EP1546776A2

EP1546776A2 - Optical fibre connector with shape memory properties

Info

Publication number: EP1546776A2
Application number: EP03780282A
Authority: EP
Inventors: Michel Bugaud; Patrick Olier
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2002-09-30
Filing date: 2003-09-26
Publication date: 2005-06-29
Also published as: JP2006501497A; US20050244112A1; WO2004029666A3; FR2845167A1; WO2004029666A2; CA2500315A1; FR2845167B1

Abstract

The invention relates to an optical fibre connector with shape memory properties. The inventive connector comprises at least one shape memory means consisting of a first sleeve (14) which is made from a shape memory material and a second sleeve (16) which is made from an elastic material. The aforementioned sleeves are coaxial and can exert radial forces on one another in order to block or release the ends (6, 8) of the fibres. The difference Sm1xMm1-Sm2xMm2, wherein Sm1 and Sm2 represent the transverse sections of the sleeves and Mm1 and Mm2 represent the moduli of elasticity thereof, is negative when the first sleeve is in the martensitic phase and positive when said sleeve is in the austenitic phase.

Description

CONNECTOR FOR OPTICAL FIBERS, SHAPE MEMORY

TECHNICAL FIELD DESCRIPTION

The present invention relates to a connector for optical fibers, more simply called "optical connector" in the following.

It applies in particular to the field of optical telecommunications.

STATE OF THE PRIOR ART

An optical connector is known comprising a first optical plug in which one end is placed a first optical fiber, a second optical plug in which one end of a second optical fiber is placed and an intermediate member designed to assemble the 'to each other the first and second optical plugs so that respective faces of the ends of the optical fibers are opposite one another and that these ends are made coaxial with great precision.

Such a connector requires very high precision machining of the first and second plugs and of the assembly member for these plugs. Indeed, this connector uses three mechanical connections between the two fibers, namely a connection between the first fiber and the first plug, a connection between the first and second plugs and a connection between the second plug and the second fiber.

It goes without saying that the positioning errors of these three links add up algebraically. The required precision is essential for single-mode optical fibers whose cores ("cores") have diameters of the order of 5 μm to 10 μm.

Thus, known connectors, of the kind described above, are expensive, especially when they are intended for the connection of single-mode optical fibers.

Reference is made in particular to the following document: [1] US 4,743,084 (R.. Manning).

This document describes an optical card comprising a sleeve of shape memory material, capable of immobilizing the end of the optical fiber associated with this optical card.

STATEMENT OF THE INVENTION

The present invention relates to an optical connector which does not require as high machining precision as the known connector, mentioned above, and which is therefore less expensive than this known connector.

The connector object of the invention is likely to have performances comparable to those of this known connector while being less expensive than the latter.

To do this, the invention uses a shape memory means allowing both the immobilization and the alignment of respective ends of two optical fibers. Specifically, the subject of the present invention is an optical connector, this connector comprising at least one shape memory means, this shape memory means being able to:. - deforming from a first state to a second state by modifying the temperature of this shape memory means, receiving, when it is in the first state, respective ends of two optical fibers in a position where the respective faces of these ends are opposite one another, and immobilize these respective ends in this position while making these ends coaxial, when it is in the second state, this connector being characterized in that the shape memory means comprises a first sleeve made of shape memory material and a second sleeve made of elastic material, the first sleeve thus being capable of being, depending on the temperature of this first sleeve, in a martensitic phase or in an austenitic phase , the first sleeve and the second sleeve being coaxial and able to exert radial actions one on the other to immobilize or, on the contrary, release the ends of the optical fibers, the empirical relationship expressing the difference SmlxMml-Sm2xMm2, where Sml and Sm2 represent the respective cross sections of the first and second sleeves and Mml and Mm2 represent the respective elastic moduli of these first and second sleeves, being negative , when the first sleeve is in its martensitic phase, and positive when this first sleeve is in its austenitic phase.

