Methods of ferrule reshaping for correcting core-to-ferrule concentricity errors, and optical fiber cable assemblies related to such methods

Methods of reshaping ferrules used in optical fiber cables assemblies are disclosed. The reshaping methods reduce a core-to-ferrule concentricity error (E), which improves coupling efficiency and optical transmission. The methods include measuring a true center of the ferrule, wherein the true center is based on an outer surface of the ferrule; and reshaping at least a portion of the ferrule to change the true center of the ferrule, wherein the reshaping includes enlarging a portion of the ferrule. A variety of reshaping techniques are also disclosed.

FIELD

The present disclosure relates to optical fiber cable assemblies, and in particular relates to methods of ferrule reshaping for correcting core-to-ferrule concentricity errors for ferrules used in optical fiber connectors.

BACKGROUND

Optical fiber connectors (“connectors”) are devices used to optically connect one optical fiber to another, or to connect an optical fiber to another device such as an optical transmitter or an optical receiver. An optical fiber cable typically carries the optical fiber, which has relatively high-index core section in which most of the light is carried, and a surrounding relatively low-index cladding section that surrounds the core. A ferrule in the connector supports a bare end section of the optical fiber. The bare end section has a polished end face that coincides with a planar front face of the ferrule. The connector and the optical fiber cable constitute a cable assembly.

An important property of a connector is its ability to provide an efficient optical connection with the optical fiber of another connector, i.e., an optical connection whereby the optical loss (also called “insertion loss”) from the light passing out of one fiber end face and into the other fiber end face is minimal. This efficiency is referred to in the art as the “coupling efficiency.” A misalignment of the end faces of the two optical fibers supported by the two connectors is one of the main sources of insertion loss. Since most of the light traveling in an optical fiber is confined to the core, the couple efficiency between two connectors depends in large measure on the amount of offset between the cores. This offset can be due to a core-to-ferrule error, i.e., an offset between the location of the core of the optical fiber and the true center of the ferrule.

Ideally, the cores of the optical fibers supported by respective connectors are perfectly axially aligned to maximize the coupling efficiency. In practice, however, there is almost always some amount of core-to-ferrule eccentricity error. It would be advantageous therefore to reduce the core-to-ferrule eccentricity error on a ferrule-by-ferrule basis to improve the coupling efficiency of connectors.

SUMMARY

An embodiment of the disclosure includes a method for reducing a core-to-ferrule concentricity error for a ferrule having an axial bore sized to operably support an optical fiber having a core. The method includes: measuring a true center of the ferrule, wherein the true center is based on an outer surface of the ferrule; and reshaping at least a portion of the ferrule to change the true center of the ferrule, wherein the reshaping includes enlarging a portion of the ferrule.

In another embodiment of the present disclosure, the step of enlarging a portion of the ferrule includes forming one or more protuberances on the outer surface of the ferrule. In another embodiment, the step of forming one or more protuberances on the outer surface of the ferrule comprises: creating, on the outer surface of the ferrule, a crater with at least one micro-protuberance on the side of the crater. In another embodiment, a depth of the crater is between 0.1 μm and 1000 μm and a height of the at least one micro-protuberance is between 0.02 μm and 100 μm. In another embodiment, creating the crater and the at least one micro-protuberance includes applying a laser beam to irradiate the outer surface of the ferrule, wherein the laser beam has a wavelength ranging between 10 nm and 20,000 nm and an average power delivered to the ferrule between 0.001 μJ/μm2and 1000 μJ/μm2, wherein the average power is based on a time period that is between 1 pico-second and 1 second.

In yet another embodiment, the laser beam has a wavelength between 100 nm and 2000 nm and an average power delivered to the ferrule between 0.01 μJ/μm2and 100 μJ/μm2, wherein the average power is based on a time period that is between 1 pico-second and 1 second. In another embodiment, the laser beam has a wavelength between 150 nm and 1000 nm and an average power delivered to the ferrule between 0.01 μJ/μm2and 100 μJ/μm2, wherein the average power is based on a time period that is between 1 pico-second and 1 second. In another embodiment, the laser beam has a wavelength between 150 nm and 1000 nm and an average power delivered to the ferrule between 0.01 μJ/μm2and 10 μJ/μm2, wherein the average power is based on a time period that is between 1 pico-second and 1 second. In another embodiment, wherein the laser beam has a wavelength between 355 nm and 532 nm and an average power delivered to the ferrule between 0.1 μJ/μm2and 10 μJ/μm2, wherein the average power is based on a time period that is between 1 pico-second and 1 second.

In yet another embodiment, the method further includes mating a sleeve having a sleeve center onto the ferrule, wherein the at least one micro-protuberance engages with the sleeve thereby distributing a force of the sleeve when applied onto the ferrule. In another embodiment, the at least one micro-protuberance engages with the sleeve to reduce an eccentricity of the core relative to the sleeve center. In another embodiment, the step of reshaping includes removing material from the at least one micro-protuberance, wherein the step of removing material includes polishing the at least one micro-protuberance.

In yet another embodiment, the at least one micro-protuberance includes a first micro-protuberance on one side of the crater and a second micro-protuberance on a second side of the crater; wherein a depth of the crater is between 0.1 μm and 1000 μm and heights of the first micro-protuberance and the second micro-protuberance are between 0.02 μm and 100 μm. In another embodiment, the first micro-protuberance and the second micro-protuberance are positioned opposite each other defining the crater therebetween. In another embodiment, the at least one micro-protuberance includes a cluster of micro-protuberances around the crater; wherein a depth of the crater is between 0.1 μm and 1000 μm and a maximum height of the cluster of micro-protuberances is between 0.02 μm and 100 μm. In another embodiment, enlarging a portion of the ferrule includes increasing a diameter of the ferrule to a predetermined value.

