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 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 duct. However, conventional optical fiber LC connectors permit rotation between the fiber and the connector when the connector is being pushed through the duct. Such rotation could cause damage to the fiber, which may result in signal degradation or signal loss.

Therefore, it may be desirable to provide an optical fiber connector that prevents rotation of the fiber relative to the connector while being pushed through a duct or conduct. <CIT> discloses a connector having a housing, a ferrule, a ferrule holder, a compression coil spring mounted inside the housing and biasing the ferrule, and a rotation-restricting slide mechanism, disposed toward the base end of the housing, restricting the ferrule from rotating relative to the housing. <CIT> discloses a coupling system for interconnecting two optical connectors. Each optical connector comprises a first part and a second part, which are joined by a ferrule holder, and a third part that houses both connectors within designated receiving spaces. Both the first and second parts of each optical connector include a connecting member attached to the ferrule holder, as well as a retaining tube. The ferrule holder is designed to rotate relative to the retaining tube, allowing a rotational movement limited to an angle of <NUM>°.

An optical fiber connector sub-assembly according to the invention is disclosed in any one of appended claims <NUM> to <NUM>. A connector according to the invention is disclosed in any one of appended claims <NUM> to <NUM>.

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

<FIG> illustrate an exemplary fiber optic connector <NUM>, for example, an LC connector, in accordance with various aspects of the disclosure. The fiber optic connector <NUM> includes a connector sub-assembly <NUM> and an outer housing <NUM>. In some aspects, the outer housing <NUM> may be an LC housing configured to be received by a conventional matching LC receptacle. That is, the outer housing <NUM> may be configured to provide LC-style push/pull engagement/disengagement with a mating optical fiber socket (not shown). The fiber optic connector <NUM> is configured to be coupled with a fiber optic cable <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 fiber optic connector <NUM>, and along its axis <NUM> has a hollow core <NUM> that holds and aligns an optical fiber <NUM> of the cable <NUM>, which will most often be a single mode glass fiber. The person skilled in the art will recognize this as a conventional arrangement, in which the fiber <NUM> 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 holder <NUM>, a generally cylindrical retaining tube <NUM>, and a connecting tube <NUM>. The ferrule holder <NUM> has a base portion <NUM> at its forward end in which the ferrule <NUM> is seated, a collar <NUM>, and a cylindrical stem portion <NUM> which extends from the collar <NUM> in an axial direction away from the ferrule <NUM>. The collar <NUM> includes an external annular shoulder <NUM> and an internal 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 <NUM> abutting a forward face 127a of the internal annular shoulder <NUM>, as would be understood by persons skilled in the art.

The retaining tube <NUM> includes a forward end portion <NUM> and a rearward end portion <NUM>. The forward end portion <NUM> and the rearward end portion <NUM> are separated at an interior of the retaining tube <NUM> by an inner annular shoulder <NUM>. The forward end portion <NUM> includes an external shoulder portion <NUM> defining a rearward facing surface. The forward end portion <NUM> includes a bore <NUM> configured to slidingly receive at least a portion of the cylindrical stem portion <NUM> of the ferrule holder <NUM>. The rearward end portion <NUM> includes a bore <NUM> configured to slidingly receive the connecting tube <NUM>, which extends through a closely fitting bore <NUM> defined by the inner annular shoulder <NUM>.

The connecting tube <NUM> includes an elongated cylindrical portion <NUM> having a head portion <NUM> at its rear end. The head portion <NUM> has a larger cross-section in a plane perpendicular to the ferrule axis than does the elongated cylindrical portion <NUM>. The head portion <NUM> may be generally cylindrical, but includes a flattened region <NUM> that forms, for example, a chord, such that the head portion <NUM> is formed in a D-shape as viewed in the axial direction.

A forward end portion of the elongated cylindrical portion <NUM> is configured to be received in the cylindrical stem portion <NUM>, for example, in a press fit relationship, more particularly, a light press fit connection. The press fit relationship should be sufficient such that the connecting tube <NUM> is rotatable with the cylindrical stem portion <NUM> about ferrule axis <NUM> and not rotatable relative to the cylindrical stem portion <NUM> when the connector subassembly <NUM> is being pushed through a duct or conduct. The forward end face <NUM> at the forward end portion of the elongated cylindrical portion <NUM> abuts a rearward face 127b of the internal annular shoulder <NUM> of the collar <NUM>. A forward face <NUM> of the head portion <NUM> abuts a rearward face 136a of the inner annular shoulder <NUM> of the retaining tube <NUM>.

