FR2569861A1 - OPTICAL COUPLING DEVICE WITH ROTATING SEAL - Google Patents

Abstract

DEPENDING ON THE DEVICE OF THE INVENTION, THE OPTICAL COUPLING IS CARRIED OUT BY USING ONE OR MORE BEAMS F OF PARALLEL RAYS WITH AN ANNULAR SECTION TRANSMITTED, UNIDIRECTIONAL OR TWO-WAY, BETWEEN TWO 1, 2 COUPLES MECANICALLY BY A JOINT 3 ROTATING AROUND AN AXIS OF ROTATION, THE BEAMS BEING COAXIAL TO THIS. M, M MIRRORS INCLINED AT AN ANGLE OF P4 RADIANS IN RELATION TO THIS AXIS BEND THE BEAM (S) ON THEM FROM AN ANGLE OF P2 RADIANS TOWARDS MEANS OF GENERATION AND OR OF OPTO-ELECTRONIC DETECTION F, L, 11, 21 , L, F. THE AXIAL REGION LEFT FREE MAY BE USED FOR ESTABLISHING AN ELECTRICAL CONNECTION C, C, 6.

Description

-1

  OPTICAL COUPLING DEVICE WITH ROTATING SEAL

  The present invention relates to a rotary coupling optical coupling device for establishing optical transmissions entte couples of receiving members and / or transmitters integral respectively uh fixed frame and a frame animated by a movement of rotation relative to an axis. By way of non-limiting example, reference may be made to data exchanges between a central data processing unit and peripheral units integral with a rotating antenna of certain types.

of radar.

  The exchanges can be of the unidirectional or bidirectional type and

  to be carried out, depending on the application envisaged, by a single route

  using multiplexing techniques, or

  contrary on several distinct paths.

  In addition to optical links, a link channel can also provide other types of links: for example signal transmission.

  by means of a coaxial cable or a waveguide.

  Finally, it is necessary to supply electrical energy to the integral units of the rotating frame. This power supply is made using cables

  usually carrying strong currents through the connecting channel.

  It is then necessary to provide turn-ring collectors or similar devices to ensure electrical continuity between

fixed and rotating parts.

  In addition to other advantages specific to optical links,

  transmission capacity they allow, the provisions and characteristics

  Some of the reasons for this type of link are justified by the fact that they also make it possible to largely escape the unavoidable parasitisms of electromagnetic origin, for example those caused by electromagnetic interference.

  the "spitting" of rotating ring collectors.

  More specifically, these optical links are made using optical fibers coupled together by means of a rotary joint. In general, this type of device comprises two endpieces rotated relative to one another about an axis, each trapping an optical fiber or a bundle of optical fibers arranged end to end, having a confused axis of propagation,

  at their ends to couple, with the axis of rotation.

  This provision is not without drawbacks. It is indeed necessary to ensure high accuracy in the alignment of the two fibers or bundles of fibers to be coupled, whatever the relative positions of the two ends around the axis of rotation. It is indeed essential to ensure quality optical coupling to minimize losses during transmissions. It follows that the degree of precision in the manufacturing tolerances of the mechanical parts is of the order of magnitude of 1 micrometer, in particular for monomode optical fiber connections. The difficulty is increased when it comes to moving parts, because the notions of wear and mechanical play must be introduced to hold

  account of the evolution of tolerances over time.

  Finally, it may be advantageous to leave the axial region of the connecting channel free to precisely allow the establishment of other types of

links recalled.

  The aim of the invention is to meet these needs and proposes a rotating optical coupling device providing the optical type links by means of one or more parallel ray beams with annular sections leaving the axial region free for others. uses and

  allowing an increase in mechanical tolerances.

  The invention therefore relates to an optical coupling device comprising two end-pieces 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 transmission beam with parallel radii and annular section propagating along an axis orthogonal to the axis of rotation; a first plane mirror secured to a first endpiece and inclined by a

  angle of ir / 2 radians in total capturing at least one beam of

  sion and retransmitting it to the second end in a direction parallel to the axis of propagation so as to establish said optical coupling; a second plane mirror secured to the second endpiece and inclined at an angle of uT / 4 radians with respect to the axis of rotation capturing this beam in its entirety and retransmitting it in a direction orthogonal to the axis of rotation; and optoelectronic means for capturing and detecting this beam, and in that the rotary joint comprises an orifice centered on the axis of rotation whose minimum dimension is greater than the largest diameter

  outside generated transmission beams.

