Patent Description:
The mechanical tolerances involved in terminating single mode optical fiber are much tighter than those for multimode optical fiber. Therefore, while it is quite common for multimode optical fiber to be terminated at the point of use, for example, at a user's premises or at an outside junction box, in most product applications, single mode optical fiber is not terminated in the field. When single mode fiber must be terminated in the field, then it can take a skilled technician between about <NUM> to <NUM> minutes to splice fibers together either by using a V-groove clamp or expensive fusion welding equipment.

Single mode fiber is therefore often provided in a range of different lengths, pre-terminated at both ends with a connector that is configured to be connected with an outer housing after the pre-terminated end is deployed to its desired location. The pre-terminated end and housing is then ready to plug into a matching receptacle.

One example of such a connector is an LC connector. The LC connector and adapters were originally developed by Lucent Technologies. The LC connector is a miniaturized version of the fiber optic SC (Subscriber Connector) connector, thus being also known as a small form factor connector. The LC connector looks somewhat similar to the SC connector, but is about half the size with a <NUM> ferrule instead of a <NUM> ferrule. LC connectors are typically composed of a plastic housing with an RJ45 push-pull style clip.

Conventional optical fiber LC connectors comprise a rigid pushable structure to allow for limited movement of the connector parts while being pushed down stretches of a duct. However, some conventional fiber optic cables include more than one fiber. For example, some fiber optic cables include two, four, or more fibers.

Conventional optical fiber LC connectors and LC connector sub-assemblies are not necessarily designed to minimize a cross-sectional footprint and, therefore, it is difficult to push multiple preconnectorized fibers of a multi-fiber cable through a duct simultaneously.

Therefore, it may be desirable to provide a preconnectorized multi-fiber drop cables having a minimal cross-sectional footprint so that the multiple fibers can be easily and smoothly pushed through a duct.

Document <CIT> discloses an optical connector comprising a ferrule basket having four flat portions and curved portions in between.

Document <CIT> discloses an optical fibre alignment apparatus directed to receive optical ferrules having asymmetric key collars comprising three flat key faces.

Document <CIT> discloses an optical fiber connector having a small footprint.

A multi-fiber drop cable according to the invention is disclosed in any one of claims <NUM>-<NUM>.

According to various aspects, an LC connector includes the aforementioned optical fiber connector sub-assembly and an outer housing configured to be coupled with the optical fiber connector sub-assembly. The outer housing is configured to provide LC-style push/pull engagement/disengagement with a mating optical fiber socket.

In accordance with some aspects, a multi-fiber drop cable includes a plurality of fibers terminated with the aforementioned optical fiber connector sub-assembly.

Embodiments of the invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which:.

<FIG> and <FIG> illustrates an exemplary LC connector <NUM> in accordance with various aspects of the disclosure. The LC connector <NUM> includes a connector sub-assembly <NUM> and an outer housing <NUM>. The outer housing <NUM> is an LC housing configured to be received by a conventional matching LC receptacle. That is, the outer housing <NUM> is configured to provide LC-style push/pull engagement/disengagement with a mating optical fiber socket (not shown). The connector <NUM> is configured to be coupled with a fiber optic cable <NUM> (FIGS. <NUM> and <NUM>). For example, an end of the cable <NUM> is configured to be terminated with the connector sub-assembly <NUM>.

The connector sub-assembly <NUM> includes an elongate cylindrical optical fiber ferrule <NUM> having at one end a termination end <NUM>. In this example, the ferrule <NUM> is of a ceramic material, although other materials may be used, as is known in the art. The ferrule <NUM> has an axis <NUM> that extends centrally through the LC connector <NUM>. The person skilled in the art will recognize this as a conventional arrangement, in which the fiber is terminated at the ferrule termination end <NUM>, which is polished to minimize insertion loss when the connector is joined to a matching optical fiber socket (not shown).

The connector sub-assembly <NUM> also includes a ferrule basket <NUM>, a generally cylindrical retaining member <NUM>, and a boot <NUM>. The ferrule basket <NUM> has a base portion <NUM> in which the ferrule <NUM> is seated and a cylindrical stem portion <NUM> that extends from the base portion <NUM> in an axial direction away from the ferrule <NUM>. The base portion <NUM> includes an external annular shoulder <NUM>. The base portion <NUM> is configured to receive the ferrule <NUM> in a press-fit relationship with a rear face of the ferrule abutting a forward face of an internal annular surface of the ferrule basket <NUM>, as would be understood by persons skilled in the art. The boot <NUM> is configured to provide strain relief for the cable <NUM> and a weather resistant seal at the rearward end of the connector <NUM>.

