Layered optical circuit

FIELD OF THE INVENTION

The present invention relates generally to optical circuits, and particularly to a multi-layered optical circuit.

DISCUSSION OF RELATED ART

Advances in optical networks, systems and connectors have resulted in a need to manage an increasing number of optical fibers in limited space. Numerous optical fibers are often managed by creating an optical circuit. An optical circuit includes a substrate to which optical fibers are arranged in a desired circuit pattern and permanently fixed to accomplish a desired fiber management, shuffling, cross-connection or distribution scheme. A typical optical circuit <b>10</b> (see <figref idref="DRAWINGS">FIGS. 1A-1D</figref>) includes a substrate <b>12</b>, such as a flexible sheet of Kapton®, supporting a layer of pressure-sensitive adhesive (not shown). Individual fibers or bundles of fibers (e.g. ribbons) <b>20</b> are laid and/or pressed onto the adhesive layer, e.g., by a CNC fiber-routing machine (not shown), in the desired circuit pattern. A protective layer (not shown) may be applied on top of the fibers to help hold them in place. The protective layer is typically a plastic, e.g. silicone-based, coating that conforms to the profile of the fibers and provides uniform coverage.

Lengths of the fibers extending beyond the edge of the substrate form termination legs <b>22</b> that are terminated with the desired connectors <b>24</b> (see FIG. <b>1</b>A), such as LIGHTRAY MPX® brand connectors. MTP®, MT-RJ or other MT-type connectors, LC-, FC-, or SC-type connectors, etc. Optically, the termination legs may be ribbonized for subsequent routing and/or convenient terminating to multi-fiber connectors. Exemplary optical circuits are shown in <figref idref="DRAWINGS">FIGS. 1A</figref>, <b>1</b>B, <b>1</b>C and <b>1</b>D. For reference, U.S. Pat. No. 5,204,925 to Bonanni et al., U.S. Pat. No. 6,005,991, to Knasel, U.S. Pat. No. 6,425,691 B1 to Demangone, and U.S. Pat. Nos. 6,427,034 B1 to Meis et al., the entire disclosures of which are hereby incorporated herein by reference, describe technology in technical areas similar to this application.

Applicant has observed that such optical circuits, though often flexible out of plane and/or having a thickness, are “planar” in that they involve either: (a) laminating portions of fibers between adjacent fiber end connectors to a single substrate; or (b) routing fibers between adjacent connectors in a single plane, on one side of a single substrate.

Such planar optical circuits are limited in the number of fibers that can be routed upon a given area of substrate. Such limitations are primarily due to a minimum bend radius characteristic of the fibers, and a maximum number of fibers that can be physically routed in stacked arrangement before causing microbends and microbend loss.

SUMMARY

The present invention provides a multi-substrate optical circuit and a layered optical circuit fabricated from the multi-substrate optical circuit. The multi-substrate optical circuit is similar to a conventional planar optical circuit in that it includes optical fibers affixed to a substrate to provide a desired circuit pattern, and in that portions of the optical fibers extend beyond the substrate(s) to form termination legs for termination to desired connectors. Hence, conventional optical circuit fabrication materials, techniques and equipment may be used to fabricate the multi-substrate optical circuit. The multi-substrate optical circuit differs from a conventional planar optical circuit, however, in that the optical fibers are routed between and bonded to multiple distinct substrates. The substrates thereby become interconnected by a free, unaffixed length of the optical fibers that permits bending of the fibers to stack the individual substrates in an overlapping manner to form a layered optical circuit in accordance with the present invention. The length should be sufficient to permit such bending without violating a minimum bend radius of the fibers. Accordingly, a continuous communications path is provided across multiple substrates, and across multiple layers of overlapping substrates.

In this manner, the layered optical circuit achieves a smaller form factor for an overall optical circuit by overlapping, e.g. stacking, planar optical subcircuits fabricated in a manner similar to that well known in the art. Accordingly, a relatively large layered optical circuit may occupy a relatively small footprint of a backplane, carrier, etc. The layered optical circuit provides a greater area of substrate for routing of fibers in a given footprint, and, therefore, a greater number of fibers, and/or a more complex circuit pattern, may be routed over that footprint while avoiding bend radius and microbend problems.

A method for fabricating a multi-substrate optical circuit and a layered optical circuit is also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIGS. 1A-1D</figref> are top views of exemplary prior art planar optical circuits.

<figref idref="DRAWINGS">FIGS. 2A-2C</figref> are top views of exemplary multi-substrate optical circuits for forming a layered optical circuit in accordance with the present invention.

