PATENT DOCUMENT

Publication Number: US-11960128-B2
Application Number: US-202117508760-A
Country: US
Kind Code: B2

Title: Fast-axis collimator with hanging connector

Abstract:
A photonics package may include a substrate, a hanging connector, and a fast-axis collimator (“FAC”). The hanging connector is typically affixed to a side of the substrate other than the side through which a light output is emitted. The hanging connector may be L-shaped in cross-section, having a base section and an extended section projecting from the base section. The base section affixes to the substrate while the extended section affixes to the FAC, so that the FAC extends downward along the emitter surface of the substrate; a vertex of the FAC is coplanar with an emitter outputting the light output.

Claims:
What is claimed is: 
     
       1. A photonics package, comprising:
 a substrate comprising:
 a connector surface; and 
 an emitter surface meeting the connector surface at an edge; 
 
 a waveguide at least partially within the substrate; 
 an emitter coupled to the waveguide; 
 a hanging connector affixed to the connector surface; and 
 an optical component affixed to the hanging connector; wherein:
 the hanging connector comprises:
 a base layer; 
 a top layer; and 
 a first layer positioned at least partially between the base layer and the top layer; and 
 
 a portion of the first layer of the hanging connector forms an angled sidewall and a vertical backstop connecting the top layer of the hanging connector to the base layer of the hanging connector; 
 the optical component extends along a portion of the emitter surface. 
 
 
     
     
       2. The photonics package of  claim 1 , wherein:
 the hanging connector comprises:
 a base section; and 
 an extended section projecting from the base section; 
 
 the optical component is a fast-axis collimator; 
 a vertex of the optical component is coplanar with the waveguide; 
 the base section is affixed to the connector surface; and 
 the extended section is affixed to the fast-axis collimator. 
 
     
     
       3. The photonics package of  claim 2 , wherein:
 The extended section is affixed to the fast-axis collimator by a first eutectic bond; and 
 the base section is affixed to the connector surface by a second eutectic bond. 
 
     
     
       4. The photonics package of  claim 1 , wherein:
 a surface of the optical component is parallel to the emitter surface; 
 the optical component and emitter surface are separated by an offset; and 
 the offset is constant. 
 
     
     
       5. The photonics package of  claim 1 , wherein:
 the waveguide is one of a set of waveguides; 
 the optical component is a multi-tiered fast axis collimator defining a set of vertices; and 
 each of the set of vertices is coplanar with one of the set of waveguides. 
 
     
     
       6. The photonics package of  claim 5 , wherein the multi-tiered fast-axis collimator comprises a unitary element defining each of the set of vertices. 
     
     
       7. A hanging connector, comprising:
 a base section comprising:
 a base layer; 
 a buried oxide layer abutting the base layer; and 
 a silicon-on-insulator layer abutting the buried oxide layer; and 
 
 an extended section connected to the base section and comprising:
 the buried oxide layer; and 
 the base layer abutting the buried oxide layer; wherein: 
 a portion of the buried oxide layer forms an external surface of the extended section; 
 an angled sidewall and a vertical backstop connect the base section to the extended section; 
 a portion of the silicon-on-insulator layer form the angled sidewall and the vertical backstop; 
 the base section is configured to be affixed to a connector surface of substrate of a photonics package; and 
 the extended section is configured to be affixed to an optical component, such that the optical component contacts the vertical backstop and a vertex of the optical component is coplanar with an emitter of the photonics package that is positioned on an emitter surface of the photonics package. 
 
 
     
     
       8. The hanging connector of  claim 7 , wherein:
 the portion of the buried oxide layer forming an external surface of the extended section is configured to be affixed to the optical component; 
 the base layer is silicon; and 
 the silicon-on-insulator layer is configured to be affixed to the connector surface. 
 
     
     
       9. A method for forming a photonics package, comprising:
 affixing an optical component to a hanging connector with a first bond between the optical component and an oxide layer of the hanging connector; and 
 affixing the hanging connector to a connector surface of a substrate with a second bond between a silicon-on-insulator layer of the hanging connector and the connector surface of the substrate, such that the optical component extends along an emitter surface of the substrate; wherein:
 a portion of the oxide layer of the hanging connector is positioned between the silicon-on-insulator layer of the hanging connector and a base layer of the hanging connector; 
 a portion of the silicon-on-insulator layer of the hanging connector forms an angled sidewall and a vertical backstop connecting the oxide layer of the hanging connector to a base layer of the hanging connector; 
 an emitter on the emitter surface is configured to emit a light output; 
 the optical component is configured to receive the light output; 
 a vertex of the optical component is coplanar with the emitter; and 
 the optical component is configured to collimate the light output. 
 