The rearward end portion <NUM> of the retaining tube <NUM> includes a small inner diameter portion <NUM> adjacent the inner annular shoulder <NUM> and a large inner diameter portion <NUM> extending axially from the small inner diameter portion <NUM> in a direction away from the inner annular shoulder <NUM>. The large inner diameter portion <NUM> has a larger inside diameter than the small inner diameter portion <NUM>. The retaining tube <NUM> may include a tapered or stepped transition between the small inner diameter portion <NUM> and the large inner diameter portion <NUM>.

The large inner diameter portion <NUM> is sized and configured to receive the cable <NUM>, including a sheath <NUM> that protects the fiber <NUM>. After receiving the cable <NUM>, including the sheath <NUM>, the large diameter portion <NUM> is crimped onto the sheath <NUM> of the cable <NUM>, as shown in <FIG>. The small inner diameter portion <NUM> has a smaller diameter than the outside diameter of the sheath <NUM> and is thus sized and configured to prevent the sheath <NUM> from entering the small diameter portion <NUM>. However, the small inner diameter portion <NUM> is sized and configured to receive the fiber <NUM> and buffering layers <NUM> that encircle the fiber <NUM> and are encircled by the sheath <NUM>. Thus, the transition between the small inner diameter portion <NUM> and the large inner diameter portion <NUM> provides a stop for limiting the axial insertion of the cable <NUM> into the retaining tube <NUM>.

The small diameter portion <NUM> of the retaining tube <NUM> includes a deformed region <NUM> that protrudes radially inward from an inner wall 135a of the bore <NUM> of the small diameter portion <NUM>. The deformed region <NUM> may be formed by controlled peening, crimping, or the like. The deformed region <NUM> forms an indent having a flattened inner region 151a configured to be aligned with the flattened region <NUM> of the head portion <NUM> of the connecting tube <NUM>. When the head portion <NUM> of the connecting tube <NUM> is received in the generally cylindrical bore small diameter portion <NUM> of the retaining tube <NUM>, the deformed region <NUM> cooperates with the flattened region <NUM> of the head portion <NUM> to prevent relative rotation between the connecting tube <NUM> and the retaining tube <NUM>.

The connector sub-assembly <NUM> further includes a coil spring <NUM> disposed between the connecting tube <NUM> and the retaining tube <NUM> in a radial direction and retained in an axial direction between a rear end face <NUM> of the cylindrical stem portion <NUM> and a forward face <NUM> of the inner annular shoulder <NUM>. The coil spring <NUM> biases the ferrule holder <NUM> forwardly relative to the retaining tube <NUM>, with the forward bias being limited by the abutment between the forward face <NUM> of the head portion <NUM> and the rearward face 136a of the inner annular shoulder <NUM> of the retaining tube <NUM>. The coil spring <NUM> is compressible in the axial direction by axial sliding movement of the stem portion <NUM> relative to the retaining tube <NUM>. The axial range of travel of the ferrule holder <NUM> and connecting tube <NUM> is determined by the axial length of the small inner diameter portion <NUM> of the retaining tube <NUM>, as shown in <FIG>.

The connector <NUM> may further include a removable protective cap <NUM> having a bore configured to receive the ferrule <NUM>. The connector <NUM> may also include a tubular member <NUM> having a through bore configured to receive the fiber <NUM> and the buffering layers <NUM> and to be inserted between the buffering layers <NUM> and the sheath <NUM> at the end of the sheath <NUM>. The tubular member <NUM> may protect the fiber <NUM> during crimping of the large diameter portion <NUM> of the retaining tube <NUM>. The tubular member <NUM> includes an outer shoulder <NUM> at its forward end to limit insertion of the tubular member <NUM> into the sheath <NUM> of the cable <NUM>. The small inner diameter portion <NUM> is sized and configured to receive the outer shoulder <NUM>. The connector <NUM> may also include a boot <NUM> around the cable <NUM> that is configured to abut the rearward end of the connecting tube <NUM> and the rearward end of the outer housing <NUM>. 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 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>, for example, 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 surfaces of the top wall <NUM> and a bottom wall <NUM> of the outer housing <NUM> include alignment ribs <NUM>. The alignment ribs <NUM> are configured to be received by axial alignment channels <NUM>, <NUM> in the outer walls of the ferrule holder <NUM> and the retaining tube <NUM>, respectively. The alignment channels <NUM>, <NUM> are disposed at diametrically opposed top and bottom portions of the ferrule holder <NUM> and the retaining tube <NUM>, respectively. In some aspects, the outer wall of the ferrule holder <NUM> may include only a single alignment rib, and the outer housing may include only a single alignment channel.

