Patent Description:
The present invention relates to coupling of light into and out of optoelectronic devices (e.g., photonic integrated circuits (PICs), laser arrays, photodiode arrays, etc.), and in particular to optical connections of optical subassemblies (e.g., optical benches, optical fiber subassemblies, etc.) to optoelectronic devices.

Optoelectronic devices may include optical and electronic components that source, detect and/or control light, converting between light signals and electrical signals. For example, a transceiver (Xcvr) is an optoelectronic module comprising both a transmitter (Tx) and a receiver (Rx) which are combined with circuitry within a housing. The transmitter includes a light source (e.g., a VCSEL or DFB laser), and the receiver includes a light sensor (e.g., a photodiode). Heretofore, a transceiver's circuitry is soldered onto a printed circuit board. Such a transceiver generally has a substrate that forms the bottom of a package (either hermetic or non-hermetic), and then optoelectronic devices such as lasers and photodiodes are soldered onto the substrate. Optical fibers are connected to the exterior of the package or fed through the wall of the package using a feedthrough (see, e.g., <CIT>, which had been commonly assigned to the Assignee/Applicant of the present application).

Optoelectronic devices may be implemented in the form of silicon photonics. Military and commercial applications of silicon photonics are emerging rapidly: optical interconnects for digital networking and super-computing, RADAR (RF over fiber), optical imaging and sensing such as laser ranging, biological sensing, environmental and gas sensing, and many others. These applications will require electronic-photonic co-packaging, and they will often require optical connections to fiber-optic cable or the inclusion of other passive optical devices such as lenses, filters, isolators, etc..

Despite wafer-scale production efficiency of the silicon photonic integrated circuit (SiPIC) and complimentary metal-oxide semiconductor (CMOS) circuits, assembling and packaging any optical elements, particularly fiber-optic connectors, remains a labor intensive and unreliable process that is not performed at wafer-scale and is performed at the back end-of-line where process failures generate valuable scraps. This is because optical assemblies require stringent tolerances on the position and alignment, and these alignment tolerances must be preserved through the manufacturing process and any subsequent environmental conditions, which can be very severe in defense related applications.

Economies of scale are driving the electronic-photonic packaging industry into the supply chain model illustrated in <FIG>, which includes separate foundry, packaging, and product assembly entities. Each entity specializes and provides high-volume production facilities. Foundries fabricate the electronic IC using leading-edge CMOS technology. A separate foundry often fabricates the photonic IC using trailing-edge lithography processes since the optical devices are much larger than transistors. Foundries may produce stacks of ICs by assembling them using wafer-to-wafer or chip-to-wafer techniques. The IC assembly is then usually shipped to a separate facility that packages the ICs onto a silicon or glass interposer and/or an electrical substrate. Organic substrates with ball grid arrays are common in commercial applications, but defense related applications still often use ceramic substrates in hermetic packages. The electronic assembly is then shipped to another facility that integrates the electronic-photonic module onto another printed circuit board during product assembly. This facility usually attaches the fiber-optic cable and is responsible for testing the electro-optical performance. If any deficiencies are found, they are obligated to repair/rework/replace expensive photonic devices or fiber-optic cables.

This supply chain is problematic for high-volume, low-cost, photonic products that require fiber-optic connectors and cabling. The foundries are well equipped with clean-room facilities and high-precision automated machinery, but this is too early in the process to attach fiber-optic cabling because the cables would interfere with the assembly of printed circuit boards at the packaging step. Unfortunately, high-precision expertise and equipment become less available at the packaging facility and even rarer at the product assembly facility. In many cases, the packager and product assembler have little if any experience with optical alignment and optical testing. This has been an extreme challenge for network switch manufacturers that have built network switches using mid-board electro-optical transceivers because it required cleanroom assembly methods and a great deal of electro-optical diagnostics and including testing of fiber-optic cables and connectors. Consequently, the switch manufacturers suffer with low yield rates due to optical connection problems that greatly increase production costs.

The Assignee of the present invention, nanoPrecision Products, Inc. (nPP), developed various proprietary optical coupling/connection devices having optical benches used in connection with optical data transmission. nPP has demonstrated the ability to manufacture metallic optical benches (MOBs) using ultra-high precision stamping process. This manufacturing technology produces low-volumes (hundreds per month) to high-volumes (millions per week) of MOBs with microscale features that have dimensional tolerances down to +/- <NUM>. This makes it possible to stamp fiber-optic connector components that require sub-micrometer tolerances for high coupling efficiency in single-mode fiber-optic cabling or connecting optical fibers to photonic chips. For example, <CIT> discloses an optical coupling device including an MOB 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 one or more surface profiles (e.g., aspherical micro-mirrors) that reshape, fold and/or reflect incident light; and an alignment structure defined on the base, configured with a surface feature to facilitate positioning one or more optical components on the base in optical alignment with the structured surface to allow light to be transmitted along one or more defined paths between the structured surface and the one or more optical components, wherein the structured surface and the alignment structure are integrally defined on the base by stamping a malleable material of the base.

For proper operation, an optoelectronic device supported on a printed circuit board needs to efficiently couple light to an external optical fiber. Most optoelectronic devices (e.g., PICs) require single-mode optical connections that require stringent alignment tolerances between optical fibers and the devices, typically less than <NUM> micrometer. This is typically done by moving the fiber-optic connector while monitoring optical power transmitted between the PIC and the fibers in the connector. This active optical alignment procedure involves relatively complex, low throughput undertakings. The current state of the art active optical alignment procedures are expensive undertakings as they exclude use of common electronics and assembly processes, and/or often not suited to single-mode applications required by many PICs. The problems are exacerbated as it becomes even more challenging when many optical fibers are required to be optically aligned to elements on the PICs using active optical alignment procedure, in which the positions and orientations of the separate optical fibers are adjusted by machinery until the amount of optical power transferred between the optical fibers and PIC is maximized.

