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Fiber optic connector for applying axial biasing force to multifiber ferruleRelated Patent Categories: Optical Waveguides, With Disengagable Mechanical Connector, Structure Surrounding Optical Fiber-to-fiber Connection, Multi-part (e.g., Two Pieces Screwed Together Or Bayonet Latched), With Additional Structure Rearward Of Fiber Joint To Secure Additional Cable LayersFiber optic connector for applying axial biasing force to multifiber ferrule description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060239619, Fiber optic connector for applying axial biasing force to multifiber ferrule. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates generally to fiber optic connectors, and more particularly, to a fiber optic connector including a multifiber ferrule and means for applying an axial biasing force to the ferrule. [0002] The proliferation of optical communications and data transfer has dramatically increased the use of fiber optic connectors including multifiber ferrules for simultaneously interconnecting a plurality of optical fibers. Not only are multifiber connectors being utilized in greater numbers, but increased performance demands are being placed upon the optical connections between mated connectors. As a result, there is an increased demand in optical communications for what has become generally known as "low-loss, intermateable, multifiber connectors." For example, in order to maximize signal transmission between pairs of opposed optical fibers, multifiber connectors are required to align each of the optical fibers very precisely, especially for single mode applications. In this regard, multifiber connectors are typically required to align each optical fiber to within about 7 to 14 microns for multimode applications and to within about 0 to 3 microns for single mode applications. [0003] In order to provide the desired alignment, conventional multifiber ferrules define a pair of elongate alignment holes that receive and cooperate with respective alignment members, such as guide pins, to accurately align opposing ferrules, and in turn, the optical fibers mounted within the multifiber ferrules. For example, one conventional type of multifiber ferrule is the MT (Mechanically Transferable) ferrule, such as described by U.S. Pat. No. 5,214,830 to Sinji Nagasawa, et al., and assigned to Nippon Telephone and Telegraph Corporation of Tokyo, Japan. The MT ferrule has a generally rectangular shape in lateral cross-section and defines a pair of guide pin holes and a plurality of optical fiber bores opening through the end face of the ferrule. The guide pin holes receive respective guide pins to align the optical fibers of a pair of opposing MT ferrules. [0004] The pair of MT ferrules that are to be interconnected are typically configured such that one of the multifiber connectors has a male configuration and the other multifiber connector has a female configuration. The male configuration of the multifiber connector includes a pair of guide pins that have been inserted within the guide pin holes defined by the MT ferrule and extend forwardly beyond the end face. In contrast, the female configuration of the multifiber connector includes an MT ferrule that defines a pair of guide pin holes for receiving the portions of the guide pins that extend beyond the end face of the male MT ferrule. During mating, insertion of the guide pins into the guide pin holes defined by the female MT ferrule aligns the male and female connectors, and in turn, aligns the optical fibers mounted within the MT ferrules. In order to snugly receive the guide pins, the guide pin holes defined by a conventional MT ferrule are cylindrical in lateral cross-section so as to have the same size and shape along their entire length. By utilizing cylindrical guide pin holes, the sidewalls of the guide pin holes contact the guide pins along their entire length, thereby maximizing the alignment provided by the guide pins. [0005] The MT ferrules of the male and female fiber optic connectors are biased towards one another so as to interconnect the optical fibers with a minimum amount of attenuation. It has long been believed that "dry physical contact" (i.e., physical contact between opposing optical fibers without the use of index-matching gel) across all of the pairs of optical fibers of mated multifiber connectors could be achieved by controlling the geometry of the opposing optical fibers and ferrules. However, significant advances in geometry control, such as optimal fiber height, array uniformity, optical fiber angle, core dip and ferrule end face angle, have not consistently resulted in dry physical contact across all of the optical fibers of opposing multifiber connector pairs. Further analysis of the factors preventing dry physical contact of the optical fibers has shown that the force applied to bias the ferrule in the axial direction of the mating ferrule very often produces a moment about a lateral axis of the ferrule. In other words, the biasing force is not always applied along the longitudinal axis of the ferrule, or at the least, is not balanced about the longitudinal axis of the ferrule. [0006] Typically, the biasing force is generated by a coil spring mounted within a connector housing between the rear face of the ferrule