This disclosure relates generally to optical connectivity, and more particularly to fiber optic cable assemblies that include over-molded strain boots (i.e., strain-relief members).
Optical fibers are useful in a wide variety of applications, including the telecommunications industry for voice, video, and data transmissions. In a telecommunications system that uses optical fibers, there are typically many locations where fiber optic cables that carry the optical fibers connect to equipment or other fiber optic cables. To conveniently provide these connections, fiber optic connectors are often provided on the ends of fiber optic cables. The process of terminating individual optical fibers from a fiber optic cable is referred to as “connectorization.” Connectorization can be done in a factory, resulting in a “pre-connectorized” or “pre-terminated” fiber optic cable, or the field (e.g., using a “field-installable” fiber optic connector).
Regardless of where installation occurs, a fiber optic connector typically includes a ferrule with one or more bores that receive one or more optical fibers. The ferrule supports and positions the optical fiber(s) with respect to a housing of the fiber optic connector. Thus, when the housing of the fiber optic connector is mated with another connector (e.g., in an adapter), an optical fiber in the ferrule is positioned in a known, fixed location relative to the housing. This allows an optical connection to be established when the optical fiber is aligned with another optical fiber provided in the mating connector.
The housing or body components of a fiber optic connector are often relatively rigid so that the fiber optic connector can withstand a variety of forces during handling and use without affecting the optical connection that may be or has been established. Having rigid components, however, presents design challenges elsewhere. For example, fiber optic cables upon which fiber optic connectors are installed are typically much less rigid than connector bodies. The rapid transition from high stiffness to low stiffness may result in stress concentrations where the cable meets the connector body. Radial loads applied to the cable may then result in the cable bending (e.g., where the stresses are concentrated) beyond a minimum bend radius that must not be exceeded for the cable to function properly.
To address the above-mentioned challenges, a fiber optic connector typically includes a flexible, strain-relieving boot that snaps onto the connector body and extends rearwardly over a portion of the cable. The boot provides a transition in stiffness between the fiber optic connector and the cable. Although many different boot designs have been proposed to properly provide this transition, new solutions are still desired.
Embodiments of fiber optic assemblies are provided in this disclosure. According to one embodiment, a fiber optic assembly comprises a fiber optic cable having at least one optical fiber, a cable jacket surrounding the at least one optical fiber, and aramid fibers between the cable jacket and the at least one optical fiber. The fiber optic cable assembly also includes a fiber optic connector installed on an end of the fiber optic cable. The fiber optic connector includes a connector body that has a back-end portion. The at least one optical fiber extends through the back-end portion of the connector body. The cable jacket includes a jacket end portion defining an end of the cable jacket that is spaced from the back-end portion of the connector body. At least some of the aramid fibers extend beyond the end of the cable jacket and over the back-end portion of the connector body. The fiber optic connector also includes a tube having a first portion positioned over the back-end portion of the connector body and a second portion positioned over the jacket end portion. At least some of the aramid fibers extend between the first portion of the tube and the back-end portion of the connector body. The fiber optic connector also includes a boot molded over the back-end portion of the connector body and the jacket end portion such that the boot is also molded over the tube. The tube is configured to prevent material of the boot from entering space between the end of the cable jacket and the back-end portion of the connector body.
According to one aspect or embodiment, the first portion of the tube is not deformed. There is no crimping of the tube, for example.
According to another aspect or embodiment, there is no heat shrink tube over the jacket end portion of the cable jacket or the tube.
According to another aspect or embodiment, the first portion of the tube is cylindrical. The second portion of the tube may also be cylindrical in some embodiments. And furthermore, the first portion of the tube may be larger than the second portion of the tube. For example, the first portion of the tube have a first outer diameter, and the second portion of the tube may have a second outer diameter that is less than the first outer diameter.
According to another aspect or embodiment, the boot conforms to the tube such that the boot contacts at least 95% of an exterior of the tube.
According to another aspect or embodiment, at least some of the aramid fibers have respective end portions extending beyond the first portion of the tube and at least partially encapsulated by the material of the boot.
According to another aspect or embodiment the material of the boot comprises a polyamide thermoplastic material. The tube may comprise a different material, such as metal.
In some embodiments, the at least one optical fiber consists of a single optical fiber, the fiber optic connector further includes a ferrule that is biased relative to the connector body, and the single optical fiber is secured to ferrule. In other embodiments, the at least one optical fiber comprises first and second optical fibers, wherein: the fiber optic connector further comprises first and second connector sub-assemblies supported by the connector body; each of the first and second connector sub-assemblies includes a connector housing and a ferrule supported within the connector housing; the first optical fiber is secured to the ferrule of the first connector sub-assembly; and the second optical fiber is secured to the ferrule of the second connector sub-assembly.
Methods of forming a fiber optic cable assembly are also provided in this disclosure, wherein the fiber optic cable assembly is formed from a fiber optic cable that includes at least one optical fiber, a cable jacket surrounding the at least one optical fiber, and aramid fibers between the cable jacket and the at least one optical fiber. According to one embodiment, a method comprises: positioning a tube on the cable jacket; removing some of the cable jacket so that a length of the at least one optical fiber and at least some of the aramid fibers extend beyond an end of the cable jacket; positioning a connector body on the length of the at least one optical fiber, wherein the connector body includes a back-end portion through which the at least one optical fiber extends, and wherein the connector body is positioned on the length of the at least one optical fiber so that the back-end portion is spaced from the end of the cable jacket; moving the tube along the cable so that a first portion of the tube is positioned over the back-end portion of the connector body and a second portion of the tube is positioned over a jacket end portion that defines the end of the cable jacket, wherein the at least some of the aramid fibers extend between the first portion of the tube and the back-end portion of the connector body; and molding a boot over the back-end portion of the connector body and the jacket end portion of the cable jacket such that the boot is also molded over the tube. The tube prevents material of the boot from entering space between the end of the cable jacket and the back-end portion of the connector body.
