WO2020081428A1

WO2020081428A1 - Ferruled fiber optic connectors and methods for positioning optical fibers in ferrules

Info

Publication number: WO2020081428A1
Application number: PCT/US2019/056061
Authority: WO
Inventors: Zhenghui Zhang; Michael Jay Follingstad; Hang Li; Zongsheng Leng; Long XIE
Original assignee: Commscope Technologies Llc
Priority date: 2018-10-15
Filing date: 2019-10-14
Publication date: 2020-04-23
Also published as: CN111045157A

Abstract

Fiber optic connectors including ferrules and fibers terminated at the ferrules, and methods of manufacturing the same. The fibers are arranged in the ferrules such that distal end portions of the fibers are biased opposite a direction of offset between the ferrule central axis and the central axis of the fiber hole defined by the ferrule. The fibers and ferrules are processed such that distal ends of the post-processed fibers are substantially centralized at the distal end faces of the ferrules.

Description

FERRULED FIBER OPTIC CONNECTORS AND METHODS FOR

POSITIONING OPTICAL FIBERS IN FERRULES

Cross-Reference to Related Application

This application is being filed on October 14, 2019 as a PCT International Patent Application and claims the benefit of Chinese Patent Application No. 201811193480.2, filed on October 15, 2018, the disclosure of which is incorporated herein by reference in its entirety.

Field

The present invention generally relates to ferruled fiber optic connectors and methods for positioning optical fibers in ferrules.

Background

Optical signals carrying data propagate through optical fibers between

telecommunications providers and subscribers. At various points along the signal paths, one optical fiber is optically coupled to another optical fiber. For example, an optical fiber in a main cable is optically coupled to an optical fiber in a distribution cable. Optical coupling can be performed in a number of different ways, depending on the

telecommunications equipment involved, where the coupling is performed, and other considerations, such as cost, environmental conditions, ease of installation, where the installation is to take place (e.g., in the field), and so forth.

Examples of optical couplings between optical fibers include splices, ferruled connectors, and ferruleless connectors. Ferruled connectors are common in fiber optic distribution networks. A first fiber is terminated at a distal end face of a ferrule of a first connector, and a second fiber is terminated at a distal end face of a ferrule of a second connector. Each ferrule includes a hole extending axially from a proximal end of the ferrule to the distal end face. The hole is open at both ends, and the fiber is distally inserted therein. In some examples, an adhesive is injected in the hole to affix the fiber to the ferrule. The end of the fiber at the distal end face of the ferrule can be cleaved and/or polished to improve optical transmission between the tip of the first fiber and the tip of the second fiber.

In some examples, one or both of the ferrules is axially spring loaded in its respective connector housing. The distal end faces of the ferrules and the fiber tips interface by loading the connectors in opposing ends of an adapter. Interfacing of the ferrules in this way provides for an optical coupling between the first fiber and the second fiber, whereby optical signals are transmitted from the first fiber to the second fiber and vice versa.

Signal transmission loss at ferrule-to-ferrule interfaces is a common problem. A major cause of transmission loss is misalignment of the first fiber relative to the second fiber at the ferrule-to-ferrule interface. Misalignment can occur due to manufacturing imprecision and inconsistencies. Generally, the more consistently precise is a fiber-ferrule- alignment, the higher the manufacturing cost. Thus, there is a need to provide low-cost fiber misalignment compensation in relatively low precision ferrules.

Summary

In general terms, the present disclosure is directed to methods for reducing optical transmission loss at ferrule-to-ferrule interfaces. One or more of the methods of the present disclosure provide for improved optical signal transmission between a first optical fiber terminated at a first ferrule and a second optical fiber terminated at a second ferrule by improving the alignment between the first and second fibers where the distal end faces of their respective ferrules interface.

While the specific embodiments described herein will be described in reference to single fiber ferrule interfaces, it should be appreciated that principles of the present disclosure may be applied to other configurations, such as multi-fiber ferrules.

The ferrules upon which the methods of the present disclosure are performed may be integrated into any suitable form factor of fiber optic connector. Such connectors may be ruggedized or non-ruggedized, and/or may support single optical fiber connections (e.g., LC connectors, SC connectors) or multiple optical fiber connections (e.g., MPO connectors).

Generally, there are two types of fiber misalignment at ferrule faces. A first misalignment type is lateral misalignment, whereby the central axis of the first fiber is laterally offset from the central axis of the second fiber. A second misalignment type is angular misalignment, whereby the central fiber axes of the first and second fibers intersect at a nonzero angle when the ferrules are optically coupled.

Generally, there are two causes of lateral misalignment. A first contributor of lateral misalignment stems from the position of the fiber within the ferrule hole, since the ferrule hole is slightly wider than the fiber, allowing for some tolerance in fiber position within the ferrule hole. A second, and generally greater, contributor of lateral misalignment stems from the position of the ferrule hole relative to the true axial center of the ferrule and the ferrule end face. Due to manufacturing tolerances and inconsistencies, the axial centers of ferrule holes are often offset from the true axial center of the ferrule.

