Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Reexamination Certificate
2002-07-16
2004-05-18
Patel, Tulsidas C. (Department: 2839)
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
Reexamination Certificate
active
06736546
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical connector ferrule. More specifically, the present invention relates to an optical connector ferrule designed for supporting and aligning precision optical fibers via exact constraint principles to aid in minimizing manufactured imperfections and mating misalignments.
As the need for bandwidth in society increases, copper-based telecommunications systems become less desirable due to their limited data carrying capacity. Thus, high-speed systems having optical fiber transmission paths that transmit light representing data signals were developed to meet the bandwidth needs. Data can be transmitted at very high rates (e.g., 10 gigabits per second) in a single optical fiber.
In order for an optical fiber to provide such high data transmission rates, it must be manufactured with precise tolerances and composed of specialty materials. Generally, an optical fiber is made from ultrapure silica in which dopants (e.g., GeO
2
) have been added in a controlled manner. The optical fiber has an inner silica layer, referred to as the “core”, covered by a secondary layer of silica which contains a different mix of dopants, referred to as the “cladding”.
Light traveling through the core of the optical fiber is guided by total internal reflection due do index differences between the core and the cladding of the fiber. Proper mixing of dopants in the fiber core and cladding creates this index difference. Optical fiber that contains only one mode of the transmitted light is called “single mode” fiber, while fiber that allows a plurality of modes is called “multi-mode.” Single mode fiber transmits data further, since it has less dispersion over distance than multi-mode fiber. Multi-mode fiber has a larger core diameter making alignment of fibers in an optical connector easier.
To couple one optical fiber to another with low loss of signal fidelity, it is necessary to properly align the cores, thereby allowing the light to be guided from one core into the next. To do this, an optical connector or mechanical splice is used. Typically, an optical connector includes a ferrule for holding optical fibers in precise positions. For two ferrules to be coupled, it is common for alignment pins to be used to guide and precisely position the fibers within each ferrule relative to its partner. In most applications, one of the ferrules is defined a male while the other is a female. This means that one of the ferrules would contain the precision pins, while the other would only contain the precision receptacles. This conventional approach either over or under constrains to determine the exact position of each fiber relative to its mate.
Over-constraining occurs when the alignment entities (pins in holes) interfere during engagement. After engagement, the relative position and orientation of the ferrules depends upon the averaged effect of elastic or plastic deformations that occur at the interface between the aligning entities. In order to achieve highly repeatable alignment, the aligning entities must be manufactured to stringent dimensional and geometric tolerances, which typically increases production costs. Despite the added costs and efforts, over-constrained systems still suffer from loss of signal fidelity associated with imperfections and mating misalignments.
The under-constrained state is one where the pins/holes combination is in clearance situation. In this case, the two ferrules align randomly within the clearance cross section. If there are any biasing forces, this will affect the location as well. Therefore, under-constrained systems typically suffer from loss of signal fidelity at the fiber-to-fiber interface. Note that it is common for over-constrained systems to wear down into under-constrained systems.
Due to the size of the optical fibers utilized, typically 125 micron (10
−6
meter) diameter with a 50 micron diameter core for a multi-mode fiber and 125 micron diameter with a 8.6-9.5 micron diameter for a single-mode fiber, it is critical to maintain precise tolerances of the ferrules. Any small manufacturing imperfection or mating misalignment leads to significant loss of signal fidelity at the fiber-to-fiber interface.
Many different ferrule designs have been proposed. For example, the MT (“Mechanical Transfer”) ferrule developed by Nippon Telegraph and Telephone Corporation utilizes precision molded rectilinear glass-filled plastic housing to support an array of optical fibers in a ribbon cable. The MAC (“Multifiber Array Connector”) connector developed by AT&T uses photolithographic techniques to precisely etch silicon chips with V-shaped grooves that are 250 microns center-to-center which hold the array of optical fibers of a ribbon cable. Various ferrule designs are disclosed in U.S. Pat. No. 5,416,868 entitled “Optical Connector Having A Resin Molding Portion Which Includes Opposite Opened Portions At Top And Bottom Surfaces”, U.S. Pat. No. 6,168,317 entitled “Alignment Adapter For An Optical Connector And Method For Making Same”, and U.S. Pat. No. 6,328,479 entitled “Multi-Terminator Optical Interconnect System”, all of which are incorporated herein by reference. These existing ferrule designs, however, are either over-constrained or under-constrained and suffer from the disadvantages described above.
The inventors of the present invention have designed a ferrule that better accommodates imperfections and mating misalignments so that the loss of signal fidelity at the fiber-to-fiber interface is minimized. The ferrule designs described and claimed herein are the result of their efforts.
SUMMARY OF THE INVENTION
It is a general object of the invention to provide a ferrule design that accommodates imperfections and misalignments to provide accurate and repeatable optical coupling so that loss of data signals at the fiber-to-fiber interface is minimized.
This and other objects of the invention are achieved by a ferrule assembly, in a preferred embodiment, having a first ferrule, a second ferrule, and at least two alignment members to align the first and second ferrules during mating. The first ferrule, the second ferrule and the alignment members interact at the mating interface of the first and second ferrules to provide three constraint lines. In one embodiment, the first ferrule has a body with at least one channel for receiving at least one optical fiber. The first ferrule body includes a first surface portion for retaining a first alignment member and a second surface portion for retaining a second alignment member, the first and second surface portions being V-shaped. The second ferrule has a body with at least one channel for receiving at least one optical fiber. The second ferrule body includes a first surface portion for retaining the first alignment member and a second surface portion for retaining the second alignment member, the first surface portion being V-shaped and the second surface portion being flat.
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Kiani Sepehr
Vallance Ryan R.
Hwang David H.
Teradyne Legal Dept.
Teradyne, Inc.
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