 
     
     
       10. The method of  claim 9 , wherein the substrate is a photonics integrated chip. 
     
     
       11. The method of  claim 9 , wherein the connector surface and the emitter surface are different surfaces of the substrate. 
     
     
       12. The method of  claim 11 , wherein the connector surface and the emitter surface meet at an edge. 
     
     
       13. The method of  claim 9 , wherein a portion of the hanging connector extends into a recess defined in the connector surface. 
     
     
       14. The method of  claim 13 , wherein the portion of the hanging connector extending into the recess is bonded to the substrate with a eutectic bond.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a nonprovisional of, and claims the benefit under 35 U.S.C. § 119(e) of, U.S. Provisional Patent Application No. 63/104,687, filed Oct. 23, 2020, the contents of which are incorporated herein by reference as if fully disclosed herein. 
    
    
     FIELD 
     Embodiments described herein relate generally to photonics packages, and more particularly to photonics integrated chips connected to a fast axis collimator by a hanging connector. 
     BACKGROUND 
     Fast-axis collimators are typically used to collimate light received from a laser diode or other light source. These collimators are often attached or adjacent to an emitter of a photonics integrated chip (“PIC”) in order to receive and collimate light from the emitter. 
     A fast-axis collimator may be affixed to, or adjacent to, an emitter in a number of ways. Fast-axis collimators may be affixed directly to the emitter or may be attached to a tab that is, in turn, bonded to a substrate of the photonics integrated chip. The tab is bonded to the same side of the substrate from which light is emitted by the emitter. Thus, the tab typically is positioned below the fast-axis collimator in order to align the collimator with the emitter. Put another way, the surface of the tab that is bonded to the substrate and the edge of the fast-axis collimator that accepts light from the emitter face the same side of the substrate (or other portion of the PIC). 
     In order to properly align the fast-axis collimator and the emitter, the fast-axis collimator is generally aligned and affixed (or the supporting tab is affixed) while the light source is active. While the fast-axis collimator and emitter may be precisely aligned through active alignment, this alignment process is time-consuming and requires very precise positioning (and changes in position). This, in turn, may slow mass manufacture of photonics packages incorporating a fast-axis collimator. 
     SUMMARY 
     One embodiment described herein takes the form of a photonics package, comprising: a substrate comprising: a connector surface; and an emitter surface meeting the connector surface at an edge; a waveguide at least partially within the substrate; an emitter coupled to the waveguide; a hanging connector affixed to the connector surface; and an optical component affixed to the hanging connector; wherein the optical component extends along a portion of the emitter surface. 
     Another embodiment described herein takes the form of a hanging connector, comprising: a base section; and an extended section connected to the base section; wherein: the base section is configured to be affixed to a connector surface of substrate of a photonics package; the extended section is configured to be affixed to an optical component, such that a vertex of the optical component is coplanar with an emitter of the photonics package that is positioned on an emitter surface of the photonics package. 
     Still another embodiment described herein takes the form of a method for forming a photonics package, comprising: affixing an optical component to a hanging connector with a first bond; and affixing the hanging connector to a connector surface of a substrate with a second bond, such that the optical component extends along an emitter surface of the substrate; wherein: an emitter on the emitter surface is configured to emit a light output; the optical component is configured to receive the light output; a vertex of the optical component is coplanar with the emitter; and the optical component is configured to collimate the light output. 
     These and other embodiments will be apparent upon reviewing this document in its entirety, and the foregoing embodiments are examples described more fully herein rather than any form of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG.  1    illustrates a sample photonics package incorporating a fast-axis collimator and a hanging connector. 
         FIG.  2    is a cross-sectional view of a portion of a photonics package, taken along line  2 - 2  of  FIG.  1   , showing an example hanging connector. 
         FIGS.  3 A- 3 D  are cross-sectional views taken along line  3 - 3  of  FIG.  1   , illustrating sample bonds between a hanging connector and a substrate of a photonics package. 
         FIGS.  4 A- 4 C  illustrate sample operations used to form an example hanging connector. 
         FIG.  5    is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  2   , and illustrating a multi-tiered FAC. 
         FIG.  6 A  is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  2   , showing another example hanging connector. 
         FIG.  6 B  is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  6 A , but in which a coating has been applied to a FAC in order to define an aperture through which light passes. 
         FIG.  7    is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  2   , and illustrating another multi-tiered FAC. 
         FIG.  8 A  is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  2   , and illustrating a prism attached to a hanging connector. 
         FIG.  8 B  is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  8 A , in which the prism and hanging connector are unitary. 
         FIG.  9    is a cross-sectional view of a portion of a photonics package similar to that of  FIG.  2   , in which a photonics component (here, a photodetector) has replaced the FAC. 
     
