Abstract:
An apparatus and method of ascertaining the position of a core within a fiberoptic cable and calculating the position of the core relative to the cladding and jacket of the fiberoptic cable. The apparatus provides for observing of the end of the fiberoptic cable by using grazing incident illumination which causes the diameter of the core, the diameter of the cladding and the diameter of the jacket of the fiberoptic cable to be readily observed and then utilizing of a microscope and associated software to read the average diameter of the core and its position relative to the average diameter of the cladding and the average diameter of the jacket which will then make a determination as to how far off center the core is relative to the cladding and the jacket.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of this invention relates to a concentricity measuring instrument for a fiberoptic cable end. 
     2. Description of the Related Art 
     Fiberoptic cables are flexible, elongated essentially transparent devices that are used for either image or data transmission with the light being propagated through the cable. The fiberoptic cable has a core with a refractive index higher than that of the surrounding cladding. Surrounding the cladding is what is called a jacket. The light is to be transmitted through the core with the cladding and jacket functioning to contain the light and not permit the light to be transmitted through the side of the cable. 
     Fiberoptic cables can be constructed of any desired length. Typically, these cables may be anywhere from a few inches in length to hundreds of feet in length. Quite often, it is required that a fiberoptic cable be connected to another fiberoptic cable with the light from the one fiberoptic cable to be transmitted through the other fiberoptic cable. Each fiberoptic cable has a core and this is where the light is being transmitted. The core of one fiberoptic cable must precisely align with the core of the other fiberoptic cable in order to obtain maximum efficiency of transmission of the light. Any misalignment, even as small as less than one micron, can cause a substantial reduction in the efficiency of the transmission of light and possibly even no transmission of light at all. 
     If a cut is transversely made through a fiberoptic cable and one was able to observe that cut surface, the core will be represented as a small centrally located circle generally only a few microns in diameter. Surrounding that core and integrally connected therewith is a cladding which is substantially greater in diameter than the core. Still further surrounding the cladding in most fibers in a concentric relationship is a jacket. The diameter of the jacket is frequently not greater than one-sixteenth or one-eighth of an inch. It is desirable to ascertain the concentricity of the core relative to the cladding and the jacket which will inform the technician the exact position of the core. This determining of the positioning of the core is at the time of manufacture of the cable. If it is determined that the core is off center beyond a certain tolerance, then that particular manufactured cable is rejected. When one cable end abuts against another cable end, the cores between the respective cable ends must be in precise alignment. At the present time, there is no known structure to clearly and easily observe the core relative to the cladding. 
     SUMMARY OF THE INVENTION 
     A concentricity measuring instrument for a fiberoptic cable end which utilizes a mounting block that is constructed of a plastic material that randomly disperses light. Formed within the mounting block is a through opening with this through opening being adapted to receive a fiberoptic cable end. The mounting block is attached to a ring with the ring having a light outlet window formed therein. Light is to be transmitted to the ring and emitted through the window into the block. The light within the block illuminates the cable end from the side. A microscope is then used to observe the cable end with the microscope being connected to software which then can calculate the position of the core relative to the cladding and the jacket of the fiberoptic cable and make a determination how far off precise center the core is relative to the cladding and the jacket. 
     A further embodiment of the present invention is where the previous apparatus utilizes a block constructed of epoxy resin and titanium dioxide particles 
     A further embodiment of the present invention is where the apparatus is constructed so that the through opening formed within the block is centrally mounted within the block. 
     A further embodiment of the present invention is where the previous apparatus is modified by the through opening including a cone-shaped enlargement within the through opening through which the observation by the microscope is to occur. 
     A further embodiment of the present invention is where the apparatus is defined to include a ring on which the block is mounted with this ring including an annular light outlet window through which the light is to be transmitted within the block. 
     A further embodiment of the present invention is where the apparatus is modified by the ring on which the block is mounted includes an annular light receiving chamber. 
     A further embodiment of the present invention is where the apparatus is modified by there being mounted on the block an iris which improves the contrast of the observation by the microscope. 
     A further embodiment of the present invention is where the just previous embodiment is modified by the iris being adjustable so as to vary the size of the aperture through the iris in order to maximize the observation by the microscope. 
     A further embodiment of the present invention relates to the method of ascertaining the concentricity of a core of a fiberoptic cable end which comprises the steps of placing the fiberoptic cable end within a block which is constructed to randomly disperse light, projecting of the light directly into the block with the light illuminating the cable end from the side of the cable end, observing of the cable end with the observation being able to detect the position of the core relative to the surrounding cladding and jacket and calculating the position of the core relative to the precise center of the cable. 
