Patent Publication Number: US-6215932-B1

Title: Stacks of optical fiber ribbons closely bound by respective buffer encasements with relatively hard exteriors and relatively soft interiors, associated methods, and associated fiber optic cables

Description:
FIELD OF THE INVENTION 
     The present invention pertains to fiber optic cables and, more particularly, to protecting stacks of optical fiber ribbons within buffer encasements. 
     BACKGROUND OF THE INVENTION 
     Optical fiber is a very popular medium for large bandwidth applications, and as a result there is a demand for fiber optic cables with greater numbers of optical fibers. In response to demands for increased optical fiber count in fiber optic cables, optical fiber ribbons have been developed. Optical fiber ribbons are planar arrays of optical fibers that are bonded together as a unit. Optical fiber ribbons are advantageous because many ribbons can be stacked on top of each other to form a stack of optical fiber ribbons. 
     It is conventional for stacks of optical fiber ribbons to be incorporated into two different types of fiber optic cables that are generally referred to as “central-core” and “loose-tube” cables. In the central-core design, a stack of optical fiber ribbons is contained within a central tube that is located at the center of the fiber optic cable. Strength members are positioned between the central tube and an outer plastic jacket of the cable. In contrast, loose-tube fiber optic cables typically include a number of relatively small buffer tubes that are positioned around a central strength member, and each buffer tube encloses a stack of optical fiber ribbons. The buffer tubes are longitudinally stranded around the central strength member, meaning that the buffer tubes are rotated around the central strength member along the length of the fiber optic cable. 
     It is conventional for the above-referenced tubes to provide at least some protection for the optical fibers therein. It is important for optical fibers to be protected from stain because strain can degrade the performance of the optical fibers. For example, it is conventional for the above-referenced tubes to be round, and for the stacks of optical fiber ribbons to be generally rectangular. Therefore, for each tube and the stack of optical fiber ribbons it contains, there is space defined between the interior surface of the tube and the periphery of the stack. In some applications that space is utilized to allow for relative movement between the stack of optical fiber ribbons and the tube, and that relative movement diminishes the stresses to which the optical fibers are exposed. However, in some applications that space can be characterized as wasted space. In some applications that space is filled with a gel, such as a thixotropic gel, that cushions the stack of optical fiber ribbons to diminish the stresses to which the optical fibers are exposed. However, in some applications those gels are considered a nuisance because they are messy and must be dealt with when entering a fiber optic cable for the purpose or inspection, for forming a splice between optical fibers, or the like. In addition, for a generally rectangular stack of optical fiber ribbons within a round tube, the optical fibers at the corners of the stack will often bear the brunt of any stresses. 
     Whereas there are several different conventional approaches for protecting stacks of optical fiber ribbons from stress by enclosing the stacks in tubes, further improvements in this area would be beneficial. 
     SUMMARY OF THE INVENTION 
     The present invention provides for the cushioned packaging of a stack of optical fiber ribbons by enclosing the stack in a buffer encasement having a relatively soft inner portion and an relatively hard outer portion. More specifically, the inner portion has an interior surface extends around and defines a longitudinally extending passage that contains the stack, and the interior surface closely bounds the stack. More specifically, the interior surface of the inner portion engages a substantial portion of the periphery of the stack. The outer portion extends around, closely bounds and contacts the inner portion, and has a modulus of elasticity that is greater than the modulus of elasticity of the inner portion. 
     In accordance with one aspect of the present invention, the inner portion has an exterior surface that extends around and is spaced apart from the passage, and the outer portion has an interior surface that extends around, closely bounds, and engages the exterior surface of the inner portion, whereby the buffer encasement has multiple plies. In contrast, in accordance with another aspect of the present invention, a surface is not defined between the inner portion and the outer portion. 
     In accordance with another aspect of the present invention, the buffer encasement is relatively thin. More specifically, each optical fiber ribbon includes a pair of longitudinally extending opposite edges and a pair of longitudinally extending opposite surfaces that extend laterally between the edges, and each optical fiber ribbon has a thickness defined between its opposite surfaces. In an end elevation view of the buffer encasement at least a majority of the buffer encasement has a thickness defined between the interior surface of the inner portion of the buffer encasement and an exterior surface of the outer portion of the buffer encasement, and the thickness of the buffer encasement is not substantially greater than the thickness of each of the optical fiber ribbons. 
     In accordance with another aspect of the present invention, the buffer encasement is sufficiently rigid to maintain the stack in a stacked configuration and sufficiently flexible to allow the optical fiber ribbons to slide laterally relative to one another so that, in an end elevation view of the stack, the stack and the buffer encasement can transition from a non-skewed configuration to a skewed configuration. The lateral displacement between the optical fiber ribbons in the skewed configuration is different from the lateral displacement between the optical fiber ribbons in the non-skewed configuration. 
     In accordance with another aspect of the present invention, the stack is longitudinally twisted, the buffer encasement is sufficiently rigid to hold the stack in the longitudinally twisted configuration, and the buffer encasement is thin such that an exterior surface of the outer portion of the buffer encasement defines ridges that correspond to the twist of the stack. 
     In accordance with another aspect of the present invention, the interior surface of the buffer encasement is unadhered to the stack and the stack is capable of moving relative to the buffer encasement. 
     In accordance with another aspect of the present invention, the periphery of the stack defines a shape in an end elevation view of the stack, and the interior surface of the inner portion of the buffer encasement defines a shape in an end elevation view of the buffer encasement that is substantially similar to the shape defined by the periphery of the stack in the end elevation view of the stack. 
     In accordance with another aspect of the present invention, in the end elevation view of the buffer encasement, the exterior surface of the outer portion of the buffer encasement defines a shape that is substantially similar to the shape defined by the periphery of the stack in the end elevation view of the stack. 
     In accordance with another aspect of the present invention, the buffer encasement is formed by coating the stack with an ultraviolet-curable material and thereafter exposing the ultraviolet-curable material to ultraviolet radiation for a predetermined period of time selected so that on a per unit basis more curing occurs in the outer portion than the inner portion. 
     In accordance with another aspect of the present invention, the buffer encasement is formed by extruding a first extrusion around the stack and extruding a second extrusion around the first extrusion so that the interior surface of the second extrusion comes into contact with the exterior surface of the first extrusion prior to solidification so that the interior and exterior surfaces become blended together. 
     In accordance with another aspect of the present invention, the buffer encasement is formed by applying a film around the stack and extruding an extrusion around the film. Alternatively, the film may be applied over the extrusion, or the extrusion may be replaced with a film. In all cases, the film may be either longitudinally folded or helically wrapped around the stack, or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an optical module in accordance with a first embodiment of the present invention. 
     FIG. 2 is an end elevation view of the optical module of FIG.  1 . 
     FIG. 3 is an isolated perspective view of an optical fiber ribbon of the optical module of FIG.  1 . 
     FIG. 4 is an isolated end elevation view of a stack of optical fiber ribbons of the optical module of FIG.  1 . 
     FIG. 5 is an end elevation view of the optical module of FIG. 1 in a skewed configuration, in accordance with the first embodiment of the present invention. 
     FIG. 6 is partially schematic, isolated end elevation view of a buffer encasement of the optical module of FIG.  1 . 
     FIG. 7 is a perspective view of an optical module in accordance with a second embodiment of th present invention. 
     FIG. 8 is a partially schematic, end elevation view of an optical module in accordance with a third embodiment of the present invention. 
     FIG. 9 is a partially schematic, end elevation view of an optical module in accordance with a fourth embodiment of the present invention. 
     FIG. 10 is a perspective view of an optical module in accordance with a fifth embodiment of the present invention. 
     FIG. 11 is an end elevation view of the optical module of FIG.  10 . 
     FIG. 12 is a perspective view of an optical module in accordance with a sixth embodiment of the present invention. 
     FIG. 13 is an end elevation view of the optical module FIG.  12 . 
     FIG. 14 is an end elevation view of an optical module in accordance with a seventh embodiment of the present invention. 
     FIG. 15 diagrammatically illustrates an assembly of manufacturing equipment that is operative for manufacturing optical modules, in accordance with several methods of the present invention. 
     FIG. 16 is a schematic end elevation view of a fiber optic cable in accordance with an eighth embodiment of the present invention. 
     FIG. 17 is a schematic end elevation view of a fiber optic cable in accordance with a ninth embodiment of the present invention. 
     FIG. 18 is a schematic end elevation view of a fiber optic cable in accordance with a tenth embodiment of the present invention. 
     FIG. 19 is a schematic end elevation view of a fiber optic cable in accordance with an eleventh embodiment of the present invention. 