Another embodiment of the disclosure includes a method of reducing misalignment between a first ferrule and a second ferrule. The method includes: measuring a first diameter of the first ferrule and a second diameter of the second ferrule, wherein the first diameter is larger than the second diameter; reshaping at least a portion of the second ferrule to increase the second diameter of the second ferrule and reduce the difference between the first diameter and the second diameter; wherein reshaping at least a portion of the second ferrule includes enlarging a portion of the second ferrule. In another embodiment, the step of enlarging a portion of the second ferrule includes forming one or more protuberances on an outer surface of the second ferrule. In another embodiment, the step of forming one or more protuberances on the outer surface of the second ferrule comprises: creating, on the outer surface of the second ferrule, a crater with at least one micro-protuberance on the side of the crater such that the at least one micro-protuberance increases the second diameter of the second ferrule to reduce the difference between the first diameter and the second diameter. In another embodiment, the reshaping step includes enlarging a portion of the first ferrule. In another embodiment, the step of enlarging a portion of the first ferrule includes forming one or more protuberances on an outer surface of the first ferrule. In another embodiment, the step of forming one or more protuberances on the outer surface of the first ferrule comprises: creating, on the outer surface of the first ferrule, a crater with at least one micro-protuberance on the side of the crater such that the at least one micro-protuberance increases the first diameter of the first ferrule.

In another embodiment of the disclosure, the step of reshaping includes irradiating one or more locations on the outer surface of the second ferrule with a laser beam, wherein the laser beam has a wavelength ranging between 10 nm and 2000 nm and an average power delivered to the second ferrule between 0.001 μJ/μm2and 1000 μJ/μm2, wherein the average power is based on a time period that is between 1 pico-second and 1 second. In another embodiment, a depth of the crater is between 0.1 μm and 1000 μm and a height of the at least one micro-protuberance is between 0.02 μm and 100 μm. In another embodiment, the at least one micro-protuberance includes a first micro-protuberance on a first side of the crater and a second micro-protuberance on a second side of the crater; wherein the first micro-protuberance and the second micro-protuberance are positioned opposite each other defining the crater therebetween. In another embodiment, a depth of the crater is between 0.1 μm and 1000 μm and heights of the first micro-protuberance and the second micro-protuberance are between 0.02 μm and 100 μm.

In yet another embodiment, the sleeve engages with the at least one micro-protuberance of the second ferrule. In another embodiment, the second diameter of the second ferrule is increased such that an offset between the first core and the second core within the sleeve is between 0 μm and 3 μm. In another embodiment, the at least one micro-protuberance engages with the sleeve such that the at least one micro-protuberance distributes a force applied by the sleeve.

Another embodiment of the disclosure includes a method of reducing misalignment between a first ferrule having a first axial bore sized to operably support a first optical fiber having a first core and a second ferrule having a second axial bore sized to operably support a second optical fiber having a second core. The method includes: measuring a first diameter of the first ferrule and a second diameter of the second ferrule, wherein the first diameter is larger than the second diameter and the core of each ferrule is off-centered; reshaping at least a portion of the first ferrule to increase the diameter of the first ferrule and center the first core of the first fiber relative to the first ferrule; reshaping at least a portion of the second ferrule to increase the second diameter of the second ferrule and reduce the difference between the first diameter and the second increased diameter and center the second core of the second fiber relative to the second ferrule; wherein reshaping at least a portion of the first ferrule and reshaping at least a portion of the second ferrule includes: creating, on an outer surface of both ferrules, a crater with at least one micro-protuberance on a side of the crater such that the at least one micro-protuberance increases the diameters of both ferrules to reduce the difference between the first diameter and the second diameter and to bring the first and second cores in each of the first and second ferrules closer to the respective ferrule centers, thereby improving alignment between the first core and the second core and improving an optical coupling between the first ferrule and the second ferrule within a sleeve.

DETAILED DESCRIPTION

Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.

The claims as set forth below are incorporated into and constitute part of this Detailed Description.

Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation.

In the discussion below, the term “cylindrical” is not limited to body having a strictly circular cross-sectional shape and can include other cross-sectional shapes.

Also in the discussion below, the term “core-ferrule concentricity” can also be referred to as the “coaxiality,” and the concentricity error can be referred to as a “coaxial error” or the “coaxiality error.”

And in this disclosure, any ranges of values includes the stated end points of the range. For example, a range that is stated as being between A and B, or from A to B, with A and B being numerical values, includes both A and B in the stated range.

Optical Fiber Connector Sub-Assembly

FIG. 1is a perspective view andFIG. 2is an exploded perspective view of an example connector sub-assembly10. The connector sub-assembly10includes a ferrule20having a front end22and back end24. The ferrule20is configured to operably support a bare fiber section40(FIG. 5A) of an optical fiber42, as discussed in greater detail below. The connector sub-assembly10includes a ferrule holder118from which the ferrule20extends. The connector sub-assembly10also includes a housing120having a cavity121and a front end122. The housing120is referred to hereinafter as an “inner housing”120since it engages an outer housing, as explained below in connection withFIG. 4. The ferrule holder118is received within cavity121of inner housing120.

The connector sub-assembly10also includes a connector body124(also referred to as “retention body124”, or “crimp body124”) configured to retain ferrule holder118within cavity121of inner housing120. More specifically, back end24of ferrule20is received in a front-end portion128of ferrule holder118and secured therein in a known manner (e.g., press-fit, adhesive, molding the ferrule holder118over the back end24of the ferrule20, etc.). The ferrule20and ferrule holder118may even be a monolithic structure in some embodiments. For convenience, the term “ferrule assembly” may be used to refer to the combination of the ferrule20and ferrule holder118, regardless of whether these elements are separate components secured together or different portions of a monolithic structure.

The ferrule holder118is biased to a forward position within the housing120by a spring132, which extends over a back-end portion130of ferrule holder118. The back-end portion130has a reduced cross-sectional diameter/width compared to the front-end portion128. The spring132also interacts with internal geometry of connector body124, which may be secured to inner housing120using a snap-fit or the like. For example,FIGS. 1 and 2illustrate a rear portion of the housing120having cut-outs or slots136on opposite sides so as to define a split shroud. The connector body124has tabs138configured to be snapped into slots136and retained therein due to the geometries of the components.

When the connector sub-assembly10is assembled as shown inFIG. 1, a front-end section23of ferrule20projects beyond front end122of housing120. The front-end section23presents bare fiber section40for optical coupling with a mating component (e.g., another fiber optic connector; not shown). Note that the ferrule20aligns the bare fiber section40generally along a longitudinal inner-housing axis AH.

FIG. 3is a cross-sectional view of the connector sub-assembly ofFIGS. 1 and 2, shown along with a fiber optic cable150(“cable”) that operably supports optical fiber42.FIG. 3illustrates an example of how cable50can be terminated with connector sub-assembly10to form a cable sub-assembly148. The particular cable150shown is merely to facilitate discussion, and other types of cables150can be used. In the embodiment shown, cable50includes an outer jacket152, inner jacket154, and strength members156in the form of aramid yarn. The optical fiber42in the embodiment shown includes a coating158and a buffer layer160(“tight buffer”).