     A further embodiment of the present invention is where the method just described utilizes unfocused light from a non-coherent source. 
     A further embodiment of the present invention is where the basic method of the present invention utilizes a microscope in conjunction with an iris in making of the observation of the cable end. 
     A further embodiment of the present invention is where the method of the present invention requires placing of the cable end in a through hole formed within the block. 
     A further embodiment of the present invention is where the just previous embodiment is modified by centrally locating of the through hole within the block. 
     A further embodiment of the present invention is where the basic method of the present invention is modified by utilizing of a block that is constructed of an epoxy resin plus titanium dioxide particles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is to be made to the accompanying drawings. It is to be understood that the present invention is not limited to the precise arrangement shown in the drawings. 
     FIG. 1 is a side elevational view of the apparatus that is used to ascertain the concentricity of a core of a fiberoptic cable end of this invention; 
     FIG. 2 is an end view of the apparatus of the present invention taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a longitudinal cross-sectional view through the apparatus of the present invention taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is an enlarged view of a fiberoptic cable end that is being observed by using of the apparatus of the present invention taken along line  4 — 4  of FIG. 3; and 
     FIG. 5 is a block diagram representation showing how the observed view by the microscope is utilized to ascertain the concentricity of the core of the fiberoptic cable end. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring particularly to the drawings, there is shown in FIG. 1 a microscope  10  or other imaging device which is deemed to be of conventional microscope construction. An observation is capable of being made by the microscope  10  through a lens assembly, which is not shown, with the observation occurring through a lens aperture  12 . Normally the microscope  10  will be mounted by a stand  14  on a supporting surface  16 . A typical supporting surface  16  would be a table or bench. 
     Light from a source  18  is supplied within a cable  20 . The cable  20  is mounted to a ring  22 . Ring  22  has an internal annular chamber  24 . The inner surface of the annular chamber  24  is closed by means of a sleeve  26 . Internally of the sleeve  26  is a through passage  28 . The light from the cable  20  is supplied within the annular chamber  24  and illuminates such. The ring  22  has a mounting surface  30 . Within the mounting surface  30  there is formed an annular window  32 . The light from the annular chamber  24  is capable of being emitted from the window  32 . 
     A block  34  is to be mounted directly against the mounting surface  30  covering the window  32 . A block  34  constitutes a light randoming disk generally no more than a couple of inches in diameter. The disk is constructed of liquid epoxy resin which is combined with a quantity of a liquid hardener to which has been added 0.6 grams of 0.2 to 0.3 micron titanium dioxide particles which are evenly dispersed in the resin. Other light scattering particles could be used. Also, the block could be made of other plastic or even glass as long as it is optically clear. This composition is placed within a mold and cured at one-hundred fifty degrees Fahrenheit for about three to four hours. The resulting block  34  is then removed from the mold and then machined so that the inner side  36  and the outer side  38  are made smooth as well as the external peripheral surface  40  of the block  34 . The function of the block  34  is to produce a random, unfocused non-coherent light source. The block  34  produces even illumination of the fiberoptic cable end  56  which is important for achieving accurate determining of the core  58  of the cable. If light was transmitted from only one direction, the light rays would reflect off the cable end  56  producing a “shifted” appearance. This “shifting” of the appearance is an effect that is canceled by the even illumination from, in affect, an infinite number of light sources by using the block  34 . The block  34  causes light to be emitted from a discrete location(s). 
     Formed centrally within the block  34  and connecting between the outer side  38  and the inner side  36  is a through opening  42 . The through opening  42  is mainly cylindrical but directly adjacent the outer side  38  the through opening  42  expands to a cone-shaped enlarged opening  44 . The block  34  is then fixedly mounted within a mounting ring  46 . The mounting ring  46  has mounted therein a plurality of threaded rods  48 . Generally, there will be at least two in number of the threaded rods, which is clearly shown in FIG.  2 . These threaded rods  48  are to be screwed tightly down against the peripheral surface  40  fixedly mounting of the block  34  in position within the mounting ring  46 . The mounting ring  46  is fixedly secured to a base plate  50 . The base plate  50  is then mounted on the supporting surface  16 . 
     A fiberoptic cable  52  is mounted within a ferrule  54 . The fiberoptic cable  52  is readily bendable and generally comprises a glass material. The fiberoptic cable  52  is fixedly mounted within the ferrule  54  which is usually constructed of a ceramic material. The ferrule  54  is then fixed within the through opening  42 . The fact that the ferrule  54  is mounted in the through opening does not insure that the core of the cable is precisely centered in the through opening. The ferrule  54  and the cable end  56  that is mounted within the ferrule  54  can be readily removed from the through opening  42 . It is important that the cable end  56 , which is generally spherical, be as clean as possible and does not protrude exteriorly of the block  34 . The best position for the cable end  56  is to be in alignment with the surface that junctions between the enlarged cone-shaped opening  44  and the cylindrical portion of the through opening  42 . 