    
    
     Shading and/or hatching is intended to illustrate separate components in cross-sections, or common components in cross-section where the same shading is used. It does not convey or indicate any particular color or material. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     A “photonics package,” as that term is used herein, refers to a set of components that are operably coupled together to emit light. Generally, a photonics package includes a light source, a waveguide or other propagation material, and an emitter. The photonics package may include one or more optical components configured to accept and modify light emitted from the light source. Some or all of the components of the photonics package may be part of a photonics integrated chip (“PIC”). For example, the light source, waveguide, and emitter may be part of a PIC although, in some embodiments, one or more of these components may be off-chip. 
     The “emitter” of the photonics integrated chip may be a separate optical component, such as a lens, outcoupler, grating, or the like, or may simply be a terminus of a waveguide. The emitter may be formed integrally with the waveguide or may be a separate component that is affixed to, or adjacent to, the waveguide. Accordingly, references herein to an emitter should be understood to encompass both an end of a waveguide and a dedicated optical component, as appropriate. 
     One example of an optical component of a photonics package is a fast-axis collimator (“FAC”). The fast-axis collimator receives a light output from an emitter and collimates it. Fast-axis collimators may be used in photonics packages where the light source is a laser diode, as one non-limiting example, since laser diodes typically emit a diverging light output. In certain embodiments, the light source, waveguide (or other propagation medium), and emitter are part of a PIC to which the FAC is connected. Thus, as light outcouples from the PIC (through the emitter), the FAC collimates the light. 
     A hanging connector may position the FAC relative to the PIC&#39;s emitter. The FAC is typically aligned so that its vertex is coplanar with the emitter. If the FAC&#39;s vertex and the emitter are not coplanar then the light output may be insufficiently collimated. Even minor misalignments on the order of several hundred nanometers may cause the FAC to be unable to collimate the light output, or to poorly collimate the light output. This, in turn, may cause the photonics package to operate incorrectly. 
     The hanging connector is typically affixed to a side of a substrate other than the side through which the light output is emitted (e.g., the side of the substrate on which the emitter is positioned, or the “emitter surface”). That is, if the emitter surface is considered a sidewall of the substrate then the hanging connector is affixed to a top or bottom of the substrate. The foregoing nomenclature is used in this document, such that the substrate surface to which the hanging connector is affixed (the “connector surface”) is a “top” of the substrate while the surface through which the light output is emitted (the emitter surface) is a “side” of the substrate. Another way to describe the relationship between the emitter surface and the connector surface is that the two meet at a right angle, presuming the substrate is a rectangular cuboid. 
     The hanging connector may be L-shaped in cross-section, defining a stepped cross-section profile. The hanging connector may include a thicker, base section and a thinner, extended section that projects from the base section. The base section affixes to the substrate while the extended section affixes to the FAC, so that the FAC extends downward along the emitter surface of the substrate. 
     Generally, the FAC is affixed to the hanging connector, which is in turn affixed to the top of the substrate. The FAC extends along a portion of the emitter surface from the hanging connector, so that the FAC is adjacent the emitter and the FAC&#39;s vertex is substantially coplanar with the emitter. “Substantially coplanar” means that the FAC&#39;s vertex and the emitter are not out-of-plane by more than the manufacturing tolerance of the substrate, plus the manufacturing tolerance of the hanging connector, plus any manufacturing tolerance of the fast-axis collimator. Generally, these manufacturing tolerances are less than five microns and may be as little as two microns. 
     By affixing the hanging connector to a top of the substrate, the dimensions and structure of the hanging connector itself may be used to properly align the FAC with respect to the emitter. For any of a group of mass-produced photonics packages, the distance of the emitter from the edge where the emitter surface and connector surface meet (the “emitter edge”) is constant, within manufacturing tolerances of the substrate. Likewise, the height of the hanging connector is constant, again within manufacturing tolerances of the connector. Accordingly, any misalignment of the FAC with respect to the emitter is governed by these two manufacturing tolerances insofar as variances in size of the FAC are extremely minor in comparison. Thus, the vertex of the FAC will never be offset from the emitter by more than the sum of the maximum manufacturing tolerances for the substrate and hanging connector. As mentioned above, this is typically less than five microns, which is small enough that the FAC may collimate substantially all of the light output from the emitter. 