Thus, it should be appreciated that a pair of fiber tips can be laterally misaligned while angularly aligned, laterally aligned while angularly misaligned, or both laterally and angularly misaligned. If the total misalignment (from both lateral and angular

misalignment) results in more than a maximum predefined signal loss at the ferrule to ferrule interface, the optical coupling of the fibers is not viable or, at the very least, suboptimal. Thus, for a given optical coupling of a first fiber to a second fiber, it should be appreciated that as one type of misalignment (lateral, angular) is reduced, more of the other type of misalignment may be tolerated without rendering the optical coupling unviable.

A typical ferrule that supports an optical fiber having a standard 9pm thick core and a standard 125 micrometers (pm) thick cladding (hereinafter referred to as a“9/125” fiber) surrounding the core will have a fiber hole with a transverse diameter that is in a range from approximately 126 pm to approximately 127 pm. For such fibers, if two of the fibers that are optically coupled at their distal ends are completely angularly aligned, typically the maximum allowable lateral offset between the centers of the fiber cores before the signal loss becomes too great is approximately lpm. For such fibers, if two of the fibers that are optically coupled are completely laterally aligned, typically the maximum angular misalignment between the fibers before the signal loss becomes too great is approximately 0.5 degrees (°).

Certain signal loss reduction techniques may focus on either minimizing or eliminating lateral misalignment or minimizing or eliminating angular misalignment. As a general principle, however, the methods of the present disclosure are not necessarily directed to reducing one or the other type of misalignment, but rather to reduce or minimize the total misalignment caused by the combination of both types of misalignment. Thus, the methods of the present disclosure can, in some examples, provide for optical fibers whose angular misalignments are reduced but not minimized, and whose lateral misalignments are reduced but minimized, while the overall misalignment of the fibers is within an acceptable range.

In some examples, the methods of the present disclosure provide for optical coupling of two fibers (e.g., two 9/125 fibers) that results in signal loss between the fibers that is less than 0.30 decibels (dB), or less than 0.25 dB, or less than 0.20 dB, or less than 0.15 dB, or less than 0.10 dB, or less than 0.09 dB, or less than 0.08 dB, or less than 0.07 dB, or less than 0.06 dB, or less than 0.05 dB, or less than 0.04 dB, or less than 0.03 dB, or less than 0.02 dB, or less than 0.01 dB.

According to certain aspects of the present disclosure, a method of terminating an optical fiber at a ferrule comprises: providing the optical fiber and the ferrule, the fiber being defined by a fiber central axis and having a distal portion ending at a pre-processed distal end of the fiber, the ferrule having a proximal end and a distal end, and being defined by a ferrule central axis, the ferrule including a fiber hole defined by a hole central axis and a wall radially surrounding the hole central axis, the fiber hole extending from the proximal end to the distal end of the ferrule; inserting the distal portion of the fiber in the ferrule hole; biasing the distal portion of the fiber across the ferrule central axis into a biased position; holding the distal portion of the fiber in the biased position; and processing a distal portion of the ferrule and a subportion of the distal portion of the fiber such that the fiber central axis at a post-processed distal end of the fiber at least substantially coincides with the ferrule central axis.

In some examples, the method further comprises injecting a thermosetting material (e.g., an epoxy) into the ferrule hole, wherein the injecting is performed prior to the holding, prior to the biasing, or prior to the inserting. In some examples, the holding comprises allowing the thermosetting material to set.

In some examples, the method further comprises determining an offset direction of the hole central axis relative to the ferrule central axis and, optionally, marking the ferrule with the offset direction. In some examples, the biasing is in a direction that is opposite to the offset direction. In some examples, the biasing causes the optical fiber to contact the wall radially surrounding the hole.

In some examples, a ferrule hub is unitarily constructed with, affixed to, or otherwise assembled to, the ferrule, the ferrule hub comprising a plurality of keys at a plurality of key positions, wherein the method further comprises assigning one of the key positions to correspond to the offset direction of the ferrule hole. In some examples, the method further comprises at least partially assembling a fiber optic connector, wherein the assembling includes radially aligning a keying feature of a connector housing with a position that is substantially 90° radially offset from the offset direction. In some examples,“substantially 90°” means“in a range from about 80° to about 100°” In some examples,“substantially 90°” means“in a range from about 85° to about 95°.” In some examples,“substantially 90°” means“in a range from about 89° to about 91°” In some examples,“substantially 90°” means“in a range from about 89.5° to about 90.5°.” In some examples,“substantially 90°” means“in a range from about 89.9° to about 90.1°.”

In some examples, the biasing is performed by a biasing tool, e.g., a lever.

In some examples, the holding comprises affixing the distal portion of the fiber in the biased position relative to the ferrule hole.

