Patent Publication Number: US-2023152538-A1

Title: Fiberless Co-Packaged Optics

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/801,682, filed on Feb. 26, 2020, and claims the benefit of U.S. Provisional Application No. 62/811,840 filed on Feb. 28, 2019. The contents of each of the above-referenced applications are incorporated herein by reference in their entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to coupling an optical fiber to a substrate, and more particularly to coupling the optical components to an optoelectronic Integrated Circuit (IC). 
     BACKGROUND 
     Communications systems and data centers are required to handle massive data at ever increasing speeds and ever decreasing costs. To meet these demands, optical fibers and optical ICs (such as, a Photonic Integrated Circuit (PIC) or integrated optical circuit) are used together with high speed electronic ICs. A PIC is a device that integrates multiple photonic functions (similar to an electronic IC or RF IC). PICs are typically fabricated using indium phosphide or silicon oxide (SiO2), which allows for the integration of various optically active and passive functions on the same circuit. 
     The coupling of PICs to optical fibers is not as well advanced as the integration and/or coupling of electronic ICs. Specifically, the challenges facing optical connections are different and much more complex than connecting electronic ICs to, for example, a Printed Circuit Board (PCB). Some difficulties are inherent in wavelength, signal losses, assembly tolerance, and polarization characteristics of optical packaging. 
     Existing solutions utilize various techniques for connecting optical fibers to PICs. One technique suggests using various types of butt connections to the edge and surface fiber connections a PIC. The butt of a fiber can be connected to a planar waveguide at the edge of a PIC. This technique is efficient only if the cross sectional of the propagating mode of the fiber and the waveguide areas of the fiber core and the waveguide are of similar size. In most cases, this technique suffers from poor assembly tolerance and is not suitable for high fiber-port count. 
     An existing technique suggests laying a section of fiber on top of the surface of the 
     PIC where the end of the fiber has been cut at an angle to form an angled tip. The angled tip has a flat surface, which reflects a light beam down to a waveguide grating coupler disposed on the integrated circuit. The light beam is reflected off the reflective surface of the angled tip by total internal reflection. The waveguide grating coupler is designed to accept the slightly diverging light beam from the reflective surface of the angled tip of the fiber. The light beam can also propagate through the fiber to a chip coupler in the opposite direction, up from the substrate through the waveguide grating and into an optical fiber after bouncing off the reflective surface of the angled tip. This technique further requires coating on the exterior of the reflective surface with epoxy. 
     Among others, all of the above-noted techniques require precise alignment and active positioning of the optical fiber to the PIC. As such, current techniques suffer from poor and very tight alignment tolerance to gain an efficient connectivity. For example, a misalignment between an optical fiber and a PIC of 1-2 microns would result in a signal loss of about 3db. Furthermore, the alignment is now performed with expensive equipment or labor-intensive assembly solutions. As a result, mass production of PICs and/or optical couplers is not feasible. Furthermore, most current Single Mode (SM) fiber- chip connection uses non-scalable assembly technologies due to active-alignment protocols. Such protocols support low volume production and cannot be scaled to application with large port count. For example, data-center switches with high density and chip-to-chip connectivity applications are not supported by the active-alignment protocol. 
     Furthermore, current wide-band optical fiber to chip connectivity uses complicated edge coupling geometry and sub-micron tight tolerance, which mostly requires active alignment of specialized tools. 
     It would therefore be advantageous to provide a solution that would overcome the challenges noted above. 
     SUMMARY 
     A summary of several example embodiments of the disclosure follows. This summary is provided for the convenience of the reader to provide a basic understanding of such embodiments and does not wholly define the breadth of the disclosure. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor to delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later. For convenience, the term “some embodiments” or “certain embodiments” may be used herein to refer to a single embodiment or multiple embodiments of the disclosure. 
     Certain embodiments disclosed herein include an electro-optical system. The electro-optical system includes a Photonic Integrated Circuit (PIC) having a laser source located on the PIC, a fiberless optical coupler located on the PIC. The fiberless optical coupler is configured to be coupled to a fiber array. The electro-optical system also includes an optical element, and a mechanical aligner. The optical element is aligned with the fiber array, via the mechanical aligner, for a light from the laser source to transmit in between the fiber array and the PIC through the optical element, when the fiberless optical coupler is coupled to the fiber array. 
