Abstract:
A connector subassembly and related connector that are configured to floatingly align and tune mated ferrules are disclosed. The connector subassembly includes a ferrule holder and a plug housing having an inner surface with slanted or sloped alignment features, such as, for example, a radially extending key. In an embodiment, the ferrule holder assembly is configured to hold the ferrule and has an outer surface defining a groove extending axially. The key is slidably disposed in the groove. The connector includes the ferrule holder, the plug housing, a spring element disposed within the plug housing and urging the ferrule holder in a direction axially toward the rearward opening, a crimp body attached to the plug housing so as to compress the spring element, a boot attached to the plug housing via the crimp body and disposed about a portion of an optical fiber, and a tube disposed about a section of the optical fiber and secured to the ferrule holder.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to floating connector subassemblies useful for optical cable connectors. More particularly, this invention relates to subassemblies and optical cable connectors that are configured to floatingly align and tune mated ferrules within the connectors. Even more particularly, this invention relates to a connector subassembly that includes a plug housing having an inner surface with slanted or sloped alignment features and a ferrule holder. The connectors may be used, for example, to join segments of optical cables and to connect an optical cable with an optical device, such as, for example, radiation sources, detectors, repeaters, switches, attenuators, and the like. 
     BACKGROUND OF THE INVENTION 
     Various types of connectors have been developed for connecting optical cables to optical system components, such as, for example, to join segments of optical cables and to connect an optical cable with an optical device, including, radiation sources, detectors, repeaters, switches, attenuators, and the like. Numerous factors influence the design of such connectors, including the diameter and makeup of the optical fiber used in the cable, the environment into which the cable and connector are placed, the space available for connection and the number of connections required in a given location, to name but a few. Standardized optical cable connector designs currently in common use include the SC-type, FC-type, ST-type, and RJ-type connectors. 
     Regardless of the optical cable connector design selected for a particular application, the central function of an optical cable connector is to maintain the optical fiber end in precise position relative to another fiber or another system component so as to maximize the signal strength as the light passes through the connection (i.e., minimize insertion losses). Even slight mispositioning of a fiber can contribute to insertion losses. In the past, industry had accepted some transmission loss due to misalignment. However, growing use of optical cables for communicating data demands near 100% transmission and reception capability and thus, minimal insertion loss. The degree of insertion loss in coupling two fibers is generally dependent on factors, such as, for example, the alignment of the fiber central axis at the ends, the width of the gap between the ends, and the optical surface condition of the ends. 
     To couple virtually all of the light from one fiber to another fiber is a particularly challenging task because the light carrying regions or “cores” of optical fibers are quite small. For example, in single mode optical fibers, the core diameter is about 8 microns. Thus, the very small end surface of the core must not only be precisely prepared, but must also be precisely located, both to tolerances in the range of fractions of microns, to achieve low insertion loss. 
     Another function of the optical cable connector is to provide mechanical stability and protection to the junction and its working environment. Stability and junction protection is generally a function of connector design. Bulkier designs may provide more stability, but may disadvantageously take up more space and cost more than other designs. 
     In a connection between a pair of optical fiber connectors, an optical fiber extending from a center of an end face of a ferrule is butted together with an end face of another ferrule and light travels from one optical fiber to the other along the central axes of the two optical fibers. One such arrangement using an LC connector is illustrated in U.S. Pat. No. 5,481,634. 
     Often, a “floating” arrangement is provided, wherein the two ferrules, once butted together, can float as a unit relative to the plug housings due to springs present in the plug housings. The butted ferrule ends are typically held in alignment by a sleeve covering both ends. Such floating arrangements are beneficial in that the ferrules can be joined together as an aligned unit without regard to any small misalignments or imperfections in the other connector elements. Thus, all connector elements need not be manufactured to extremely tight tolerances to achieve a well-aligned pair of ferrules and fibers, so long as the ferrules and certain alignment elements (e.g., the sleeve) are precisely manufactured and assembled. 