The retaining member <NUM> includes a forward end portion <NUM> and a rearward end portion <NUM>. The forward end portion <NUM> includes an external shoulder portion <NUM> defining a rearward facing surface. The forward end portion <NUM> includes an axial bore configured to receive at least a portion of the cylindrical stem portion <NUM> of the ferrule basket <NUM>. The rearward end portion <NUM> includes an axial bore configured to receive the fiber optic cable <NUM>, including a sheath <NUM> that protects the fiber. An outer surface of the rearward end portion <NUM> includes one or more barbs <NUM> for engagement with an internal surface of the boot <NUM>.

The connector sub-assembly <NUM> further includes a coil spring <NUM> disposed between the external annular shoulder <NUM> of the base portion <NUM> and a forward end of the retaining member <NUM>. The coil spring <NUM> biases the ferrule basket <NUM> forwardly relative to the retaining member <NUM>. The coil spring <NUM> is compressible in the axial direction by axial sliding movement of the stem portion <NUM> relative to the retaining member <NUM>. The axial range of travel of the ferrule basket <NUM> is limited by the compressed coil spring <NUM>. The connector <NUM> may further include a removable protective cap <NUM> having a bore configured to receive the ferrule <NUM>.

The outer housing <NUM> is configured in a substantially square shape with a release lever <NUM> projecting outward from a top wall <NUM> of the outer housing <NUM>, as is typical with conventional LC connectors. The outer housing <NUM> includes a through bore <NUM> configured to receive the connector sub-assembly <NUM> such that the ferrule <NUM> can be exposed at a front end <NUM> of the outer housing <NUM>. The inner surface of the top wall <NUM> of the outer housing <NUM> includes an alignment rib <NUM>. The alignment rib <NUM> is configured to be received by an axial alignment channel <NUM> in the top wall of the retaining member <NUM> and extending the length of the retaining member <NUM>.

The outer housing <NUM> further includes side walls <NUM> having resilient fingers <NUM> extending inward into the through bore <NUM>. Each of the resilient fingers <NUM> is cantilevered at its rear end <NUM>, and the free forward end <NUM> of each finger <NUM> is configured to engage the retaining member <NUM> at a position rearward of the rearward facing surface of the external shoulder portion <NUM> of the forward end portion <NUM> of the retaining member <NUM> when the retaining member <NUM> is inserted into the outer housing <NUM> to couple the housing <NUM> with the sub-assembly <NUM>.

Referring now to <FIG>, a cross-sectional shape of the base portion <NUM> of the ferrule basket <NUM> of the LC connector sub-assembly <NUM> is illustrated. As shown, an outer periphery of the base portion <NUM> includes two flat portions <NUM> arranged at a right angle relative to one another. Ends <NUM> of the two flat portions <NUM> that are nearest to one another along the periphery of the base portion are connected by a curved bottom portion <NUM>. Two side curved portions <NUM> extend from the ends <NUM> of the two flat portions <NUM> that are furthest from one another along the periphery of the base portion <NUM>. A top curved portion <NUM> connects the two side curved portions <NUM>. A portion <NUM> of the through bore of the outer housing <NUM> of the LC connector <NUM> includes has a shape that is complementary to the aforementioned shape of the outer periphery of the base portion <NUM> of the ferrule basket <NUM> in order to provide a keyed interface between the ferrule basket <NUM> and the outer housing <NUM>. The keyed interface ensures relative alignment between the ferrule basket <NUM> and the outer housing <NUM> and prevents relative rotation between the ferrule basket <NUM> and the outer housing <NUM>.

As shown in <FIG>, when a multi-fiber cable having two fibers terminated with LC connector sub-assemblies <NUM> are positioned with the bottom curved portions <NUM> of each of the two base portions <NUM> adjacent to and facing one another, the outer footprint of the cross-sectional profile of the two side-by-side base portions <NUM> falls within a circle having a diameter that is only slightly larger than a combined dimension of the diameters of the two ferrules <NUM>.

Similarly, as shown in <FIG>, when a multi-fiber cable having four fibers terminated with LC connector sub-assemblies <NUM> are positioned with the flat portions <NUM> of adjacent base portions <NUM> contacting one another and with the bottom curved portions <NUM> of each of the four base portions <NUM> facing a centerpoint between the four base portions <NUM>, an opening is formed between the four bottom curved portions <NUM>. However, the outer footprint of the cross-sectional profile of the four circumferentially-arranged base portions <NUM> falls within a circle having a diameter that is only about <NUM>% larger than a combined dimension of the diameters of the two ferrules <NUM>.