     FIG. 20 is a schematic an end elevation view of a fiber optic cable in accordance with a twelfth embodiment of the present invention. 
     FIG. 21 is a schematic end elevation view of a fiber optic cable in accordance with a thirteenth embodiment of the present invention. 
     FIG. 22 is an isolated perspective view of a central member of a fiber optic cable in accordance with a first version of the thirteenth embodiment of the present invention. 
     FIG. 23 is an isolated perspective view of a central member of a fiber optic cable in accordance with a second version of the thirteenth embodiment of the present invention. 
     FIG. 24 is a schematic end elevation view of a fiber optic cable in accordance with a fourteenth embodiment of the present invention. 
     FIG. 25 is a schematic end elevation view of a fiber optic cable in accordance with a fifteenth embodiment of the present invention. 
     FIG. 26 is a schematic end elevation view of a fiber optic cable in accordance with a sixteenth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     FIGS. 1-14 illustrate optical modules  30   a ,  30   b ,  30   c ,  30   d ,  30   e ,  30   f ,  30   g  in accordance with preferred embodiments of the present invention. Methods of manufacturing the optical modules  30   a ,  30   b ,  30   c ,  30   d ,  30   e ,  30   f ,  30   g  are described with reference to FIG. 15, which diagrammatically illustrates an assembly of manufacturing equipment. Each of the optical modules  30   a ,  30   b ,  30   c ,  30   d ,  30   e ,  30   f ,  30   g  in isolation can be characterized as a fiber optic cable, or each of the optical modules can be a component of a fiber optic cable that includes other components, such as an outer jacket that surrounds one or more optical modules. FIGS. 16-26 illustrate such fiber optic cables and components thereof. Accordingly, this Detailed Description of the Invention section includes an Optical Modules subsection, a Methods of Manufacturing Optical Modules subsection, and a Fiber Optic Cables subsection. 
     OPTICAL MODULES 
     First Embodiment 
     FIGS. 1 and 2 are perspective and end elevation views, respectively, of an optical module  30   a  in accordance with a first embodiment of the present invention. The optical module  30   a  extends in a longitudinal direction and is uniform along its length. The optical module  30   a  includes a longitudinally extending ribbon stack  32   a . The ribbon stack  32   a  is uniform along its length and is a stack of longitudinally extending optical fiber ribbons  34 . The optical module  30   a  further includes a longitudinally extending buffer encasement  36   a , which is preferably in the form of a thin sheath, that is uniform along its length and extends around and closely encases the ribbon stack  32   a . The buffer encasement  36   a  can also be referred to or characterized as an enclosure. The buffer encasement  36   a  is preferably constructed of a polymeric material. Specifically, the buffer encasement  36   a  preferably has a modulus of elasticity between approximately 5×10 4  pounds per square inch and 1×10 2  pounds per square inch, and most preferably the modulus of elasticity is approximately 5×10 3  pounds per square inch. 
     As best seen in FIG. 2, in accordance with the first embodiment, in an end elevation view thereof the optical module  30   a  defines a generally parallelogram-like shape having rounded corners. More specifically, as illustrated in FIGS. 1 and 2, the optical module  30   a  is in a generally rectangular configuration, which can also be characterized as a non-skewed configuration. For example, the optical module  30   a  can be characterized as being in the generally rectangular configuration because, as best seen in FIG. 2, angles of approximately ninety degrees are defined between the vertical and horizontal segments of the buffer encasement  36   a.    
     As shown in FIG. 2, a height “H” cross-dimension is defined between opposite top and bottom sides of the optical module  30   a . In addition, a width “W” cross-dimension that is perpendicular to the height H is defined between opposite right and left sides of the optical module  30   a . As will be discussed in greater detail below with reference to FIGS.  21  and  24 - 26 , fiber optic cables having combinations of optical modules with different heights H and widths W are within the scope of the present invention. 
     Throughout this Detailed Description of the Invention section of this disclosure, items are described in the context of specific orientations, such as horizontal and vertical orientations. Those orientations are intended to provide a frame of reference to aid in the explanation of the present invention. The present invention can be described in the context of other orientations and is not limited to any specific orientation. 
     FIG. 3 is a perspective view of a representative optical fiber ribbon  34  of the optical module  30   a  (FIGS.  1  and  2 ). In accordance with the present invention, one acceptable design for the optical fiber ribbons  34  is described in U.S. Pat. No. 4,900,126, which is incorporated herein by reference. More specifically, each optical fiber ribbon  34  extends longitudinally and includes a lateral array of conventional coated optical fibers  38  that transmit light. Whereas eight optical fibers  38  are shown in FIG. 3, it is generally preferred for there to be twelve or twenty-four optical fibers in each optical fiber ribbon  34 , and it is within the scope of the present invention for each optical fiber ribbon to include a greater or lesser number of optical fibers. 
     Each optical fiber ribbon  34  further includes a solidified bonding material  40  that fills the interstices between the optical fibers  38 , binds together the optical fibers, and extends to the outside boundary of the optical fiber ribbon  34 . Each optical fiber ribbon  34  includes a pair of opposite edges  42 ,  44  that extend in the longitudinal direction, and a pair of opposite flat lateral surfaces  46 ,  48  that extend laterally between the edges  42 ,  44  and in the longitudinal direction. Referring back to FIG. 2, the generally rectangular configuration of the optical module  30   a  is further characterized by the flat lateral surfaces  46 ,  48  (FIG. 3) of adjacent optical fiber ribbons  34  being substantially entirely contiguous. 
     The solidified bonding material  40  (FIG. 3) is acceptably a known ultraviolet-curable matrix material that includes a resin, a diluent and a photoinitiator. The resin may include a diethylenic-terminated resin synthesized from a reaction of hydroxy-terminated alkyl acrylate with the reaction product of a polyester of polyethyl polyol of molecular weight of 1,000 to 6,000 with an aliphatic or aromatic diisocyanate, or diethylenic-terminated resin synthesized from the reaction of glycidyl acrylate with a carboxylic-terminated polymer or polyether of molecular weight 1,000 to 6,000. The diluent may include monofunctional or multifunctional acrylic acid esters having a molecular weight of 100 to 1,000 or N-vinylpyrrolidinone. For the photoinitiator, the composition may include ketonic compounds such as diethoxyacetophenone, acetophenone, benzophenone, benzoin, anthraquinone, and benzil dimethyl ketal. In a typical composition, the bonding matrix may include a resin (50-90%), diluents (5-40%), and a photoinitiator (1-10%). All percentages are by weight unless otherwise noted. Other bonding matrices may include a methacrylate, an ultraviolet-curing epoxide or an unsaturated polyester. 
     FIG. 4 is an isolated end elevation view of the ribbon stack  32   a  of the optical module  30   a  (FIGS. 1 and 2) in the generally rectangular configuration. That is, as illustrated in FIG. 4, the ribbon stack  32   a  defines a generally rectangular shape and the flat lateral surfaces  46 ,  48  (FIG. 3) of adjacent optical fiber ribbons  34  are substantially entirely contiguous. In FIG. 4, the ribbon stack  32   a  is illustrated as including four optical fiber ribbons  34 , with each of the optical fiber ribbons containing eight optical fibers  38 . In FIG. 4 only a few of the optical fibers  38  are specifically identified with their reference numeral. In accordance with the first embodiment, it is preferred for the ribbon stack  32   a  to be in the form of a stack of twelve longitudinally extending optical fiber ribbons  34 , with each optical fiber ribbon including a laterally extending one-dimensional array of twelve optical fibers  38 . However, ribbon stacks  32   a  containing different numbers of optical fiber ribbons  34  and optical fiber ribbons containing different numbers of optical fibers  38  are within the scope of the present invention. 
     In accordance with the first embodiment, the buffer encasement  36   a  (FIGS. 1 and 2) may or may not be adhered to the ribbon stack  32   a . As best seen in FIG. 4, the ribbon stack  32   a  has a top side  52 , bottom side  54 , right side  56 , and left side  58 . In accordance with an unadhered version of the first embodiment, which is most preferred, the buffer encasement  36   a  is not adhered to the sides  52 ,  54 ,  56 ,  58  of the ribbon stack, so that the ribbon stack can move relative to the buffer encasement. As will be discussed in greater detail below, in accordance with this unadhered version, each of the sides  52 ,  54 ,  56 ,  58  is lubricated, in contact with the interior surface of the buffer encasement  36   a , and can move longitudinally relative to the buffer encasement. In contrast, in accordance with an adhered version of the first embodiment, the buffer encasement  36   a  is adhered to the sides  52 ,  54 ,  56 ,  58  of the ribbon stack  32   a , so that the ribbon stack is restricted from moving relative to the buffer encasement. 