In some examples, the processing comprises cleaving the fiber. In some examples, the processing comprises polishing the fiber and a distal end face of the ferrule. In some examples, the processing comprises removing a section from the distal end of the ferrule, the section having an axial depth in a range from about 5 pm to about 100 pm. In some examples, the axial depth of the removed section is in a range from about 15 pm to about 75 pm. In some examples, the axial depth of the removed section is in a range from about 25 pm to about 65 pm. In some examples, the axial depth of the removed section is in a range from about 35 pm to about 55 pm. In some examples, the axial depth of the removed section is in a range from about 40 pm to about 50 pm. In some examples, the axial depth of the removed section is in a range from about 43 pm to about 47 pm. In some examples, the axial depth of the removed section is in a range from about 44 pm to about 46 pm.

In some examples, the processing causes the fiber central axis at the post-processed distal end of the fiber to be less than 1 pm, less than 0.9 pm, less than 0.8 pm, less than 0.7 pm, less than 0.6 pm, less than 0.5 pm, less than 0.4 pm, less than 0.3 pm, less than 0.2 pm, less than 0.1 pm, less than 0.05 pm, less than 0.02 pm, or less than 0.01 pm from the ferrule central axis.

In some examples, the optical fiber is a first optical fiber and the ferrule is a first ferrule, and the method further comprises: providing a second optical fiber and a second ferrule, the second optical fiber being defined by a fiber central axis and being affixed to a ferrule hole of the ferrule; and optically coupling the first fiber to the second fiber at distal end faces of the first and second ferrules such that an angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than about 0.5°, or less than about 0.4°, or less than about 0.3°, or less than about 0.2°, or less than about 0.1°, or less than about 0.05°, or less than about 0.02°, or less than about 0.01°.

In some examples, the optical coupling is such that a lateral offset between the fiber central axes of the first and second fibers at the distal ends of the first and second fibers is less than 1 pm, less than 0.9 pm, less than 0.8 pm, less than 0.7 pm, less than 0.6 mih, less than 0.5 mih, less than 0.4 mih, less than 0.3 mih, less than 0.2 mih, less than 0.1 mih, less than 0.05 mih, less than 0.02 mih, or less than 0.01 mih.

In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.4° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.8 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.3° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.7 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.3° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.6 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.3° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.5 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.2° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.8 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.2° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.7 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.2° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.6 pm. In some examples, the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.2° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.5 pm.

In some examples, the hole central axis is parallel to and offset from the ferrule central axis.

In some examples, the ferrule central axis extends through the hole central axis, and the hole central axis is offset from the ferrule central axis.

According to further aspects of the present disclosure, a fiber optic connector comprises a ferrule and an optical fiber terminated at the ferrule, the fiber being defined by a fiber central axis, the ferrule having a proximal end and a distal end and being defined by a ferrule central axis, the ferrule including a fiber hole defined by a hole central axis and a wall radially surrounding the hole central axis, the fiber hole extending from the proximal end to the distal end of the ferrule, wherein the hole central axis is laterally offset from the ferrule central axis, and wherein a distal portion of the fiber central axis extending proximally from a distal end of the fiber intersects the ferrule central axis at an oblique angle.

In some examples, the hole central axis is laterally offset from the ferrule central axis in an offset direction, and the fiber optic connector comprises a ferrule hub, the ferrule hub including a hub key (e.g., a radial projection from an outer surface of the hub) that is radially aligned with the offset direction. In some examples, the hub key includes a marking indicating that the hub key is aligned with the offset direction.

In some examples, the fiber optic connector further comprises a connector housing radially surrounding the optical fiber, the ferrule, and the ferrule hub, the connector housing including a connector key (e.g., a radial projection from an outer surface of the housing), the connector key being substantially 90° radially offset from the offset direction of the ferrule hole. In some examples,“substantially 90°” means“in a range from about 80° to about 100°” In some examples,“substantially 90°” means“in a range from about 85° to about 95°.” In some examples,“substantially 90°” means“in a range from about 89° to about 91°” In some examples,“substantially 90°” means“in a range from about 89.5° to about 90.5°.” In some examples,“substantially 90°” means“in a range from about 89.9° to about 90. G.”

A variety of additional aspects will be set forth in the description that follows. The aspects relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based.

Brief Description of the Drawings

The following drawings are illustrative of particular embodiments of the present disclosure and therefore do not limit the scope of the present disclosure. The drawings are not to scale and are intended for use in conjunction with the explanations in the following detailed description. The size and dimensions of certain features depicted in the drawings may be exaggerated to aid illustration. Embodiments of the present disclosure will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

FIG. l is a schematic axial cross-sectional view of an optical coupling between first and second fibers of first and second ferrules, the first and second fibers being laterally misaligned.

FIG. 2 is a schematic axial cross-section of an optical coupling between first and second fibers of first and second ferrules, the first and second fibers being angularly misaligned.

FIG. 3 is a schematic axial cross-sectional view of a ferrule having a fiber hole with a central axis that is laterally offset from the central axis of the ferrule.