Portions of outer jacket152and inner jacket154have been removed from cable50to expose strength members156, which are cut to a desired length and placed over a rear portion162of connector body124. The strength members156are coupled to connector body124by a crimp band164(also referred to as a “crimp ring”) that has been positioned over a portion of strength members156and inner jacket154. Again, cable150is merely an example, as persons skilled in optical connectivity will appreciate how different cable and connector designs may be used in connection with the methods discussed below.

FIG. 4is a perspective view of a cable assembly170formed by operably engaging an outer housing180with inner housing120. The connector sub-assembly10and outer housing180define a connector182. A flexible boot151is employed to assist in mechanically connecting cable150to connector body124of inner housing120and to protect the components that are attached to rear portion162of connector body124.

The Ferrule

FIG. 5Ais a perspective view of an example of ferrule20and optical fiber42, andFIG. 53is a side view of the ferrule20. The ferrule20has a ferrule body21that is substantially cylindrical and in an example has a substantially circular cross-sectional shape. The ferrule20(i.e., ferrule body21) has the aforementioned front and back ends22and24, as well as an outer surface26, and an axial bore28. As can be appreciated, the outer surface26and axial bore28generally extend between the front and back ends22and24. The front-end section23of ferrule20is adjacent front end22. The ferrule20also includes a back-end section25adjacent back end24.

The ferrule20has an axial length LF defined between the front and back ends22and24, which may be 10.5 mm for an SC-type connector and 7.5 mm or an LC-type connector. The ferrule20also has a nominal diameter dF, which in this disclosure generally refers to the stated value for the diameter of ferrule20and/or a commonly-accepted value for an actual value of the diameter. For example, the nominal diameter dF may be 2.5 mm for SC-type connectors and 1.25 mm for LC-type connectors. Generally, ferrule20is not limited to specific types of connectors and so can have any reasonable nominal diameter dF and any reasonable length LF that might be used to form an optical fiber connector. An exemplary material for ferrule20is zirconia. Other materials for ferrule20include glass, metal, polymers, ceramics, and like materials, including combinations of the aforementioned materials, etc.

In an example, ferrule20includes a beveled section27at the front end22adjacent outer surface26. The beveled section27transitions from the diameter of the front end22to the nominal diameter dF (generally defined by the outer surface26in the embodiment shown). As also shown inFIG. 3, axial bore28is sized to hold bare fiber section40formed at an end of optical fiber42. A front end face44of bare fiber section40resides substantially at front end22of ferrule20. The bare fiber section40includes a central core (“core”)46surrounded by a cladding48. The core46has a central axis AC.

The axial bore28has a central axis (“bore axis”) AB while ferrule body21has a central axis AF that runs through a “true center”30of the ferrule body that is based on outer surface26. The true center30may, for example, represent the geometric center of ferrule body21based on the cross-sectional shape of outer surface26. In other words, in such an example, true center30corresponds to the geometric center of the cross-sectional shape of ferrule20.

In an example, the cross-sectional shape of outer surface26is perfectly circular, in which case the true center30is at the center of the circle, with central axis AB of axial bore28running through the true center30and thus being coaxial with the central axis AF of ferrule20.FIG. 4shows this ideal case where the central axis AH of inner housing120, the central axis AB of axial bore28, the central axis AF of ferrule20, and the central axis AC of core46are all co-axial. In practice, there can and will be some amount of lateral offset between these axes due to manufacturing errors. For example, in practice, axial bore28may only be nominally centered on the true center30of ferrule20, i.e., to within a manufacturing tolerance, e.g., 1.0 micron (μm), 0.5 μm, or 0.3 μm.

FIGS. 5C and 5Dare similar toFIG. 5AandFIG. 5B, and illustrate an example ferrule20having a two-part ferrule construction wherein ferrule body21includes or consists of an inner member21A (or “inner part21A”) and an outer member21B (or “outer part21B”) that surrounds the inner member and defines outer surface26. The inner member21A includes axial bore28in its center and, in the embodiment shown, is generally cylindrical. The inner member21A may be formed from a first material, and the outer member21B (also generally cylindrical) may be formed from a second material that is less rigid than the first material. For example, the first material may comprise a ceramic material, and the second material may comprises a polymer, metal, glass, or different ceramic material. Unless otherwise noted, any discussions herein relating to ferrule20may apply to either one-piece ferrules (e.g., ferrule20inFIGS. 5A and 5B) or multi-piece ferrules (e.g., two-piece ferrule20inFIGS. 5C and 5Dand variations where there may be one or more intermediate layers or members between inner member21A and outer member21B).

Various techniques for determining true center30of ferrule20will be appreciated by those skilled in the art. For example, true center30may be determined by axially rotating ferrule20while measuring a distance between the outer surface26and a reference point. For a perfectly circular ferrule, a plot of this distance versus the angle of rotation traces a sinusoid if the rotation axis is not on the true center. The true center30can be determined from the shape of the sinusoid. If the ferrule is not perfectly circular (perfectly circularly symmetric), then the plot of distance vs. rotation angle will show small deviations from a perfect sinusoid that are indicative of the magnitude of the asymmetry. Regardless, curve fitting techniques may be used to associate a curve with the distance values measured at different rotation angle so that true center30can be determined from the shape of the curve (e.g., a line in the event the rotational axis is aligned with the true center and a sinusoid in the event the rotational axis is not aligned with the true center). Detailed examples based on these and related principles are disclosed in US. Patent Application Publication No. US2015/0177097 (“the '097 Publication), the disclosure of which is incorporated herein by reference.

In some embodiments, true center30may be based on only some of the measurements between outer surface26and a reference point when rotating ferrule20. For example, the measurements taken for a 360 degree rotation of ferrule20may be analyzed to determine the “highest” locations on outer surface26. These are the points on outer surface26most likely to influence how ferrule20fits within a sleeve of an adapter or the like. As few as three points (e.g., the three “highest” locations on outer surface26) may be used in some embodiments to determine true center30. To this end, true center30may represent the geometric center of the selected points (three or more) used for such a “high fitting” approach.

