Patent Publication Number: US-2022221670-A1

Title: Apparatus and method for hybrid opto-electrical multichip module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/707,764 filed on Dec. 9, 2019, and presently allowed. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under Contract No. DE-AC52-07NA27344 awarded by the United States Department of Energy. The Government has certain rights in the invention. 
    
    
     FIELD 
     The present disclosure relates to optical modules, and more particularly to a hybrid opto-electrical multi-chip module which involves waveguides implemented using through glass via technology, as well as optical wire bonding to create a high density, small form factor, opto-electrical multi-chip module for handling both optical and electrical signals. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Current optical modules rely on planar technology to generate routing of optical signals into waveguides on a planar surface. The alignment of external components to these waveguides is complex and challenging, and represents an expensive task, due to the tight alignment requirements needed to mitigate optical signal loss. In addition, the form factor of such an assembly is relatively large due to the physical space needed for electrically and optically connecting both optical and electrical components. 
     Accordingly, there is a need in the art for an opto-electrical module having even higher interconnect density in an even smaller form factor. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one aspect the present disclosure relates to a monolithic waveguide substrate for enabling routing of at least one optical signal. The monolithic waveguide substrate comprises a monolithic engineered substrate having a uniform material composition throughout, with a first index of refraction, and with a plurality of three-dimensional waveguides each being formed fully within an interior volume thereof by a corresponding plurality of three-dimensional waveguide channels. The three-dimensional waveguide channels are formed by wall portions each having a second index of refraction different from the first index of refraction. 
     In another aspect the present disclosure relates to a monolithic waveguide substrate for enabling routing of at least one optical signal. The monolithic waveguide substrate comprises a monolithic engineered substrate having a uniform material composition throughout having a first index of refraction. The monolithic waveguide substrate further includes a plurality of three-dimensional waveguides each being formed fully within an interior volume thereof by a corresponding plurality of three-dimensional waveguide channels. The three-dimensional waveguide channels are formed by wall portions each having a second index of refraction different from the first index of refraction. A first subplurality of the three-dimensional waveguide channels each form an L-shape to form a non-straight path to enable communicating optical signals from a first surface portion of the monolithic engineered substrate to a second surface portion of the monolithic engineered substrate which is non-parallel to the first surface portion. 
     In still another aspect the present disclosure relates to a method for forming a monolithic waveguide substrate for enabling routing of at least one optical signal. The method may include providing a monolithic engineered substrate comprised of at least one of glass or silicon, and having a uniform material composition throughout with a first index of refraction. A laser is used to selectively remove material from the monolithic engineered substrate to form a plurality of independent, three-dimensional waveguide channels, each being formed fully within an interior volume of the monolithic engineered substrate. The laser is further used to change the refractive index of wall portions of the three-dimensional waveguide channels such that the wall portions have a second index of refraction different from the first index of refraction. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
       Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
         FIG. 1  is a perspective view of a hybrid opto-electrical module in a accordance with one embodiment of the present disclosure; 
         FIG. 2  is a side view of the module of Figure one taken in accordance with directional line  2  in  FIG. 1 ; 
         FIG. 2 a    is a highly enlarged perspective view of just one VCSEL with a portion of one optical wire bond formed over the output of the VCSEL; 
         FIG. 3  is a perspective view of just the optical substrate of the module of  FIG. 1 ; and 
         FIG. 4  is a plan view looking down onto an upper surface of the module of  FIG. 1  in accordance with directional arrow  4  in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     The present disclosure provides a hybrid opto-electrical, multi-chip module apparatus having a highly compact form factor, relatively low manufacturing cost, and high-density component interconnect capability. At a high level, the present disclosure provides a hybrid, opto-electrical, multi-chip module which makes use of a multi-layer 3D waveguide substrate and optical wire bonds to provide an opto-electrical module in an extremely small form factor which can both receive and communicate optical signals out from the module to external components. The 3D waveguide substrate also provides an improved level of electrical interface capability to complement the multilayer waveguide architecture without interfering with, or unduly complicating, the optical waveguides and/or optical wire bonds used to transmit optical signals to and from the module. 