Further in this regard, the PIC must be energized during the active alignment process. If a laser is attached to the PIC, the laser must be energized for active optical alignment. This requires that the laser to be assembled to the PIC first and that electrical power be provided to the laser before the optical fiber connector can be aligned. If instead optical signals are sent through the optical fibers in the connector, the PIC still needs to be powered or otherwise energized and/or activated to provide a reading of the optical power from the optical signals to determine the maximum when optical alignment is achieved. Thus heretofore, electrical connections to the PIC is required for active optical alignment processes. <CIT> discloses wafer designs, testing systems and techniques for wafer-level optical testing by coupling probe light to/from the top of the wafer. A test system uses an optical probe to search for and align with an optical alignment loop. A located alignment loop is used as a reference point to locate other devices on a wafer. The test system tests operation of selected devices on the wafer.

What is needed is an improved approach to optically align an optical subassembly (e.g., an MOB) to an optoelectronic device (e.g., a PIC), without having to provide electrical connections to the optoelectronic device, which would improve throughput, tolerance, manufacturability, ease of use, functionality and reliability at reduced costs.

The present invention provides an optoelectronic structure according to claim <NUM>, and a method of optically aligning an optical subassembly to an optoelectronic device according to claim <NUM>. Preferred embodiments are defined in dependent claims. The present invention overcomes the drawbacks of the prior art, by providing alignment features for optical aligning an optical subassembly (e.g., an optical subassembly including an MOB) to an optoelectronic device (e.g., a PIC) without requiring an electrical connection to the optoelectronic device. The inventive optical alignment scheme improves throughput, tolerance, manufacturability, ease of use, functionality and reliability at reduced costs.

In the context of the present invention, optical alignment involves positioning of the optical subassembly relative to the optoelectronic device, to align the optical axis of the respective optical elements or components of the optical subassembly to the optical axis of the corresponding optical elements or components of the optoelectronic device, so as to minimize optical signal attenuation between the optoelectronic device and optical subassembly to within acceptable tolerance.

In accordance with the present invention, the optoelectronic device is not provided with an active component (e.g., a laser, a photodiode, etc.) for optical alignment. Optical alignment of the optical subassembly and the optoelectronic device is achieved using an optical source and an optical receiver external to the optoelectronic device. The inventive optical alignment features and method achieves sub-micrometer optical alignment between the optical subassembly and the optoelectronic device, by using the optical receiver to measure feedback of optical power of an optical alignment signal provided by the optical source, which has been transmitted between optical alignment features provided on the optical subassembly and the optoelectronic device.

In one embodiment, an alignment feature in the form of a passive waveguide is provided in the optoelectronic device, and the position of the waveguide in relation to the alignment features on the optical subassembly is relied upon to determine optical alignment between the optical subassembly and the optoelectronic device.

In one embodiment, the passive waveguide is disposed outside the active region of the optoelectronic device. In the context of the present invention, the active region of the optoelectronic device is the region where the optical paths are defined for transmissions of optical data signals between the optical subassembly and the optoelectronic device during normal active operations of the optoelectronic device.

In one embodiment, the optical subassembly is provided with alignment features including a first alignment reflective surface directing (i.e., folding, reshaping and/or focusing) an optical alignment signal from the optical source to the input of the waveguide on the optoelectronic device, and a second alignment reflective surface directing (i.e., folding, reshaping and/or collimating) to the optical receiver the alignment signal directed from the output of the waveguide after the alignment signal has been transmitted from the input to the output through the waveguide. By adjusting the relative position between the optical subassembly and the optoelectronic device, and detecting the optical power of the alignment signal reflected from the second alignment reflective surface, the position of optimum optical alignment of the optical subassembly and the optoelectronic device can be determined (e.g., at a detected maximum optical power; i.e., at lowest optical signal attenuation).

The input and output of the waveguide each comprises a grating coupler, with a first grating coupler receiving the alignment signal from the first alignment reflective surface of the optical subassembly, and a second grating coupler outputting the alignment signal to the second alignment reflective surface of the optical subassembly.

The optical source and optical receiver are provided external of the optical subassembly.

In one embodiment, the optical subassembly comprises an optical bench subassembly, having optical data reflective surfaces defined thereon for directing operational data signals between the optical bench subassembly and the optoelectronic device during normal active operations of the optoelectronic device. In one embodiment, the optical bench subassembly is in the form of an optical fiber subassembly (OFSA) supporting one or more optical fibers in optical alignment with the data reflective surfaces (i.e., with the optical axis of the respective optical fibers aligned with the optical axis of the corresponding data reflective surface).

In one embodiment, the first and second alignment reflective surfaces are each formed by stamping a malleable metal.

According to the claimed invention, the optical subassembly further comprises a separate alignment structure having optical alignment features. The alignment structure comprises an alignment foundation supporting the optical bench subassembly in physically alignment to the foundation. The foundation is optically aligned to the optoelectronic device in accordance with the inventive alignment scheme, thereby optically aligning the optical bench subassembly supported on the foundation to the optoelectronic device. In one embodiment, the foundation is provided with alignments features including similar alignment reflective surfaces as the previous embodiment. In another embodiment, the foundation is provided with alignment features including a first pair of alignment reflective surfaces directing an optical alignment signal from the optical source to the input of the waveguide on the optoelectronic device, and a second pair of alignment reflective surfaces reflecting to the optical receiver the alignment signal directed from the output of the waveguide after the alignment signal has been transmitted from the input to the output through the waveguide. By adjusting the relative position between the foundation and the optoelectronic device, and detecting the optical power of the alignment signal reflected from the second pair of alignment reflective surfaces, the optimum optical alignment of the foundation and the optoelectronic device can be determined (e.g., at a detected maximum optical power).

