HK1028451B - Flexfoils having connector tabs - Google Patents

Description

Flexfoil with connecting tongues

Technical Field

The present invention relates to an optical fibre connection device for a flexfoil, a so-called flexfoil being a flexible sheet having optical waveguides arranged therein or thereon, the connection device being intended for example to be used for connection to circuit boards and backplanes.

Background

As data rates of computers, telecommunications, and the like have increased, optical fiber communications, which have been well established over long-distance broadband communications for a long time, are also being introduced to short-range applications within switches and computers. For such applications, the number of optical fiber interconnections becomes important. This requires control and manipulation of the arrangement of the optical fibers, and more generally of the optical waveguides.

One practical approach to this is to use a single optical layer to contain all the fiber connections within a fiber flexfoil with internal fibers/waveguides that can be connected to the optoelectronic device and external devices such as circuit backplanes using fiber optic connectors at the ends of the fibers/waveguides.

In some patents of AT & T, and particularly U.S. patent 5,204,925 to Bonnani et al, the use of fiber optic flexfoils is described which are provided with tabs extending from the body that can be twisted AT 90 ° relative to the body in order to accomplish a "side-to-side" backplane connection in which the sides of both the body of the circuit board and the body of the backplane flexfoil are disposed perpendicular to each other. This is an unusual appearance for typical systems, as compared to the more common case where the circuit board extends perpendicularly from the backplane. In the AT & T solution this state may possibly be achieved by folding the flexfoil.

The AT & T concept has a serious limitation in that it is not possible to connect one edge of the circuit board to the backplane AT several different locations using the simple geometry disclosed. Although this connection is possible in principle, it seems that it is possible to extend the tongue further so that it can be both twisted and bent. But with the tabs extending from the edges, the length of the edges of the backplane flex is much greater than the original dimension required due to the spacing between the boards, which is particularly significant when more tabs are required per circuit.

A method of manufacturing an optical flexfoil is disclosed in U.S. patent No. 5,259,051 to Burack et al, to AT & T. In the embodiment of the patent described in connection with fig. 7, a base foil is used which has a plurality of tongues projecting from the body. On this base foil one or more optical fibres are arranged, which are then cut, whereupon the top foil can be applied. Finally the edges and borders of the tongues are cut.

Overview

It is an object of the present invention to provide a connection arrangement for optical waveguides on an optical flexfoil that allows the flexfoil to have a compact profile and allows for a flexible wiring of the substrate and circuit board served by the flexfoil.

It is another object of the invention to provide a flexfoil which is constructed so that the attachment tabs can be polished in a simple apparatus.

The problem to be solved by the invention can thus be attributed to how to manufacture a flexfoil which can be handled easily, can be connected to the outside anywhere on the flexfoil and which can be polished in a simple manner at the waveguide end on the connection tab.

In an optical flexfoil having optical waveguides, such as optical fibers, it is possible to position the ends of the optical fibers at both the inner end and the edge of the flexfoil. The circumference of the optical fiber tip can be largely cut to form a tab, with the tip of the optical fiber being positioned on the outer edge of the tab. The tongues are made so that they can be bent out of the plane of the main body of the flexfoil and so that they project out of this plane. The tongues may then be positioned substantially at the inner end of the flex foil such that none of the tongue portions project beyond the edge of the flex foil in the plane of the flex foil. The tab can be bent so that its outer region is e.g. perpendicular to the plane of the flexfoil when polishing the optical fibres at the edge of the tab and holds the tab firmly in this position during the polishing operation. The tongue tip can be provided with a suitable optical connector prior to the polishing operation.

Thus, these tabs cut from the flexfoil body can be used, for example, not only as a means of attachment to an optoelectronic device on a circuit board located proximate to one of the major surfaces of the flexfoil body, but also as a means of achieving a 90 bend in the flexfoil oriented parallel to, and on the rear side of, a conventional circuit board, acting as an optical board. With this type of layout technique, multiple optical connection points can be made between the backplane and the circuit board without increasing the edge length of the backplane flex to expect more tabs per board. An opening is made in the circuit board through which a tab bent from the fiber board passes to allow a mixture of circuit and optical connection points to be obtained on the board edge. With this arrangement it is also possible to orient the optical connector, for example in the form of a multichannel, at the end of the tongue parallel to the circuit board, so that the tongue does not require any twisting.

