Optical fiber ribbon fusion-splicing device
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical fiber ribbon fusion-splicing device and, more particularly, to an improvement in the resolution of an image of fibers of an optical fiber ribbon. 
     2. Description of the Related Art 
     A method of fusion-splicing optical fiber ribbons is known which comprises, as shown in FIG. 1, steps performed prior to a fusion-splicing step, of placing exposed portions 12 1  and 12 2  of the fibers of a pair of optical fiber ribbons 10 1  and 10 2  on a pair of grooved supporting members 11 1  and 11 2 , respectively, so that the exposed fibers 12 1  and 12 2  are arranged in the coaxial direction of the supporting members 11 1  and 11 2 , of clamping the fiber ribbons 10 1  and 10 2  with a pair of clamps 13 1  and 13 2 , respectively, of moving the clamps towards each other so that the joining ends of the fibers 12 1  and 12 2  close to each other, and of monitoring the alignment of the joining portions of the fibers. For monitoring the fiber alignment, a TV camera 16 is incorporated in the device to pick up via an optical system 26 including an objective lens 14 a light beam having passed through the fibers 12 1  and 12 2  to form images of the joining portions of the fibers. The images 12 1  &#39; and 12 2  &#39; are displayed on the screen 20 of a TV monitor 18. The joining portions of the fibers 12 1   and 12 2  are monitored to determine whether they are aligned or not. If misalignment exists, an alarm-sound is given or an alarm-sign is displayed on the screen. Then, the fiber ribbons 10 1  and 10 2  are removed from the clamps 13 1  and 13 2 , and the above setting operation is repeated. When the misalignment is within a permissible range, the clamps 13 1  and 13 2  are further advanced toward each other to further advance the fibers 12 1  and 12 2  towards each other with their joining ends being pressed and fusion-spliced to each other by means of an arc generated by applying a high voltage across a pair of electrodes 22 1  and 22 2 . A reflecting mirror 24 is provided behind the fibers 12 1  and 12 2 . 
     The monitoring will be carried out to determine the fiber alignment before and after the fusion-splicing procedure. 
     In order that an image of the entire of the joining portions of the fibers is provided in a form of a single frame, the entire of the joining portions has to be fallen within a field of view of the TV camera 16 or an image sensor 17. 
     Meanwhile, the number of fibers of an optical fiber ribbon has been increased to enhance the packing density, and 12-fiber optical fiber ribbon is now introduced for practical use. Also in aligning such optical fiber ribbons having an increased number of fibers, the entire of the joining portions of the fibers should be picked up within the view field of a TV camera in order to provide an image of the entire of the joining portions of the fibers in a form of a single frame. In order to pick up the entire joining portions, in a prior art method, the power factor of the TV camera is lowered to expand the view field of the camera. As the result, the resolution of the image on the screen is decreased and the fiber misalignment will be detected with less accuracy. 
     In a prior art method, the joining portions of fibers of an optical fiber ribbon having less than 8-fibers can be displayed at high resolution on a monitor screen, and the alignment can be determined with an accuracy of less than 1.0 μm, even when the power factor of the TV camera is reduced so that the entire joining portions can be exhibited within a view field of the TV camera. 
     However, when it is required that the entire joining portions of the fibers of 12-fiber optical fiber ribbon be taken into the view field, the power factor is greatly lowered, and the resolution of the fiber image displayed on the monitor screen will be decreased, thus resulting in less accurate monitoring. 
     In the prior art device, the TV camera 16 is set such that the horizontal direction (H-direction in FIGS. 1 and 2) of the image sensor 17 in which direction a horizontal scanning is carried out and the resolution of the image sensor is higher than that in the vertical direction (V-direction in FIGS. 1 and 2) in which a vertical scanning is carried out corresponds to or coincides with the coaxial direction (X-direction in FIGS. 1 and 2) of the grooved supporting members 11 1  and 11 2 , so that, when fibers 12 1  and 12 2  of a pair of optical fiber ribbons 10 1  and 10 2  are set on the supporting members in the coaxial direction thereof, the horizontal direction of the image sensor corresponds to or coincides with the coaxial direction (X-direction in FIGS. 1 and 2) of the fibers of the optical fiber ribbons. In misalignment, the fibers 12 1  and 12 2  are displaced from each other in the direction (Y-direction in FIGS. 1 and 2) perpendicular to the coaxial direction (X-direction in FIGS. 1 and 2) of the fibers, and thus the displacement is seen in the vertical direction (V-direction) on the image sensor. In order to enhance the accuracy in detection of misalignment, we may increase the V-directional resolution of the image sensor, thereby to provide the image of the joining portions of the fibers with high resolution. However, in fact, even when the V-directional resolution of the image sensor is increased, the resolution of the image of fibers displayed on the TV screen cannot be enhanced, since video signals for TV image reproduction are designated in the standard specification, thus limiting the V-directional resolution of the TV monitor. 