  Other features and advantages of the invention will appear more

  clearly with the aid of the description below and the appended figures

which:

  Figure 1 schematically illustrates a first embodiment variant

  tion of a rotary coupling optical coupling device according to the invention. This device comprises two tips 1 and 2, movable relative to each other in rotation about an axis A. It will be assumed arbitrarily in what follows, to simplify, that the tip 1 is fixed in the space, by

  example is attached to the chassis of an installation.

  The tip 2 is then secured to a rotating frame, for example a

  rotating antenna if it is a radar installation.

  The two ends 1 and 2, are mechanically coupled so

  conventionally using a rotary joint 3 or a similar member.

  These provisions are common to most sealant devices

turning of the known art.

  One of the main characteristics of the device according to the invention is that the transmission optically between the two end pieces: 1 and 2 is effected by means of a beam Ft of parallel radii with an annular cross-section of symmetry coincides with the axis of rotation A. The beam is therefore in the form of a "tube" of beam light

internal Ri and outer radius Re-

  At the joint 3, the only constraint to be respected is that it has an opening 30 centered on the axis A of dimensions greater than the outer diameter of the annular beam Ft

  The device also comprises, according to an important characteristic

  te, planar mirrors, M1 and M12, respectively arranged in the ends 1 and 2 and inclined at an angle equal to ir / 4 radians relative to the axis of rotation A, so as to fold the next transmission beam Ft two axes, A and A 2 'orthogonal to the axis To leave free the axial region, according to an advantageous arrangement of

  the invention, the mirrors each comprise a central opening, 10 and 20.

  The projections of the central openings 10 and 20 on a plane orthogonal to the axis A must be inscribed in a circle of radius at most equal to the radius R 1. In the same way, the dimensions of the mirrors are determined to intercept the entire beam Ft. Practically, the mirrors

  are preferably provided with an annular structure.

  To complete this set, it is necessary to provide at least

  level of the luminous energy emitting organs, if it is a transmission

  unidirectional, an optical element for creating a beam of parallel rays of annular section from the beam emitted by the source. For the envisaged optical transmission applications, it is generally used laser sources emitting either a parallel ray beam of circular section, as is the case of gas laser sources, or a divergent beam, such as is the case for a semiconductor laser source or for the output face of an optical fiber. These optical beam conversion elements have been represented under the references

11 and 21 in FIG.

  To fix ideas, it is assumed that the optical link is unidirectional type between a transmitter member 12 located in the fixed part 1 of the installation and a receiver member 22 in the mobile part 2. It is also assumed that, so In practice, intermediate links using optical fibers, respectively f1 and f2, are formed between, on the one hand, the transmitter 12 and the optical element 11 and, on the other hand, the receiver 22.

and the optical element 21.

  In the exemplary embodiment, illustrated in FIG. 1, the optical elements 11 and 21 are intended to convert a beam of parallel rays of annular section into a beam of parallel rays of circular section.

or the opposite.

  Conventionally, it is also planned to convert the diverging beam output of the optical fiber f1 into a cylindrical beam with a lens or a lens system referenced L1. In the same manner, the cylindrical beam at the output of the optical element 11 is focused on the input face of the fiber f2 with the aid of a second lens or a second lens.

  lens system referenced L2.

  A simplified embodiment of the optical elements 11 and 21 would consist of a simple diaphragm of radius Ri masking the central region of the cylindrical beam. In practice this arrangement can not be retained because it involves energy losses proportional to the ratio of the surfaces of the sections concealed and transmitted beam. In addition, it is necessary to have a beam extender so that the

  Incident beams have a section of external diameter equal to 2 Re.

  An embodiment of optical beam converter element according to a first approach, which may be suitable in the context of the invention, is illustrated in FIG. 2. It is an optical element known as

denomination of axicon ".

  To fix the ideas, it is supposed that it is the element II of the

  Figure 1, the element 21 may be identical.

  The axicon 11 comprises a cone 111 and a mirror 110 consisting of a

  section with symmetry of revolution whose inner wall 1100 is reflective

  at the wavelength of the beam emitted by the laser source 12.

  The cone 111 and the mirror 110 have their axes of revolution merged with the axis A 1 inclinations relative to the axis A 1 of the reflecting surfaces, the inner surface 1100 of frusto-conical mirror 110 and the surface 1110 of cone 111 compared with the surface 1100 should be chosen so that, after reflection and division on the surface 1110 and new reflection on the surface 1100, the beam emerging Ft axicon 11 is propagated along a direction substantially parallel to For example, the two angles of inclination can be chosen equal to

A / 4 radians.