Since the tabs formed by slitting have to remove a part of the surface from the flexfoil, which part of the surface could otherwise be provided with light guides, it is required that the tabs are not unnecessarily elongated so that they can be bent out of the main plane of the flexfoil with a small radius. It is also desirable for the optical backplane to maintain a reasonable spacing from the printed circuit board to be connected to the backplane. It is further required that the optical fibres arranged in the flexfoil must be arranged with a small radius around the slit formed tabs, since the number of optical fibres that can be arranged in the flexfoil is even reduced if arranged with a large radius. This can be done by any suitable flex foil production method. Since the appropriate optical fiber arrangement and lamination techniques of the optical flexfoil enable this without impairing reliability. In this respect, reference is made to the international patent applications "laying of optical fibres on a substrate" and "lamination of optical foils" filed simultaneously. In addition to laminating optical fibers within a flex foil, a flex foil provided with a polymer waveguide fabricated in accordance with a pattern can also be used.

The two advantages of the tab for the circuit board formed by slitting and the absence of the tab projecting beyond the edge of the foil stack are both ease of routing the optical fibre circuit and ease of manufacture. This manufacturing advantage applies equally to the base plate.

When the tongues project outside, i.e. from the edge of the flexfoil, the former, although having more undisturbed surface area on the flexfoil for arranging the optical fibre lines when arranging the optical fibre lines, is smaller than the latter in terms of the total surface area available for arranging the optical fibre lines, compared to a flexfoil having a number of clearly internal tongues which are parallel to the large surface of a conventional circuit board. This is because by definition an external tab means a tab used with a generally rectangular flex foil that is generally smaller than the circuit board, but the flex foil can be made the same size as the circuit board when the location of the tab used is optional. The optional tab position then allows the corresponding fiber optic connectors on the circuit board to be less constrained in deployment, e.g., not necessarily at the board edges. But the importance of this may be limited to some special cases only.

The continuous lay-up process is mentioned in the above-mentioned AT & T patents. The optical fibre lay down scheme used is now discontinuous in order to make the internal tabs in the optical flexfoil practical, and the optical fibres can be cut and laid again starting at several positions, which has certain advantages because otherwise there will be a lot of excess loose optical fibres laid down on the flexfoil. This may be acceptable as long as the lamination process of the flex does not cause too much loss at the locations where the optical fibers cross each other. Such an arrangement, which does not require the use of a continuous optical fibre during the laying of the optical fibre, is described in the above-mentioned concurrently filed international patent application "laying of an optical fibre on a substrate". This is not a problem for flexfoils with polymer, e.g. thin film type waveguides.

A flex foil with tabs extending from its edge is not well-handled for manufacturing purposes, for example, for connector finishing operations. For such an operation, the flexfoil with the tongues inside can be easily mounted on a simple rectangular frame, and the tongues are then bent from the plane of the flexfoil body by means of movable holder means so that the end regions of the tongues are at a predetermined angle, e.g. at right angles, to said plane. The end surface of the waveguide terminating at the end of the bent tab is then polished and the bent tab is finally restored to its original position in the plane of the main body of the flex foil. Generally, an optical connector, such as an MT connector, can be attached to the end of the tongue prior to the polishing operation.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, apparatuses and combinations particularly pointed out in the appended claims.

Brief description of the drawings

While the novel features of the invention are set forth with particularity in the appended claims, a full understanding of the invention, including the organization, content, and features thereof, is best understood from the following detailed description of the non-limiting embodiments when read in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic perspective view of a circuit board having an optical flexfoil applied thereto;

FIG. 2 is a schematic perspective view of a circuit backplane having an optical flexfoil mounted behind it;

FIG. 3 is a schematic transverse cross-sectional view of the assembly of FIG. 2 with an optical flexfoil in addition to the wiring board;

FIG. 4 is a schematic perspective view of an apparatus for polishing fiber ends in a flex foil connector.

Detailed Description

Fig. 1 shows a flexfoil with optical waveguides, in the preferred embodiment the optical fiber lengths 3 are joined along well-defined paths between two identical flexible plastic sheets, which are stacked on top of each other to form a rectangular flexible composite structure. The flexfoil 1 is placed on top of and parallel to one large surface of the printed circuit board 5. The circuit board 5 is also rectangular like the flexfoil 1, but is generally slightly smaller. Cuts 7, 9 are made in the flexfoil 1 to form inner tongues 11 and edge tongues 13, the tongues 11 and 13 being positioned such that the ends of the optical fibre lengths 3 are located at the ends or outermost edges of the tongues 11, 13. When the cut-outs or through-holes 7 are made at internal positions of the flexfoil 1 to form the internal tongues 11, they may have a generally U-shaped form, they may also be made as two parallel elongated areas 9 for making tongues 13 on the edges of the flexfoil, such that the outermost part or end of an edge tongue 13 is a part of the edge of the flexfoil 1.