In an example, ferrule20need not have a perfectly circular cross-sectional shape; it just needs to fall within an overall diameter tolerance (i.e., have a maximum outer diameter within a certain range of the nominal diameter dF). In some embodiments, ferrule20may additionally or alternatively need to satisfy a circularity tolerance. As used herein, “circularity” refers to all points on outer surface26, when viewed in a cross-section perpendicular to central axis AF of ferrule20, being equidistant from true center30. The term “circularity error” or “circularity value” is used as a characterization of non-circularity (i.e., out-of-roundness) and is considered as the difference in radius between the two best fitting concentric circles within which the cross-sectional profile of outer surface26is contained.

The term “circularity tolerance” refers to the maximum acceptable circularity error, i.e. the maximum acceptable radial distance between two concentric circles within which all points on the cross-section of outer surface26lie.

For the purpose of the present disclosure, higher values for circularity error reflect the circularity error becoming worse (e.g., ferrule20becoming less circular) whereas lower values reflect the circularity error being improved (e.g., ferrule20becoming more circular). For a ferrule20that has a nominal diameter dF of 1.25 mm or 2.5 mm, an example diameter tolerance is +/−1.0 μm or even +/−0.5 μm, and an example circularity tolerance is 1.0 μm or even 0.5 μm. The diameter tolerance and the circularity tolerance may alternatively or additionally be defined in relation to the nominal diameter dF. For example, the diameter tolerance may be +/−0.04% or +/−0.02% of the nominal diameter dF of ferrule20, while the circularity tolerance may be 0.04% or 0.02% of the nominal diameter dF. In other examples, there is no tolerance on the circularity or the diameter, as explained below.

The overall diameter tolerance and overall circularity tolerance, if required, constrain the amount by which outer surface26of ferrule20can be reshaped. Spreading out the reshaping over a relatively large portion of outer surface26, e.g., over a quadrant, allows the reshaping process to not exceed the applicable tolerance(s), as discussed below. The applicable tolerance(s) may facilitate the portion of front-end section23of ferrule20establishing the optical connection between connectors using an adapter module with an alignment sleeve, as described below. In some cases where the ferrule reshaping is more than just a slight deformation to the shape of outer surface26, the circularity and diameter tolerances can become extremely relaxed or non-existent since ultimately the main consideration at play is a decrease in the insertion loss.

FIG. 6Ais a front-end view of an example ferrule20showing the end face44of bare fiber section40within axial bore28. A Cartesian coordinate system in a plane perpendicular to central axis AF of ferrule20may be defined with an x-axis and y-axis passing through true center30, as shown in the close-up view ofFIG. 6B. The ferrule20can be divided into four quadrants Q1, Q2, Q3and Q4, as shown, based on the Cartesian coordinate system.

FIG. 6Aalso illustrates an example core-to-ferrule concentricity error, which is exaggerated for ease of illustration. The close-up view ofFIG. 6Bshows core46of bare fiber section40offset from true center30by an amount (magnitude) δ in a direction (angle) θ measured relative to the +x axis in the plane perpendicular to the central axis AF. Thus, the core-to-ferrule concentricity error can be represented an error vector E=(δ,θ) using polar coordinates, wherein the bold denotes vector status. Hereinafter, the core-to-ferrule concentricity error is simply referred to as the “concentricity error E”. As noted above, this error is also referred to in the art as the “coaxial error” or “coaxiality error.” Also note that the offset distance δ of core46is generally measured with reference to central axis AC of core46(i.e., the distance δ is measured from true center30to the center of core46), at the front end face44of bare fiber section40(which, as mentioned above, resides substantially at front end22of ferrule20).

FIG. 6Dis similar toFIG. 6Band shows an example ferrule without the bare fiber section40within axial bore28, illustrating an offset distance Dbas measured radially from true center30to central axis AB of axial bore28.

There are a number of manufacturing errors that can contribute to the concentricity error E, including: 1) offset of core46relative to cladding48; 2) an offset of bare fiber section40within axial bore28; and 3) an offset (non-centering) of axial bore28relative to true center30of ferrule20. These error contributions tend to be random so that the precise location of core46relative to the outer surface26(and thus relative to the true center30) in a given cable sub-assembly110is typically not known unless it is measured.

Measurement of concentricity error E may be made using a non-contact measurement system, such as disclosed the aforementioned '097 Publication. It is noted that such non-contact measurements are made with increasing accuracy and precision if more of the outer surface26is exposed in front-end section23of ferrule20because distance sensors can be used to measure the outer surface at more axial locations than just a small exposed end portion of the outer surface.

Alternatively, the concentricity error E may be measured using a contact method that does not utilize a master connector (i.e., a reference connector) to establish an optical connection. An example of such a method is employed by the Koncentrik-V2 measurement system from Data-Pixel SAS of Chavanod, France, wherein ferrule20of cable sub-assembly110is disposed on a precision ball array or sleeve. In other examples, the concentricity error E may be measured using a contact method that utilizes a master connector.

Measurements of concentricity error E made on about 1000 cable sub-assemblies148indicate that the magnitude δ of the concentricity error E generally falls in the range from about 0 μm to about 1.2 μm, with the average being about 0.4 μm.

Once the concentricity error E is measured, the next step of the method is to reduce this error by defining a “new” true center30′ by reshaping outer surface26of ferrule20, as shown inFIG. 6Cto form a new outer surface26′. This can be accomplished by selectively removing material from ferrule body21at one or more portions of outer surface26of ferrule20. Alternatively or additionally, this can be done by enlarging ferrule body21at one or portions of outer surface26(e.g., by localized expansion of existing material or by adding new material).

The term “deformation” is used herein to generically refer to a deviation or change from the initial cross-sectional shape of outer surface26that results from the reshaping process. Thus, a deformation may result from either removal of material from ferrule body21or enlarging ferrule body21(e.g., either by localized expansion or adding material) at the location of the change in shape. In other words, the reshaping process may include making at least one deformation to outer surface26. The deformation(s) may, for example, comprise one or more of the following: a segment on the outer surface26of reduced curvature relative to a remainder of the outer surface; a groove in the outer surface; a protuberance formed on the outer surface by local expansion of material of the ferrule; and a protuberance formed on the outer surface by applying additional material to the ferrule. Depending on the particular embodiment, there may be deformation(s) in all of the quadrants Q1, Q2, Q3, Q4(FIG. 6A) or in less than all of the quadrants (e.g., in only one of the quadrants or in only two of the quadrants).

