DEMOUNTABLE OPTICAL CONNECTOR FOR OPTOELECTRONIC DEVICES

A reconnectable connection between an optical bench supporting an optical fiber and a photonic integrated circuit (PIC), which a foundation and a connector that is configured and structured to be removably attachable for reconnection to the foundation in alignment therewith. The foundation can be aligned to electro-optical elements in the PIC. The foundation may be permanently attached with respect to the opto-electronic device. The optical bench can be removably attached to the foundation. Alignment between the foundation and the connector is achieved by kinematic coupling, quasi-kinematic coupling, or elastic-averaging coupling.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to coupling of light into and out of optoelectronic devices (e.g., photonic integrated circuits (PICs)), and more particular to the optical connection of optical fibers to PICs.

2. Description of Related Art

Photonic integrated circuits integrate multiple electro-optical devices such as lasers, photodiodes, modulators, and waveguides into a single chip. It is necessary for these PICs to have optical connections to other PICs, often in the form an organized network of optical signal communication. The connection distances may range from a several millimeters in the case of chip-to-chip communications up to many kilometers in case of long-reach applications. Optical fibers can provide an effective connection method since the light can flow within the optical fibers at very high data rates (>25 Gbps) over long distances due to low-loss optical fibers.

One of the most expensive components within photonic networks are the fiber-optic connectors. For proper operation, a PIC typically needs to efficiently couple light between an external optical fiber and one or more of on-chip waveguides. Most PICs require single-mode optical connections that require stringent alignment tolerances between optical fibers and the PIC, typically less than1micrometer. This is challenging and so much optical fibers are aligned to elements on the PICs using an active alignment approach in which the position and orientation of the optical fiber(s) is adjusted by machinery until the amount of light transferred between the fiber and PIC is maximized. This is a time consuming process that is generally done after the PIC is diced from the wafer and mounted within a package. This postpones the fiber-optic connection to the end of the production process. Once the connection is made, it is permanent, and would not be demountable, separable or detachable without likely destroy the integrity of connection for any hope of remounting the optical fiber to the PIC. In other words, optical fiber is not removably attachable to the PIC, and the fiber connection, and separation would be destructive and not reversible (i.e., not reconnectable).

It would be advantageous if the fiber-optic connections could be created prior to dicing the discrete PICs from the wafer; this is often referred to as wafer-level attachment. Manufacturers of integrated circuits and PICs often have expensive capital equipment capable of sub-micron alignment (e.g. wafer probers and handlers for testing integrated circuits), whereas companies that package chips generally have less capable machinery (typically several micron alignment tolerances which is not adequate for single-mode devices) and often use manual operations. However, it is impractical to permanently attach optical fibers to PICs prior to dicing since the optical fibers would become tangled, would be in the way during the dicing operations and packaging procedures, and are practically impossible to manage when the PICs are pick-and-placed onto printed circuit boards and then soldered to the PCBs at high temperatures.

The current state-of-the-art attempts to achieve stringent alignment tolerances using polymer connector components, but polymers have several fundamental disadvantages. First, they are elastically compliant so that they deform easily under external applied loads. Second, they are not dimensionally stable and can change size and shape especially when subjected to elevated temperatures such as those found in computing and networking hardware. Third, the coefficient of thermal expansion (CTE) of polymers is much larger than the CTE of materials that are commonly used in PICs. Therefore, temperature cycles cause misalignment between the optical fibers and the devices on the PIC. In some cases, the polymers cannot withstand the processing temperatures used while soldering PICs onto printed circuit boards.

What is needed is an improved approach to optically couple input/output of optical fibers to PICs, which improves tolerance, manufacturability, ease of use, functionality and reliability at reduced costs.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of the prior art by providing a demountable/separable and reconnectable connection between an optical bench (e.g., supporting an optical fiber) and an opto-electronic device (e.g., grating coupler of a photonic integrated circuits (PIC)). The novel connection includes a foundation and a connector that is configured and structured to be removably attachable for reconnection to the foundation in alignment therewith. The foundation may be an integral part of the opto-electronic device (e.g., part of a PIC packaging), or a separate component attached to the opto-electronic device.