The tongues 11, 13 have a substantially rectangular shape with long sides parallel to the optical fibres located in the tongues to be connected to some device. The outermost short side is the end or outermost edge of the tongue where the fiber terminates in a direction perpendicular to the side. On the inside of the short side is a tongue connected to the flexfoil 1. The cuts 7, 9 are preferably made by removing some of the material from the flex, such as a narrow U-shaped strip or straight strip. The tabs 11, 13 can be bent out of the plane of the flexfoil 1, provided that the plastic sheets of the flexfoil are flexible and that the laminate is suitably made so that the tabs have a sufficient length without damaging the optical fibres or causing unwanted attenuation therein. Some conventional optical fiber connection means 15, such as an MT connector, may be attached to the tongue end to form a suitable optical fiber interface for the optical fibers terminated at the tongue end. The opto-electronic module 17 attached to the wiring board 5 is thus connected to the optical fibres of the inner tongue 11. The edge tabs 13 may be attached to a fiber optic backplane connector 19, which connector 19 is mounted on the edge of the circuit board 5 to be attached to the backplane. It is also possible that the cut-out portion 7' leaves a strip 20 on the edge of the flex 1 when such a backplane connector 19 is mounted on the board 5 at a distance from the edge, as shown in fig. 1 near the lower right corner of the flex. In order to make this connection, the tongues 11, 13 have to be bent into an S-shape, the two end portions of which are in two parallel planes at a small distance from each other.

In the perspective view of fig. 2, the flexfoil 1' is shown positioned closely behind the circuit substrate 21, which acts as a complementary substrate for the optical fibers. The printed circuit board extends perpendicularly from the front surface of the backplane 21 and is connected to the backplane by cooperating conventional electrical edge points 23 and backplane connector strips 25. Fig. 3 is a cross-sectional view showing the same components as in fig. 2, except that here also an optical flexfoil 1 is located on the surface of the circuit board 5, in the same way as in fig. 1, which board carries an electrical and optical component 24 and an optoelectronic device 17. The printed circuit board 5 is provided with an optical connector on its rear side, whereas the optical connector 19 in fig. 1 is not. At the connector strip 25 or a position close to and parallel to it corresponding to the optical connector 27 on the printed circuit board 5, a rectangular through hole 29 is made in the circuit board 21 so that the tongue 11 protruding from the flexfoil 1 is connected to the optical connector 30 mounted on the front side of the board 21, the tongue, after bending, having its end perpendicular to the main body of the flexfoil 1 and the optical connector 30 inserted into the rear end of the board 21. The optical connectors 30 on the circuit substrate are arranged so that when the circuit board 5 is attached to the substrate, the corresponding optical connectors 27 fit snugly therein.

Since the attachment tabs on the flex foil do not extend beyond the substantially rectangular extent of the flex foil, it can be easily handled without risk of damage to the tabs. Thus, as shown in FIG. 4, it can be mounted with its periphery on a stage 31 of a polishing machine 33 movable in the X-Y direction for polishing. It can be repeatedly positioned piece by piece, so that each time the tongue 11 can be placed directly under the holder of the connector attached to the fixed arm 37 of the machine 33. The holder 35 of the connector is provided with means for bending the tongue such that its end region is at an oblique or right angle to the flex 1 and the table 31, as seen in the downward direction in the figure. A stationary polishing apparatus having a rotating polishing wheel 41 is positioned below the X-Y table 31. The polishing means can polish the ends of the optical fibers on the end edges of the tongue 11 after the tongue is bent by the holder 35 of the connector. The axis of rotation of the polishing wheel may be perpendicular to the flexfoil body and the table 31, but it is equally useful when it is positioned at an oblique angle, such as about 45. The holder 35 of the connector always bends the tongue to be polished so that its end region is parallel to the axis of rotation or forms a slight predetermined angle with it.

While specific embodiments of the present invention have been illustrated and described, it will be appreciated that numerous modifications and changes will readily occur to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. And various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. It is therefore intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Claims (12)

1. A coupling device for coupling an optical waveguide of an optical flexfoil to an external device at a first portion of the optical waveguide for inputting or outputting light into or from the optical waveguide of the optical flexfoil, wherein the optical flexfoil has a body in one plane, characterized in that the coupling device has an opening in the first portion of the optical waveguide in such a way that a tab is formed leaving an area on the optical flexfoil for supporting the first portion, whereby the first portion and the tab can be bent or flexed laterally, i.e. away from the plane of the optical flexfoil and the first portion and the tab cannot protrude beyond the edge of the optical flexfoil in the plane of the optical flexfoil.

2. The connection device of claim 1, wherein said first portion is positioned at an inner end of said optical flexfoil plane, said inner end being spaced from said optical flexfoil edge, said opening being U-shaped.