     Further, because the FAC&#39;s vertex is always substantially aligned with the emitter by the hanging connector, there is no need to actively align the FAC with the emitter. Thus, the hanging connector may be affixed to the substrate without powering on the photonics package. This substantially accelerates photonics package manufacture, leads to fewer defects when mass producing photonics packages, and reduces manufacturing cost. 
     Embodiments are described as employing a FAC, and particularly are discussed with respect to a FAC affixed to a hanging connector. However, it should be understood that many different optical components may be affixed to, and positioned relative to other parts of a photonics package by, a hanging connector. The hanging connector may be affixed to a slow axis collimator, aspheric or spherical lens, microlens array, turning mirror, or any other suitable optical component. Accordingly, discussions herein regarding the use of a hanging connector with a FAC should be understood to encompass the use of a hanging connector with any other suitable optical component. 
     These and other embodiments are discussed below with reference to  FIGS.  1 - 6   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
       FIG.  1    illustrates a photonics package  100 , including a photonics integrated chip  110 , a fast-axis collimator  120 , a waveguide  130 , and a hanging connector  140 . The photonics package typically includes one or more light sources (not shown) operative to emit a light output; each light source may be operably connected to a waveguide such that the light output propagates through the waveguide  130 . Each waveguide  130  may be connected to an emitter (not shown in  FIG.  1   , but visible in  FIG.  2   ) that outcouples the light output from the PIC  110  to the FAC  120  where the light output is collimated. In some embodiments, the light sources are laser diodes, although other embodiments may use other types of light sources. 
     The waveguides  130  may be fully or partially within the PIC  110 . In some embodiments, a surface of the waveguide  130  is coplanar with a surface of the PIC  110  (such as its connector surface) and so the waveguide is partially within the PIC. In other embodiments, the waveguide  130  may be fully within the PIC  110  except for its terminus at the emitter, as shown. In either embodiment, they optically couple the light source(s) to the emitter. 
     The FAC  120  is configured to receive light from the emitter and may be separated from the emitter by an offset  260 . The FAC  120  collimates the light output received from the emitter as the light output passes through the FAC. The light output may propagate from the FAC  120 , through free space, and to another component of the photonics package  100 , such as optical components or the like. The surface of the fast-axis collimator closest to the emitter is generally parallel to the emitter surface, so the offset is substantially constant. 
     The hanging connector  140  is affixed to the PIC  110 , which is a substrate for the hanging connector in this embodiment. Specifically, the hanging connector  140  is affixed to a connector surface of the PIC  110  and is also affixed to the FAC  120 . The hanging connector  140  is positioned so that the FAC  120  extends along (and is parallel to) a portion of the emitter surface of the PIC  110 . It should be appreciated that the term “top side” is relative and given with respect to the orientation of the PIC  110  shown in  FIG.  1   . 
     The FAC  120  extends sufficiently far along the emitter surface of the PIC  110  that the vertex  225  of the FAC (or other optical component) is coplanar with the emitter  250 , as shown in  FIG.  2   .  FIG.  2    is a cross-sectional view of the PIC  110 , hanging connector  140 , and FAC  120  taken along line  2 - 2  of  FIG.  1   . Generally, the hanging connector  140  is affixed to the FAC  120  by a first bond  220  and to the PIC  110  by a second bond  230 . The first and second bonds  220 ,  230  are discussed in more detail below with respect to  FIGS.  3 A- 3 C . 
     The FAC  120  acts as an aspheric lens and is flat on a side facing the emitter  250  and convex on its opposing side. The FAC  120  (or other optical component) is separated from the emitter  250  by an offset  260 . The size of the offset varies between embodiments (although it is generally constant within an embodiment), but is typically in the tens of microns. Pick and place operations may place the hanging connector  140  on the PIC  110  at a designated point; variances in such pick and place operations may cause the size of the offset to be up to five microns larger or smaller, and in some embodiments as little as one micron larger or smaller. Generally, the closer the size of the offset is to its design size, the tighter or narrower the collimated beam outputted by the FAC  120 . 
