Patent Description:
The present disclosure generally relates to optical assemblies and, more particularly, to optical assemblies incorporating fiber array spacers having a precise height provided by precision-diameter optical fiber.

Benefits of optical fiber include extremely wide bandwidth and low noise operation. Because of these advantages, optical fiber is increasingly being used for a variety of applications, including, but not limited to, broadband voice, video, and data transmission. Outdoor fiber networks are popular to support the demand of data consumption. Due to high speed wireless communication networks and the Internet of Things, many communication devices and antennas need to be equipped with a fiber optic connection for communicating data into the optical fiber infrastructure required of such communication networks.

Low-cost fiber array assemblies are important components for connectors and photonic integrated circuit interconnections. For example, two-dimensional fiber arrays on a precise pitch may be required for low-loss coupling to arrays of lenses on a separate substrate. Two-dimensional fiber array interconnections can also be used in high density interconnections to photonic chip grating couplers. Such fiber arrays require not only a precise lateral pitch between adjacent optical fibers, but also a precise vertical pitch between optical fibers of adjacent rows of optical fibers. Precise height placement of optical components may be required in other optical applications as well.

However, substrates of a precise thickness to provide such precise height tolerances are costly and difficult to fabricate. For example, it may be difficult to precisely draw a glass sheet having a desired thickness. Additionally, it may be time consuming and costly to machine or etch a substrate to a desired thickness.

<CIT> discloses fiber array assemblies which include an interdigitated signal-fiber array supported on a support substrate and formed by front-end sections of first signal fibers interdigitated with either front-end sections of second signal fibers or spacer fibers. The assemblies also include a fiber pusher device that may comprise glass and first and second ends. The fiber pusher device is disposed so that its first and second ends contact and push against first and second edges of the interdigitated signal-fiber array to remove gaps between adjacent signal fibers. A cover sheet is disposed atop the interdigitated signal-fiber array and covers at least a portion of the fiber pusher device to define a ferrule. A securing material is disposed within a ferrule interior to secure the cover sheet, the interdigitated signal-fiber array and the fiber pusher devices. The fiber array assemblies can be connectorized by adding an interconnect device or the like.

<CIT> discloses a two-dimensional fiber array structure including a base which includes a baseboard, a cover board and a spacer layer, and an optical fiber cable is positioned between the baseboard and the cover board, positioning fibers are positioned at two external sides of the optical fiber cable, the spacer layer is abutted with two adjacent fiber layers of the optical fiber cable to reduce the position tolerance along X axis for further improving accuracy.

Embodiments described herein are directed to fiber array spacers that provide a precision-thickness spacer for optical components, as well as optical assemblies that incorporate fiber array spacers and methods of fabricating the same. The fiber array spacers described herein are fabricated from optical fibers and leverage the precise diameter of exposed glass optical fibers to enable fiber array spacers of a highly precise thickness. The precision of the thickness of the fiber array spacer is based on the tolerance of the diameter of the spacer fibers that make up the fiber array spacer. It is much easier to fabricate drawn glass optical fibers having a precise diameter than it is to fabricate a sheet having a uniformly precise thickness. Thus, embodiments described herein enable low-cost fabrication of two-dimensional fiber arrays as well as other optical components where precision along the Y-axis (i.e., vertical direction) may be required.

Various embodiments of fiber array spacers comprising spacer fibers, optical fiber assemblies optical components, and methods of manufacture are described in detail herein.

Referring now to <FIG>, an example multi-fiber cable <NUM> (i.e., a fiber ribbon) for fabricating a fiber array spacer for an optical fiber assembly is illustrated. The multi-fiber cable <NUM> comprises an array of optical fibers <NUM> that are supported by a cable jacket <NUM>. The front end of the cable jacket <NUM> is stripped away, thereby exposing the array of optical fibers <NUM>. As a non-limiting example, the stripping process for removing the cable jacket <NUM> may be carried out using mechanical strippers, which heat and soften the cable jacket <NUM> prior to removal using a pair of serrated blades.

A protective coating <NUM> is stripped away at the front end of the array of optical fibers <NUM> to expose an glass portion <NUM>. However, it should be understood that embodiments are not limited to optical fibers <NUM> having an exposed cladding. For example, the glass portion <NUM> may be a core portion. The protective coating <NUM> may be removed using a similar mechanical process referred to above with respect to the cable jacket <NUM>, or it may be removed by a laser-based stripping process. Although <FIG> illustrates a portion of the protective coating <NUM> present on the exposed array of optical fibers, embodiments are not limited thereto. For example, <FIG> illustrates a multi-fiber cable <NUM> wherein substantially all of the protective coating <NUM> is removed from the exposed array of optical fibers <NUM>.

Referring to <FIG>, each optical fiber <NUM> comprises a core <NUM>, a cladding <NUM> surrounding the core, and a protective coating <NUM> surrounding the cladding. As stated above, the protective coating is stripped way to provide an glass portion <NUM>. The core <NUM> has a core diameter DC, the cladding has a cladding layer diameter DCL, and the protective coating has a protective coating layer DPL. Because the diameter of optical fibers is precisely controlled, the glass portion (i.e., the cladding) has a precise diameter DCL that is utilized form a fiber array spacer with a precise height to precisely align optical fibers of an optical connector or an optical assembly. An example optical fiber for the optical fiber <NUM> is Corning SMF-<NUM>® fiber manufactured and sold by Corning, Inc. or Corning, New York, which has a diameter of <NUM>. However, embodiments are not limited thereto. As another example, the optical fiber may have a cladding layer diameter DCL (or a core diameter DC) of <NUM>. Optical fibers may be selected based on their diameter, and also may be custom manufactured to have a desired diameter within a specified tolerance.

