Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
1999-12-14
2004-07-13
Robinson, Mark A. (Department: 2872)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
C385S060000, C385S072000
Reexamination Certificate
active
06761489
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to ferrules, molds for forming ferrules and methods for fabricating ferrules and, more particularly, to a ferrule having first and second ferrule body portions that have different nominal widths and an associated mold and fabrication method.
BACKGROUND OF THE INVENTION
Optical fibers are utilized for a variety of applications, including data transmission and the like. In order to interconnect the optical fibers, fiber optic connectors are mounted upon the end portions of the optical fibers, and pairs of the fiber optic connectors are thereafter mated. In order to provide an optical connection with the relatively low attenuation and the small return loss now demanded by many applications, fiber optic connectors are generally designed such that fiber-to-fiber contact is established between the optical fibers upon which the respective fiber optic connectors are mounted. For example, fiber-to-fiber contact is preferably established between each optical fiber of a first fiber optic cable upon which a first fiber optic connector is mounted and the respective optical fibers of a second fiber optic cable upon which a second fiber optic connector is mounted, once the first and second fiber optic connectors have been mated.
In order to establish fiber-to-fiber contact, the front surface of the ferrule of each fiber optic connector must be extremely smooth and planar and must only have minimal, if any, angular errors relative to the optical fiber bores defined by the ferrule. In other words, the front surface of the ferrule preferably defines a planar surface that extends perpendicular to the longitudinal axes of the optical fiber bores. By way of example, the front face of most ferrules must generally have an angular error of less than 0.2° relative to the optical fiber bores to ensure that the optical fibers upon which the ferrule is mounted can be brought into dry physical contact with the optical fibers of another fiber optic connector.
Although ferrules are typically molded to within relatively specific tolerances, the front surfaces of the ferrule are generally unable to be molded to have a sufficiently smooth front surface and to have a sufficiently small angular error. As such, the front surface of the ferrule must typically be polished after the ferrule has been mounted upon the end portions of the optical fibers. Not only does the polishing serve to smooth the front surface and to reduce the angular error of the front surface of the ferrule to within acceptable limits, such as less than 0.2°, but the polishing also serves to ensure that the ends of the optical fibers are properly positioned relative to the front surface of the ferrule, such as by either being flush with the front surface of the ferrule or by protruding by a predetermined amount relative to the front surface of the ferrule.
The front face of the ferrule is generally polished to have a predetermined angular relationship, such as 90°, with respect to the longitudinal axes of the optical fiber bores defined by the ferrule. Since the longitudinal axes of the optical fiber bores are inaccessible for use as a reference point or datum during polishing operations, ferrules are typically designed to have some other reference point or datum that has a predefined positional or angular relationship with respect to the longitudinal axes of the optical fiber bore. As such, the polishing of the front face of the ferrule can be done with respect to the datum that is accessible in order to appropriately polish the front face of the ferrule relative to the longitudinal axes of the optical fiber bores. In this regard, multifiber ferules having a substantially rectangular shape in lateral cross-section, such as an MT ferrule, generally include a shoulder between the ferrule shaft and the enlarged rear portion that serves as the datum for polishing purposes.
In order to take advantage of the efficiencies introduced by the factory assembly of the connectors, it is increasingly desired to polish the front face of the ferrule after the ferrule has been preassembled into a connector. Thus, the datum preferably remains accessible even after the ferrule has been assembled into a connector. As such, the connector can be efficiently assembled and the front face of the ferrule can still be polished after mounting the connector upon end portions of a plurality of optical fibers in the field. Unfortunately, the ferrule shoulder that serves as the datum for rectangular multifiber ferules is generally inaccessible once the connector has been assembled, thereby limiting the preassembly of connectors having rectangular multi fiber ferrules.
A significant portion of the shaft of a rectangular multifiber ferrule is typically accessible even after preassembly of the connector. Thus, consideration has been given to using the exterior surfaces of the shaft portion of a rectangular multifiber ferrule as the datum for polishing purposes, much like the outer diameter of a cylindrical ferrule serves as the polishing datum. Unfortunately, the exterior dimensions of a rectangular multifiber ferrule, cannot generally be defined to within small enough tolerances, such as +/−5 microns, in order to effectively serve as a datum. In this regard, the exterior surfaces of a rectangular multifiber ferrule cannot be formed to within the exacting tolerances required for a polishing datum due to limitations in the molding process.
Rectangular multifiber ferrules are generally formed by injecting a plastic material, such as a thermoplastic or thermoset material, into a mold cavity defined by a pair of mold halves or components that mate along a parting line. Although the mold components can be formed of different materials, the mold components are typically formed of steel, such as D2 steel or stainless steel. The mold cavity as well as the resulting rectangular multifiber ferrule have a nominal thickness and a nominal width. Typically, the thickness of the rectangular multifiber ferrule can be defined to be within a very tight tolerance, such as to within 50 microns, of the nominal thickness during the initial fabrication of the mold. In this regard, the mold components are generally formed by an Electrical Discharge Machine (EDM) that cuts a steel workpiece with a wire. While forming the mold components by cutting a steel workpiece with a wire is efficient, the resulting mold components cannot generally be defined within tight enough tolerances, such as +/−5 microns, to form parts that can serve as a datum during subsequent polishing operations. Thus, the mold components are typically further processed by removing mold material at the parting line of the mold until the thickness of the mold cavity is equal to the desired nominal thickness. For example, mold material is commonly removed from the parting line by a grinding process that is quite accurate.
Unfortunately, the width of a rectangular multifiber ferrule cannot be defined as precisely as the thickness according to conventional fabrication techniques. In this regard, inaccuracies in the width of a rectangular multifiber ferrule generally stem from two different causes. First, the width of the mold cavity as formed by the first and second mold components is not typically defined as precisely as the thickness of the mold cavity. In this regard, even though the mold can be formed such that the mold cavity is slightly undersized, it is relatively difficult to remove mold material from within the portions of the mold cavity defined by the first and second mold components so as to broaden the mold cavity until the actual width of the mold cavity approaches the desired nominal width.
In addition, the second cause for inaccuracies in the width of a rectangular multifiber ferrule stems from offsets that may occur in mating the pair of mold components along the parting line in order to define the mold cavity. In order to reduce the offset between the mold components, the mold is generally keyed such that a pin protruding from one mold co
Dean, Jr. David L.
Malanowski Alan J.
Amari Alessandro
Corning Cable Systems LLC
Robinson Mark A.
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