In one embodiment, the optical bench subassembly and the foundation may be coupled by a reconnectable or demountable connection that is configured and structured to allow the optical bench assembly to be removably attachable for reconnection to the foundation in alignment therewith, after the foundation has be optically aligned to optoelectronic device. The foundation may be permanently attached with respect to the optoelectronic device. Alignment between the foundation and the optical bench subassembly may be achieved by passive, kinematic coupling, quasi-kinematic coupling, or elastic-averaging coupling. The passive alignment coupling allows the optical bench subassembly to be detachably coupled to the optoelectronic device, via a foundation that has been optically aligned to the optoelectronic device. The connector can be detached from the foundation and reattached to the foundation without compromising optical alignment. Accordingly, the foundation can be attached to a circuit board by optical alignment in accordance with the present invention, and after the circuit board is completely populated, an optical bench subassembly with optical fiber cables can be connected to the circuit board. Consequently, the optical fiber cables are not in the way during the assembly of the circuit board.

The present invention provides a method for optical alignment of an optical subassembly to an optoelectronic device which can be implemented with pick-and-place machinery with about a <NUM> micrometer positioning accuracy. This is adequate for single-mode optical connections.

For a fuller understanding of the nature and advantages of the invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.

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 scope of the invention.

The present invention overcomes the drawbacks of the prior art, by providing alignment features and method for optical aligning an optical subassembly (e.g., an optical subassembly including an MOB) to an optoelectronic device (e.g., a PIC) without requiring an electrical connection to the optoelectronic device. The inventive optical alignment structure and method improves throughput, tolerance, manufacturability, ease of use, functionality and reliability at reduced costs.

In the context of the present invention, optical alignment involves positioning of the optical subassembly relative to the optoelectronic device, to align the optical axis of the respective optical elements and/or components of the optical subassembly to the optical axis of the corresponding optical elements and/or components of the optoelectronic device, so as to minimize optical signal attenuation between the optoelectronic device and optical subassembly to within acceptable tolerance.

In accordance with the present invention, the optoelectronic device is not provided with an active component (e.g., a laser, a photodiode, etc.) for optical alignment. Optical alignment of the optical subassembly and the optoelectronic device is achieved using an optical source and optical receiver external to the optoelectronic device. The inventive optical alignment scheme achieves sub-micrometer optical alignment between the optical subassembly and the optoelectronic device, by using the optical receiver to measure feedback of optical power of an optical alignment signal provided by the optical source, which has been transmitted between optical alignment features provided on the optical subassembly and the optoelectronic device.

By way of example and not limitation, the present invention will be described below in connection with an optoelectronic device in the form of a photonic integrated circuit (PIC), e.g., a silicon PIC (SiPIC), and an optical subassembly (OSA) in the form an optical fiber subassembly (OFSA). However, other types of optoelectronic devices (e.g., discrete devices such as lasers, photodiodes, transmitters, receivers and/or transceivers, which may not be implemented in a PIC) and optical subassemblies (e.g., with other optical elements or components, such as lenses, filters, lasers, photodiodes, etc., with or without optical fibers) may implement the optical alignment structure and method disclosed herein without departing from the scope of the present invention.

In one embodiment, the optical subassembly comprises an optical bench subassembly, having optical data reflective surfaces defined thereon for directing operational data signals between the optical bench subassembly and the optoelectronic device during normal active operations of the optoelectronic device. In the illustrated embodiment, the OSA is in the form of an OFSA supporting one or more optical fibers in optical alignment with the data reflective surfaces (i.e., with the optical axis of the respective optical fibers aligned with the optical axis of the corresponding data reflective surface).

Referring to the embodiment illustrated by <FIG>, which is not according to the claimed invention, the OSA <NUM> comprises an optical bench subassembly, which more specifically is in the form of an OFSA. The OSA <NUM> comprises a base <NUM> and a core <NUM> supported in a space <NUM> within the base <NUM>. The core <NUM> defines a plurality of grooves <NUM> for securely holding the end sections <NUM> of optical fibers <NUM> (i.e., bare sections having cladding exposed, without protective buffer and jacket layers <NUM>) in the optical fiber cable <NUM>. The core <NUM> also defines a plurality of data reflective surfaces <NUM> (e.g., concave aspherical micro-mirror surfaces) arranged in a row, which are each aligned to a corresponding groove <NUM>, so that the end sections <NUM> of the optical fibers <NUM> held in grooves <NUM> are in optical alignment with the data reflective surfaces <NUM>. Similar structures to base <NUM> and a core <NUM> and forming process thereof are disclosed in detail in <CIT> (commonly assigned to the assignee of the present invention), which discloses stamping to form a composite structure of dissimilar materials having structured features, including microscale features that are stamped into a more malleable material (e.g., aluminum) for the core, to form open grooves to retain optical fibers in optical alignment with a stamped array of aspherical micro-mirrors. As a result of stamping the features of the core while the material for the core is in place in the base, the core is attached to the base like a rivet. The present invention takes advantage of the concepts disclosed therein.

The grooves <NUM> are structured to securely retain the fibers sections <NUM> (bare section with cladding exposed, without protective buffer and jacket layers) by clamping the fiber section <NUM>, e.g., by a mechanical or interference fit (or press fit). The interference fit assures that the fiber sections <NUM> are clamped in place and consequently the position and orientation of the fiber section <NUM> with respect to the data reflective surfaces <NUM> are set by the location and longitudinal axis of the grooves <NUM>. Further details of the clamping open groove structure can be found in <CIT> (commonly assigned to the assignee of the present invention). The present invention takes advantage of the concepts disclosed therein.

As shown in the illustrated embodiment, a cable strain relief <NUM> is provided on the OSA <NUM> to provide protection to the optical fiber cable <NUM>. In addition, a cover <NUM> is provided over the grooves <NUM>, to reduce the risks of the fiber section <NUM> coming loose from the grooves <NUM>. The cover <NUM> also functions as a spacer, as more clearly shown in <FIG>.