<figref idref="DRAWINGS">FIGS. 3A-3H</figref> illustrate formation of exemplary layered optical circuits by planar rotation.

<figref idref="DRAWINGS">FIGS. 4A-4E</figref> illustrate formation of exemplary layered optical circuits by inversion.

<figref idref="DRAWINGS">FIGS. 5A-5B</figref> illustrate formation of an exemplary layered optical circuit by translation.

<figref idref="DRAWINGS">FIG. 6A</figref> is a top view of another exemplary multi-substrate optical circuit for forming a layered optical circuit in accordance with the present invention.

<figref idref="DRAWINGS">FIGS. 6B and 6C</figref> are top views of a partially and fully formed layered optical circuit, respectively, formed from the multi-substrate optical circuit of FIG. <b>6</b>A.

DETAILED DESCRIPTION

Conceptually, the present invention provides an optical circuit that is layered to achieve a smaller form factor for an optical circuit by overlapping, e.g. stacking, multiple interconnected planar optical circuits. A layered optical circuit provides a greater area of substrate for routing of fibers in a given footprint (e.g. surface area on a backplane or carrier), and, therefore, a greater number of fibers, and/or a more complex circuit pattern, may be routed over that footprint while avoiding bend radius and microbend problems. The optical circuit may be constructed from a multi-substrate optical circuit including separate substrate supported optical subcircuits connected by free fibers having a length sufficient to permit overlapping of the substrates while maintaining at least a minimum bend radius for the fibers.

<figref idref="DRAWINGS">FIGS. 2A-2C</figref> are top views of exemplary multi-substrate optical circuits <b>40</b> for forming a layered optical circuit in accordance with the present invention. The exemplary multi-substrate optical circuit <b>40</b> of <figref idref="DRAWINGS">FIG. 2A</figref> includes two substrates <b>42</b>, <b>44</b>. The desired number of fibers, which may or may not be ribbonized, are affixed to the first and second substrates <b>42</b>, <b>44</b> using fabrication techniques generally known in the art for forming optical circuits, to achieve the desired circuit pattern (exemplary shuffle pattern shown) and provide termination legs <b>55</b> extending beyond substrate edges <b>42</b><i>a</i>, <b>44</b><i>a </i>to which the desired connectors (not shown) may be applied. It will be understood that additional fibers may be part of the layered optical circuit although they are not affixed to both the first and second substrates.

More specifically, the first substrate <b>42</b> supports a first portion <b>54</b> of each the optical fibers, e.g. by supporting the fibers on a pressure sensitive adhesive coating of the substrate <b>42</b> and/or fixing them with a protective layer, as generally known for planar optical circuits, to form a first optical subcircuit <b>60</b>. The second substrate <b>44</b> supports a second portion <b>56</b> of each of the optical fibers, e.g. by arranging the fibers on a pressure sensitive adhesive coating of the substrate <b>42</b> and/or fixing them with a protective layer as generally known for planar optical circuits, to form a second optical subcircuit <b>70</b>. Each of the first optical subcircuit <b>60</b> and second optical subcircuit <b>70</b> is therefore similar to a planar optical circuit of the prior art. However, the subcircuits <b>60</b>, <b>70</b> are interconnected by free fibers to form a continuous communication path across these, and potentially other, substrates. As used herein, the term “free fiber” refers to fibers that are not affixed to a substrate, regardless of whether such fibers are ribbonized.

It will be appreciated by those skilled in the art that optical fibers, particularly when ribbonized, have limited flexibility for bending while maintaining desirable signal transmission capabilities. This is partly due to the structure of flat, multi-fiber ribbons which readily permit bending primarily out-of-plane, but prevents substantial bending in-plane. This limited flexibility is accounted for in constructing a multi-substrate optical circuit for fabrication into a layered optical circuit, by providing a sufficiently long length of free fibers between the first and second substrates to permit the desired bending, e.g. bending for overlapping the first and second substrates/optical subcircuits without violating a minimum bend radius parameter, typically approximately one (1) inch, of each of the optical fibers within the region of the free fibers. For example, a length of approximately six (6) inches to approximately seven (7) inches has been found sufficient for bare fibers, and a length of approximately seven (7) inches to eight (8) inches has been found sufficient for ribbonized fibers. Accordingly, the length of free fibers may be bent, twisted or otherwise routed as the substrates are repositioned into a different arrangement, such as a compact overlapping layered arrangement.