     The problem associated with the prior art is that a the number of fibers of an optical fiber ribbon is increased, the resolution of the video image of the fibers displayed on a screen is decreased, thus lowering accuracy in detection of misalignment. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved optical fiber ribbon fusion-splicing device capable of fusion-splicing a pair of optical fiber ribbons without decreasing the resolution of an image of the fibers of the optical fiber ribbon, even when the number of fibers of the optical fiber ribbon is increased, so that fiber misalignment can be detected with high accuracy. 
     In an optical fiber ribbon fusion-splicing device according to the present invention, as shown in FIGS. 3 and 4, a TV camera 16 is set such that the horizontal direction (H-direction in FIGS. 3 and 4) of an image sensor 17 contained in the TV camera in which direction a horizontal scanning is carried out and the resolution of the image sensor is higher than that in the vertical direction (V-direction in FIGS. 3 and 4) in which a vertical scanning is carried out corresponds to or coincides with a direction (Y-direction in FIGS. 3 and 4) perpendicular to the coaxial direction (X-direction in FIGS. 3 and 4) of a pair of grooved supporting members 11 1  and 11 2  for supporting fibers 12 1  and 12 2  of a pair of optical fiber ribbons 10 1  and 10 2  to be fusion-spliced, so that, when the fibers of the pair of optical fiber ribbons are set on the supporting members in the coaxial direction thereof, the horizontal direction of the image sensor corresponds to or coincides with the direction perpendicular to the coaxial direction of the fibers of the optical fiber ribbon. Since, therefore, misalignment of the fibers is involved in the high resolution direction, the misalignment can be detected with high precision, without decreasing the power factor of the image sensor. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a presently preferred embodiment of the invention, and together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention. 
     FIG. 1 is a view showing a prior art device of fusion-splicing a pair of optical fiber ribbons to each other; 
     FIG. 2 is a view showing the arrangement of the fibers of the optical fiber ribbons loaded on the prior art device illustrated in FIG. 1 in relation to an image sensor; 
     FIG. 3 is a view of an optical fiber ribbon fusion splicing device showing a embodiment of the present invention; 
     FIG. 4 is a view showing the arrangement of the fibers of the optical fiber ribbon set on the fusion splicing device shown in FIG. 3 in relation to the image sensor; 
     FIG. 5 is a view showing the positional arrangement of the reflecting mirror, the fibers of the fiber ribbon, and the TV camera, in the fusion-splicing device shown in FIG. 4; 
     FIG. 6 is a view showing an image of the fibers of the fiber ribbons; 
     FIG. 7 is a view showing a brightness distribution characteristic curve which is taken along cursor Cl on the image shown in FIG. 6; 
     FIG. 8 is a view showing a video image of the fibers of the optical fiber ribbons displayed on the screen of TV monitor illustrated in FIG. 3; 
     FIG. 9 is a view showing a video image of the fibers of the optical fiber ribbons displayed on the TV monitor screen when it is turned 90°; and 
     FIG. 10 is a view showing an image of the fibers of the optical fiber ribbons formed in an image sensor of square shape. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will be described in the form of an optical fiber ribbon fusion-splicing device, referring to the accompanying drawings. 
     In the optical fiber ribbon fusion-splicing device T shown in FIG. 3, exposed portions 12 1  and 12 2  of the optical fibers of a pair of optical fiber ribbons 10 1  and 10 2  are placed on a pair of grooved supporting members 11 1  and 11 2 , respectively, with joining portions of the fibers projected from the supporting members. The grooves are formed, through not shown for simplicity of illustration, on the top of the supporting members, and extend in the coaxial direction (X-direction) of the supporting members. The fibers are placed in the grooves. The pair of fiber ribbons 10 1  and 10 2  are clamped by a pair of clamps 13 1  and 13 2 , respectively. A TV camera 16 having an image sensor 17 is directed such that the image sensor 17 can pick up a light beam from the fibers through an optical system 26 including an objective lens 14 mounted on the top of the TV camera. The TV camera 16 is also arranged such that the direction (H-direction in FIGS. 3 and 4) of the image sensor in which direction a horizontal scanning is carried out and the resolution of the image sensor is higher than that in the vertical direction (V-direction in FIGS. 3 and 4) in which a vertical scanning is carried out is perpendicular to the coaxial direction (X-direction in FIGS. 3 and 4) of the grooved supporting members 11 1  and 11 2 . The TV camera 16 is connected to a TV monitor 18 which has a monitor screen 20. 