     Referring to  FIG. 1 , a hybrid opto-electrical multi-chip module apparatus  10  (hereinafter simply “module  10 ”) is shown in accordance with one embodiment of the present disclosure. The module  10  in this example includes a module substrate  12 , which in one example may be a printed circuit board (PCB), a silicon substrate, a glass substrate, etc. For convenience and without limitation, the module substrate  12  will be referred to throughout the following discussion as “PCB”  12 . 
     The PCB  12  may include one or more electrically conductive circuit traces  14  (for example, gold or copper traces) formed thereon or therein. The module  10  also includes a three dimensional (3D) “Through Glass Via” (TVG) glass waveguide substrate  16  (hereinafter simply “waveguide substrate”  16 ). The waveguide substrate  16  may be supported on or adjacent to the PCB  12 , or even more preferably just above an upper surface  12   a  of the PCB  12 . 
     The module  10  further includes one or more electronic components, which in this example are a plurality of application specific integrated circuits (ASICs)  18 . The ASICs  18  are mounted on an upper surface  16   a  of the waveguide substrate  16 . The attachment may be effected via a conventional die attachment process where the components are electrically connected either via flip-chip or wire bonding processes as with conventional die mounting. One or more transducers are also supported on the waveguide substrate  16 . In this example the transducers include both one or more electro-optical transducers and one or more opto-electrical transducers. The electro-optical transducers in this example are vertical cavity surface emitting lasers (VCSELs)  20  which are each manufactured and mounted on an associated one of the ASICs  18 , and thus form an integrated portion of its associated ASIC  18 . Optionally, the VCSELs  20  could be mounted on the waveguide substrate  16 , but mounting them directly on the ASICs  18  minimizes point to point wiring, and is therefore likely to be a preferred manufacturing approach, and particularly so for minimizing the form factor of the module  10 . 
     The one or more opto-electrical transducers may include, for example, one or more photodetector modules  22   a ,  22   b  and  22   c  which may also be supported on associated ones of the ASICS  18 , or optionally directly on the waveguide substrate  16 . Photodetector modules  22   a  are illustrated as having four photodetectors (i.e., a four channel photodetector), while photodetector modules  22   b  are illustrated as having three photodetectors (i.e., a three channel photodetector), and photodetector modules  22   c  are illustrated as having two photodetectors (i.e., a two channel photodetector). However, the module  10  could incorporate other combinations of photodetector modules  22   a ,  22   b    22   c , with a total number of photodetector modules being greater or lesser than that shown in  FIG. 1 . Accordingly, the illustration of two, three and four channel photodetector modules is only meant to illustrate one specific example configuration for the module  10 , and a wide variety of other configurations is also possible. Optionally, other types of opto-electrical transducers or components could be used, for example optical switches, multiplexers and/or demultiplexers. 
     The module  10  further includes a plurality of independent optical waveguide elements  24  and a corresponding plurality of optical wire bonds  26  for coupling the waveguide elements  24  to corresponding waveguides formed within the waveguide substrate  16 . The optical waveguide elements  24  may be comprised of any suitable material or polymer, but in one preferred implementation are formed using ORMOCOMP® hybrid organic-inorganic polymer. Intense ultra short laser pulses are tightly focused inside transparent materials, which causes a non-linear absorption in the focal volume to take place, leading to optical breakdown and formation of microplasma, thus inducing permanent structural and refractive index modification within the polymer. An additional corresponding plurality of optical wire bonds  28  is used to couple the waveguides of the waveguide substrate  16  to inputs of the photodetector modules  22   a ,  22   b  and  22   c . The optical wire bonds  26  readily accommodate minor misalignments between the waveguide elements  24  and the waveguides formed in the waveguide substrate  16 , and the optical wire bonds  28  accommodate any misalignments between the waveguides in the waveguide substrate  16  and outputs of the photodetector modules  22   a ,  22   b  and  22   c . The optical wirebonds  26  and  28  may be formed from any material which can transmit an optical signal, however ORMOCOMP® hybrid organic-inorganic polymer is especially well suited for this purpose, as it lends itself well to an additive manufacturing (i.e., 3D printing) process. The ORMOCOMP® polymer is also well suited for the optical wavelengths used with the components like the module  10 . 