In accordance with one embodiment of the present invention, the foundation is initially attached to a support (e.g., housing) of the opto-electronic device (e.g., PIC). This foundation can be aligned to electro-optical elements in the device. The foundation may be permanently attached with respect to the opto-electronic device. The optical bench (e.g., supporting an optical fiber) can be removably attached to the foundation, via a ‘separable’ or ‘demountable’ or ‘detachable’ action that accurately optically aligns the optical components/elements in the optical bench to the opto-electronic device along a desired optical path. In accordance with the present invention, a detachable connector supports or is part of the optical bench. In order to maintain optical alignment for each connect and disconnect and reconnect, this connector needs to be precisely and accurately aligned to the foundation. In one embodiment of the present invention, the connector and foundation are aligned with one another using a passive mechanical alignment constructed from geometric features on the two bodies.

In a further embodiment, the present invention provides a structure and method for this passive alignment using kinematic coupling, quasi-kinematic coupling, or elastic-averaging couplings. One approach is a kinematic coupling with six points of contact between the connector and the foundation. Six points is the minimum necessary for rigid body static equilibrium and consequently provides a deterministic and repeatable alignment between the bodies. An alternate approach that provides additional stiffness at the interface and reduces the dependence on the bending stiffness of the connector is to use a quasi-kinematic approach which adds additional contact points or replaces a contact point with a contact line. Additional contact points and contact lines increases the stiffness of the interface with modest reductions in the repeatability. In this embodiment, the contact is spread over larger area between the two bodies and stiffens the bending modes of the connector. A third embodiment maximizes the stiffness of the interface using many, perhaps hundreds or thousands, of contact points or small surfaces (e.g. tetrahedral) that are spread over as much area as possible. This requires accurate location of the mating surfaces and more stringent tolerances on the shape and size of the surfaces. However, this can be accomplished with ultra-high precision stamping.

In another aspect of the present invention, the passive alignment features on the foundation and connector can be integrally/simultaneous formed by precision stamping, which allows the components to be produced economically in high or small volumes, while improving tolerance, manufacturability, ease of use, functionality and reliability. Further, either or both of the foundation and the connector (e.g., a micro optical bench (MOB)) can be precisely formed by high-precision stamping. The foundation and/or optical bench components should be made of a stampable materials like ductile metals such as Kovar, Invar, stainless steel, aluminum. The optical bench and foundation should both have similar coefficients of thermal expansion (CTEs), so that misalignment does not occur during temperature cycles and stress/strains are not generated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is described below in reference to various embodiments with reference to the figures. While this invention is described in terms of the best mode for achieving this invention's objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.

The present invention provides a novel approach to coupling light between an optical bench (e.g., supporting an optical fiber) and an opto-electronic device (e.g., grating coupler of a photonic integrated circuits (PIC)). The novel connection includes a foundation and a connector that is configured and structured to be removably attachable for reconnection to the foundation in alignment therewith.

The concept of the present invention will be discussed with reference to an example of a PIC as an opto-electronic device, and an optical bench as an optical coupling device (connector) for use to optically coupling an input/output end of an optical component (e.g., an optical fiber) supported in the optical bench with the opto-electronic device. The present invention may be applied to provide removable/reconnectable form structures and parts used in other fields.

FIGS. 1A-1Billustrate an optical coupling device in the form of an optical connector10, incorporating a micro optical bench11for use in connection with an optical component in the form of optical fibers. The optical fiber cable22has four optical fibers20protected by protective buffer and jacket layers23. The connector10includes a base16, which defines structured features including an alignment structure comprising open grooves25for retaining bare sections of optical fibers20(having cladding exposed, without protective buffer and jacket layers23), and structured reflective surfaces12(i.e., four reflectors) having a plane inclined at an angle relative to the greater plane of the base16. Each structured reflective surface12may have a flat, concave or convex surface profile and/or possess optical characteristics corresponding to at least one of the following equivalent optical element: mirror, focusing lens, diverging lens, diffraction grating, or a combination of the foregoing. The structure reflective surface12may have a compound profile defining more than one region corresponding to a different equivalent optical element (e.g., a central region that is focusing surrounded by an annular region that is diverging). In one embodiment, the structure reflective surfaces12may have a concave aspherical reflective surface profile, which serves both functions of reflecting and reshaping (e.g., collimating or focusing) a diverging incident light, without requiring a lens. Accordingly, each structured reflective surface12functions as an optical element that directs light to/from an external optical component (in this case an opto-electronic component, such as a photonic integrated circuit (PIC)2, by reflection from/to the output/input end21of the optical fiber20, along a defined optical path100(schematically shown inFIG. 1C) that is aligned to the optical axis of the various optical components and elements (i.e., optical fibers20, structured reflective surfaces12, and PIC2).