     As shown in  FIG.  2   , the hanging connector  140  is L-shaped in cross-section. The hanging connector includes a base section  210  and an extended section  215 ; the extended section is stepped down in cross section from the base section and projects from the base section toward the emitter surface. Thus, although one surface of the base section and extended section is common or coplanar, opposing surfaces of the base section  210  and extended section  215  are separated by a sidewall. This creates the stair-step cross-section shown in  FIG.  2   . 
     The base section  210  is affixed to the PIC  110  by the second bond  220 . Likewise, the extended section  215  is affixed to the FAC  120  (or other optical component) by the first bond  220 . Since the vertex  225  of the FAC  120  is aligned with the emitter  250  and the emitter is generally near or at the connector surface of the PIC  110 , the extended section  215  is cross-sectionally thinner than the base section  210  from which it projects, in order to facilitate this alignment. Further, although the base section  210  is shown in  FIG.  2    as extending to the emitter edge, this is not necessary. The base section  210  may be recessed from the emitter edge or may extend past the emitter edge, in various embodiments. 
       FIGS.  3 A- 3 D  illustrate different examples of bonds  230  between the hanging connector  140  and the substrate  110  (here, a PIC, although other embodiments may use other substrates), each taken along line  3 - 3  of  FIG.  1   . In particular, each of  FIGS.  3 A- 3 D  illustrate example bonds between the base section  210  of the hanging connector  140  and the substrate  110 , although these examples are equally applicable to the bond  220  between the FAC  120  and the extended section  215 . Accordingly, the following discussion should be understood to apply to that bond  220 , as well, with any discussion of the substrate  110  applying to the FAC  120  and discussion of the base section  210  applying to the extended section  215 . Additionally, the waveguides  130  are omitted from the views of  FIGS.  3 A- 3 D  for simplicity. 
     As shown in  FIG.  3 A , an underside of the hanging connector  140  may define a recess  310  that is filled with an adhesive  300 . The adhesive may form the bond  230  shown in  FIG.  2   , securing the hanging connector  140  to the substrate  110 . The size and shape of the recess  310  may vary between embodiments. Generally, the recess  310  is sized so that the adhesive  300  does not exit the recess, including during curing or setting. In some embodiments, the adhesive is a heat-activated film. 
       FIG.  3 B  illustrates a multi-part recess formed from first and second overflow chambers  310   a ,  310   b  and a center channel  310   c . As with the embodiment shown in  FIG.  3 A , an adhesive  300  may fill (or substantially fill) the center channel  310   c . As the adhesive sets or cures, it may expand or travel into one or both of the overflow chambers  310   a ,  310   b  in order to prevent the adhesive from leaking beyond the center channel  310   c , or from dislodging the base section  210  of the hanging connector  140 . 
     Certain embodiments may forego adhesive when bonding the hanging connector  140  to the substrate  110 . For example and as shown in  FIG.  3 C , a eutectic bond  320  may affix the base section  210  directly to the substrate  110 . As another option and as shown in  FIG.  3 D , one or more holes, depressions, or other recesses  330   a ,  330   b  may be formed in the substrate  110 . The base section  210  may include or form protrusions, such as legs, configured to be received in the substrate recesses  330   a ,  330   b . Eutectic bonds  320   a ,  320   b  may be formed to hold the hanging connector&#39;s  140  protrusions to the portion of the substrate exposed by the recesses  330   a ,  330   b , as shown in  FIG.  3 D . Additionally, during an assembly operation in which the hanging connector  140  is placed on the substrate  110 , the recesses  330   a ,  330   b  may function as fiducials to align the hanging connector with respect to the substrate. In some embodiments, the recesses  330   a ,  330   b  may expose an inner layer of the substrate  110 ; this inner layer may be metalized or otherwise formed from a material suitable for eutectic bonding to the base section  210  of the hanging connector  140 . 
     As mentioned above, any or all of the bonds discussed with respect to  FIGS.  3 A- 3 D  may be used to affix the FAC  120  to the hanging connector  140 , including the use of a eutectic bond. Eutectic bonds may be particularly suitable for certain embodiments insofar as they are relatively thin and highly controllable, and thus have relatively little dimensional variance between different photonics packages. Thus, where these photonics packages are mass-produced, eutectic bonds may introduce less opportunity for misalignment or dimensional offset between components such as the FAC  120  and hanging connector  140 , or the hanging connector and the substrate  110 , and so ultimately less misalignment between the FAC and the emitter. Additionally, the eutectic bond (or the use of a thermally conductive epoxy) may ensure that a temperature of the hanging connector  140  and/or FAC  120  (or other optical element or component attached to the hanging connector) are at approximately the same temperature as the substrate  110 , thereby reducing any movement, shift, cracking, or misalignment due to thermal differences between components. 