According to a further aspect or embodiment, the method further comprises: placing the back-end portion of the connector body, the tube, and a portion of the fiber optic cable within a cavity of a mold; flowing the material of the boot into the cavity of the mold, wherein the material is kept at a temperature below 240° C. and at a pressure less than 4000 kPa; solidifying the material to form the boot within the mold; and removing the portion of the fiber optic cable, the back-end portion of the connector body, and the boot from the mold.
Additional features and advantages will be set out in the detailed description which follows, and in part will be readily apparent to those skilled in the technical field of optical connectivity. It is to be understood that the foregoing general description, the following detailed description, and the accompanying drawings are merely exemplary and intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments. Features and attributes associated with any of the embodiments shown or described may be applied to other embodiments shown, described, or appreciated based on this disclosure.
Various embodiments will be further clarified by examples in the description below. In general, the description relates to fiber optic cable assemblies having over-molded connector boots. In other words, the description relates to fiber optic cables assembled with fiber optic connectors (thereby forming fiber optic cable assemblies), with at some of the connectors having a boot molded over a region where the cable joins to another component of the connector. The connector may otherwise have a conventional design, like the examples shown in
As shown in
The connector 10 further includes a latch arm 26 extending outwardly and rearwardly from (e.g., in a slanted direction relative to) a portion of the connector body 18. In this regard, the latch arm 26 has a proximal end 28 coupled to the connector body 18 and a distal end 30 spaced from the connector body 18, with the connector body 18 and the latch arm 26 being separated from one another and defining a space therebetween. An intermediate portion of the latch arm 26 includes cantilever latch tabs, which protrude laterally from the latch arm 26. The distal end 30 of the latch arm 26 may be depressed toward the connector body 18 to disengage the connector 10 from another structure, such as an adapter or a dust cap (neither shown in
Normally a crimp ring or band 32, a heat shrink tube 34, and elastomeric boot 36 are provided with the connector 10; they are installed at the time of installing other components of the connector 10 onto a cable (not shown in
Still referring to
Having described the connector 10 shown in
Starting with
As shown in
Still referring to
Although the molding material may be flowable when being introduced into the cavity 116, the tube 80 prevents the molding material from entering into the connector body 46 and jacket 74. For example, this may be due to the close-fitting arrangement between: a) the first portion 84 of the tube 80 and the back-end portion 96 of the connector body 46, and b) the second portion 88 of the tube 80 and the jacket end portion 82. The ends 98 of the aramid fibers 76 that remained exposed (see
Ultimately the molding material fully occupies the cavity 116 and is brought into a non-flowable state, such as by allowing to cool or by actively cooling. As shown in
The same can be said with respect to the crimp ring 32 (
As can be appreciated, although the molding step may be needed to form the cable assembly 132, multiple steps that are traditionally required can be avoided. Manufacturing process flows can be streamlined, and the total amount of equipment needed for forming the cable assembly can be reduced.
Advantageously, the molding may be performed using thermoplastic materials having properties suitable for low pressure molding (LPM). This type of molding may be characterized by relatively low pressures and temperatures. For example, the material of the boot 130 may be kept at a temperature below 240° C. and at a pressure less than 4000 kPa during the molding process. Molding may be performed relatively fast, with the boot 130 being formed in less than 60 seconds, or even in less than 30 seconds in some embodiments.
Examples of thermoplastic materials that may be suitable for low pressure molding include polyamide-based materials, such as TECHNOMELT® PA 6208, 6790, 633, 641, 652, or 673 (Henkel Corp., Dusseldorf, Germany). These materials have viscosities in the range of about 3000 mPa:s to about 7000 mPa:s at 210° C., glass transition temperatures of no greater than −35° C., and service temperatures that range from no less than about −40° C. to no greater than about 140° C. A glass transition temperature is the point at which a material goes from a hard brittle state to a flexible or soft rubbery state as temperature is increased. A common method for determining glass transition temperature uses the energy release on heating in differential scanning calorimetry. In certain embodiments, service temperature of a thermoplastic material may be determined by compliance with one or more industry standards for telecommunication fiber reliability testing, such as (but not limited to): ITU-T G.652, IEC 60793-2, Telcordia GR-20-CORE, and TIA/EIA-492.
Those skilled in the art will appreciate that modifications and variations can be made without departing from the spirit or scope of the invention. For example, although LC connectors are described above and shown in the drawings, the same principles may be applied to other connector designs, such as SC connectors (e.g., according to IEC 61754-4:2013) and MPO connectors (e.g., according to IEC 61754-7:2014). Similarly, the mold 110 should be seen merely as an example, as noted above. Different mold designs may be used to form the boot 130 by applying the principles of this disclosure. This includes embodiments of molds having multiple cavities (e.g., 12 or more) for forming multiple boots simultaneously, thereby increasing manufacturing capacity/overall throughput.
Since modifications, combinations, sub-combinations, and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.
This application is a continuation of International Application No. PCT/CN2018/118529, filed on Nov. 30, 2018, the content of which is relied upon and incorporated herein by reference in its entirety.
Number | Date | Country | |
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Parent | PCT/CN2018/118529 | Nov 2018 | US |
Child | 17325372 | US |