GB2163617A - Optical coupling device with rotating joint - Google Patents

Abstract

According to the device of the invention, optical coupling is provided by means of one or several parallel ray beams (Ft) of annular cross-section, transmitted in unidirectional or bidirectional form, between two ferrules (1, 2) mechanically coupled by a joint (3) rotating about an axis of rotation ( DELTA ), with which the beam(s) are coaxial. Mirrors (M1, M2) inclined at an angle of pi /4 radians relative to this axis ( DELTA ) each fold the beam, or beams, back on itself through pi /2 radians towards opto-electronic means of generation and/or detection (f1, L1, 11, 21, L2, f2). The axial region which is left clear may be used to establish a connection by electrical path (C1, C2, 6). <IMAGE>

Description

SPECIFICATION Optical coupling device with rotating joint The present invention relates to a rotating joint optical coupling device which makes it possible to provide optical transmission between pairs of receiver and/or transmitter units, securely fastened to a fixed structure and to a structure which has a rotational movement about one axis.

By way of non-limiting example, reference may be made to the data transfers between a central data processing unit and peripheral units securely fastened to a rotating antenna of certain types of radar.

The transfers may be of the unidirectional or bidirectional type and effected, according to the application envisaged, by a single path which may employ multiplexing techniques if necessary, or otherwise on several separate paths.

In addition to optical path connections, a connection channel may also provide other types of connection: for example the transmission of electrical signals by means of a coaxial cable or by a waveguide.

Finally, it is necessary to supply electrical energy to the units which are securely fastened to the rotating structure. This supply is provided, using the connecting channel, by means of cables carrying, in general, high currents.

It is therefore necessary to provide for rotating slip rings or similar devices to ensure electrical continuity between the fixed and rotating parts.

In addition to other inherent advantages of optical connections, especially the high transmission rate that they permit, the aptitude and characteristics which have just been referred to justify use of this type of connection, since, in addition, they make it possible to avoid in large measure the inevitable interference of electromagnetic origin, for example that due to arcing of the rotating slip rings.

More precisely, these optical connections are made by means of optical fibers coupled to each other by means of a rotating joint. In general, this type of device has two ferrules the one rotating relative to the other about an axis, each encasing an optical fiber or a bundle of optical fibers, and arranged end to end, having a propagation axis which, at the ends to be coupled together, is coincident with the axis of rotation.

This arrangement is not without disadvantages. It is in fact necessary to ensure a high accuracy in the alignment of the two fibers or bundles of fibers to be coupled together, whatever the relative positions of the two ferrules about the axis of rotation. It is in fact of prime importance to ensure a high quality optical coupling in order to minimize losses during transmission. It follows from this that the degree of accuracy in manufacturing tolerances in the mechanical parts is of the order of magnitude of a micron, especially for connections using monomode optical fibers. The difficulty is increased when moving pieces are involved, since wear and. mechanical play must be taken into account in considering the change in tolerances with time.

Finally, it may be advantageous to leave clear the axial region of the connecting channel in order specifically to make it possible to provide the other types of connection referred to.

The invention has the aim of responding to these needs and offers a rotating optical coupling device providing optical connections by means of one or several parallel ray beams of annular cross-section leaving the axial region clear for other purposes and permitting an increase in mechanical tolerances.

The subject of the invention is thus an optical coupling device comprising two ferrules which are mechanically coupled by a joint rotating about an axis of rotation; characterized in that it comprises at least: -opto-electronic means for generating at least one parallel ray transmission beam of annular cross-section propagating along an axis orthogonal to the axis of rotation; -a first plane mirror securely fastened to a first ferrule and inclined at an angle of ill/4 radians capturing the whole of at least one transmission beam and retransmitting it towards the second ferrule, along a direction parallel to the axis of propagation, in such a way as to establish the said optical coupling;; -a second plane mirror securely fastened to the second ferrule and inclined at an angle of n/4 radians relative to the axis of rotation, capturing the whole of this beam and retransmitting it along a direction orthogonal to the axis of rotation; and opto-electronic means for capturing and detecting this beam, and in that the rotating joint comprises an orifice centered about the axis of rotation whose minimum dimension is greater than the largest external diameter of the generated transmission beams.

