Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
1999-10-28
2003-08-05
Cherry, Euncha (Department: 2872)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
C385S137000, C451S041000
Reexamination Certificate
active
06601996
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to ferrules having a polished front surface and, more particularly, to ferrules having alignment features to facilitate the polishing of their front surfaces following the preassembly of the ferrules into connectors, as well as an associated jig and method for holding a ferrule during polishing operations.
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 demanded by many modem 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 precisely formed to ensure that the front surface is extremely smooth and planar and to minimize any angular errors relative to the optical fiber bores defined by the ferrule. In other words, the front surface of the ferrule is preferably formed to define 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.
Most ferrules are molded from a plastic material. Although the 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 surfaces of the ferrule must generally 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.
With respect to cylindrical single fiber ferrules, the outer diameter of the cylindrical shaft portion of the single fiber ferrule is typically used as the datum. The cylindrical shaft portion of a single fiber ferrule is an effective datum for polishing purposes for at least two reasons. First, the outer diameter of the cylindrical shaft of a single fiber ferrule has a predefined relationship with the longitudinal axis of the optical fiber bore, namely, the longitudinal axes of the optical fiber bore and the cylindrical shaft of the single fiber ferrule are usually coincident. Secondly, the outer diameter of the cylindrical shaft portion of a single fiber ferrule is required to be precisely formed since the outer diameter of the cylindrical shaft of a single fiber ferrule is also utilized to align the optical fiber upon which the ferrule is mounted with another optical fiber during the process of mating a pair of single fiber connectors. In this regard, the outer diameter of the cylindrical shaft portion of a single fiber ferrule is typically formed to within a tolerance of one micron.
In order to polish the front face of the single fiber ferrule, the cylindrical shaft portion of the ferrule is positioned within a precision bore defined by a polishing fixture. As will be apparent, the precision bore has a precise size, such as to within a tolerance of one micron or so, and a predetermined orientation. While the single fiber ferrule is held by the precision bore of the polishing fixture, the front surface of the single fiber ferrule is brought into contact with the polishing media and polished.
While the outer diameter of a ferrule is an effective datum for cylindrical single fiber ferrules, the exterior dimensions of a multifiber ferrule are not generally defined to within such exacting tolerances since the exterior surfaces of a multifiber ferrule are not referenced in the same fashion as the outer diameter of the cylindrical shaft portion of a single fiber ferrule during the interconnection of a pair of multifiber connectors. In this regard, the outer surfaces of most multifiber ferrules are generally only formed to within tolerances of five microns or more. As such, the exterior dimensions of a multifiber ferrule generally cannot serve as a polishing datum.
Since the exterior surface of a multifiber ferrule does not generally serve as a polishing datum, multifiber ferrules must include other features to serve as a polishing datum. In this regard, the shoulder, or at least portions of the shoulder, defined between the shaft of a multifiber ferrule and the enlarged rear portion of a multifiber ferrule typically serves as a polishing datum. In this regard, the shoulder of a multifiber ferrule is typically formed to be within fairly specific tolerances and to have a predefined relationship with respect to the longitudinal axes defined by the optical fiber bores, namely, a perpendicular relationship with respect to the longitudinal axes defined by the optical fiber bores. However, the shoulder of a multifiber ferrule is typically inaccessible once the multifiber ferrule has been assembled within a connector housing of a multifiber connector. As such, the front face of a multifiber ferrule must typically be polished after the multifiber ferrule has been mounted upon the end portions of a plurality of optical fibers, but prior to assembling the multifiber connector. Since the multifiber ferrule must be mounted upon the end portions of a plurality of optical fibers prior to assembling the multifiber connector, multifiber connectors are not typically assembled in the factory, at which time the assembly process could be efficiently performed in an automated fashion. Instead, a multifiber connector is typically assembled in the field once a technician has mounted a multifiber ferrule upon the end portions of a plurality of optical fibers and the front surface of the ferrule has been polished. As such, polishing the front surface of a multifiber ferrule prior to assembling the multifiber connector decreases the efficiency with which the connector can be assembled and is generally a much less cost effective technique for producing multifiber connectors.
While the exterior surfaces of a multifiber ferrule could
Luther James P.
Rosson Joel
Cherry Euncha
Corning Cable Systems LLC
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