     Any radial eccentricity of a fiber within a ferrule (i.e., when a fiber&#39;s central axis is spaced from the ferrule&#39;s central axis) may be compensated for by “tuning” the ferrule by orienting the eccentricity in a given direction relative to its ferrule holder and/or plug housing. When the ferrule is connected to another ferrule, having both ferrules tuned in the same direction may reduce insertion loss by improving alignment if the fiber positioning within each of ferrules is within certain tolerances. 
     Some connectors use a straight (i.e., substantially rectangular, radially extending) key and groove feature to tune a ferrule relative to a plug housing. In such case, a substantially rectangular key extends from the plug housing into a substantially rectangular groove in a ferrule holder. Due to the substantially rectangular and radially extending complimentary shapes of the key and groove, the ferrule&#39;s ability to compensate for any misalignments between the ferrule and the plug housing inner surface is limited. Thus, by maintaining precise tuning and alignment of the ferrule relative to its plug housing, the ferrule has little if any ability to float. By loosening the fit of such a key structure, for example by making the key smaller or the groove bigger, the precision of the tuning and alignment of the ferrule relative to its plug housing suffer, potentially defeating the purpose of the key and groove. Thus, a trade off exists between the precision of the floating capability and the precision of the tuning and alignment capability in available connectors. At present, mating components of available tunable connectors typically have used relatively tight tolerances, which in turn reduces the ability of the ferrule to float. In addition, conventional connector designs fail to include means to further minimize or compensate for alignment errors and manufacturing inaccuracies that would otherwise result in insertion losses. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of this invention to provide a connector subassembly and a related connector having a floating capability and a tuning and aligning capability, wherein the component parts of the connector subassembly and connector are simple, reliable, and economical to manufacture, assemble, and use. Other objectives and advantages of the invention will be apparent from the following description and the attached drawings, or can be learned through practice of the invention. 
     According to an aspect of the invention, a connector subassembly includes a plug housing and a ferrule holder that provide floating capability and tuning and alignment capability of a ferrule. The connector subassembly includes a plug housing having an inner surface that defines a cavity extending longitudinally therethrough. The plug housing defines a forward opening in communication with the cavity for receiving an optical fiber extending into a ferrule and a rearward opening in communication with the cavity and configured for the optical fiber and the ferrule to extend substantially axially. The plug housing inner surface further defines a key extending into the cavity. The key defines a height along the plug housing inner surface that extends in a radial direction and decreases in a direction axially away from the rearward opening. The ferrule holder includes an inner surface configured to hold the ferrule and an engaging surface configured to mate with and engage an engaging surface of the plug housing, wherein the engaging surface of the plug housing is at least a portion of the inner surface of the plug housing. The outer surface of the ferrule holder defines a longitudinally extending axial groove for slidably receiving the key so that the ferrule holder is increasingly radially movable relative to the inner surface of the plug housing as the ferrule holder moves relative to the plug housing in a direction axially away from the rearward opening. 
     The cavity of the plug housing includes a forward cavity in communication with the forward portion. The forward cavity may be substantially conical and may define a circular cross-section decreasing radially in a direction axially toward the rearward opening. The ferrule holder engaging surface is configured to mate with and engage the plug housing engaging surface and thus, at least a portion of a forward end of the outer surface of the ferrule holder may also be substantially conical and decrease radially in a direction axially toward a rearward end of the ferrule holder. 
     The ferrule holder may define a radially extending stop portion disposed proximate to the forward end of the outer surface of the ferrule holder, and the plug housing inner surface may define a complimentary stop portion, the groove extending axially across at least a portion of the ferrule holder stop portion. 
     The key may have a cross-section including a rounded tip. The groove may have a generally flared cross-section, which more particularly may be generally v-shaped. It is to be noted that the shapes of the key and the corresponding groove may be altered without losing the functionality of this invention. For example, the key may have a cross-section including a semi-circular, rounded, or rectangular tip, and the groove may have a corresponding matable cross-section. In addition, the key and groove combinations in the disclosed embodiments may be replaced by other connection means furnishing the same function. 
