Abstract:
The present invention discloses a loose tube ribbon optical cable, which includes at least one reinforced ribbon optical fiber bundle that includes a multifiber cable arrayed in parallel, a ribbon optical fiber bundle formed of multi-layered ribbon optical fibers for coating the multifiber cable, and a pair of reinforcing layers with both edges bent towards the periphery of the ribbon optical fiber bundle, the pair of reinforcing layers being formed on the outside of the bundle. The loose tube is packed with the reinforced ribbon optical fiber bundle, and an outer coating disposed in a peripheral of the ribbon optical cable, enclosing the loose tube(s).

Description:
CLAIM OF PRIORITY  
         [0001]    This application claims priority to an application entitled “A Ribbon Optical Cable with a Loose Tube” filed in the Korean Industrial Property Office on Aug. 28, 2001 and assigned Serial No. 2001-51943, the contents of which are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to ribbon optical cables. More particularly, the present invention relates to a ribbon optical cable with a loose tube.  
           [0004]    2. Description of the Related Art  
           [0005]    In the art, a ribbon optical cable is defined as an optical cable having a ribbon optical fiber as the transmission medium for an optical signal. The ribbon optical fiber i is a congregated multifiber cable that is arrayed in parallel. In order to manufacture the ribbon optical fiber, the multifiber cable is first congregated in parallel, and subsequently, the optical fiber is coated with an ultraviolet curable resin. After the coating, the cable is exposed to unltraviolet to cure the resin and prepare the ribbon optical fiber.  
           [0006]    In addition, the ribbon optical fiber can be manufactured with a matrix structure by laying a plurality of the ribbon optical fibers described above. Since the multifiber cable is congregated to make the ribbon optical fiber, the density of the optical fiber in a limited space is relatively very high. Considering that the most conduct lines available today are already paved with a number of optical cables, and that a new paving space in the conduct line is seriously deficient, the high-density ribbon optical cable, if it can be implemented, will be one of the best options people have right now. In fact, there have been some attempts to diminish the outer diameter of the optical cable in order to pave more optical fibers in that narrow conduct line, increasing the packing density of the optical fibers.  
           [0007]    [0007]FIG. 1 is a front cross sectional view showing a loose tube paved with a ribbon optical fiber bundle in the prior art, and FIG. 2 is a side cross sectional view showing the loose tube as taken along line A-A′ of FIG. 1. With reference to FIG. 1, the loose tube ribbon optical cable includes: a plurality of optical fibers  120  that coat multifiber cables  110  arrayed in parallel, ribbon optical fiber bundle  130  that are prepared by layering the plural ribbon optical fibers one at a time in order, a loose tube  150  that is paved with the ribbon optical fiber bundle  130 , and a jelly  140  that packs the empty space inside of the loose tube  150 .  
           [0008]    As shown FIG. 2, the ribbon optical fiber bundle  130  is smoothly bent, so as not be arranged in a straight line, along the longitudinal direction of the loose tube  150 . The reason that the ribbon optical bundle  130  is bent is because the bundle grows longer than the loose tube  150 , the the loose tube  150  contracts due to changes in the external environment. In addition, for the purpose of improving a lay ratio, the ribbon optical fiber bundle  130  in the loose tube  150  can be arranged in spiral lengths as well.  
           [0009]    Again referring to FIGS. 1 and 2, the four edges (C, D, E and F) of the ribbon optical fiber bundle  130  are adhered closely to the inner wall of the loose tube  150 , so the edges (C, D, E and F) of the ribbon optical fiber bundle  130  are subjected to a compressive force. This compressive force, on the other hand, is proportional to the lay ratio of the ribbon optical fiber bundle  130 , while inversely proportional to a clearance inside of the loose tube  150 . Unfortunately, such compressive force can cause microbending on the surface of the optical fiber comprising the ribbon optical fiber bundle  130 , or even can be caused by flaws on the surface optical fiber. Further, the microbending is a main factor in decreasing optical signals forwarding to the optical fiber  110 .  
           [0010]    Although the microbending problem might be overcome by extending the diameter of the loose tube  150 , this approach has been considered unworkable because the diameter of the ribbon optical fiber bundle for paving the loose tube  150  with the extended diameter becomes consequently enlarged as well.  