As noted above, in some examples, the surface reshaping may be constrained by at least one of a diameter tolerance and a circularity tolerance. In other examples, the surface reshaping can be performed without regard to either or both of these tolerances, as the ultimate objective is a decrease in the insertion loss as compared to the original-shaped ferrule. Insertion loss may be determined using any suitable technique. For example, insertion loss may be determined using contact-based techniques where cable assembly170(or cable sub-assembly148) is mated to one or more reference cable assemblies (“reference jumpers”) with “reference grade connectors”. Some of such techniques use light sources and power meters, while others use an optical time domain reflectometer (OTDR). Alternatively, insertion loss may be determined using non-contact-based techniques, such as those disclosed in U.S. Patent Application Pub. Nos. 2016/0033325 and 2016/0061690, both of which are herein incorporated by reference.

With reference again toFIG. 6C, the portion of outer surface26in the lower right quadrant Q2has been reshaped to move the true center30of ferrule20to a new true center30′ that coincides with the central axis AC of core46of bare fiber section40residing within axial bore28. Ideally, the new true center30′ created by the surface reshaping process resides exactly on central axis AC of core46as shown inFIG. 6C, so that δ=θ. However, a substantial reduction in the size (magnitude) of the concentricity error E to a new value E′=(δ′, θ′), wherein |E′|<|E| (i.e., δ′<δ) can be satisfactory if it substantially reduces the insertion loss and increases the coupling efficiency as compared to the insertion loss and coupling efficiency associated with the original concentricity error E. In an example, a substantial reduction in the insertion loss is 0.01 dB or greater.

In various examples, the magnitude of the new concentricity error |E′|=6′ is at least 5% less than |E|=6, or is at least 10% less than |E|=6, or at least 20% less than |E|=6, or is at least 50% less than |E|=δ, or is at least 75% less than |E|=δ, or is at least 90% less than |E|=δ. In an example, the direction component θ of the concentricity error E provides information about which portion of outer surface26to reshape, e.g., the portion of the outer surface that resides generally at (e.g., centered at) θ for material enlargement/addition and θ-180 degrees for material removal.

The magnitude of the new concentricity error |E′|=6′ can alternatively or additionally be expressed in terms of the nominal diameter dF of ferrule20. In some embodiments, the magnitude of the new concentricity error |E′|=6′ is less than 0.048% of the nominal diameter dF, or even less than 0.024% of the nominal diameter dF, or even smaller (e.g., less 0.012% of the nominal diameter dF). The distance δ′ may be, for example, less than 1.2 μm, less than 0.6 μm, or even less than 0.3 μm for a ferrule having a nominal diameter dF of 1.25 mm or 2.5 mm.

FIG. 7Ashows cable assemblies170aand170bwith respective cables150a,150b, connectors190a,190b, and boots151a,152b. The cable assemblies170a,170bare operably connected (“mated” or “coupled”) using via an adapter module (or simply “adapter”)200that includes opposite input ends202a,202b. The adapter module200is configured to receive connectors190a,190bin respective input ends202a,202bto establish an optical connection between the optical fibers42a,42brespectively carried by cables150a,150b.

The adapter module200also includes an alignment sleeve210, as shown in the perspective view ofFIG. 7B. The alignment sleeve210in the embodiment shown has a C-shaped cross-section defined by an axially running slot212. The alignment sleeve210also has an interior214with a diameter that is slightly smaller than the diameter of ferrules20a,20b(FIG. 7C) of connectors190a,190b.

FIG. 7Cis a cross-sectional view of alignment sleeve210with the respective front-end sections23a,23bof ferrules20a,20bresiding in interior214so that respective front ends22aand22bof ferrules20a,20bare confronting. The axially running slot212allows alignment sleeve200to expand slightly to accommodate the front ends23a,23b. This results in a tight fit of respective front-end sections23a,23bof ferrules20a,20bwithin interior214of alignment sleeve210so that the respective ferrule axes AFaand AFbare substantially aligned. The respective lengths of the front-end sections23a,23bare denoted inFIG. 7Cas EFaand EFbrespectively. In an example, EFaand EFbare in the range from 2 mm to 5 mm, or 2 mm to 4 mm.FIG. 7Cillustrates how the shape of the front-end section23of each ferrule20determines how each ferrule will sit within the interior214of alignment sleeve210and align with the other ferrule.

When two connectors190are modified using the methods disclosed herein to have a reduced concentricity error E and are then mated (e.g. using adapter module200), the resulting connection has improved (and in some cases, may even maximize) coupling efficiency. As noted above, in some examples, the main criterion—and perhaps only criterion—for the reshaping process may be that the coupling efficiency be increased, i.e. the insertion loss be reduced, by decreasing the lateral offset between fiber cores (e.g., central core46) of each connector.

Ferrule Reshaping Methods

FIGS. 8A through 8Eillustrate several different example methods of reshaping a portion of outer surface26of ferrule20. Each of the examples may involve remaining within a circularity and/or diameter tolerance of the ferrule if such tolerances are required, or may be performed without regard to any diameter and/or circularity tolerances.

To this end,FIG. 8Ais a close-up front-end view of ferrule20that shows an example wherein an abrasive belt310with an abrasive surface312engages a portion26P of outer surface26to remove material therefrom. The abrasive surface312may hew to the curved shape of the ferrule20as much as possible. The amount of surface area of outer surface26engaged by abrasive belt310can be varied as needed, e.g., by changing angles ϕ1 and ϕ2 the abrasive belt makes with the outer surface. An example abrasive belt310is or includes a diamond lapping film. Material removal rates can be controlled by the belt speed, the belt pressure, and the grit or roughness of the abrasive belt310.

FIG. 8Bis a close-up front-end view of ferrule20andFIG. 8Cis a front-elevated view of cable sub-assembly110, both showing an example wherein a rotating cylindrical abrasive member320engages portion26P of outer surface26to remove material therefrom. The abrasive member320has a central axis AM that is substantially parallel to ferrule central axis AF. The abrasive member320has an abrasive outer surface322. Because the contact area between abrasive member320and outer surface26of ferrule20is relatively thin and long, the abrasive member is also translatable to cover a desired amount of surface area of outer surface26in portion26P. The rate of material removal can be controlled by the rotation rate, pressure, and surface roughness of abrasive member320.

FIG. 8Dis similar toFIG. 8Band illustrates an example wherein an array326of multiple rotating cylindrical abrasive members320engage outer surface26at portion26P. Each abrasive member320can be independently translatable, and the array326can also be translatable, i.e., the abrasive members can be moved together.