The OSA <NUM> is provided with alignment features including a first alignment reflective surface <NUM> and a second alignment reflective surface <NUM> on the core <NUM>. In the illustrated embodiment, the first and second alignment reflective surfaces <NUM> and <NUM> are located beyond the two ends of the row of data reflective surfaces <NUM>, in a notch (<NUM>', <NUM>,) at each side of the core <NUM>. Generally, the first alignment reflective surface <NUM> directs (i.e., by folding, reshaping and/or focusing) an optical alignment signal <NUM> from an external optical source (e.g., a laser, not shown) to the PIC <NUM> (which will be further discussed later below in reference to grating couplers in <FIG> and <FIG>), and the second alignment reflective surface <NUM> directs (i.e., by folding, reshaping and/or collimating) to an external optical receiver (e.g., a photodiode, not shown) the same alignment signal <NUM> from the PIC <NUM> (which will be discussed further below in reference to grating couplers in <FIG> and <FIG>). The first and second alignment reflective surfaces <NUM> and <NUM> are not aligned to any optical fiber groove. These reflective surfaces <NUM> and <NUM> are used only for optical alignment purpose in accordance with the present invention, and they are not used for directing data optical signals during normal active operations of the PIC <NUM>. As discussed further below, by adjusting the relative position between the OSA <NUM> and the PIC <NUM>, and detecting the optical power of the alignment signal <NUM> reflected from the second alignment reflective surface <NUM>, the position of optimum optical alignment of the OSA and the optoelectronic device can be determined (e.g., at a detected maximum optical power; i.e., at lowest optical signal attenuation).

In the illustrated embodiment, the optical source and optical receiver for alignment are provided external of the OSA <NUM>. Clearances should be provided in the base <NUM> to allow the alignment optical signal <NUM> from the external source to be incident through the base <NUM> at the reflective surface <NUM> on the core <NUM>, and to allow alignment optical signal <NUM> to be redirected from the alignment reflective surface <NUM> through the base <NUM> to the external receiver. In the illustrated embodiment, an opening, notch or cutout <NUM> is provided on the side of the base <NUM> matching the notch <NUM>' on the side of the core <NUM>, for the incident alignment optical signal <NUM>, and an opening, notch or cutout <NUM> is provided on the side of the base <NUM> matching the notch <NUM>' on the side of the core <NUM>, for the redirected alignment optical signal <NUM> from the alignment reflective surface <NUM>.

In one embodiment, the first and second alignment reflective surfaces <NUM> and <NUM>, and the data reflective surfaces <NUM> are formed together by stamping a malleable metal of the core <NUM>, so as to accurately define the relative positions of the alignment reflective surfaces <NUM> and <NUM> with respect to the data reflective surfaces <NUM> in a single stamping operation to achieve tight tolerances.

<CIT> (commonly assigned to the assignee of the present invention) 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 structure disclosed herein. The disclosed stamping processes involve stamping a bulk material (e.g., a metal blank), 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. The present invention takes advantage of the concepts disclosed therein.

In accordance with the present invention, the reflective surfaces and grooves are dimensionally accurate to better than +/- <NUM>, which is sufficient to achieve desirable optical alignment tolerance and low insertion loss of less than <NUM> dB (><NUM>% coupling efficiency) for single-mode fiber-optic connections, and even achieving an insertion loss of as low as <NUM> dB (<NUM>% coupling efficiency).

In one embodiment, an alignment feature in the form of a passive waveguide is provided in the optoelectronic device, and the position of the waveguide in relation to the alignment features on the optical subassembly is relied upon to determine optical alignment between the optical subassembly and the optoelectronic device. In the illustrated embodiment, the input and output of the waveguide each comprises a grating coupler, with a first grating coupler <NUM> receiving the alignment signal <NUM> from the first alignment reflective surface <NUM> of the OSA <NUM>, and a second grating coupler <NUM> outputting the alignment signal <NUM> to the second alignment reflective surface <NUM> of the OSA <NUM>.

<FIG> is a top view schematically illustrating the layout of waveguides and grating couplers at the top surface of the PIC <NUM>, in accordance with one embodiment not according to the claimed invention. Specifically, an alignment waveguide <NUM> is provided with an alignment grating coupler <NUM> at an input port of the alignment waveguide <NUM>, and an alignment grating coupler <NUM> at an output port of the alignment waveguide <NUM>. The alignment grating couplers <NUM> and <NUM> couple an alignment optical signal <NUM> for optical alignment of the PIC <NUM> and the OSA <NUM>, which will be discussed in greater detail below (see also <FIG>). The alignment waveguide <NUM> transmit optical signal between the grating coupler <NUM> at the input port and the grating coupler at the output port. In addition, there are data grating couplers <NUM> and corresponding data waveguides <NUM> leading to optical elements, optical components and/or photonic circuits <NUM>, (e.g., lasers, photodiodes, etc., collectively and schematically depicted in <FIG>) on the PIC <NUM>. The waveguides <NUM> and <NUM> are passive optical waveguides, which route optical signals therethrough. The data grating couplers <NUM> couple optical data signals between the PIC and an OSA during normal active operation of the PIC <NUM>, whereby each of the grating couplers <NUM> correspond to a data reflective surface <NUM>/optical fiber section <NUM> in the OSA <NUM>. The alignment grating couplers <NUM> and <NUM>, the data grating couplers <NUM>, the alignment waveguide <NUM> and the data waveguide <NUM> can be formed on the PIC <NUM> by, e.g., lithographically patterning those features onto the surface of PIC <NUM>.

Generally, optical coupling between PIC and an OSA (in particular an OSA comprising an OFSA) is discussed in <CIT> (commonly assigned to the assignee of the present invention). As disclosed therein, aspherical concave mirrors in the OFSA fold, reshape and/or focus light entering or exiting the array of optical fibers into diffractive grating couplers on the surface of the PIC, so as to allow the axis of the optical fiber to be oriented at small angles or parallel to the surface of the PIC, and lowered close to the surface of the PIC. The mirror is further configured to reshape light from a flat polished optical fiber to produce a mode field resembling the mode field of an angled polished optical fiber, to match the design angle of existing grating couplers that are designed to work with angled polished optical fibers. The mirror and optical fiber alignment structure in the optical connector are integrally/simultaneous formed by precision stamping. The present invention takes advantage of the concepts disclosed therein.