         SUMMARY OF THE INVENTION  
         [0011]    It is, therefore, an object of the present invention to provide a loose tube ribbon optical cable with a smallest diameter to prevent the microbending of edges of a ribbon optical fiber bundle.  
           [0012]    To achieve the above object, there is provided a loose tube ribbon optical cable, which includes at least one reinforced ribbon optical fiber bundle that comprising a multifiber cable arrayed in parallel, a ribbon optical fiber bundle formed of multi-layered ribbon optical fibers for coating the multifiber cable, and a pair of reinforcing layers with both edges bent towards the outer ribbon optical fiber bundle, being formed on the outside of the bundle; at least one loose tube packed with the reinforced ribbon optical fiber bundle; and an outer coating disposed in a peripheral of the ribbon optical cable, enclosing the loose tube(s). 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The foregoing and other object and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 is a front cross sectional view showing a loose tube paved with a ribbon optical fiber bundle in the prior art;  
         [0015]    [0015]FIG. 2 is a side cross sectional view showing the loose tube as taken along line A-A′ of FIG. 1;  
         [0016]    [0016]FIG. 3 is a front cross sectional view showing a stiffed ribbon optical fiber bundle in accordance with a preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 4 is a side cross sectional view showing the loose tube as taken along line B-B′ of FIG. 3;  
         [0018]    [0018]FIG. 5 is a cross sectional view showing a loose tube ribbon optical cable in accordance with a preferred embodiment of the present invention; and  
         [0019]    [0019]FIG. 6 is a cross sectional view showing a loose tube ribbon optical cable in accordance with an alternative preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. In the following description, the same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description are provided for explanatory purposes to assist an artisan in a comprehensive understanding of the invention, but the invention is not limited to the examples provided. The present invention can be carried out without the matters defined in the description. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0021]    [0021]FIG. 3 is a front cross sectional view illustrating a stiffed ribbon optical fiber bundle in accordance with a preferred embodiment of the present invention, and FIG. 4 is a side cross sectional view illustrating of the loose tube as taken along line B-B′ of FIG. 3.  
         [0022]    With reference to FIG. 3, the reinforced ribbon optical fiber bundle  250  includes a ribbon optical fiber bundle  230  with multilayered ribbon optical fibers  220  that coat 12-fiber cables  210  with a ultraviolet curable resin, and a pair of reinforcing layers  240  disposed at a upper portion and a lower portion of the ribbon optical fiber bundle  230 . The ultraviolet curable resin is first coated with the optical fibers  210  at a liquid phase, and later cured when it is irradiated by ultraviolet light.  
         [0023]    The reinforcing layer  240  preferably has the equivalent elastic modulus to that of the ribbon optical fiber  220  by way of assuring that the reinforcing layer  240  and the ribbon optical fiber bundle  250  similarly react to any outer changes, such as temperature change or physical force. In other words, the reinforcing layer  240  can successfully prevent interfacial separation, cleavage or microbending. Moreover, the edge of the reinforcing layer  240  preferably has the equivalent curvature to that of the inner wall of the loose tube  270 . In this way, the clearance of the reinforced ribbon optical fiber bundle  250  can be minimized, and the compressive force applied on the contact area between the loose tube&#39;s inner wall and the reinforced layer can be efficiently absorbed thanks to the expanded the contact area. A preferable material for the reinforcing layer  240  is selected from a group consisting of fiberglass reinforced plastic, glass steel, plastic and so forth.  
         [0024]    The empty space inside of the loose tube  270  is packed with jelly  260 , where the jelly  260  absorbs moisture permeated into the loose tube  270 , and absorbs the impact or shock from the outside. In some cases, a strand-form swellable yarn (not shown) that is known to swell when absorbing moisture can be used, instead of the jelly  260 .  
         [0025]    Referring back to FIG. 3 and FIG. 4, the four edges (G, H, I and K) of the reinforced ribbon optical fiber bundle  250  receive the compressive force as they get adhered closely to the inner wall of the loose tube  270 . At this time, the reinforcing layer  240  absorbs the compressive force applied, which consequently minimizes the force to be transmitted to the ribbon optical fiber bundle  230 .  