     The plug housing may optionally include at least two keys disposed circumferentially about the plug housing inner surface, and the ferrule holder may then include at least two grooves disposed about the ferrule holder engaging surface, each of the grooves slidably receiving a respective key. The at least two keys may be disposed nonsymmetrically circumferentially about the plug housing inner surface. 
     The plug housing inner surface may optionally include a planar aligning section and the outer surface of the ferrule holder may then include a planar aligning section, the planar aligning sections being engageable with each other. At least two planar aligning sections may be provided on each component. 
     A compression spring element may be disposed within the plug housing for urging the ferrule holder in a direction axially toward the rearward opening. 
     According to another aspect of the invention, the connector subassembly includes a plug housing having an inner surface with at least two orienting elements disposed thereon and a matable ferrule holder having an outer surface with at least two orienting elements disposed thereon. At least one of the orienting elements of the plug housing inner surface may include a second key, and at least another of the orienting elements of the ferrule holder may then include a second groove for slidably receiving the second key. Alternately or in addition, at least another of the orienting elements of the plug housing inner surface may include a planar aligning section, and at least another of the orienting elements of the outer surface of the ferrule holder may then include a planar aligning section engageable with the plug housing inner surface planar aligning section. 
     According to another aspect of the invention, a spring element is disposed within the plug housing and urges the ferrule holder in a direction axially toward the rearward opening. A crimp body is attached to the plug housing so as to compress the spring element. A boot is attached to the plug housing via the crimp body and is disposed about a portion of the optical fiber. In a preferred embodiment, the boot is a flexible boot; however, rigid boots may be used in alternate embodiments. The connector may also include a tube disposed about a section of the optical fiber and secured to the ferrule holder. It is to be noted that the arrangement of the spring element, crimp body, boot, and tube may be altered without losing the merit of this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, advantages, and objectives of this invention and apparent from the detailed description below in combination with the drawings, in which: 
     FIG. 1 is a perspective view of an exemplary embodiment of an optical cable connector according to an embodiment of this invention; 
     FIG. 2 is a sectional view of the optical cable connector of FIG. 1 taken along line II—II in FIG.  1  and also showing one embodiment of a connector subassembly according to an embodiment of this invention; 
     FIG. 3 is a sectional view of the optical cable connector of FIG. 1 taken along line III—III in FIG. 1; 
     FIG. 4 is a perspective view of one embodiment of a ferrule holder according to this invention; 
     FIG. 5 is a perspective view of another embodiment of a ferrule holder according to this invention; 
     FIG. 6 is a sectional view of a portion of a one embodiment of a plug housing according to this invention and taken along line VI—VI in FIG. 2; 
     FIG. 7 is a partial sectional view of one example of an arrangement including a ferrule holder and a plug housing according to an embodiment of this invention; 
     FIG. 8 is a partial sectional view of a portion of the ferrule holder and the plug housing taken along line VIII—VIII in FIG. 7; 
     FIG. 9 is a partial sectional view of another arrangement including a ferrule holder and a plug housing according to an embodiment of this invention; 
     FIG. 10 is a partial sectional view of the ferrule holder and the plug housing 
     FIG. 11 is a partial sectional view of another arrangement including a ferrule holder and a plug housing according to an embodiment of this invention; and 
     FIG. 12 is a partial sectional view of the ferrule holder and the plug housing taken along line XII—XII in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed reference will now be made to the drawings in which examples embodying this invention are shown. The drawings and detailed description provide a full and detailed written description of the invention, and of the manner and process of making and using it, so as to enable one skilled in the pertinent art to make and use it, as well as the best mode of carrying out the invention. However, the examples set forth in the drawings and detailed description are provided by way of explanation of the invention and not meant as a limitation of the invention. This invention thus includes any modifications and variations of the following examples as come within the scope of the appended claims and their equivalents. 