FIG. 8Eis similar toFIG. 8Aand illustrates an example wherein a laser beam340from a laser system350is used to remove (e.g., ablate) material from outer surface26at portion26P.

FIG. 8Fis similar toFIG. 8Eand illustrates an example wherein a laser beam340from a laser system350is used to form protuberances370on outer surface26at portion26P. The protuberances370in this example are formed by the ferrule material undergoing local expansion or swelling when locally irradiated by laser beam340. An example process for forming such laser-induced protuberances370is described in U.S. Pat. Nos. 7,724,992, 7,792,404, 8,291,729 and 8,397,537, which are incorporated by reference herein. It will be appreciated, however, that protuberances370may alternatively be formed by other techniques, such adhering, fusing, or otherwise depositing material on outer surface26.

In some embodiments, protuberances370may be formed along the length of the ferrule20in select locations on outer surface26so that three high-point locations (deformations)26′ on outer surface26can cause and adjustment of the ferrule location within alignment sleeve200(FIG. 7B). The protuberances370in these and other embodiments may be arranged in a variety of configurations. For example, there may be a plurality of protuberances370circumferentially distributed on outer surface26of ferrule20. Alternatively, there may be a plurality of protuberances370distributed on outer surface26in a ring-shaped or spiral-shaped pattern along a length of ferrule20. These possibilities may apply not just to arrangements of the protuberances370, but also more generally to arrangements of other types of deformations.

FIG. 8Falso shows a reference line RL that passes through deformation26′ and through true center30. The deformation26′ in surface26formed by protuberances370deviate from the original or nominal surface26(dashed line) by a distance Ddas measured along reference line RL. Any of the different types of deformations disclosed herein can be measured by distance Dd, and this distance is illustrated in connection with protuberances370by way of illustration. In embodiments where ferrule20has a nominal diameter dF of at least 1.25 mm (e.g., 1.25 mm or 2.5 mm, as may be the case for ferrules used with LC or SC connectors, respectively), the distance Ddmay be at least 0.05 μm. The distance Ddmay even be at least 0.1 μm in such embodiments. An alternative way of characterizing the distance Ddmay in terms of the nominal diameter dF, such the distance Ddbeing at least 0.04% of the nominal diameter dF.

In another embodiment, as shown inFIGS. 10A, 10B, laser beam340irradiates outer surface26of ferrule20to create, from outer surface26, a crater372(FIG. 10B) on ferrule surface26with protuberances370′ positioned opposite each other on either side of crater372. Stated another way, protuberances370′ are positioned opposite each other and define a crater372therebetween. Protuberances370′ can be formed by swelling of the outer surface26of ferrule20. Protuberances adjacent a crater, like protuberances370′, will be referred to as “micro-protuberances” in this disclosure. The wavelength of laser beam340may be between 10 nanometers (nm) and 20,000 nm, between 100 nm and 2000 nm, or 150 nm and 1000 nm. In one specific embodiment, the laser wavelength of laser beam340is between 355 nm and 532 nm.

When applied onto outer surface26of ferrule20, laser beam340is focused onto ferrule20such that an average power delivered to ferrule20, within a time period that is between 1 pico-second to 1 second, is between 0.001 μJ/μm2and 1000 μJ/μm2, or between 0.01 μJ/μm2and 100 μJ/μm2, or between 0.1 μJ/μm2and 10 μJ/μm2. It is contemplated that outer surface26may be irradiated by a laser beam340as a single laser pulse or burst or as a series of laser pulses or bursts. In one embodiment, the laser radiation (i.e., laser beam340) can include pulses with an individual pulse width that ranges between 1 pico-second and 1 second.

As mentioned previously, the application of laser beam340onto outer surface26of ferrule20can create a crater372with micro-protuberances370′ on either side of crater372as shown inFIG. 10B.FIG. 10Bshows crater372having a parabolic shape and micro-protuberances370′ having a hill-like shape. In one embodiment, crater372has a depth that ranges between 0.1 μm and 1000 μm, and micro-protuberances370′ have a maximum height that ranges between 0.02 μm and 100 μm. In another embodiment, crater372includes a cluster of micro-protuberances370′ on at least one side of crater372where the dept of the crater is between 0.1 μm and 1000 μm and the maximum height of the cluster of micro-protuberances370′ is between 0.02 μm and 100 μm It is contemplated and within the scope of the present disclosure that crater372and micro-protuberances370′ may have suitable alternate shapes and sizes.

Craters372and micro-protuberances370′ can provide greater force distribution of sleeve210(FIG. 7B) when sleeve210is mated with ferrule20. That is, a singular or a series of craters372and micro-protuberances370′ can distribute the force applied by sleeve210such that the outer surface26of ferrule20bears less of the applied force of sleeve210. As shown inFIG. 11, a line crater372and corresponding micro-protuberances370′ are shown where micro-protuberances370′ bear the majority of the force applied by sleeve210(as indicated by the darker shading of micro-protuberances370′) thereby reducing the amount of force applied onto outer surface26of ferrule20and crater372by sleeve210.

Micro-protuberances370′ on ferrule surface26can also increase the diameter of ferrule20as shown inFIG. 12where micro-protuberances370′ increase the diameter of ferrule20from R to R1.

As shown inFIGS. 13A-Band discussed herein, an increase in ferrule diameter can also improve optical coupling between ferrules20A,20B with different diameters.FIG. 13Ashows a first ferrule20A and a second ferrule20B inserted into sleeve210where the first ferrule20A has a diameter R1and the second ferrule20B has a diameter R2that is less than diameter R1. Each ferrule20A,20B includes a bore28A,28B that extends between the front ends22A,22B and back ends24A,24B of ferrules20A,20B, respectively. Bores28A,28B receive optical fibers42A,42B, respectively. As shown, within sleeve210, ferrules20A,20B and optical fibers42A,42B are misaligned due to the difference in diameters of first ferrule20A and second ferrule20B. The misalignment yields poor optical coupling between the optical fibers42A,42B even if there is no fiber core misalignment with the ferrule. For the purpose of the discussion herein with respect toFIGS. 13A and 13B, it is assumed that there is no fiber core misalignment with the ferrule unless otherwise stated. However, it is within the scope of the present disclosure that there may also be fiber core misalignment with the ferrule as discussed herein.