The alignment ribs <NUM> are tapered from a first width (i.e., in a direction perpendicular to the ferrule axis) at a forward end <NUM> to a second width at a rearward end <NUM>. The first width of the ribs <NUM> substantially matches a width of the alignment channels <NUM>, <NUM>. The tapered profile allows freedom of movement and the rearward end <NUM> of the ribs <NUM> serves as a hard stop relative to a rearward end of the alignment channels <NUM> of the retaining tube <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> may be cantilevered at its rear end <NUM>, and the free forward end <NUM> of each finger <NUM> is configured to engage the rearward facing surface of the external shoulder portion <NUM> of the forward end portion <NUM> of the retaining tube <NUM> when the retaining tube <NUM> is inserted into the outer housing <NUM> to couple the housing <NUM> with the sub-assembly <NUM>.

Referring now to <FIG>, another exemplary fiber optic connector <NUM>, for example, an LC connector, in accordance with various aspects of the disclosure is illustrated. The exemplary fiber optic connector <NUM> is similar to the fiber optic connector described above, except that the small diameter portion <NUM> of the retaining tube <NUM> includes a cross-sectional profile <NUM> along its length that matches the D-shaped profile of the head portion <NUM> of the connecting tube <NUM>. When the head portion <NUM> of the connecting tube <NUM> is received in the generally cylindrical bore small diameter portion <NUM> of the retaining tube <NUM>, the cross-sectional profile <NUM> cooperates with the D-shaped profile of the head portion <NUM> to prevent relative rotation between the connecting tube <NUM> and the retaining tube <NUM>.

As shown in <FIG>, the outer walls of the ferrule holder <NUM> and the retaining tube <NUM> may be generally cylindrical with flattened regions <NUM>, <NUM> that are aligned with one another. The outer housing <NUM> may include a bore having a top wall <NUM> with a flattened inner surface <NUM> configured to be aligned with the flattened regions <NUM>, <NUM> of the ferrule holder <NUM> and the retaining tube <NUM>, respectively, to prevent relative rotation between the outer housing <NUM> and the connector sub-assembly <NUM>.

Referring now to <FIG>, another exemplary fiber optic connector subassembly <NUM> in accordance with various aspects of the disclosure is illustrated. The exemplary fiber optic connector sub-assembly is for use with the fiber optic connector <NUM>, and is similar to the fiber optic connector sub-assemblies <NUM>, <NUM> described above, except that head portion <NUM> of the connecting tube <NUM> has a hex profile, and the small diameter portion <NUM> of the retaining tube <NUM> includes a matching hex profile <NUM> along its length. When the head portion <NUM> of the connecting tube <NUM> is received in the generally cylindrical bore small diameter portion <NUM> of the retaining tube <NUM>, the cross-sectional hex profile <NUM> cooperates with the hex profile of the head portion <NUM> to prevent relative rotation between the connecting tube <NUM> and the retaining tube <NUM>.

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.

It should be noted that although the specific example described above relates to LC-type connectors, the optical fiber connector sub-assembly can be adapted for use with other types of optical fiber connector systems, for example SC-type connectors and ST-type connectors.

Claim 1:
An optical fiber connector sub-assembly for an optical fiber connector, comprising:
a ferrule (<NUM>) configured to hold an optical fiber therein;
a ferrule holder (<NUM>; <NUM>) configured to hold the ferrule (<NUM>);
a retaining tube (<NUM>; <NUM>) configured to hold the ferrule holder (<NUM>; <NUM>) and receive a fiber optic cable (<NUM>); and
a connecting tube (<NUM>; <NUM>) configured to be rotatingly coupled with the ferrule holder (<NUM>; <NUM>), a forward end portion of the connecting tube (<NUM>; <NUM>) being configured to be received in the ferrule holder (<NUM>; <NUM>) and to be slidingly received by the retaining tube (<NUM>; <NUM>),
wherein the ferrule holder, the retaining tube, and the connecting tube are configured to receive an optical fiber,
wherein the retaining tube (<NUM>; <NUM>) and the connecting tube (<NUM>; <NUM>) are configured to cooperate with one another to prevent relative rotation between the ferrule holder (<NUM>; <NUM>) and the retaining tube (<NUM>; <NUM>),
wherein the retaining tube (<NUM>; <NUM>) includes a forward end portion (<NUM>) and a rearward end portion (<NUM>), the forward end portion and the rearward end portion being separated at an interior of the retaining tube (<NUM>; <NUM>) by an inner annular shoulder (<NUM>),
characterized in that the connecting tube (<NUM>; <NUM>) includes an elongated cylindrical portion (<NUM>) having a head portion (<NUM>; <NUM>) at its rear end, the head portion including a flattened region (<NUM>), and
wherein the rearward end portion (<NUM>) of the retaining tube (<NUM>; <NUM>) includes an inner wall having a flattened inner region (151a) configured to be aligned with the flattened region (<NUM>) of the connecting tube (<NUM>; <NUM>).