According to a preferred embodiment of the connector which is the subject of the invention, that of the first and second sleeves which is closest to the respective ends of the optical fibers comprises an internal face by means of which these ends respective are immobilized, this internal face comprising approximation means which are capable of bringing these ends closer to one another when these ends are immobilized. Preferably, the approximation means are located on one side of the internal face, corresponding to one of the respective ends of the optical fibers, and are capable of pushing this end longitudinally towards the other end.

In this case, the approximation means preferably comprise sawtooth indentations.

According to a first particular embodiment of the connector which is the subject of the invention, the second sleeve is placed inside the first sleeve, this first sleeve being capable of exerting pressure on the second sleeve to immobilize the ends of the optical fibers, when this first sleeve is in the austenitic state, the second sleeve being able to exert pressure on the first sleeve and to release these ends when this first sleeve is in the martensitic state.

According to a second particular embodiment, the first sleeve is placed inside the second sleeve, this second sleeve being capable of exerting pressure on the first sleeve to immobilize the ends of the optical fibers, when this first sleeve is in the martensitic state, the first sleeve being able to exert pressure on the second sleeve and to release these ends when this first sleeve is in the austenitic state. The elastic material of the second sleeve can be a polymer.

The first sleeve may have the shape of a tube which is continuous or split longitudinally or even perforated. It can also be made from a wire of shape memory material, this wire being wound or meshed or screened.

The connector object of the invention may comprise a plurality of copies of the shape memory means, which are made rigidly secured to each other and provided for connecting a plurality of optical fibers respectively to a plurality of other 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:

- Figures 1A and 1B are schematic longitudinal section views of a first particular embodiment of the optical connector object of the invention respectively before (Figure 1A) and after (Figure 1B) immobilization and alignment of the fibers optical,

- Figures 2A and 2B are schematic cross-sectional views of the first particular embodiment of the optical connector object of the invention respectively in a state where it allows the immobilization and alignment of the optical fibers (Figure 2A) and in a state where it allows the introduction of the fibers (FIG. 2B), - Figures 3A to 3D are schematic perspective views of examples of the sleeve of shape memory material, which can be used in the invention, - Figure 4 is a schematic longitudinal sectional view of a variant for making the optical connector of FIGS. 1A and 1B,

- Figures 5A and 5B are schematic cross-sectional views of a second particular embodiment of the optical connector object of the invention respectively in a state where it allows the immobilization and alignment of the optical fibers (Figure 5A) and in a state where it allows the introduction of the fibers (FIG. 5B), FIG. 6A is a schematic perspective view of a connector according to the invention, making it possible to connect a plurality of optical fibers respectively to another plurality of optical fibers, and - Figure 6B is a schematic and partial perspective view of an alternative embodiment of the connector of Figure 6A.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS The optical connector conforms to

1 invention, which is schematically shown in Figures 1A, 1B, 2A and 2B, is intended to connect two optical fibers 2 and 4 so that the respective ends 6 and 8 of these fibers 2 and 4 are coaxial, the respective axes X and Y of these ends 6 and 8 then being combined, and that the respective faces 10 and 12 of these two ends 6 and 8 are opposite one another as seen in Figures 1A and 1B.

This connector includes a first sleeve

14 made of shape memory material. This material is for example the TiNi alloy. However, in the present invention, any other shape memory material can be used.

The connector also includes a second sleeve 16 made of an elastic material such as a polymer, for example a polyimide.

The sleeves 14 and 16 are coaxial. The one of the sleeves which is surrounded by the other has an external diameter equal to the internal diameter of the one which surrounds it and an internal diameter equal to or slightly greater than the diameter of the optical fibers.

In the example of FIGS. 1A and 1B, the sleeve made of shape memory material 14 surrounds the sleeve made of elastic material 16.

It is specified that, for the purpose of mounting the ends of the optical fibers in the connector, it is possible to leave, on these ends, the protective sheath with which the fibers are provided, or, on the contrary, remove this protective sheath from these ends.