  The difference between the two reflective surfaces determines the radius Re

  considering the section of the incident beam F1.

  The assembly between them elements constituting the axicon can be

  realized in any appropriate way.

  FIG. 3 represents a first practical variant.

  The cone 111 is secured to the truncated-conical mirror 110 by means of

  diaire of two rods, 112 and 113, of small section and, preferably, diametrically opposite to the vertex O and aligned on an axis A 'orthogonal to the axis A 1 The small section of the rods 112 and 113 allows

  to intercept only a very small fraction of the trans-

by beam F1.

  FIG. 4 represents in section a second possible variant of assembly of the elements of the axicon 11. The truncated-conical mirror 110 comprises, extending its outlet face 1101, an annular groove 1102 intended to receive a blade 114 with parallel main faces . This blade must be transparent to the wavelength of the beam emitted by the source

laser 12.

  It must also be anti-reflective on both sides

main.

  The cone 111 is then fixed, for example by screwing means 115, in the center of the blade 114 so that the tip O is aligned on the axis A 1 At the cost of a slight increase in complexity, this assembly has the advantage of allowing a more precise fixing and centering of the cone 111 which rests on a flat base and not to intercept any part of the beam, as is the case in the embodiment described in relaiton with FIG. , a fraction of the annular beam, Ft being intercepted by

the rods 112 and 113.

  It should be noted that the effect of the optical element 11 on the transmission

  light energy does not depend on the direction of transmission. If it is a unidirectional transmission as illustrated in FIG. 1, the element 21 will have a reciprocal effect and will transform the incident beam Ft of

  annular section in a cylindrical beam F2.

  If it is a bidirectional transmission, each element, 11 or

21, performs both conversions.

  It should also be noted that, if two optical conversion elements are used, then four reflections of the beam, two in each element, occur naturally, in addition to reflections on the mirrors.

plans M1 and M2.

  A typical reflection coefficient can be estimated at about 0.95. It follows that, in those circumstances, the reflection coefficient is equivalent to the

  two elements 11 and 21- is equal to 0.8.

  It is possible, by using other techniques, to reduce reflection losses. FIG. 5 illustrates, in section, a conversion optical element 11 '

  a second approach that improves energy efficiency.

  The configuration remains that of an axicon, but it is realized in the form of a monoblock prism with total reflections. It is a block of refractive material inscribed, on the one hand, between two parallel planes which constitute the input and / or output faces, 116 and 117, of the optical element I-I1 'of conversion of beam and, secondly, between two conical surfaces 1110 'and truncated-conical 1100' whose axes of revolutions coincide with the axis A 1. These two surfaces constitute reflecting surfaces for the light rays and play the role reflecting surfaces 1-110 and 1100 (Figures 2 to 4) with a reflection coefficient close to unity. Losses to spurious reflections on the input and / or output faces, 116 and 117, can be minimized by performing anti-reflective treatment

  classic. The reflection coefficient can be made much lower than 1%.

  The inner radius Ri of the annular beam Ft depends only on the radius of the input face 116, assuming that the tip O of the conical surface 1110 'is flush with the surface 116, beam entry surface F1 in the illustrated example. . More generally, the radius Ri depends only on

  the gap between the two surfaces 1100 'and 1110'.

  The outer radius R of the beam Ft depends, on the one hand, on the radius R1 of the cylindrical beam F1 and, on the other hand, on the distance between the two reflecting surfaces. It is still possible to extend one or the other or both input and / or output faces of a uniform thickness of refractive material. This variant embodiment is shown in FIG. 5. The conical bearing surfaces 1110 'and 1100' of the one-piece prism 11 'are extended by "blades" 118 and 119 of the refractive material. Naturally, the new input and / or output faces 116 'and 117' must remain parallel to each other and orthogonal to the axis A. Similarly, the point O vertex of the conical surface 1110 'remains centered on the axis A. 1

  Typically the elements 12 and 22 (FIG. 1) of transmission and / or reception

  of light energy may include, for the emission, diodes

  laser or light-emitting diodes and, for the reception,

  PIN type diodes or avalanche photodiodes. It is also possible to use an optoelectronic component capable of operating alternately as a transmitter and as a light energy detector of the same wavelength. This component is preferably the semiconductor diode

  described in patent FR-B-2 396 419. This patent concerns a semiconductor diode

  conductive which, polarized in the forward direction, emits light and which, polarized in the opposite direction, is capable of detecting light of the same

wave length.