Other features and advantages of the invention will be more clearly apparent with the help of the following description and the annexed figures amongst which: Figure 1 show schematically a first alternative embodiment of a rotating joint optical coupling device according to the invention.

An example of optical element beam converter construction according to a first approach, coming within the scope of the invention is shown in Figure 2. It consists of an optical element known by the name "Axicon".

Figure 3 represents a first variant of practical embodiment.

Figure 4 represents a cross-sectional view of a second possible variant for the assembly of the elements of Axicon.

Figure 5 shows, in cross-section, an optical conversion element.

A variant of construction is represented in Figure. 6.

Figure 7 shows a construction illustrating the conveyance of electrical signals.

Figure 8 represents a cross-sectional orthogonal to the axis of an output beam from a beam converter.

A first example of a multi-path rotation joint coupling device is shown schematically in Figure.

9.

Figure 10 illustrates a further structure in accordance with the invention.

Referring to Fig. 1 this device comprises two ferrules, 1 and 2, able to move relative to each other by rotating about an axis A. To simplify matters it will be arbitrarily assumed in the following text that ferrule 1 is fixed in space, for example is securely fastened to the chassis of an installation.

Ferrule 2 is thus securely fastened to a rotating structure, for example a rotating antenna if the installation is a radar.

The two ferrules 1 and 2 are mechanically coupled in a conventional manner by means of a rotating joint 3, or similar unit.

These arrangements are common to the majority of rotating joint devices of the known art.

One of the principal characteristics of the device according to the invention is that the optical path transmission between the two ferrules: 1 and 2, is provided by means of a parallel ray beam F, of annular cross-section with its axis of symmetry coincident with the axis of rotation A.

The beam thus appears in the form of a "tube" of light of internal radius R, and external radius R,.

At joint 3 the only constraint that need be noted is that it must have an aperture 30, centered about axis A, of dimensions greater than the external diameter of the annular beam F,.

The device also comprises, according to one important characteristic, plane mirrors, M1 and M2, arranged respectively in ferrules 1 and 2, and inclined at an angle of 11/4 radians relative to the axis of rotation A, so as to fold the transmission beam F1, along two axes A1, and A2, both axes being orthogonal to the axis of rotation A.

In order to keep the axial region clear, according to an advantageous arrangement of the invention, the mirrors each have a central aperture, 10 and 20.

The projections of the central apertures, 10 and 2 in a plane orthogonal to the axis A must inscribe a circle of radius at least equal to the radius R,. In the same manner, the dimensions of the mirrors are defined by the need to interrupt the whole of the beam F,. For practical reasons the mirrors preferably have an annular construction.

In order to complete this assembly, it is necessary to provide, at least within the luminous energy transmission units, if unidirectional transmission is concerned, an optical element making it possible to create a parallel ray beam of annular cross-section from the beam transmitted by the source.

In the optical path transmission applications envisaged, laser sources are generally used and these transmit either a parallel ray beam of circular cross-section, as is the case with gas lasers, or a divergent beam as is the case for a semiconductor laser source or the output face of an optical fiber. These beam conversion optical elements are represented by references 11 and 21 in Fig. 1.

In order to make the description clear it is assumed that the optical connection is of the unidirectional type between a transmitter unit 12 situated in the fixed part 1 of the equipment and a receiver unit 22 in the movable part 2. It is also assumed that intermediate connections are provided in a practical manner by means of optical fibers, f1 and f2 respectively, between transmitter 12 and optical element 11 on the one hand, and between receiver 22 and optical element 21 on the other.

In the example of embodiment shown in Fig. 1, optical elements 11 and 21 are intended to convert a parallel ray beam of annular cross-section into a parallel ray beam of circular crosssection or vice versa.