In this manner, layers of the layered optical circuit are interconnected, and may communicate, via continuous communications paths, e.g. via continuous lengths of optical fiber or separate lengths of connectorized optical fibers connected by a suitable connector. This latter arrangement may be particularly useful to construct relatively large layered optical circuit having many multi-substrate optical circuits and/or optical subcircuits. Rather than routing and fixing fibers in essentially two dimensions as in a typical planar optical circuit, fibers may thereby be routed over three dimensions as multiple interconnected planar optical circuits are stacked over a given footprint area, thereby providing greater substrate area for routing of fibers per unit of footprint area.

With specific reference of the embodiment of <figref idref="DRAWINGS">FIG. 2A</figref>, the second portion <b>56</b> of each optical fiber is longitudinally spaced from the first portion <b>54</b> along each of the optical fibers, such that the second substrate <b>44</b> is spaced from the first substrate <b>42</b> along the length of the fibers to define a third portion <b>58</b> of each of the fibers between the first and second portions <b>54</b>, <b>56</b>, and between the first and second substrates <b>42</b>, <b>44</b>. A length of free fibers (third portion <b>58</b>) between the portions attached to the substrates <b>60</b>, <b>70</b> is not affixed to any substrate.

A layered optical circuit <b>100</b> (see <figref idref="DRAWINGS">FIGS. 3A-6C</figref>) may be fabricated from a multi-substrate optical circuit <b>40</b> (see <figref idref="DRAWINGS">FIGS. 2A-2C</figref>) using various techniques for positioning the second substrate in at least partially overlapping relationship to the first substrate (e.g. visually as viewed from the top). Such overlapping creates the layered effect that allows for substantial space savings as compared to having all optical circuits in a single plane.

<figref idref="DRAWINGS">FIGS. 3A-3D</figref> show formation of an exemplary layered optical circuit <b>100</b> by a planar rotation. As shown in <figref idref="DRAWINGS">FIG. 3A</figref>, the second substrate <b>44</b> of the multi-substrate optical circuit <b>40</b> of <figref idref="DRAWINGS">FIG. 2A</figref> is rotated, in substantially a plane as shown by arrow X in <figref idref="DRAWINGS">FIG. 3A</figref>, until positioned adjacent the first substrate, as shown in FIG. <b>3</b>B. This causes the free fibers <b>58</b><i>a</i>, <b>58</b><i>b </i>(third portions) of the fibers to form loops. The second substrate <b>44</b> is displaced out of plane, but still substantially in the same plane, to at least partially overlap the first substrate <b>42</b>, as shown in FIG. <b>3</b>C. This causes a twist at Y in one of the loops, which is optionally manually untwisted, as shown in FIG. <b>3</b>D. As a result of this planar rotation, the side of first substrate to which the optical fibers are affixed (front side) is positioned facing the back side (opposite the side to which the optical fibers are affixed) of the second substrate. This is also shown in <figref idref="DRAWINGS">FIGS. 3E and 3F</figref>.

In this particular example, each of the optical fibers has a first end extending beyond an edge <b>42</b><i>a </i>of the first substrate <b>42</b>, and a second end extending beyond an edge of the second substrate <b>44</b>. These ends form the termination legs <b>55</b> that are positioned adjacent one another and may therefore be easily re-ribbonized and/or terminated to a connector <b>64</b>, as desired. The co-location and alignment of multiple fibers/termination legs from multiple layers of the layered optical circuit is particularly well-suited to termination to a multi-row ferrule, such as recently developed multi-row MPX connectors. Additionally, such multi-substrate optical circuits permit interconnection of fibers within a row, or between rows, of a single multi-row ferrule.

<figref idref="DRAWINGS">FIG. 3G</figref> shows an alternative multi-substrate optical circuit <b>40</b> including three substrates <b>42</b>, <b>44</b>, <b>46</b> having exemplary fiber routing (not shown) providing exemplary termination legs <b>55</b>. As shown in <figref idref="DRAWINGS">FIG. 3H</figref>, the multi-substrate optical circuit <b>40</b> of <figref idref="DRAWINGS">FIG. 3G</figref> may be formed into a layered optical circuit <b>100</b> by planar rotation of substrates <b>44</b> and <b>46</b>, in a manner similar to that described above with reference to <figref idref="DRAWINGS">FIGS. 3A-3D</figref>. In this embodiment, each of substrates <b>44</b> and <b>46</b> entirely overlap substrate <b>42</b>, but do not overlap one another.

