Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Reexamination Certificate
2000-11-06
2004-06-01
Glick, Edward J. (Department: 2882)
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
C385S052000
Reexamination Certificate
active
06742936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical fiber connectors and a method for orienting the optical fiber within the bore of a ferrule of a fiber optic connector to create a population of ferrules and connectors with improved mating characteristics.
BACKGROUND OF THE INVENTION
Optical fibers are widely used in a variety of applications, including the telecommunications industry. For example, optical fibers not only serve as a medium for long distance signal transmission, but are being increasingly routed directly to the home or, in some instances, directly to the desk or another work location.
With the increasing use of optical fibers, an efficient means of coupling fibers, such as to other optical fibers, to a patch panel in the central office or office building, or to various remote terminals or pedestals is required. However, in order to efficiently couple the signals transmitted by the respective optical fibers, an optical fiber connector must not significantly attenuate or alter the transmitted signals.
A number of factors affect the performance of mated optical fiber connectors. These include surface finish of the optical fiber in the connector and the alignment of the optical fiber of one connector with the optical fiber of a second connector and, more specifically, the alignment of the cores of the respective fibers. The loss or attenuation of an optical fiber with a 50 micrometer core diameter due to surface reflection is about 0.3 dB and is also about 0.3 dB due to offset, or lateral displacement. See Y. Koyama et al., Development and Application of Precision Optical Fiber Connectors, Bull. Japan Soc. of Prec. Eng., Vol. 15, No. 3 (Sep. 1981). Various methods, including mechanical polishing alone or in combination with laser polishing as are well-known in the art, have been developed to improve the surface finish of the fiber, thereby reducing attenuation as shown, for example, in U.S. Pat. No. 5,317,661 to Szentesi et al. Developing efficient and economical methods to minimize lateral displacement of mated fiber cores with respect to each other has been, however, more elusive.
Lateral displacement or offset of fiber cores of mated connectors results from the contribution of three factors: (1) eccentricity of the ferrule bore with respect to the ferrule's outside surface, (2) eccentricity of the fiber core relative to the fiber cladding, and (3) differences in the outside diameter of the fiber and the inside diameter of the bore of the ferrule in which the fiber is set. While the quality of ferrules has improved over time, ferrules are not perfectly concentric, i.e., the central axis of the cylindrical bore does not coincide with the central axis of the outside surface of the ferrule. Furthermore, the degree of eccentricity varies in a large population of ferrules, some being more eccentric, i.e., less concentric, than others. Similarly, the inside diameter of the ferrule bores in a large population of ferrules varies within certain limits, about 125.0-126.0 &mgr;m, so that the fiber does not fit tightly within the ferrule bore, thereby adding to the overall lateral displacement of the core of the optical fiber relative to the outside of the ferrule. Of three factors discussed above, the eccentricity of the fiber core relative to the cladding is the least significant contributing factor to overall eccentricity of the fiber optic connector.
An early method of minimizing overall connector eccentricity, i.e., centering the fiber within the ferrule, is disclosed by N. Suzuki et al., “A New Demountable Connector Developed For A Trial Optical Transmission System, p. 351-354, IOOC 1977. This method involved minimizing the eccentricity of connectors comprised of a fiber, a stainless steel plunger, a glass tube, and a stainless steel pivot. The plunger is machined and polished to a outside diameter of 2.499 mm with a 0.001 mm accuracy and a roundness of 0.6 microns. Unlike ferrules presently being used, however, the plunger has a large bore for receiving the stainless steel pivot. The optical fiber is inserted in a glass tube filled with epoxy resin. The glass tube is then inserted into the stainless steel pivot which is also filled with epoxy resin. After the epoxy is cured, the pivot is polished. Using a microscope, TV camera and monitor, V groove or V block, micromanipulator, and dummy plunger (alignment jig), the fiber is centered inside the plunger with respect to the outside surface of the plunger. First, the jig is placed in the V groove and positioned using the micromanipulator so that by rotating the jig, markers on the jig trace concentrically along a target circle drawn on the screen. The connector plunger then replaces the dummy plunger in the V groove, and the pivot containing the optical fiber is inserted into the plunger. The pivot is then moved by the micromanipulator until the core of the fiber is centered in the target circle on the monitor, thereby positioning the fiber at the center of the plunger. This method is expensive, time consuming, and not suitable for mass production of connectors.
Another example is U.S. Pat. No. 4,880,291, entitled “Optical Fiber Connector and Methods of Making.” That patent discloses two ferrules to be used in a connector that are provided from contiguous portions of the same tubular preform. Prior to separation of the ferrules from the preform, the free end portion of each ferrule (called plugs in the patent) is mounted in a connector body. The connectors are provided with a tab and the connectors are attached to the ferrules so that tabs are aligned longitudinally. As a result, the end faces of the ferrules that were once contiguous can then be aligned longitudinally when mated and the fibers in the ferrules will also be aligned. However, this method does not allow for alignment of ferrules that are not from the same preform. These connectors also require that the installers keep the connectors paired to each other. If one connector is bad or must be changed, then both connectors must be discarded/changed. This increases not only the costs, but the number of paired connectors the installers must carry at each job site.
Other methods have attempted to center the optical fiber within the ferrule differently. For example, one method, disclosed by G. Khoe in “Single-Mode Fiber Connector Using Core-Centered Ferrules”, IEEE Transactions On MicroWave Theory And Techniques, Vol. MT-30, No. 10, October 1982, is to first glue the fiber into a ferrule without regard to the position of the fiber relative to the outer surface of the ferrule. A special lathe, comprising a micromanipulator, an optical alignment system, and a diamond cutter, is then used to cut down the ferrule outer surface until the fiber is centered within the ferrule. Again, this method is not cost-effective, nor suited to mass production.
More recent assembly methods have focused on assembling the optical fiber within the ferrule, and then orienting the resulting total offset relative to a key on the ferrule. Because the eccentricity errors are positioned randomly, these errors can result in very high total offset, i.e., the eccentricity of the ferrule bore relative to the outer surface of the bore and the eccentricity of the optical fiber relative to the bore may be oriented in the same direction resulting in a large offset of the fiber relative to the outer surface of the ferrule. The attenuation of the signal introduced by the offset is somewhat reduced when mating the connector with a second connector by mating the connectors in various orientations until the lowest attenuation is achieved. This process is expensive and is limited in effectiveness by the size of the resulting offset distribution. The typical connector alignment hardware is capable of only coarse adjustments (typically 90° to 180°) that make it difficult and expensive to obtain maximum performance from the fiber optic connector. Furthermore, the process of determining the offset by repeated mating and de-mating results in wear and tear on the connector.
Alternative
Knecht Dennis M.
Luther James P.
Szentesi Otto I.
Corning Cable Systems LLC
Glick Edward J.
Kao Chih-Cheng Glen
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