The open grooves25are sized to receive and located to precisely position the end section of the optical fibers20in alignment with respect to the structured reflective surfaces12along the optical path100. The end face21(input/output end) of each optical fibers20is maintained at a pre-defined distance with respect to a corresponding structured reflective surface12.

In a further aspect of the present invention, the mirror/structured reflective surface and optical fiber alignment structure in the optical connector can be integrally/simultaneous formed by precision stamping of a stock material (e.g., a metal blank or strip), which allows the connector components to be produced economically in high or small volumes, while improving tolerance, manufacturability, ease of use, functionality and reliability. By forming the structure reflective surface, the passive alignment features (discussed below) and the optical fiber alignment structure simultaneously in a same, single final stamping operation, dimensional relationship of all features requiring alignment on the same work piece/part can be maintained in the final stamping step. Instead of a punching operation with a single strike of the punch to form all the features on the optical bench, it is conceivable that multiple strikes may be implemented to progressive pre-form certain features on the optical bench, with a final strike to simultaneously define the final dimensions, geometries and/or finishes of the various structured features on the optical bench, including the mirror, optical fiber alignment structure/groove, passive alignment features discussed below, etc. that are required to ensure (or play significant role in ensuring) proper alignment of the respective components/structures along the design optical path.

The Assignee of the present invention, nanoPrecision Products, Inc., developed various proprietary optical coupling/connection devices having optical benches used in connection with optical data transmission. The present invention is more specifically directed to detachably/reconnectably coupling optical fibers to grating couplers in PICs, while adopting similar concept of stamping optical benches including stamped mirrors practiced in the earlier optical coupling devices.

For example, US2013/0322818A1 discloses an optical coupling device having a stamped structured surface for routing optical data signals, in particular an optical coupling device for routing optical signals, including a base; a structured surface defined on the base, wherein the structured surface has a surface profile that reshapes and/or reflect an incident light; and an alignment structure defined on the base, configured with a surface feature to facilitate positioning an optical component on the base in optical alignment with the structured surface to allow light to be transmitted along a defined path between the structured surface and the optical component, wherein the structured surface and the alignment structure are integrally defined on the base by stamping a malleable material of the base.

US2013/0294732A1 further discloses a hermetic optical fiber alignment assembly having an integrated optical element, in particular a hermetic optical fiber alignment assembly including a ferrule portion having a plurality of grooves receiving the end sections of optical fibers, wherein the grooves define the location and orientation of the end sections with respect to the ferrule portion. The assembly includes an integrated optical element for coupling the input/output of an optical fiber to optoelectronic devices in an optoelectronic module. The optical element can be in the form of a structured reflective surface. The end of the optical fiber is at a defined distance to and aligned with the structured reflective surface. The structured reflective surfaces and the fiber alignment grooves can be formed by stamping.

U.S. patent application Ser. No. 14/695,008 further discloses an optical coupling device for routing optical signals for use in an optical communications module, in particular an optical coupling device in which defined on a base are a structured surface having a surface profile that reshapes and/or reflect an incident light, and an alignment structure defined on the base, configured with a surface feature to facilitate positioning an optical component on the base in optical alignment with the structured surface to allow light to be transmitted along a defined path between the structured surface and the optical component. The structured surface and the alignment structure are integrally defined on the base by stamping a malleable material of the base. The alignment structure facilitates passive alignment of the optical component on the base in optical alignment with the structured surface to allow light to be transmitted along a defined path between the structured surface and the optical component. The structured surface has a reflective surface profile, which reflects and/or reshape incident light.

U.S. Pat. No. 7,343,770 discloses a novel precision stamping system for manufacturing small tolerance parts. Such inventive stamping system can be implemented in various stamping processes to produce the devices disclosed in above-noted nanoPrecision patent documents, and can similarly be implemented to produce the structures disclosed herein (including the structures for the optical bench11discussed above, as well as the structure of the foundation1discussed below. These stamping processes involve stamping a bulk material (e.g., a metal blank or stock), to form the final surface features at tight (i.e., small) tolerances, including the reflective surfaces having a desired geometry in precise alignment with the other defined surface features.

