electrical connection lines that comprise the network 14 and the read circuit 16 are also not shown.

 Regarding a hybridization between a VCSEL network and a read circuit, see for example document [1].

 For the implementation of the present invention, the reading circuit 16 has undergone a precision cutting on its outer perimeter. The VCSEL 20 are perfectly referenced in relation to this precision cutting. In FIG. 2, we see two opposite faces L1 of the circuit 16 which result from this precision cutting. These faces are separated from each other by a distance Dl.

 As seen in Figure 3, there is also an intermediate piece 22 forming an auxiliary alignment plate. This part 22 is pierced with three holes.

 Among these three holes, two holes 24 are intended to receive and guide the guide pins 12 of the connector 2. The axes of the two holes 24 are parallel and coplanar.

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 The third hole 26 is located between the two holes 24. The dimensions of this hole 26 are slightly greater than those of the periphery of the reading circuit 16 (which has been cut with precision).

 The hole 26 is intended to receive this reading circuit (carrying the network of VCSEL) and constitutes what is called the positioning imprint of the electronic chip formed by the network of VCSEL which is hybridized on its reading circuit. 16.

 Two opposite walls L2 of the hole 26 are intended to be opposite the faces L1 of the circuit 16 and are separated from each other by a distance D2.

 It is specified that the two holes 24 and the hole 26 are perfectly referenced with respect to each other. Their relative positions are determined so as to correspond to the relative positions of the ends 10 of the fibers and of the guide pins 12 and thus allow the ends 10 and the VCSEL 20 to coincide.

 It is clear that, if the reading circuit 16 is fitted into the hole or recess 26, the positions of the VCSELs will be perfectly referenced with respect to the holes 24 corresponding to the guide pins of the connector 2.

 Note the alignment error, that is to say the space between the edges of the reading circuit 16 and the positioning imprint 26.

 The resulting error is broken down into three errors El, 82, E3 and a positioning margin e.

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The error E1 is the positioning error of the cutting edge of the reading circuit 16 with respect to the target dimension and to the cutting marks which are present on this reading circuit. A control of 2 pm is possible on this cut.

 The error E2 is the error on the opening of the imprint 26 in the auxiliary plate 22. This error can be small, for example if a photolithography precise to 12 μm is used to form this imprint 26.

 This photolithography can for example use plasma etching, when the auxiliary plate is made of silicon, or chemical etching.

 The error E3 is the positioning error of the cavity 26 in the auxiliary plate 22 with respect to the holes 24 intended to receive the guide pins 12.

 This error c3 is zero when the holes 24 and the imprint 26 are formed by etchings using the same mask.

 The margin e is the minimum insertion step that we set on average.

 We can write: D2 = D1 + e c2.

The positioning error of the read circuit 16 relative to the auxiliary plate 22 is therefore at most equal to the sum of the relative errors and the insertion margin.

We can write that the alignment error is equal to half of (jel! +! E2) + e).

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 It is thus possible to obtain an average positioning better than 4.5 μm between the reading circuit 16 and the guide pins 12 at maximum value.

 It is specified that the reading circuit 16 can be cut out precisely by conventional techniques on its periphery and it is the same for the auxiliary plate 22 comprising the holes 24 of the guide pins and the imprint 26 of the reading circuit. These conventional techniques can be easily implemented at low cost.

 With the invention, assemblies of optical connectors and VCSEL networks become easy and assembly costs, which can represent up to 80% of the cost of an optical connector, are substantially reduced.

 As a purely indicative and in no way limitative, it is possible to assemble an MT type connector, comprising 12 optical fibers with a pitch (pitch) of 250 μm, and an emitter circuit comprising a strip of lasers of the VCSEL type at 250 μm pitch which is hybridized on a control circuit whose length and width are respectively 3.5 mm I 2 μm and 1 mm 2 μm.

3, 555 mm I 2 um et 1, 005 mm I 2 um, la marge d'insertion e étant égale à 5 um. The guide holes 24 then have a diameter of 705 μm and the opening 26, intended to receive the chip carrying the VCSELs, has the dimensions

3.555 mm I 2 μm and 1.005 mm I 2 μm, the insertion margin e being equal to 5 μm.

 The connector is therefore positioned with an accuracy of 0 +/- 4.5 μm with respect to the chip when

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 the guide pins are introduced into the holes 24 provided on the auxiliary plate 22.

 For multimode fibers, these positioning tolerances are sufficient for a low cost connection. In the case of single-mode fibers, which require more severe positioning tolerances, the manufacturing tolerances of the auxiliary assembly part as well as the cutting tolerances of circuit 16 are reduced to I 1 pm.

 We now consider the production of the auxiliary alignment plate 22. It can be produced by photolithography. To do this, auxiliary alignment plates can be produced collectively by photolithography on a silicon plate.

 The manufacturing steps are then as follows: 10 A mask is produced comprising the images of numerous auxiliary alignment plates 22 (each comprising the two holes 24 intended to receive the guide pins 12 as well as a hole 26 intended to receive the substrate 16 of the optoelectronic chip).

 Patterns corresponding to these images are formed by photolithography on a silicon wafer, without alignment on a previous level. This silicon plate is then etched over its entire thickness.

 The plate thus photolithographed is cut to obtain the various auxiliary plates.

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 As a variant, each auxiliary alignment plate is cut using the preceding photolithography.

 Instead of using photolithography, the auxiliary alignment plate 22 can be manufactured by molding (using an inexpensive plastic) or by machining a metallic material.