     Also, a pair of electrodes 22 1  and 22 2  for arc discharge are provided adjacent to the grooved supporting members 11 1  and 11 2 . 
     In joining the fibers 12 1  and 12 2  of the fiber ribbons 10 1  and 10 2  by the fusion-splicing device shown in FIG. 3, the exposed fiber portions 12 1  and 12 2  of the pair of fiber ribbons 10 1  and 10 2  are first placed on the pair of grooved supporting members 11 1  and 11 2 , respectively, so that the fibers are arranged in the coaxial direction of the grooved supporting members 11 1  and 11 2  to bring the joining ends of the fibers face each other. Thereafter, the pair of fiber ribbons 10 1  and 10 2  are clamped by the pair of clamps 13 1  and 13 2 , respectively. The clamps 13 1  and 13 2  are then moved towards each other to bring the joining ends of the fibers close to each other. Then, the alignment of the fibers is checked by monitoring alignment of the joining portions. To determine the alignment of the fibers, images of the joining portions are taken through an optical system 26 including an objective lens 14 by the TV camera 16, and the images 12 1  &#39; and 12 2  &#39; are displayed on the monitor screen 20 of the TV monitor 18. 
     More specifically, a light beam having passed through the joining portions is transmitted via the optical system 26 including the objective lens 14 to the image sensor 17 and picked up by the image sensor, which in turn develops a video image corresponding to the light beam. Since the TV camera 16 is arranged such that the horizontal direction (the H-direction) of the image sensor 17 in which direction a horizontal scanning is carried out and the resolution of the image sensor is higher than that in the vertical direction in which a vertical scanning is carried out corresponds to or coincides with the direction in which misalignment of the fibers may occur, the misalignment of the fibers is involved in the high resolution direction (H-direction). 
     The video image formed by the TV camera 16 is transmitted to the TV monitor 18 and displayed on the monitor screen 20, as shown in FIG. 3. 
     As shown in FIG. 5, a parallel light beam 11 emitted by a light source (not shown) is reflected by the reflecting mirror 24 to direct in a P direction, passed through the respective fibers f 11  -f 15  of fiber ribbon 10 1  and the respective fibers f 21  -f 25  of fiber ribbon 10 2  (not shown in FIG. 5) in the P direction, and picked up by the TV camera 16 to form an image of the fibers f 11  -f 15  and f 21  -f 25  in the P direction. In FIG. 5, fibers of the fiber ribbons 10 1  and 10 2  are denoted by reference characters f 11  -f 15  and f 21  -f 25 . Another parallel beam 12 emitted by the light beam (not shown) is passed through the fibers f 11  -f 15  and f 21  -f 25  in a Q direction, and reflected by the reflecting mirror 24 to direct in the P direction, and picked up by the TV camera 16 to form an image of the fibers f 11  -f 15  and f 21  -f 25  in the Q direction. The camera 17 is moved in the Q direction to pick up one of the light beams 11 and 12 so that the image of the fibers f 11  -f 15  and f 21  -f 21  -f 25  in the P direction or the Q direction is displayed on the monitor screen 20. 
     FIG. 6 shows an image of the fibers of the fiber ribbons, in which the fibers of the fiber ribbons 101 and 10 2  are denoted by reference characters f 11  -f 15  and f 21  -f 25 . 
     The image signal from the TV camera 16 is A/D-converted on cursor C 1  shown in FIG. 6, so that, as shown in FIG. 7, the brightness distribution curve of, for example, the P direction images f 11  -f 15  of the fibers f 11  -f 15  on the cursor C 1  is provided. Points A, B, C, . . . I, J of the brightness curve crossing threshold brightness TH shown by a solid line in FIG. 7 correspond to the ends A, B, C, . . . I, J of the diameters of the fibers f 11  -f 15  in FIG. 6. Therefore, the ends A, B, C, . . . I, J of the diameters of the fibers are obtained from the brightness curve. The centers of the diameters of the fibers correspond to the centers of the pairs of A and B, C and D, E and F, G and H, and I and J. Therefore, the centers of the diameters of the fibers can be obtained from portions A, B, C, . . . I, J on cursor C 1 . A, B, C, . . . I and J on the brightness distribution can be selected from the plural crossing points of the brightness distribution, because the intervals of crossing points A and B, C and D, E and F, G and H, and I and J correspond to the diameters of the fibers f 11  -f 15 . 