     Certain embodiments disclosed herein also include a method of manufacturing the electro-optical system. The method includes forming a Photonic Integrated Circuit (PIC), the PIC having a laser source formed on the PIC, forming an optical element, forming a mechanical aligner, coupling the PIC on a Multi-Chip Module (MCM), coupling the MCM on a Printed Circuit Board (PCB), and coupling a fiberless optical coupler to the PIC, the fiberless optical coupler configured to be coupled to a fiber array. The optical element is aligned with the fiber array via the mechanical aligner, for a light from the laser source to transmit in between the fiber array and the PIC through the optical element, when the fiberless optical coupler is coupled to the optical connector via the mechanical aligner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter disclosed herein is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the disclosed embodiments will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG.  1    is a top view of the electro-optical interconnection platform for co-packaging a high-speed switch to high-density optical engine showing the position of the fiberless optical coupler according to some embodiments. 
         FIG.  2    is a magnified view of the electro-optical interconnection platform according to some embodiments. 
         FIG.  3    is a side schematic view of the electro -optical interconnection platform according to some embodiments. 
         FIG.  4    is a magnified schematic view of the fiberless optical coupler according to some embodiments. 
         FIG.  5    is a schematic side view of the fiberless optical coupler on the Photonic Integrated Circuit (PIC) according to some embodiments. 
         FIG.  6    is a schematic side view of a PIC mounted with a fiberless optical coupler that is attached to a fiber array according to some embodiments. 
         FIG.  7    is a magnified schematic side view of the self-aligning optics according to some embodiments. 
         FIG.  8    is a schematic side view of the electro -optical interconnection platform according to some embodiments. 
         FIG.  9    is a flowchart of a method of manufacturing an electro-optical interconnection platform according to some embodiments. 
         FIG.  10    is a schematic side view of the electro-optical interconnection platform according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     It is important to note that the embodiments disclosed herein are only examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed embodiments. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in plural and vice versa with no loss of generality. In the drawings, like numerals refer to like parts through several views. 
     Based on the problems stated above, a scalable single-mode fiber to chip assembling methodology is needed in applications where fiber high density or large port count is used, for example, co-packaged optical Switch connectivity. Co-packaged optical connectivity brings multiple fibers closer to Switch die which is packaged on an expensive packaging platform such as a Multi-Chip Module (MCM). Therefore, co-packaged optical connectivity should be compatible with standard chip packaging methodologies and equipment. Separating the fiber from the MCM packaging steps, and keeping the fiber and MCM packaging to the last stage in a pluggable way is not only unique, but also makes the process a scalable technology. 
     Furthermore, fiberless detachable connections are suitable not only in switches, but also in transceivers and other applications such as connections between memory and processors and chip-to-chip connectivity in general. 
     According to some embodiments, an electro-optical interconnection platform for co- packaging a high-speed switch to high-density optical engine is disclosed. In an embodiment, the platform includes a fiberless optical coupler that may cover various geometries. The coupler includes a plurality of mirrors, one or more mechanical aligners for fiber mount connector, that are rods located in V-grooves, which are accurately placed relative to the optics, and a waveguide (e.g., a polymeric waveguide or other types of mirror with different optical arrangements). In an example embodiment, the chip includes a plurality of mirrors, and a positive tapered wave guide, an interface medium, (e.g., MCM), and a high-speed switch&#39;s die. In an example embodiment, a laser can be part of the platform. 
     In yet another embodiment, a fiberless optical coupler for interfacing with an optical fiber connector and a Photon Integrated Circuit (PIC) is disclosed. The coupler includes a plurality of mirrors, one or more mechanical alignment rods, and a waveguide, (e.g., a polymeric or Si waveguide). 
       FIG.  1    is a top view of an electro-optical interconnection platform  100  according to an embodiment. The platform  100  includes a fiberless optical coupler  101  (also known as fiberless Photonic Plug (PP) coupler), an Integrated Circuit (IC)  105 , and a laser source  116  packaged on a PIC  102  (also known as a photonic chip or high-density optical engine), and a high-speed switch&#39;s die  104  co-packaged with the PIC  102  as a set of electronic components on an MCM  103 . 
     The fiberless optical coupler  101  is designed with an optical arrangement that provides high tolerance alignment and a passive positioning of the fiberless optical coupler, thus aligning the optical fiber with respect to the PIC. An example optical arrangement of the coupler  101  can be found in U.S. Pat. No. 9,840,334 and U.S. patent application Ser. No. 14/878,591, each of which are herein incorporated by reference in their entirety and assigned to the common assignee. The fiberless optical coupler  101  can be mass-produced and its design further allows for compact and secured packaging of PICs. 