<figref idref="DRAWINGS">FIGS. 4A-4E</figref> show formation of exemplary layered optical circuits by inversion. For example, second substrate <b>44</b> of the multi-substrate optical circuit <b>40</b> of <figref idref="DRAWINGS">FIG. 2A</figref> may be rotated 180 degrees (e.g. to turn substrate <b>44</b> face down as viewed from the top in <figref idref="DRAWINGS">FIG. 4A</figref>) and then rotated in plane as described above with reference to <figref idref="DRAWINGS">FIGS. 3A-3D</figref>. Alternatively, second substrate <b>44</b> may be flipped out of plane in the direction of arrow Z of <figref idref="DRAWINGS">FIG. 4A</figref> to achieve the same positioning, as shown in FIG. <b>4</b>B. In this manner, the side of the first and second substrates <b>42</b>, <b>44</b> to which the optical fibers are affixed (front sides) are positioned facing one another, as shown in <figref idref="DRAWINGS">FIG. 4C</figref>, in at least partial overlapping arrangement.

<figref idref="DRAWINGS">FIG. 4D</figref> shows an alternative embodiment of a multi-substrate optical circuit <b>40</b> that is similar to that shown in <figref idref="DRAWINGS">FIG. 2A</figref> in that it includes first and second substrates <b>42</b>, <b>44</b>. However, in the multi-substrate optical circuit <b>40</b> shown in <figref idref="DRAWINGS">FIG. 4D</figref>, the optical fibers are laid during fabrication of the multi-substrate optical circuit <b>40</b> to provide a twist in the third region <b>58</b> between the substrates <b>42</b>, <b>44</b>. For example, the individual portions <b>58</b><i>a</i>, <b>58</b><i>b </i>may simply be crossed as shown, or they may be twisted (i.e. to invert the ribbons between the substrates) and crossed. Accordingly, the second substrate <b>44</b> may be inverted as described above, e.g. by rotating 180 degrees out of plan and then rotating in plane or by flipping out of plane, to reposition the second substrate <b>44</b> the multi-substrate optical circuit <b>40</b> of <figref idref="DRAWINGS">FIG. 2A</figref> in at least partial overlapping relationship with the first substrate <b>42</b>, as shown in FIG. <b>4</b>E. As described above with reference to <figref idref="DRAWINGS">FIG. 4C</figref>, the sides of the first second substrates <b>42</b>, <b>44</b> to which the optical fibers are affixed (front sides) are then facing one another in the layered optical circuit <b>100</b>. In this manner, the twist in third portion <b>58</b> during fabrication of the multi-substrate optical circuit <b>40</b> is untwisted during fabrication of the layered circuit <b>100</b>.

<figref idref="DRAWINGS">FIGS. 5A and 5B</figref> shown formation of an exemplary layered optical circuit <b>100</b> by translation. More specifically, the second substrate <b>44</b> of the multi-substrate optical circuit <b>40</b> of <figref idref="DRAWINGS">FIG. 2A</figref> may be simply translated, e.g. moved toward, the first substrate <b>42</b> and be displaced slightly out of plane to allow the second substrate <b>44</b> to at least partially overlap the first substrate <b>42</b> to form the layered optical circuit <b>100</b>. In this particular exemplary arrangement, the various termination legs <b>55</b> of the individual substrates <b>42</b>, <b>44</b> are not conveniently located for reribbonization and/or termination to a multi-row ferrule because they are positioned at opposite ends of the layered optical circuit <b>100</b>.

It should be appreciated that numerous layers may be stacked, using any desired combination of techniques such as planar rotation, inversion and translation, to form a layered optical circuit in accordance with the present invention. The individual planar subcircuits may be formed as discussed above, in a suitable circuit pattern to achieve the desired connectivity, fiber routing, etc. and layered optical circuit. By way of further example, <figref idref="DRAWINGS">FIG. 6A</figref> is a top view of another, slightly more complex, exemplary multi-substrate optical circuit <b>40</b>. As shown in <figref idref="DRAWINGS">FIG. 6A</figref>, the multi-substrate optical circuit <b>40</b> includes four substrates <b>42</b>, <b>44</b>, <b>46</b>, <b>48</b> supporting a plurality of optical fibers/ribbons routed in a desired circuit pattern (not shown in detail) to provide sixteen termination legs <b>55</b>. As shown in <figref idref="DRAWINGS">FIGS. 6A and 6B</figref>, a first fabrication step includes a planar rotation (shown by arrow X) of substrate <b>44</b> to overlap substrate <b>44</b> with substrate <b>42</b>. Similarly, substrate <b>48</b> undergoes a planar rotation (shown by arrow X′) to overlap substrate <b>46</b>. This produces the partially formed layered optical circuit <b>100</b> of FIG. <b>6</b>B. Substrates <b>46</b> and <b>48</b> then undergo a planar rotation (shown by arrow X″) to overlap substrates <b>42</b> and <b>44</b> to form the layered optical circuit <b>100</b> of FIG. <b>6</b>C. In this example, certain termination legs <b>55</b>, namely C<b>2</b>, C<b>4</b> and D<b>2</b>, D<b>4</b> are positioned adjacent one another for easy reribbonization and/or termination to a multi-row ferrule or other connector, as desired.