3. The connection device of claim 1, wherein the first portion is located on an edge of the optical flexfoil, and wherein the opening has a strip shape extending perpendicularly inward from the edge of the optical flexfoil.

4. A method of making a connection for an optical waveguide of an optical flexfoil, wherein the optical flexfoil has a body in a plane, comprising the steps of:

-manufacturing the optical waveguides of the optical flexfoil such that at least one optical waveguide has a first portion and an optical connection of the optical waveguide to an external device is to be made on the first portion for inputting light into or outputting light from the optical waveguide of the optical flexfoil;

-then forming an opening in the optical flexfoil at the first portion, i.e. forming a tab leaving an area in the optical flexfoil for supporting the first portion, such that the first portion and the tab can be bent or flexed laterally, i.e. away from the plane of the optical flexfoil and the first portion and the tab cannot protrude beyond the edge of the optical flexfoil in the plane of the optical flexfoil.

5. The method of claim 4,

-said first portion is arranged to be positioned at an inner end position of said optical flexfoil plane at a distance from said optical fiber flexfoil edge when manufacturing said optical waveguide,

-making the opening U-shaped when forming the opening.

6. The method of claim 4,

-the first portion is positioned on an edge of the fiber optic flexfoil when manufacturing the optical waveguide,

-when forming the opening, the opening is made to have a strip-like shape extending perpendicularly from the edge of the optical flexfoil.

7. An optical flexfoil comprising at least one optical waveguide having a first portion on which an optical connection of the optical waveguide to an external device is to be made, so as to input light into or output light from the light guide of the optical flexfoil, wherein said optical flexfoil has a body in one plane, characterized in that said optical waveguide has a connection means, said connection means thus having an opening on said first part of said optical waveguide, i.e. leaving a region for supporting said first portion on said optical flexfoil forming a tab, such that the first portion and the tab can bend or flex laterally, i.e. out of the plane of the optical flexfoil and the first portion and the tab cannot protrude beyond the edge of the optical flexfoil in the plane of the optical flexfoil.

8. The optical flexfoil of claim 7, wherein the first portion is located at an inner end of the plane of the optical flexfoil, the inner end being spaced from the edge of the optical flexfoil, the opening being U-shaped.

9. The optical flexfoil of claim 7, wherein the first portion is located on an edge of the optical flexfoil, and the opening has a stripe shape extending perpendicularly from the edge of the optical flexfoil.

10. A backplane assembly having a circuit backplane with a first surface electrical connector for a circuit board to be connected to the backplane assembly, the backplane assembly further having an optical flexfoil, said optical flexfoil comprising at least one optical waveguide with a first portion on which an optical connection of said optical waveguide with an external device is to be made for inputting light into or outputting light from said optical waveguide of said optical flexfoil, wherein said optical flexfoil has a body in one plane, characterized in that said optical waveguide has a connection means having an opening in said first portion of said optical waveguide such that a region for supporting said first portion is left on said optical flexfoil forming a tab, whereby the first portion and the tongue are able to bend or flex laterally, i.e. out of the plane of the optical flexfoil, and the first portion and the tongue do not protrude beyond the edge of the optical flexfoil in the plane of the optical flexfoil, the optical flexfoil being positioned on and parallel to a second surface of the circuit substrate, which second surface is opposite to the first surface, the circuit substrate being provided with a through hole for passing the tongue of the optical flexfoil.

11. A method of manufacturing an optical flexfoil, comprising the steps of:

-manufacturing an optical flexfoil having at least one optical waveguide and at least one connection means having at least one flexible connection tab, whereby one end of the at least one optical waveguide is positioned at one end of the at least one flexible connection tab on which an optical connection is to be made from the at least one optical waveguide to an external device for inputting light into or outputting light from the at least one optical waveguide, wherein the optical flexfoil has a body in one plane and the connection means has an opening in the body face area such that a tab is formed leaving an area on the optical flexfoil for supporting the first portion, whereby the first portion and the tab can be bent or flexed laterally, i.e. away from the plane of the optical flexfoil and the first portion and the tab cannot be bent in the plane of the optical flexfoil An inner protrusion beyond an edge of the optical flexfoil;

-bending said at least one flexible connection tab such that an end region of said at least one connection tab is positioned at a predetermined angle with respect to said plane;

-polishing an end surface of said at least one optical waveguide terminating on the end of said bent at least one flexible connection tongue;

-returning the bent at least one flexible connection tab to an original position on the main body plane of the optical flexfoil.

12. The method of claim 11, wherein an optical connector is attached to said end of said at least one flexible attachment tab prior to said polishing.