In one embodiment, the alignment waveguide <NUM> is disposed outside the active region <NUM> of the PIC <NUM>. In the context of the present invention, the active region <NUM> of the optoelectronic device is the region where optical paths are defined for transmissions of optical data signals between the optical subassembly and the PIC during normal active operations of the PIC. In the illustrated embodiment of <FIG>, the input grating coupler <NUM> and the output grating coupler <NUM> are located at two ends of the alignment waveguide <NUM> that extends along one side of the row of data grating couplers <NUM>.

<FIG> illustrate placement of the OSA <NUM> on the PIC <NUM> for optical alignment not according to the claimed invention. <FIG> is a perspective view of the OSA <NUM> in <FIG>, showing signal paths of data optical signals and alignment optical signals. Referring to <FIG>, the optical path <NUM> of the alignment optical signal <NUM> is shown. The alignment optical signal <NUM> from the external source is incident onto the aspherical concave alignment reflective surface <NUM>, which folds, reshapes and/or focuses the optical signal <NUM>, to be incident at the grating coupler <NUM> at the input port of the alignment waveguide <NUM>. In this embodiment, the alignment optical signal <NUM> enters through the base <NUM> from its side. The alignment optical signal <NUM> transmits through the alignment waveguide <NUM>, and exits through the grating coupler <NUM> at the output port of the alignment waveguide <NUM>. The aspherical concave alignment reflective surface <NUM> folds, reshapes, and/or collimates the alignment optical signal <NUM> to be transmitted to the external receiver. In this embodiment, the alignment signal <NUM> exists through the base <NUM> from its opposing side. By monitoring the power level of the alignment optical signal <NUM> from the alignment reflective surface <NUM>, the best optical alignment is at the point of maximum power level reading at the power meter. After achieving optical alignment, the OSA <NUM> is attached to the PIC <NUM> using epoxy or soldering, to secure the relative positions of the OSA <NUM> and the PIC. After optical alignment, the data grating couplers <NUM> on the PIC <NUM> would also be optically aligned with the corresponding data reflective mirrors <NUM> in the OSA <NUM>. In accordance with the present invention, no active alignment using optical signals via the fiber sections <NUM>, data reflective surfaces <NUM> and grating couplers <NUM> would be required to achieve optical alignment of the OSA <NUM> and the PIC <NUM>.

As can be understood, the alignment optical signal <NUM> is a dedicated signal for optical alignment of the OSA <NUM> and the PIC <NUM>. Such alignment optical signal <NUM> is not present after the optical alignment process, and during normal action operations of the PIC <NUM>.

In practice, a pick-and-place gripper mechanism holds the OSA <NUM> on a stage that can translate and orient the OSA <NUM> with respect to the PIC <NUM>. An optical fiber cable extends from the external source (e.g., a laser) to the body of the gripper. The gripper provides optical alignment between the tip of the fiber-optic cable and the alignment reflective surface <NUM>. A second optical fiber cable would run from the gripper to the receiver (e.g., a photodiode connected to a power meter), and the gripper would assure alignment between this optical fiber cable and the alignment reflective surface <NUM>. These two optical fiber cables would be attached in the gripper so that each time the gripper picks-up a new OSA, it is automatically aligned to the input and output end faces of the optical fiber cables. Lenses can be added into the gripper to focus the light exiting/entering the end faces of the optical fiber cables. The configuration of the pick-and-place gripper will not be further discussed herein, as such gripper can be configured using state of the art gripper mechanisms that are modified to operate in accordance with the present invention. The present invention thus provides a method for optical alignment of an optical subassembly to an optoelectronic device which can be implemented with pick-and-place machinery with about a <NUM> micrometer positioning accuracy. This is adequate for single-mode optical connections.

In accordance with the present invention, at least the following advantages can be achieved:.

Instead of data grating couplers <NUM> on the PIC, the present invention can also be used with other surface-emitting or surface-receiving photonic devices, including vertical cavity surface emitting lasers and photodiodes. This is illustrated by example in <FIG> for the case of a 1x4 VCSEL (Vertical-Cavity Surface-Emitting Laser) array <NUM>. Similar alignment grating couplers <NUM>' and <NUM>' and alignment waveguide <NUM>' could also be lithographically patterned onto the surface of a VCSEL chip, then an optical subassembly could be optically aligned with the emitting areas of the VCSEL array <NUM>. A similar approach could also be used with a photodiode array (not illustrated).

<FIG> illustrates a further embodiment according to the claimed invention. The inventive concept of optical alignment is similar to the previous embodiment, namely, optical alignment between an optical subassembly and an optoelectronic device by measuring feedback of optical power of an optical alignment signal provided by an external optical source, which has been transmitted between optical alignment features provided on the optical subassembly and the optoelectronic device. In this embodiment, the optical subassembly further comprises a separate alignment structure having optical alignment features in combination with the optical bench assembly. The alignment structure comprises an alignment foundation supporting the optical bench subassembly in physically alignment to the foundation. The foundation is optically aligned to the optoelectronic device in accordance with the inventive alignment scheme, thereby optically aligning the optical bench subassembly supported on the foundation to the optoelectronic device. In one embodiment, the foundation is provided with alignments features including similar alignment reflective surfaces as the previous embodiment. In another embodiment, the foundation is provided with alignment features including a first pair of alignment reflective surfaces directing an optical alignment signal from the optical source to the input of the waveguide on the optoelectronic device, and a second pair of alignment reflective surfaces reflecting to the optical receiver the alignment signal directed from the output of the waveguide after the alignment signal has been transmitted from the input to the output through the waveguide. By adjusting the relative position between the foundation and the optoelectronic device, and detecting the optical power of the alignment signal reflected from the second pair of alignment reflective surfaces, the optimum optical alignment of the foundation and the optoelectronic device can be determined (e.g., at a detected maximum optical power).