It should be noted that a multi-substrate optical circuit and a layered optical circuit in accordance with the present invention may have numerous configurations, as desired. For example, <figref idref="DRAWINGS">FIGS. 2B and 2C</figref> illustrate that the individual multi-substrate optical circuits <b>40</b> may include as many substrates as desired, and the individual substrates <b>42</b>, <b>44</b>, <b>46</b>, <b>48</b> may have any shape desired to provide the desired numbers of layers and the desired connectivity and/or routing, as will be understood by those skilled in the art.

In any of the foregoing embodiments, after the substrates are positioned in at least partially overlapping relationship, they will tend to move or separate to allow the fibers to relax from their bent state. To maintain the substrates in the desired relative positions, the substrates may be affixed in fixed relative positions in any suitable manner, e.g. by adhesively or otherwise bonding the substrates to one another, mechanically fastening the substrates to one another by pins, screws, etc., or by mounting both substrates to a common carrier, such as a backplane, cabinet, etc.

A multi-substrate optical circuit may be fabricated by providing a first substrate and a second substrate in substantially the same plane as the first substrate. The second substrate is preferably positioned at a distance from the first substrate to provide a desired length between adjacent edges of the first and second substrates, as discussed further below. Alternatively, the substrates are closely positioned and a loop of desired length is left between edges of the adjacent substrates. Substrates of a type typically used for optical circuits are suitable, e.g. a flexible substrate provided with a pressure sensitive adhesive layer. For example, these substrates may be provided on a substantially planar bed of a CNC fiber routing machine typically used to fabricate optical circuits, and the fibers may be laid/routed in the usual manner, except that the fibers are routed, in part, over an area that is not provided with a substrate, and that is positioned between substrates to which the fibers are to be affixed (the free fiber area).

The fabrication includes mounting to the first substrate a first portion of each of a plurality of optical fibers. This may be performed in a traditional manner by pressing the fibers onto the pressure sensitive adhesive of a substrate, and/or providing a protective top coating as is well known in the art. This effectively forms an optical circuit of the prior art.

In accordance with the present invention, the method also involves mounting to the second substrate a second portion of each of the plurality of optical fibers. The second portion is a portion longitudinally spaced from the first portion by a third portion of each of the plurality of optical fibers. In other words, a portion of the same fibers affixed to the first substrate are then affixed to the second substrate in a similar manner, e.g. by pressing the fibers on the pressure sensitive adhesive of the second substrate and/or providing a protective layer. The second portion is thereby affixed to the second substrate to leave a third portion that has a length for permitting overlapping of the first and second substrates without exceeding a minimum bend radius of each of the optical fibers within the third portion. The length required is in part a function of the flexibility of the optical fibers (with cladding, jacketing, etc.), whether the fibers are ribbonized, and the number of fibers in the ribbon, etc. Determining a length for permitting desired bending of fibers without exceeding a minimum bend radius is well known in the art.

A layered optical circuit may then be fabricated from the multi-substrate optical circuit by positioning at least a portion of the second substrate to overlap the first substrate. The causes the portion to be displaced from the plane of the first substrate and the substrates to overlie one another to create a space savings. As discussed above, the positioning of the substrates in a layered orientation may include a planar rotation, a planar translation or an inversion of at least one of the substrates. Preferably, the layered substrates are then affixed in fixed relative positions.

Optionally, mounting of fibers to the second substrate may involve twisting the plurality of optical fibers in a transition area (third portion) defined between the first and second portions of the optical fibers, such that the inversion of the substrate(s) tends to untwist the optical fibers. Alternatively, a twist may be built into the fibers of the multi-substrate optical circuit, as discussed above, such that the inversion tends to untwist the fibers.

The layered optical circuit may then be used substantially similarly to a planar optical circuit of the prior art, e.g. by terminating the termination legs to desired connectors, mounting the layered optical circuit on a carrier, backplane, cabinet, etc. and/or connecting the layered optical circuit to other circuits, signal transmission hardware, etc.

Having thus described particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements as are made obvious by this disclosure are intended to be part of this description though not expressly stated herein, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only, and not limiting. The invention is limited only as defined in the following claims and equivalents thereto.