Optical fiber tunable connector adapter

Details Optical fiber tunable connector adapter Optical fiber tunable connector adapter

1999-10-06

2001-07-03

Ullah, Akm E. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Reexamination Certificate

active

06254278

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an optical fiber connector adapter and, more particularly, to a tunable adapter for minimizing insertion loss.
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 singlemode fiber is approximately nine (9) microns (0.009 mm). Good aligmnent (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 typically 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 maximum 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 fiber cores, 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.
In the foregoing cited patent applications, there are shown connectors, apparatus, and methods for tunable, fully assembled, connectors, the apparatus for determining the eccentricities of the connector or connectors, and the method and apparatus for tuning the connectors, relying upon a predetermined eccentricity vector as a reference point. The tunable connectors are then usable in the field with other connectors, whether tunable or not. Inasmuch as there exists large numbers of connectors ready for use, or already in use, that are not tunable, there exists a need for enabling an installer to make connections having a minimum insertion loss, even though the connectors themselves are not tunable. Also, where there is a large number of fiber channels, the channel balance is as important as minimum insertion loss.
SUMMARY OF THE INVENTION
The present invention is a connector adapter for abutting two connectors (or equivalents) against one another in, most commonly, a field installation, which, in itself, is tunable for achieving maximum possible signal transmissivity or minimum insertion loss between the two connectors, or for achieving channel balance.
In greater detail, the adapter comprises a housing member which has spring latch members thereon for mounting and affixing the housing to a plate or panel which generally is present in field installations. Preferably the housing member also has a key on the exterior circumference thereof for locating the housing in a particular orientation relative to the panel, usually or preferably a vertical orientation. The housing has, at one end thereof, a retaining wall which functions as a seat for a circular warped leaf spring or wave washer, the function of which will be discussed more fully hereinafter.
Within the housing intermediate the ends thereof is a wall or disc member having a centrally located jack or receptacle for receiving an optical connector. In the figures and discussion to follow, the principles and features of the invention are illustrated as configured to receive LC type connectors. However, it is to be understood that these principles and features of the invention are applicable to numerous other types of connectors such as, for example, SC, FC, and ST types, all in use today in optical fiber circuitry, as well as to other types of optical fiber type devices. The wall or disc member thus, for illustrative purposes, has a centrally located receptacle for receiving an LC type connector. The wall itself is mounted within the housing by suitable spring latch means and is stationary with respect thereto. In a circular array surrounding the centerline of the jack are a plurality of indexing projections preferably, although not necessarily twelve in number. A movable wall member is contained within the housing between the disc member and the retaining wall of the housing and has a tubular portion extending therefrom which extends through an opening in the retaining wall. The movable wall member has a connector receiving receptacle centrally located thereon and axially aligned with the receptacle on said disc member. On the rear surface of the movable wall member is a circular array of locating slots adapted to receive the indexing projections on the disc member, and surrounding the jack on said movable wall member. That

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