     As best seen in FIG. 4, in accordance with the first embodiment, interstices  50  that are arranged along the right and left sides  56 ,  58  of the ribbon stack  32   a  are defined between the edges  42 ,  44  (FIG. 3) of adjacent optical fiber ribbons  34 . As best seen in FIG. 2, in accordance with the illustrated version of the first embodiment, interstices  50  are not filled by the buffer encasement  36   a . In accordance with another version of the first embodiment, the interstices  50  are filled by the buffer encasement  36   a . Whether or not the interstices  50  are filled by the buffer encasement  36   a  generally depends on the method by which, and the material from which, the buffer encasement is formed. As will be discussed in greater detail below, numerous methods for forming the buffer encasement  36   a  are within the scope of the present invention. 
     As shown in FIG. 4, each optical fiber ribbon  34  defines approximately the same thickness T 1 . As best seen in FIG. 6, which is an isolated end elevation view of the buffer encasement  36   a  of the optical module  30   a  (FIGS. 1 and 2) in the rectangular configuration, the buffer encasement  36   a  can be characterized as including four separate walls, each of which defines approximately the same thickness T 2 . In accordance with the first embodiment, the thickness T 1  (FIG. 4) of each of the optical fiber ribbons  34  (FIGS. 1-3) is preferably at least approximately as great as the thickness T 2  of the buffer encasement  36   a . Stated more specifically and differently, in accordance with the first embodiment in the entirety of the buffer encasement  36   a  has a thickness of approximately T 2  that is preferably not greater than the thickness T 1  of each optical fiber ribbon  34 . In accordance with the first embodiment, the thickness T 1  of each optical fiber ribbon  34  is approximately 0.012 to 0.02 inches, or most preferably approximately 0.012 inches. In accordance with the first embodiment, the thickness T 2  of the buffer encasement  36   a  is approximately 0.003 to 0.012 inches, or more preferably approximately 0.007 to 0.012 inches, or most preferably approximately 0.008 to 0.009 inches. 
     FIG. 5 is an end elevation view of the optical module  30   a  in a skewed configuration, in accordance with the first embodiment. For example, the optical module  30   a  can be characterized as being in the skewed configuration because oblique angles are defined between the generally vertical and horizontal segments of the buffer encasement  36   a , and the lateral surfaces  46 ,  48  (FIG. 3) of adjacent optical fiber ribbons  34  are not entirely contiguous. That is, adjacent optical fiber ribbons  34  are at least partially laterally displaced from one another. Because the buffer encasement  36   a  is constructed of a relatively thin flexible material, the optical fiber ribbons  34  are capable of sliding laterally relative to one another when oppositely oriented lateral forces are applied against the optical module  30   a , so that the optical module transitions from the generally rectangular configuration (FIGS. 1 and 2) to the skewed configuration. That is, the buffer encasement  36   a  is constructed and arranged to be flexible enough to allow the optical fiber ribbons  34  to slide laterally relative to one another so that, in an end elevation view thereof, the stack can transition from an approximately rectangular arrangement to the skewed configuration. The buffer encasement  36   a  is further constructed and arranged to be rigid enough to maintain the stack of optical fiber ribbons  34  in a stacked configuration when the optical module  30   a  is transitioned from the generally rectangular configuration to the skewed configuration. Further, the buffer encasement  36   a  is constructed and arranged so that the optical module  30   a  is biased toward the generally rectangular configuration. 
     In accordance with the illustrated version of the first embodiment, the ability of the optical module  30   a  to be readily transitioned between the generally rectangular configuration (FIGS. 1 and 2) and the skewed configuration (FIG. 5) is enhanced by virtue of the interstices  50  (FIG. 4) defined between the edges  42 ,  44  (FIG. 3) of adjacent optical fiber ribbons  34  not being filled by the buffer encasement  36   a . Further, in accordance with the unadhered version of the first embodiment, a coating of lubricant (not shown), such as oil or the like, as will be discussed in greater detail below, is upon the edges  42 ,  44  and lateral surfaces  46 ,  48  (FIG. 3) of each of the optical fiber ribbons  34 . The lubricant enhances the ability of the optical fiber ribbons  34  to be moved laterally and longitudinally relative to one another and relative to the buffer encasement  36   a . Therefore, the lubricant enhances the ability of the optical module  30   a  to be transitioned between the generally rectangular configuration and the skewed configuration. 
     As best seen in FIG. 6, the buffer encasement  36   a  includes an interior surface  60   a  and an exterior surface  62   a . The interior surface  60   a  extends around and defines a longitudinally extending passage  64 . In accordance with the first embodiment, in both the generally rectangular configuration (FIGS. 1 and 2) and the skewed configuration (FIG.  5 ), the interior surface  60   a  closely bounds the periphery of the ribbon stack  32   a  (FIGS. 1,  2 , and  3 ) and the exterior surface  62   a  closely bounds the interior surface. The close bounding of the interior and exterior surfaces  60   a ,  60   b  provides for efficient packaging of multiple of the optical modules  30   a  (FIGS. 1,  2 , and  5 ), as will be discussed in greater detail below. More specifically, in an end elevation view of the optical module  30   a  during both the generally rectangular configuration and the skewed configuration, the interior surface  60   a  defines a shape that is substantially similar to the shape defined by the periphery of the ribbon stack  32   a  (FIGS. 1,  2 ,  4 , and  5 ), with substantially the only difference between the shapes being that the interstices  50  (FIG. 4) are not filled by the buffer encasement  36   a . In addition, in the end elevation view of the optical module  30   a  during both the generally rectangular configuration and the skewed configuration, the exterior surface  62   a  also defines a shape that is substantially similar to the shape defined by the periphery of the ribbon stack  32   a , with substantially the only difference between the shapes being that the interstices  50  are not filled by the buffer encasement  36   a . In both the generally rectangular configuration and the skewed configuration, in the end elevation view of the optical module  30   a , the periphery of the ribbon stack  32   a  bounds a first area and the interior surface of the buffer encasement  36   a  bounds a second area, and the first and second areas are approximately equal. 
     In accordance with a first version of the first embodiment, the buffer encasement  36   a  is homogenous, meaning that all portions of the buffer encasement have approximately the same properties, such as hardness and modulus of elasticity. As best understood with reference to FIG. 6, in accordance with a second version of the first embodiment, the buffer encasement  36   a  has an inner portion  68 a and an outer portion  70   a  that are preferably not physically separate from one another but that have different properties, such as hardness and modulus of elasticity. Although there is not necessarily a clearly visible distinction between the inner and outer portions  68   a ,  70   a  with the naked eye and the transition between the inner and outer portions may be gradual, for purposes of explanation a separation line  66  is illustrated by broken lines in FIG. 6 to demonstrate a boundary between the inner and outer portions. In accordance with the second version of the first embodiment, the outer portion  70   a  has a hardness and modulus of elasticity that are greater than the hardness and modulus of elasticity of the inner portion  68   a . More specifically, in accordance with the second version of the first embodiment, the inner portion  68   a  of the buffer encasement  36   a  preferably has a modulus of elasticity between approximately 2×10 4  pounds per square inch and 1×10 2  pounds per square inch, and most preferably the modulus of elasticity of the inner portion is approximately 1×10 3  pounds per square inch. In contrast, in accordance with the second version of the first embodiment, the outer portion  70   a  of the buffer encasement  36   a  preferably has a modulus of elasticity between approximately 6×10 5  pounds per square inch and 2×10 4  pounds per square inch, and most preferably the modulus of elasticity of the outer portion is approximately 2×10 5  pounds per square. 
     In accordance with the first embodiment, it is preferred for the optical fibers  38  and the optical fiber ribbons  34  to be conventionally color-coded or marked with identifying indicia, or the like, for identification purposes. It is preferred for the buffer encasement  36   a  to be clear so that the identifying colors or markings of the optical fiber ribbons  34  and/or optical fibers  38  can be seen through the buffer encasement. Alternatively or in addition, different buffer encasements  36   a  are color-coded or marked with identifying indicia, or the like, for identification purposes. 
     In accordance with a version of the first embodiment, the buffer encasement  36   a  can be easily torn so that the buffer encasement can be easily removed from the ribbon stack  32   a . In accordance with one example of this easily torn version, the buffer encasement  36   a  has an ultimate tensile strength of less than approximately 2×10 3  pounds per square inch and a thickness T 2  (FIG. 6) of less than approximately 0.020 inches. In accordance with this example of the easily torn version, the buffer encasement  36   a  is acceptably constructed of low-density polyethylene, or the like. 