Referring now to <FIG>, an example assembly bench <NUM> used to fabricate an optical fiber array spacer is illustrated. As described in more detail below, the assembly bench <NUM> is used to interdigitate optical fibers of two multi-fiber cables <NUM>. The term "interdigitate" or "interdigitated" as used herein means that the first and second optical fibers of two multi-fiber cables <NUM> (e.g., A and B) are arranged in an alternating pattern A-B-A-B-A-B and so on.

The illustrated assembly bench <NUM> includes a support plate <NUM> (i.e., a first support substrate), a first release sheet 131A, a first pusher element 110A, a second pusher element 110B, a second release sheet 131B, and a cover plate <NUM> (i.e., a second support substrate).

The support plate <NUM> supports all of the elements of the assembly bench <NUM> and serves as a bearing surface for applied vertical squeeze forces V1 and V2 (<FIG>). The support plate <NUM> has a precision flat surface <NUM> such that any deviation from an ideal plane fitted to the precision flat surface <NUM> is less than or equal to <NUM>. The surface flatness of the precision flat surface <NUM> should be precisely controlled to ensure uniform height of the resulting fiber array spacer. The support plate <NUM> may be fabricated from any suitable material. As a non-limiting example, the support plate <NUM> may be a fusion drawn glass substrate having a uniform thickness.

The first release sheet 131A is disposed on the precision flat surface <NUM> of the support plate <NUM>. The first release sheet 131A (and the second release sheet 131B) may be implemented as a thin polymer sheet of uniform thickness (e.g., a sheet of polytetrafluoroethylene (PTFE), polyvinylidene chloride (PVDC), and low-density polyethylene (LDPE)), or it may be thin surface coating (e.g., PTFE or oil coating) of controlled uniform thickness applied to the precision flat surface <NUM> prior to adhesive application. The first release sheet 131A should be thin enough to enable sufficient ultra-violet (UV) radiation transmission to enable adhesive curing, as described in more detail below. Additionally, the first release sheets described herein should be thin enough (e.g., less than or equal to <NUM> or less than or equal to <NUM>) such that deformation of the release sheet(s) during fabrication does not contribute to error in the vertical alignment of the spacer fibers. , as described in more detail below. Further, the release sheets described herein should be precisely thick such that the release sheet(s) do not contribute to error in the vertical alignment of the spacer fibers. As a non-limiting example.

In a specific, non-limiting example, the first release sheet 131A and/or the second release sheet 131B may be configured as a fluorosilane coating that is applied to at least the precision flat surface <NUM>, such as by a dipping process. The fluorosilane coating results in a durable monolayer that does not bond to UV cured adhesives. Because fluorosilane release coating may be applied to any material with surface oxides, such as metals or certain ceramics, they are also useful for coating other fixture elements, such as the first and second pusher elements 110A, 110B described below.

A first multi-fiber cable 60A and a second multi-fiber cable 60B are used to fabricate the fiber array spacer. The first multi-fiber cable 60A includes a first cable jacket 61A having been stripped to expose an array of first optical fibers 52A, which have a first protective coating portion 76A and a first glass portion 74A (which may be exposed cladding or core). It should be understood that embodiments may not use a multi-fiber cable but rather bare optical fibers that have neither a protective coating nor a cable jacket.

Similarly, the second multi-fiber cable 60B includes a second cable jacket 61B having been stripped to expose an array of second optical fibers 52B, which have a second protective coating portion 76B and a second glass portion 74B (which may be exposed cladding or core). The second multi-fiber cable 60B provides an additional array of optical fibers.

The first and second glass portions 74A, 74B may be exposed cladding or core. However, in some embodiments, the first and second glass portions 74A, 74B may be coated with a coating to increase durability, or to improve laser bonding as described in more detail below. A non-limiting example is a titanium coating. The coating should be thin enough and its thickness controlled so that the coating does not adversely affect the precise diameter of the drawn fibers that enable the precision spacing of the fiber spacer array.

The glass portions 74A, 74B of the first and second optical fibers 52A, 52B are arranged in opposition and interdigitated on the first release sheet 131A. Thus, the interdigitated array of optical fibers comprises alternating first optical fibers 52A and second optical fibers 52B.

The cover plate <NUM> includes a precision flat surface <NUM> such that any deviation from an ideal plane fitted to the precision flat surface <NUM> is less than or equal to <NUM>. A non-limiting example material is fusion drawn glass. As described in more detail below, the cover plate <NUM> applies a vertical downward force on the interdigitated glass portions 74A, 74B of the first and second optical fibers 52A, 52B.

An adhesive <NUM>, such as a UV-curable adhesive, is disposed on the interdigitated glass portions 74A, 74B of the first and second optical fibers 52A, 52B. A second release sheet 131B is disposed on the glass portions 74A, 74B of the first and second optical fibers 52A, 52B and the adhesive <NUM>. The second release sheet 131B may be a polymer sheet or a coating (e.g., a fluorosilane coating) that is applied to the precision flat surface <NUM> of the cover plate <NUM> as described above with respect to the first release sheet 131A. Thus, the first release sheet 131A and the second release sheet 131B are positioned between the interdigitated glass portions 74A, 74B and the support plate <NUM> and the cover plate <NUM>, respectively, to prevent the interdigitated glass portions 74A, 74B from becoming permanently bonded to the support plate <NUM> and the cover plate <NUM>.