Provision is also made, in a conventional manner, for converting the divergent beam coming from optical fiber f1 into a cylindrical beam by means of a lens or a system of lenses with the reference L,. In the same way the cylindrical beam output from optical element 11 is focussed on the input face of fiber f2 by means of a second lens or a second system of lenses with the reference L2.

A simplified embodiment of optical elements 11 and 21 would consist of a simple diaphragm of radius Ri, masking the central region of the cylindrical beam. In practise this arrangement cannot be considered since it entails energy losses which are proportional to the ratio of the areas of the obscured and transmitted sections of the beam. In addition it is necessary to \ provide a beam enlarger so that the incident beams may have a cross-sectional external diameter equal to 2 R,,.

An example of optical element beam converter construction according to a first approach coming within the scope of the invention is shown in Fig. 2. It consists of an optical element known by the name "Axicon".

In order to make the description clear, it is assumed that element 11 of Fig. 1 is such an Axicon, it being possible for element 21 to be identical.

Axicon 11 comprises a cone 111 and a mirror 110 composed of a section of symmetrical revolution whose internal wall 1100 is reflecting at the wavelength of the beam transmitted by laser source 12.

The axes of revolution of cone 111 and mirror 110 coincide with the axis A1 The inclinations of the reflecting surfaces, the internal surface 1100 of the frustoconical mirror 110, and the surface 1110 of cone 111 facing surface 1100, all relative to the axis A1, must be chosen in such a manner that after reflection and division on surface 1110 and further reflection on surface 1100, the emergent beam F, of Axicon 11 propagates along a direction which is nominally parallel to the axis A1 For example, the two angles of inclination may be chosen equal to ill/4 radians.

The distance between the two reflecting surfaces determines the radius R, taking account of the cross-section of the incident beam F,.

The interassembly of the elements constituting the Axicon may be provided in any appropriate manner.

Fig. 3 represents a first variant of practical embodiment. Cone 111 is securely fastened to the frustoconical mirror 110 by means of two pins, 112 and 113, of small cross-section and, preferably, diametrically opposed relative to the apex 0 and aligned along an axis ', orthogonal to the axis A1. The small cross-section of the pins 112 and 113 ensures that only an equally very small fraction of the energy conveyed by beam F1 is interrupted.

Fig. 4 represents a cross-sectional view of a second possible variant for the assembly of the elements of Axicon 11. The frustoconical mirror 110 contains an annular groove 1102, extending its output face 1101, and intended to receive a thin plate 114 with parallel principal faces.

This thin plate must be transparent to the wavelength of the beam transmitted by the laser source 12.

It must also have anti-reflective coatings on these two principal faces.

Cone 111 is fixed, for example by screwing means 115, at the center of the thin plate 114 in such a way that the point 0 is aligned on axis A1. At the cost of a small increase in complexity, this assembly has the advantage of allowing a more accurate centering and fastening of cone 111, which rests on a flat base, and also the advantage of not interrupting any part of the beam as is the case with the construction described in Fig. 3, where a fraction of the annular beam F, is interrupted by pins 112 and 113.

It should be noted that the effect of optical element 11 on the transmission of luminous energy does not depend on the direction of transmission. Where unidirectional transmission is concerned, as shown in Fig. 1, the element 21 will have a reciprocal effect and transform the incident beam F1 of annular cross-section into a cylindrical beam F2.

Where bidirectional transmission is concerned, each element 11 and 21 performs both conversions.

It should also be noted that, if two optical conversion elements are used, four beam reflections are produced, two in each element, and this is naturally in addition to the reflections at the plane mirrors M1 and M2.

A typical coefficient of reflection may be taken to be approximately 0.95. It thus follows that, under these conditions, the equivalent coefficient of reflection at the two elements 11 and 21 is equal to 0.8.

It is possible, by making use of other techniques, to reduce the reflection losses.