     In accordance with another example of the easily torn version, the buffer encasement  36   a  is easily tearable because it is constructed of a polymeric material that contains one or more fillers, such as inorganic fillers, that reduce the elongation and/or tensile strength of the polymeric material. Preferably this easily tearable buffer encasement has a tensile strength of less than approximately 2,000 pounds per square inch, an elongation of less than approximately 400 percent, and most preferably less than approximately 200 percent. In accordance with this example, suitable base resins or polymers include polyethylene, ethylene-vinyl acetate, ethylene-acrylic acid, or the like. In accordance with this example, suitable fillers include talc, calcium carbonate, aluminum trihydrate, or the like. 
     Second Embodiment 
     FIG. 7 is a perspective view of an optical module  30   b  in accordance with a second embodiment of the present invention. The optical module  30   b  of the second embodiment is identical to the optical module  30   a  (FIGS. 1,  2 , and  5 ) of the first embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the second embodiment, the ribbon stack  32   b  of the optical module  30   b  is longitudinally twisted when its buffer encasement  36   b  is formed therearound, and the buffer encasement  36   b  is sufficiently rigid to hold the ribbon stack  32   b  in its twisted configuration. In addition, as described above for the first embodiment, the buffer encasement  36   a  of the second embodiment is relatively thin and conforms closely to the exterior surface of the ribbon stack  32   a . As a result, the longitudinally extending four corners  71  of the buffer encasement  36   a  are arranged so as to define a longitudinal twist that corresponds to the twist of the ribbon stack  32   b , as is shown in FIG.  7 . That is, the exterior surface  62   b  of the buffer encasement  36   b  defines ridgelike corners  71 , which can be characterized as ridges, that define a lay length that corresponds to the lay length of the twisted ribbon stack  32   b . The corners  71  are preferably somewhat rounded. 
     The optical module  30   b  can have a continuous helical twist or an S-Z twist. More specifically, the ribbon stack  32   b  can be longitudinally twisted in the same direction for the entire length of the buffer encasement  36   b  to provide the continuous helical twist. In contrast, it is preferred for the longitudinal twisting of the ribbon stack  32   b  to be periodically reversed, so that the optical module  30   b  has what is referred to by those of ordinary skill in the art as an S-Z twist. In this regard, along a first section of the buffer encasement  36   b  the ribbon stack  32   b  is longitudinally twisted in a first direction to define a lay length, and the ribbon stack is longitudinally twisted in an opposite second direction along a contiguous second section of the buffer encasement to again define the lay length. The lay length is the longitudinal distance in which the ribbon stack  32   b  makes a complete revolution. That alternating twisting pattern is repeated along the entire length of the ribbon stack  30   b . In accordance with the second embodiment, the lay length of the S-Z twist is preferably in the range of approximately twelve to thirty-six inches, and most preferably the lay length is approximately twenty-four inches. 
     Third Embodiment 
     FIG. 8 is an end elevation view of an optical module  30   c  in accordance with a third embodiment of the present invention. The optical module  30   c  of the third embodiment is identical to the optical module  30   a  (FIGS. 1,  2 , and  5 ) of the first embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the third embodiment, the buffer encasement  36   c  defines a longitudinally extending weakened portion. The weakened portion preferably extends for the length of the optical module  30   c  and is preferably in the form of a longitudinally extending frangible portion  72 . Whereas the frangible portion  72  is shown in the form of a trough-like cutout, the frangible portion can be in the form of a series of perforations or other voids or means that weaken the buffer encasement  36   c . The buffer encasement  36   c  can be manually longitudinally torn along the frangible portion  72  more easily than the buffer encasement can be torn at other locations. Nonetheless, the frangible portion  72  is preferably constructed and arranged so that it does not tear inadvertently. 
     The frangible portion  72  is longitudinally torn to provide access to the optical fiber ribbons  34  contained within the buffer encasement  36   c . More specifically, by tearing the buffer encasement  36   c  along the frangible portion  72 , opposite longitudinally extending torn edges  74 ,  76 , which are illustrated by broken lines in FIG. 8, are formed. The torn edges  74 ,  76  are manually lifted away from the optical fiber ribbons  34  contained by the buffer encasement  36   c  so that a longitudinally extending opening  78   c  is defined between the torn edges, as is illustrated by broken lines in FIG.  8 . The optical fiber ribbons  34  contained by the buffer encasement  36   c  can be accessed through the opening  78   c . In accordance with an alternative embodiment of the present invention, the buffer encasement  36   c  is constructed of a material that can be easily torn so that the buffer encasement can be readily manually longitudinally torn without including a frangible portion  72 . 
     Fourth Embodiment 
     FIG. 9 is an end elevation view an optical module  30   d  in accordance with a fourth embodiment of the present invention. The optical module  30   d  of the fourth embodiment is identical to the optical module  30   a  (FIGS. 1,  2 , and  5 ) of the first embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the fourth embodiment, the buffer encasement  36   d  is preferably a longitudinally extending piece of polymeric film or tape. The tape preferably cannot be penetrated by water and/or may be coated with a conventional powder that absorbs water, or the like. The buffer encasement  36   d  includes opposite longitudinally extending edges  80 ,  82  that overlap one another so the optical fiber ribbons  34  are enclosed within the buffer encasement. 
     The surfaces of the edges  80 ,  82  that are overlapping and facing one another are preferably held together by a conventional adhesive so that those edges remain in their overlapping arrangement. In accordance with the unadhered version of the fourth embodiment, the adhesive does not cover the entire interior surface of the buffer encasement  36   d  so the optical fiber ribbons  34  contained by the buffer encasement can move relative to one another and relative to the buffer encasement. In accordance with the adhered version of the fourth embodiment, the entire interior surface of the buffer encasement  36   d  is be covered by the adhesive so that movement of the optical fiber ribbons  34  relative to one another as well as relative to the buffer encasement is impeded. 
     In accordance with the fourth embodiment, when access to the optical fiber ribbons  34  within the buffer encasement  36   c  is desired, the edges  80 ,  82  are manually separated to provide access to the optical fiber ribbons within the buffer encasement. More specifically, the separated edges  80 ,  82  are lifted away from the optical fiber ribbons  34  contained by the buffer encasement  36   d  so that a longitudinally extending opening  78   d  is defined between the edges, as is illustrated by broken lines in FIG.  9 . The optical fiber ribbons  34  contained by the buffer encasement  36   d  can be accessed through the opening  78   d . In addition, the edges  80 ,  82  can be returned to their original configurations to again fully enclose the optical fiber ribbons  34 , if desired. 
     In accordance with an alternative embodiment of the present invention, the polymeric tape or sheet from which the buffer encasement  36   d  is constructed is wrapped helically around the optical fiber ribbons  34  to form the buffer encasement, rather than being longitudinally applied to the optical fiber ribbons. 
     Fifth Embodiment 
     FIGS. 10 and 11 are perspective and end elevation views, respectively, of an optical module  30   e  in accordance with a fifth embodiment of the present invention. The optical module  30   e  of the fifth embodiment is identical to the optical module  30   a  (FIGS. 1,  2 , and  5 ) of the second version of the first embodiment, which is discussed above with reference to FIG. 6, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the fifth embodiment, the buffer encasement  36   e  has multiple plies. More specifically, the inner and outer portions  68   e ,  70   e  are separate plies. The inner portion  68   e  includes an outer surface  86   e  and the outer portion  70   e  includes an inner surface  88   e . In accordance with the fifth embodiment, the entire inner surface  88   e  extends around and is in contact with the entire outer surface  86   e  for the entire length of the optical module  30   e . In accordance with a first version of the fifth embodiment, the inner and outer portions  68   e ,  70   e  are coaxial thermoplastic coextrusions. In accordance with a second version of the fifth embodiment, the inner portion  68   e  is like the tapes or films described above with reference to the fourth embodiment, and the outer portion  70   e  is a polymeric extrusion, with the thickness of the multi-ply buffer encasement  36   e  being identical to the thickness T 2  (FIG. 6) of the buffer encasement  36   a  (FIGS. 1,  2 , and  5 ) of the first embodiment. Alternatively the thickness of the multi-ply buffer encasement  36   e  is greater than the thickness of the buffer encasement  36   a  of the first embodiment. A third version of the fifth embodiment is identical to the second version of the fifth embodiment, except that both the inner portion  68   e  and the outer portion  70   e  are like the tapes or films described above with reference to the fourth embodiment. 