The first and second pusher elements 110A, 110B apply horizontal forces that squeeze the interdigitated glass portions 74A, 74B together from opposite sides. The first and second pusher elements 110A, 110B should have a thickness that is less than a diameter of the glass portions 74A, 74B of the first and second optical fibers 52A, 52B to enable them to slide between the support plate <NUM> and the cover plate <NUM>. Examples of the first and second pusher elements 110A, 110B include, but are not limited to, solid sheets of glass, metal, plastic, or ceramic. In another non-limiting example, the first and second pusher elements 110A, 110B may be an array of optical fibers having a diameter less than the diameter of the interdigitated glass portions 74A, 74B. As stated above, the first and second pusher elements 110A, 110B may be coated with a fluorosilane release coating, which may be beneficial over PTFE-coated elements because PTFE-coated pusher elements can experience delamination during pusher element removal after adhesive curing, which results in damage to the pusher elements and residual PTFE material remaining along the sides of the fiber array where it can inhibit precision passive alignment to other components.

Referring to <FIG>, the interdigitated glass portions 74A, 74B are squeezed by the first pusher element 110A applying a first lateral force L1 and the second pusher element 110B applying a second, opposing lateral force L2. The first and second lateral forces L1, L2 drive the interdigitated glass portions 74A, 74B into contact with one another such that there is substantially no gap (less than <NUM> as a non-limiting example) between adjacent glass portions of the first and second optical fibers 52A, 52B. A first vertical force V1 is applied by way of the cover plate <NUM> and a second vertical force V2 is applied by way of the support plate <NUM>. The first and second vertical forces V1, V2 establish the location of the interdigitated glass portions 74A, 74B in the Y-direction.

<FIG> provides a cross-section view looking down the axes of the interdigitated glass portions 74A, 74B. As shown in <FIG>, interdigitated glass portions 74A, 74B are an array of alternating first optical fibers 52A and second optical fibers 52B. The interdigitated glass portions 74A, 74B define an interdigitated array of optical fibers <NUM>. The first and second pusher elements 110A, 110B may push the first optical fibers 52A and second optical fibers 52B such that there is substantially no gap between adjacent optical fibers. This may be beneficial in applications wherein the resulting fiber array spacer provides a V-groove surface on its top surface for placement of optical fibers. For example, center-to-center spacing between adjacent optical fibers may be determined by the diameter of the optical fibers, such as <NUM>, for example. In other embodiments, there is no requirement as to the spacing between adjacent optical fibers.

In some embodiments, a rigid mechanical bond can be formed between adjacent glass portions of optical fibers using laser joining technology. For example, metallized optical fibers are fabricated to enable soldered feedthrough ports in hermetically packaged phonic components (e.g., erbium pump amplifiers). Fiber metallization can involve deposition of a thin layer (e.g., <NUM>-500Å) of optically absorbing material (e.g., stainless steel, chromium). The additional metallization layer is sufficiently thin to not alter the diameter of the optical fiber beyond target specifications.

Referring now to <FIG>, an assembly bench <NUM>' is modified to include a laser beam delivery system <NUM> that is positioned directly over the interdigitated array of optical fibers <NUM>. The laser may be, without limitation, a Nd:YAG laser with a wavelength of <NUM> that delivers a laser beam <NUM> having pulses with <NUM>-<NUM> kW pulse power. A laser beam focal spot <NUM> (<NUM>-<NUM> diameter) can be moved up-down and left-right so that the focus may be located at the joining interface between adjacent fibers.

After squeezing force is applied to the interdigitated array of optical fibers <NUM> the laser beam focal spot <NUM> is used to join each neighboring optical fiber 52A, 52B in the interdigitated array of optical fibers <NUM>. Laser activation heats the optical fibers 52A, 52B where they contact each other so that the metal coating on adjacent optical fibers 52A, 52B melts and flows together. After laser heating is terminated the metal cools and solidifies, a metallized bond <NUM> is formed that holds the optical fibers 52A, 52B together. The laser bond <NUM> is confined to the contact region between adjacent optical fibers 52A, 52B so that the distance between the top and bottom surfaces of each optical fiber 52A, 52B equals the original fiber diameter.

The laser beam focal spot <NUM> can also be translated parallel to the optical fiber axis to provide a long, metallized bond between adjacent optical fibers 52A, 52B that may be more mechanically robust than bonding at a single point. The first and second release sheets 131A, 131B shown in <FIG> may not be needed if the interdigitated array of optical fibers <NUM> can be easily removed from the support plate <NUM> and the cover plate <NUM> after laser bonding.

Depending on the optical properties of cover plate <NUM> and the first release sheet 131A (if used), it may be desirable to split these components into two parts to provide an unobstructed optical path between the laser beam <NUM> and the interdigitated array of optical fibers <NUM>. While these components are split, they are still able to provide vertical squeeze force in close proximity to laser bonding region. This ensures that during laser bonding the interdigitated array of optical fibers <NUM> are correctly aligned to each other and the top and bottom plates. The top plate can also be made of one piece of glass with a hole in the middle so that its left and right bottom surfaces are guaranteed to be coplanar.

Referring now to both <FIG>, the elastic modulus of the first and second release sheets 131A, 131B may be sufficiently low to allow deformation of the release sheets during application of the first and second vertical forces V1, V2. Release sheet deformation should be approximately uniform across the interdigitated glass portions 74A, 74B, ensuring that the squeezed interdigitated glass portions 74A, 74B remains parallel to the support plate <NUM> and the cover plate <NUM>. Release sheet deformation helps ensure that substantially no adhesive remains on the top and bottom surfaces of the interdigitated glass portions 74A, 74B so that the distance between these surfaces is precisely determined by the diameter of the optical fibers.

The first and second pusher elements 110A, 110B can be designed to be removed after fiber array spacer assembly. For example, if the pusher elements 110A, 110B are designed to only extend between the support plate <NUM> and the cover plate <NUM> by a small distance (e.g., <NUM>-<NUM>), it may be removed after adhesive curing. Adhesion of the adhesive to the pusher elements 110A, 110B may be prevented using non-stick coatings or other release materials.