Essentially, for the optical connector10, the base16defines an optical bench11for aligning the optical fibers20with respect to the structured reflective surfaces12. By including the grooves25on the same, single structure that also defines the structured reflective surfaces12, the alignment of the end sections21of the optical fibers20to the structured reflective surfaces12can be more precisely achieved with relatively smaller tolerances by a single final stamping to simultaneous define the final structure on a single part, as compared to trying to achieve similar alignment based on features defined on separate parts or structures. By forming the structure reflective surfaces12and the optical fiber alignment structure/grooves25simultaneously in a same, single final stamping operation, dimensional relationship of all features/components requiring (or play a role in providing) alignment on the same work piece/part can be maintained in the final stamping step.

The overall functional structures of the optical bench11generally resemble the structures of some of the optical bench embodiments disclosed in nanoPrecision's earlier patent documents noted above (i.e., fiber alignment grooves aligned with structured reflective surfaces, and addition features to facilitate proper optical alignment). In the present invention, however, the optical benches are stamped passive alignment features. In the views ofFIGS. 1A and 1B, mechanical fiducial or alignment features14are formed on the planar surface15of the base16, which facilitates alignment and/or accurate positioning the optical bench11with respect to the PIC2, as will be explained later below.

FIGS. 2A to 2Dillustrate the presence of a foundation1to serve as a connector body to mechanically couple with the optical bench11in the optical connector10, to bring the optical bench11in optical alignment with the PIC2. The foundation1is attached to the top surface of PIC2, at a precise location such that when the connector10is connected to the foundation1, the optical bench11would be in optical alignment with the electro-optical components in the underlying PIC2. Preferably, the foundation1is initially attached to the PIC2at wafer-level prior to dicing process. The foundation1can be aligned to elements on the PIC2using precise machinery and then permanently joined to the PIC via epoxy or solder. The foundation1remains attached to the PIC2during the dicing and packaging processes. The packaged die is then mounted onto the printed circuit board3(PCB) using conventional PCB assembly methods (e.g. pick-and-place and wave soldering). This requires that the foundation be able to withstand the elevated temperatures during the soldering operations.

The foundation is provided with grooves, matching/complementing the alignment features14under the connector10. This aspect will be discussed below in connection with the passive alignment approaches in reference toFIGS. 3A to 3C.

Referring toFIG. 2B, after the PCB3is populated (other items not labeled inFIG. 2A), an optical fiber cable24supported by the optical connector10can be removably attached the foundation1or detached from the foundation1that is permanently mounted on the PIC2via a ‘separable’, ‘demountable’, ‘detachable’, or ‘re-attachable’ action that accurately aligns the ends of the optical fibers with the active electro-optical elements on the PIC2.FIG. 2Dis a sectional illustrating the state ofFIG. 2C, in which the connector10is attached to the foundation1on the PIC2that is supported on the PCB3. The foundation1and the optical bench11could be maintained in a coupled state by an appropriate biasing device to keep the optical bench11/connector10against the foundation1. See, for example, the embodiment ofFIGS. 4A to 4G.

The invention may use different embodiments for aligning the connector (optical bench) to the foundation. In accordance with the present invention, the connector10and foundation1are aligned with one another using a passive mechanical alignment constructed from geometric features in the two bodies. This invention provides a structure and method for this alignment using kinematic coupling, quasi-kinematic coupling, or elastic-averaging couplings, each with a different configurations of complementary passive alignment features.FIGS. 3A to 3Cillustrates various embodiments of passive alignments adopting various coupling approaches.

FIG. 3Ashows the first approach, which is a kinematic coupling with six points of contact between the optical bench11and the foundation1.FIG. 3Ais similar to the embodiment shown inFIGS. 1 and 2. There are three semi-circular protrusions14on the surface15, and three complementary grooves6(which may having a generally V-shape cross section) on the top surface of the foundation1. The grooves6are in a direction radiating from the center of the foundation1. Six points is the minimum necessary for rigid body static equilibrium and consequently provides a deterministic and repeatable alignment between the bodies. Since there are only six contact points, there is minimum chance of the alignment being influenced by particles between the mating surfaces of the optical bench11and the foundation1. The disadvantage is that the stiffness of the interface between the two bodies depends on the Hertzian contact at the six points. Furthermore, portions of the optical bench11that are not immediately near the contact points are stiffened only by the bending stiffness of the optical bench11.