       FIGS.  4 A- 4 C  show a sample stackup  400  that ultimately forms one example of a hanging connector  140 , at various processing stages. Initially and as seen in  FIG.  4 A , the stackup  400  includes multiple layers. In this embodiment, the stackup  400  includes three layers, namely a silicon substrate or base layer  415 , a buried oxide (BOX) layer  410  abutting the base layer  405 , and a silicon-on-insulator (SOI) layer  405  abutting the BOX layer  410 . Thus, as shown, the BOX layer  410  is sandwiched between, and separates, the base layer  415  and the SOI layer  405 . The thicknesses of the layers  405 ,  410 ,  415  may vary in different embodiments; in some embodiments the entire stackup may be relatively thin, as on the order of 725-850 microns. Other embodiments may employ a stackup  400  having more or fewer layers, or layers made from different materials, and so the discussion of  FIGS.  4 A- 4 C  is intended as an example and not any requirement. 
     A portion of the SOI layer  405  may be mechanically or chemically removed, for example by etching, grinding, polishing, vaporizing, and so on. The stackup  400  is illustrated in  FIG.  4 B  with the SOI layer  405  having undergone this processing. Removing the portion of the SOI layer  405  forms the stair-step profile of the hanging connector  140  illustrated in  FIGS.  1  and  2   . The part of the stackup where no material was removed is effectively the base section  210  of the hanging connector  140 , while the thinned part of the stackup  400  is the extended section  215 ; the BOX layer  405  therefore forms an external surface of the extended section. Both the base section  210  and extended section  215  are discussed in more detail above, with respect to  FIG.  2   . 
     In some embodiments the SOI layer  405  is three to five microns thick, and so the distance between the substrate  110  and the extended section  215  is three to five microns, insofar as this distance equals the thickness of the SOI layer. Accordingly, it should be appreciated that the extended section may be relatively close to the surface of the substrate  110  to which the base section is bonded. 
       FIG.  4 C  shows the stackup  400  inverted and with the FAC  120  attached to the BOX layer  410 , functioning as a hanging connector. The BOX layer is bonded to the FAC  120 , for example by a eutectic bond as discussed earlier. Generally, bonding the FAC  120  to the BOX layer  410  that forms the external surface of the extended section is highly precise and the amount of material removed (including, in some cases, a portion of the BOX layer) may be finely controlled through chemical or mechanical removal. Further, the exposed portion of the BOX layer  410  is clean and defect-free following the removal process, providing an excellent surface for bonding to the FAC  120 . Just as the BOX layer forms a surface of the hanging connector that is bonded to the FAC  120 , so does the SOI layer  405  form a surface of the hanging connector that is bonded to the connector surface of the substrate, as described above. 
     As discussed above with respect to  FIGS.  1  and  2   , a vertex of the FAC  120  is substantially coplanar with an emitter of the PIC  110 , once the FAC  120  is affixed to the hanging connector  140  and the hanging connector affixed to the PIC  110 . Generally, this alignment may be finely controlled because the three variables in the alignment are finely controlled. First, the amount of material removed from the stackup  400  may be precisely controlled and the exposed surface of the stackup  400  to which the FAC  120  is bonded is generally free of any surface defects. Second, an overall thickness of the stackup  400  (and thus the hanging connector  140 ) is dictated by wafer tolerances achievable when forming the stackup  400 , for example through depositing or growing the various layers  405 ,  410 ,  415 . Finally, eutectic bonds, such as those used to affix the hanging connector  140  to the FAC  120  and the PIC  110 , are dimensionally controllable and repeatable with a high degree of precision. The combined variances of these three sources of potential misalignment may be as little as one to two microns, and are typically anywhere from three to five microns. This is well within the alignment tolerance of the FAC and the emitter for many photonics packages. 
       FIG.  5    illustrates a photonics package  500  incorporating a multi-tiered FAC  520 . Generally and as described with respect to prior figures, the multi-tiered FAC  520  is affixed to the hanging connector  140  by a first bond  220  and the hanging connector, in turn, is affixed to the PIC  110  by a second bond  230 . The first and second bonds  220 ,  230  may be eutectic bonds, again as described above. 