         [0026]    [0026]FIG. 5 is a cross sectional view illustrating a loose tube ribbon optical cable according to a preferred embodiment of the present invention. As shown in FIG. 5, the loose tube ribbon optical cable includes a reinforced ribbon optical fiber bundle  350 , a loose tube  370  for packing the reinforced ribbon optical fiber bundle  350 , a jelly for filling the empty space inside of the loose tube  370 , a waterproof tape  380  for enclosing the peripheral side of the loose tube  370 , an outer coating  390  disposed at a peripheral of the loose tube ribbon optical cable, and a pair of tension lines  400  inserted along the longitudinal direction of the outer coating  390 .  
         [0027]    Similar to before, the reinforced ribbon optical fiber bundle  350  includes the matrix structured ribbon optical fiber bundle  330  with multilayered ribbon optical fibers that coat 12-fiber cables  310  arrayed in parallel with a ultraviolet curable resin, and a pair of reinforcing layers  340  disposed at a upper portion and a lower portion of the ribbon optical fiber bundle  330 .  
         [0028]    In the meantime, the jelly  360  protects the reinforced ribbon optical fiber bundle  350  from external shocks, and absorbs moisture permeated into the loose tube  370 .  
         [0029]    In addition, the waterproof tape  380  has a function of absorbing the permeated moisture into the outer coating  390 . In some cases, a metallic tape can be used instead of the waterproof tape  380  for protecting the outer coating from any rodent attacks.  
         [0030]    The pair of tension lines  400  is arrayed around the loose tube  370  to be symmetrical to each other. The tension lines provide anti-tension against the outer tension, and improve the mechanical strength of the loose tube ribbon optical cable.  
         [0031]    Nest, FIG. 6 is a cross sectional view illustrating a loose tube ribbon optical cable in accordance with another preferred embodiment of the present invention. Here, the loose tube ribbon optical cable includes a central tension line  510 , a plurality of loose tubes  550 , a binder  560 , and an auxiliary tension bar  570 , and an outer coating  580 .  
         [0032]    The central tension line  510  provides for the loose tube ribbon optical cable the anti-tension, and thus it is located at the center of the cable. As for the central tension line  510 , a fiberglass reinforced plastic (FRP) is typically used. And as for the material of a coating layer on the central tension line  510 , a polymer, such as polyvinyl chloride (PVC) or polyethylene (PE) is often used.  
         [0033]    The loose tube  550  packs the reinforced ribbon optical fiber bundle  530 . Here, the reinforced ribbon optical bundle  530  includes the matrix structured ribbon optical fiber bundle having multilayered ribbon optical fibers that coat 12-fiber cables with ultraviolet curable resin, and a pair of reinforcing layers disposed at a upper portion and a lower portion of the ribbon optical fiber bundle. Again, the empty space inside of the loose tube  550  is packed with jelly  540  that protects the reinforced ribbon optical fiber bundle  530  from the outer shocks, and absorbs moisture permeated into the loose tube  550 .  
         [0034]    The binder  560  encompasses the plural loose tube  550 , and has a function of maintaining the congregation state of the loose tubes. A preferably used material for the binder  560  is selected from a group consisting of aramid yarn, polyester yarn, polyester film and so forth.  
         [0035]    The auxiliary tension bar  570  encloses the binder  560 , and has a function of improving the anti-tension of the loose tube ribbon optical cable. Preferably, aramid yarn or glass yarn is used for the auxiliary tension bar.  
         [0036]    The outer coating  580  is positioned at the peripheral of the loose tube ribbon optical cable. Typically used material for the outer coating is a polymer, such as PVC or PE, which is prepared by an extrusion process. In addition, the outer coating  580 , for the convenience of molting, or unwrapping, can fill a rip cord adjacent to the inner wall.  
         [0037]    In conclusion, the loose tube ribbon optical cable with the reinforced layer can successfully prevent interfacial separation that often occurs to the edges of the ribbon optical fiber bundle, cleavage or microbending in advance.  
         [0038]    While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.