     Sixth Embodiment 
     FIGS. 12 and 13 are perspective and end elevation views, respectively, of an optical module  30   f  in accordance with a sixth embodiment of the present invention. The optical module  30   f  of the sixth embodiment is identical to the optical module  30   a  (FIGS. 1,  2 , and  5 ) of the first embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     As best seen in FIG. 13, in accordance with the illustrated version of the sixth embodiment, the interstices  50  (FIG. 4) defined between the edges  42 ,  44  (FIG. 3) of the optical fiber ribbons  34 ′ are filled by portions of the buffer encasement  36   f . In addition, the buffer encasement  36   f  includes thickened portions  90  at the opposite four corners thereof. The thickened portions  90  preferably define bulbous-like shapes that cushion the optical fibers positioned at the opposite four corners of the ribbon stack  32   f . Except for the thickened portions  90 , the thickness of the buffer encasement  36   f  is identical to the thickness T 2  (FIG. 6) of the buffer encasement  36   a  (FIGS. 1,  2 ,  5 , and  6 ) of the first embodiment. Accordingly, a vast majority of the buffer encasement  36   f  has a thickness defined between the interior and exterior surfaces thereof that is not greater than the thickness of each of the optical fiber ribbons  34 ′ contained by the buffer encasement  36   f.    
     Seventh Embodiment 
     FIG. 14 is an end elevation view of an optical module  30   g  in accordance with a seventh embodiment of the present invention. The optical module  30   g  of the seventh embodiment is identical to the optical module  30   a  (FIGS. 1,  2 , and  5 ) of the first embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     The optical module  30   g  is illustrated in the non-skewed configuration in FIG.  14  and therefore can be characterized as including a generally round ribbon stack  32   g  and a round buffer encasement  36   g . In contrast, the ribbon stack  32   g  and the buffer encasement  36   g  may be oblong in an end elevation view thereof while the optical module  30   g  is in the skewed configuration. The optical fiber ribbons  34 ,  34 ′,  34 ″,  34 ′″,  34 ″″ of the ribbon stack  32   g  have different widths, and some of the optical fiber ribbons are in a side-by-side arrangement. In addition, the thickness of the buffer encasement  36   g  is measured in the direction of radii that radiate from the center of the optical module  30   g  in an end elevation view thereof. Whereas that thickness varies with the angle of the radii, the average thickness of the buffer encasement  36   g  corresponds to the thickness T 2  (FIG. 6) of the buffer encasement  62   a  (FIGS. 1,  2 ,  5 , and  6 ) of the first embodiment. That is, a majority of the buffer encasement  36   g  has a thickness defined between the interior and exterior surfaces thereof that is not greater than the thickness (for example see the thickness T 1  illustrated in FIG. 4) of each of the optical fiber ribbons  34 ,  34 ′,  34 ″,  34 ′″,  34 ″″ contained by the buffer encasement  36   g.    
     Methods of Manufacturing Optical Modules 
     FIG. 15 diagrammatically illustrates an assembly of manufacturing equipment  92  that is capable of acceptably manufacturing optical modules, such as the above-discussed optical modules  30   a ,  30   b ,  30   c ,  30   d ,  30   e ,  30   f ,  30   g  of the present invention. For the purpose of describing methods of operation of the assembly of manufacturing equipment  92 , the above-described optical modules, ribbon stacks, and buffer encasements are referred to generically as optical module  30 , ribbon stack  32 , and buffer encasement  36 . The assembly of manufacturing equipment  92  operates such that the optical fiber ribbons  34  and the formed ribbon stack  32 , buffer encasement  36 , and optical module  30  are continuously longitudinally advanced. 
     Upstream Guiding Mechanism 
     As seen in FIG. 15, separate optical fiber ribbons  34  are drawn in parallel into an upstream guiding mechanism  94 . Whereas only four optical fiber ribbons  34  are illustrated in FIG. 15, it is within the scope of the present invention for more and less than four optical fiber ribbons to be drawn into the assembly of manufacturing equipment  92 . The process of feeding the optical fiber ribbons  34  to the upstream guiding mechanism  94  preferably includes conventionally dispensing previously manufactured optical fiber ribbons  34 , such as dispensing the optical fiber ribbons from reels that are positioned upstream from the upstream guiding mechanism. 
     In accordance with one example of the present invention, the guiding mechanism  94  includes multiple rollers, or the like, that defined nips through which the optical fiber ribbons  34  are drawn for generally aligning the optical fiber ribbons with one another and maintaining spaces between the optical fiber ribbons. It is conventional to draw optical fiber ribbons into a parallel arrangement, so the operations of the upstream guiding mechanism  94  should be understood by those of ordinary skill in the art. 
     Lubricating Mechanism 
     As illustrated in FIG. 15, the aligned optical fiber ribbons  34  are drawn from the upstream guiding mechanism  94  to a lubricating mechanism  96 . The lubricating mechanism  96  applies lubricant to the edges  42 ,  44  (FIG. 3) and the lateral surfaces  46 ,  48  (FIG. 3) of each of the optical fiber ribbons  34 . The lubricant can be acceptably applied to the optical fiber ribbons  34  by any of numerous conventional coating techniques. For example, liquid lubricant can be applied to the optical fiber ribbons  34  by a spraying assembly including pump(s) that force liquid lubricant to flow from a reservoir, through piping, and out of spray nozzles that direct the lubricant onto the optical fiber ribbons  34 . An example of an assembly for applying lubricant to optical fiber ribbons is disclosed in U.S. patent application Ser. No. 09/179,721, which is incorporated herein by reference. In addition, the optical fiber ribbons  34  can be drawn through a bath of the lubricant, or drawn between absorbent rollers that are saturated with the lubricant. Alternatively, powder-type lubricants can be sprinkled and blown onto the optical fiber ribbons  34 . 
     It is preferred for the applied lubricant not to adversely interact with the optical fiber ribbons  34  or the buffer encasement  36  formed around the optical fiber ribbons. For example, it is preferred for the lubricant not to cause the buffer encasement  36  to swell. For example, in accordance with some embodiments of the present invention “E”-type hydrocarbon oils are used when the buffer encasement  36  is constructed of a low density polyethylene material. Specifically, “E”-type hydrocarbon oil comprises 22.5% by weight of SHF-402 polyalphaolefin oil; 75.5% by weight of SHF-82 polyalphaolefin oil; and 2% by weight of IRGANOX® 1076 antioxidant. These polyalphaolefin oils are commercially available from Mobil Chemical Company, and the antioxidant (stabilizer) is commercially available from the Ciba-Geigy Company. This oil has a viscosity between 54 and 82 centistrokes at 40° C., and a viscosity between 8 and 12 centistrokes at 100° C. when measured in accordance with the method of ASTM D-445. These oils were selected to have a kinematic viscosity that is less than 4000 centistrokes at 100° C. 
     In accordance with other embodiments of the present invention a more polar oil, such as glycol, is used when the buffer encasement  36  is constructed of ethylene-vinyl acetate copolymer. It is also preferred for the lubricant that is applied to the optical fiber ribbons  34  to be water resistant or contain a water absorbent powder, or the like. For a majority of the embodiments of the present invention, including the second embodiment, a preferred lubricant is stabilized polyalphaolefin oil, or the like. Other suitable lubricants include glycol, silicone oils, or the like. 
     It is also within the scope of the present invention for the assembly of manufacturing equipment  92  not to include the lubricating mechanism  96 . For example, it is within the scope of the present invention for the optical fiber ribbons  34  of an optical module  30  to not be lubricated, such as for the unadhered versions of the optical module discussed above with reference to the first embodiment. 
     Downstream Guiding Mechanism 
     As illustrated in FIG. 15, the optical fiber ribbons  34  are drawn from the lubricating mechanism  96  to a downstream guiding mechanism  98 . The downstream guiding mechanism  98  includes multiple rollers that guide the optical fiber ribbons  34  so that the optical fiber ribbons are formed into a ribbon stack  32 . It is conventional to arrange optical fiber ribbons  34  into a ribbon stack  32 , so the operations of the downstream guiding mechanism  98  should be understood by those of ordinary skill in the art. 
     Twisting Mechanism 
     The assembly of manufacturing equipment  92  is illustrated as further including a twisting mechanism  99 . In accordance with those embodiments of the present invention in which the ribbon stack  32  is twisted, the ribbon stack  32  is drawn from the downstream guiding mechanism  98  to the twisting mechanism  99 . The twisting mechanism  99  is operative to impart either a continuous helical twist in the ribbon stack  32  or an S-Z twist, as described above with reference to the second embodiment of the present invention. 