In other embodiments, the first and second pusher elements 110A, 110B may be designed to break off in subsequent assembly steps so that the tip of the first and second pusher elements 110A, 110B remains. The length of the first and second pusher elements 110A, 110B may be extended to allow them to be used as a handle to simplify fiber array spacer positioning in subsequent assembly steps.

After adhesive curing (which may be by UV curing and/or thermal curing steps), the first and second multi-fiber cables 60A, 60B are removed from the assembly bench <NUM>. If the first and second release sheets 131A, 131B are implemented as discrete sheets or films (as opposed to coatings), then the first and second release sheets 131A, 131B will initially remain on the interdigitated glass portions 74A, 74B as shown in <FIG>. After the removal of the first and second release sheets 131A, 131B, the assembly appears as shown in <FIG>. Note that the first or second cable jacket 61A, 61B is not shown in <FIG>. Compression of the first and second release sheets 131A, 131B by the interdigitated glass portions 74A, 74B during assembly produces undulating top fiber surfaces T (i.e., first surfaces) and bottom fiber surfaces B (i.e., second surfaces). As shown in <FIG>, the top fiber surfaces T define a first plane P<NUM> and the bottom fiber surfaces B define a second plane P<NUM> that is parallel to the first plane P<NUM>. The adhesive <NUM> does not extend beyond the first plane P<NUM> and the second plane P<NUM>. This surface variation may reduce the influence of dust and debris during fiber array spacer stacking as described below.

The adhesive <NUM> used to join adjacent optical fibers may be a flexible low modulus adhesive, which allows the resulting fiber array spacer to conform to the surface it is placed on so that the fiber array spacer is positioned at a precision vertical offset from a mounting surface. A high modulus adhesive can also be used between adjacent optical fibers to produce a rigid fiber array spacer. This type of fiber array spacer may be desirable in applications where the fiber array spacer serves as a geometrical datum surface for additional elements that are joined to the fiber array spacer.

In some embodiments, the support plate <NUM> and/or the cover plate <NUM> are elements of the resulting fiber array spacer. Referring once again to <FIG>, the first release sheet 131A and/or the second release sheet 131B may not be provided. Thus, the interdigitated array of optical fibers <NUM> will be bonded to the support plate <NUM> when the first release sheet 131A is not provided, and the interdigitated array of optical fibers <NUM> will be bonded to the cover plate <NUM> when the second release sheet 131B is not provided.

The support plate <NUM> and/or the cover plate <NUM> may be fabricated with a precise thickness. A glass support plate <NUM> can be fabricated with an extremely flat surface (e.g., deviation of less than <NUM> from an ideal plane) using fusion draw processes. The support plate <NUM> may be made of other materials, such as a CTE-matched silicon substrate, a glass-ceramic material, or a ceramic material. The same process can produce glass sheets with parallel top and bottom surfaces and precise thickness control. In these embodiments, the entire fiber array and its support plate can serve as a precision spacer.

<FIG> illustrates an embodiment wherein no first release sheet 131A is provided on the surfaces <NUM> of the support plate <NUM> such that the adhesive <NUM> bonds the interdigitated array of optical fibers <NUM> to the support plate <NUM> during the interdigitating process described above and illustrated by <FIG>. This is a single step process.

It is also possible to fabricate an interdigitated array of optical fibers <NUM> bonded to the support plate <NUM> by a two-step process. First the interdigitated array of optical fibers <NUM> are fabricated as shown in <FIG> by the process of <FIG> and <FIG>. Next, a layer of adhesive is applied to a support plate <NUM> to subsequently bond the interdigitated array of optical fibers <NUM> to the surface <NUM> of the support plate.

In each case, the lower support plate <NUM> may be a thin sheet of glass, or a fiber array spacer that is fabricated to be precisely flat (by forming between flat sheets, such as fusion drawn glass sheets).

<FIG> illustrates a first multi-fiber cable 60A and a second multi-fiber cable 60B that are joined at the interdigitated glass portions 74A, 74B by the process using the assembly bench <NUM> described above. Multiple fiber array spacers can be harvested from a single interdigitated array of optical fibers <NUM>. As shown in <FIG>, the interdigitated array of optical fibers <NUM> is cut along a cut line CL, such as, without limitation, by scoring and breaking the bare fibers, diamond sawing, or laser cleaving.

After cutting, a first interdigitated array of optical fibers 75A is attached to the first multi-fiber cable 60A and a second interdigitated array of optical fibers 75B is attached to the second multi-fiber cable 60B, as shown in <FIG>. The first interdigitated array of optical fibers 75A comprises alternating first glass portions 74A of the first optical fibers 52A and spacer fibers <NUM> which are fiber stubs cut from the second optical fibers 52B of the second multi-fiber cable 60B. Fiber stubs are short lengths of optical fiber that do not pass optical signals. The second interdigitated array of optical fibers 75B comprises alternating second glass portions 74B of the second optical fibers 52B and spacer fibers <NUM> which are fiber stubs cut from the first optical fibers 52A of the first multi-fiber cable 60A.

In some applications, it is desirable for the fiber array spacer to remain attached to the multi-fiber cable to simplify handling and positioning of the fiber array spacer. In the embodiment shown in <FIG>, a first fiber array spacer 80A is defined by the first interdigitated array of optical fibers 75A and a second fiber array spacer 80B is defined by the second interdigitated array of optical fibers 75B.

In other applications, an individual fiber array spacer without the attached multi-fiber cable may be desired. <FIG> illustrate a cut line CL that may be used to fully separate the first fiber array spacer 80A from the first multi-fiber cable 60A. <FIG> illustrates a fully separated fiber array spacer <NUM> that may be used in an optical device, such as an optical connector.

<FIG> illustrates a fiber array spacer <NUM> with substantially no gap between adjacent spacer fibers <NUM>. Additionally, the spacer fibers <NUM> do not need to be parallel to one another.