FIG. 4 is a schematic distal end view of the ferrule of FIG. 3.

FIG. 5 is a schematic axial cross-sectional view of the ferrule of FIG. 3, including a pre-processed fiber at an unbiased position with respect to the fiber hole.

FIG. 6 is a schematic axial cross-sectional view of the ferrule of FIG. 3, including the fiber of FIG. 5, the fiber being pre-processed and in a biased position with respect to the fiber hole in accordance with the present disclosure.

FIG. 7 is a schematic axial cross-sectional view of the ferrule of FIG. 3, including the fiber of FIG. 5, the fiber being post-processed and in the biased position of FIG. 6 in accordance with the present disclosure.

FIG. 8 is a process flow of an example method in accordance with the present disclosure.

FIG. 9 is a schematic axial cross-sectional view of an optical coupling between first and second fibers of first and second ferrules that have been processed according to methods of the present disclosure.

FIG. 10 is a schematic view of the optical coupling between the first and second fibers of FIG. 9, including ferrule hubs assembled to the ferrules.

FIG. 11 is a schematic view of the optical coupling between the first and second fibers of FIG. 9, including connector housings assembled to the ferrule hubs of FIG. 10.

FIG. 12 is a schematic end view of one of the assemblies of a connector housing, ferrule hub, ferrule, and fiber of FIG. 11.

FIG. 13 is a schematic representation of an example fiber biasing apparatus that can be used to bias the pre-processed fiber of FIG. 6 to the biased position shown in FIG. 6 Detailed Description

Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention.

FIG. l is a schematic axial cross-sectional view of an optical coupling between first and second fibers 100, 200 of first and second ferrules 102, 202, the first and second fibers 100, 200 being laterally misaligned.

Referring to FIG. 1, the ferrules 102, 202 are defined, respectively, by central axes 108, 208 and have, respectively, a distal end face 104, 204 and a fiber hole 106, 206 that is radially surrounded by a wall 110, 210. In some examples, the ferrules 102, 202 are substantially cylindrical bodies defined by their central axes 108, 208. The ferrules 102, 202 can be made of any suitable material or materials, e.g., ceramic and/or metal. The fiber hole 106, 206 is defined by a central axis 112, 212, respectively. In some examples, the fiber holes 106, 206 are tubular bores defined by their central axes, 112, 212. The optical fibers 100, 200 extend through the respective fiber holes 106, 206 and interface where the distal end faces 104, 204 of the ferrules 102, 202 meet. Optionally, one or both of the ferrules 102, 202, is axially distally biased (e.g., by a spring) to provide sufficient optical coupling between the optical fibers where the end faces 104, 204 meet. Such a spring can be captured in a spring seat received in a housing of a fiber optic connector that houses the ferrule 101, 102.

As shown, the central axes 112, 212 of the fiber holes 106, 206 are laterally offset from ferrule central axes 108, 208, respectively. This lateral offset is denoted OS in FIG.

1, and the offset direction is denoted by the arrows 109, 209. The lateral offset OS can contribute to signal loss between the optical fibers 100, 200 since the true center of the ferrule does not correspond to the true center of the fiber hole.

Each fiber 100, 200, is defined by a central axis 114, 214, respectively. In some examples, the fibers 100, 200 include a single central core surrounded by a cladding. In some examples, the fibers 100, 200 are 9/125 fibers. In other examples, the fibers can be multi-element fibers (e.g., ribbonized fibers with each fiber surrounded by its own cladding) or multi-core fibers (with all cores surrounded by the same cladding). Optical coupling generally occurs at the interface between the fibers’ distal end faces 116, 216, with optical signals propagating from one of the fibers to the other fiber via the distal end faces 116, 216. To achieve the needed interfacing between the fibers, the ferrules 102, 202 can be assembled as parts of fiber optic connectors (not shown) that can be connected to each other using a fiber optic adapter (not shown).

As shown in the example in FIG. 1, the central axes 114, 214 of the fibers 100, 200 are parallel to each other and laterally offset from each other. Because the central axes 114, 214 are parallel to each other, there is no angular misalignment between the fibers 100, 200 and, consequently, there is no signal transmission loss that would otherwise result from angular misalignment. However, there can be signal transmission loss due to the lateral misalignment of the fibers 100, 200, i.e., due to the lateral offset between the central axes 114, 214 of the fibers 100, 200. In FIG. 1, the amount of lateral misalignment or lateral offset is denoted as LMA. Generally speaking, the greater the amount of LMA, the greater the signal transmission loss. If the LMA is too great, even without any angular misalignment, the optical coupling between the fibers 100 and 200 can be nonviable due to the amount of signal loss.

FIG. 2 is a schematic axial cross-section of an optical coupling between first and second fibers 100, 200 of first and second ferrules 102, 202, the first and second fibers being angularly misaligned. Many of the structures and features of the optical coupling of FIG. 2 are the same as in FIG. 1 and so will not be repeated.