     The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. 
     As embodied in FIGS. 1-3, a connector  10  for connecting an optical fiber cable  12  to a receptacle (not shown), such s another connector or optical device, is provided. As shown in the Figures, connector  10  forms a portion of a cable assembly with an LC connector attached at one end. While the Figures illustrate a portion of a preassembled cable assembly (an LC connector mounted on the end of an optical fiber), the floating connector subassembly, discussed in greater detail below, can be incorporated into previously assembled cable assemblies or utilized during the assembly of new cable assemblies. It should be understood that the following description of the disclosed embodiments is not intended to limit this invention to use only on such preassembled connectors or to LC connectors or to RJ-type connectors. Accordingly, this invention is suitable for use with various types of connectors, such as, for example, SC, DC, Unicam, LC, FC, ST, MTP, MU, MTRJ, and similar connectors. 
     With more particular reference to the Figures, connector  10  is attached to optical fiber cable  12 . Connector  10  includes a connector subassembly  14 , a trigger member  16 , and a flexible boot  18 . Trigger member  16  is optional and need not be used with connector subassembly  14  according to an embodiment of this invention. A detailed description of trigger member  16  is set forth in U.S. patent application Ser. No. 09/737,040, entitled “Trigger Mechanism, Optical Cable Connector Including Same, and Method of Assembling an Optical Cable Connector,” filed Dec. 14, 2000, and is incorporated by reference herein. 
     Connector subassembly  14  includes a plug housing  20 , a crimp body  22 , a compression spring element  24 , and a ferrule assembly  26 . A dust cap  28 , which is shown in U.S. Design patent application Ser. No. 29/127,591, incorporated by reference herein, is removably securable at a forward end of plug housing  20 . An optical fiber  30  that extends out of cable  12  extends into a ferrule  32  of ferrule assembly  26 . A ferrule holder  34  and a tube  36  also form part of ferrule assembly  26 . Tabs  38  on crimp body  22  snap into openings  40  in plug housing  20  to secure the crimp body to the plug housing. Compression spring element  24  is compressed between crimp body  22  and ferrule holder  34  to provide floating performance, if desired. Interfering ridges  42 ,  44 , and  46  matingly engage to securing boot  18  to crimp body  22 , and to connector subassembly  14  in general. Trigger member  16  is attached to boot  18 , if desired, using an interference fit so that the trigger member may interact with a latch  48  extending from plug housing  20 , as set forth in U.S. patent application Ser. No. 09/737,040. 
     As shown in greater detail, for example, in FIGS. 2 and 3, plug housing  20  has an inner surface  50  defining a cavity  52  that extends axially within the plug housing. Inner surface  50  includes a plug housing engaging surface  54  for mating with and engaging an engaging surface  66  of ferrule holder  34 , as will be described below. Plug housing  20  also includes a forward opening  56  in communication with cavity  52  for receiving optical fiber  30  and a rearward opening  58  in communication with the cavity through which the optical fiber and ferrule  32  extend substantially axially. For purposes herein, axially means along axis  60  (see FIGS. 2 and 3) and radially means outward from that axis. 
     Plug housing inner surface  50  includes a key  62  extending into cavity  52 . Key  62  has a height in the radial direction (i.e., relative to axis  60 ) that decreases in a direction axially away from rearward opening  58  (i.e., to the left in FIG.  2 ). Key  62  is discussed in more detail below. Key  62  may have a cross-section including a flared tip (that is, decreasing in width in a radially inward direction) or more particularly a generally rounded tip, as shown best in FIG.  8 . 
     Plug housing engaging surface  54  is located near rearward opening  58 . Plug housing engaging surface  54  may be formed in a substantially conical shape, and may have a circular cross-section that decreases radially in a direction axially toward rearward opening  58  (that is, to the right in FIG.  2 ). Plug housing inner surface  50  may also include a stop portion  64  which may extend radially. 
