FR2515363A1 - Optical fibre coupling with min. signal losses - uses bore receiving connector pins and cuff around at least one pin - Google Patents

Abstract

The coupling comprises a connector block with an axial reception bore with two sections of different dia. each end of the smaller dia. section receiving a complementary connector pin at the end of a respective optical fibre. The larger dia. section contains a cuff fitting around the outside of one of the connector pins, with a resilient coupling element between the latter and the cuff. Pref. a second cuff is positioned around the second connector pin with a similar resilient coupling element between them. The connector block may have a number of similar pairs for connecting several optical fibre pairs.

Description

DEVICE FOR COMPENSATING FOR VARIATIONS
LENGTH OF AT LEAST ONE SHEATHED OPTICAL FIBER
ARRANGED IN AN ENVELOPE
The present invention relates to devices making it possible to compensate for variations in the length of the targets of optical fibers surrounded by a sheath, all of these sheathed optical fibers being surrounded by an envelope which is generally closed.

The technique of information transmission by light beams by means of optical fibers, is taking more and more importance, and it is therefore necessary to be able to adapt, use, etc., all these targets in any field.

In particular, it is advantageous to be able to use these optical fiber targets anywhere, and even in those where the temperature variation can be carried out over large ranges.

However, as is well known, optical fibers are generally made from silica, or more generally from glass in dimensions which can be very small, for example of the dimension of a hair.
In addition, the outer surface of these fibers is protected by sheaths made of a material which is generally based on plastic.

Owing to this particular structure, and the association of a glass fiber which has a relatively low coefficient of expansion, with a plastic material which has a higher coefficient of expansion, manufacturers and users have realized that, when these fiber optic targets were subjected to variations in temperature, the variation in length of these targets was absolutely not negligible. This therefore posed problems, in particular to avoid untimely disconnections are made at both ends of the targets
However, in order to be able to use these optical fiber wheats, the manufacturers generally used an envelope whose internal diameter was greater than the external diameter of the assembly of optical fibers occupying the interior of this envelope.

Thus, the different length variations were absorbed by the fact that the optical fibers assumed more or less wavy positions inside the envelope.

However, this technique undoubtedly has drawbacks because it requires a much larger envelope diameter than necessary and, moreover, the variations in absorbed length do not allow significant target lengths to be achieved.

The present invention aims to overcome these drawbacks and to provide a device to compensate for variations or fluctuations in length of at least one sheathed optical fiber disposed in an envelope which allows the use of these optical fibers contained in targets anywhere, even in those which may other subject to significant temperature variations, while minimizing the importance of the envelope and therefore of gaining weight on these cabs, and having, in spite of everything, operational safety by being certain that the The ends of the optical fibers will always remain correctly associated with the connector which, generally, terminates them.

More specifically, the subject of the present invention is a device making it possible to compensate for the variations in length of at least one optical fiber surrounded by a sheath, said optical fiber being arranged in an envelope, characterized in that it comprises at least one mandrel, a turn of said sheathed optical fiber surrounding a surface portion of said mandrel, and means for positioning the part of said optical fiber forming said turn obtained at the mandrel, around said surface portion.

The present invention also relates to optical fiber targets comprising the device as described above.

Other characteristics and advantages of the present invention will appear during the following description given with reference to the drawings annexed by way of illustration, but in no way limitative, in which - Figure 1 represents, seen in perspective, partially cut away, a cable of a plurality of optical fibers, as it is currently produced, - Figures 2, 3A-B, 4, 5, 6A-B and 7 show different advantageous embodiments of a device making it possible to compensate for variations in length of at least one sheathed optical fiber, placed in an envelope.

Returning more particularly to FIG. 1, this represents, seen in section and partially cut away, an embodiment of a target of a plurality of optical fibers such as those currently commonly found in commerce.

This target 1 comprises an envelope 2 of generally cylindrical shape, made of a material such as, for example, a rubberized resin, a dlaster, etc.

Inside this envelope 2, a plurality of optical fibers 3 are arranged, all surrounded by a sheath 4.

 All of these optical fibers 3, 4, surrounds a core 5 and occupies a volume which can very schematically be assimilated to a cylinder whose diameter is much smaller than the inside diameter 8 of the envelope 2.

Up to now, this difference in size made it possible to compensate for the variations in length of the sheathed optical fibers 3,4 by the fact that all of these arranged around a core 5 took corrugations inside this envelope 2
The object of the present invention is to provide a device capable of compensating for the variations in length of all of these optical fibers mounted around the core 5 without it being necessary to obtain an envelope 2 having an internal diameter significantly greater than the volume occupied by all optical fibers 3,4.