In some embodiments, the fiber array spacer <NUM> further includes a precision support plate <NUM> as shown in <FIG> and described above.

<FIG> illustrates how multiple cut lines CL may be used to separate multiple fiber array spacers <NUM> from a single interdigitated array of optical fibers <NUM>. <FIG> illustrates three separated fiber array spacers <NUM> from the single interdigitated array of optical fibers <NUM> shown in <FIG>.

It is noted that a fiber array spacer may be fabricated with as few as two precision diameter optical fibers. In embodiments having just two optical fibers, the fiber array spacer will be most stable if it is fabricated with the two optical fibers spaced as far apart as is practical.

Referring now to <FIG>, in some embodiments, a fiber array spacer <NUM>-<NUM> may include at least two spacer fibers <NUM> that are spaced apart by an intermediary spacer sheet <NUM> having a height HS that is less than the diameter of the spacer fibers <NUM> (e.g., the diameter of the cladding layer DCL). Having the HS of the intermediary spacer sheet <NUM> ensures that only the upper and lower surfaces of the at least two spacer fibers <NUM> define the thickness of the fiber array spacer <NUM>-<NUM>. The fiber array spacer <NUM>-<NUM> of <FIG> may be fabricated in a similar manner as shown in <FIG> and described above except internal spacer fibers are replaced by at least two outer spacer fibers <NUM>. The intermediary spacer sheet <NUM> may be bonded to the spacer fibers <NUM> by an adhesive <NUM> as shown in <FIG> or it may be bonded to the spacer fibers <NUM> by laser bonding. The intermediary spacer sheet <NUM> may be fabricated from any suitable material. For example, the intermediary spacer may be a flexible elastomer or a rigid material, such as glass.

The fiber array spacer may also be fabricated with an integral support sheet (not shown) that stiffens the fiber array. For example, referring to <FIG>, a support sheet may be provided between the interdigitated array of optical fibers <NUM> and the support plate <NUM>. An adhesive bonds the interdigitated array of optical fibers <NUM> to the support sheet. The support sheet may be fabricated from any material that provides a flat surface, such as polished glass, ceramic, or metal materials. For example, a glass support sheet may be fabricated with an extremely flat surface (e.g., deviation of less than <NUM> from an ideal plane) using a fusion draw process. The support sheet may be rigid in some embodiments. However, the support sheet may also be thin enough to be flexible. If the support sheet is fabricated from metal, metalized optical fibers may be laser bonded to the support sheet by a laser bonding process as described above.

Referring now to <FIG>, a support sheet may be replaced by a second fiber array spacer that is positioned beneath a first fiber array spacer, thereby resulting in a two-layer fiber array spacer comprising optical fiber stubs. In <FIG>, the first multi-fiber cable 60A is arranged transverse to the second multi-fiber cable 60B. Adhesive <NUM> is applied to a top surface of the second interdigitated array of optical fibers 75B (i.e., a second fiber array spacer 80B still attached to the second multi-fiber cable 60B). Referring to <FIG>, the second interdigitated array of optical fibers 75B and the first interdigitated array of optical fibers 75A (i.e., a second fiber array spacer 80A still attached to the first multi-fiber cable 60A) are brought into contact with one another by vertical forces. The adhesive <NUM> is then cured to secure the first fiber array spacer 80A to the second fiber array spacer 80B, thereby forming a two-layer fiber array spacer <NUM>'.

Although the spacer fibers <NUM> of the first fiber array spacer 80A are shown as orthogonal to the spacer fibers <NUM> of the second fiber array spacer 80B, embodiments are not limited thereto. The fiber stubs of the first fiber array spacer 80A and the second fiber array spacer 80B should be transverse to one another but an orthogonal arrangement is not required.

Excess fiber array material may be removed from the first fiber array spacer 80A and/or the second fiber array spacer 80B before or after adhesive joining. <FIG> illustrates a two-layer fiber array spacer <NUM>' after the remaining portion of the second multi-fiber cable 60B is cut away and removed from the second fiber array spacer 80B. The remaining first optical fibers 52A and first cable jacket 61A may be used as a handle to support and align the two-layer fiber array spacer <NUM>' during subsequent alignment and assembly operations.

<FIG> illustrates a perspective view of an example wherein the two-layer fiber array spacer <NUM>" is separated from both the first multi-fiber cable 60A and the second multi-fiber cable 60B. <FIG> illustrates a cross-section view of the two-layer fiber array spacer <NUM>" illustrated by <FIG>. The first layer is defined by a first fiber array spacer 80A having an array of spacer fibers <NUM> and the second layer is defined by a second fiber array spacer 80B having an additional array of spacer fibers <NUM>.

Referring now to <FIG>, a two-layer fiber array spacer with perpendicular fiber array spacers can also be assembled via a laser joining processes. <FIG> illustrates a cross-section view of an assembly bench <NUM>' where a laser beam delivery system <NUM> is used to laser bond metallized optical fibers. Laser bonds <NUM> bond adjacent optical fibers within the same array of interdigitated optical fibers. Additionally, the laser bonds <NUM> bond the first interdigitated array of optical fibers 75A to the second interdigitated array of optical fibers 75B.

The advantage of the fiber array spacers described herein is that the optical fibers precisely set the thickness of the fiber array spacer. Therefore, if a precision spacer is required of a given thickness in an optical assembly (e.g., an optical connector) or any of the type of assembly not limited to optical assemblies, it can be fabricated by drawing optical fibers of the desired diameters. This is much easier to do than to, for example, draw a sheet of glass to a target thickness using a fusion draw process, or to polish a substrate to the target thickness. As an example, a series of optical fibers could be drawn at different standard diameters so that, by mixing and matching upper and lower fiber array spacer thicknesses, the desired combined thickness can meet the target thickness.

