Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-05-17
2002-05-21
Epps, Georgia (Department: 2873)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S147000, C385S089000
Reexamination Certificate
active
06390690
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber connector system. More particularly, the present invention relates to a connector assembly for optically coupling optical devices mounted on planar substrates oriented at intersecting angles with respect to each other.
The use of optical fibers for high-volume high-speed communication and data transfer is well established. As the volume of transmitted information grows, the desire for optical fiber cables including multiple optical fibers, and of systems using cables containing multiple optical fibers, has increased.
In traditional cabinet designs, such as a telephone exchange, the cabinet comprises a box having a plurality of internal slots, generally parallel to each other. Components are mounted on planar substrates, to form cards known as circuit boards. A recent technological goal has been the incorporation of optical and opto-electronic devices coupled by optical waveguide buses on the boards. In one preferred embodiment, the optical fibers are arranged in multi-fiber parallel arrays, forming parallel communications buses. The resulting optical cards would desirably be designed to slide into the slots or racks within the cabinet and to interconnect with other components and other boards.
The use of the optical circuit boards in the racked arrangement of traditional electronic cabinets presents new connectorization challenges. Within the cabinet structure, it is common for devices to be mounted on boards that define intersecting planes, such as the perpendicular arrangement of a motherboard and a backplane. A “backplane” derives its name from the back (distal) plane in a parallelepipedal cabinet and generally is orthogonal to the printed circuit (PC) board cards. The term backplane in the present invention refers to an interconnection plane where a multiplicity of interconnections may be made, such as with a common bus or other external devices. For explanation purposes, a backplane is described as having a front or interior face and a back or exterior face.
The need exists to provide a means to allow optical signals to “turn the corner,” that is, to couple optically components on intersecting boards. However, optical waveguide signal transmission relies on total internal reflection of a light signal within the waveguide and optical waveguides bent at sharp angles suffer unacceptable microbend and/or macrobend optical signal losses. Furthermore, many optical waveguides, such as glass optical fibers, are fragile and may fracture or crack when bent past a certain physical tolerance. Different optical waveguides have different optical transmission and physical integrity qualities. The acceptable signal losses and the physical flexibility of a waveguide determine the acceptable radius of curvature for a particular fiber. The radius of this curve is defined as the critical bend radius for the particular fiber. It is therefore desirable that an inter-card connector system account for the critical bend radius of the optical waveguide connections.
In addition, in cabinet connection applications, users slide the cards in and out of the cabinet racks. It would be desirable to have a disconnectable fiber connection along the insertion axis of each card. Such a connection would preferably be capable of absorbing excessive insertion pressure, such as that caused by a user “jamming in” a card, while still maintaining the desired bend radius and exerting sufficient connection pressure along the ends of the fibers to ensure a reliable optical connection.
Finally, it would be desirable for a multi-fiber inter-plane connector to maintain the parallel alignment of the fibers in the optical bus, for ease of connectorization, without subjecting the fibers to uneven twisting or tensile stresses.
For the purposes of the present description, the axis of interconnection along one of the planes is called the longitudinal or y-axis and is defined by the longitudinal alignment of the optical fibers at the point of connection. Generally, in backplane applications, the longitudinal axis is collinear with the insertion axis of the cards and the axis of connection of the optical fibers in and out of the cabinets. The lateral or x-axis is defined by the axis of connection of the optical fibers on the other substrate plane. Generally, the x and y-axes are mutually perpendicular. Finally, the intersection of the two planes defines a transverse or z-axis, also called the intersection axis. Again, in most applications, the z-axis is orthogonal to the x-axis and y-axis.
Different connection methods have been suggested to couple optical circuit cards. Some references, such as U.S. Pat. Nos. 4,498,717 or 5,639,263, suggest the use of electrical connections between the intersecting substrates. However, the use of electrical connections necessitates the conversion of optical signals to electrical signals and vice versa at each connection. Optical fiber “jumper” cables have been suggested, but such individual optical fibers are susceptible to damage and to the risk of bending past the critical bend radius of the fiber.
To support the fibers, some references, such as U.S. Pat. Nos. 5,155,785 and 5,204,925, discuss placing the fibers in groves or channels or laminating the fibers to a flexible substrate. In these patents, the optical backplane is a custom backplane designed to contain the optical fibers within it. The bend radius of the fiber is controlled by the thickness of the backplane. As described in the '785 reference, “[t]he optical backplane member
32
has a sufficient thickness between opposite surfaces
33
and
34
to provide an appropriately large radius of curvature through which each optical fiber must be bent in making the connection between the surface
34
and the MAC connector
25
. Typical dimensions of the backplane
32
are eight inches by sixteen inches by three inches in thickness. It can be shown that, for digital transmission at practical power levels, the minimum radius of curvature through which an optical fiber may be bent without incurring significant losses is one inch”.
An obvious constraint of such design is the required use of specially grooved very thick substrates. The backplane design is described as containing “a complex arrangement of arcuate grooves of varying depth . . . ” and as such would appear to be very difficult to design and manufacture for each application.
U.S. Pat. No. 5,793,919, references a backplane interconnect system that connects optical signals from a number of daughter cards on to an optical fiber backplane bus. As such, the backplane fibers are not coupled end to end with the daughter card fibers in a point to point connection system, and the backplane fibers are not terminated in a backplane connector at each daughter card location. The optical signals from each daughter card are added to the continuous fibers of the backplane bus, and the bus fibers carry all signals simultaneously to all coupling locations. This design requires a special “D” fiber profile to enable this longitudinal coupling to take place.
U.S. Pat. No. 5,204,925 relates to an interconnection system containing termination tabs that connect through openings in the electrical backplane, but do not connect to the backplane. This might be considered as an example of a custom optical jumper cable and connector system, not a backplane and connector system. The jumper cable assembly does not provide strain relief or bend radius control for the optical fibers. In use, the fibers are twisted from the plane of the optical jumper circuit in order to connect to the circuit boards. In twisting the termination tabs containing the optical fibers, a torsional force is applied to the fibers in the tab, which will impart a long-term stress on the individual fibers, or may cause the fibers to shift within the assembly in order to relieve stress.
The need remains for an effective connector for optically coupling parallel multifiber optical devices in intersecting optical boards.
SUMMARY OF THE INVENTION
A connecto
Igl Scott Anthony
Lee Nicholas Anthony
Meis Michael Alan
3M Innovative Properties Company
Epps Georgia
Harrington Alicia M.
Ho Nestor F.
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