FIG. 3Bshows an alternate approach that provides additional stiffness at the interface and reduces the dependence on the bending stiffness of the optical bench11′. This approach uses a quasi-kinematic coupling, which adds additional contact points or replaces a contact point with a contact line. In this embodiment, more semi-circular protrusions are provided on the surface15′ of the optical bench11′, and more V-grooves6′ are provided on the top surface of the foundation1. Additional contact points and contact lines increases the stiffness of the interface with modest reductions in the repeatability. In this embodiment, the contact is spread over larger area between the two bodies and stiffens the bending modes of the optical bench11′.

FIG. 3Cis a third embodiment, an elastic averaging coupling, which maximizes the stiffness of the interface using many, perhaps hundreds or thousands, of contact points or small surfaces (e.g. tetrahedral) that are spread over as much area as possible. This embodiment requires accurate location of the mating surfaces and more stringent tolerances on the shape and size of the surfaces. However, this can be accomplished with ultra-high precision stamping the top surface of the foundation1″ with the numerous contact points (e.g., tetrahedral) and the top surface15″ of the optical bench11″ with the contact point (e.g., tetrahedral).

Either or both of the foundation and the connector (e.g., an optical bench), including the passive alignment features, can be precisely formed by high-precision stamping. The foundation and/or optical bench components should be made of a stampable materials like ductile metals such as Kovar, Invar, stainless steel, aluminum. If epoxy is used to attach to the foundation to the PIC, then the subsequent process temperatures should not exceed the temperature limit of the epoxy. Solder attachment of the foundation to the optical bench can provide higher process temperatures. The optical bench and foundation should both have similar CTEs so that misalignment does not occur during temperature cycles and stress/strains are not generated.

In accordance with the present invention, stamping is a cost effective means to economically manufacture the geometric features of these couplings in high volumes necessary for commercialization of PICs.

One of the intended commercial use of the invention is in the field of electro-optical transceivers.

FIGS. 4A to 4Gillustrate another embodiment of removably/reconnectably coupling an optical bench directly to a foundation that is an integral part of the PIC package (i.e., the package includes surface alignment features, hence functioning similar to a “foundation” in the embodiments discussed above), which involves passive alignment.

FIG. 4Aillustrates two jumper optical fiber cables connected to a SiPIC package102within a large enclosure155with a lid152.FIG. 4Billustrates the assembled structure of the optical benches/connectors and the SiPIC package within the enclosure155, with the components held together by a clip.FIG. 4Cillustrates one of the connectors110separated from the PIC housing.FIGS. 4D and 4Eillustrate the connector110, having an optical bench111defined therein. Optical fibers20are supported and aligned by the optical bench111in the connector110.

Referring toFIGS. 4F and 4G, the SiPIC package102includes area for a grating coupler70. The alignment features includes a row of teeth51adjacent a front edge grating coupler region70on the SiPIC package102, serving X-location alignment. Three stops52(depressions) are distributed on the top surface115in a triangular fashion, near the lateral and rear edge of the grating coupler region70, serving Y-location alignment. Two notches53, on either sides of the SiPIC package102, serving Z-location alignment. Referring toFIG. 4D and 4E, the complementary alignment features on the connection110includes X-location control teeth61, three Y-location control pads62, and two Z-location control snaps63(e.g., spring clips). The connector110can be coupled to the SiPIC package102by clipping and snapping the connector110onto the region shown inFIG. 4G, in which the control pads62would be fit into the stops52, with the control teeth61messed against the teeth51, and the extended tips of the snaps63snapped into place in the notches53. This forms a removable/reconnectably coupling between the connector110and the SiPIC package102, which relies on passive alignment of the above-described alignment features.

The above described alignment features of the SiPIC package may be formed by silicon etching. The connector110/optical bench111may be formed by stamping, as discussed in the embodiments above.

The optical benches discussed having the structured features for optical alignment can be formed by stamping. By including the passive alignment features (14,14′ or14″) discussed above on the same, single structure that also defines the structured reflective surfaces12on the optical bench, optical alignment of the end sections21of the optical fibers20to the PIC2and SiPIC102can be more precisely achieved with relatively smaller tolerances by a single final stamping to simultaneous define the final structure on a single part, as compared to trying to achieve similar alignment based on features defined on separate parts or structures. By forming the alignment structures simultaneously with rest of the structured features on the optical bench in a same, single final stamping operation, dimensional relationship of all features/components requiring (or play a role in providing) alignment on the same work piece/part can be maintained in the final stamping step.

The passive alignment coupling allows the connector to be detachably coupled to the PIC, via a foundation. The connector can be detached from the foundation and reattached to the foundation without compromising optical alignment.

While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope, and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.