Abstract:
A device for accurately positioning wire-shaped articles. The device includes positioning means comprising two groups of pins which are parallel to each other and which are provided with grooves. The articles to be positioned are disposed in the grooves. Fixing means and elastic means are provided to keep the articles in tension in the grooves. Translation means comprise a movable block on which the articles are placed, one at a time during the positioning. Optical means are provided for accurately measuring the positions of the articles. 
     Several methods of positioning optical fibers by means of this device yield a rigid assembly in which the optical fibers are immovably enclosed between two rigid blocks by an adhesive, by pressure or by any other means.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for positioning several wire-shaped articles with respect to each other and to methods of positioning several optical fibers by means of this device. 
     In the use of optical fibers, it is often necessary to position several fibers with respect to each other with a high degree of accuracy. This is the case, for example, in certain wavelength multiplexers/demultiplexers. 
     Wavelength multiplexing is a technique in which several luminous signals of different wavelengths are caused to travel in the same optical fibers. These signals are each modulated independently of each other so that the transmission capacity of the fiber is increased. When this technique is used, it is necessary to utilize devices (multiplexers) which inject the light emitted by several transmitters (having different wavelengths) into the same optical fiber. It is also necessary to utilize devices (demultiplexers) which separate the different wavelengths of light emitted from the fiber The essential part of these multiplexer/demultiplexer devices is a wavelength dispersive element: a prism, a network, a non-achromatic lens. 
     In the demultiplexer mode of operation, the light beam emitted by the end of the emitting fiber is collimated by a collimator lens. The collimated beam is then dispersed by the dispersive element. At the output of the dispersive element several distinct emerging beams are obtained which are passed to a decollimator lens. Several monochromatic or quasi monochromatic images of the end of the emitting fiber are produced in the focal plane of the decollimator lens. 
     The receiving fibers are arranged so that the end of each of them coincides with one of the monochromatic images. Thus, the signals separated according to their wavelength are collected in the receiving fibers. With the same device, the multiplexer mode of operation can be realized if the direction of propagation of the light in each of the fibers is reversed. 
     Irrespective of the chosen mode of operation, it is necessary to arrange the ends of each of the receiving fibers so as to coincide with the position of each of the monochromatic images of the emitting fiber. Each fiber has to be positioned with a high degree of accuracy. For example, in the case of a fiber whose core diameter is 50 μm, the positioning has to be ensured with an accuracy of a few microns. 
     Among the known devices for positioning and connecting optical fibers is the device described in French Pat. No. 2,411,424. This device uses the usual technique of etching diffraction networks, and it ensures an accurate positioning of the fibers with respect to each other. In this device, a matrix is formed by deposition of a thin metal layer on a support polished to be optically flat. Parallel slots for receiving the are then cut into the metal layer by means of a diamond machine tool provided with interferometer control systems. The cost of such a matrix is of course extraordinarily high. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a device of simple construction, of small volume and of low cost for positioning optical fibers with respect to each other with a high degree of accuracy. 
     The device according to the invention comprises positioning means, fixing means, translation means and optical means. 
     The positioning means includes two groups of pins which are mounted on a support. The pins are parallel to each other and are grouped in pairs according to several levels slightly offset with respect to each other. Each pin has a nonthreaded part provided with a groove and a threaded part. These parts pass through nonthreaded holes, respectively, formed opposite each other in the support. Each wire-shaped article to be positioned bears in the grooves of a pair of pins so that rotation of the pins leads to a displacement of the wire-shaped article supported thereby. 
     The fixing means includes means for fixing the ends of the wire-shaped articles on the support. This is accomplished with elastic means for pressing each wire-shaped article to bear in the grooves with a small amount of tension. 
     The translation means includes means ensuring the translation of a movable block between the pins of each pair of pins in a direction at right angles to the assembly of the wire-shaped articles. This is so that the articles bear on the upper surface of the block. 
     Finally, the optical means permit the accurate controlling of the position of the wire-shaped articles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a first embodiment of the device according to the invention. 
     FIGS. 2a and 2b are side and top cross-sections, respectively, of the first embodiment of the device according to the invention. 
     FIG. 3 is a partly elevational, partly cross-sectional view of a pin and fiber showing the form of the groove provided in the non-threaded part of the pins. 
     FIG. 4 is a perspective view of the rigid assembly in which the optical fibers are positioned according to the first embodiment. 
     FIG. 5 is a cross-section of a second embodiment of a device according to the invention. 
     FIG. 6 is a cross-section of a modification of the second embodiment. 
