# Patent

## Title
Protective cover for field-installable connector

## Abstract

A cap for a field-installable optical connector having a front and rear orientation, a housing, an axially-actuated clamping mechanism in the housing, and a ferrule assembly forward of the clamping mechanism and forwardly biased in the housing, the ferrule assembly comprising a holder and a ferrule extending from the holder, the cap comprising a front end defining a cavity for receiving the ferrule and having an outer surface defining at least part of a front-end geometry, a back end defining an opening through which the ferrule is received and a perimeter around the opening, the perimeter configured to contact the holder when the cap is pushed rearward in the housing, the front and back ends being unitary such that any rearward force on the front end is transferred to the back end and through the perimeter to the holder and a retention portion for contacting the housing to secure the cap to the housing.

## Background
FIELD OF THE INVENTION
The present invention relates generally to a protective cap for the ferrule of a fiber optic connector, and, more specifically, to a robust ferrule cap for a field-installable fiber optic connector that remains in situ during fiber termination.
BACKGROUND OF INVENTION
Optical fiber connectors are an essential part of practically all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of an optical fiber connector is to optically couple a fiber with the mating device (e.g., another fiber, an active device or a passive device). This is achieved by holding the end of the fiber such that the core of the fiber is axially aligned with the optical pathway of the mating device.
To facilitate an effective optical coupling, the end face of the ferrule is typically polished. This is usually performed in a controlled setting wherein precision equipment and skilled personnel are available to cleave the fiber, terminate it in a ferrule, and polish the ferrule to exacting tolerances. Frequently, however, connectors must be terminated in the field where such facilities and personnel are not available. Under these conditions, it is desirable to omit the step of the polishing the ferrule by instead terminating the fiber in a connector which has a fiber stub already terminated and polished in a ferrule. The terminating fiber is optically coupled to the fiber stub in the connector, often with the use of a refractive index matched gel to improve optical coupling therebetween.
The terminating fiber is held in intimate contact with the fiber stub by virtue of a clamping mechanism, which applies a radial force to the terminating fiber to secure it to the connector. Advantageously, this clamping mechanism facilitates straightforward field assembly by obviating the need to handle epoxy and for curing ovens during field termination.
Tyco Electronics (Harrisburg, Pa.) offers a family of field-installable connectors that are axially-actuated (see, for example, U.S. Application No. 20070127873, which is hereby incorporated by reference). Each connector comprises a connector housing, a ferrule assembly having a ferrule which projects from the front of the connector housing, a fiber stub which is contained in the ferrule and extends from the back of the ferrule assembly, a clamping mechanism behind the ferrule assembly into which the back end of the fiber stub extends, and a spring in the connector housing to bias the combination of the ferrule assembly and the clamping mechanism forward relative to the connector housing. The clamping mechanism comprises camming means and a plunger to actuate the camming means. These field-installable connectors are available as SC, LC and ST type connectors.
Termination of a fiber in a field-installable connector is typically performed using a tool resembling a pair of pliers. Specifically, the pliers comprise two arms that urge together when the tool is actuated or squeezed. One arm comprises a die, which is configured to receive the ferrule of the connector, while the other arm comprises a die that is configured to receive the plunger. After the fiber is inserted in the back of the connector and into the clamping mechanism, the unactuated connector is disposed in the pliers and they are squeezed causing the two arms to draw together, thereby urging the ferrule assembly back into the plunger. Because the clamping mechanism is sandwiched between these two components, the cam means are actuated by the plunger, and the fiber is secured to the clamping mechanism. Once released, the ferrule assembly returns to its forwardly-biased position within the housing.
Although field termination using the system described above is convenient, Applicants have nevertheless identified a number of shortcomings. For example, typically, there is a protective dust cover or cap on the ferrule that must be removed prior to actuation. Removing the protective cap prior to actuation, however, is undesirable for a number of reasons. First, it presents an opportunity for the ferrule to be damaged or otherwise compromised by the crimping tool. Likewise, during this procedure, debris may be deposited on the end face of the ferrule thereby diminishing its optical performance. Furthermore, removing the cap necessarily requires putting it back, thus, creating additional steps and the chance that the installer may simply forget to do so, thereby leaving the ferrule unprotected after fiber termination.
Therefore, what is needed is an approach for terminating a field-installable connector that does not subject the ferrule to damage and or debris by removing the cap. The present invention fulfills this need among others.
SUMMARY OF THE INVENTION
