Abstract:
A tight buffer optical fiber ribbon is formed from a plurality of optical fibers, each of which has a glass core, a primary coating and a second tight buffer layer. The ribbon includes first and second stand off legs, each having an inner strength core and an outer tight buffer layer. The plurality of optical fibers are coupled to one another in a substantially sequential ribbon arrangement via their tight buffer layer. The first stand off leg is attached to the substantially sequential ribbon arrangement of the optical fibers at a first end, and the second stand off leg is attached to the substantially sequential ribbon arrangement of the optical fibers at a an opposite second end.

Description:
FIELD OF THE INVENTION 
   This invention relates to optical fibers. More particularly, this invention relates to tight buffer optical fiber cables. 
   BACKGROUND OF THE INVENTION 
   Optical fibers are generally constructed with a glass core of approximately 125 micron thickness, and are used to transmit signals across the fiber in the form of light or light pulses. Currently, optical fibers are typically produced with a UV-curable coating, such as a UV acrylate material. This primary buffer is applied in the fiber drawing process in a drawing tower. The UV curable coating increases the overall size of the outside diameter of the fiber to approximately 250 microns. UV coated fibers are typically individually inked with different colors for identification. The fibers may then placed into a ribbon matrix or otherwise bundled together and placed into plastic tubing for use in outdoor applications. 
   For indoor applications it is required that the fibers meet certain fireproofing standards. However, the standard UV curable coating described above, is highly flammable. To meet the fireproofing standards, a second fire retardant PVC-jacket is extruded onto the base UV coated optical fiber, forming what is know as tight buffer fibers. These tight buffer fibers are typically in the thickness range of 900 microns and bundled and jacketed for use in mostly indoor applications and some outdoor applications as well. 
   However, there is no current solution for indoor use fiber cable arrangements that meet the necessary fire standards, can be handled regularly for splicing operations and are also capable of standing alone use without the need for a secondary bundling, such as insertion within a tube or other external binding. 
   OBJECTS AND SUMMARY OF THE INVENTION: 
   The present invention looks to overcome the drawbacks associated with the prior art by providing a stand alone fiber optical cable, containing plurality of fibers, that can be handled regularly for splicing or other such operations, that is fireproofed to the extent necessary to meet industry standards and is also economically designed in that it does not require a secondary outer sheathing or tubing for the fibers. 
   To this end, the present invention provides for a tight buffer optical fiber ribbon having a plurality of optical fiber, where each of the optical fibers has a glass core, a primary coating and a second tight buffer layer. First and second stand off legs each have an inner strength core and an outer tight buffer layer, where the plurality of optical fibers are coupled to one another in a substantially sequential ribbon arrangement via their tight buffer layer and where the first stand off leg is attached to the substantially sequential ribbon arrangement of the optical fibers at a first end, and where the second stand off leg is attached to the substantially sequential ribbon arrangement of the optical fibers at a second end, opposite the first end. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with features, objects, and advantages thereof may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
       FIG. 1  is a cross section diagram of tight buffer optical fiber ribbon, in accordance with one embodiment of the present invention; 
       FIG. 2  is a close up view of an individual tight buffer optical fiber from  FIG. 1 , in accordance with one embodiment of the present invention; 
       FIG. 3  is a close up view of a stand off leg from  FIG. 1 , in accordance with one embodiment of the present invention; 
       FIG. 4  is a cross section diagram of tight buffer optical fiber ribbon, in accordance with another embodiment of the present invention; 
       FIG. 5  is a cross section diagram of a fiber matrix formed from the tight buffer optical fiber ribbon of  FIG. 1 , in accordance with another embodiment of the present invention; and 
       FIG. 6  is a cross section diagram of a fiber matrix formed from the tight buffer optical fiber ribbon of  FIG. 4 , in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   As illustrated in  FIG. 1 , the present invention provides for a tight buffer optical fiber ribbon  10 . Generally, ribbon  10  is composed of a number of tight buffer optical fibers  20  and stand off legs  40  formed into a ribbon matrix. 
   In one embodiment of the present invention, as illustrated in  FIG. 2 , a single tight buffer optical fiber  20  comprises three basic components, a glass core  22 , a UV cured layer  24  and a tight buffer layer  26 . 