       FIGS. 1 and 2  also show a separate plurality of electrical wire bonds  30  which are used to couple select ones of the VCSELs  20  to their associated ASICs  18 . The wire bonds  30  enable each of the VCSELs to be independently controlled by electrical signals generated by its associated ASIC  18 , or possibly even by two or more of the ASICs. A separate plurality of optical wire bonds  31 , preferably ORMOCOMP® hybrid organic-inorganic polymer wirebonds, may be used to couple the optical output from each VCSEL  20  into the waveguides formed inside the waveguide substrate  16 . And while VCSELs  20  are shown, it will be appreciated that one or more other forms of lasers (e.g., Horizontal Cavity Surface Emitting Lasers (HCSELs)), or other type of electro-optical transducers, could potentially be used instead of a VCSEL, and the present module  10  is therefore not limited to use with only VCSELs. 
       FIG. 2 a    shows one highly enlarged illustration of how the optical wire bond  31  may be formed using ORMOCOMP® polymer to interface directly to an output  20   a  of one of the VCSELs  20  using an additive manufacturing operation and 3D printing the wire bond  31 . These connections may be formed in-situ after the VCSELs  20  (or other form of edge emitting lasers) is/are attached to connect to the next waveguide or other optical element. 
     In operation, the photodetector modules  22   a ,  22   b  and  22   c  operate to receive optical signals input to the waveguide elements  24  from external optical sources, and to convert the received optical signals to corresponding electrical signals. The corresponding electrical signals are transmitted to the ASIC  18  associated with the photodetector module  22   a ,  22   b  or  22   c . The ASIC  18  generates electrical signals which can be used to control the VCSELs  20 , and/or which may also be transmitted over one or more of the circuit traces  14  to other remote electrical components. The VCSELs  20  may output optical signals back over the same waveguide elements  24  or possibly over different ones of the waveguide elements, or possibly even as inputs to one or more other ones of the photodetector modules  22   a ,  22   b  and/or  22   c , depending on the design of the waveguide substrate  16 . As such, it will be appreciated that certain of the waveguide elements  24  may thus be configured to function as both inputs and outputs. 
     With specific reference to  FIG. 2 , a side view of the module  10  is shown. The module  10  preferably includes a cover  32 , in this example a hollowed out glass lid, secured to an upper surface  16   a  of the waveguide substrate  16 . The attachment may be effected by any means that provides an excellent seal, but preferably one that forms a hermetic seal. In one example a seal at a perimeter area  34  where the edges of the cover  32  and the upper surface  16   a  of the waveguide substrate  16  meet is formed by a laser welded glass joint. Optionally, a suitable adhesive/sealant may be used to form the seal at the perimeter area  34  It is expected that hermetic bonding will be critical in many applications to protect optical elements such as laser diodes, as well as the optical wirebonds used, and possibly other components as well. 
       FIG. 2  also shows a plurality of internally formed, three dimensional (3D) waveguides  16   b  and a plurality of through vias  16   c  formed within the waveguide substrate  16 . Electrically conductive standoffs  36  help to provide both physical support to space the waveguide substrate  16  slightly apart from the upper surface  12   a  of the PCB  12 , as well as electrical connections between associated ones of the circuit traces  14  and the through vias  16   b . The electrically conductive standoffs  36  may be formed by soldering or any other suitable means, and may be made from tungsten, gold, copper or from any other electrically conductive material that can be deposited to form electrical connection paths through select areas of the waveguide substrate  16 . 