  One of the main features of the device of the invention is

  leave free the axial region, ie a cylinder of radius equal to Ri.

  This characteristic can be used to convey through this channel

electrical signals.

  Figure 7 illustrates such an arrangement.

  In reality, the parts 1 and 2 of the device as described in relation with FIG. 1 only constitute the tips of an optical coupler,

  fixed ends respectively of a fixed frame 4 and mobile 5, for example.

  It goes without saying that the rotary joint 3 only serves to ensure the relative mobility of the two end pieces 1 and 2. The movable frame 5, for example the antenna mast in a radar, is in no way supported by the rotary joint 3 but

  by any appropriate means (not shown in Figure 7).

  An example of a structure that can be adopted in the context of

  the invention is described in the French patent application FR-A-2,448,728.

  The electrical signals, in the illustrated example, are conveyed by a coaxial cable split into two parts C1 and C2 and aligned on the axis of rotation. The junction between these two coaxial cable portions is provided by an additional rotary joint 6 arranged between the two mirrors M1 and M2, preferably in the space 30 left free at the rotary joint 3. The coaxial cable must be sufficiently rigid to avoid any exaggerated bending which would cause the interception of the luminous flux of the beam Ft,

in particular by the rotary joint 6.

  Means for tensioning and holding the cable 40 and 41 may be

  provided at the passages through the walls of the end pieces 1 and 2.

  The emission and the processing of the electrical signals take place outside the end-pieces 1 and 2 by conventional means. The same may be the case with optical signals, as illustrated in FIG. 7. In the device represented in this figure, the optical fibers f1 and f2 exit end-pieces 1 and 2 to be coupled to transmission means.

  and / or receiving light energy not shown.

  The coaxial cable (C1, C2) can be replaced by any other type of

  binding: for example a waveguide.

  The device according to the invention which has just been described thus has the following advantages: - availability of the axis of rotation; - easy adaptation of the size of the hollow cylinder of transmitted light

  in the air simply by playing on the geometrical dimensions of the ele-

  optical elements used: lenses L1 and L2, mirrors M1 and M2 and beam converter elements 11 and 21;

  - increased mechanical tolerances compared to those associated with

  optical rotating joints of the prior art, this being due to the increase in

  the diameter of the transmitted optical beam; - low energy losses, even in the configuration that comes

  to be described in connection with Figure 7.

  Indeed, in this configuration, the beam Ft is intercepted at two

  parts C1 and C2 of the coaxial cable.

  FIG. 8 represents a section orthogonal to the axis A 1 of the beam Ft at the output of the converter element of the flange 11. Part of the light energy conveyed by the beam Ft is intercepted by the cable C1 over a width d . This phenomenon is reproduced after reflection of the beam Ft on the mirror M2. The energy intercepted depends on the diameters of the cables C1 and C2 which will be assumed equal in the following and the existing ratio

between the rays Ri and Re-

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

(R2 - R.2)

  PM = 0 log (2 l it (R e2 Ri2) -2 (Re-R) d

  d being the common diameter of the coaxial cables C1 and C2.

  If the drop shadow of guide C1 is matched to that of guide C2, the transmission loss is reduced to:

(R 2 R.2

  PlM = 10 log (2 (R 2 R 2) - (R - R) d e By way of example, typical values are: d = 2 cm, Ri = 4 cm,

R = 8 cm.

e

  Under these conditions PM: 0.49 db and P'M # O0.24 db.

  Experimental results verify this data. It is furthermore noted that the fluctuations due to the rotation are of small amplitudes and do not affect the optical transmission, especially if this is done by means of

  light waves encoded in digital code or in frequency modulation.

  So far, it has been implicitly considered that the

  the invention allowed the transmission of a single information channel. How-

  usual time or frequency multiplexing techniques using different wavelengths can convey two or

  more generally, several signals simultaneously or sequentially

  is lying. The use of differently polarized light waves, for example two waves with directions of orthogonal polarizations between them, allows

  also to convey several different signals. Polarizer games-

  analyzer are then used for this purpose.

  However, and this is an additional advantage, the invention also allows the creation of several physically distinct transmission paths.

  A first example of a multi-rotary joint coupling device

  path is schematically illustrated in FIG.