Fig. 5 shows, in cross-section, an optical conversion element 11' according to a second approach which makes it possible to improve the energy efficiency. The configuration remains that of an Axicon, but this latter is made in the form of a total reflection monobloc prism. It consists of a block of refracting material registered, on the one hand between two parallel planes which constitute the input and/or output faces 116 and 117 of the optical beam conversion element 11', and, on the other hand, between two surfaces, conical 1110' and frustoconical 1100', whose axes of revolution are coincident with axis A1. These two surfaces constitute reflecting surfaces for the light rays and act as reflecting surfaces 1110 and 1100 (Figs. 2 to 4) with a coefficient of reflection close to unity.The losses due to interference reflections at the input and/or output faces, 116 and 117, may be minimized by applying a conventional anti-reflective treatment. The coefficient of reflection may be made much less than 16.

The interior radius Rj of the annular beam F, is dependent only on the radius of the input Xface 116 assuming that the point 0 of the conical surface 1110' is level with surface 116, the beam F1 input surface in the example shown. More generally, the radius Rj is dependent only on the separation existing between the two surfaces 1100' and 1110'.

The external radius F0 of beam F, is dependent on the one hand on the radius Rl of the cylindrical beam F1 and, on the other hand, on the separation between the two reflecting surfaces.

It is again possible to extend one or other or both of the input and/or output faces by a uniform thickness of refracting material. This variant of construction is represented in Fig. 6. The conical projections 1110' and 1100' of the monobloc prism 11' are extended by "thin sections" 118 and 119 of the refracting material. Naturally, the new input and/or output faces 116' and 117'must remain parallel to each other and orthogonal to axis A1. In the same way the point 0, apex of the conical surface 1110', remains centered about axis A1.

Typically, the luminous energy transmitting and/or receiving elements 12 and 22 (Fig. 1) may comprise, for transmission, laser diodes or light emitting diodes and, for reception, photodiodes of the "PIN" type or avalanche photodiodes. It is also possible to use an opto-electronic component capable of functioning alternately as transmitter and as detector for luminous energy of the same wavelength. This component is preferably the semi-conducting diode described in French Patent B-2,396,419. This patent relates to a semiconducting diode which transmits light when polarized in the positive direction, and which is capable of detecting light of the same wavelength when polarized in the reverse direction.

One of the principal characteristics of the device of the invention is that it leaves clear the axial region, that is to say a cylinder of radius equal to R,. This characteristic can be turned to advantage in order to convey electrical signals by this channel.

Fig 7 shows such an arrangement.

In reality parts 1 and 2 of the device as described by reference to Fig. 1 constitute only the ferrules of an optical coupler, ferrules which are securely fastened to a fixed structure 4 and a movable structure 5 respectively, for example. It follows therefore that the rotating joint 3 serves only to provide the capability for relative movement of the two ferrules 1 and 2. The movable structure 5, for example the antenna mast in a radar system, is in no way supported by the rotating joint 3 but by any appropriate means (not represented on Fig. 7).

An example of a construction which may be adopted within the scope of the invention is described in French Patent Application A-2,448,728.

In the example shown, the electrical signals are conveyed by a coaxial cable divided into two parts, C, and C2, and aligned with the axis of rotation A.

The connection between these two parts of coaxial cable is provided by a supplementary rotating joint 6 arranged between the two mirrors M1 and M2, preferably in the space 30 left clear in the region of the rotating joint 3. The coaxial cable must be sufficiently rigid to avoid any excessive flexure which would cause interruption of the luminous flux of beam F1, especially by the rotating joint 6.

Means of cable tensioning and retention, 40 and 41, can be provided at the passages of the cable through the walls of the ferrules 1 and 2.

The transmission and processing of the electrical signals is performed outside the ferrules 1 and 2 by conventional means.

The same applies to the optical signals as shown in Fig. 7. In the device represented in this figure, optical fibers f, and f2 leave ferrules 1 and 2 to be coupled to non-represented means of transmission and/or reception of luminous energy.

The coaxial cable (C1, C2) may be replaced by any other type of connection: for example by a waveguide.