Referring to <FIG>, <FIG> shows an OSA <NUM> in accordance with an embodiment of the present invention, mounted onto a PIC <NUM> that is supported on a circuit board <NUM> having a ball-grid array (BGA); and <FIG> is an exploded view thereof. <FIG> are various views of the OSA <NUM> attached to the <NUM> with the securing clip <NUM> removed. As shown, an electro-optical module <NUM> is mounted on the circuit board <NUM>. The circuit board <NUM> supports an anchor <NUM> for anchoring the clip <NUM>.

In this illustrated embodiment, the OSA <NUM> includes an optical bench subassembly in the form of an OFSA <NUM> and an alignment foundation <NUM> to which the OFSA <NUM> is to be mounted. The foundation <NUM> of the OSA <NUM> in this embodiment provides the alignment features (namely, alignment reflective surfaces) for optical alignment of the foundation <NUM> (and thus OSA <NUM>) to the PIC <NUM>. As will be further explained later below, the OFSA <NUM> can be mounted onto the foundation <NUM> after optical alignment of the foundation <NUM> and the PIC <NUM> had been achieved and secured.

Referring to the embodiment illustrated by <FIG>, the OFSA <NUM> has a similar "rivet" structure as the OSA <NUM> in the previous embodiment, comprises a base <NUM> and a core <NUM> supported in a space <NUM> within the base <NUM>. The core <NUM> defines a plurality of grooves <NUM> for securely holding the end sections <NUM> of optical fibers <NUM> (i.e., bare sections having cladding exposed, without protective buffer and jacket layers <NUM>) in the optical fiber cable <NUM>. For simplicity, the optical fiber components are not shown in <FIG>, but may be referred in other drawings in connection with the earlier described embodiment. The core <NUM> also defines a plurality of data reflective surfaces <NUM> (e.g., concave aspherical micro-mirror surfaces) arranged in a row, which are each aligned to a corresponding groove <NUM>, so that the end sections <NUM> of the optical fibers <NUM> held in grooves <NUM> are in optical alignment with the data reflective surfaces <NUM>. Similar structures to base <NUM> and a core <NUM> and forming process thereof are disclosed in detail in <CIT> (commonly assigned to the assignee of the present invention), which discloses stamping to form a composite structure of dissimilar materials having structured features, including microscale features that are stamped into a more malleable material (e.g., aluminum) for the core, to form open grooves to retain optical fibers in optical alignment with a stamped array of aspherical micro-mirrors. As a result of stamping the features of the core while the material for the core is in place in the base, the core is attached to the base like a rivet. The present invention takes advantage of the concepts disclosed therein.

As shown in <FIG>, the surface <NUM> on the same side as the data reflective surfaces <NUM> is provided with surface textures for demountable passive alignment coupling (to be discussed later below).

<FIG> is a top view schematically illustrating the layout of waveguides and grating couplers at the top surface of the PIC <NUM>, in accordance with one embodiment of the present invention. As in the previous amendment, an alignment waveguide <NUM> is provided with an alignment grating coupler <NUM> at an input port of the alignment waveguide <NUM>, and an alignment grating coupler <NUM> at an output port of the alignment waveguide <NUM>. The alignment grating couplers <NUM> and <NUM> couple an alignment optical signal <NUM> for optical alignment of the PIC <NUM> and the OSA <NUM> (via the foundation <NUM>). The alignment waveguide <NUM> transmit optical signal between the grating coupler <NUM> at the input port and the grating coupler at the output port. In addition, there are data grating couplers <NUM> and corresponding data waveguides <NUM> leading to optical elements, optical components and/or photonic circuits <NUM>, (e.g., lasers, photodiodes, etc., collectively and schematically depicted in <FIG>) on the PIC <NUM>. The waveguides <NUM> and <NUM> are passive optical waveguides, which route optical signals therethrough. The data grating couplers <NUM> couple optical data signals between the PIC <NUM> and the OSA <NUM> during normal active operation of the PIC <NUM>, whereby each of the grating couplers <NUM> correspond to a data reflective surface <NUM>/optical fiber section <NUM> in the OSA <NUM>. The alignment grating couplers <NUM> and <NUM>, the data grating couplers <NUM>, the alignment waveguide <NUM> and the data waveguide <NUM> can be formed on the PIC by, e.g., lithographically patterning those features onto the surface of PIC <NUM>.

In the illustrated embodiment, the alignment waveguide <NUM> is disposed outside the active region <NUM> of the PIC <NUM>. In this embodiment, the input alignment grating coupler <NUM> and the output alignment grating coupler <NUM> are located at two ends of the alignment waveguide <NUM> that extends generally along one side of the row of data grating couplers <NUM>. Unlike the previous embodiment, the ends of the alignment waveguide <NUM> curve towards the row of grating coupler <NUM>, such that alignment grating couplers <NUM> and <NUM> are generally in line with the line of grating couplers <NUM>. The alignment grating couplers <NUM> and <NUM> are nonetheless outside of the active region <NUM>. This modified layout geometry corresponds to the relative location of the alignment reflective surfaces on the foundation <NUM> with respect to the data reflective surfaces on the OFSA <NUM>, which does not affect the inventive concept of the present invention.

As shown in the figures, the foundation <NUM> is configured as a unitary, monolithic U-shaped block, with a thinner middle section <NUM> flanked on each side by two thicker sections <NUM>, which defines a space <NUM> for receiving the OFSA <NUM> (as shown in <FIG>). An opening is provided at the middle section <NUM> to allow passage of data optical signals between the OFSA <NUM> and the PIC <NUM>. The top surface of the section <NUM> is provided with surface textures for demountable passive alignment coupling to the OFSA <NUM> (to be discussed later below).

Not illustrated in the figures, the foundation <NUM> of the OSA <NUM> may be provided with alignments features including similar alignment reflective surfaces provided on the core <NUM> in the previous embodiment (i.e., providing first and second alignment reflective surfaces on the foundation <NUM> (instead of the core of the OFSA), and providing an external alignment signal <NUM> entering the side of the foundation <NUM> to incident on a first alignment reflective surface to be redirected to the alignment grating coupler <NUM> on the PIC <NUM>, and the same alignment signal output from the grating coupler <NUM> is redirected by a second alignment reflective surface to exit the opposing side of the foundation <NUM>).

