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Fiber optic connector with double-clad stub fiber

Fiber optic connector with double-clad stub fiber description/claims

This application is a continuation of U.S. patent application Ser. No. 11/683,809, filed Mar. 8, 2007 and is incorporated by reference in its entirety.

The present invention relates generally to fiber optic connectors, and, more particularly, to a field-terminated, pre-polished fiber optic connector having a double-clad stub fiber for minimizing optical interference effects caused by excitation of higher-order modes.

Field-terminated pre-polished fiber optic connectors include an interface at which two optical fibers, a field optical fiber (“field fiber”) and an internal stub optical fiber (“stub fiber”), are coupled. Such connectors include a pre-polished front face that enables a connection with another compatible fiber optic connector. In such a connector, the stub fiber is essentially disposed between two interfaces: the field fiber-stub fiber interface, and the connector interface with the compatible connector at the pre-polished front face.

Ideally, all of the light energy passing through the core of a single-mode field fiber will continue unimpeded across the interface into the core of the stub fiber in the pre-polished fiber optic connector. In this ideal scenario, the interface between the field fiber and the stub fiber is said to have a coupling efficiency, η1, equal to one, because all light traveling in the core of the field fiber becomes coupled into a primary mode, designated as LP01 for single-mode fibers, and travels through the stub fiber core. But in reality, optical interference effects occur as a result of misalignment of the cores of the field and stub fibers or mismatch of the mode-field diameter (MFD) or optical-power distribution for the field and stub fibers. This misalignment or mismatch excites unwanted higher-order coherent modes, such as the LP11 and LP02 modes for single-mode fibers, which interfere with one another within the short length of the stub fiber. This interference can be constructive or destructive, which, in the latter case, causes an overall increase in insertion loss of the connector interface.

A need exists for a pre-polished quick-terminated fiber optic connector that overcomes these and other problems.

A field-terminated pre-polished fiber optic connector assembly for terminating a single-clad optical field fiber includes a double-clad optical stub fiber and an alignment member. The alignment member receives the cleaved end of the field-terminated optical field fiber, which abuts against an end of the double-clad optical stub fiber forming an interface at the point of abutment. The double-clad optical stub fiber includes a core having a radius rc, an inner cladding having a radius r1, and an outer cladding having a radius r2. The ratio r1:rc is less than 6.5:1. The refractive index of the inner cladding is down-doped to result in an effective refractive index that is at least 0.0025 lower than that of the core but higher than that of the outer cladding's refractive index. The mode field diameter (MFD) of the double-clad optical stub fiber approximately matches the MFD of the field fiber. In one implementation, the optical field fiber and double-clad optical stub fiber are of the single-mode type. In another implementation, the optical field fiber and double-clad optical stub fiber are of the multimode type. The optical field fiber can also be a double-clad fiber.

A method of terminating a single-clad optical field fiber includes positioning an end of a field fiber in a fiber optic connector assembly such that that end contacts an end of a double-clad optical stub fiber that is at least partially disposed within the fiber optic connector assembly.

FIG. 1 is a cross-sectional side illustration of an exemplary field-terminated pre-polished fiber optic connector 10 for terminating a field fiber 12, according to an aspect of the present invention; and

FIG. 2 is a cross-sectional illustration of a double-clad stub fiber 14 that is incorporated in the exemplary fiber optic connector 10 of FIG. 1 and an index profile of the respective indices of refraction of the core and claddings of the double-clad stub fiber 14.

FIG. 1 is a cross-sectional side illustration of a field-terminated pre-polished fiber optic connector 10 for terminating a field fiber 12, according to an aspect of the present invention. The field fiber 12 is a single-mode optical fiber having a single cladding. The connector 10 couples together the field fiber 12 with a stub fiber 14, which forms an interface 16 where the two fibers 12, 14 abut against one another within the connector 10. The connector 10 is optionally of the type generally described in commonly assigned, U.S. Pat. No. 7,011,454, entitled “Reversible Fiber Optic Stub Fiber Connector,” issued Mar. 14, 2006, though other fiber optic connectors can be used. An alignment member 18 may comprise v-groove planks for aligning ends of the fibers 12, 14 in a fixed relationship with one another. A ferrule 20 surrounds part of the stub fiber 14, and a pre-polished end of the stub fiber 14 is positioned at a pre-polished front face 22 of the ferrule 20 so that together they can be received in an appropriately configured port in a patch panel or other device. A conventional buffer 24 surrounds part of the field fiber 12.

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