 We now consider the assembly of the connector 2, of the hybrid network 14 of the substrate 16, and of the auxiliary plate 22, which has been described with reference to FIGS. 1 to 3. - For this assembly, reference is made in Figures 4 and 5.

 We start by putting a layer of glue 28 on the periphery of the substrate 16 carrying the network 14 of VCSEL. For example, an adhesive polymerizable by ultraviolet radiation is used.

 Then, the auxiliary alignment part 22 is placed above the substrate 16, making the hole 26 coincide with this substrate 16. Then the part 22 is lowered until the substrate 16 is in this hole 26 and the the adhesive 28 is polymerized.

 The guide pins 12 are then inserted into the corresponding holes 24 and the body 6 of the connector 2 is pressed against the network 14 of VCSEL. Each fiber is then optically coupled to one of these VCSELs.

 As a variant, instead of pressing the body 6 against the network 14, this connector body is kept at a predefined distance from the VCSEL network by means of spacers 30 of appropriate height, which are placed beforehand on the assembly. formed by the

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pièce 22 et le substrat 16, entre cet ensemble et le corps 6 du connecteur 2.

part 22 and the substrate 16, between this assembly and the body 6 of the connector 2.

It is then possible to mechanically fix the body 6 of the connector 2 to the auxiliary part 22, for example using standard springs (spring clips) 32 which are specific to the MT connectors. On this subject, see document [2].

 Instead of forming holes 24 and 26 which cross the part 22 (FIG. 3), it is possible to form these holes 24 and 26 from one of the faces of this part 22 (upper face in FIG. 3) without causing them to lead to the other face of the part 22. Pins 22 are then used which are short enough so as not to prevent approaching the connector body of the VCSEL network up to the desired distance (which may be zero).

 In the example of FIGS. 1 to 5, the connection of a linear network of optical fibers to a linear network of VCSEL has been considered. However, it is possible to connect, in accordance with the invention, any set of fibers (with parallel ends) to a corresponding set of VCSELs: it is possible, for example, to use a connector carrying a matrix of ends of optical fibers between two guide pins and couple this connector, via an auxiliary alignment piece to a VCSEL matrix which is able to coincide with the matrix of the fiber ends and hybridized to a substrate (which is then inserted into the corresponding hole of the auxiliary part).

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 The invention is not limited to the connection of optical fibers and VCSEL. A multifiber optical connector can be coupled, in accordance with the invention, to a set of optical elements formed on a support which is inserted into an intermediate piece for coupling.

Claims (13)

 1. Method for passive alignment of a connector (2) of optical fibers and an optical component (14-16), the connector comprising respective ends (10) of optical fibers (4), whose axes are parallel , these ends opening onto one face of the connector, and also comprising guide elements (12), the component comprising optical connection zones (20) which are capable of being optically coupled respectively to the ends of the optical fibers, this method being characterized in that: - an auxiliary part (22) is formed comprising guide holes (24), formed from one face of this auxiliary part and provided for inserting the guide elements therein respectively, and an auxiliary hole (26 ), formed from this face of the auxiliary part and intended to insert the component therein, the relative positioning of the guide holes and the auxiliary hole on the auxiliary part allowing the alignment of the connection zones optics and axes of the ends of the optical fibers, - this component is placed in the auxiliary hole and - the guide elements are placed in the guide holes.  2. Method according to claim 1, wherein the guide elements comprise guide pins (12) whose axes are parallel to the axes of the ends (10) of the optical fibers. <Desc / Clms Page number 19>  3. Method according to claim 2, wherein the guide pins (12) are arranged on either side of the set of ends (10) of the optical fibers (4) and the axes of the guide pins and ends optical fibers are coplanar.  4. Method according to any one of claims 1 to 3, wherein the connector (2) is brought into contact with the component (14-16).  5. Method according to any one of claims 1 to 3, wherein there is provided, between the connector (2) and the assembly formed by the auxiliary part (22) and the component (14-16), spacers ( 30) able to maintain a predefined distance between this connector and this assembly.  6. Method according to any one of claims 1 to 5, wherein there is provided means (32) for fixing the connector (2) to the auxiliary part (22).  7. Method according to any one of claims 1 to 6, wherein the auxiliary part (22) is manufactured in several copies by photolithography.  8. Method according to any one of claims 1 to 6, wherein the auxiliary part (22) is manufactured by molding or machining.  9. Method according to any one of claims 1 to 8, in which the optical connection zones are zones (20) and / or receptors of light.  10. The method of claim 9, wherein the component (14-16) comprises lasers <Desc / Clms Page number 20>  emission by the surface and with vertical cavity forming zones (20) emitting and / or receiving light which constitute the optical connection zones.  11. Method according to any one of claims 1 to 10, in which the optical component comprises a substrate (16) and an optoelectronic component (14) which comprises the optical connection areas (20) and which is hybridized to the substrate.  12. Device for passive alignment of a connector (2) of optical fibers and of an optical component (14-16), the connector comprising respective ends (10) of optical fibers (4), the axes of which are parallel , these ends opening onto one face of the connector, and also comprising guide elements (12), the component comprising optical connection zones (20) which are able to be optically coupled respectively to the ends of the optical fibers, this device being characterized in that it comprises an auxiliary part (22) comprising guide holes (24), formed from one face of this auxiliary part and provided for inserting the guide elements therein respectively, and an auxiliary hole (26) , formed from this face of the auxiliary part and intended to insert the component therein, the relative positioning of the guide holes and the auxiliary hole on the auxiliary part allowing the alignment of the connection zones. n optics and axes of the ends of the optical fibers.  13. Device according to claim 12, in which the auxiliary part (22) is made of silicon.