     It is preferred, when practicable, for many of the optical modules  30  of the present invention to be constructed so that their ribbon stacks  32  are S-Z twisted. For example, in accordance with alternative embodiments of the present invention, optical modules  30  similar to the optical modules  30   a  (FIGS. 1,  2 , and  5 ),  30   c  (FIG.  8 ),  30   d  (FIG.  9 ), and  30   e  (FIGS.  10  and  11 ), and discussed variants thereof, have twisted ribbon stacks  32 . 
     It is conventional to longitudinally twist ribbon stacks  32 , so the operations of the twisting mechanism  99  should be understood by those of ordinary skill in the art. An acceptable example of a twisting mechanism is disclosed in U.S. patent application Ser. No. 09/179,721, which has been incorporated herein by reference. In accordance with embodiments of the present invention in which the ribbon stack  32  is twisted, the ribbon stack is drawn from the twisting mechanism  99  to the encasing mechanism  100 . 
     In accordance with some of the embodiments of the present invention, the ribbon stack  32  is not twisted, in which case the twisting mechanism  99  is bypassed or omitted from the assembly of manufacturing equipment  92 . That is, in accordance with embodiments of the present invention in which the ribbon stack  32  is not twisted, the ribbon stack is drawn from the downstream guiding mechanism  98  to an encasing mechanism  100 . 
     Encasing Mechanism 
     The encasing mechanism  100  forms the buffer encasement  36  around the ribbon stack  32  to form the optical module  30 . Multiple variations of the encasing mechanism  100  are within the scope of the present invention, and examples of them will be briefly described, followed by a more detailed discussion of each. In accordance with a first method of the present invention, the encasing mechanism  100  applies a polymeric tape or film to the ribbon stack  32  to form the buffer encasement  36 . In accordance with a second method of the present invention, the encasing mechanism  100  extrudes thermoplastic material around the ribbon stack  32  to form the buffer encasement  36 . In accordance with a third method of the present invention, the encasing mechanism  100  applies an ultraviolet-curable material onto the ribbon stack  32  and cures that material to form the buffer encasement  36 . In accordance with a fourth method of the present invention, the encasing mechanism  100  performs the above operations in various combinations and subcombinations to provide composite buffer encasements  36 . 
     First Method: In accordance with the first method of the present invention, the buffer encasement  36  is formed by way of the encasing mechanism  100  applying a longitudinally extending polymeric tape or film to the ribbon stack  32 , or helically wrapping the tape or film around the ribbon stack to produce an optical module  30 . It is conventional in the construction of fiber optic cables to apply a longitudinally extending tape to a longitudinally advancing member, and to helically wrap tape around a longitudinally advancing member, so those of ordinary skill in the art should be able to select a suitable encasing mechanism  100  for carrying out the first method. 
     Optical modules  30  constructed in accordance with the first method include those described above with reference to the fourth embodiment and variations thereof. It is also within the scope of the present invention for other optical modules  30  to be constructed in accordance with the first method. 
     In accordance with the first method, the tapes or films from which the buffer encasement  36  is constructed are acceptably constructed from thermoplastic materials, or more specifically polyolefin materials, or more specifically polyethylene. In accordance with the fourth embodiment discussed above, a particularly suitable tape is conventional water-blocking tape with conventional nonwoven polyester backing. 
     Second Method: In accordance with the second method of the present invention, the encasing mechanism  100  includes one or more extruders that extrude the buffer encasement  36  over the ribbon stack  32 . It is conventional in the construction of fiber optic cables to utilize an extruder to extrude a thermoplastic material onto a longitudinally advancing member, so those of ordinary skill in the art should be able to select a suitable encasing mechanism  100  for carrying out the second method. 
     In accordance with the second method, the material being extruded is acceptably a thermoplastic material, or more specifically a polyolefin material, or more specifically polyethylene. Further, in accordance with the second method, the extrusion(s) may be sufficiently solidified through exposure to the ambient air. Alternatively or in addition, the encasing mechanism  100  can include cooling mechanism(s) that aid in the cooling and solidification of the extrusion(s). Acceptable cooling mechanisms include water baths, or the like. 
     In accordance with a first version of the second method, the encasing mechanism  100  extrudes a thermoplastic extrusion around the ribbon stack  32 , and that extrusion solidifies to form the buffer encasement  36 . More specifically, the initially formed extrusion has internal dimensions that are larger than the external dimensions of the ribbon stack  32 , and as the extrusion solidifies the extrusion is “drawn down” to the ribbon stack  32  to form the buffer encasement  36 . As a result of the drawing down, the internal dimensions of the buffer encasement  36  are approximately equal to the external dimensions of the ribbon stack  32 . For example, the optical module  30   a  (FIGS. 1,  2  and  5 ) of the first version of the first embodiment and the optical modules  30   b ,  30   c  of the second and third embodiments, respectively, can be constructed in accordance with the first version of the second method. In accordance with the first version of the second method, a particularly suitable material for extruding to form the buffer encasements  36 , and the material that is preferably used to construct the buffer encasement  36   b  (FIG. 7) of the second embodiment, is low-density polyethylene, or the like. 
     Second and third versions of the second method are similar to the first version of the second method, except in accordance with the second and third versions the encasing mechanism  100  forms thermoplastic coextrusions around the ribbon stack  32 . In accordance with the second version of the second method, the facing surfaces of the coextrusions partially blend together before solidifying, for example to produce the nonhomogenous buffer encasement  36   a  (FIG. 6) of the second version of the first embodiment. In accordance with the second version of the second method, a preferred material for extruding to form the inner portion  68   a  (FIG. 6) of the buffer encasement  36   a  is very low density polyethylene-vinyl acetate, ethylene-acrylic acid, or the like. In accordance with the second version of the second method, a preferred material for extruding to form the outer portion  70   a  (FIG. 6) of the buffer encasement  36   a  is medium or high density polyethylene, or the like. 
     In accordance with the third version of the second method, the coextrusions do not partially blend together before solidifying, for example to produce the buffer encasement  36   e  (FIGS. 10 and 11) of the fifth embodiment. In accordance with the third version of the second embodiment, a preferred material for extruding to form the inner portion  68   e  (FIGS. 10 and 11) of the buffer encasement  36   e  is very low density polyethylene, ethylene-vinyl acetate, ethylene-acrylic acid, or the like. In accordance with the third version of the second embodiment, a preferred material for extruding to form the outer portion  70   e  (FIGS. 10 and 11) of the buffer encasement  36   e  is impact modified polypropylene (propylene-ethylene copolymer), or the like. 
     Third Method: In accordance with the third method of the present invention, the encasing mechanism  100  applies an uncured ultraviolet-curable material onto and around the ribbon stack  32  and thereafter cures the ultraviolet-curable material to form the buffer encasement  36  around the ribbon stack. The ultraviolet-curable material is cured by exposure to ultraviolet radiation. As mentioned above, it is conventional to use ultraviolet-curable materials is the construction of optical fiber ribbons  34 , so those of ordinary skill in the art should be able to select a suitable encasing mechanism  100  for carrying out the third method. 
     In accordance with the third method, the uncured ultraviolet-curable material can be applied to the ribbon stack  32  through the use of several different techniques. For example, the uncured ultraviolet-curable material can be extruded onto the ribbon stack  32 , sprayed onto the ribbon stack, or the ribbon stack can be drawn through a bath of the uncured ultraviolet-curable material. Thereafter, the uncured ultraviolet-curable material on the ribbon stack  32  is cured by exposure to ultraviolet radiation. 
     Optical modules  30  constructed in accordance with the third method include those described above with reference to the sixth and seventh embodiments. For example, when constructing the optical module  30   f  (FIGS. 12 and 13) of the sixth embodiment, preferably a thick ultraviolet-curable material is extruded onto the ribbon stack  32   f  (FIGS.  12  and  13 ), and the die that is used for the extruding is constructed and arranged to define the shape of the resulting buffer encasement  36   f  (FIGS.  12  and  13 ). 
     In accordance with the third method, buffer encasements  36  having inner and outer portions, such as inner and outer portions  68   a ,  70   a  (FIG.  6 ), with different properties can be produced by controlling the application of the ultraviolet radiation to the uncured ultraviolet-curable material that has been applied to the ribbon stack  32 . For example, a homogenous ultraviolet-curable gel can be applied to a ribbon stack  32  and then the duration and intensity of the ultraviolet radiation imparted on the applied ultraviolet-curable material is controlled so the resulting buffer encasement  36  has an inner portion and an outer portion, such as inner and outer portions  68   a ,  70   a , having different hardness and modulus of elasticity. For example, it is preferred for the inner portion to be softer and have a lower modulus of elasticity, and for the outer portion to be harder and have a higher modules of elasticity, as described above with reference to the second version of the first embodiment. That is, the forming of the buffer encasement  36  is carried out by coating the stack of optical fiber ribbons  34  with the ultraviolet-curable material and thereafter exposing the ultraviolet-curable material to ultraviolet radiation for a predetermined period of time selected so that on a per unit basis more curing, such as polymerization, occurs in the outer portion  70   a  than the inner portion  68   a.    
