Patent Publication Number: US-2022221661-A1

Title: Strain relief boot

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is being filed on Jun. 10, 2020 as a PCT International Patent Application and claims the benefit of U.S. Patent Application Ser. No. 62/859,406, filed on Jun. 10, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to terminating the ends of fiber optic cables in fiber optic connectors and modules. More particularly, the present disclosure relates to strain relief boots. 
     BACKGROUND OF THE INVENTION 
     Fiber optic communication systems are becoming prevalent as service providers deliver high bandwidth communication capabilities (e.g., data and voice) to customers. Fiber optic communication systems employ a network of fiber optic cables to transmit large volumes of data and voice signals over relatively long distances. 
     Optical fiber connectors are an important part of most fiber optic communication systems. Fiber optic connectors allow two optical fibers to be optically connected quickly without requiring a splice. Fiber optic connectors can be used to optically interconnect two lengths of optical fiber. Fiber optic connectors can also be used to interconnect lengths of optical fiber to passive and active equipment. 
     A typical fiber optic connector includes a ferrule assembly supported at a distal end of a connector housing. The ferrule functions to support an end portion of at least one optical fiber (in the case of a multi-fiber ferrule, the ends of multiple fibers are supported). When two fiber optic connectors are interconnected, the distal end faces of the ferrules abut one another thereby aligning the end faces of the optical fibers directly opposed to one another. Optical signals can be transmitted from optical fiber to optical fiber through the aligned end faces of the optical fibers. 
     Fiber optic connectors often include strain relief boots mounted at proximal ends of the connector housings. Strain relief boots are designed to prevent the optical fibers within the fiber optic cables secured to the fiber optic connectors from bending to radii less than the minimum bend radii of the optical fibers when side loads are applied to the fiber optic cables. Example strain relief boot configurations are disclosed in U.S. Pat. Nos. 8,702,323; 8,342,755; 7,942,591; 7,677,812; 7,147,385; 5,915,056; 5,390,272; and 5,261,019. Some strain relief boots are designed to prevent the optical fiber cable from bending sharper than its minimum bend radius when a large side load is applied to the cable. Other strain relief boots are designed to prevent the optical fiber cables from bending sharper than its minimum bend radius when small side loads are applied to the boot. There is a need for strain relief boots that bend under small side loads to protect the optical fiber and also resist bending under large side loads to protect the optical fiber. 
     A number of factors are important with respect to the design of a fiber optic connector. One such factor relates to connector size and the ability to provide enhanced connector/circuit densities. Another factor relates to the ability to provide high signal quality connections with minimal signal degradation. 
     SUMMARY 
     The present disclosure provides a strain relief boots and fiber optic connectors and modules that include strain relief boots. The strain relief boots of the present disclosure are flexible enough to bend when small side loads are applied thereto and stiff enough to resist bending when large side loads are applied thereto. The strain relief boots of the present disclosure are capable of protecting a cable within the boot from bending sharper than its minimum bend radius when exposed to both low side load forces and high side load forces. In one embodiment, the strain relief boots of the present disclosure are constructed of multiple different materials each having different stiffness properties. In one embodiment, the strain relief boots are manufactured from a multiple-shot/multiple-material injection molding process. A variety of additional aspects will be set forth in the description that follows. The aspects relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a boot according to an embodiment of the present disclosure; 
         FIG. 2  is a top view of the boot of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the boot of  FIG. 1 ; 
         FIG. 4  is an isometric view of an alternative embodiment of a boot according to the present disclosure; 
         FIG. 5  is a top view of the boot of  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of the boot of  FIG. 4 ; 
         FIG. 7  is a cross-sectional view of a fiber optic connector according to the principles of the present disclosure; and 
         FIG. 8  is an isometric view of a telecommunication module according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Strain relief boots function to prevent the optical fiber cable from bending sharper than a predetermined minimum bend radius for the particular optical fiber cable. The minimum bend radii for optical fiber cables varies depending on the particular construction of the optical fiber cable and its application. For one commonly used optical fiber, the minimum bend radius is 30 mm at 100 turns. For another commonly used optical fiber, the minimum bend radius is 5 mm at 1 turn. The minimum bend radius of an optical cable is a known predetermined number that is determined via testing done by the optical cable manufacturer. 