As shown inFIG. 13B, micro-protuberances370′ positioned along outer surface26B of ferrule20B can increase the diameter R2of ferrule20B and reduce or eliminate the difference in diameters between ferrules20A,20B. As a result and as shown, the alignment between both the ferrules20A and20B and the optical fibers42A and42B is improved and thus, the optical coupling within sleeve210is also improved. Stated another way, micro-protuberances370′ increase the diameter R2of the second ferrule20B, which reduces the mismatch between the core of fiber42B in the second ferrule20B relative to the core of fiber42A in the first ferrule20A thereby improving the optical coupling between ferrules20A,20B and the respective optical fibers42A,42B by at least 0.01 decibels (dB). In one embodiment, the resulting offset/mismatch between the core of fiber42A and the core of fiber42B within sleeve212is between 0 μm and 3 μm. In another embodiment, both the diameters R1, R2of first ferrule20A and second ferrule20B are increased (via the addition of micro-protuberances370′) to improve/reduce misalignment between the ferrules20A,20B. In yet another embodiment, the diameters R1, R2of first ferrule20A and second ferrule20B are increase to a predetermined value. It is contemplated and within the scope of the present disclosure that the respective diameters and core alignments of ferrules20A,20B may be measured and/or altered either prior to insertion of ferrules20A,20B within sleeve210or after insertion of ferrules20A,20B within sleeve210.

In another embodiment, the cores of fibers42A,42B are off-center with respect to the respective ferrules20A,20B (in which fibers42A,42B are housed) and ferrules20A,20B are also misaligned/mismatched with each other (due to the difference in diameters R1, R2). In this embodiment, one or both ferrules20A,20B may be reshaped by creating craters372(FIGS. 10B, 11) and micro-protuberances370′ on the respective outer surfaces26A,26B of ferrules20A,20B. In this way, the outer diameters of ferrules20A,20B are increased such that the offset of fibers42A,42B with respect to the centers of ferrules20A,20B is reduced. Also, the increase in diameters R1, R2via craters372and micro-protuberances370′ reduce the offset between ferrule20A and ferrule20B within sleeve210as previously described.

As shown inFIGS. 14A, 14B, micro-protuberances370′ can also bring the center of the fiber core46closer to alignment with a center30A of sleeve210(i.e., reducing the eccentricity of fiber core46relative to the center30A of sleeve210) when ferrule20is received in sleeve20. As shown inFIG. 14A, a first micro-protuberance370′ is positioned within slot212of sleeve210, and fiber core46is misaligned with center30A. To align fiber core46with center30A, an additional micro-protuberance370′ is created along outer surface26and spaced apart from the first micro-protuberance370′ by a distance that is larger than the opening dimension of slot212. The additional micro-protuberance370′ engages with sleeve210and repositions fiber core46relative to center30A to offset the previous alignment difference between fiber core46and center30A. It is contemplated that variations in micro-protuberance pattern along the outer surface26of ferrule20and/or polishing may also be used to alter the physical properties of (e.g., geometrical relationships between) the micro-protuberances370′, fiber core46, ferrule20, etc. (e.g., reducing the height of micro-protuberances370′ to bring the center of fiber core46closer to the true center30A of sleeve210).

In addition, micro-protuberances370′ can be positioned around outer surface26to increase the diameter of ferrule20and to simultaneously reduce or eliminate misalignment with fiber core46as discussed herein. That is, prior to altering outer surface26of ferrule20(i.e., via crater372and micro-protuberances370), ferrule20may have a core to ferrule concentricity error or concentricity error E as discussed previously with respect toFIGS. 6A and 6B. Once the concentricity error E is measured, a “new” true center30″ (FIG. 12) can be defined by reshaping outer surface26of ferrule20(i.e., via craters372and micro-protuberances370′) to reduce the concentricity error E. In another embodiment, micro-protuberances370′ can be positioned around outer surface26to increase the diameter of ferrule20to a predetermined value to reduce or eliminate misalignment with fiber core46as discussed herein.

In all of the aforementioned examples of selectively shaping outer surface26of ferrule20, experiments can be performed to establish a database of empirical surface shaping data. The data can then be used to establish the rates of change of the surface shape for a given process based on the process parameters, e.g., abrasive roughness, pressure, amount of surface area being treated, laser intensity, time of exposure, wavelength, etc. The database can then be used to select the duration and process parameters to achieve the select surface reshaping required to substantially reduce the concentricity error E to a new concentricity error E′<E, including getting δ′ as small as possible. The reshaped outer surface26′ of ferrule20can be re-measured to confirm that the new concentricity error E′<E. In examples where there is at least one of a circularity tolerance and a diameter tolerance, outer surface26can be measured after reshaping to ensure that one or both of these tolerances are met.

FIG. 9Ais a column plot of the magnitude core-to-ferrule offset δ for before (B), during (D), and after (A) ferrule reshaping us the abrasive belt technique described above in connection withFIG. 8A. The measurements of core-to-ferrule concentricity for the “during material removal” phase D was after 15 material-removal steps, while for the “after material removal” phase A was after 25 material-removal steps. The bar for each measurement phase represent a measurement at an axial position along outer surface26of ferrule20and indicates the improvement in concentricity at the axial position.

FIG. 9Bplots the displacement vector (δ, θ) for the above-mentioned three material removal phases B, D, and A, illustrating how both the magnitude of the displacement δ as well as the displacement direction (angle) changed during the material removal process relative to the true center of the ferrule.

FIG. 9Cis a plot of the insertion loss IL (dB) (horizontal axis) versus the number N of IL measurements (vertical axis) made on a pair of connectors before and after ferrule reshaping (solid and dashed line, respectively), showing an overall reduction in the insertion loss due to the reshaped ferrule.

Reshaping Method Considerations

As noted above, in some embodiments reshaping of ferrule20is subject to the constraint that the circularity and diameter must remain within select tolerances. However, ferrules20could be made to have a slightly larger diameter than normal in anticipation of being reshaped. For example, in some cases it may be easier to process outer surface26over all four quadrants Q1through Q4, with the overall effect including a slight reduction in the overall ferrule diameter to ultimately result in the desired nominal diameter dF and a shape that complies with diameter and circularity tolerances.

In other embodiments, the diameter and/or circularity tolerances may be loosened or for all practical purposes eliminated if the reshaped surface26′ is beyond the usual circularity tolerances but still provides for a reduction in the concentricity error, which in turn may lead to a reduction in insertion loss. For example, a normal circularity tolerance for ferrules having a nominal diameter dF of 1.25 mm or 2.5 mm is 0.5 μm. Thus, in some embodiments, where ferrule20has a nominal diameter dF of 1.25 mm or 2.5 mm, the cross-sectional shape of ferrule20may have a circularity error greater than 0.5 μm, yet have a concentricity error E′ whose magnitude δ′ is small, such as less than 1.2 μm, less than 0.6 μm, or even less than 0.3 μm. The magnitude δ′ of the concentricity error E′ may even be greater than 1.0 in such embodiments.