  - A first set of two mirrors M1 and M21 inclined at rf / 4 radians with respect to the axis of rotation A allows the creation of a first optical transmission channel via a transmission beam. Ftl with parallel rays of annular section, inner radius Ril and outer radius Rel. Mirrors M1 and M12 fold the Fti beam by an angle of r / 2 radians. The folded beams propagate along axes AL and A21 orthogonal to the axis A. All these arrangements are identical to those described in relation to the beam Ft and the mirrors M1 and M2 illustrated in FIG. 1. A second optical transmission path is created using a second set of mirrors M12 and M22 also inclined at r / 4 radians with respect to the axis a so as to fold on itself a second transmission beam Ft2, with parallel radii of annular section, of inner radius Ri2 and outer radius Re2. The folded beams propagate along axes A 12 and A 22 orthogonal to the axis

12 22

  Sets of beam converters (not shown in FIG. 9) intercept the folded beams identically to what has been described with reference to FIG. Transmitting and / or receiving luminous energy devices are also provided and have not been shown for purposes of simplification. These organs also play a role identical to those

  described in connection with Figure 1.

  For the device to work properly, the following conditions must be fulfilled simultaneously: a / R <Ri2

-20 el - il2 -

  b / that the overall dimensions of the Mtl and M21 mirrors projected onto

  a plane orthogonal to the axis A are less than Ri2 -

  c) that the mirrors M and M21 of a party and M12 and M22, on the other hand, are arranged along the axis A so as to intercept only the transmission beam, Ftl or Ft2 which is intended for them. and that the projections of the central apertures of the mirrors on a plane orthogonal to the axis A: 101 and 201 for the mirrors M1 and M21, 102 and 202 for the mirrors M21 and M22, must be less than or equal to

respectively Ril and Ri2-

  The number of separate channels is of course not limited to two.

  In FIG. 9, the directions of propagation of the beams have been indicated from

  arbitrary way. The transmission can also be bidirectional.

  Finally, the provisions of the known art which have been recalled: multiplexing in time or in frequency-for example, can be implemented on any

  or part of the transmission channels.

  The orientations of the mirrors M1 to M22 about the axis A and consequently the relative angular offsets of the axes A1 to A22 in a plane orthogonal to the axis A have also been arbitrarily represented and can be selected at the convenience of the user. The device structure that has just been described allows a great decoupling of the transmission channels and minimizes the risks of cross-talk between these channels. This structure, however, requires the use of two sets of inclined mirrors. It is possible to escape this constraint by adopting the architecture illustrated in Figure 10. The same mirrors, M1 and

  M2, identical to those illustrated in Figure 1, serve to fold on them-

  even the different beams of transmissions, reduced to two Ftl and Ft2

  in the example illustrated in Figure 10, for simplification purposes.

  As previously, it is necessary that the condition Rel <Ri2 be respected and that the dimentions of the central orifices 10 and 20 are such that their projections on a plane orthogonal to the axis A are lower or

equal to the radius Rii.

  Under these conditions, two sets of beam conversion optical elements, 111 and 211 on the one hand, 112 and 212, on the other hand, are arranged in cascade along the respective axes A 1 and A2, axes of propagation of the beams. Ftlet Ft2 folded by mirrors M1 and M2. These axes are naturally orthogonal, as before, to the axis of rotation. The optical elements 111, 112, 211 and 212 transform the transmission beams Fti and Ft2 of annular sections into beams F11 F12 F21

  and F22 circular section or vice versa.

  These can be generated and / or captured as previously using focusing lenses: LI ,, L12, L21 and L22; associated optical fibers: F11, F12, F21 and F22 coupled to transmission devices

  and / or light energy detection (not shown).

  An additional condition to be respected is that the dimensions outside

  all of the beam converter elements 111 and 211 associated with the transmission beam Ft1 of smaller section are smaller than the inside diameter (2 Ri2) of the transmission beam Ft2 so as not to intercept it. Under these conditions, a very small fraction of the energy of the latter beam after reflection on the mirrors M1 and M2 is intercepted, on the one hand by the optical fibers wire and f21 which is negligible and, on the other hand, by means for attaching the optical beam conversion elements 111 and 211 to the ends 1 and 2 (FIGS. 1 and 7). These fixing means 1110 and 2110 may be constituted by rods which can be arranged in space so as to merge with the shadows of a possible central connecting channel (Fig.7: C1 - C2). We can still use means

  fasteners transparent to the wavelengths used, antireflection treated.

  The invention is not limited to the exemplary embodiments described for the sole purpose of illustrating it. All variants to the

  The scope of those skilled in the art falls within the scope of the invention. particular

  combinations of the different coupling device structures

  multipath can be realized.