Prior to the description of the various advantageous embodiments of the device, in the present description, reference will only be made to a single optical fiber and this for the sake of simplification of the drawings, and for the purpose of a more complete understanding. easy of the structure of the device and of its operation. It is obvious that without any difficulty, those skilled in the art will be able to adapt this device to a plurality of optical fibers.

With this in mind, FIG. 2 represents a first mode of such a device.

This device comprises a mandrel 210 disposed in an envelope 220 which may possibly also be a continuity of the envelope 230 surrounding an optical fiber 240 surrounded by a sheath.

This envelope 220 is, in this embodiment associated for example with a nille 250 connector of optical fibers well known in itself.
The mandrel 210 is fixed relative to the casing 220 and has, on its periphery 211, a helicoSdale groove 260, forming several turns at the lateral periphery 211 of the mandrel 210 so that the ends 280, 290 of this groove open out. on either side of this mandrel 210.

The fiber 240 generally has a diameter which has a certain value, well known to those skilled in the art, for this, the groove 260 is produced in such a way that it has a depth much greater than the diameter of the optical fiber 240.

In the assembly shown in Figure 2, the optical fiber 240, which is connected to the connector 250, is disposed in the groove 260 of this mandrel so that it forms a number of turns.

This optical fiber 240 is disposed in the bottom 261 of this groove 260 when the optical fiber has its minimum length.

Thus, when variations in the length of this fiber 240 are obtained, in particular due to corresponding variations in temperature which, in the case under consideration should only allow the optical fiber to stall, these are compensated by an increase in the diameter of the 240 fiber optic turns,
This increase in diameter will be possible as much as possible so that these turns come substantially into contact with the interior surface 245 of the envelope 220.

Those skilled in the art can easily calculate the depth of this groove 260 and the number of these turns so that, in the variations in diameter of these turns, this device can compensate. and absorb all possible variations in the length of the fiber 240.

In fact, this maximum compensation is easily verified by formula 2. (Rr) .x; in which
R represents the internal diameter 245 of the envelope 220, and r the minimum diameter of the groove 210 (which is assumed to be cylindrical), x being the number of possible turns or turns for the optical fiber 240.

In this modest embodiment, the axis 285 of the mandrel is substantially coincident with Itaxe 295 of the envelopes 220, 230, and the groove 260 has its helical shape around these same axes 285, 295.

The fiber 3A, B, represents another embodiment of a device which, in principle, is identical to that of FIG. 2, but, in this case, the mandrel 310 is placed in the envelope 320 and affects the general shape of a sphere in which a groove 360 is made, the two ends 380,390 of which are situated substantially on an axis 385 which is substantially perpendicular to the axis 395 of the envelopes 320,330.

FIG. 3A shows in longitudinal section, the device in which the optical fiber 340 forms substantially a plurality of turns 341 which are guides in the groove 360 where it can be seen that a part 342 of these spores is distant from the bottom 300 of this groove 360.

The representation of the shape of the turns of the fiber 340 around the mandrel 310 suggests, given that a part of these turns is not pressed, on the one hand, against the bottom 300 of the groove 360; and, on the other hand, against the inner surface of the envelope 320, that the fiber 340 has an average length and that the latter may, depending on temperature variations, either shrink or lengthen without this affects the position of the emerging part 345 of the fiber 340 which, in the embodiment, can other considered as the part of the fiber 340 represented on the left part of FIG. 3A.

In these two embodiments, according to FIGS. 2 and 3A> B, dew identical principle, the two mandrels will be fixed adequately with respect to their respective casings 220 and 320 and more particularly in the case of FIG. 2, the mandrel will be positioned between two stops 26f, 275 one of which 265 may be fixed and the other consisting of a clip 275.

On the other hand, in the case of the mandrel according to FIG. 3, the latter may be further maintained by bearings 301, 302 produced in collaboration with the wall of the envelope 320.

FIG. 4 represents another embodiment of a device according to the invention which essentially comprises a mandrel 410 disposed in an envelope 420, so that the internal surface 400 of the envelope 420 defines, with the external conical surface 405 of the mandrel 410, a space 403 in the form of an annular conical trunk, having a thickness substantially greater than the diameter of the fiber 442.

The mandrel 410 is fixed integrally to the casing 420 by means of a bottom 4110
This bottom 411 has an opening 412 allowing the passage of the optical fiber 442 which can be connected to the connector as for example explained with reference to FIG. 2.