     Ferrule holder  34  is configured to hold ferrule  32  and includes an engaging surface  66  that is engageable with plug housing engaging surface  54 . Engaging surface  66  may be substantially conical for centering and matingly engaging plug housing engaging surface  54  if surface  54  is also conical. Other centering or mating shapes are also possible. 
     As shown in FIG. 4, ferrule holder  34  also includes an outer surface  68  defining a groove  70  extending axially for slidably receiving key  62 . When assembled, ferrule holder  34  is increasingly radially moveable relative to plug housing inner surface  50  as the ferrule holder moves relative to plug housing  20  in a direction axially away from rearward opening  58 . Thus, when the ferrule assembly  26  is pushed in that direction (to the left as shown in FIG. 2 or to the right as shown in FIGS. 7,  9 , and  11 ), the radial length of the portion of key  62  disposed over a given point in groove  70  becomes smaller. The depth of groove  70  does not change, but the depth of extension into groove  70  of key  62  at a given point in the groove does change during such movement. The further the movement in the direction axially away from rearward opening  58 , the more ferrule assembly  26  is radially moveable relative to plug housing  20 . In other words, the further ferrule assembly  26  is pushed in, the more ferrule assembly  26  can float radially. Once compression spring element  24  is fully compressed, ferrule assembly  26  can no longer be pushed in any further and, thus, maximum float is achieved. If desired, a stop (not shown) may also be employed to limit ferrule assembly sliding. 
     Limitations on the extent of float are set by various factors, such as the amount of compression available by way of compression spring element  24 , the force required to compress the compression spring element, the depth and shape of groove  70 , the depth, shape, and axial length of key  62 , and other connection elements. Thus, depending upon the size of the particular connector elements used (e.g., fiber  30 , ferrule  32 , plug housing  20 , etc.), the sizes and shapes of the various elements described above can be modified from that shown herein to suit the particular application. Also, while this disclosure shows a ferrule used within an LC connector for a given cable size (900 micron), it should be understood that the invention has applications of various other types and sizes of connectors. 
     As shown in FIGS. 7,  9 , and  11 , ferrule holder  34  may include a radially-extending stop portion  72  disposed proximate ferrule holder engaging surface  66 . Stop portion  72  of ferrule holder  34  matingly engages stop portion  64  of housing  20  when urged in that direction by compression spring element  24 . A shoulder  74  may be provided on ferrule holder  34  for seating compression spring element  24 . 
     As shown in FIGS. 4 and 8, groove  70  preferably has a generally flared cross-section (that is, an increasing width in a radially outward direction). More particularly, groove  70  may have a generally v-shaped cross-section. Use of a flared key and groove combination where the groove flares out wider than the key allows ferrule holder  34  to be increasingly radially moveable as it moves relative to housing  20  in a direction axially away from rearward opening  58 , while also keeping frictional forces low and without causing tolerances to be high (for example, as compared to a substantially square groove and key). The rounded key and flared groove combination shown provides contact at only two points on the key and groove. A negligible amount of relative rotation between the ferrule and the plug housing is permitted, but not so much that the tuning or alignment are significantly impacted. 
     However, modifications of the depicted rounded key and v-shaped groove cross-section shapes are possible within the scope of the invention. For example, it would be possible to receive at least some of the benefits of the invention by providing a generally rectangular or otherwise non-flared groove in combination with a rounded or flared key. Alternately, it would be possible to change the cross-section of the key to a non-flared shape for use with a flared groove. Also, neither the key nor the groove could be radially flared, but the thickness of key or the groove (or both) could change in the axial direction. For example, a generally sloped rectangular shape key and corresponding groove would provide improved alignment. Thus, various modifications of the key and groove shapes are possible within the scope of the invention in order to provide radial floating while still achieving alignment of the optical fiber. 