The present invention provides a robust cap for a field-installable connector that remains in place during termination of the fiber to the connector. Specifically, Applicants have designed a cap that can withstand the forces inherent in actuating a clamping mechanism and, thus, can remain in place during termination. The cap not only remains in place during actuation, but also is configured to translate the compressive load away from the ferrule and direct it instead to the ferrule holder of the ferrule assembly, thereby minimizing stresses on the ferrule itself.
Applicants also recognize that, by leaving the cap in place during fiber termination, standardization in connector termination apparatus can be facilitated. More specifically, there are two factors that essentially determine the configuration of the die set for the crimping tool. The first is the distance between the ferrule tip and the end of the plunger prior to actuation of the connector. This is referred to herein as the “un-actuated connector length.” This length tends to be different for different connector types, thus requiring different die sets to accommodate the difference. The other factor is the geometry of the front of the connector that is received in the die of the first arm. More specifically, different ferrule arrangements and different housing front ends require dies having customized recesses to receive them.
Applicants realized that by leaving the cap in situ during fiber termination, differences between the unactuated connector length and the front-end geometry could be accommodated by the cap. For example, if one connector has a shorter unactuated length than another connector, one cap can be made longer to make up the difference. Likewise, since the cap is disposed at the front end of the connector, it can define a common front-end geometry among different connectors. Accordingly, rather than having different die sets for different connectors, different protective caps can be used to standardize the unactuated length of the connector and its front-end geometry, thus allowing a set of common dies to be used for different connectors.
Accordingly, one aspect of the present invention is a protective ferrule cap that is configured to remain in place during fiber termination in a connector. The connector has a front and rear orientation, a housing, an axially-actuated clamping mechanism in the housing, and a ferrule assembly forward of the clamping mechanism and forwardly biased in the housing, the ferrule assembly comprising a holder and a ferrule extending from the holder. In one embodiment, the cap comprises: (a) a front end defining a cavity for receiving the ferrule and having an outer surface defining at least part of a front-end geometry; (b) a back end defining an opening through which the ferrule is received and a perimeter around the opening, the perimeter configured to contact the holder when the cap is pushed rearward in the housing, the front and back ends being unitary such that any rearward force on the front end is transferred to the back end and through the perimeter to the holder; and (c) a retention portion for contacting the housing to secure the cap to the housing.
Another aspect of the invention is a family of protective caps for different connectors that standardize the connectors' unactuated length and front-end geometry. Specifically, each connector has a front and rear orientation, a housing, an axially-actuated clamping mechanism in the housing, and a ferrule assembly forward of the clamping mechanism and forwardly biased in the housing, the ferrule assembly comprising a holder and a ferrule extending from the holder, each connector having a different unactuated length and a front face. In one embodiment, the family of caps comprises: different caps, each different cap corresponding to one of the different connectors, and comprising at least, a front end defining a cavity for receiving the ferrule and having an outer surface defining at least part of a front-end geometry; a back end defining an opening through which the ferrule is received and a perimeter around the opening, the perimeter configured to contact the holder, the front and back end being unitary such that any rearward axial force on the front end is transferred to the back end and through the perimeter to the holder; and a retention portion for contacting the housing to secure the cap to the housing; wherein the distance from the front end to back end for each different cap is different, but the front-end geometry of each different cap is essentially the same, wherein the different connectors with their corresponding cap have a common unactuated length and a common first end geometry such that they are received in a common crimp tool.
Yet another aspect of the present invention is a method of terminating a connector with a protective cap in place. In one embodiment, the method comprises: (a) providing a connector having a front and rear orientation, a housing, a clamping mechanism in the housing, and a ferrule assembly forward of the clamping mechanism and comprising a holder and a ferrule extending from the holder, the ferrule being covered by a cap; (b) inserting a fiber into the clamping mechanism from the rear of the connector; and (c) while the cap is on the ferrule, actuating the clamping mechanism to secure the fiber to the connector by urging the cap rearward relative to the clamping mechanism.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows an assembly of an SC connector and a preferred embodiment of the cap of the present invention.
FIG. 2 shows a perspective view of the cap of FIG. 1.
FIG. 3 shows an assembly of the cap of FIG. 1 with an SC connector having an outer housing.
FIG. 4 shows an assembly of an LC connector and a preferred embodiment of the cap of the present invention.
FIG. 5 shows a cross section of the assembly of FIG. 1.
FIG. 6 shows a cross section of the assembly of FIG. 4.
FIG. 7 shows an alterative embodiment of the cap of the present invention.