     With brief reference to  FIG. 3  the waveguide substrate  16  can be seen without any other components secured thereto. The internally formed 3D waveguide channels  16   b  operate to channel optical signals to the photodetector modules  22   a ,  22   b  and  22   c , and also to channel the optical output signals from the VCSELs  20  out to the PCB  12  mounted waveguide elements  24 . One or more of the 3D waveguide channels  16   b  may also be configured to handle both incoming optical signals and out-going optical signals, depending on the specific design of the waveguide substrate  16 . One or more of the waveguide elements  24  may be coupled to external, remote components, for example a corresponding plurality of photodetectors associated with a remote electronic subsystem communicating with the module  10 , or one or more remote optical signal sources that are supplying optical signals as inputs to the module  10 . The waveguide substrate  16  in one preferred implementation is formed from a single, monolithic planar piece of glass. Other suitable materials may be BOROFLOAT® glass, fused silica or BK7 and its equivalent. Currently known manufacturing techniques involving use of a femtosecond laser may be used to pattern the 3D waveguides  16   b  by controlling the depth of penetration into the glass block substrate as the laser beam is moved in desired paths. The ultra short laser pulses create a microplasma confined to the focal plane within the material, which creates a change in the refractive index of the material, and thus enables the formation of the 3D waveguide channels within the volume of the waveguide substrate  16 . As such, the depth control of the laser beam, in connection with the X-Y position of the laser beam, can thus create 3D waveguides within the glass block that are non-straight (e.g., which have curves, turns, etc.), and thus which extend in three dimensions within the glass block. Holes can then be formed in the glass block (or alternatively the holes can be formed before forming the 3D waveguides  16   b  with the femtosecond laser), and then the holes may be filled with the desired conductive metallic material (e.g., tungsten, gold, copper, etc.) in a molten state to create the finished through vias  16   c.    
     With further reference to  FIG. 3 , the waveguide substrate  16  can be seen in isolation. The through vias  16   c  are arranged to extend perpendicularly through the full thickness of the waveguide substrate  16  without interfering with any of the 3D waveguides  16   b . And while the through vias  16   c  are illustrated as extending perpendicularly through the thickness of the waveguide substrate  16 , they need not necessarily be formed to extend perfectly perpendicularly and/or they need not be formed as perfectly straight through vias. The through vias  16   c  enable electrical connections with the circuit traces  14  without interfering with the optical paths formed by the 3D waveguides  16   b . Including the through vias  16   c  inside the waveguide substrate  16  further helps to minimize the form factor of the module  10 . 
     The waveguide substrate  16  thus provides the unique ability to channel electrical signals between PCB  12  mounted components and the circuit traces  14 , as well as to provide 3D waveguides for channeling optical signals between the module  10  and other remote components. The ability to route two distinct types of signals through the waveguide substrate  16  (i.e., electrical and optical) helps significantly to make the overall module  10  particularly compact and easy to construct. The waveguide substrate  16  also helps to provide a modular feature to the module  10  because changes to any of the electronic components can potentially be made by substituting a new waveguide structure having a different collection of electronic components, without necessarily requiring modification of the PCB  12 . 
     The circuit traces  14  may be used to receive electrical signals from other components, for example probes implanted in human or animal tissue, where the probes have one or more microelectrodes which receive electrical signals from the tissue. The circuit traces  14  may also be used to supply electrical signals generated by the ASICs out to external remote electrical/electronic components, or event to remote probes implanted in human or animal tissue. Electrical signals being input TO the module  10  may be received by the ASICs  18  and converted to associated electrical signals for driving the VCSELS  20  and/or helping to control the photodetector modules  22   a ,  22   b  and  22   c . The photodetector modules  22   a ,  22   b  and  22   c  each may convert received optical signals into electrical signals which are routed to its associated ASIC  18 , and or to one or more of the other ASICs, or transmitted out from the module  10  over the circuit traces  14 . 
     The module  10  thus forms a powerful, high density opto-electrical module that can interface with a large plurality of external optical or electrical/electronic components. The small form factor of the module  10  also makes it ideally suited for implantation into humans and animals for biomedical applications. The module as shown in  FIGS. 1 and 2  may have dimensions of 5 mm×5 mm×5 mm thick, or even smaller. The use of the independently constructed waveguide substrate  16  further adds a degree of modularity to the construction of the module  10 , which can enhance the ease with which later modifications or improvements (e.g., different or updated electrical/electronic or optical components) can be implemented in the module. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.