In the optical coupling represented in FIG. 2, there is no lateral offset between the fiber central axes 114, 214 at the fiber end faces 116, 216. Thus, there is zero lateral misalignment between the fibers 100, 200. However, the fiber central axis 114 is not parallel to the fiber central axis 214 at the end faces 116, 216. More specifically, at the end faces 116, 216, the fiber central axes 114, 214 intersect at an oblique angle, resulting in non-zero angular misalignment between the fibers 100, 200. Generally speaking, the greater the amount of angular misalignment, the greater the signal transmission loss. If the angular misalignment is too great, even without any lateral misalignment, the optical coupling between the fibers 100 and 200 can be nonviable due to the amount of signal loss.

It should be appreciated that an optical coupling of fibers can have both lateral and angular misalignment, the effects of which on signal loss can be cumulative. Thus, it is important to control both angular and lateral misalignment. Referring now to FIGS. 3-4, a pre-processed ferrule 111 is shown before an optical fiber has been inserted into the fiber hole 106. In FIG. 4, the ferrule 111 extends proximally into the page, and has a cylindrical shape and a round pre-processed distal end face 122. In FIG. 4, the ferrule central axis 108 extends into the page, and the fiber hole central axis 112 extends into the page. Although the ferrule central axis 108 is laterally offset from the fiber hole central axis 112, the fiber hole 106 nevertheless encompasses the ferrule central axis 108. That is, the wall 110 radially surrounds the ferrule central axis 108.

FIG. 5 is a schematic axial cross-sectional view of the ferrule 111 of FIG. 3, including a pre-processed fiber 100 at an unbiased position with respect to the fiber hole 106. The fiber 100 has a pre-processed distal end face 120 and the ferrule 102 has the pre- processed distal end face 122. As compared with FIGS. 3-4, the fiber 100 has been distally advanced through the fiber hole 106. Optionally, as shown, a distal portion of the pre- processed fiber 100 protrudes beyond the pre-processed distal end face 122 of the ferrule 102. As shown in FIG. 5, the fiber central axis 114 does not intersect the ferrule central axis 108 at any point that axially coincides with a portion of the fiber 100 and the ferrule 102.

FIG. 6 is a schematic axial cross-sectional view of the pre-processed ferrule 111 of FIG. 3, including the pre-processed fiber 100 of FIG. 5, the fiber 100 being in a biased position with respect to the fiber hole 106 relative to the unbiased position of the fiber 100 in FIG. 5. In particular, compared with FIG. 5, the fiber 100 has been biased towards the ferrule central axis 108 such that the fiber central axis 114 intersects the ferrule central axis 108 at a point P. The point P lies on a reference line RL that is perpendicular to and intersects the ferrule central axis 108. The point P is positioned proximally from the pre- processed distal end face 122 of the ferrule 111. The point P also lies within the fiber hole 106 and is distanced from the wall 110. Before the fiber and ferrule processing, the results of which are illustrated in FIG. 7, the pre-processed fiber 100 of FIG. 6 can be held and/or affixed (e.g., mechanically, or with an epoxy or other thermosetting material injected into the fiber hole 106) in the biased position shown in FIG. 6 in which the fiber central axis 114 intersects the ferrule central axis 108 within the fiber hole 106. In some examples, as shown in FIG. 6, the biasing is sufficient such that in the biased position, the pre- processed fiber 100 contacts the wall 110 that surrounds the fiber hole 106.

FIG. 7 is a schematic axial cross-sectional view of the ferrule of FIG. 3, including the fiber of FIG. 5, the fiber being post-processed and in the biased position of FIG. 6 in accordance with the present disclosure. Referring to FIGS. 6-7, a distal end portion of the pre-processed fiber 100 of FIG. 6 is cleaved and an axial depth D from the distal end of the pre-processed ferrule 111 is removed to obtain the post-processed ferrule 131 of FIG.

7. In some examples, the removal of material includes a polishing process.

In some examples, the axial depth D of removed material is in a range from about 5 pm to about 100 pm. In some examples, the axial depth D is in a range from about 15 pm to about 75 pm. In some examples, the axial depth D is in a range from about 25 pm to about 65 pm. In some examples, the axial depth D is in a range from about 35 pm to about 55 pm. In some examples, the axial depth D is in a range from about 40 pm to about 50 pm. In some examples, the axial depth D is in a range from about 43 pm to about 47 pm. In some examples, the axial depth D is in a range from about 44 pm to about 46 pm.