     Unlike prior embodiments, multiple waveguides  130   a ,  130   b ,  130   c  extend through the PIC  110 ; additionally, waveguide  130   a  is shown at or near the connector surface of the PIC  110 . Each waveguide  130   a ,  130   b ,  130   c  propagates a light output  510   a ,  510   b ,  510   c  from a light source to a separate vertex of the multi-tiered FAC  520 , which collimates the respective light output. As shown in  FIG.  5   , the waveguides  130   a ,  130   b ,  130   c  are positioned at different distances from the connector surface of the PIC  110 , where the connector surface is the surface to which the hanging connector  140  is affixed. The multi-tiered FAC  520  extends along (and is parallel to) a portion of the emitter surface of the PIC  110 , such that each of its vertices is coplanar with a unique waveguide. In this manner, a single hanging connector  140  may support a FAC (or set of FACs) configured to collimate light outputs from multiple waveguides. 
     The multi-tiered FAC  520  of  FIG.  5    may be formed as a single, unitary element that defines each of the vertices or may be formed from multiple FACs that are affixed to one another. In embodiments where the multi-tiered FAC  520  is formed from individual, affixed components, eutectic bonds may be used to attach each FAC to another. Additionally, each vertex of the multi-tiered FAC may be aligned along an axis parallel to the emitter surface of the PIC  110 . Alternatively, one or more of the individual vertices (or FACs) may be off-axis, with respect to such an axis. Further, the multi-tiered FAC  520  may be a two-dimensional array of N×M FACs and is not limited to a 1×M configuration. This may be implemented where waveguides  130  form a grid. 
     Although  FIG.  5    shows each FAC of the multi-tiered FAC  520  as the same cross-sectional size, there is no requirement that they are. Embodiments may have individual FACs that are more or less concave, or that extend further along the emitter surface of the PIC  110 . This may be useful where the waveguides  130   a ,  130   b ,  130   c  propagate light of different wavelengths or that have other, different properties. 
       FIG.  6 A  illustrates a photonics package  600 ′ similar to the photonics package  100  shown in  FIG.  1    but with a different hanging connector  610 . Accordingly, like-numbered elements shown in  FIG.  6 A  generally operate and/or are configured as described with respect to those same elements in  FIG.  1    and will not be discussed further. 
     The hanging connector  610  includes a backstop  620  and angled sidewall  630 . The backstop  620  abuts (e.g., touches) a side of the FAC  120  nearest the emitter surface of the PIC  110 . The angled sidewall extends from the surface of the hanging connector  610  affixed to the PIC  110  by the bond  230 . The backstop  620  thus may orient the FAC  120  with respect to the emitter surface. That is, the backstop may align the FAC  120  with respect to the emitter surface, ensuring the two are parallel. Further, the combination of the backstop and angled sidewall set the size of the offset  260 , just as the extended section aligns the FAC  120  with the waveguide  130  (or an associated emitter). The angled sidewall  630  may be replaced with a stair-stepped structure in some embodiments. 
     The backstop  620  and angled sidewall  630  may be formed as part of the process for forming a stackup into a hanging connector, as generally detailed with respect to  FIGS.  4 A- 4 C . The backstop  620  and angled sidewall  630  may be formed through any suitable operation, including chemical etching, mechanical grinding or polishing, laser vaporization, and so on. 
       FIG.  6 B  illustrates a photonics package  600  of  FIG.  6 A , but one in which the FAC  120  has a coating  650  applied to a surface of the FAC nearest the substrate  110 . The coating  650  defines an aperture  660 ; the aperture  660  is essentially a portion of the FAC surface to which no coating is applied. Light  640  passes through the aperture  660  but not the coating  650 ; the coating may instead reflect, scatter, or absorb light. The aperture  660  and coating  650  help ensure that light  640  exiting the FAC  120  is properly aligned for reception by later optical components or other elements. 
       FIG.  7    illustrates a hanging connector  140  affixed to a substrate  110  by a first bond  230  and to a multi-tiered FAC  720  by a second bond  220 , similar to the embodiment of  FIG.  5   . In this embodiment  700 , the substrate  110  has a stepped emitter edge, effectively defining multiple “layers” of the substrate  110 , each with its own waveguide  130   a ,  130   b ,  130   c . Each of these layers may extend further than the layer “above” it (e.g., the layer closer to the hanging connector  140 ). Thus, the layer closes to (and affixed to) the hanging connector  140  extends less than the layer below it, which extends less than the layer below that, and so on. This forms the stair-step emitter edge shown in  FIG.  7   . 
     The multi-tiered FAC  720  may be stepped along an edge closest to the emitter edge of the substrate  110 . Generally, the step pattern of the multi-tiered FAC  720  matches the step pattern of the emitter edge, such that the gap between any single FAC of the multi-tiered FAC and its corresponding emitter (and/or portion of the emitter edge) is identical. Thus, the multi-tiered FAC  720  may accept and collimate light  710   a ,  710   b ,  710   c  from multiple waveguides  130   a ,  130   b ,  130   c . As with the embodiment of  FIG.  5   , the multi-tiered FAC  720  may be formed as a single, unitary element or may be formed from multiple FACs that are affixed to one another. 