The device according to the invention which has just been described thus has the following advantages: -a rotating axis; -easy adjustment of the size of the hollow cylinder of light transmitted in air by simply altering the geometric dimensions of the optical elements used: lenses L1 and L2, mirrors M1 and M2 and beam converter elements 11 and 21; -increase in mechanical tolerances relative to those associated with optical rotating joints of the known art, this being due to the increase in diameter of the transmitted optical beam; -low energy losses, even in the configuration which has just been described with reference to Fig. 7.

In fact, in this configuration the beam F1 is interrupted twice by the parts C1 and C2 of the coaxial cable.

Fig. 8 represents a cross-section orthogonal to the axis A1 of beam F1 output from the beam converter element 11. One part of the luminous energy conveyed by beam F1 is interrupted by cable Ct over a width d. This phenomenon is repeated after reflection of beam Fit at mirror M2.

The energy interrupted is dependent upon the diameters of cables C1 and C2, which are assumed to be equal in the following text, and upon the ratio between the radii Rj and Fe.

The maximum transmission loss in db is given by the formula:

d being the common diameter of the coaxial cables Ct and C2.

If the shadow cast by guide C1 and that by guide C2 coincide, the transmission loss reduces to:

By way of example, typical values are: d=2 cm, R,=4 cm, R,=8 cm.

In these conditions PM &num; 0.49 db and P'M # 0.24 db.

Experimental results confirm these figures. It is also established that the fluctuations due to rotation are of low amplitude and have little effect on the optical transmission especially if the latter is provided by digitally coded or frequency modulated light waves.

Up to the present it has been implicitly assumed that the device of the invention allowed transmission of a single channel of data. However, the customary techniques of time multiplexing or of frequency multiplexing using different wavelengths make it possible to convey two, or more generally several, signals simultaneously or sequentially.

The use of light waves of different polarization, for example two waves with directions of polarization orthogonal to each other, also makes it possible to convey several different signals.

Polarizer-analyzer sets are then used to this effect.

As a supplementary advantage, however, the invention also makes it possible to create several physically distinct transmission paths.

A first example of a multi-path rotating joint coupling device is shown schematically in Fig. 9.

A first set of two mirrors M11 and M21 inclined at n/4 radians relative to the axis of rotation A makes it possible to create a first optical transmission path by means of a parallel ray transmission beam F11 of annular cross-section, of internal radius R,1 and of external radius Rel. Mirrors M1, and M,2 each bend the beam F,1 through n/2 radians. The folded beams propagate along the axes A11 and A21, orthogonal to axis A. All these arrangements are identical to those described by reference to beam F, and mirrors M1 and M2 shown in Fig. 1.

A second optical transmission path is created by using a second set of mirrors M12 and M22 a-lso inclined at ill/4 radians relative to the axis A in such a way at to fold back on itself a second parallel ray transmission beam F12 of annular cross-section, of internal radius R,2 and external radius Rue2. The folded beams propagate along axes A12 and A22, orthogonal to axis A.

Sets of beam converters (not represented in Fig. 9) interrupt the folded beams in an identical manner to that which has been described with reference to Fig. 1. Light energy transmission and/or reception units are also provided and have not been represented for reasons of simplification. These units also serve identical purposes to those described with reference to Fig. 1.

In order that the device operates correctly, it is necessary that the following conditions are simultaneously complied with: a) Re1 < R,2 b) that the overall dimensions of mirrors M1l and M21 projected on a plane orthogonal to axis A are less than R12 c) that mirrors M11 and M21 on the one hand, and M12 and M22 on the other hand, are disposed along axis A in such a way as to interrupt only the transmission beam F,1 or F,2 intended for them d) and that the projections of the mirror central apertures onto a plane orthogonal to axis A: 101 and 201 for mirrors M11 and M21, 102 and 202 for mirrors M12 and M22, must be less than or equal to R,1 and R,1 respectively.