     FIG. 7 is a perspective view of the rigid assembly in which the optical fibers are positioned according to the second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view of the device according to the invention. FIG. 2a is a section of the device taken on the vertical plane indicated by the line AA&#39; in FIG. 2b which shows the plan view. The corresponding parts in FIGS. 1 and 2 are designated by the same reference symbols. 
     The means for positioning the wire-shaped articles are pins 11 to 16 which are passed through a support 10. These pins are parallel to each other and are grouped in pairs according to several horizontal levels slightly offset with respect to each other. The number of pairs of pins is equal to the number of articles that should be positioned. 
     By way of example, three articles (optical fibers) are shown in the views of FIGS. 1, 2a and 2b. It should be appreciated, however, that the device according to the invention can be used to position an arbitrary number of fibers. 
     Each of the pins 11 to 16 is threaded over a part of its length. Each pin traverses the support 10 through two holes. One hole is a non-threaded hole into which the non-threaded part of the pin penetrates. The other hole is a threaded hole into which the threaded part penetrates. 
     The diameters of the holes provided in the support 10 have very narrow tolerances. Moreover, the pins are provided with elastic means 21 to 26 (FIG. 2b) which eliminate the clearances of the threaded parts. 
     The pins 11 to 16 are provided on their non-threaded parts with grooves 31 to 36. (FIG. 2b.) The optical fibers 41 to 43 to be positioned are arranged so that each fiber bears in the grooves provided in two pins situated at the same level. Thus, each of the fibers can be displaced by rotation of the pins 11 to 16. This displacement can be very accurate. For example, if the pitch of each of the threaded parts supported by the pins is 0.5 mm, a rotation of a pin of 1/100 revolution, i.e. 3.6°, leads to a translation of the corresponding wire of 5 μm. 
     The fibers 14 to 43 are fixed by their ends to the base of the support 10 by fixing means 51 to 56 and are kept in tension by elastic means 61 to 63. 
     Between the pins of each pair of pins and below the optical fibers there is provided a movable block 70. Block 70 is adapted to slide vertically in a recess formed in a vertical part of the support 10. The position of block 10 is controlled by means of, for example, a screw 71 traversing the horizontal part of the support or by means of any other device ensuring a gradual vertical displacement of the block. 
     Elastic means 72 bear against another vertical part of the support 10 parallel to the preceding part. Elastic means 72 presses the block 70 against the support 10 so that it is prevented from moving horizontally. 
     Thus, when the block 70 is displaced upward, the optical fibers can come to bear on its upper surface. The fibers are kept in place on the upper surface of block 70 by the aforementioned elastic means 61 to 63. 
     Finally, a microscope 80 or other optical magnifying device is provided. The microscope 80 is movable according to three axes for observing the fibers 41 to 43 in the central region of their horizontal part. The microscope 80 is provided with a micrometric ocular for measuring the distances in the plane of observation. 
     It should be noted that the dimensions of the grooves 31 to 36 are chosen so that the fibers 41 to 43 are accurately guided. That is, each fiber is tangent to the walls of the groove, as shown in FIG. 3. 
     Various methods of positioning fibers or wires by means of the device according to the invention will now be described. In a first embodiment, the elements 41 to 43 are lengths of the optical fiber whose positioning in the multiplex/demultiplexer should be ensured. These lengths of fibers are held in place in horizontal planes slightly offset in height with respect to each other. By rotation of the pins 11 and 12 about their axes, the fiber 41 can be displaced arbitrarily in a horizontal plane. Likewise by rotation of the pins 13 and 14 the fiber 42 is displaced, and so on. 
     By operating the screw 71, the movable block 70 is moved upward until it is very close to the fiber 43, but is not in contact with it. The fiber 43 can then be positioned accurately with respect to the ribs of the block 70 by actuating the pins 15 and 16, while observing the position of the fiber by means of the microscope 80. 
     Subsequently, the block 70 is moved upward until it is very close to the fiber 42, but is not in contact with it. The fibers 42 and 43 are then observed clearly simultaneously in the microscope 80. By rotating the pins 13 and 14, the fiber 42 is displaced until it becomes parallel to the fiber 43, and the distance between the fibers 42 and 43 is adjusted so that their relative distance is equal to the distance which has to exist between two optical fibers in the multiplexer/demultiplexer. The parallelism and the relative distance between the fibers 43 and 42 are checked with the aid of the microscope 80. 
     Subsequently, the screw 71 is turned so that the block 70 is moved upward until it is very close to the fiber 41, but without being in contact with it. During this process step, the block 70 is displaced vertically and consequently the parallelism and the relative distance between the fibers 42 and 43 are not modified. 