     Typical construction of the diameter of the cable  52  will generally be no more than one-eighth or one-sixteenth of an inch in diameter. The fiberoptic cable  52  is constructed to have a centrally located core  58 . The core  58  is constructed to have a high degree of transparency so as to readily transmit light. Surrounding the core  58  is a cladding  60  with the cladding  60  having a high degree of reflectivity. It is the function of the cladding  60  to keep the light channeled within the core  58  and not permit the light to be conducted laterally exteriorly of the fiberoptic cable  52 . Protecting and mounted exteriorly around the cladding  60  is a jacket  62 . The ferrule  54  is mounted directly onto the jacket  62 . The diameter of the core  58  is generally no more than a few microns in diameter. The diameter of the cladding  60  is generally about ten times the diameter of the core  58  with the diameter of the jacket  62  being two to three times as great as the diameter of the cladding  60 . It is to be understood that the core  58 , cladding  60  and jacket  62  are all constructed of a glass material. 
     Fixedly mounted onto the outer surface  38  of the block  34  is an iris diaphragm  64 . The iris diaphragm  64  includes a through passage  66  which is to be aligned with the conical shaped enlarged opening  44 . Mounted within the through passage  66  is a shutter  68 . The shutter  68  has a center hole  70 . Connected with the shutter  68  and extending exteriorly of the iris diaphragm  64  is a lever  72 . Manual movement of the lever  72  will cause the center hole  60  to be made smaller or to be enlarged. The lens aperture  12  of the microscope  10  is to be located directly adjacent the through passage  66  and in alignment with such. One reason for the iris diaphragm  64  is so that the contrast can be improved by narrowing or enlarging of the opening  70  when using of the microscope  10  to observe the cable end  56 . Another reason for the iris diaphragm is that light is received only directly in axial alignment with the cable end  56  with the structure surrounding the opening  70  functioning to block all light that is not axially reflected. This is desirable to produce the optimal image of the cable end  56 . 
     The light, represented by arrows  76  in FIG.  3  and FIG. 4, is being transmitted through the sidewall of the through opening  42  to illuminate the cable end  56 . The light is random, unfocused, non-coherent light. The illumination occurs at what is termed a grazing incident, that is from the side. The light being emitted from the block  34  is directed to the cable end  56  anywhere from zero degrees to about forty-five degrees. This angular direction of light is what is deemed as a grazing incident. The reflection of this grazing incident is what is observed by the microscope  10 . This side illumination is what results in the microscope  10  being able to accurately differentiate surfaces with varying indices of refraction which results in observing the barrier circle  76  located between the core  58  and the cladding  60  and also barrier circle  78  located between the cladding  60  and the jacket  62 . The most desirable position for the center of the core  58  is to coincide with center point  80  of the fiberoptic cable  52 . However, in the manufacture of the fiberoptic cable  52 , it is almost impossible to get the center point of the core  58  precisely in alignment with the center point  80 . However, it is possible to get the center point  80  of the core  58  exceedingly close (within one micron or possibly even less than one micron) in alignment with the center point  80 . If, by the observation of the microscope  10  a determination is made that the center point of the core  58  is not in alignment (within the established tolerance) with the center point  80 , which is shown in FIG. 4 of the drawings, then that particular fiberoptic cable  52  will be rejected by the manufacturer. If the core  58  is precisely centered within certain limits with the center point  80 , then that particular fiberoptic cable  52  will constitute a saleable item. It is to be remembered that fiberoptic cables  52  are commonly joined together. In the joining process, it is necessary to achieve the maximum amount of transmission of the light from one fiberoptic cable to another by the cores  58  of the joined fiberoptic cables being in precise alignment. It doesn&#39;t take much of a misalignment to result in a substantial loss of light transmission and even possibly a complete loss of light transmission. 
     The microscope  10  is connected to some calculating software  82 . The calculating software  82  is in turn connected to a display  84 . The microscope  10  is designed to make a series of readings on the cable end  56  making measurements relative to the center point  80  arriving at an average diameter arrangement for the core  58 , for the cladding  60  and for the jacket  62 . The numerous readings that are made by the calculating software  82  is then averaged and this average number is then displayed by the display  84 . If the display  84  shows that the diameter of the core  58  is within the established tolerance, then that particular fiberoptic cable  52  is deemed to be constructed satisfactorily and is then available to be used.