As shown in FIG. 7, the processed fiber 100 has a distal end 134 and the post- processed ferrule 131 has a post-processed distal end face 132. The distal end portion of the post-processed fiber 100 remains in the biased position such that the ferrule central axis 108 and the fiber central axis intersect or nearly intersect (at the intersection point P) at the distal end 134 of the post-processed fiber 100. In some examples, the processing causes the fiber central axis 114 at the post-processed distal end 134 of the fiber to be less than 1 pm, less than 0.9 pm, less than 0.8 pm, less than 0.7 pm, less than 0.6 pm, less than 0.5 pm, less than 0.4 pm, less than 0.3 pm, less than 0.2 pm, less than 0.1 pm, less than 0.05 pm, less than 0.02 pm, or less than 0.01 pm from the ferrule central axis 108.

Referring now to FIG. 8, an example method 300 of assembling a fiber optic connector in accordance with the present disclosure will now be described.

In a step 302 of the method 300, a ferrule having a fiber hole extending from a proximal end to a pre-processed distal end face of the ferrule is provided, and an offset direction of the fiber hole relative to the central axis of the ferrule is determined and demarcated. In some examples, to determine the offset direction, optical equipment can be used, e.g., a CCD camera. In some examples, if it is determined that the central axis of the ferrule is not within the fiber hole, the ferrule is discarded and the method 300 terminates with respect to the discarded ferrule.

In some examples, the demarcating of the offset direction can be physically manifested. For example, a hub of the ferrule can include a plurality of keys radially projecting in different directions away from the central axis of the ferrule. The hub key that radially projects in the direction that most closely corresponds to the offset direction of the fiber hole can be marked, e.g., with a pen, or with some other indicia (e.g., a nick, a coloration, a removal of the key, or a removal of all of the other keys). In other examples a mark is placed on the exterior surface of the ferrule itself.

In a step 304, a distal end portion of the fiber is biased in a direction that is radially opposite or approximately radially opposite the offset direction determined in the step 302. In some examples, the biasing is performed with a tool, such as a lever. The biasing causes the fiber central axis to intersect and cross over the ferrule central axis. In some examples, the amount of biasing is sufficient to cause the pre-processed fiber to contact the wall surrounding the fiber hole. An example fiber biasing apparatus is schematically depicted in FIG. 13 and is described below.

In a step 306, the fiber is held in the biased position within the ferrule hole. For example, an epoxy or other thermosetting material is injected in the fiber hole of the ferrule and allowed to set or harden with the fiber in the biased position. The

thermosetting material can be injected into the fiber hole before or after the fiber is inserted in the fiber hole, and before or after the biasing step 304.

In a step 308, the ferrule is processed by cleaving a distal end portion of the biased fiber and removing material (e.g., by polishing or cutting material) from the distal end of the pre-processed ferrule until the fiber central axis at the distal end of the post-processed ferrule substantially coincides with the ferrule central axis at the post-processed distal end face of the ferrule, as shown in FIG. 7.

It should be appreciated that the steps 302 through 308 can be performed on multiple ferrule-fiber assemblies to provide a set of ferrules that are known to have distal fiber ends that are at least substantially centralized on the end faces of the ferrules. Thus, the steps 302 through 308 can provide a set of ferrules that have known, and consistent across the ferrules, lateral positions of the fibers at the ferrule distal end faces.

In a step 310, a fiber optic connector is assembled including the post-processed ferrule and fiber, such that a keying feature of the connector housing is substantially 90° radially offset from the offset direction determined in step 302.

In at least some examples, the substantially 90° radial offset is in a consistent orientation across a set of ferrules processed according to the method 300. For example, looking along the central axis of the ferrule from the distal end face of the ferrule, the substantially 90° radial offset of the housing key is always clockwise or always counterclockwise from the offset direction determined in step 302 across a set of ferrules and fibers processed according to the method 300. The purpose of the 90° offset of the connector housing key will be described below. Referring now to FIGS. 9-12, optical coupling of two fiber-ferrule assemblies processed according to the method 300 of FIG. 8 will now be described.

FIG. 9 is a schematic axial cross-sectional view of an optical coupling between first and second fibers 100, 200 of first and second ferrules 131, 231 that have been processed according to method 300 of FIG. 8.

The two ferrules 131, 231 are shown interfacing at their post-processed distal end faces 132, 232. In some examples, the interfacing would result in the distal end faces 132, 232 abutting each other, which is not shown in the drawings for purposes of aiding illustration. The two ferrules 131, 231 are coaxially aligned, i.e., their central axes 108,

208 are aligned. The fiber central axis 114 of the fiber 100 substantially intersects the ferrule central axis 108 at the post-processed distal end face 132 of the ferrule 131.

Likewise, the fiber central axis 214 of the fiber 200 substantially intersects the ferrule central axis 108 at the post-processed distal end face 232 of the ferrule 231. Thus, there is minimal, if any, lateral misalignment between the post-processed distal ends 134, 234 of the fibers 100, 200.

In addition, due to the orientations of the two fibers 100, 200 relative to the directions of their biasing, there is minimal, if any, angular misalignment between the fibers 100, 200 at their post-processed distal ends 134, 234. That is, the fiber axes 114 and 214 are substantially parallel or aligned.