In addition, in all of FIGS. 1A, 1B, 4, 6A and 6B, the faces of these ends are shown spaced from one another for greater clarity in these figures, but, in reality, these faces are one against the other.

They can be spaced from each other but then an index adapter liquid is placed between them.

Details of the sleeves 14 and 16 are given below with reference to FIGS. 2A and 2B which correspond to a cross section at the end 6 of the fiber 2.

We denote by Tr the phase transition temperature of the shape memory material, that is to say the temperature at which this material passes from the martensitic phase to the austenitic phase.

At high temperature (FIG. 2A), that is to say at a temperature higher than Tr, which corresponds to the nominal state of the sleeve 14 in the position where the fibers are connected, this sleeve 14 is in the state shrunk which ensures the compression of the internal sleeve 16 of polymer.

Under the effect of this compression, the sleeve 16 immobilizes the ends 6 and 8 of the fibers. It is specified that the sleeve 14 is designed to exert sufficient pressure on the internal sleeve 16 so that the latter immobilizes these ends.

To do this, we make sure that, above Tr, the empirical relationship expressing the difference SmlxMml-Sm2xMm2 is positive by noting Sml (respectively Sm2) the cross section of the sleeve 14 (respectively of the sleeve 16) and Mml (respectively Mm2) the elastic modulus of the sleeve 14 (respectively of the sleeve 16). At low temperature (FIG. 2B), that is to say at a temperature below Tr, the shape memory material sees its modulus of elasticity reduced. The sleeve 14 is expanded by the elastic action of the polymer sleeve 16, which can optionally be associated with hydraulic or mechanical inflation.

To do this, we make sure that, below Tr, the difference mentioned above is negative. As a purely indicative and in no way limitative,

- Tr = -30 ° C is chosen for a sleeve 14 operational between -15 ° C and +85 ° C; by way of example, this sleeve in its "full tube" variant 14 a, in the martensitic state

(respectively austenitic), an internal diameter of

2mm (respectively 1.94mm) and an external diameter of

2.05mm (respectively 1.99mm); - the sleeve 16 of polymer has an external diameter of 2mm (respectively 1.94mm) in the uncompressed state (respectively in the compressed state) and an internal diameter of 0.128mm (respectively 0.12mm) in the non-compressed state compressed (respectively in compressed state); - The elastic modulus of the sleeve 14 in the martensitic (respectively austenitic) state is worth 25 to 45 GPa (respectively 70 to 90GPa), the elastic modulus of the sleeve 16 is worth 3 GPa;

- the optical fibers have a diameter of 125 μm.

The low temperature (below -30 ° C in the example above) can be obtained in the field using a commercially available vaporizer which allows a temperature of -50 ° C to be obtained.

The polymer sleeve 14 can be kept expanded (at room temperature, for example for the storage of the connector) by a rigid wire of appropriate diameter (for example 150 μm in the example considered above). This wire will become free and can be removed when the temperature drops below Tr. This wire will then be replaced by the optical fibers to be connected. FIGS. 3A to 3D are schematic perspective views of various possible shapes for the sleeve 14 made of shape memory material.

This sleeve 14 can have the shape of a tube 18 (FIG. 3A), which is closed (around its periphery) or the shape of a longitudinally split tube 20 (FIG. 3B) or even perforated (FIG. 3D).

The percentage of aperture relative to a cross section will proportionally reduce the elastic modulus of the sleeve of alloy with shape memory, which will also modify the dimensions given by way of example with a sleeve in solid tube (Fig 3A).

The sleeve 14 can also be made of a coiled (helical) wire 22 of shape memory material (FIG. 3C) or of a mesh or wire mesh 24 of shape memory material (FIG. 3D).

In an alternative embodiment schematically illustrated in FIG. 4, the internal wall of the sleeve 16 is provided with a thread constituting sawtooth indentations 26.