     In an embodiment, multiple sets of the fiberless optical coupler  101 , the PIC  102 , the IC  105  and the laser source  116  are assembled surrounding the high-speed switch die  104  on the MCM  103 . 
     Each of the fiberless optical coupler  101  may be connected to electrical-optical connectors  120  and the fiber array  130  to transmit power or data to the components mounted on the MCM  103 , the details of which will be further discussed below. Also, the fiberless optical coupler  101  is assembled on the PIC  102  through a flip-chip machine (not shown) with passive alignment and large tolerances using “self-aligning optics”. Such alignment does not require additional adjustments or alignment of the optical components are necessary, and accurate placement of mechanical aligners with reference to optics at wafer level sizes are enabled. The details of the “self-aligning optics” are explained below with reference to  FIGS.  4  through  7   . 
     It should be appreciated that by using the flip-chip machine using self-aligning optics, surface coupling may be achieved, and issues with complicated edge geometry may be removed. 
       FIG.  2    is an example magnified view of the electro-optical interconnection platform  100  according to an embodiment. In one embodiment, the fiberless optical coupler  101  includes a mechanical aligner  201  that is compatible with various types of electrical optical connectors  120  that ensure mechanical alignment of fiber ribbon relative to the optics on the fiberless optical coupler  101 . 
     In another embodiment, the mechanical aligner  201  may be a pair of cylindrical rods arranged on opposite sides of the fiberless optical coupler  101  at a distal end, both of which are connectible to the electrical optical connectors  120 . The pair of cylindrical rods may be parallel to each other and be of the same length. The assembly of the electro- optical interconnection platform  100  can be performed by connecting the fiberless optical coupler  101  on the MCM module  103  to a switch board (not shown). 
       FIG.  3    is an example schematic side view of the electro-optical interconnection platform  100  according to an embodiment. The fiberless optical coupler  101 , which is also known as an optical die and includes the mechanical aligner  201 , is mounted on the PIC  102  adjacent to the IC  105 , which is also known as the switch IC die. The PIC  102  is in turn mounted on the MCM module  103 , and the entire assembly including the fiberless optical coupler  101 , the mechanical aligner  201 , IC  105 , PIC  102 , and the MCM module  103  is mounted on a printed circuit board (PCB)  301 . 
     As shown in the example  FIG.  3   , the co-packaged components reduce power consumption, as this arrangement brings the components closer to the IC  105 , thereby reducing the electrical port&#39;s length to about 2-3 millimeters, compared to the 10-15 centimeters electrical link seen in typical pluggable transceiver optics connectivity. 
       FIG.  4    is an example diagram of a high magnification of the fiberless optical coupler  101  according to an embodiment. The mechanical aligner  201 , embodied as a pair of mechanical alignment rods are included on the fiberless optical coupler  101 . The fiberless optical coupler  101  also includes wafer-level optical elements  410 . Based on the description below, these optical elements  410  may be “self-aligning.” 
     In an embodiment, the optical elements  410  may include a plurality of waveguides  413 - 1  through  413 - n  (collectively referred to as a waveguide  413  or waveguides), deflectors  415 - 1  through  415 - n  (collectively referred to as a deflector  415  or deflectors  415 ) and curved mirrors  417 - 1  through  417 - n  (collectively referred to as a curved mirror  417  or curved mirrors  417 ). The optical elements  410  may be arranged between the mechanical alignment rods within the fiberless optical coupler  101 , and are arranged to guide light waves to and from the fiber array (not shown) and elements, the details of which will be further described in  FIG.  5   . 
     It is noted that other types of mechanisms besides mechanical alignment rods may be used to ensure alignment. An example of such an alternative embodiment will be discussed with respect to  FIG.  8   . 
       FIG.  5    is a schematic side view of the fiberless optical coupler  101  on the PIC  102  according to an embodiment. The fiberless optical coupler  101  includes the optical elements  410 , which may include the waveguide  413 , the deflector  415 , and the curved mirror  417 . 
     The waveguide  413  may be a polymeric or a silicon (Si) waveguide. When polymer is used for the waveguide  413 , the polymer may be designed to match the single-mode fiber optics in terms of mode diameter. Also, the deflector  415  may be a reflective surface, preferably a tilted reflective surface. 