   Glass core  22  is any glass optical core generally used for forming optical fibers and is preferably 125 microns in diameter. UV cured layer  24  is any typical primary UV coating, such a UV acrylate primary coating. UV cured layer  24  is generally translucent, applied during the fiber drawing process in a drawing tower, and preferably brings the total diameter of optical fiber  20  to 250 microns is diameter. 
   Tight buffer layer  26  is extruded onto optical fiber  20  and generally consists of PVC (Polyvinyl Chloride) buffer, however any similar polymers such as amorphous polyethylene may be used as well. Tight buffer layer  26  preferably brings the total diameter of optical fiber  20  to 900 microns in total thickness. It is possible to add color pigmentation during the extruding process such that tight buffer layer  26  exhibits a unique color for each of the plurality of optical fibers  20  in ribbon  10 . 
   As such, a tight buffer fiber optic cable  20  is produced with a significant PVC coating that allows the cable  20  to meet the necessary standard fire safety ratings such as UL 910 (plenum), and UL 1666 (riser). 
   It is understood that the above materials and sizes used for tight buffered optical fiber  20  are by way of example. However, any similar tight buffer optical fiber used in a similar ribbon  10 , is within the scope of the present invention. 
   In one embodiment of the present invention, as illustrated in  FIG. 3 , stand off leg  40  is shown having two basic components, strength core  42  and tight buffer layer  44 . Strength core  42  is preferably 900 microns in diameter and can be formed of any number of materials suitable for providing the proper balance of strength and flexibility to ribbon  10 . Such materials for strength core  42  can be any number of commercially available materials, including but not limited to, GRP (Glass Reinforced Plastic), FRP (Fiber Reinforced Plastic), Kevlar™ aramid fibers and Kevlar™ rip cords. 
   Tight buffer layer  44  is similar in composition to tight buffer layer  26  of optical fiber  20 , and is preferably an extruded layer of PVC buffer, that brings the total diameter of stand off leg  40  to about 1500–1800 microns. As with tight buffer layer  26 , tight buffer layer  44  is of sufficient thickness so that complete stand off leg  40  meets the same necessary fire safety standards as optical fiber  20 . 
   Again, as with optical fiber  20 , the above described materials and sizes used for stand off leg  40  are by way of example. However, any similar stand off leg used in a similar ribbon  10 , is within the scope of the present invention. 
   Once optical fibers  20  and stand off legs  40  are formed, tight buffer optical fiber ribbon  10 , as illustrated in  FIG. 1 , is constructed using assembly methods for producing ribbon cables. 
   Using a ribbon cable loom, the various desired strands of optical fibers  20  (12 in this example) are drawn from their individual spools and assembled into a side by side and substantially sequential arrangement, with one stand off leg  40  on either side of the arrangement. In order to complete and secure individual optical fibers  20  and stand off legs  40  into ribbon  10 , they are treated with a solvent as they are brought into contact with one another. Typical examples for solvents may include but are not limited to MEK (Methyl Ethyl Ketone) or Cyclohexanone. 
   As the strands of optical fibers  20  and stand off legs  40  are pulled through the loom from the originating spools into the arrangement shown in  FIG. 1 , the treatment by the solvent causes the outer portions of tight buffer layer  26  of optical fibers  20  and tight buffer layer  44  of stands of legs  40  momentarily dissolve. In this partially dissolved state, as the loom pulls fibers  20  and stand off legs  40  in contact slightly pressured contact with one another, the various tight buffer layers  26  and tight buffer layers  44  chemically weld themselves to one another. As the amount of solvent is minimal, when the optical fibers  20  and stand off legs  40  are removed from the solvent (or the solvent evaporates), the resulting structure provides a tight buffer optical fiber ribbon  10 , having twelve connected optical fibers  20 , with stand off legs  40  on either side, as illustrated in  FIG. 1 . 
   It is understood that although tight buffer optical fiber ribbon  10  is described above as being formed using chemical welding, the invention is not limited in that respect. Any manner for forming a similar tight buffer optical fiber ribbon  10  that results in a substantially similar structure, is within the contemplation of the present invention. 
   In this arrangement tight buffer optical fiber ribbon  10 , acts as a self contained fiber optic cable without the need for an additional tubing or jacketing. The tight buffer layer  26  of optical fibers  20  is sufficient for protecting glass core  22  and is also sufficient to meet the necessary indoor fire safety ratings. 