and a spring push. An off-axis biasing force oftentimes results because the coil spring buckles within the connector housing and introduces a component of the spring force that is offset from the longitudinal axis of the ferrule, or is applied at an angle other than normal to the end face of the ferrule. Even if the coil spring does not buckle, the geometry and inherent nature of the coil spring makes it likely that an unbalanced biasing force will be applied to the rear face of the ferrule in a direction other than along the longitudinal axis. As a result, the biasing force will apply an undesired moment to the ferrule in addition to the desired axial force. Thus, despite the presence of substantially perfect geometry features in mating optical fibers and ferrules, a biasing force that is not applied along the longitudinal axis of a multifiber ferrule, or is not balanced about the longitudinal axis of a multifiber ferrule, will not consistently produce dry physical contact between a mated pair of fiber optic connectors. SUMMARY OF THE INVENTION [0007] The above described and other deficiencies of conventional fiber optic connectors are addressed and overcome by a fiber optic connector according to the present invention that includes a multifiber ferrule and force centering means for applying an axial biasing force to the ferrule. [0008] In one advantageous embodiment, a fiber optic connector includes a multifiber ferrule having an end face and an opposed rear face. The end face defines a plurality of optical fiber bores opening therethrough for receiving respective optical fibers and the fiber optic connector defines a longitudinal axis that is generally parallel to each of the optical fiber bores. The fiber optic connector further includes at least one force centering element for applying a biasing force to the ferrule in the direction of the longitudinal axis without generating a moment about a lateral axis defined by the end face of the ferrule. The fiber optic connector further includes a coil spring and a spring seat disposed between the coil spring and the ferrule. The spring seat has a forward portion that engages the rear face of the ferrule and a rearward portion opposite the forward portion. The at least one force centering element is disposed medially on the rearward portion of the spring seat in the form of a protrusion that extends outwardly from the rearward portion. The protrusion engages the coil spring that exerts the biasing force on the ferrule and the forward portion engages the rear face of the ferrule to transfer the biasing force to the ferrule. Alternatively, the protrusion may be disposed medially on the forward portion of the spring seat that engages the rear face of the ferrule. The spring seat may also have an arcuate side wall for engaging an interior surface of a connector housing such that the spring seat is movable only in the direction of the longitudinal axis. [0009] In another advantageous embodiment, a fiber optic connector includes a multifiber ferrule having an end face and an opposed rear face. The end face defines a plurality of optical fiber bores opening therethrough for receiving respective optical fibers and the fiber optic connector defines a longitudinal axis that is generally parallel to each of the optical fiber bores. The fiber optic connector further includes at least one force centering element for applying a biasing force to the ferrule in the direction of the longitudinal axis without generating a moment about a lateral axis defined by the end face of the ferrule. The fiber optic connector further includes a coil spring and a spring seat disposed between the coil spring and the ferrule. The end face of the ferrule defines a first lateral axis generally perpendicular to the longitudinal axis and the rear face defines a convex surface in the direction of the first lateral axis. The end face of the ferrule may further define a second lateral axis generally perpendicular to the longitudinal axis and to the first lateral axis and the rear face may further define a convex surface in the direction of the second lateral axis. Alternatively, the forward portion of the spring seat may define a convex surface in the direction of the first lateral axis and may further define a convex surface in the direction of the second lateral axis. [0010] In another advantageous embodiment, a fiber optic connector includes a multifiber ferrule having an end face and an opposed rear face. The end face defines a plurality of optical fiber bores opening therethrough for receiving respective optical fibers and the fiber optic connector defines a longitudinal axis that is generally parallel to each of the optical fiber bores. The fiber optic connector further includes at least one force centering element for applying a biasing force to the ferrule in the direction of the longitudinal axis without generating a moment about a lateral axis defined by the end face of the ferrule. The fiber optic connector further includes a coil spring and a spring seat disposed between the coil spring and the ferrule. The spring seat has a forward portion for engaging the rear face of the ferrule and a rearward portion opposite the forward portion for engaging the coil spring. The ferrule is provided with at least one first force centering element