More generally, the circularity error and concentricity error may be expressed in terms of the nominal diameter dF. A ferrule with poor circularity but good concentricity may be one where: a) the circularity error is greater than 0.04%, or perhaps even greater than 0.08% of the nominal diameter dF; and b) the concentricity error E′ has a magnitude δ′ less than 0.048%, or perhaps even less than 0.012% of the nominal diameter dF.

As alluded to above, outer surface26of ferrule20may be reshaped in all of the quadrants Q1, Q2, Q3, Q4(FIG. 6A) or in less than all of the quadrants. Thus, depending on the particular embodiment, the circularity error of ferrule20may exceed normal circularity tolerances in only one of the quadrants, in only two of the quadrants in other embodiments, in only three of the quadrants, or in all of the quadrants.

The initial outer diameter (i.e., before ferrule reshaping), diameter tolerance, and circularity tolerance are not the only dimensional requirements that may be loosened or for all practical purposes eliminated as a result of reshaped outer surface26′ resulting in low concentricity error E′. The concentricity error of axial bore28, i.e. the offset distance Db(FIG. 6D) of central axis AB from true center30, may alternatively or additionally be loosened or eliminated. For example, for ferrules having a nominal diameter dF of 1.25 mm or 2.5 mm, the offset distance Dbis normally less than 0.3 μm. Thus, in some embodiments where ferrule20has a nominal diameter dF of at least 1.25 mm (e.g., 1.25 mm or 2.5 mm), the offset distance Dbmay be greater than 0.3 μm, greater than 0.5 μm, or even greater than 1.0 μm. The ferrule reshaping process effectively “corrects” this source of concentricity error E so that the new (i.e., post-reshaping) concentricity error E′ has a small magnitude δ′, such as less than 1.2 μm, less than 0.6 μm, or even less than 0.3 μm.

Another example of a dimensional requirement that may be loosened or eliminated is the diameter of the axial bore28. For example, most optical fibers used in telecommunication applications have a bare glass nominal diameter of 125 μm. In other words, the cladding that surrounds the core and defines an outer surface of the bare glass optical fiber has a nominal diameter of 125 μm. Ferrule bores are designed to closely receive such optical fibers to reduce the potential for offset between the optical fiber and the central axis AB (noted above as one of the primary sources of concentricity error E). In particular, ferrule bores normally have diameters less than 128 μm, with diameters closer to 125 μm (e.g., 125 μm) generally considered to be more ideal. With this in mind, in embodiments where optical fiber42—or more specifically, bare fiber section40—have a nominal diameter of 125 μm, axial bore28may have a diameter that is at least 128 μm, or perhaps even at least 130 μm. Although the large diameter of axial bore28increases the potential for concentricity error E, the ferrule reshaping process can effectively be used as a correction mechanism for this source of error, similar to the preceding paragraph.

As can be appreciated, any combination of the above-mentioned dimensional requirements may be relaxed or eliminated by the ferrule reshaping process. This, in turn, may result in new ferrule shapes or designs having one or more attributes normally considered to be unacceptable.

Additionally, as mentioned above, any reshaping approach or combination of reshaping approaches may be used. For example, some methods may include removing material from one portion of outer surface26while enlarging another portion of the outer surface (e.g., by way of forming protuberances370from localized expansion or by adding material). It is possible that a given reshaping process overshoots or undershoots a target surface profile. In this case it is possible to apply a different reshaping process to correct the surface profile to achieve a desired concentricity error E. For example, the laser irradiation process described above could create protuberances370that are too high. The protuberance heights could be reduced by abrasive polishing techniques. In another example, protuberances370can be formed in an area that experienced excessive material removal to bring the local surface profile back to the desired position.

Certain materials (e.g., Fe-doped glasses) have the useful property that protuberances370can be grown and then subsequently reduced in height through application of reduced laser power illumination, with or without applied compression force on the protuberances, such as described in the aforementioned U.S. Pat. No. 8,291,729. This feature could be used to enable oversized protuberances370to be reduced in height using the same laser processing equipment that was used to create them.

Also in an example, protuberances370can be distributed on outer surface26in a specific pattern that avoids some or all of the protuberances being located at the slot202(FIG. 7B) of alignment sleeve210. For example, as mentioned above, the protuberances can be arranged along a certain axial length of ferrule20in a ring-shaped or spiral-shaped pattern, or in an arcuate or axial line.

Although protuberances370are described as being formed by laser system350in the example shown inFIG. 8F, in alternative embodiments one or more protuberances may be formed by adding new material to ferrule body21. Other types of deformations may also be formed by adding new material to ferrule body21. The new material may be the same as or different than the existing material of ferrule body21. Additionally, the new material may be applied and coupled to outer surface26using any suitable technique. For example, the new material may be an adhesive or other material configured to bond to the existing material of ferrule body21, and may be fused, printed, or otherwise deposited on outer surface26.

The ferrule reshaping methods disclosed herein may offer a number of main advantages, which may include: 1) making use of ferrules that would otherwise need to be scrapped; 2) relaxed manufacturing tolerances; and 3) a reduction in the insertion loss, i.e., greater coupling efficiency. Additional advantages may be obtained when a ferrule has a multi-piece construction, like ferrule20inFIGS. 5C and 5D, in that the materials of the ferrule can be selected to facilitate the reshaping process and/or reduce the cost of the ferrule. For example, for ferrule20inFIGS. 5C and 5D, inner member21A may be made from a ceramic or other material designed to meet durability requirements (e.g., ability to withstand a certain number of matings). Outer member21B may be made from a cheaper material (e.g., a metal or polymer material) that can be more easily reshaped. As a result of such a construction and the reshaping process, ferrule20may be lower in cost than conventional ferrules yet have the same or better performance characteristics.

It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. For example, part of the measurement of the concentricity error E is measuring the true center30of ferrule20, as discussed above. And each of the re-shaping techniques involve changing the true center30. The same principles may be applied with the aim of reducing the offset distance Dbof the true center30from central axis AB of axial bore28. Thus, an optical fiber may or may not be present in the axial bore.

Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.