The number of separate paths is naturally not limited to two. In Fig. 9 the directions of beam propagation have been indicated in an arbitrary manner. The transmission can equally be bidirectional. Finally, the arrangements of the known art which have been referred to: time multiplexing or frequency multiplexing for example, can be implemented over all or part of the transmission paths.

The orientations of mirrors M11 to M22 about the axis A and consequently the relative angular displacements of axes A11 to A22 in a plane orthogonal to axis A have also been represented in an arbitrary manner and may be chosen to suit the convenience of the user.

The structure of the device which has just been described makes a large decoupiing of the transmission paths possible and reduces to a minimum risks of crosstalk between these paths.

However, this structure demands the use of two sets of inclined mirrors. It is possible to avoid this constraint by adopting the architecture shown in Fig. 10. The same mirrors M, and M2 identical to those shown in Fig. 1, serve to fold back upon themselves the different transmission beam, which in the example shown in Fig. 10 have been reduced to two, Ftl and F,2, with the aim of simplification.

As before, it is necessary that the condition F,1 < F12 is respected, and that the dimensions of the central orifices 10 and 20, are such that their projections onto a plane orthogonal to the axis A are less than or equal to the radius R,1.

Under these conditions two sets of optical beam conversion elements, 111 and 211 on the one hand, 112 and 212, on the other hand, are arranged in cascade along the axes A1 and A2 respectively, these being the axes of propagation of the beams F,1 and F,2 folded back by mirrors M1 and M2. These axes are naturally orthogonal, as in the previous case, to the axis of rotation.

Optical elements 111, 112, 211 and 212 transform the transmission beams F,1 and F,2 of annular cross-section into beams F,1, F,2, F21 and F22 of circular cross-section or vice-versa.

These latter may be generated and/or captured as previously with the help of focussing lenses: L11, L12, L21 and L22; associated with the optical fibres: F11, F12, F21 and F22 coupled to the luminous energy transmission and/or detection units (not represented).

A supplementary condition to be respected is that the overall dimensions of the beam converter elements 111 and 211 associated with the transmission beam F,1 of the smallest crosssection shall be less than the internal diameter (2F,2) of the transmission beam F,2 in such a way as not to interrupt it.

Under these conditions, after reflection at mirrors M1 and M2, a very small fraction of energy of this latter beam is interrupted, on the one hand by the optical fibres fl, and f21, which is negligible, and on the other hand by means of fixing the optical beam conversion elements 111 and 211 to the ferrules 1 and 2 (Fig. 1 and Fig. 7). These fixing means, 1110 and 2110, may be composed of fine pins which can be arranged in space in such a way as to coincide with the shadows produced by a central connection channel if fitted (Fig. 7: C,-C2). Alternatively, means of fixing which are transparent to the wavelengths used may be employed, with antireflective treatment.

The invention is not limited only to the embodiments described with the sole aim of illustrating the invention. Every variant within the capability of the man skilled in the arts falls within the scope of the invention. In particular, combinations of different structures of the device for multipath coupling may be constructed.

Claims (12)

1. Optical coupling device comprising two ferrules (1, 2) which are mechanically coupled by a joint (3) rotating about an axis of rotation (A) characterized in that it comprises at least: -opto-electronic means (12, fl, L1, 11) for generating at least one parallel ray transmission beam (F,) of annular cross-section propagating along an axis (81) orthogonal to the axis of rotation (A); -a first plane mirror (Ml) securely fastened to a first ferrule (1) and inclined at an angle of H/4 radians capturing the whole of at least one transmission beam (F,) and retransmitting it towards the second ferrule (2) along a direction parallel to the axis of propagation (A) in such a way as to establish the said optical coupling;; -a second plane mirror (M2) securely fastened to the second ferrule (2) and inclined at an angle of n/4 radians relative to the axis of rotation (A) capturing the whole of this beam (F,) and retransmitting it along a direction (A2) orthogonal to the axis of rotation (A); -opto-electronic means (21, L2, f2, 22) for capturing and detecting this beam (F1); and in that the rotating joint (3) comprises an orifice (30) centered about the axis of rotation (A) whose minimum dimension is greater than the largest external diameter (2rye2) of the generated transmission beams (F,).