Claims (11)

  I. Optical coupling device comprising two end pieces (1, 2) mechanically coupled by a seal (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 beam (Ft) for parallel ray transmission and with an annular section propagating along an axis (A 1) orthogonal to the axis of rotation (A); a first plane mirror (M1) secured to a first end-piece (1) and inclined at an angle of wr / 2 radians completely capturing at least one transmission beam (Ft) and retransmitting it to the second end-piece (2) in a direction parallel to the propagation axis (A) so as to establish said optical coupling; a second plane mirror (M2) integral with the second endpiece (2) and inclined at an angle of 7r / 4 radians with respect to the axis of rotation (a) capturing this beam (Ft) in its entirety and retransmitting it in accordance with a direction (A 2) orthogonal to the axis of rotation (A); optoelectronic means (21, L2, f2, 22) for capturing and detecting this beam (Ft); and in that the rotary joint (3) has an orifice (30) centered on the axis of rotation (A) whose minimum dimension is greater than the   large outside diameter (2 Re2) generated transmission beams (Ft).   2. Device according to claim I characterized in that the inclined mirrors (M1, M2) comprise openings (10,20) centered on the axis of rotation (A) whose maximum dimensions projected on a plane orthogonal to this axis ( A) are less than or equal to the smallest inside diameter   (2 Ril) transmission beams (Ft) generated.   3. Device according to claim 2 characterized in that it further comprises a channel (C1, C2) for transmitting electrical signals provided with a rotary joint (6) centered on the axis of rotation (A) and in that that the section of this channel has a maximum dimension smaller than the smallest diameter   inside (2 R1il) generated transmission beams (Ft).   4. Device according to any one of claims I to 3 character-   Characterized in that the optoelectronic means for generating and capturing transmission beams (Ft) comprise optical elements of   conversion of beams (11,21) transmitting reciprocally a   beam (F1, F2) of parallel rays with circular section propagating along an axis (A 1i A 2) orthogonal to the axis of rotation (A) in a beam (Ft) of parallel rays with annular section propagating according to the same axis (A1, A2)   5. Device according to claim 4 characterized in that the beam conversion optical elements (1 1, 21) are each constituted   by an axicon comprising - a cone (111) i with an outer wall (1110) reflecting   of axis of revolution coincides with the axis (ee) of propagation of the beams and a mirror (110) comprising a truncated-conical cavity wall (1100) reflecting, axis of revolution coincides with said axis of propagation (A1); and in that the reflective surfaces (1100, 1110) form an angle equal to tr / 4 radians with this axis (A 1 6. Device according to claim 4 characterized in that the optical beam conversion elements are constituted by total reflection prisms in the form of parallel-sided blades (116, 117) of refractive material having a conical wall cavity (1110). ') of axis of revolution coincides with the axis (A l) of propagation of the beams and delimited at the periphery by a truncated-conical wall of axis of revolution also coincides with the axis (A 1) of propagation of the beams and in that the walls (1100 ', 1110') are total reflection surfaces for the rays propagating inside the refractive material and are inclined at an angle equal to / r 4 radian with respect to this axis (A 1)   7. Device according to any one of claims 4 to 6 character-   in that the opto-electronic means for generating and collecting the beam comprise optical fibers (F1, F2) coupled to the beams (F1 F2) of parallel radii of circular sections through focusing lenses (L1 L2).   8. Device according to any one of claims I to 7 characterized   in that it comprises at least a first (wire, LI1, 111, 211, L21 f21) and a second (f12, L12, 112, 212, L22 'f22) set of optoelectronic generation and capture-de parallel beam beams with annular sections so as to couple the two end pieces (1, 2) by means of at least two concentric transmission beams (Ftl, Ft2) and in that the internal radii (Ril, R.i2 ) and external (Rel 'Re2) annular sections of the transmission beams are determined so that these annular sections have no common part. 9. Device according to claim 8 characterized in that it comprises a single set of two mirrors (M1, M2) inclined at an angle equal to t / 4 radians each capturing all the transmission beams (Ftl, Ft2) and folding them on themselves in orthogonal directions (A 1 A 2) to the axis of rotation (A).   10. Device according to claim 8 characterized in that it comprises several sets of two mirrors (Mil - M21, M12 - M22) and in that each set of mirror captures one of the transmission beams (Ftl, Ft2) and folds   on itself in directions (A 11 - A 21, 12 - A22) to the axis of rotation (A).   11. Device according to any one of claims 1 to 10   characterized in that the optical coupling being of the bidirectional type, each end piece (1, 2) comprises opto-electronic means providing the simultaneous functions of generating and capturing at least one beam transmission (F).