Optical waveguides – With disengagable mechanical connector
Reexamination Certificate
1999-07-28
2002-10-15
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With disengagable mechanical connector
C385S055000, C385S056000, C385S070000, C385S134000
Reexamination Certificate
active
06464402
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical fiber connector indexable tuning tool and, more particularly to a tool for testing an calibrating tunable optical fiber connector and apparatus for tuning it.
BACKGROUND OF THE INVENTION
In optical fiber communications, connectors for joining fiber segments at their ends, or for connecting optical fiber cables to active or passive devices, are an essential component of virtually any optical fiber system. The connector or connectors, in joining fiber ends, for example, has, as its primary function, the maintenance of the ends in a butting relationship such that the core of one of the fibers is axially aligned with the core of the other fiber so as to maximize light transmissions from one fiber to the other. Another goal is to minimize back reflections. Such alignment is extremely difficult to achieve, which is understandable when it is recognized that the mode field diameter of, for example, a single mode fiber is approximately nine (9) microns (0.009 mm). Good alignment (low insertion loss) of the fiber ends is a function of the alignment, the width of the gap (if any) between the fiber ends, and the surface condition of the fiber ends, all of which, in turn, are inherent in the particular connector design. The connector must also provide stability and junction protection and thus it must minimize thermal and mechanical movement effects.
In the present day state of the art, there are numerous, different, connector designs in use for achieving low insertion loss and stability. In most of these designs, a pair of ferrules (one in each connector), each containing an optical fiber end, are butted together end to end and light travels across the junction. Zero insertion loss requires that the fibers in the ferrules be exactly aligned, a condition that, given the necessity of manufacturing tolerances and cost considerations, is virtually impossible to achieve, except by fortuitous accident. As a consequence, most connectors are designed to achieve a useful, preferably predictable, degree of alignment, some misalignment being acceptable.
Alignment variations between a pair of connectors are the result of the offset of the fiber core centerline from the ferrule centerline. This offset, which generally varies from connector to connector, is known as “eccentricity”, and is defined as the distance between the longitudinal centroidal axis of the ferrule at the end face thereof and the centroidal axis of the optical fiber core held within the ferrule passage and is made up of three vectors. It is often the case, generally, that the ferrule passage is not concentric with the outer cylindrical surface of the ferrule (vector I), which is the reference surface. Also, the optical fiber may not be centered within the ferrule passage (vector II whose magnitude is the diametrical difference divided by two) and, also, the fiber core may not be concentric with the outer surface of the fiber (vector III). Hence eccentricity can be the result of any one or all of the foregoing. The resultant eccentricity vector has two components, magnitude and direction. Where two connectors are interconnected, rotation of one of them will, where eccentricity is present, change the relative position of the fibers, with a consequent increase or decrease in the insertion loss of the connections. Where the magnitude of the eccentricities are approximately equal the direction component is governing, and relative rotation of the connectors until alignment is achieved will produce maximum coupling.
There are numerous arrangements in the prior art for “tuning” a connector, generally by rotation of its ferrule, to achieve an optimum direction of its eccentricity. One such arrangement is shown in U.S. Pat. No. 5,481,634 of Anderson et al., wherein the ferrule is held within a base member which maybe rotated to any of four rotational or eccentricity angular positions. In U.S. Pat. No. 4,738,507 of Palmquist there is shown a different arrangement and method for positioning two connectors relative to each other for minimum insertion loss or maximum coupling. The arrangements of these patents are examples of the efforts to achieve optimum reliable coupling, there being numerous other arrangements and methods.
In all such arrangements for achieving optimum coupling with connectors having different magnitudes and directions of eccentricities, the tuning takes place, usually, if not always prior to the final assembly of the connector. As a consequence, an installer in the field has no control over the degree of coupling, other than by trial and error. Further, tuning of the connector cannot be performed after production of the connector is completed. Thus tuning prior to final assembly of the conductor is a step in the production process.
An optical fiber connector that can be tuned for optimum performance after the connector has been assembled would greatly decrease production costs and further, impart a greater measure of reliability to the connectors. Such a connector would be of significant commercial value.
SUMMARY OF THE INVENTION
The present invention is a tuning index tool for use in tuning tunable optical fiber connections for achieving maximum possible signal transmissivity or minimum insertion loss despite the connector being fully assembled. In a preferred embodiment of the invention the principles thereof are illustrated with a connector of the LC type for single mode fibers. It is to be understood that the principles of the invention are applicable to numerous other types of connectors such as, for example, the SC, FC and ST type connectors, as well as to other fiber optic type devices.
A connector for which the present invention is used is, for purposes of illustration, is a modified LC type connector, as shown in U.S. patent application Ser. No. 09/363,906. The basic components of such a connector as shown in that patent application comprise a ferrule-barrel assembly for holding the end of an optical fiber extending axially therethrough and a plug housing member which contains the barrel-ferrule assembly. A coil spring member contained within the housing surrounds the barrel and bears against an interior wall of the housing and an enlarged barrel member, thereby supplying forward bias to the barrel-ferrule assembly relative to the housing. The barrel member, referred to as a flange in the Anderson et al. patent, is shaped to be supported within an interior cavity within the housing in any one of four rotational orientations with respect to the central axis of the fiber holding structure. A ferrule extends axially from the enlarged barrel member and contains a fiber end therein. Thus the direction of eccentricity of the fiber relative to the central axis can have any one of four rotational or angular orientations. The connector is “tuned” to the extent that four orientations are possible. However, the “tuning” is a manufacturing step preceding final assembly of the connector, after which it is no longer “tunable”.
The ferrule-barrel assembly of the connector is modified so that the enlarged barrel member or flange is optimally hexagonal in shape, and has a tapered or chamfered leading surface which may be slotted. The housing is also modified so that the interior cavity is hexagonal in shape to accommodate the barrel member in any of six rotational orientations and a sloped constriction against which the leading surface bears in its forward position. Tuning of the fully assembled connector is accomplished by the application of an axial force to the barrel member, as by a spanner wrench fitted within the slots in the leading surface, sufficient to overcome the bias of the coil spring and to push the barrel portion rearwardly out of engagement with the hexagonally shaped recess in the housing and the sloped constriction. The ferrule-barrel assembly is then incrementably rotatable to any of six angular orientations, sixty degrees (60°) apart. It should be noted that a lesser number of surfaces can be used if the diagonal distance of the barrel cross-section is
Andrews Scott R.
Lampert Norman Roger
Mock Robert Wayne
Sandels Gregory A.
Subh Naif Taleb
Fitel USA Corp.
Pak Sung
Sanghavi Hemang
Thomas Kayden Horstemeyer & Risley LLP
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