2. Device as claimed in claim 1, characterized in that the inclined mirrors (M, M) contain apertures (10, 20) centred about the axis of rotation (A) whose maximum dimensions projected onto a plane orthogonal to this axis (A) are less than or equal to the smallest internal diameter (2F,1) of the generated transmission beams (F,).

3. Device as claimed in claim 2 characterized in that it comprises in addition an electric signal transmission channel (C1, C2) supplied with a rotating joint (6) centered about the axis of rotation (A) and in that the cross-section of this channel has a maximum dimension which is less than the smallest internal diameter (2R,1) of the generated transmission beams (F,).

4. Device as claimed in any one of claims 1 to 3, characterized in that the opto-electronic means for generating and capturing transmission beams (F,) contain beam conversion optical elements (11, 21) which transform in a reciprocal manner a parallel ray beam (F1, F2) of circular cross-section propagating along an axis (A 2) orthogonal to the axis of rotation (A) into a parallel ray beam (F,) of annular cross-section propagating along the same axis (A A2).

5. Device as claimed in claim 4 characterized in that the beam conversion optical elements (11, 21) are each composed of an Axicon comprising a cone (111) with external reflecting wall (1110) of axis of revolution coincident with the beam propagation axis (A1) and a mirror (1 tO) comprising a frustoconical cavity with reflecting wall (1100), of axis of revolution coincident with the said axis of propagation (A,); and in that the reflecting surfaces (1100, 1110) form an angle equal to n/4 radians with this axis (A

6.Device as claimed in claim 4, characterized in that the beam conversion optical elements are composed of total reflection prisms having the form of thin plates with parallel faces (116, 117) in refracting material comprising a conical wall cavity (1110') of axis of revolution coincident with the beam propagation axis (A,) and bounded at its periphery by a frustoconical wall of axis or revolution which is also coincident with the beam propagation axis (A1) and in that the walls (1100', 1110') are total reflection surfaces to the beams propagating within the refracting material and are inclined at an angle equal to ill/4 radians relative to the axis (A1).

7. Device as claimed in any one of claims 4 to 6, characterized in that the opto-electronic means for generating and capturing the beam include optical fibers (f1, f2) coupled to the parallel ray beams (F1, F2) of circular cross-section by means of focussing lenses (L1, L2).

8. Device as claimed in any one of claims 1 to 7, characterized in that it comprises at least a first (f11, L11, 111, 211, L21, f21) and a second (fl2, L12, 112, 212, L22, f22) set of opto-electronic means for generating and capturing parallel ray beams with annular cross-sections in such a way as to couple the two ferrules (1, 2) by means of at least two concentric transmission beams (F,l, F,2) and in that the internal radii (tri,, Raj2) and external radii (Re1, Re2) of the annular crosssections of the transmission beams are determined in such a way that these annular crosssections have no common part.

9. Device as claimed in claim 8, characterized in that it comprises a unique set of two mirrors (Ml, M2) inclined at an angle equal to ill/4 radians each capturing the whole of the transmission beams (F,l, F,2) and folding them back upon themselves along directions (A1, 2) orthogonal to the axis of rotation (A).

10. Device as claimed in claim 8, characterized in that it comprises several sets of two mirrors (Mll-M2l, M12-M22) and in that each set of mirrors captures one of the transmission beams (F,1, F,2) and folds it back upon itself along the directions (All-A2l; A12-A22) orthogonal to the axis of rotation (A).

11. Device as claimed in any of claims 1 to 10, characterized in that the optical coupling being of the bidirectional type, each ferrule (1, 2) comprises opto-electronic means for ensuring the simultaneous operation of generation and capturing at least one transmission beam (F,).

12. An optical coupling device substantially as hereinbefore described, with reference to, and as illustrated in the accompanying drawings