Patent Publication Number: US-2016238786-A1

Title: Flexible glass optical waveguide structures

Description:
This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/894139, filed on Oct. 22, 2013, the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to optical waveguides and, more particularly, to flexible glass optical waveguide structures and devices formed therefrom. 
     BACKGROUND 
     As the performance of microprocessors continues to increase, electrical interconnects for data flow to and from processors can increasingly become a bottleneck for overall system performance. Replacing electronic interconnects with optical interconnects can provide a higher bandwidth-length product and higher density. 
     Flexible optical waveguide interconnects can provide an important component in optical interconnection technology for optically connected mediation systems (e.g., board-to-board or chip-to-chip interconnections). Polymer-based flexible optical waveguides have been proposed as short distance interconnects. However, the polymers may not be suitable for high temperature processes. Accordingly, there remains a need for flexible waveguides and devices for optical interconnect applications. 
     SUMMARY 
     One technique to improve optical waveguide interconnects is to provide a flexible glass optical waveguide. The flexible glass optical waveguide includes a substrate that is formed of an ultra-thin flexible glass having a thickness of no more than about 0.3 mm, which can also support relatively high temperatures (e.g., greater than 250° C.) that is suitable for printed circuit board (PCB) processing. 
     Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the disclosure as exemplified in the written description and the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the disclosure, and are intended to provide an overview or framework to understanding the nature and character of the disclosure as it is claimed. 
     The accompanying drawings are included to provide a further understanding of principles of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain, by way of example, principles and operation of the disclosure. It is to be understood that various features of the disclosure disclosed in this specification and in the drawings can be used in any and all combinations. By way of non-limiting example the various features of the disclosure may be combined with one another according to the following aspects. 
     According to a first aspect, an optical waveguide device comprises: 
     a flexible glass optical waveguide structure comprising a flexible glass substrate having a thickness of no greater than about 0.3 mm, the flexible glass substrate having at least one waveguide feature that transmits optical signals through the flexible glass substrate, the at least one waveguide feature being formed of glass material that forms the flexible glass substrate; and 
     an electrical device located on a surface of the flexible glass substrate. 
     According to a second aspect, there is provided the optical waveguide device of aspect 1, wherein an intermediate substrate connects the electrical device to the surface of the flexible glass substrate. 
     According to a third aspect, there is provided the optical waveguide device of aspect 1, wherein the electrical device is formed directly on the surface of the flexible glass substrate. 
     According to a fourth aspect, there is provided the optical waveguide device of any of aspects 1-3, wherein the electrical device is a first device, the optical waveguide device further comprising a second device located on the surface of the flexible glass substrate. 
     According to a fifth aspect, there is provided the optical waveguide device of aspect 4, wherein the second device is an optical device, the optical waveguide device comprising an electrical connection carried by the flexible glass optical waveguide structure that sends electric signals between the first and second devices. 
     According to a sixth aspect, there is provided the optical waveguide device of any of aspects 1-5, wherein the electrical device is a first device, the optical waveguide device further comprising a second device located on an opposite surface of the flexible glass substrate. 
     According to a seventh aspect, there is provided the optical waveguide device of aspect 6, wherein the second device is an optical device, the optical waveguide device comprising an electrical connection carried by the flexible glass optical waveguide structure that sends electric signals between the first and second devices. 
     According to an eighth aspect, there is provided the optical waveguide device of aspect 7, wherein the electrical connection extends through the flexible glass substrate. 
     According to a ninth aspect, there is provided the optical waveguide device of any of aspects 1-8, wherein the at least one waveguide feature is at least partially bounded by surrounding glass material of the flexible glass substrate. 
     According to a tenth aspect, there is provided the optical waveguide device of any of aspects 1-9, comprising multiple waveguide features that transmit optical signals through the flexible glass substrate. 
     According to an eleventh aspect, there is provided the optical waveguide device of any of aspects 1-10, wherein the at least one waveguide feature is at least partially buried within the flexible glass substrate. 
     According to a twelfth aspect, there is provided the optical waveguide device of aspect 11, wherein the flexible glass substrate has opposite broad surfaces, the at least one waveguide feature intersecting at least one of the broad surfaces. 
     According to a thirteenth aspect, there is provided the optical waveguide device of aspect 11, wherein the at least one waveguide feature is buried within the flexible glass substrate such that at least a portion of the at least one waveguide feature is spaced from both the broad surfaces. 
     According to a fourteenth aspect, there is provided the optical waveguide device of any of aspects 1-13, further comprising a polymer layer that coats a broad surface of the flexible glass substrate. 
     According to a fifteenth aspect, there is provided the optical waveguide device of any of claims 1-14, wherein the at least one waveguide feature has a width of no more than about 100 μm. 
     According to a sixteenth aspect, a device assembly comprises: 
     a substrate; 
     a first device connected to the substrate, where the first device is an electrical device; 
     a second device connected to the substrate; and 
     a flexible glass optical waveguide structure that optically connects the first and second devices, the flexible glass optical waveguide comprising a flexible glass substrate having a thickness of no greater than about 0.3 mm, the flexible glass substrate having at least one waveguide feature that transmits optical signals through the flexible glass substrate between the first and second optical devices, the at least one waveguide feature being formed of glass material that forms the flexible glass substrate. 
     According to a seventeenth aspect, there is provided the device assembly of aspect 16, wherein the first device is located on one broad surface of the substrate and the second device is located on an opposite surface of the substrate. 