   Furthermore, stand off legs  40  of ribbon  10  add additional strength allowing ribbon  10  to be stapled to structures or used in otherwise high stress environments, by providing a crush resistant barrier on either side of optical fibers  20 . Stand off legs  40  also provide additional structural support to ribbon  10 , allowing it to bend around corners, or doors or even to be used in high stress installation methods such as being blown into ducts with compressed air. 
   Additionally, in this arrangement of ribbon  10  each of the optical fibers  20  can be easily separated for connectorizing, yet the ribbon keeps optical fibers  20  together neatly in the cabinet space. 
   In one embodiment of the present invention, as illustrated in  FIG. 4 , an alternative tight buffer optical ribbon  100  arrangement is shown, using only six optical fibers  20  with one stand off leg  40  on either side. This provides a lighter version of ribbon  10  as shown in  FIG. 1 . It is understood that any such arrangement of tight buffer optical fibers with stand off legs  40  disposed on either side of ribbon  10  or  100 , is within the contemplation of the present invention. 
   Furthermore, in one embodiment of the present invention, it is also contemplated that multiple ribbons  10 / 100  could be combined into a larger fiber matrix  200  by combining multiple tight buffer optical fiber ribbons  10  or tight buffer optical fiber ribbons  100  together with one another within an outer matrix jacket  202 . These matrix arrangements discussed below have additional advantages over cables that simply place loose, non-ribboned tight buffer fibers within an outer jacket For example, cables using fiber matrix  200  can be used for bulk fuse splicing and also keep the splice cabinet in better order by holding the fibers in a close arrangement with one another within the cabinet. Also, because strength members  40  are already incorporated into ribbons  10  used in fiber matrix  200 , there is less or even no need to add additional strength members to the fiber optic cable, thereby allowing for smaller overall jacket cross section area needed to contain the same amount of fibers. 
   A first example of larger fiber matrix  200  is shown in  FIG. 5 , where a 36 fiber matrix is formed by placing three  12  fiber tight buffer optical fiber ribbons  10  on top of one another and placed within extruded jacket  202 . As shown in  FIG. 5 , fiber matrix  200  has three fiber ribbons  10  within outer jacket  202 . As described in detail above, each ribbon  10 , already includes strength members  40 , and thus fiber matrix  200  does not require additional strengthening bands or fibers within jacket  202 . Thus, in this stacked arrangement assuming jacket  202  having an outer thickness of 0.040″ the cross section of fiber matrix  200  can be reduced to 0.109 in 2  as opposed to a conventional cable having 36 separate tight buffer fibers in a loose arrangement within the outer jacket which would exhibit a cross section of 0.220 in 2 . 
   In addition to simply placing multi-fiber ribbons  10  into fiber matrix  200  in a simple stacking arrangement, additional stranding of the ribbons  10  and  100  within a jacket may be used to reduce microbending stresses on the glass within tight buffer fibers  20  within ribbons  10  and  100 . Further arrangements, as illustrated in  FIG. 6  may include the addition of an up-jacketed yarn  304  placed in the middle of a fiber ribbon matrix  300  in order to allow a folding or curling point for the stranding of ribbons  100  of matrix  300  within jacket  202 . 
   For example, a larger fiber matrix  300  is shown in  FIG. 6 , where a 72 fiber matrix is formed by winding twelve  6  fiber tight buffer optical fiber ribbons  100  around a central core such as a Kevlar™ aramid yarn  304  all of which are held within outer jacket  302 . Similar to matrix  200  illustrated in  FIG. 5 , even though yarn  304  may be used for the stranding of ribbons  100 , still the overall cross section area of a cable having matrix  300  within jacket  302  is significantly less than would be found in the typical cable with 72 loose tight buffer fibers within the jacket because no additional strength members need to be added beyond strength members  40  already incorporated into ribbons  100 . 
   In both of these arrangements significantly less strength material needs to be used because fiber ribbon  10  and fiber ribbon  100  already contain strength giving stand off legs  40  within their own structure. 
   It is understood that such examples of multi-ribbon fiber matrixes  200  and  300  are by way of example. Any multi-ribbon matrix that utilizes similar tight buffer optical fiber ribbons  10 / 100  are within the contemplation of the present invention. 
   While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents will now occur to those skilled in the art. It is therefore, to be understood that this application is intended to cover all such modifications and changes that fall within the true spirit of the invention.