disposed on an exterior surface of the ferrule medially between the end face and the rear face, and the spring seat is provided with at least one second force centering element disposed on the rearward portion. The spring seat may further have at least one transfer arm extending outwardly from the forward portion for transferring a portion of the biasing force to the at least one first force centering element on the ferrule. The end face of the ferrule further defines a first lateral axis perpendicular to the longitudinal axis and a second lateral axis perpendicular to the longitudinal axis and to the first lateral axis. Preferably, the ferrule is provided with a pair of first force centering elements spaced apart laterally in the direction of the second lateral axis and symmetrical about a plane comprising the second lateral axis and the longitudinal axis. Preferably, the spring seat is provided with a pair of second force centering elements spaced apart laterally in the direction of the first lateral axis and symmetrical about a plane comprising the first lateral axis and the longitudinal axis. [0011] In another advantageous embodiment, a fiber optic connector includes a multifiber ferrule having an end face and an opposed rear face. The ferrule further has a plurality of optical fiber bores extending therethrough for receiving the end portions of respective optical fibers adjacent the end face and at least one guide pin hole for receiving a guide pin to align the multifiber ferrule with a mating multifiber ferrule. The guide pin hole defines an axis that is parallel to each of the optical fiber bores and the fiber optic connector defines a longitudinal axis that is generally parallel to the axis defined by the guide pin hole. The fiber optic connector further includes at least one force centering element for applying a resultant biasing force to the ferrule in the direction of the longitudinal axis such that the ferrule is not subjected to a moment about a lateral axis defined by the end face of the ferrule and generally perpendicular to the longitudinal axis. [0012] In another advantageous embodiment, a multifiber ferrule is movably disposed within a fiber optic connector. The multifiber ferrule has an end face, an opposed rear face and a plurality of optical fiber bores extending between the end face and the rear face. The optical fiber bores open through the end face and the end face defines a plane that is generally perpendicular to each of the optical fiber bores. The multifiber ferrule further includes force centering means for exerting a biasing force on the ferrule such that the ferrule moves only in an axial direction that is parallel to each of the optical fiber bores and does not produce a moment about a lateral axis in the plane defined by the end face. The force centering means may be provided in the form of a coil spring and a spring seat disposed between the coil spring and the ferrule with a forward portion of the spring seat engaging the rear face of the ferrule and a rearward portion of the spring seat engaging the coil spring opposite the forward portion. [0013] In another advantageous embodiment, a multifiber ferrule for a fiber optic connector includes a ferrule body extending between an end face and an opposed rear face. The ferrule body has a plurality of optical fiber bores opening through the end face. The end face defines a first lateral axis in a first direction and a second lateral axis in a second direction generally perpendicular to the first direction. The rear face of the ferrule body defines a first convex surface in the first direction and a second convex surface in the second direction. Preferably, the radius of curvature of the first convex surface in the first direction is smaller than the radius of curvature of the second convex surface in the second direction. BRIEF DESCRIPTION OF THE DRAWINGS [0014] The above described and other features, aspects, and advantages of the present invention are better understood when the following detailed description of the invention is read with reference to the accompanying drawings, wherein: [0015] FIG. 1 is an exploded perspective view of a fiber optic connector according to an exemplary embodiment of the present invention; [0016] FIG. 2 is a perspective view of the force centering assembly of the fiber optic connector shown in FIG. 1 illustrating the multifiber ferrule, the spring seat and the coil spring; [0017] FIG. 3 is a top view of the force centering assembly shown in FIG. 2; [0018] FIG. 4 is a rear end view of the force centering assembly shown in FIG. 2 with the coil spring removed for purposes of clarity; [0019] FIG. 5 is a perspective view of a fully assembled fiber optic connector according to another exemplary embodiment of the present invention; [0020] FIG. 6 is a lengthwise cross-sectional view of the fiber optic connector shown in FIG. 5 taken along the line 6-6 in FIG. 5; [0021] FIG. 7 is an exploded perspective view of the force centering assembly of the fiber optic connector shown in FIG. 5 illustrating the multifiber ferrule, a guide pin, the pin keeper, the spring seat, the coil spring and the lead-in tube; Continue reading about Fiber optic connector for applying axial biasing force to multifiber ferrule... 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