     A suitable ultraviolet-curable material is that which is described above as being used in the formation of the optical fiber ribbons  34 . Other suitable ultraviolet-curable materials include acrylate materials that are polymerized when exposed to ultraviolet radiation to create polyacrylate. 
     Fourth Method: In accordance with the fourth method of the present invention, the first, second, and third methods are combined and/or varied to produce other optical modules  30 . For example, in accordance with the second version of the fifth embodiment, the inner portion  68   e  (FIGS. 10 and 11) is constructed of a tape or film of polymeric material that blocks water, and the outer portion  70   e  (FIGS. 10 and 11) is an extrusion of polymeric material. 
     Weakening Mechanism 
     In accordance with embodiments of the present invention in which the buffer encasement  36  includes a frangible portion  72  (FIG.  8 ), or the like, the optical module is drawn from the encasing mechanism  100  to a weakening mechanism  101 . The weakening mechanism  101  forms a longitudinally extending frangible portion, such as the illustrated frangible portion  72 , in the buffer encasement  36 . Suitable frangible portions can be formed through the use of a wide variety of devices, such as cutting, scoring, or piercing devices, or the like. 
     In accordance with the third embodiment, the weakening mechanism  101  is preferably a machine that generates a laser beam that is used to cut the buffer encasement  36   c  (FIG. 8) to form the frangible portion  72  (FIG.  8 ). Cutting machines that form precise cuts by means of a laser are conventional and readily available 
     Storing Mechanism 
     As illustrated in FIG. 15, the completely manufactured optical module  30  is drawn to a conventional storing mechanism  102 . A suitable storing mechanism can include a reel that the manufactured optical module  30  is drawn onto and wrapped around. Optical modules  30  that have been longitudinally twisted, such as the optical module  30   b  (FIG. 7) and round optical modules, such as the optical module  30   g  (FIG.  14 ), are particularly well suited for being wound onto reels. Alternatively, the storing mechanism  102  can include barrels that the manufactured optical modules  30  are continuously drawn toward and dropped into. 
     Irrespective of the manner in which an optical module  30  is stored, it is preferred for the opposite ends of the optical module to be readily available so that the optical integrity of the optical module can be tested prior to incorporating the optical module into a fiber optic cable. This is particularly advantageous with respect to fiber optic cables that include multiple optical modules  30  in parallel. 
     Fiber Optic Cables 
     FIGS. 16-21 and  24 - 26  illustrates fiber optic cables in accordance with embodiments of the present invention. For the purpose of describing the fiber optic cables, the above-described optical modules  30   a ,  30   b ,  30   c ,  30   d ,  30   e ,  30   f ,  30   g  of the present invention are referred to generically as optical modules  30 , because it is within the scope of the present invention for each of the below-described fiber optic cables, and/or variations thereof, to be constructed with each of the above-described optical modules and combinations thereof, with exceptions being noted or apparent to those of ordinary skill in the art. Likewise, the above-described ribbon stacks and buffer encasements are respectively referred to generically as ribbon stacks  32  and buffer encasements  36 . 
     Eighth Embodiment 
     FIG. 16 is a schematic end elevation view of a fiber optic cable  108   a  in accordance with an eighth embodiment of the present invention. The fiber optic cable  108   a  includes a centrally located and longitudinally extending optical module  30  that is preferably surrounded by a conventional, longitudinally extending piece of water-blocking tape  110 . A conventional outer jacket of polymeric material  112   a  extends around the water-blocking tape  110  and longitudinally extending outer strength members  114   a  are embedded in the outer jacket. The space between the water-blocking tape  110  and the optical module  30 , as well as the space between the outer jacket  112   a  and the water-blocking tape, can be filled with a conventional filler material, such as a thixotropic gel. It is preferred for each of the fiber optic cables of the present invention not to include any filler materials, such as thixotropic gels, but it is also within the scope of the present invention for each of the fiber optic cables of the present invention to include filler materials, such as thixotropic gels. In accordance with the present invention, it is preferred for the buffer encasements  36  to sufficiently protect the ribbon stacks  32  so that filler materials are not required. 
     The outer jacket  112   a  can incorporate more than two outer strength members  114   a . In addition, the outer jacket  112   a  can be constructed of a metallic material or a dialectric material. Also, the fiber optic cable  108   a  can further include metal armor that extends around and further protects the optical module(s)  30 . 
     Ninth Embodiment 
     FIG. 17 is a schematic end elevation view of a fiber optic cable  108   b  in accordance with a ninth embodiment of the present invention. The fiber optic cable  108   b  of the ninth embodiment is identical to the fiber optic cable  108   a  (FIG. 16) of the eighth embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     The fiber optic cable  108   b  of the ninth embodiment includes multiple ribbon stacks  32  (for example see FIG. 4) that are in a symmetrical stacked arrangement that is generally uniform along the length of the fiber optic cable and results in dense packaging of optical fibers. The multiple ribbon stacks  32  are preferably components of multiple optical modules  30 . The optical modules  30  are preferably not twisted, are preferably generally polygonal, and are preferably maintained in the stacked symmetrical arrangement along the entire length of the fiber optic cable  108   b . Although not shown in FIG. 17, the group of optical modules  30  can be collectively encircled by water-blocking tape (for example, see the water-blocking tape  110  (FIG.  16 )). Because the optical modules  30  are discreet units, operative optical modules can be readily salvaged from the fiber optic cable  108   b  if the fiber optic cable becomes damaged. 
     Tenth Embodiment 
     FIG. 18 is a schematic end elevation view of a fiber optic cable  108   c  in accordance with a tenth embodiment of the present invention. The fiber optic cable  108   c  of the tenth embodiment is identical to the fiber optic cable  108   b  (FIG. 17) of the ninth embodiment, except for noted variations and variations apparent to one of ordinary skill in the art. 
     The fiber optic cable  108   c  of the tenth embodiment includes multiple ribbon stacks  32  (for example see FIG. 4) that are stacked, but they are not in a completely symmetrical arrangement. The multiple ribbons stacks  32  are preferably components of multiple optical modules  30 . The optical modules  30  are preferably not twisted and are preferably generally polygonal and maintained in the stacked arrangement along the entire length of the fiber optic cable  108   c.    
     Eleventh Embodiment 
     FIG. 19 is a schematic end elevation view of a fiber optic cable  108   d  in accordance with an eleventh embodiment of the present invention. The fiber optic cable  108   d  of the eleventh embodiment is identical to the fiber optic cable  108   a  (FIG. 16) of the eighth embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     The fiber optic cable  108   c  includes multiple ribbon stacks  32  (for example see FIG. 4) that are laterally spaced apart from one another in a somewhat random arrangement so the optical modules are not in a symmetrical stacked configuration. The multiple ribbons stacks  32  are preferably components of multiple optical modules  30 . Whereas the fiber optic cable  108   d  of the eleventh embodiment is illustrated as including a central strength member  116  in addition to the outer strength members  114   a , it is preferred for the fiber optical cable  108   d  to have either the central strength member or the outer strength members, but not both. Although not shown, the group of optical modules  30  can be collectively encircled by water-blocking tape (for example, see the water-blocking tape  110  (FIG.  16 )). 
     Twelfth Embodiment 
     FIG. 20 is a schematic end elevation view of a fiber optic cable  108   e  in accordance with a twelfth embodiment of the present invention. The fiber optic cable  108   e  of the twelfth embodiment is identical to the fiber optic cable  108   d  (FIG. 19) of the eleventh embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the twelfth embodiment, the multiple ribbon stacks  32  (for example see FIG. 4) are tightly packed into the outer jacket  112   e . The multiple ribbons stacks  32  are preferably components of multiple optical modules  30 . As one example, the optical modules  30  can be characterized as being in a somewhat random arrangement such that they are not in a symmetrical stacked configuration. In accordance with the twelfth embodiment, the enclosing of the optical modules  30  in the longitudinally extending passage defined by the outer jacket  112   e  causes lateral forces to be applied to the at least one or more of the optical modules so that those optical modules are transitioned from their non-skewed configuration to their skewed configuration. As discussed above and illustrated in FIG. 5, the skewed configuration occurs when a buffer encasement  36  is laterally deformed and the optical fiber ribbons  34  therein slide laterally relative to one another. 