     Typically, strain relief boots are optimized to protect the optical fiber either when large side loads are applied to the cable or when small side loads are applied to the cable, not both. Strain relief boots that are reactive to low side loads tend to collapse and fold over on themselves when large side loads are applied. Conversely, strain relief boots that are stiff enough to resist bending under large side loads tend not to react (bend) when small side loads are applied. The space constraints for strain relief boots makes it particularly challenging to construct strain relief boots that are both flexible enough to bend to protect the cable under small side loads and also stiff enough to resist bending to protect the cable under large side loads. Given the application and the density of optical fiber connectors in a field application, there are practical limitations to the length of the strain relief boots as well as their maximum diameter. 
     The present disclosure provides strain relief boots that bend under small side loads to protect the optical fiber while at the same time resist bending under large side loads. The strain relief boot of the present disclosure protects the optical fiber in all conditions. In one embodiment, the boot of the present disclosure bends under as little as 0.2 lbs-force side load and resists bending beyond a predetermined bend radius under a side load of as great as 7.5 lbs-force. 
     The strain relief boots of the present disclosure have application anywhere in an optical system where the bending of the fiber sharper than its minimum bend radius is possible. One common application of the boot of the present disclosure is at a proximal end of a telecommunication connector. Another common application of the boot is at the exit/entry of a telecommunication module. 
     Referring to the FIGS., the present disclosure is described in further detail. Referring to  FIGS. 1-3 , a strain relief boot  10  of an SC type connector according to the principles of the present disclosure is shown.  FIG. 7  depicts the strain relief boot  10  as part of an SC type connector  12 . 
     Referring to  FIGS. 1-3 and 7 , an embodiment of the fiber optic connector  12  according to the principles of the present disclosure is described. In the depicted embodiment, the fiber optic connector  12  includes a connector housing  14 . The connector housing  14  includes a first end  16  and a second end  18 . The connector housing  14  includes a connector housing axial passage  20  that extends from the first end  16  of the connector housing  14  to the second end  18  of the connector housing  14 . It should be appreciated that other housing configurations are also possible. 
     In the depicted embodiment, the fiber optic connector  12  includes a ferrule  22 . The ferrule  22  has a first end  24  and a second end  26 . The second end  26  of the ferrule  22  is secured to the first end  16  of the connector housing  14 . The ferrule  22  includes a ferrule axial passage  28  that extends from the first end  24  of the ferrule  22  to the second end  26  of the ferrule  22 . In the depicted embodiment, the ferrule axial passage  28  is coaxially arranged with the connector housing axial passage  20 . In the depicted embodiment, the ferrule  22  is spring loaded so that it can move axially. In other embodiments, the ferrule  22  could be fixed axially. It should be appreciated that many other ferrule configurations are also possible. 
     In the depicted embodiment, the fiber optic connector  12  includes a boot  30 . The boot  30  is similar to the boot  10  and hence are described herein simultaneously with like reference numerals. The boot  30  includes a first end  32  and a second end  34 . The boot  30  has a boot axial passage  36  that extends from the first end  32  of the boot  30  to the second end  34  of the boot  30 . In the depicted embodiment, the boot axial passage  36  is coaxially arranged with the connector housing axial passage  20 . In the depicted embodiment, the boot axial passage  36  is sufficiently large to slidably receive a fiber optic cable. 