     Similarly, the brightness distribution of images f 11  -f 15  on cursor C 2  and those of images f 21  -f 25  on cursors C 3  and C 4  are obtained. The ends of the diameters of the fibers f 11  -f 15  on cursor C 2  and the ends of the diameters of the fibers f 21  -f 25  on cursors C 3  and C 4  are obtained from these brightness distributions. The centers of the diameters of the fibers can be obtained from the diameter ends. 
     Basing on data of the diameter centers of the fibers f 11  -f 15  thus obtained on the cursors C 1  and C 2  and data of the diameter centers of fibers f 21  -f 25  also obtained on cursors C 3  and C 4 , center lines of the fibers f 11  -f 15  and f 21  -f 25  are determined and it is obtained how the center line of one of the paired fibers opposed to each other is shifted from that of the other. In this way, their center shifts in the P direction ΔP 1  -ΔP 5  are obtained. 
     The same operation for center shifts is conducted to the Q direction images (not shown) to obtain center shifts ΔQ 1  -ΔQ 5  in the Q direction. A resultant center shifts or misalignment ΔR 1  -ΔR 5  of the fibers opposed to each other are calculated by ΔR i  =√ΔPi 2  +ΔQ1 2  (i=1 to 5). The resultant center shifts are then compared with a reference permissible value. 
     If the degree of the misalignment is greater than the permissible value, an alarm-sound is emitted and an alarm-sign is displayed on the TV screen. The operator is then required for opening the clamps 13 1  and 13 2  and repeating the same setting operation. When the misalignment falls within the permissible level, a voltage is applied across the electrodes 22 1  and 22 2  for generating an arc. The joining ends of the fibers of the fiber ribbons are fused by the arc, while the clamps are moved in the X-directions so that the joining ends close each other, and finally are pushed against each other. As the result, the fibers 12 1  and 12 2  of the fiber ribbons 10 1  and 10 2  are fusion-spliced to each other. 
     In the fusion-splicing device, the direction in which misalignment of the fibers may occur corresponds to or coincides with the direction (the H-direction) in which direction the resolution of the image sensor is higher than that in the other direction (the V-direction). Thus, the resolution of the image of the fibers remains high. 
     Moreover, the length in the H-direction of the image sensor is greater than that in the V-direction. Accordingly, even when the image of the joining portions of fibers of optical fiber ribbons having an increased number of fibers are taken by a TV camera, the entire joining portions can be covered with a high power factor. Hence, the resolution of the image of the fibers will remain high. 
     According to the above embodiment, the fibers are displayed in the vertical direction on the monitor screen 20 of the TV monitor 18, as shown in FIG. 8. The direction in which the image is displayed is perpendicular to the direction in which the fibers are actually disposed on the fusion-splicing device, which involves the operator in the working with a little difficulty and decreases the working efficiency. 
     To overcome the difficulty, the TV monitor 18 is turned 90°. Then, as shown in FIG. 9, the fiber image is displayed in the horizontal direction on the TV screen which corresponds to the coaxial direction of the fibers in which the fibers are actually disposed on the grooved members, whereby the operator can monitor with ease and his working efficiency will be increased. 
     Also when an image sensor is used which has a square shape as shown in FIG. 10, if the monitor is disposed in the ordinary mode, the image is displayed in the vertical direction, as shown in FIG. 10. Then, when the TV monitor 20 is turned 90° as shown in FIG. 9, the fiber image is displayed in the horizontal direction and the working efficiency will remain high. 
     As set forth above, in the optical fiber ribbon fusion-splicing device according to the present invention, the TV camera 16 is set such that the horizontal direction (H-direction in FIGS. 3 and 4) of the image sensor 17 contained in the TV camera in which direction a horizontal scanning is carried out and the resolution of the image sensor is higher than that in the vertical direction (V-direction in FIGS. 3 and 4) in which a vertical scanning is carried out is direction (Y-direction in FIGS. 3 and 4) perpendicular to the coaxial direction (X-direction in FIGS. 3 and 4) of the pair of grooved supporting members 111 and 112 for supporting fibers 121 and 12 2  of a pair of optical fiber ribbons 10 1  and 10 2  to be fusion-spliced. Therefore, when the fibers of the pair of optical fiber ribbons are set on the supporting members in the coaxial direction thereof, the horizontal direction of the image sensor is perpendicular to the coaxial direction of the fibers of the optical fiber ribbon. Since, therefore, misalignment of the fibers is involved in the high resolution direction, the misalignment can be detected with high precision, without increasing the power factor of the image sensor. Furthermore even when the optical fiber ribbons have an increased number of fibers, an image of the entire of the joining portions can be provided in a single frame. As the result, the detection of misalignment of the fibers will be executed with ease. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices, shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.