The fiber 442 is therefore placed inside this envelope and around the mandrel so that it partially emerges 443 through the orifice 412, and -that it makes, around this mandrel 410, a certain number of turns 422, and that its other end 444 is directed towards the very long envelope 430, that is to say in fact the target of optical fibers.

In this way, it can be considered that the end 443 of the fiber is relatively fixed relative to the bottom 411, but that, on the other hand, the end 444 can undergo displacements due to variations in length of the optical fiber as said previously, due for example to temperature variations.

In this case, as the thickness of space 403 separating the mandrel 410 from the envelope 420 is slightly greater than the diameter of the fiber, the latter can slide relatively freely around the conical part 401 of the mandrel 410 and the variations even impertinent in length, due to the helical shape of these turns which have superimposed on each other, a variation in length may otherwise be compensated for by new turns forming around the mandrel 410
Those skilled in the art can, of course, determine the value and in particular the length of the mandrel 410 so that it can absorb all possible variations in length under given conditions, this determination presenting no difficulty.

FIG. 5 represents another embodiment of a device which is substantially identical in principle to that of FIG. 4, but, in this case, the mandrel 510 is delimited by two surfaces, respectively a cylindrical surface 501 terminated by a conical surface 502.
This device has an advantage over the previous one; ctest that it makes it possible to have, over the length of the cylindrical surface 501, a diameter of turns more
large which results in greater compensation for variations in length of the optical fiber 542 over a shorter length 0
Consequently, the essential advantage of the device according to FIG. 5 compared to the device according to FIG. 4, is that for the same possible variation.

length of the optical fiber, the length of the mandrel along the axes respectively 450 (Figure 4) and 550 (Figure 5), will be shorter for the embodiment of the device according to Figure 5 than that according to * i-, xre 4.

In the embodiments illustrated above, the compensations for variation in length of the sheathed optical fiber relative to the envelope surrounding it, are essentially carried out by the fact that this excess length of the optical fiber is positioned around a reference surface, essentially designated around the mandrel, in such a way that the fiber moves away from this mandrel, or else spools itself around it.

In some embodiments, the fiber may even be guided by grooves.

FIG. 6 represents another embodiment in which the excess length of the optical fiber is wound around a movable mandrel which can pivot around an axis under the action of different means, essentially as illustrated in the embodiment by a return spring.

More specifically, the device shown in FIG. 6 comprises in a casing 620, a mandrel 610 mounted pivoting about two axes 611, which is supported on bearings 612,613 produced for example in the wall of the casing 620.

This mandrel essentially consists of two juxtaposed coils 621 and 622, having respectively different diameters in the illustrated embodiment.

Thus, the fiber 642 is rolled in a first direction around the first spool 622, and then passes, for example, through the middle wall 623 in a conduit 680 to continue winding on the spool 621, but in an opposite direction to the direction d winding of the fiber on the reel 622.

In the illustrated mode, the coil 621 has a larger diameter than that of the coil 622, therefore, the end. 643 of the optical fiber emerging from this coil 622 will be the optical fiber which has a length much more important than the length, towards which the end 644 of the optical fiber 642 is turned.

In addition, the device comprises a return spring 650 which is fixed at one end 651 on the axis 611, and at its other end 652 on the mandrel 610.

Therefore, If a decrease in length occurs on the optical fiber 642, this amounts to exerting, respectively on the ends 643 and 644 of this optical fiber 642, a tract tending to unwind the two spools 621 and 622 respectively, produced in the mandrel 610.

Therefore, we understand why the two coils are wound in the opposite direction, this to allow that the two parts of optical fiber 690 in the coil 627 and 691 in the coil 622 can take place when the mandrel 610 rotates in one and same sense.

In this hypothesis, that is to say that which tends to unwind the optical fiber 642, the return spring 650 is bandaged to store elastic energy, which will be restored when, for example, the optical fiber 642 has the reverse tendency and therefore to lengthen.

Because the spring remains bandaged, the mandrel will be rotated to rewind the excess length of the optical fiber which will have lengthened.

Of course, if the lengths of optical fiber on either side of this mandrel are substantially equal, the diameters of the coils 621 and 622 will then be substantially equal.

On the other hand, the largest coil diameter and associates with the length of the optical fiber which is the shortest. In fact, the diameters of the coils are substantially a function inversely proportional to the length of fibers to be compensated.

Finally, FIG. 7 represents another embodiment of a device making it possible to compensate for the variations in length of at least one sheathed optical fiber 742 relative to an envelope 720.

This device finds a particularly advantageous application in cables of very long lengths.

It can be arranged in a staggered fashion all along these targets so that these variations in length as explained above can be compensated.