Another advantage is that the optical fibers provide lines of contact on both top and bottom surfaces that are more immune to debris contamination that would otherwise contribute to thickness errors during stacking. The cavities formed between the optical fibers during interdigitation provide a place for debris to flow through during surface mating. Meanwhile, the limited total surface area during optical fiber contact with other fiber arrays or flat sheets can produce high pressures that tends to compact debris to reduce its error contribution to stacking height.

Referring once again to <FIG>, the illustrated optical fiber assembly <NUM> may be utilized as a one-dimensional fiber array wherein the second fiber array spacer 80B is used as a spacing element in a final optical package, and the first interdigitated array of optical fibers 75A is used to transmit and/or receive optical signals. Thus, the first multi-fiber cable 60A is a fiber optical cable that may be housed in a connector body (see <FIG>, described in more detail below). The optical fibers of the illustrated optical fiber assembly <NUM> comprise an array of interdigitated first glass portions 74A (from the first optical fibers 52A) and lateral spacer optical fibers <NUM> (cut from the second multi-fiber cable 60B as described above with respect to the spacer fibers <NUM>). The first optical fibers 52A are signal optical fibers in the present embodiment because they propagate optical signals for optical communication. The lateral spacer optical fibers <NUM> are fiber stubs similar to the spacer fibers <NUM> and are therefore dummy optical fibers because they are not used for optical communication.

Prefabricated optical fiber assemblies (comprising a fiber array spacer and an array of interdigitated glass portions of optical fibers and spacer fibers) can be stacked to implement two-dimensional optical fiber arrays. In one approach shown in <FIG>, optical fiber assemblies <NUM> as shown in <FIG> are used, where a one-dimensional array of signal optical fibers 52A are on precise pitch provided by lateral spacer optical fibers <NUM> and supported by a fiber array spacer <NUM> of spacer fibers <NUM>. The fiber array spacer <NUM> is shifted laterally relative to the interdigitated array signal optical fibers 52A and lateral spacer optical fibers so that it undercuts the interdigitated array by a distance D1, where <NUM> ≤ D1 ≤ D/<NUM>, and where D is the optical fiber diameter. The opposite end of the fiber array spacer <NUM> extends beyond the interdigitated array by a distance D2, where, for example, <NUM> ≤ D1 ≤ <NUM>. These offsets aid the assembly of two-dimensional optical fiber arrays as described below.

Referring now to <FIG>, an assembly bench 111A may be constructed by mounting a precision vertical alignment block <NUM> on a precision flat surface <NUM> of a support plate <NUM>. The precision flat surface <NUM> of the support plate <NUM> serves as the bottom-side alignment surface. The precision flat surface <NUM> of the vertical alignment block <NUM> serves as the left-side alignment surface. Together, the precision vertical alignment block <NUM> and the support plate <NUM> provide a precise right-angle corner that enables left-right alignment of first and second interdigitated array of optical fibers <NUM>, <NUM>'. In some embodiments, the vertical alignment block <NUM> and the support plate <NUM> serving as a horizontal alignment block are integrated into a single, right angle component.

In the illustrated embodiment, a first optical fiber assembly <NUM> comprising a first fiber array spacer <NUM> is disposed on a release sheet <NUM> on a precision flat surface <NUM> of the support plate <NUM>. A first interdigitated array of optical fibers <NUM> of the first fiber optical assembly <NUM> is secured to the first fiber array spacer <NUM> as described above. A second optical fiber assembly <NUM>' comprising a second fiber array spacer <NUM>' secured to a second interdigitated array of optical fibers <NUM>' is stacked onto the first optical fiber assembly <NUM> such that the second fiber array spacer <NUM>' is positioned on the first interdigitated array of optical fibers <NUM>. An additional top precision spacer sheet <NUM> (e.g., precision flat fusion glass) is applied on the second interdigitated array of optical fibers <NUM>', and a cover plate <NUM> is positioned on the top precision spacer sheet <NUM>. In some embodiments, no top precision spacer sheet <NUM> is provided. Alternatively, a release sheet may be provided on the bottom surface <NUM> of the top precision spacer sheet <NUM> such that the precision support sheet is not a component of the resulting two-dimensional optical fiber array.

Downward force V1 applied using the cover plate <NUM> forces the first and second optical fiber assemblies <NUM>, <NUM>' into contact with each other. Adhesive <NUM> is applied between the first and second optical fiber assemblies <NUM>, <NUM>'. The adhesive <NUM> is prevented from attaching to the vertical alignment block <NUM> and the support plate <NUM> by use of first and second release sheets <NUM>, <NUM>, respectively. As stated above, the first and second release sheets <NUM>, <NUM> may be configured as individual sheets, or a coating, such as a fluorosilane coating, for example.

The first and second optical fiber assemblies <NUM>, <NUM>' are pushed laterally into the precision flat surface <NUM> of the vertical alignment block <NUM> using first and second pusher elements 110A, 110B that contact the outermost optical fibers in the first and second interdigitated array of optical fibers <NUM>, <NUM>', respectively. The first and second pusher elements 110A, 110B are guided into contact with the outermost optical fibers by the portions of the fiber array spacers <NUM>, <NUM>' that extend a distance D2 to the right (see <FIG>). The first and second pusher element 110A, 110B force the outermost optical fiber in each interdigitated array of optical fibers be pushed into contact with the release sheet <NUM> attached to the vertical alignment block <NUM>. Since the thickness of the release sheet <NUM> is precisely controlled, the optical fibers in the first and second interdigitated array of optical fibers <NUM>, <NUM>' become vertically aligned to each other (i.e., each fiber core is located directly over the fiber core beneath it). This causes all optical fibers in the two-dimensional optical fiber array to be precisely located relative to one another in a grid. In this example, the two-dimensional horizontal fiber array pitch equals twice the optical fiber diameter, while the two-dimensional vertical fiber array pitch equals the sum of the optical fiber diameter and the spacer fiber <NUM> diameter.