Referring now to <FIG>, termination of a multi-fiber drop cable, for example, an LC quattro drop cable is described. First, four PTFE tubes <NUM> are potted, as shown in <FIG>. Next, as shown in <FIG>, a protective sleeve <NUM> is slid over the tubes <NUM> and the multi-fiber cable, four fibers from the multi-fiber cable are fed through the tubes <NUM>, and a crimp sleeve <NUM> is slid over the potted tubes <NUM>. As shown in <FIG>, the crimp sleeve <NUM> is crimped into two places - onto the multi-fiber cable and onto the potted tubes. Each of the fibers is then terminated with an LC connector sub-assembly <NUM> and the four sub-assemblies <NUM> are arranged in the configuration shown in <FIG>, as discussed above. As shown in <FIG>, a ferrule cap <NUM> having four channels <NUM> sized and arranged to receive the four LC connector sub-assemblies <NUM> in the nestled configuration of <FIG> is attached to the sub-assemblies <NUM>. Then, as shown in <FIG>, the protective sleeve <NUM> is slid in a forward direction over the four LC connector sub-assemblies <NUM> and onto the ferrule cap <NUM>. The nestled LC connector sub-assemblies <NUM> can then be deployed through a duct to a desired location while be protected by the sleeve <NUM> and occupying a minimal cross-sectional footprint. If the multi-fiber cable includes two fibers terminated with two LC connector sub-assemblies <NUM>, a ferrule cap <NUM>' having two channels <NUM> sized and arranged to receive the two LC connector sub-assemblies <NUM> in the side-by-side configuration of <FIG> is attached to the sub-assemblies <NUM>.

Referring now to <FIG>, assembly of the LC connector <NUM> is described. After the LC connector sub-assemblies <NUM> (e.g., two or four) are deployed to a desired location, the protective sleeve <NUM> and the ferrule cap <NUM>, <NUM>' are removed, as shown in <FIG>. The fiber optic pigtails terminated with LC connector sub-assemblies <NUM> are then separated, and boots <NUM> are slid over each of the sub-assemblies <NUM> such that the boot <NUM> is spaced rearward from a rearward end of the stem portion <NUM> of the ferrule basket <NUM>, as shown in <FIG>. As shown in <FIG>, each fiber is slid through the axial alignment channel <NUM> in the top wall of the retaining member <NUM> to a position along a center axis of the retaining member <NUM>. The boot <NUM> is then slid in a forward direction over a rearward end of the retaining member <NUM> such that the one or more barbs <NUM> engage the internal surface of the boot <NUM>, as shown in <FIG>. As shown in <FIG>, the outer housing <NUM> is pushed onto the LC connector sub-assembly <NUM> until the fingers <NUM> engage the retaining member <NUM> at a position rearward of the rearward facing surface of the external shoulder portion <NUM> of the forward end portion <NUM> of the retaining member <NUM>. The dust cap <NUM> may be inserted into a forward opening of the outer housing <NUM> to protect the ferrule <NUM>, as shown in <FIG>.

It should be appreciated that although the outer housing <NUM> is illustrated as transparent to facilitate an understanding of the connector, the outer housing is not typically transparent.

Additional embodiments include any one of the embodiments described above, where one or more of its components, functionalities or structures is interchanged with, replaced by or augmented by one or more of the components, functionalities, or structures of a different embodiment described above.

It should be understood that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the scope of the present disclosure and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

Claim 1:
A multi-fiber drop cable, wherein the multi-fiber drop cable includes a plurality of optical fibers terminated with an optical fiber connector sub-assembly (<NUM>) for an optical fiber connector (<NUM>), said optical fiber connector sub-assembly (<NUM>) comprising:
a ferrule (<NUM>) configured to hold an optical fiber therein along an axis of the connector (<NUM>);
a ferrule basket (<NUM>) configured to hold the ferrule (<NUM>) at a front portion of the connector (<NUM>);
a retaining member (<NUM>) having a front end portion configured to hold the ferrule basket (<NUM>) and a rear end portion configured to receive a fiber optic cable (<NUM>); and
a boot (<NUM>) configured to be coupled with the retaining member (<NUM>),
wherein the ferrule basket (<NUM>) includes a base portion (<NUM>) and a stem portion (<NUM>) that extend rearward from the base portion (<NUM>),
characterised in that
an outer periphery of the base portion (<NUM>) includes two flat portions (<NUM>) arranged at a right angle relative to one another, first ends of the two flat portions (<NUM>) that are nearest to one another along the outer periphery of the base portion (<NUM>) are connected to one another by a curved bottom portion (<NUM>), and
two side curved portions (<NUM>) extend from second ends of the two flat portions (<NUM>) that are furthest from one another along the outer periphery of the base portion (<NUM>), and top curved portion (<NUM>) connects the two side curved portions (<NUM>),
the multi-fiber cable includes four optical fibers terminated with the connector sub-assembly (<NUM>) and when
the four base portions (<NUM>) are circumferentially arranged with the flat portions (<NUM>) of adj acent base portions (<NUM>) contacting one another and with the bottom curved portions (<NUM>) of the four base portions (<NUM>) facing a centerpoint between the four base portions (<NUM>), an opening is formed between the four bottom curved portions (<NUM>), and
an outer footprint of a cross-sectional profile of the four circumferentially-arranged base portions (<NUM>) falls within a circle having a diameter that is about <NUM>% larger than a combined dimension of the diameters of two ferrules (<NUM>).