Figure 7 shows, very schematically, one of these devices arranged in a cabal. It is essentially composed of two parts, a first part r, comprising means making it possible to position and maintain, with relative rigidity, the optical fiber, and a second part 722 and 723 making it possible to compensate for variations in length.

This device therefore comprises a mandrel 710 essentially comprising the two cylindrical parts 721 and 722,723 of different diameter, the cylindrical part 721 being located substantially between the two cylindrical surfaces 722,723
In addition, this cylindrical part 721 has a continuous groove 713, the two ends 714 and 715 of which open on either side of this cylindrical surface 721, at the level of the cylindrical surfaces of smaller diameter 722,723.

The optical fiber 742 is then placed on this mandrel 710 so that it makes a certain number of turns around respectively the two parts of the cylindrical surfaces 722,723, on either side of the cylindrical surface 721 while passing through the groove 713 .

Therefore, the optical fiber 742 is substantially maintained in the cylindrical part 721 in the manner of dead towers on a capstan, and, on the other hand, the two parts of cylindrical surface 722,723 make it possible to absorb the fluctuations in length on both sides 743,744 of the optical fiber 742 relative to this mandrel 710 in the same way as explained for example for the devices as illustrated in FIGS. 4 and 5.

Of course, this mandrel 710 is positioned in the sheath 720, so that it is held between two stops 750 and 757 consisting for example of clips so as to be able to slide slightly laterally and to position the mandrel in the envelope 720 with regard in particular also to the fiber. 742.

Thus, a fiber optic cable of the same type as that which has been shown in FIG. 1 may include a plurality of such devices distributed repetitively along this cable, and it is now possible to design fiber optic targets of very long length. important, something that has not been possible until now due to the negligible length variations nr of the sheathed optical fibers.

Claims (14)

 1 / Device for compensating for variations in length of at least one optical fiber (3) surrounded by a sheath (4), said optical fiber (3) being disposed in an envelope (2), characterized in that it carries at least one mandrel (210,310,410, ...), a turn (342,422,690,691, ...) of said sheathed optical fiber surrounding a surface portion of said mandrel, and means for positioning the part of said optical fiber forming said turn obtained at level of the mandrel around said surface portion.  2 / Device according to claim 1, characterized in that said means are constituted by the space (403,360, ...) between said surface portion of said mandrel and said envelope, this space having a thickness much greater than the thickness of said optical fiber.  3 / Device according to claim 2, charac terized by the fact that said optical fiber is guided in said space in a groove (260,360, ...) formed around said mandrel  4 / Device according to one of claims 1 to 3, characterized in that said portion of surface of the mandrel hose is cylindrical (211,722, ...)  5 / Device according to one of claims 1 to 3, characterized in that said surface portion is conical (401.502, ..,),  6 / Device according to one of claims 1 to 3, characterized in that said surface portion consists of two adjacent surfaces (501a502) respectively cylindrical and conical  7 / Device according to claim 1, characterized in that it comprises mounting means (265,275,301,302,612,613) of said mandrel in said envelope.  8 / Device according to claim 7, characterized in that said mounting means comprise an axis of rotation adapted to cooperate with a bearing respectively on one of the two elements constituted by said casing and said mandrel.  9 / Apparatus according to claim 7, characterized in that said mounting means are constituted by a mandrel capable of sliding in said envelope by at least one portion (211) of its outer surface between two stops (265,275,750, 751) limiting its race.  10 / Apparatus according to claim 1, characterized in that said mandrel comprises at least two portions (621,622,722,723) of surface around which are able to surround themselves with portions of turn of said optical fiber.  1 1 / Device according to claim 10, characterized in that the two said surface portions are separated by a middle wall (623> 721) in which is formed a groove (680,713) 0  12 / Device according to one of claims 10 and 11, characterized in that the two surface portions are respectively constituted by two coils (621,622), said optical fiber being surrounded at least partially, respectively around the two said coils in two opposite directions of the elastic means (650) acting on said mandrel to return it to a determined position.  13 / optical fiber cable comprising at least one device according to one of the preceding claims  14 / Cabal according to claim 13, characterized in that it comprises a plurality of devices distributed along said target.  15 / Cable according to one of claims 13 and 14, characterized in that it comprises an envelope (720), a mandrel (710), consisting of three parts substantially respectively of two side parts (722,723) of substantially cylindrical shape and / or conical, of a diameter less than the inside diameter of said envelope, a middle part (721) disposed between the two said side parts, this middle part having a diameter substantially identical to the inside diameter of said envelope, this said side part comprising a continuous groove (713) opening out (714,715) on either side thereof> respectively towards the two said lateral parts