Preferably, as shown in FIG. 4, this thread is asymmetrical: it is formed only on one side of the internal face of the sleeve 16, corresponding to one of the ends 6 and 8 of the fibers, namely the end 6 in the example.

By compression, when the temperature is higher than Tr, the threading provides a longitudinal thrust on the end 6 of the fiber 2, to hold it in abutment against the other end 8 of the fiber 4. This gives a sleeve 16 with action positive which improves the optical coupling between these ends. A positive action sleeve 16 is thus obtained, which improves the optical coupling between these ends.

Another example of the connector which is the subject of the invention is given below with reference to FIGS. 5A and 5B which correspond to a cross section at the level of the end 6 of the fiber 2.

In this other example, the sleeve 14 constitutes the internal sleeve: it is surrounded by the sleeve 16 which constitutes the external sleeve.

We also note Tr the phase transition temperature of the shape memory material, that is to say the temperature at which this material passes from the martensitic phase to the austenitic phase.

At low temperature (FIG. 5A), that is to say at a temperature below Tr, which here corresponds to the nominal state of the sleeve 14 in the position where the fibers are connected, the sleeve 16 ensures the setting in compression of the internal sleeve 14 which is ductile: it is in the martensitic phase.

Under the effect of this compression, this sleeve 14 immobilizes the ends 6 and 8 of the fibers.

It is specified that the sleeve 16 is designed to exert sufficient pressure on the internal sleeve 14 so that the latter immobilizes these ends.

To do this, we make sure that, below Tr, the difference SmlxMml-Sm2xMm2 is negative, again noting Sml (respectively Sm2) the cross section of the sleeve 14 (respectively of the sleeve 16) and Mml (respectively Mm2) the elastic module of the sleeve 14 (respectively of the sleeve 16). At high temperature (FIG. 5B), that is to say at a temperature above Tr, the sleeve 14 in its austenitic phase exerts sufficient force on the sleeve 16 to expand the latter and allow the ends 6 to be freely introduced. and 8 of the optical fibers in this sleeve 14.

To do this, we make sure that, beyond Tr, the difference mentioned above is positive. An internal sheathing 28 of polymer can be provided inside the sleeve 14, this sheathing being thus interposed between this sleeve 14 and the ends 6 and 8 of the fibers.

For purely indicative and in no way limitative

- Tr = 125 ° C is chosen for a sleeve 14 operational at less than 85 ° C;

- By way of example, this sleeve 14 will, in the martensitic (respectively austenitic) state, have an internal diameter of 0.15mm (respectively 0.145mm) and an external diameter of 0.350mm (respectively 0.337mm);

- the sleeve 16 in polymer has an external diameter of 2mm (respectively 1.99mm) and an internal diameter of 0.350mm (respectively 0.337mm) in the state where it compresses the sleeve 14 (respectively where it is compressed by the sleeve 14 ); the elastic modulus of the sleeve 14 in the martensitic (respectively austenitic) state is worth 25 to 45GPa (respectively 70 to 90 GPa);

- The elastic modulus of the sleeve 16 is 3 GPa; - in the uncompressed state, the sheathing 28 in polymer has a thickness of 12 μm;

- the optical fibers have a diameter of 125 μm. In the case of FIGS. 5A and 5B, the sleeve 14 can also have one of the shapes mentioned in the description of FIGS. 3A to 3D.

Of course, a combination of these two arrangements (Figures 1A-2A and 1B-2B) described is also possible to adapt the dimensions to the values of the moduli of elasticity of the materials with shape memory alloy and of the polymer or polymers chosen.

In addition, the internal face of this sleeve 14 can also be provided, on one side, with indentations of the kind which have been described with reference to FIG. 4.

In FIG. 6A, a connector according to the invention is seen, comprising several connectors 30 of the kind which have been described previously, for example with reference to FIGS. 1A and 1B.

