Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber bundle-to-bundle connection
Reexamination Certificate
2000-11-09
2003-02-18
Nasri, Javaid (Department: 2839)
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber bundle-to-bundle connection
C439S289000, C439S378000
Reexamination Certificate
active
06520686
ABSTRACT:
BACKGROUND OF THE INVENTION
A typical fiber optic cable includes a fiber for carrying light from one end to the other. In general, the fiber includes a core, a surrounding cladding and an outer jacket. Typically, the core is translucent material (e.g., glass, plastic, etc.) through which pulses of light (i.e., representing binary data) can propagate. The surrounding cladding includes material similar to that of the core but provides a lower refractive index than that of the core in order to cause properly angled light within the core to reflect back into the core with minimal light energy loss. The outer jacket (or buffer) protects and strengthens the cable.
A fiber optic connector typically resides at each end of the fiber optic cable. Such a connector typically includes a precision molded component called a ferrule (e.g., an MT ferrule). The ferrule, which is typically made out of metal, ceramic, plastic, or a combination of ceramic and plastic, holds the end of the fiber (i.e., the end of the fiber core and cladding) using epoxy or solder. The connector precisely positions the fiber end relative to another fiber optic component (e.g., a laser which outputs pulses of light, a sensor for receiving pulses of light, an end of a fiber belonging to another fiber optic cable, etc.) in order to minimize light energy loss.
Some fiber optic cables include multiple fibers (e.g., a bundle of fibers) which terminate at specialized connectors that position the ends of the fibers in a row (i.e., a row of fiber ends). A user can attach two of these cables together to form longer fiber optic pathways through the lengths of the two cables using a specialized coupling called an adaptor. The adaptor receives and holds the specialized connectors which terminate the ends of the cables.
One approach to aligning together two fiber optic connectors is called the pin-in-hole approach. Here, the user plugs the connector of a first cable into an adaptor, and then plugs the connector of a second cable into the adaptor such that the row of fiber ends of the first cable face a corresponding row of fiber ends of the second cable. A pair of metal pins residing on the ends of the row of fiber ends of the first cable extend outward in a direction parallel to the fibers. The metal pins are located and held in the ferrule. As the user plugs the cable of the second connector into the adaptor, this pair of metal pins inserts into corresponding holes residing on the ends of the row of fiber ends of the second cable to properly position the two connectors relative to each other. Once the fiber ends of the first cable are properly aligned with the fiber ends of the second cable, light from a fiber end of one cable can pass to a corresponding fiber end of the other cable with minimal light energy loss.
Fiber optic cables which have two, four, eight or 12 fibers typically terminate using connectors which configure the fiber ends into a single row configuration (e.g., a single row of two, four, eight or 12 fiber ends). A fiber optic cable having 24 fibers typically terminates in a double row configuration (e.g., two rows with each row having 12 fiber ends). In both the single row configuration and the double row configuration, a pair of metal pins, one at each end of the single or double row configuration, aligns the two connectors relative to each other.
SUMMARY OF THE INVENTION
Unfortunately, there are deficiencies to the above-described conventional pin-in-hole approach for connecting two fiber optic cables. For example, the conventional pin-in-hole approach relies on the placement of a pair of metal pins (one metal pin at each end of a single or double row configuration of fiber ends) to properly hold the fiber optic cable connectors in place relative to each other. As each metal pin inserts into its corresponding hole, any minor anomalies or subtle irregularities in the pins or connector bodies (e.g., a bent pin, an irregular pin hole, etc.) could result in a substantial stress on the connector bodies that either damages or distorts the connector bodies and prevents the fiber ends from aligning properly. In some cases, the stresses and distortions result in an air gap between the fiber ends which causes light energy loss between the fiber ends (e.g., due to lack of contact between corresponding fiber ends) and provides an area that can collect dirt. This is due, at least in part, to each metal pin having to restrain connector movement in multiple directions, e.g., along a direction perpendicular to the row of fiber ends (the X-direction), along a direction parallel to the row of fiber ends (the Y-direction), etc. This situation, which often involves the metal pins competing with each other, is typically referred to as an overconstrained situation.
Additionally, the metal pins typically concentrate connector stiffness and alignment near the center of the row configuration of fiber ends held within the connectors. As a result, the fiber ends at the center of the row configuration are typically aligned properly. However, the fiber ends toward the ends of the row configuration and near the metal pins, i.e., the metal pins furthest away from the center, can easily be misaligned and/or have air gaps therebetween. In some situations, such misalignment can cause a loss of light energy through the fiber optic pathways formed by the two connected cables (e.g., due to air gaps, collected dirt, lack of contact between fiber ends, etc.), or in extreme cases, complete loss of a light signal.
Furthermore, the sides of the ferrule having the exposed fiber ends are often polished to improve surface quality (e.g., to remove surface defects) to minimize light energy loss between fibers and such polishing, in some situations, tends to exacerbate the loss of light energy exchanged between some fiber ends. In particular, such polishing tends to leave the fiber ends near the center of the row at clean right angles (i.e., perpendicular) for optimal light exchange, but tends to taper the fiber ends toward the edges of the row such that the fiber ends near the ends of the row typically have non-perpendicular surfaces. If there is no compensation for the non-perpendicular surfaces of these fiber ends (e.g., pressure placed on the fiber ends to make them perpendicular, joining with other fiber ends having complementary non-perpendicular surfaces, etc.), air gaps (a source of high light energy loss) will form between the fiber ends resulting in lack of contact between corresponding fiber ends and less than optimal light transfer. As such, the amount of lost light energy tends to be greatest through the fiber ends near the ends of the fiber end row where tapering results in non-perpendicular fiber end surfaces.
In contrast to the above-described conventional pin-in-hole approach to connecting fiber optic cables, the invention is directed to techniques for forming a fiber optic connection through the application of kinematic coupling concepts to properly align corresponding fiber ends (e.g., a “perfectly constrained” situation). A thorough discussion of kinematic coupling concepts is found in a book entitled, “Precision Machine Design,” by Alexander H. Slocum, Prentice-Hall, Englewood Cliffs, N.J., 1992.
The fiber optic connection forms between a first connection assembly that provides alignment members and a second connection assembly that provides grooves such that a central axis of each groove of the second connection assembly is substantially perpendicular with a central axis of a corresponding alignment member of the first connection assembly. Each alignment member/groove pair can be positioned and oriented to control positioning of the first and second connection assemblies relative to each other in a single direction while allowing movement in other directions to prevent physical stressing of the connection assemblies. That is, the alignment members of the first connection assembly can be arranged around a periphery of a first array of fiber ends of a first fiber optic cable, and the grooves of the second connection assembly can be arr
Chapin & Huang , L.L.C.
Huang, Esq. David E.
Nasri Javaid
Teradyne, Inc.
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