DETAILED DESCRIPTION
Referring to FIGS. 1, 2, and 5, an assembly 100 of a cap 102 on a field-installable optical connector 101 is shown. The connector 101 has a housing 109 having a front and rear orientation and containing an axially-actuated clamping mechanism 502. Also in the housing is a ferrule assembly 501 forward of the clamping mechanism and forwardly biased in the housing 109. The ferrule assembly 501 comprises a holder 504 and a ferrule 503 extending from the holder. Although an SC connector is depicted in these figures, the cap of the present invention can be used with any field-installable connector. For example, as shown in the assembly 400 of FIG. 4, the cap can be used with an LC type connector 401 as shown in FIG. 4. These are two well known connectors the details of which will not be considered herein.
The cap 102 comprises a front end 103 defining a cavity 505 for receiving the ferrule 503 and an outer surface 106 defining at least part of a front-end geometry 130. The cap 102 also comprises a back end 104 defining an opening 110 through which the ferrule 503 is received and a perimeter 111 around the opening. The perimeter 111 is configured to contact the ferrule holder 504. The front and back ends 103, 104 are unitary such that any rearward axial force on the front end is transferred to the back end and through the perimeter to the holder 504. The cap 102 also has a retention portion 120 for contacting the connector housing 109 to secure the cap to the connector. The features of the cap are considered below in detail in addition to a method of terminating the fiber in the connector using the cap and a system for standardizing connectors using the caps.
The front end 103 functions to both cover and protect the ferrule and to define, at least in part, a front-end geometry 130 with its outer surface 106. The front end 103 protects the ferrule by covering it entirely or almost entirely. Preferably, although not necessarily, the cap avoids contact with the ferrule to avoid damaging it. The front end of the cap may define the entire front-end geometry, or it may define part of the front-end geometry. As used herein, the front-end geometry is the shape of the cap and possibly the connector that is received in a crimp tool die described below. Specifically, referring to FIG. 4, cap 402 covers the entire front end of the LC connector 401 and thus defines the entire front-end geometry 430. On the other hand, referring to FIG. 1, the front end 103 of cap 102 cooperates with a front face 112 of the SC connector 102 to define the entire front-end geometry 130.
The front-end geometry 106 is important because the crimping tool used to actuate the connector comprises a die that is configured with a corresponding geometry to receive that the front end of the connector. The cap of the present invention allows the front-end geometry to be standardized. In this regard, it is interesting to note that a portion 406a of the outer surface 406 (see FIG. 4) is configured to mimic the front face 112 of the SC connector 102 (see FIG. 1). Because the front-end geometry of the connector/cap assembly is common among different connector types, a common crimp tool and die can be used to actuate different connectors.
The rear end 104 of the cap functions to seat against a portion of the connector, other than the ferrule, to translate forces applied at the front end to the connector. It is well known that ferrules are sensitive components, which may break or otherwise be compromised if subjected to excessive force. To avoid this, the cap of the present invention avoids channeling compressive loads through the ferrule during actuation. Referring to FIGS. 2 and 5, the perimeter 111 of the rear end 104 is configured to seat on the holder 504, around the ferrule 503. This way, any force applied to cap is translated from the front end 103 and through the rear end 104 into the holder, which then is pushed rearward during the actuation process as described above.
To facilitate this force transfer, the front end 103 and rear end 104 are unitary, meaning they are either integrally molded or assembled into a single component with essentially no relative movement allowed between them. Preferably, the front and rear ends are integrally molded.
Referring to the LC embodiment in FIG. 6, the rear end 404 extends rearward from the front end 403 and is configured to seat against the ferrule holder 602 once the cap 402 is pushed rearward during actuation. This way, forces applied to the front end 403 are transferred to the rear portion 404 and into the ferrule holder 602. Therefore, with both the SC and LC connector cap embodiments, the actuating force is not transferred through the ferrule 503, 603, respectively.
In general, the cap must be capable of withstanding compressive loads and, thus, tends to be noncompliant. As used herein, the term non-compliance refers to a material having a compression modulus greater than 3000 MPa for common cap geometries. Preferably, the material is also capable of being injection molded to facilitate economical manufacturing. Suitable materials include, for example, polyetherimide or polybutylene terephthalate. Preferably, the material is A glass-filled Ultem resin.
The retention portion 120 of the cap functions to retain the cap on the connector to prevent the cap from falling off under its own weight. Generally, a retention force greater than about 1 N is required to secure the cap to the connector. The retention force cannot be so great, however, that the first and second ends of the cap cannot move relative to the housing. That is, during actuation, the front and rear ends must be free to move backward relative to the housing to push the ferrule assembly backward, and then be able to move forward again to allow the ferule assembly to return to its forwardly-biased position.
The present invention may achieve this retention force in different ways. One approach is to have the retention portion 120 slidably contact the housing such that it moves back and forth on the connector during actuation. This may be achieved though a friction fit between the cap and the housing. To this end, the retention portion urges against the housing to provide the desired degree of friction. In this approach, the retention force should not be too high; otherwise, it may exceed the spring force that urges the ferrule assembly forward. In other words, after actuation, the ferrule assembly should return to its forwardly-biased position. If the retention force exceeds the spring force of the ferrule assembly, the ferrule assembly will remain pushed backward. A typical ferrule assembly is biased forward with minimum force of about 5 N and 7.8 N for SFF and standard connectors, respectively. Therefore, suitable retention forces range from greater than about 1 N to below about 7.6 N.