       FIG.  8 A  illustrates another example optical element  800  attached to a substrate  110  by a hanging connector  140 . Here, however, the optical element  800  is a prism rather than a FAC. The prism  800  may redirect light  810  exiting the substrate  110  (or a waveguide  130  on the substrate) so that the light is emitted in a vertical, rather than horizontal, direction. Essentially, the angled edge  802  of the prism  800  functions as a reflector to redirect light. As with other embodiments, the hanging connector  140  is affixed to the substrate  110  via an adhesive, solder, or the like. 
       FIG.  8 B  shows an alternative to  FIG.  8 A . Here, the prism  800  is itself the hanging connector. Put another way, the prism  800  body is shaped to position the reflected, angled edge or facet  802  over an edge of the substrate  110  in order to reflect light  810  as described with respect to  FIG.  8 A . Thus, the embodiment omits a separate hanging connector entirely and uses a unitary element as both connector and prism. 
       FIG.  9    shows yet another variant  900  in which a photodetector  910  replaces a FAC. Thus, it can be seen that the hanging connector  140  may position and/or attach any suitable component to a substrate  110  and not just an optical element such as a FAC or prism, and such components may receive light from a waveguide  130  of the embodiment. The remaining elements of the embodiment  900  are substantially identical to those illustrated in prior figures, such as  FIG.  2   . 
     Although the embodiments of  FIGS.  8 A- 9    show a waveguide  130  within the substrate  110 , for example beneath a cladding layer that may be part of the substrate, it should be understood that the waveguide(s)  130  may extend along a top surface of a respective substrate  110 , or be positioned within a channel defined in such a surface. Either waveguide option (e.g., embedded within a substrate or beneath a cladding layer of a substrate, or extending along a surface of a substrate) may be used in any embodiment described herein with respect to any figure. 
     Hanging connectors, as described herein, may be manufactured through a variety of methods. As non-limiting examples, a silicon substrate may be diced with a blade or laser to form multiple tabs accurately from a single substrate. A series of kiss cuts (e.g., cuts that do not extend through an entirety of the substrate) may define the bodies of the hanging connectors, each of which remain attached to a common substrate and separated from one another by the remnants left after the kiss cut process. That is, the substrate is formed into an alternating series of bodies and remnants after the first cutting operation, where a remnant connects two bodies to one another. The bodies may be separated from one another with a second cut (again, made by a blade, laser, or the like); the series of second cuts generally passes through one end of each of the remnants, leaving one body attached to a single remnant. The remnant thus forms the portion of the hanging connector to which the FAC, optical element, or other component is attached by the first bond  220  (as shown in  FIG.  2   ) while the body forms the portion of the FAC  120  attached to a substrate  110  by the second bond  230  (again, as shown in  FIG.  2   ). In some embodiments the remnant may be attached to the substrate and the body to the FAC or the like. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20211022
Publication Date: 20240416
Grant Date: 20240416
Priority Date: 20201023
Inventors: GOLDIS, ALEXANDER
HILL, Jeffrey T.
BISHOP, MICHAEL J.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/4219", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4244", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4296", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/4204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/4206", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4219", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4244", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4296", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B19/0057", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4262", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4206", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4213", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4219", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4244", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B19/0057", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B3/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4213", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4224", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B3/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4296", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4262", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4206", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B19/0057", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/4262", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4206", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B19/0057", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 81258243