     By rotating the pins 11 and 12 about their axes, the parallelism and the relative distances between the fiber 41 and the fibers 42 and 43 are adjusted with the aid of the microscope 80. 
     The positions of the fibers have thus been adjusted successively with respect to each other. Throughout this process, the assembly of the fibers 41 to 43 is kept in tensioned by the action of the elastic means 61 to 63. As a result, the fibers on the movable block 70 at the end of the adjustment stage. 
     On the movable block 70, the fibres 41 to 43 are parallel to each other and are spaced in the manner required in the multiplexer/demultiplexer. The spacing is calculated beforehand as a function of the properties of the dispersive element, as a function of the focal distance of the decollimator lens and as a function of the different wavelengths used in multiplexing. 
     It should be noted that the fibers 41 to 43 need not be positioned parallel to each other. If desired, some of the fibers can be positioned so that they subtend an adjustable angle with the other fibers. However, it is generally desired that the fibers be arranged parallel to each other. 
     After having positioned the lengths of fibers 41 to 43 on the movable block 70, the microscope 80 is removed. Next, an adhesive 73 (FIG. 4) is applied to the upper surface of the block 70 in a sufficient quantity to cover all the lengths of fiber. Finally, another block 74 whose dimensions are approximately equal to those of the block 70 is arranged above the assembly. 
     After the adhesive 73 has dried, the fixing means 51 to 56 and the elastic means 61 to 63 are detached. The fibers 41 to 43 are then cut flush with one end of the block 70. After this operation, a rigid assembly is obtained consisting of the two blocks 70 and 74 and the fibers 41 to 43 fastened therebetween. 
     After having polished the surface 75 common to the blocks 70 and 74 on the side where the fibers have been cut, the rigid assembly of FIG. 4 is obtained. In this assembly the fibers are arranged in positions identical to those assigned to them during the positioning step. Consequently, this assembly can be directly positioned in the focal plane of the decollimator lens with which the multiplexer/demultiplexer is provided. 
     In a second embodiment of the invention, the wire-shaped articles on the device are wires made of a material which is hard and resistant to scratching and whose outer diameter is approximately equal to the outer diameter of the optical fibers which have to be positioned in the multiplexer/demultiplexer. 
     After having positioned the wires in the manner described above for the optical fibers, the assembly of the wires 81 to 83 bears on the movable block 70, as shown in FIG. 5. 
     The microscope 80 having been removed, another block 76 made of a plastic material is pressed on the top of the movable block 70. The pressure exerted must be sufficient to press the wires 81 to 83 into the block 76. After this operation, the block 76 has on one of its surfaces a series of grooves whose number is equal to the number of wires. 
     A modification of this second embodiment which can be realized in a simpler manner consists in that the wires 81 to 83 are made of a metallic hard material (e.g. steel, refractory metal), while the block 70 and the pins 11 to 16 are made of a material which is hard, electrically insulating and resistant to heat. In this case, the block 76 may advantageously be made of a thermoplastic material (for example, methyl polymethacrylate). 
     FIG. 6 shows an elevational view of this device in the state in which it is shown in FIG. 5 with the addition of electric current generators 91 to 93. Current generators 91 to 93 are coupled to switches 94 to 96, respectively, to feed the assembly of wires with current. 
     After wires 81 to 83 are positioned, the block 76 is then pressed against the top of the block 70, as shown in FIG. 6. When the switches 94 to 96 are closed, an electric current is passed through the wires 81 to 83. The current is of an intensity sufficient to ensure that the heating of the wires causes the block 76 to be softened around the wires. Afterward, block 76 has on one of its surfaces a series of grooves whose number is equal to the number of wires. The depth of these grooves can be adjusted by regulating the pressure exerted on the block 76 during the engraving operation, as well as by adjusting the intensity and the duration of the application of the current to the wires 81 to 83. 
     After this pressing operation, the block 76 serves as a support for the optical fibers used in the multiplexer/demultiplexer. The fibers 41 to 43 are positioned in the grooves of the block 76. After the fibers are positioned, another block 77 of dimensions approximately equal to those of the block 76 is arranged above the assembly and fixed by means of an adhesive 73 or by any other fixing means. After the fibers are cut flush with one end of the block 76, and the surface 78 common to the blocks 76 and 77 is polished on the side where the fibers have been cut, the rigid assembly of FIG. 7 is obtained. In this assembly, the fibers are located at the positions of wires 81 to 83 during the positioning step. Subsequently, the rigid assembly can be directly positioned in the focal plane of the decollimator lens with which the multiplexer/demultiplexer is provided.