     In the depicted embodiment, the boot  30  includes a boot first end portion  38  adjacent the first end  32  of the boot  30 . The boot first end portion  38  is connected to the second end  18  of the connector housing  14 . In the depicted embodiment, the boot first end portion  38  is stretched and placed over a portion of the second end  18  of the connector housing  14 . The boot first end portion  38  is adapted to retain the connector housing  14  once it has been stretched and placed over the connector housing  14 . In the depicted example, the first end portion  38  includes retention features which are snap-on features. The snap-on features attach over a portion of the connector housing  14  in order for the boot  30  to retain the connector housing  14  and the connector  12 . The first end portion  38  can also include other retention features (e.g., threads). In the depicted embodiment, the boot  30  includes a boot second end portion  40  adjacent the second end  34  of the boot  30 . The boot  30  also includes a boot middle portion  42 . 
     In the depicted embodiment, the boot middle portion  42  is constructed of a first material and the boot second end portion  40  is constructed of a second material. In the depicted embodiment, the second material is different than the first material. In the depicted embodiment, the first end portion  38  is constructed from the first material. In the depicted embodiment, the boot middle portion  42  is constructed unitarily with the first end portion  38 . In the depicted embodiment, the second material is softer than the first material. In the depicted embodiment, the first material is a polybutylene terephthalate material and the second material is a thermoplastic vulcanizate material. In the depicted embodiment, the second material is Santoprene. It should be appreciated that many alternative embodiments are possible. For example, the first material could be softer than the second material. It should also be appreciated that any or all of the first end portion  38 , boot middle portion  42 , and the boot second end portion  40  could be constructed of a composite blend of materials. Each of the first or the second material could be a composite of materials. In addition, each of the first end portion  38 , boot middle portion  42  and the boot second end portion  40  could be constructed in subparts having different materials in each of the subparts. It should be appreciated that many alternatives are possible. 
     In the depicted embodiment, the boot middle portion  42  utilizes geometry to provide progressive flex. In particular, the boot middle portion  42  includes a plurality of co-axial rings  44  separated by axial gaps  46 . The rings  44  are interconnected by links  48  that extend across the axial gaps  46 . The overall profile of the boot middle portion  42  tapers towards the first end  32  to the second end  34  of the boot. In the depicted embodiment, the boot first end portion  38 , and second end portion  40  include a continuous smooth exterior surface profile. 
     In the depicted embodiment, the boot second end portion  40  is molded to the boot middle portion  42 . In the depicted embodiment, the boot second end portion  40  is molded over a proximal end portion of the boot middle portion  42 . In the depicted embodiment, the second material used to construct the second end portion  40  is molded to at least partially fill an axial gap  46  of the boot middle portion  42 . The second material is anchored to the first material. 
     In the depicted embodiment, the boot  30  is between 37 to 47 millimeters long. In the depicted embodiment, the boot  30  is between 40 and 44 millimeters long. In the depicted embodiment, the second end portion  40  is between 10 to 18 millimeters long. In the depicted embodiment, the second end portion  40  is between 12 and 16 millimeter long. In the depicted embodiment, the axial passage  36  is between 2 to 2.5 millimeters in diameter. The outer diameter of the second end portion  40  is between 3 to 4 millimeters in diameter. In the depicted embodiment, the portion of the second end portion  40  that is molded over a portion of the middle portion  42  is between 1 to 4 millimeters long. 
     Referring to  FIGS. 4-6 , an alternative embodiment of a boot according to the present disclosure is described. The boot  50  has similar features of the boot  10 . The boot  50  includes a first end  52  and a second end  54 . The boot  50  has a boot axial passage  56  that extends from the first end  52  of the boot to the second end  54  of the boot. The boot  50  includes a boot first end portion  58  adjacent the first end  52  of the boot configured to mount to a telecommunication housing. The boot  50  includes a second end portion  60  adjacent the second end  54  of the boot  50 . The boot  50  includes a boot middle portion  62 . The boot middle portion  62  is constructed of a first material and the boot second end portion  60  is constructed of a second material. In the depicted embodiment, the first end portion  58  is also constructed of the first material. In the depicted embodiment, the second material is different than the first material. In the depicted embodiment, the first material is a reinforced thermoplastic material and the second material is a softer more flexible material. As discussed above, many alternative materials could be used in many different combinations. 