     Another embodiment to the key and groove structure is set forth in FIGS. 9 and 10, which disclose a second embodiment of a plug housing and ferrule holder combination. In FIGS. 9 and 10, like reference numerals are intended to refer to like parts discussed above in connection with the first embodiment. As set forth in FIGS. 9 and 10, a second key  162 ′ is provided in housing  120 . Key  162 ′ is circumfentially spaced from key  162  within housing inner surface  150 . Groove  170 ′ receives key  162 ′ in the same fashion as groove  170  receives groove  162 . Key  162 ′ may have the configurations discussed above with regard to key  62 , and groove  170 ′ may have the configurations discussed above with regard to groove  70 . 
     Although shown in FIG. 10 as identical, key  162 ′ may differ slightly from key  162  if desired, and groove  170 ′ may differ slightly from groove  170  if desired. Also, more than two key and groove combination may be provided if desired. Thus, three or more sets may be provided. The sets may be spaced as shown in FIG. 10 so that only one possible orientation allows keys  162  and  162 ′ to fit into grooves  170  and  170 ′. Alternately, keys and grooves may be spaced symmetrically around the optical fiber so that multiple orientations are possible. If so, the greater the number of keys and grooves, the greater number of possible orientations of the optical fiber in relation to the plug housing. Thus, the optical fiber may be tunable in multiple orientations if multiple keys and grooves are spaced symmetrically. 
     As an additional option, the number of keys and grooves need not be identical. That is, more grooves may be provided than keys. Thus, for example, two or more grooves may be provided for use with a single key thereby effectively providing the floating capability shown in FIG. 8, as the key would be resident in only one of the various grooves. Generally, a greater number of grooves than keys could be used to provide such optional relative orientations. Thus, it should be understood that the number and location of keys and grooves may be modified in various ways within the scope of this invention. 
     Another embodiment of a plug housing and ferrule holder combination is set forth in FIGS. 11 and 12, and a perspective view of the ferrule assembly of that embodiment is also shown in FIG.  5 . Again, like numerals are used to identify like parts. As shown in FIGS. 5,  11 , and  12 , housing engaging surface  254  may include a planar aligning surface  276 , and ferrule holder engaging surface  266  may include a mating planar aligning surface  278 . As oriented in FIG. 11, surfaces  276  and  278  slope upwardly to the left. When ferrule holder  234  is urged completely to the left so that stop portion  272  engages stop portion  264  of housing  220 , aligning surfaces  276  and  278  also engage. Aligning surfaces  276  and  278  are spaced from each other slightly as shown in FIG. 12 when ferrule holder  234  is pushed inward to achieve floating orientation. Surfaces  276  and  278  thus provide an alternate form of tuning and aligning floating orientation. If desired, more than one set of aligning surfaces may be provided circumfentially around optical fiber  230 . 
     The disclosed embodiments provide floating alignment and tuning of an optical fiber with relation to a plug housing, wherein the degree of float increases slightly as the ferrule assembly is pushed backward against the compression spring. Alignment is maintained with only negligible rotational play. The ferrule assembly may be selectively tunable relative to the plug housing. The connector can be plugged into various commonly available types of receptacles or joined to another connector while still providing the above benefits. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in this invention without departing from the scope and spirit of the invention. It is to be noted that the shapes of the key and the corresponding groove may be altered without losing the functionality of this invention. For example, the key may have a cross-section including a semi-circular, rounded, or rectangular tip, and the groove may have a corresponding matable cross-section. In addition, the key and groove combinations in the disclosed embodiments may be replaced by other connection means furnishing the same function. Still further, specific shapes of various elements of the illustrated embodiments may be altered to suit particular connector or receptacle applications. Thus, the invention can be applied to or used with various types of connectors. Accordingly, one skilled on the art would understand that the specific shapes of the ferrule assembly components and plug housing interior can be modified in numerous ways, some of which are specifically set forth above. It is intended that this invention include such modifications and variations as come within the scope of the appended claims and their equivalents.