These connectors 30 are rigidly secured to one another by means of elements 32, for example made of stainless steel, and so that the axes of the respective longitudinal bores of the connector sleeves are parallel to each other.

Each of these connectors 30 makes it possible to connect an optical fiber 2 to an optical fiber 4 so that the connector of FIG. 6A makes it possible to optically connect a first set of optical fibers 2 to a second set of optical fibers. FIG. 6B is a schematic and partial perspective view of an alternative embodiment of FIG. 6A where the connectors 30 are made rigidly secured to each other by means of two identical plates 34 and 36, for example made of ceramic or of glass with parallel V-shaped grooves

Each groove comprises a portion 38 capable of accommodating one of the sleeves 14 and, on either side of this portion 38, two portions 40 and 42 capable of respectively accommodating portions of the fibers 2 and 4 which are located on the side and on the other side of the sleeve in question.

Claims

1. Optical connector, this connector comprising at least one shape memory means (14, 18), this shape memory means being able to: - deform by passing from a first state to a second state by modifying the temperature of this shape memory means, receiving, when it is in the first state, respective ends (6, 8) of two optical fibers (2,4) in a position where the respective faces (10, 12) of these ends are opposite one another, and immobilize these two respective ends in this position while making these ends coaxial, when it is in the second state, this optical connector being characterized in that the means with shape memory comprises a first sleeve (14) of shape memory material and a second sleeve (18) of elastic material, the first sleeve being thus able to be, depending on the temperature of this first sleeve, in a martensitic phase or in an austenitic phase, the first sleeve and the second sleeve being coaxial and able to exert radial actions one on the other to immobilize or, on the contrary, free the ends (6, 8) of the optical fibers, the empirical relationship expressing the difference SmlxMml-Sm2xMm2, where Sml and Sm2 represent the respective cross sections of the first and second sleeves (14, 16) and Mml and Mm2 represent the respective elastic moduli of these first and second sleeves, being negative, when the first sleeve is in its martensitic phase, and positive when this first sleeve is in its austenitic phase.

2. The connector of claim 1, wherein that of the first and second sleeves (14, 16) which is closest to the respective ends (6, 8) of the optical fibers comprises an internal face through which these respective ends are immobilized, this internal face comprising approximation means (26) which are capable of bringing these ends closer to one another when these ends are immobilized.

3. Connector according to claim 2, wherein the approximation means (26) are located on one side of the internal face, corresponding to one of the respective ends (6, 8) of the optical fibers, and are capable of push this end longitudinally towards the other end.

4. The connector of claim 3, wherein the approximation means comprise indentations (26) sawtooth.

5. Connector according to any one of claims 1 to 4, in which the second sleeve (16) is placed inside the first sleeve (14), this first sleeve being able to exert pressure on the second sleeve to immobilize the ends of the optical fibers, when this first sleeve is in the austenitic state, the second sleeve being able to exert pressure on the first sleeve and to release these ends when this first sleeve is in the martensitic state.

6. Connector according to any one of claims 1 to 4, wherein the first sleeve (14) is placed inside the second sleeve (16), this second sleeve being able to exert pressure on the first sleeve to immobilize the ends of the optical fibers, when this first sleeve is in the martensitic state, the first sleeve being able to exert pressure on the second sleeve and to release these ends when this first sleeve is in the austenitic state.

7. Connector according to any one of claims 1 to 6, wherein the elastic material of the second sleeve (16) is a polymer.

8. A connector according to any one of claims 1 to 7, wherein the first sleeve (14) has the form of a tube (18, 20) which is continuous or split longitudinally or perforated.

9. Connector according to any one of claims 1 to 7, in which the first sleeve

(14) is made from a wire (22, 24) of shape memory material, this wire being wound or meshed or screened.

10. Connector according to any one of claims 1 to 9, comprising a plurality of copies (30) of the shape memory means, which are made rigidly integral with each other and provided for connecting a plurality of optical fibers (2 ) respectively to a plurality of other optical fibers (4).