     In the depicted embodiment, the boot middle portion  62  includes a plurality of co-axial rings  64  separated by axial gaps  66 . The rings  64  are interconnected by links  68  that extend across the axial gaps  66 . In the depicted embodiment, the boot second end portion  60  is molded over a portion of the boot middle portion  62 . In the depicted embodiment, the second material molded at least partially fills an axial gap  66  of the boot middle portion  62 . This construction results in an interlocking configuration that further anchors the boot second end portion  60  to the boot middle portion  62 . In the depicted embodiment, the boot first end portion  58 , and second end portion  60  include a continuous smooth exterior surface profile. 
     In the depicted embodiment, the boot  50  is between 37 to 47 millimeters long. In the depicted embodiment, the boot  50  is between 40 and 44 millimeters long. In the depicted embodiment, the second end portion  60  is between 10 to 18 millimeters long. In the depicted embodiment, the second end portion  60  is between 12 and 16 millimeters long. In the depicted embodiment, the axial passage  56  is between 2 to 3 millimeters in diameter. The outer diameter of the second end portion  60  is between 3 to 4 millimeters in diameter. In the depicted embodiment, the portion of the second end portion  60  that is molded over a portion of the middle portion  62  is between 1 to 4 millimeters long. It should be appreciated that many other configurations are possible. In the depicted embodiment, the boot of the present disclosure has a broad range of capabilities yet takes up essentially no more space than boots that lack such capabilities. 
     In the depicted embodiment, the telecommunication housing that the first end  52  of the boot  50  is configured to be mounted to is the housing of a fiber optic connector. In the depicted embodiment, the fiber optic connector is an LC type connector. LC type connectors are described and shown in U.S. Pat. No. 8,752,022, which is incorporated by reference herein in its entirety. Referring to  FIG. 8 , the boot is shown mounted to a fiber optic module  70 . It should be appreciated that the boot of the present disclosure can be mounted to any type of telecommunication housing. As discussed above, the boot of the present disclosure has applicability to any area where an optical fiber enters or exits a housing and is susceptible to being potentially bent beyond its minimum bend radius. The boot in the depicted embodiment is shown connected to a particular type of module  74  but it should be appreciated that the boot could alternatively be connected to any other type of module (e.g., splitter, furcation, etc.). The boot of the present disclosure has broad applicability in telecommunication fiber optic systems. 
     Referring to  FIG. 8 , an alternative embodiment of the boot  72  is shown. In the depicted embodiment, the boot  72  is configured to protect multiple cables flowing into a module. The module is constructed of a first material  74  and a second material  76 . It should be appreciated that third and fourth materials and many more can also be incorporated into the boots. The multiple materials enable the boots of the present disclosure to have wider range of flexibility/stiffness than boots constructed of a single material. Flexibility in single material boots is modulated by geometry (radius, tappers, reliefs, axial gaps, etc.). However, geometry is only one of a number of ways the boots of the present disclosure utilize to modulate flexibility in the boot. The present disclosure allows for more compact, responsive and protective boot constructions. 
     It should be appreciated that although the difference in material is described in terms of difference in flexibility/stiffness, many other material differences are also possible. The ability to mix and match material to build a boot results in boots with improved features. In addition, it should be appreciated that the material having different properties can be arranged in any manner desired. For example, the softer material can be located at the distal end of the boot rather than the proximal end of the boot if such is desirable for a particular outcome. The boot could include a flex zone where both materials are present. Many configurations are possible. 
     The above specification, examples and data provide a complete description of the manufacture and use of the disclosure. Since many embodiments of the disclosure can be made without departing from the spirit and scope of the inventive aspects, the inventive aspects resides in the claims hereinafter appended.