Effecting a friction fit is complicated, however, by the incompressibility of the cap. In other words, the cap of the present invention cannot rely on the elasticity of the cap material to provide the desired friction fit since the cap must be made of an essentially incompressible material. Rather, compliance is provided by introducing slots 107 that define beams 113 capable of flexing as shown in FIG. 2. These compliant beams comprise raised bumps 105, which are configured to contact the inside of the housing. The location of these raised bumps along the beams 113 is one of the factors that governs the retention force. Specifically, as the bumps are moved to the more-compliant, distal ends of the beams, the less normal force they exert against the inside of the housing when the cap is installed on the connector, thus reducing the frictional retention force. Therefore, the location of the bumps provides a convenient mechanism for tuning the retention portion to provide the desired retention force.
The retention portion 120 of the embodiment of FIG. 2 also has the benefit of being internal to the connector 101 (see FIG. 1). That is, the retention force is imparted on the inside of the connector, rather than on the outside, thereby leaving the outside of the connector 101 relatively uncluttered. This enables an outer housing 301 to be installed on the connector 101 without removing the cap 102.
Another way to provide retention force is by exploiting structure elements on the housing of the connector. For example, referring to FIG. 4, the retention portion exploits the latch 408 and shoulder 409 of the LC connector. Specifically, the retention portion 405 comprises a tab 410, which interengages the shoulder 409 on the latch 408 to secure the cap 402 to the connector 201. This allows the cap to slide over the housing but not fall off. Because this approach relies on a mechanical interconnection rather than a friction fit with the housing, compliance of the cap is not as critical as in the SC approach described above. The cap can therefore be configured to fit loosely over the connector (relative to the SC connector) such that it slides essentially frictionless over the connector housing. Consequently, there is no need for slots as mentioned above to introduce compliance, although it may be advantages to introduce them to reduce material requirements. For example, the cap 402 in FIG. 4 has a slot 407 defined in its top (exposing the latch 108).
Yet another way involves employing a living hinge to allow the front and rear ends to move independently of the retention portion. Specifically, rather than having the retention portion slidably engaged with the connector housing, it may be secured to the housing with a frictional or mechanical interengagement, which exceeds the spring force of the ferrule assembly, but has a compliant member that enables the front and rear ends can move relative to the connector housing during actuation. Such an embodiment is shown in FIG. 7. As shown, the cap 702 comprises a retention portion 704 which is secured to the housing 701 and a compliant member 705 in the form of a living hinge that allows the front end 703 and rear end (not shown) of the cap to move rearward during actuation.
Still another approach to provide retention force involves contacting the ferrule rather than the housing. Specifically, referring back to FIG. 2, the raised bumps may protrude inwardly instead of outwardly. Such a configuration causes the bumps to apply pressure against the ferrule, therefore providing a friction fit between the bumps and the ferrule. Because this approach involves contacting the ferrule, which is regarded as relatively delicate, the other approaches mentioned above tend to be more preferred, although this approach may be preferable in situations in which contact with the housing is difficult or the ferrule is particularly robust.
The present invention also provides for a family of protective caps for different connectors that standardize the connectors' unactuated length and front-end geometry. In one embodiment, the family of caps comprises different caps with each different cap corresponding to one of the different connectors. As described above, each cap also comprises at least a front end defining a cavity for receiving the ferrule and having an outer surface defining at least part of a front-end geometry, a back end defining an opening through which the ferrule is received and a perimeter around the opening, the perimeter configured to contact the holder, the front and back end being unitary such that any rearward force on the front end is transferred to the back end and through the perimeter to the holder, and a retention portion for contacting the housing to secure the cap to the housing.
A critical feature of the family of caps is that the distance from the front end to back end for each different cap is different, but the front-end geometry of each different cap is essentially the same. The difference in length of the different caps is calculated to accommodate the difference in the length of the different connectors. For example, referring to FIGS. 5 and 6, cross sections of the SC type connector/cap assembly and the LC type connector/cap assembly are shown, respectively. These drawings are essentially in common scale such that one can see that the LC connector 401 has a shorter un-actuated length l than the un-actuated length l′ of the SC connector 101. Nevertheless, the overall length of each assembly is the same because cap 402 is longer to make up the difference. Furthermore, as mentioned above, each assembly has a common front-end geometry 103, 403. Because the different connectors with their corresponding cap have a common unactuated length and a common first end geometry, they are received in a common crimp tool.
It should be understood that the description above provides illustrative embodiments of the present invention and other embodiments exist.