After adhesive UV exposure and curing, the two-dimensional optical fiber array <NUM> is removed from the assembly bench <NUM>, as shown in <FIG>. The two-dimensional optical fiber array <NUM> may be disposed in an optical connector, for example. The first interdigitated array of optical fibers <NUM> comprises alternating lateral spacer optical fibers <NUM> and signal optical fibers 52A and is supported by the first fiber array spacer <NUM>. The second interdigitated array of optical fibers <NUM>' comprises alternating lateral spacer optical fibers <NUM>' and signal optical fibers 52A' and is supported by the second fiber array spacer <NUM>'.

<FIG> depicts another assembly bench 111B for assembling a two-dimensional optical fiber array that is similar to the assembly bench 111A illustrated by <FIG>. In this embodiment, an extended length of the spacer fibers <NUM>, <NUM>' of the first and second fiber array spacers <NUM>, <NUM>', respectively, is used to simplify the process of forcing the outermost optical fibers (i.e., leftmost optical fibers in <FIG>) of the first and second interdigitated array of optical fibers <NUM>, <NUM>' against the precision flat surface <NUM> of the vertical alignment block <NUM>. A large pusher element 110C (e.g., a pusher block) contacts the spacer fibers <NUM>, <NUM>' and applies a lateral force L. The pusher element 110C may have a thickness that is closely matched to the total thickness of stack of first and second fiber optic assemblies <NUM>, <NUM>'. In the illustrated embodiment, an elastomeric pad <NUM> is disposed on the end of the pusher element 110C so that force is transferred to each spacer fiber <NUM>, <NUM>', even if the spacer fibers <NUM>, <NUM>' are of different lengths.

<FIG> depicts another assembly bench 111C for assembling a two-dimensional optical fiber array that is similar to the assembly bench 111B illustrated by <FIG>. In this example, an extended length of the spacer fibers <NUM>, <NUM>' of the first and second fiber array spacers <NUM>, <NUM>', respectively, is such that D2 (see <FIG>) is approximately <NUM>-<NUM>. This additional length allows the spacer fibers <NUM>, <NUM>' to flex as force is applied to them via a pusher element 110D, such as first and second pusher elements 110A, 110C (see <FIG>) configured as pusher fibers that squeeze the first and second optical fibers 52A, 52B to form an interdigitated array. The example pusher element 110D is configured as a block having a pocket <NUM> with raised shoulders <NUM> that prevents the deflected spacer fibers <NUM>, <NUM>' from slipping off of the end of the pusher element 110D. The elastomeric pad <NUM> may or may not be utilized in this embodiment. After alignment and adhesive curing, the excess length of the spacer fibers <NUM>, <NUM>' may be removed via cutting or grinding operations.

Referring now to <FIG>, another assembly bench 111D for assembling a two-dimensional optical fiber array that is similar to the assembly benches 111B and 111C illustrated by <FIG>. In this example, the spacer fibers <NUM>, <NUM>' are reduced in length such that D2 (see <FIG>) is approximate <NUM>. Thus, the ends of the spacer fibers <NUM>, <NUM>' line up with outer optical fibers (i.e., rightmost optical fibers) in each of the first and second interdigitated arrays of optical fibers <NUM>, <NUM>'. A pusher element 110E having an elastomeric pad <NUM> on the end is used to simultaneously push the first and second optical fiber assemblies <NUM>, <NUM>' into the release sheet <NUM> on the precision flat surface <NUM> of the vertical alignment block <NUM>.

Referring to <FIG>, a two-dimensional optical fiber array <NUM> may be fabricated using only one fiber array spacer <NUM> that is disposed between a first interdigitated array of optical fibers <NUM> and a second interdigitated array of optical fibers <NUM>'. In the example, a first interdigitated array of optical fibers <NUM> is disposed on a first release sheet <NUM> on the precision flat surface <NUM> of the support plate <NUM> of an example assembly bench 111E. Next, a support interdigitated array of optical fibers <NUM>" is disposed on the first interdigitated array of optical fibers <NUM> such that its longitudinal axis is transverse (e.g., perpendicular) to the longitudinal axis of the first interdigitated array of optical fibers <NUM>. As used herein, "perpendicular" means within ± <NUM> degrees of <NUM> degrees. The support interdigitated array of optical fibers <NUM>" will become spacer fibers <NUM> upon cutting the glass portion <NUM> and separating the coating portion <NUM> from the assembly. The second interdigitated array of optical fibers <NUM>' are disposed on the support interdigitated array of optical fibers <NUM>". A vertical force V is applied by way of the cover plate <NUM> to establish the position of the first and second interdigitated arrays of optical fibers <NUM>, <NUM>' in the Y-direction. First and second pusher elements 110A, 110B apply lateral forces L1, L2 to the first and second interdigitated array of optical fibers <NUM>, <NUM>', respectively, to force the outermost optical fibers (e.g., the leftmost optical fibers) first and second interdigitated array of optical fibers <NUM>, <NUM>' into contact with the release sheet <NUM> on the precision flat surface of the vertical alignment block <NUM>. After adhesive curing, the fiber assembly is removed from the vertical alignment block <NUM>, the support plate <NUM>, and the cover plate <NUM>. The excess optical fiber of the support interdigitated array of optical fibers <NUM>" is removed by cutting, thereby forming a fiber array spacer <NUM> disposed between the first and second interdigitated arrays of optical fibers <NUM>, <NUM>'.