     The PIC  102  includes a second plurality of optical elements  510  for coupling with the wafer-level optics elements  410  of the fiberless optical coupler  101 . The second plurality of optical elements  510  includes a curved mirror  513 , a deflector  515 , and a tapered polymer waveguide  517 . In an embodiment, a silicon waveguide  517  may be used. The PIC  102  can also include an additional polymeric or a silicon waveguide  519 . In some embodiments, the waveguide  519  may be coupled to the tapered polymer waveguide  517 . 
     Optical elements  410 , 510  may be “self-aligning,” in the sense that the components of the optical elements  410 , 510  are adjustable so that the beams of light are properly guided by the components from waveguide  201  to waveguide  519 , and vice-versa. That is, the corresponding deflectors  415 ,  515 , and curved mirrors  417 ,  513  within the respective fiberless optical coupler  101  and PIC  102  may be individually movable to adjust the path of the light beam from either the waveguide  201  or  519 , to account for slight misalignment of the components during the manufacturing process. Therefore, adjustment of the optical elements  410 ,  510  allows for slight tolerance for misalignment during manufacturing. 
     Additionally, a spacer  520  may be included in between the fiberless optical coupler  101  and the PIC  102 , for light from the waveguides  201 ,  517  to travel through after being reflected by the corresponding deflectors  415 ,  515  and curved mirrors  417 ,  513 . The spacer  520  may be made of a transparent and non-conductive material, such as glass, polydimethylsiloxane, air, or any other index matching materials. The height of the spacer  520  determines, in part, the efficiency of the light beam (optical signal) that propagates through the spacer  520 . In an exemplary and non-limiting embodiment, the height of the spacer  520  may be about  300  microns. 
       FIG.  6    is a schematic side view of the fiberless optical coupler  101  on the PIC that is attached to the fiber array  130 , according to an embodiment. Here, the various components of the fiberless optical coupler  101 , PIC,  102 , and the spacer and the spacer  520  are substantially the same as that shown in  FIG.  5   , with the spacer  520 . The fiberless optical coupler  101  is coupled to the optical connector  120  via the mechanical aligner  201 , which houses the end tips of the fiber array  130 . 
     The mechanical aligner  201  is arranged so that when the aligner  201  is inserted into the optical connector  120 , the fiber array  130  is accurately aligned to the polymeric waveguide  413  with the same beam mode size within the fiberless optical coupler  101 , with a space defined by the length of the mechanical aligner  201  in between the fiberless optical coupler  101  and the optical connector  120 . 
     In an embodiment, the positioning of the mirrors  417 ,  513 , and the deflectors,  415 ,  515  can be performed using a wafer level process such as, but not limited to, grayscale lithography. The mirrors  417  and  513 , are placed and created during fabrication, which ensures high accuracy positioning and accurate reflective mirrors. For example, the curved mirror  417 , deflector  415 , and waveguide  413  are all placed by wafer level process with high accuracy. On the PIC  102  side, waveguide  517 , deflector  515 , and curved mirror  513  are accurately placed by wafer level process. 
     As a non-limiting example, the fabrication process utilized to create the mirrors may include wafer level imprint lithography, and may include the use of a Silicon-On-Insulator (SOI), and Complementary Metal-Oxide Semiconductor (CMOS). 
       FIG.  7    is an example magnified schematic side view of the self-aligning optics, according to an embodiment. Here, the waveguide  413 , the deflector  415 , and the curved mirror  417  within the fiberless optical coupler  101 , which is herein described as a Photonic Plug (PP), and the curved mirror  513  and the deflector  515  within the PIC  102 , which is herein described as the photonic chip, are arranged in substantially the same way as that described in  FIG.  5    and  FIG.  6   . 
     In an embodiment, as light beam is received at the waveguide  413  within the fiberless optical coupler  101  side, it is expanded and redirected by the deflector  415  at an angle to the curved mirror  513  at the PIC  102  side through a medium (not shown). The curved mirror  513  receives the expanded light beam and reflects the expanded light beam to the curved mirror  417  on back on the fiberless optical coupler  101  side. The curved mirror  417  then further reflects the expanded light beam to the deflector  515  back on the PIC  102  side, where the expanded light beam is collimated and further processed by the PIC  102 . 