<FIG> illustrate a modified optical alignment features which accommodate an alignment optical signal <NUM> that is incident vertical with respect to the OSA <NUM>. Specifically in this embodiment, the foundation <NUM> is provided with alignment features including a first complementary pair of alignment reflective surfaces directing an optical alignment signal from the optical source to the input of the waveguide on the optoelectronic device, and a second pair of complementary alignment reflective surfaces reflecting to the optical receiver the alignment signal directed from the output of the waveguide after the alignment signal has been transmitted from the input to the output through the waveguide. By adjusting the relative position between the foundation and the optoelectronic device, and detecting the optical power of the alignment signal reflected from the second pair of alignment reflective surfaces, the optimum optical alignment of the foundation and the optoelectronic device can be determined (e.g., at a detected maximum optical power). The first and second pairs of alignment reflective surface are more clearly shown in <FIG>.

The first pair <NUM> of alignment reflective surfaces are provided at the portion <NUM> of the foundation <NUM>, and the second pair <NUM> of alignment reflective surfaces are provided at the portion <NUM> of the foundation <NUM>. The first pair <NUM> comprises alignment reflective surfaces 1324a and 1324b; the second pair <NUM> comprises alignment reflective surfaces 1325a and 1325b. Alignment reflective surfaces 1324a and 1325a may be flat reflective surfaces, and the alignment reflective surface 1324b and 1325b may be concave aspherical reflective surfaces. Regardless, the geometry of the alignment reflective surfaces in each pair is matched, so that incident external alignment optical signal <NUM> is shaped, fold, and/or focused onto the corresponding grating coupler <NUM> with a vertical optical path, and the alignment optical signal <NUM> from the grating coupler <NUM> is shaped, folded and/or collimated to be directed to the external power meter with a vertical optical path.

As illustrated, the alignment reflective surfaces in each pair are configured to fold the alignment optical signal twice to follow a zig-zag optical path <NUM> (<FIG> and <FIG>), such that the incident optical path and the output optical path for each pair are generally parallel. As shown in <FIG> and <FIG>, the alignment reflective surface 1324a folds incident alignment optical signal <NUM>, redirect alignment optical signal <NUM> to alignment reflective surface 1324b, which folds the alignment optical signal <NUM> and redirect to the grating coupler <NUM> on the PIC <NUM>. The alignment reflective surfaces 1324a, 1324b, 1325a, 1325b may be formed by stamping a dissimilar core materials within the portions <NUM> and <NUM>, using the "rivet" approach to stamping disclosed in detail in <CIT> (commonly assigned to the assignee of the present invention). This is analogous to stamp forming the core <NUM> in the base <NUM> of the OSA <NUM> in the earlier embodiment. By using the appropriate die and punch set, the two alignment reflective surfaces for both pairs (i.e., all four alignment reflective surfaces) may be stamp simultaneously in a final stamping operation, so as to accurately define the relative position of the two alignment reflective surfaces with the foundation <NUM>. As illustrated, the rivet 1424a defines the alignment reflective surface 1324a, the rivet 1424b defines the alignment reflective surface 1324b, the rivet 1425a defines the alignment reflective surface 1325a, and the rivet 1425b defines the alignment reflective surface 1325b.

<FIG> and <FIG> illustrate placement of the foundation <NUM> on the PIC <NUM> for optical alignment in accordance with the present invention. The optical path <NUM> of the alignment optical signal <NUM> is shown. As shown in <FIG> and <FIG>, the alignment reflective surface 1324a folds the vertical incident alignment optical signal <NUM>, redirect alignment optical signal <NUM> to alignment reflective surface 1324b, which folds the alignment optical signal <NUM> and redirect to the grating coupler <NUM> on the PIC <NUM>. In this embodiment, the alignment optical signal <NUM> enters through the foundation <NUM> from its top side. Referring also to <FIG>, the alignment optical signal <NUM> transmits through the alignment waveguide <NUM> on the PIC <NUM>, and exits through the grating coupler <NUM> at the output port of the alignment waveguide <NUM>. The alignment reflective surface 1325b folds, reshapes, and/or collimates the alignment optical signal <NUM> to be redirected to the alignment reflective surface 1325a to be redirected vertical to the foundation to the external receiver. In this embodiment, the alignment signal <NUM> exists through the foundation <NUM> vertically, parallel to the incident alignment optical signal <NUM> to foundation <NUM>. See also <FIG> for a three-dimensional perspective of the optical path <NUM> of the optical alignment signal <NUM>. By monitoring the power level of the alignment optical signal <NUM> from the alignment reflective surface 1325a, the best optical alignment is at the point of maximum power level reading at the power meter. Once optical alignment is achieved, the foundation <NUM> is attached to the PIC <NUM> using epoxy or soldering, to secure the relative positions of the foundation <NUM> and the PIC <NUM>.