The optical coupling of FIG. 9 can significantly reduce signal loss at the interface between the fibers 100, 200.

FIG. 10 is a schematic view of the optical coupling between the first and second fibers 100, 200 of FIG. 9, including ferrule hubs 150, 250 assembled to the ferrules 131, 231. For purposes of illustration, the ferrule hubs 150, 250, are not shown in cross-section. It should be appreciated that the fiber holes 106, 206, axially continue through the respective ferrule hubs 150, 250.

The ferrule hubs 150, 250 can be formed integrally with the ferrules 131, 231, or optionally, manufactured separately and affixed to the ferrules 131, 231. The hubs 150, 250 can include a plurality of keys (e.g., radial projections). In the example shown, each hub 150, 250, includes a single key projection 152, 252 which, for each ferrule 131, 231, corresponds to the offset direction of the ferrule central axis 108, 208 relative to the fiber hole central axis 112, 212. The appropriate key 152, 252 or other marker, can be assigned after determining the offset direction of the ferrule central axis relative to the fiber hole central axis. It should be appreciated that, relative to these offset directions, the ferrule 231 is rotated 180° relative to the ferrule 131 to allow the fibers and distal end faces of the ferrules to interface.

FIG. 11 is a schematic view of the optical coupling between the first and second fibers 100, 200 of FIG. 9, including connector housings 154, 254 assembled to the ferrule hubs 150, 250 of FIG. 10. For purposes of illustration, the connector housings 154, 254 are not shown in cross-section. It should be appreciated that the fiber holes 106, 206, axially continue through the respective connector housings 154, 254.

Still referring to FIG. 11, the two connector housings 154, 254 are received in opposing receptacles of an adapter 180, which is schematically represented. The adapter 180 holds the connectors 170, 270 in a position that allows optical coupling between the fibers 100, 200. The two connector housings 154, 254, include an adapter keying feature 156, 256. In this example, the keying feature 156, 256 is a projection projecting radially out of the page. The adapter 180 includes keying features 182, 184 configured to receive the keying features 156, 256, such that the connector housings 154, 254 can be inserted into the adapter receptacles in only one rotational orientation relative to the ferrule central axes 108, 208. In this example, the keying features 182, 184 are slots shaped and sized to receive the projections 256. It should be appreciated that, relative to the fiber hole to ferrule center offset directions, the connector 270 is rotated 180° relative to the connector 170 to allow the fibers and distal end faces of the ferrules to interface.

FIG. 12 is a schematic end view of the connector 170 of FIG. 11. The connector 170 includes the housing 154 with adapter keying feature 156, the ferrule hub 150, with keying feature 152, and the processed ferrule 131 having the fiber hole 106 and the processed fiber 100. Optionally, the housing 154 defines a keying feature 172 that complements the hub key 152 such that the ferrule 131 can be received in the housing 154 in only one rotational orientation. As shown in FIG. 12, the keying feature 172 is 90° radially offset in a counter-clockwise manner from the keying feature 156 to thereby fix the rotational orientation of the bias of the fiber relative to the keying feature 156 and to minimize angular misalignment when optically coupling the connector 170 to another connector similarly manufactured (e.g., the connector 270 of FIG. 11).

FIG. 13 is a schematic representation of an example fiber biasing apparatus 400 that can be used to bias the pre-processed fiber 100 of FIG. 6 to the biased position shown in FIG. 6. The apparatus 400 includes a work surface 402. Clamps 404 are affixed to the work surface 402. The pre-processed ferrule is secured on the surface 402 between the clamps 404. Then, a press block or lever 406 resting on the surface 402 is pressed against a side of the fiber 100 protruding from the fiber hole to bias the fiber 100. The ferrule 111 is positioned in the clamps 404 and the press block 406 is positioned and moved such that the fiber is pressed and biased in a direction that is at least substantially radially opposite the direction of the lateral offset between the central axis of the fiber hole and the central axis of the ferrule.

Although in the foregoing description, terms such as“distal” and“proximal” were used for ease of description and illustration in relating features to one another, no restriction on the use of the components and assemblies of this disclosure is intended by such use of the terms.

Having described the preferred aspects and embodiments of the present disclosure, modifications and equivalents of the disclosed concepts may readily occur to one skilled in the art. However, it is intended that such modifications and equivalents be included within the scope of the claims which are appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A method of terminating an optical fiber at a ferrule, comprising:

providing the optical fiber and the ferrule, the fiber being defined by a fiber central axis and having a distal portion ending at a pre-processed distal end of the fiber, the ferrule having a proximal end and a distal end, and being defined by a ferrule central axis, the ferrule including a fiber hole defined by a hole central axis and a wall radially surrounding the hole central axis, the fiber hole extending from the proximal end to the distal end of the ferrule;

inserting the distal portion of the fiber in the ferrule hole;

biasing the distal portion of the fiber across the ferrule central axis into a biased position;

holding the distal portion of the fiber in the biased position; and

processing the fiber and the ferrule such that the fiber central axis at a post- processed distal end of the fiber at least substantially coincides with the ferrule central axis.