     The arrangement described above allows for the separation of the fiber array  130  from the PIC  102 , thereby gaining high and relaxed alignment tolerances between the fiberless optical coupler  101  and PIC  102  (in three-dimensions). Also, the scalability of the disclosed fiberless optical coupler  101  is achieved due to its optical arrangement that provides high tolerance alignment and a passive positioning of the fiberless optical coupler  101 , thus aligning the optical fiber with respect to the PIC. Therefore, the disclosed fiberless optical coupler  101  can be mass-produced. In certain embodiments, the disclosed fiberless optical coupler  101  further allows for compact and secured packaging of PICs. 
       FIG.  8    is a schematic side view of the electro-optical interconnection platform  100  According to an embodiment. An MCM  103  is shown along with the PIC  102  including an SOI wafer  820  mounted on a socket  830 , the socket  310  being coupled to the MCM  103 . The fiberless optical coupler  101  is located on the PIC  102 , with the fiberless optical coupler  101  coupled to the fiber array  130 . The fiberless optical coupler  101  includes a first set of optical elements  410 , and the SOI wafer  820  includes a second set of optical elements  510 . Each of the first and second sets of the optical elements  410 ,  450  have similar components as described in  FIGS.  4  and  5   . 
     In an embodiment, the mechanical aligner  201  previously described in  FIG.  1    is configured as a Mechanical Optical Device (MOD)  840  located between the fiberless optical coupler  101  and the PIC  102 . The first set of optical elements  410  and the second set of optical elements  510  are aligned with the fiber array  130 , via the MOD  840 , in order for light to transmit in between the fiber array  130  and the PIC  102  through the sets of the optical elements  410 , 510 . 
     In the embodiment, the MOD  840  allows light to pass through between the sets of the optical elements  410 , 510  within the fiberless optical coupler  101  and the PIC  102 . Also, the MOD  840  further includes V-shaped grooves  850  that receive the fiberless optical coupler  101 , so that the optical elements  410 ,  510  are in alignment with the fiber array  130  when receiving light transmitted to and from the fiber array  130 . That is, the V-shaped grooves  850  ensures a later aligned placement of additional optical elements  410  included in the fiberless optical coupler  101 . 
     Also, the optical elements  510  may be formed on the SOI wafer  820  as a bump via a wafer level process, and may include various expansion and collimating optics, including the mirror  513 , deflector  515 , and waveguide  517  described in  FIG.  5   . 
       FIG.  9    is an example flowchart  900  of a method of manufacturing an electro-optical interconnection platform  100 , according to an embodiment. At S 910 , the PIC  102  is formed, in which the laser source  116  is also formed on the PIC  102 . Next, at S 920 , the second optical elements  510  are formed on the PIC  102 , while the optical elements  410  are separately formed on the fiberless optical coupler  101 . Further, at S 940 , a mechanical aligner  201  is formed. 
     Additionally, at S 940 , the PIC  102  is coupled on the MCM  103 , and at S 950 , the MCM  103  is coupled on the PCB  301 . Next, at S 960 , the fiberless optical coupler  101  is coupled to the PIC  102 , and at S 970 , the fiberless optical coupler  101  is coupled to the fiber array  130 . 
     With the method  900  above, a flip-chip assembly process may be used to employed to couple components of the PIC  102  together (e.g., coupling SOI wafer with the socket) and with other elements, and coupling the mechanical aligner  201  to the PIC  102  or the fiberless optical coupler  101 . This ensures accurate placement of the optics on the PIC  102 . Also, when the MOD  840  is used, additional accuracy in aligning optical elements  410 , 510 , along with added optical functionality of the MOD  840  may be achieved. 
       FIG.  10    is a schematic side view of the electro-optical interconnection platform  100  according to an embodiment. Here, the components of the platform  100  are arranged in substantially the same way as depicted in  FIG.  8   . However, the optical elements  510  that were previously located within the PIC  102  are instead formed within the MOD  840 . By having the optical elements  510  formed in the MOD  840 , further alignment of the optical components may be assured, and the MOD  840  may be given additional optical functionality besides being just a medium or spacer that provides merely mechanical alignment between the various optical elements  410 ,  510  and the fiber array  130 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
     It should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations are generally used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise, a set of elements comprises one or more elements. 
     As used herein, the phrase “at least one of” followed by a listing of items means that any of the listed items can be utilized individually, or any combination of two or more of the listed items can be utilized. For example, if a system is described as including “at least one of A, B, and C,” the system can include A alone; B alone; C alone; 2A; 2B; 2C; 3A; A and B in combination; B and C in combination; A and C in combination; A, B, and C in combination; 2A and C in combination; A, 3B, and 2C in combination; and the like.