In one embodiment, the OFSA <NUM> and the foundation <NUM> may be coupled by a reconnectable or demountable connection that is configured and structured to allow the OFSA <NUM> to be removably attachable for reconnection to the foundation <NUM> in alignment therewith, after the foundation <NUM> has been optically aligned to PIC <NUM>. The foundation <NUM> may be permanently attached with respect to the PIC <NUM>, but the OFSA <NUM> would still be demountable. Alignment between the foundation <NUM> and the OFSA (i.e., an optical bench subassembly) may be achieved by passive, kinematic coupling, quasi-kinematic coupling, or elastic-averaging coupling. In the embodiment illustrated in <FIG>, the demountable passive alignment coupling is achieved by the surface textures <NUM> and <NUM> provided on the facing surfaces of the OFSA <NUM> and the section <NUM> of the foundation <NUM>. The passive alignment coupling allows the OFSA <NUM> to be detachably coupled to the optoelectronic device, via a foundation <NUM> that has been optically aligned to the optoelectronic device. The OFSA <NUM> can be detached from the foundation <NUM> and reattached to the foundation <NUM> without compromising optical alignment. Accordingly, the foundation <NUM> can be attached to the PIC <NUM> on a circuit board <NUM> by optical alignment in accordance with the present invention, and after the circuit board <NUM> is completely populated, an optical bench subassembly (e.g., OFSA <NUM>) with optical fiber cable <NUM> can be operatively connected to the circuit board <NUM>. Consequently, the optical fiber cable <NUM> is not in the way during the assembly of the circuit board <NUM>. Demountable connection with passive alignment discussed above and the benefits thereof are discussed in detail in <CIT> (commonly assigned to the assignee of the present invention). The present invention takes advantage of the concepts disclosed therein.

The clip <NUM> provides a means of securing the demountable OFSA <NUM> onto the foundation <NUM>, but clamping onto the anchor <NUM> attached to the circuit board <NUM>.

After optical alignment, the data grating couplers <NUM> on the PIC <NUM> would be optically aligned with the corresponding data reflective mirrors <NUM> in the OFSA <NUM>. In accordance with the present invention, as in the previous embodiment, no active alignment using optical signals via the fiber sections <NUM>, data reflective surfaces <NUM> and grating couplers <NUM> would be required to achieve optical alignment of the foundation <NUM> (and hence the OSA <NUM>) and the PIC <NUM>.

As can be understood, the alignment optical signal <NUM> is a dedicated signal for optical alignment of the foundation <NUM> of the OSA <NUM> and the PIC <NUM>. Such alignment optical signal <NUM> is not present after the optical alignment process, and during normal action operations of the PIC <NUM>.

As in the previous embodiment, in practice, a pick-and-place gripper mechanism holds the foundation <NUM> on a stage that can translate and orient the foundation <NUM> with respect to the PIC <NUM>. An optical fiber cable extends from the external source (e.g., a laser) to the body of the gripper. The gripper provides optical alignment between the tip of the fiber-optic cable and the alignment reflective surface 1324a. A second optical fiber cable would run from the gripper to the receiver (e.g., a photodiode connected to a power meter), and the gripper would assure alignment between this optical fiber cable and the alignment reflective surface 1325a. These two optical fiber cables would be attached in the gripper so that each time the gripper picks-up a new foundation <NUM>, it is automatically aligned to the input and output end faces of the optical fiber cables. Lenses can be added into the gripper to focus the light exiting/entering the end faces of the optical fiber cables. The configuration of the pick-and-place gripper will not be further discussed herein, as such gripper can be configured using state of the art gripper mechanisms that are modified to operate in accordance with the present invention.

Referring 11A and 11B, the optically aligned and attached foundation <NUM> and PIC <NUM> are positioned on the circuit board <NUM> that had been populated, with, e.g., electro-optical module <NUM> (as shown in <FIG>) to obtain the structure shown in <FIG>, ready for mounting the OFSA <NUM>. More specifically, referring to the flow of the supply chain model shown in <FIG>, at the Foundry facility, the pick-and-place mechanism align the foundation <NUM> to the PIC <NUM>. The foundation <NUM> is, for example, soldered to the PIC <NUM>. This is then shipped to a Packaging facility, where a lower precision pick-and-place mechanism positions and attaches the PIC <NUM> with the foundation <NUM> attached thereon onto the circuit board <NUM>. There may be additional components pre-populated or to be populated on the circuit board. The circuit board <NUM> with the PIC <NUM> and foundation <NUM> is then shipped to a Product Assembly facility, where the OFSA <NUM> is attached to the foundation during product assembly using passive-alignment features discussed above. The present invention thus provides a method for optical alignment of an optical subassembly to an optoelectronic device which can be implemented with pick-and-place machinery with about a <NUM> micrometer positioning accuracy. This is adequate for single-mode optical connections.

The present embodiment shares most of the advantages of the previous embodiment. In particular, the present embodiment achieves at least the following advantages:.

As for the previous embodiment, the PIC <NUM> may be replaced with other surface-emitting or surface-receiving photonic devices, including vertical cavity surface emitting lasers and photodiodes, as illustrated by way of example in <FIG>.

Claim 1:
An optoelectronic structure, comprising:
an optoelectronic device (<NUM>), wherein the optoelectronic device comprises an optical alignment waveguide (<NUM>) outside an active region (<NUM>) of the optoelectronic device, wherein the alignment waveguide (<NUM>) includes an input alignment grating coupler (<NUM>) and an output alignment grating coupler (<NUM>); and
an optical subassembly (<NUM>) optically aligned to the optoelectronic device, comprising:
a foundation (<NUM>), wherein the foundation comprises a body having a first alignment reflective surface and a second alignment reflective surface, wherein the first alignment reflective surface is configured to be accessible to an external optical source of an optical alignment signal (<NUM>), wherein the first alignment reflective surface reflects the optical alignment signal to the input alignment grating coupler (<NUM>), and the output alignment grating coupler (<NUM>) directs the same optical alignment signal to the second alignment reflective surface, and wherein the second alignment reflective surface is accessible to an external optical receiver of the optical alignment signal; and
an optical bench subassembly (<NUM>) demountably coupled to the foundation (<NUM>), wherein the first alignment reflective surface defines a first optical path that directs the optical alignment signal from the optical source to the input alignment grating coupler (<NUM>) of the alignment waveguide (<NUM>) on the optoelectronic device (<NUM>), and the second alignment reflective surface defines a second optical path reflecting to the optical receiver the alignment signal directed from the output alignment grating coupler (<NUM>) after the alignment signal has been transmitted from the input alignment grating coupler (<NUM>) to the output alignment grating coupler (<NUM>) through the alignment waveguide (<NUM>), so as to determine an optically aligned position between the foundation (<NUM>) and the optoelectronic device (<NUM>).