<FIG> illustrates another example assembly bench 111F that may be utilized to fabricate two-dimensional fiber arrays of various configurations. Particularly, a vertical alignment block <NUM> is mounted on a precision rotation stage (represented by array A) that is capable of rotating relative to a fixed support plate <NUM>. In the illustrated embodiment, a two-dimensional optical fiber array <NUM> as illustrated by <FIG> is disposed on a bottom precision spacer sheet <NUM> (e.g., a precision fusion drawn glass sheet). The bottom precision spacer sheet <NUM> provides clearance C1 for the vertical alignment block <NUM> to rotate. In cases where the bottom precision spacer sheet <NUM> is not desired in the final product, a release sheet may be provided on the top surface of the bottom precision spacer sheet <NUM>.

In the example of <FIG>, a top precision spacer sheet <NUM> is disposed on the second interdigitated array of optical fibers <NUM>'. The top precision spacer sheet <NUM> provides clearance C2 for the vertical alignment block to rotate. In cases where the top precision spacer sheet <NUM> is not desired in the final product, a release sheet may be provided on the bottom surface of the top precision spacer sheet <NUM>.

A precise right angle between the vertical alignment block <NUM>' and the support plate <NUM> may be established by placing a right-angle gage block on the support plate <NUM> and adjusting the vertical alignment block <NUM>' until it is parallel with the vertical side face of the right angle gage block. Alternatively, the vertical alignment block <NUM>' may be aligned via optical power peaking of retro-reflected light from a collimator that produces a precise beam that extends parallel to the support plate <NUM>. Thus, a light signal parallel to the precision flat surface <NUM> of the support plate <NUM> may be emitted such that it is reflected by the precision flat surface <NUM> of the vertical alignment block <NUM>'. The reflected light signal is detected by a detector, and the vertical alignment block <NUM>' is rotated until peak-power is received at the detector.

The angular adjustment of the vertical alignment block <NUM>' enables different configurations of the two-dimensional fiber array. For example, it is possible to fabricate two-dimensional fiber arrays where the optical fiber cores are not positioned directly on top of one another but rather offset laterally along the X-direction by a precise offset distance. <FIG> depicts an offset distance OD of zero. However, rotation of the vertical alignment block <NUM>' causes an offset distance OD between the cores of stacked optical fibers to be present.

Any of the fiber array spacers and the fiber arrays described herein may be implemented in any optical component. The precision diameter of the optical fibers used to fabricate the fiber spacers enable a low-cost method of setting the position of the signal optical fibers (or waveguides) along the X-axis.

Referring now to <FIG>, an optical component in the form of a fiber optic connector <NUM> for an optical cable assembly <NUM> is illustrated. The example fiber optic connector <NUM> has a connector body <NUM> having a mating face <NUM> that may be mated to a receptacle, a waveguide assembly (e.g., a waveguide assembly of a photonic integrated circuit (PIC)), or any other optical component. The connector body <NUM> may take on any shape and include any retention features to facilitate physical mating.

The mating face <NUM> has an opening <NUM> that exposes an end face of an optical fiber assembly <NUM> disposed within connector body <NUM>. The optical fiber assembly <NUM> includes a one-dimensional interdigitated array of optical fibers <NUM> comprising alternating spacer fibers <NUM> and signal optical fibers <NUM> of a multi-fiber ribbon cable <NUM>. The interdigitated array of optical fibers <NUM> is supported on a two-layer precision fiber array spacer <NUM>" that precisely establishes a height of the end faces of the signal optical fibers <NUM> with respect to a bottom surface <NUM> of the opening by the precise diameter of the spacer fibers <NUM>.

It should be understood that multi-dimensional fiber arrays may be utilized, and any number of signal optical fibers may be provided. Any of the fiber array spacers and fiber arrays described herein may be provided within a connector.

The fiber array spacers described herein may also be employed in photonics applications. <FIG> illustrates an example photonics assembly <NUM> comprising PIC <NUM> mounted on a two-layer fiber array spacer <NUM>". The PIC <NUM> may be bonded to the two-layer fiber array spacer <NUM>" by adhesive or by laser bonding, for example. The PIC <NUM> has a plurality of integrated waveguides <NUM> that are optically coupled to one or more active optical components <NUM> (e.g., optical emitters and/or optical receivers) and terminate at an optical coupling face <NUM>.

The two-layer fiber array spacer <NUM>" includes a first fiber array spacer 80A and a second fiber array spacer 80B. The height h of the two-layer fiber array spacer <NUM>" is equal to the diameter of the spacer fibers of the first fiber array spacer 80A plus the diameter of the spacer fibers of the second fiber array spacer 80B. The two-layer fiber array spacer <NUM>" precisely sets the location of the end-faces of the waveguides <NUM> along the Y-axis, thereby enabling precision coupling with an optical component that mates to the PIC <NUM> at the optical coupling face <NUM>.

Claim 1:
An optical fiber assembly (<NUM>, <NUM>, <NUM>) comprising:
a first fiber array spacer (<NUM>, 80A, 80B) comprising:
an array of spacer fibers, wherein individual spacer fibers (<NUM>) of the array of spacer fibers are bonded to one another; and
a first fiber ribbon (<NUM>) comprising a first array of optical fibers (<NUM>, <NUM>), wherein:
each optical fiber of the first array of optical fibers comprises a glass portion (<NUM>, 74A, 74B); and
the glass portion (<NUM>, 74A, 74B) of each optical fiber (<NUM>, <NUM>) of the first array of optical fibers (<NUM>, <NUM>) is bonded to the first fiber array spacer (<NUM>, 80A, 80B) such that a longitudinal axis of the individual spacer fibers (<NUM>) is transverse to a longitudinal axis of individual optical fibers (<NUM>, <NUM>) of the first array of optical fibers;
characterised in that there is substantially no gap between adjacent spacer fibers (<NUM>).