## Claims

1. A cap for a field-installable optical connector, said connector having a front and rear orientation, a housing, an axially-actuated clamping mechanism in said housing, and a ferrule assembly forward of said clamping mechanism and forwardly biased in said housing, said ferrule assembly comprising a holder and a ferrule extending from said holder, said connector being actuated by a crimp tool, said crimp tool configured to receive a component having a certain geometry at a forward end of said connector, said cap comprising:
a front end defining a cavity for receiving said ferrule and having an outer surface defining at least part of said certain geometry;
a back end defining an opening through which said ferrule is received and a perimeter around said opening, said perimeter configured to contact said holder when said cap is pushed rearward in said housing, said front and back ends being unitary such that any rearward force on said front end is transferred to said back end and through said perimeter to said holder; and
a retention portion for contacting said housing to secure said cap to said housing.

2. The cap of claim 1, wherein said retention portions secures said cap to said housing with a friction fit.

3. The cap of claim 2, wherein said friction fit is sufficient to prevent cap from falling off the connector under its own weight but low enough to allow said ferrule assembly to return to its forwardly-biased position after actuation.

4. The cap of claim 3, wherein cap comprises raised bumps that contact said housing when the cap is installed to generate said friction fit.

5. The cap of claim 4, wherein said cap comprises a material that is essentially non compliant and wherein said cap defines slots for compliance.

6. The cap of claim 5, wherein said slots are elongated and run essentially front to back.

7. The cap of claim 1, wherein said connector comprises a latch and wherein said retention portion comprises a tab to interengage said latch to prevent cap from falling off said connector under its own weight.

8. The cap of claim 1, wherein said front end defines the entire front-end geometry.

9. The cap of claim 1, further comprising said connector.

10. The cap of claim 9, wherein said front end and a front surface of said connector define said certain geometry.

11. The cap of claim 1, further comprising said connector, wherein said ferrule extends from said holder a certain distance, and said cavity has a depth greater than said certain distance.

12. The cap of claim 1, further comprising said crimp tool.

13. A family of caps for different types of field-installable connectors, each connector having a front and rear orientation, a housing, an axially-actuated clamping mechanism in said housing, and a ferrule assembly forward of said clamping mechanism and forwardly biased in said housing, said ferrule assembly comprising a holder and a ferrule extending from said holder, each connector having a different unactuated length and a front face, each connector being configured to be actuated by a crimp tool, said crimp tool configured for receiving a component having a certain geometry at a forward end of each connector, said family of caps comprising:
different caps, each different cap corresponding to one of said different connectors, and comprising at least, a front end defining a cavity for receiving said ferrule and having an outer surface defining at least part of said certain geometry;
each different cap comprising a back end defining an opening through which said ferrule of its corresponding connector is received and a perimeter around said opening, said perimeter configured to contact said holder of said corresponding connector, said front and back end being unitary such that any rearward axial force on said front end is transferred to said back end and through said perimeter to said holder;
each different cap comprising a retention portion for contacting said housing of its corresponding connector to secure it to said housing;
wherein the distance from said front end to back end for each different cap is different but said certain geometry of each different cap is essentially the same to be received by said crimp tool,
wherein said different connectors with their corresponding cap mounted thereon have a common unactuated length such that they are received in said crimp tool.

14. The family of caps of claim 13, wherein the front end of one said different caps defines entirely said front-end geometry while the front end of another of said different caps and a front face of the connector corresponding to said another of said different caps define said front-end geometry.

15. The family of caps of claim 13, further comprising at least two different types of connectors, each of which has a ferrule extending from a holder a certain distance, and wherein said cavity of each cap has a depth greater than said certain distance of its respective connector.

16. The cap of claim 13, further comprising said crimp tool.

17. The cap of claim 13, further comprising different first and second connectors, and wherein said different caps comprise at least a first cap attached to said first connector, and a second cap attached to said second connector.

18. The cap of claim 17, wherein said first connector is an SC connector and said second connector is an LC connector.