2. The method of claim 1, further comprising:

injecting a thermosetting material into the ferrule hole,

wherein the injecting is performed prior to the holding, prior to the biasing, or prior to the inserting.

3. The method of claim 2, wherein the holding comprises allowing the thermosetting material to set.

4. The method of any preceding claim, further comprising:

determining an offset direction of the hole central axis relative to the ferrule central axis and, optionally, marking the ferrule with the offset direction.

5. The method of claim 4, wherein the biasing is in a direction that is opposite to the offset direction.

6. The method of claim 4 or 5, wherein the biasing causes the fiber to contact the wall radially surrounding the hole.

7. The method of any preceding claim,

wherein a ferrule hub is unitarily constructed with, affixed to, or otherwise assembled to, the ferrule, the ferrule hub comprising a plurality of keys at a plurality of key positions,

wherein the method further comprises:

assigning one of the key positions to the offset direction, the assigned key position being radially aligned with the offset direction, or radially offset from the offset direction by substantially 90°.

8. The method of claim 7, further comprising assembling the ferrule hub to the ferrule such that at least one of the key positions is radially aligned with, or substantially 90° radially offset from, the offset direction of the ferrule hole.

9. The method of claim 4, further comprising at least partially assembling a fiber optic connector, wherein the assembling includes radially aligning a keying feature of a connector housing with a position that is substantially 90° radially offset from the offset direction.

10. The method of claim 9, wherein the radially aligning the keying feature of the connector housing is in a range from about 89° to about 91° from the offset direction.

11. The method of any preceding claim, wherein the holding comprises affixing the distal portion of the fiber in the biased position relative to the ferrule hole.

12. The method of any preceding claim, wherein the processing comprises cleaving the fiber.

13. The method of any preceding claim, wherein the processing comprises polishing the fiber and a distal end face of the ferrule.

14. The method of any preceding claim, wherein the processing comprises removing a section from the distal end of the ferrule, the section having an axial depth in a range from about 40 pm to about 50 pm.

15. The method of claim 14, wherein the axial depth of the removed section is in a range from about 43 pm to about 47 pm.

16. The method of any preceding claim, wherein the processing causes the fiber central axis at the post-processed distal end of the fiber to be less than less than 0.05 pm from the ferrule central axis.

17. The method of any preceding claim, wherein the processing causes the fiber central axis at the post-processed distal end of the fiber to be less than less than 0.01 pm from the ferrule central axis.

18. The method of any preceding claim, wherein the hole central axis is parallel to the ferrule central axis.

19. A fiber optic connector partially assembled according to the method of any preceding claim.

20. The method of any preceding claim, wherein the optical fiber is a first optical fiber and the ferrule is a first ferrule, and the method further comprises:

providing a second optical fiber and a second ferrule, the second optical fiber being defined by a fiber central axis and being affixed to a ferrule hole of the second ferrule; and optically coupling the first fiber to the second fiber at distal end faces of the first and second ferrules such that an angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than about 0.1°.

21. The method of claim 20, wherein the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than about 0.02°.

22. The method of claim 20 or 21, wherein the optical coupling is such that a lateral offset between the fiber central axes of the first and second fibers at the distal ends of the first and second fibers is less than 0.1 pm.

23. The method of claim 22, wherein the lateral offset between the fiber central axes of the first and second fibers at the distal ends of the first and second fibers is less than 0.02 mih.

24. The method of any of claims 20-23, wherein the optical coupling is such that the angle between the fiber central axis of the first fiber and the fiber central axis of the second fiber is less than 0.2° and the lateral offset between the fiber central axes of the first and second fibers is less than 0.5 pm.

25. A fiber optic connector comprising:

a ferrule; and

an optical fiber terminated at the ferrule, the fiber being defined by a fiber central axis, the ferrule having a proximal end and a distal end and being defined by a ferrule central axis, the ferrule including a fiber hole defined by a hole central axis and a wall radially surrounding the hole central axis, the fiber hole extending from the proximal end to the distal end of the ferrule, wherein the hole central axis is laterally offset from the ferrule central axis, and wherein a distal portion of the fiber central axis extending proximally from a distal end of the fiber intersects the ferrule central axis at an oblique angle.

26. The fiber optic connector of claim 25, wherein the hole central axis is laterally offset from the ferrule central axis in an offset direction, and the fiber optic connector comprises a ferrule hub, the ferrule hub including a hub key that is radially aligned with the offset direction.

27. The fiber optic connector of claim 26, wherein the hub key includes a marking indicating that the hub key is aligned with the offset direction.

28. The fiber optic connector of any of claims 25-27, wherein the fiber optic connector further comprises a connector housing radially surrounding the optical fiber and the ferrule, the connector housing including a connector key, the connector key being substantially 90° radially offset from the offset direction of the ferrule hole.