     It is within the scope of the present invention for the enclosing of the optical modules in the longitudinally passage defined by the outer jacket  112   e  to include operations prior thereto. For example, the lateral forces that result in the skewed configuration of optical modules  30  can be caused when the optical modules are drawn together in preparation for being enclosed in the outer jacket  112   e . As an additional example, in accordance with the twelfth embodiment, the group of optical modules  30  can be collectively encircled by water-blocking tape (for example, see the water-blocking tape  110  (FIG.  16 )), and the application of the tape may result the lateral forces that result in the skewed configurations of at least some of the optical modules. 
     Thirteenth Embodiment 
     FIG. 21 is a schematic end elevation view of a fiber optic cable  118   a  in accordance with a thirteenth embodiment of the present invention. The fiber optic cable  118   a  includes multiple ribbon stacks  32  (for example see FIG.  4 ), which are preferably components of optical modules  30 . More specifically, the fiber optic cable  118   a  includes a longitudinally extending central member  120   a  defining a longitudinally interior passage through which an optical module  30  longitudinally extends. The central member can be a relatively strong central strength member, or it can be a central spacer that is not as strong as the central strength member. The optical module  30  extending through the central member  120   a  can be characterized as a central optical module. Multiple optical modules  30  are arranged radially around the periphery of the central member  120   a . Those radially arranged optical modules  30  can be characterized as peripheral optical modules. 
     In accordance with the thirteenth embodiment, the ribbon stack  32  (see FIG. 4 for example) of the central optical module  30  is in the form of a stack of twelve optical fiber ribbons  34  (see FIG. 3 for example) with each of those optical fiber ribbons containing twelve optical fibers  38  (see FIG. 3 for example). In accordance with the thirteenth embodiment, each of the peripheral optical modules  30  is in the form of a stack of twelve optical fiber ribbons  34  with each of those optical fiber ribbons containing twelve optical fibers  38 . Therefore, the optical fiber cable  118   a  has a total fiber count of 1008. Variations of the optical fiber cable  118   a  have different fiber counts. 
     In accordance with the thirteenth embodiment, each of the optical modules  30  have approximately the same height H (FIG. 2) and each of the optical modules have approximately the same width W (FIG.  2 ). In the end elevation view of the fiber optic cable  118   a , for each of the peripheral optical modules  30  the height H is the radial cross-dimension of the peripheral optical modules, with the radial directions extending from the center of the center optical module  30  toward the peripheral optical modules. 
     Longitudinally extending strength members  122  extend between the peripheral optical modules  30 , and a longitudinally layer of armor  124   a  encircles the peripheral optical modules. A longitudinally extending outer jacket  126   a  constructed of a polymeric material extends around the armor  124   a . In accordance with the thirteenth embodiment, the central optical module  30  is approximately centrally located with respect to the outer jacket  126   a , and a radial distance is defined between the center of the central optical module and the center of each of the peripheral optical modules  30 . The radial distances defined between the center of the central optical module  30  and the center of each of the peripheral optical modules  30  are approximately equal. 
     In accordance with one version of the thirteenth embodiment, voids within the fiber optic cable  118   a  are filled with a conventional flooding material, such as a thixotropic gel. In contrast, in accordance with another version of the thirteenth embodiment, interior spaces of the fiber optic cable  118   a  are not filled with a flooding material, such as a thixotropic gel. 
     In accordance with a first version of the thirteenth embodiment, the peripheral optical modules  30  are not stranded. In accordance with this first version, it is preferred for the central member  120   a  not to define a lay length. For example, FIG. 22 is an isolated perspective view of the central member  120   a  of the fiber optic cable  118   a  (FIG. 21) in accordance with the first version of the thirteenth embodiment. As illustrated in FIG. 22, the outer surface of the central member  120   a  does not define a lay length. 
     In accordance with a second version of the thirteenth embodiment, the peripheral optical modules  30  are longitudinally stranded around the central member  120   a . In accordance with one example, the peripheral optical modules  30  are helically stranded around the central member  120   a , and in accordance with another example the peripheral optical modules are S-Z stranded around the central member. In accordance with this second version, it is preferred for portions of the exterior surface of the central member  120   a  to define the same type of stranding and lay length as the peripheral optical modules. For example, FIG. 23 is an isolated perspective view of the of the central member  120   a  of the fiber optic cable  118   a  (FIG. 21) in accordance with the second version of the thirteenth embodiment. 
     As best seen in FIG. 21, the outer surface of the central member  120   a  defines a six-sided polygon-like shape, and the fiber optic cable  118   a  contains a corresponding number of peripheral optical modules  30 . In accordance with an alternative to the thirteenth embodiment, the outer surface of the central member  120   a  defines a circular shape. In accordance with another alternative to the thirteenth embodiment, the fiber optic cable  118   a  does not include the central member  120   a , in which case stranding of the peripheral optical modules  30  is with respect to the central optical module  30 . 
     Fourteenth Embodiment 
     FIG. 24 is a schematic end elevation view of a fiber optic cable  118   b  in accordance with a fourteenth embodiment of the present invention. The fiber optic cable  118   b  of the fourteenth embodiment is identical to the fiber optic cable  118   a  (FIG. 21) of the thirteenth embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the fourteenth embodiment, each of the optical modules  30  of the fiber optic cable  118 b have approximately the same width W (FIG.  2 ), and the height H (FIG. 2) of the central optical module  30  is greater than the height H of the peripheral optical modules  30 . Incorporating optical modules  30  having different heights H and/or widths W advantageously provides for flexibility in cable designs and efficient packaging of optical fibers in fiber optic cables with high fiber counts. 
     In accordance with the fourteenth embodiment, the ribbon stack  32  (see FIG. 4 for example) of the central optical module  30  is in the form of a stack of eighteen optical fiber ribbons  34  (see FIG. 3 for example) with each of those optical fiber ribbons containing twenty-four optical fibers  38  (see FIG. 3 for example). In accordance with the fourteenth embodiment, each of the peripheral optical modules  30  is in the form of a stack of six optical fiber ribbons  34  with each of those optical fiber ribbons containing twenty-four optical fibers  38 . Therefore, the optical fiber cable  118   b  has a total fiber count of 1296. Variations of the optical fiber cable  118   b  have different fiber counts. 
     Fifteenth Embodiment 
     FIG. 25 is a schematic end elevation view of a fiber optic cable  118   c  in accordance with a fifteenth embodiment of the present invention. The fiber optic cable  118   c  of the fifteenth embodiment is identical to the fiber optic cable  118   a  (FIG. 21) of the thirteenth embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. 
     In accordance with the fifteenth embodiment, both the height H (FIG. 2) and the width W (FIG. 2) of the central optical module  30  is greater than the height H and width W of each of the peripheral optical modules  30 . In accordance with the fifteenth embodiment, the ribbon stack  32  (see FIG. 4 for example) of the central optical modules  30  is in the form of a stack of eighteen optical fiber ribbons  34  (see FIG. 3 for example) with each of those optical fiber ribbons containing twenty-four optical fibers  38  (see FIG. 3 for example). In accordance with the fifteenth embodiment, each of the peripheral optical modules  30  is in the form of a stack of twelve optical fiber ribbons  34  with each of those optical fiber ribbons containing twelve optical fibers  38 . Therefore, the optical fiber cable  118   c  has a total fiber count of 1296. Variations of the optical fiber cable  118   c  have different fiber counts. 
     Sixteenth Embodiment 
     FIG. 26 is a schematic end elevation view of a fiber optic cable  118   d  in accordance with a sixteenth embodiment of the present invention. The fiber optic cable  118   d  of the sixteenth embodiment is identical to the fiber optic cable  118   c  (FIG. 25) of the fifteenth embodiment, except for noted variations and variations apparent to those of ordinary skill in the art. In accordance with the sixteenth embodiment, the outer surface of the central member  120   d  defines an eight-sided polygon-like shape and there are eight peripheral optical modules. Therefore, the optical fiber cable  118   d  has a total fiber count of 1584. 
     The fiber optic cables  118   a-c  (FIGS.  21  and  24 - 26 ) illustrate that in fiber optic cables of this type, maximum packaging efficiency may be achieved with a central stack of optical fiber ribbons with relatively wide (relatively high fiber count) ribbons and peripheral stacks of optical fiber ribbons with relatively narrow (relatively low fiber count) ribbons. 
     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.