     According to a eighteenth aspect, there is provided the device assembly of aspect 16 or 17, wherein the substrate has an opening extending through a thickness of the substrate, the flexible glass optical waveguide structure extending through the opening. 
     According to a nineteenth aspect, there is provided the device assembly of any one of aspects 16-18, wherein the flexible glass optical waveguide structure has a portion extending contiguously with the substrate. 
     According to a twentieth aspect, there is provided the optical structure of any one of aspects 16-19, wherein the flexible glass optical waveguide structure has a portion spaced from the substrate. 
     According to a twenty-first aspect, there is provided the optical structure of any one of aspects 16-20, wherein the second device is an optical device. 
     According to a twenty-second aspect, there is provided the optical structure of any one of aspects 16-21, wherein the substrate is formed of multiple layers, the flexible glass optical waveguide structure at least partially extending between the multiple layers of the substrate. 
     According to a twenty-third aspect, an optical waveguide device comprises: 
     a flexible glass optical waveguide structure comprising a flexible glass substrate having a thickness of no greater than about 0.3 mm, the flexible glass substrate having at least one waveguide feature that transmits optical signals through the flexible glass substrate, the at least one waveguide feature being formed of glass material that forms the flexible glass substrate; and 
     an electrical device and/or an optical device at least partially buried within the flexible glass substrate. 
     According to a twenty-fourth aspect, there is provided the optical waveguide device of aspect 23, wherein the electrical and/or optical device is a first device, the electrical and/or optical device comprising a second device carried by the flexible glass substrate. 
     According to a twenty-fifth aspect, there is provided the optical waveguide device of aspect 24, comprising an electrical connection carried by the flexible glass optical waveguide structure that carries electric signals between the first and second devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages of the present disclosure are better understood when the following detailed description of the disclosure is read with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates an embodiment of a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 2  illustrates schematically an embodiment of a process and apparatus for forming a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 3  illustrates an embodiment of a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 4  illustrates an embodiment of a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 5  illustrates an embodiment of an optical waveguide device including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 6  illustrates another embodiment of an optical waveguide device including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 7  illustrates another embodiment of an optical waveguide device including a flexible glass optical waveguide in accordance with aspects of the disclosure; 
         FIG. 8  illustrates operation of another embodiment of an optical waveguide device including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 9  illustrates an embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 10  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 11  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 12  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 13  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 14  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 15  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 16  illustrates another embodiment of a device assembly including a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 17  illustrates an embodiment of a waveguide feature for a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 18  illustrates another embodiment of a waveguide feature for a flexible glass optical waveguide structure in accordance with aspects of the disclosure; 
         FIG. 19  illustrates another embodiment of a waveguide feature for a flexible glass optical waveguide structure in accordance with aspects of the disclosure; and 
         FIG. 20  illustrates another embodiment of a waveguide feature for a flexible glass optical waveguide structure in accordance with aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of various principles of the present disclosure. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present disclosure may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of various principles of the present disclosure. Finally, wherever applicable, like reference numerals refer to like elements. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Directional terms as used herein—for example up, down, right, left, front, back, top, bottom—are made only with reference to the figures as drawn and are not intended to imply absolute orientation. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “component” includes aspects having two or more such components, unless the context clearly indicates otherwise. 
     Embodiments described herein generally relate to flexible glass optical waveguide structures and devices that are formed using a flexible glass substrate. One or more waveguide features can be carried by the flexible glass substrate and the waveguide features may be formed of glass forming the flexible glass substrate such that they are also flexible. The waveguide features may be exposed at (i.e., intersect) or located near a surface of the flexible glass substrate or the waveguide features may be buried within the flexible glass substrate, or a combination thereof. In some embodiments, the waveguide features form part of the surface of the flexible glass substrate. The flexible glass substrate can support relatively high temperatures (e.g., greater than 250° C.) that are suitable for printed circuit board (PCB) processing, while the flexibility of the flexible glass substrate facilitates connection of various electrical and/or optical components. 
     Referring to  FIG. 1 , a flexible glass optical waveguide structure  10  has a width W and a length L and includes a flexible glass substrate  12  and an array  14  of waveguide features  16  extending along the length of the flexible glass substrate  12  for transmitting optical signals there through. The waveguide features  16  may be discrete formations that are at least partially or completely bounded about their perimeters by the surrounding glass material of the flexible glass substrate  12 . The flexible glass substrate  12  may be thin (e.g., less than about 0.5 mm, such as less than about 0.3 mm), which can be advantageous over polymer substrates for higher processing temperatures, nearly zero birefringence (less than about ten nm in retardation) and neutral color. 
     The flexible glass substrate  12  may have any suitable length L (e.g., between about 1 cm to several meters), a width W (e.g., between about 1 mm to  10  cm) and a thickness of about 0.3 mm or less including but not limited to thicknesses of, for example, about 0.01-0.05 mm, about 0.05-0.1 mm, about 0.1-0.15 mm, about 0.15-0.3 mm, 0.3, 0.275, 0.25, 0.225, 0.2, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01 mm. The flexible glass substrate  12  may be formed of glass, a glass ceramic, a ceramic material or composites thereof. In some embodiments, the flexible glass substrate including the waveguide features may have a bend radius of at least about 100 mm. A fusion process (e.g., downdraw process) that forms high quality flexible glass sheets can be used in a variety of devices and one such application is flat panel displays. Glass sheets produced in a fusion process have surfaces with superior flatness and smoothness when compared to glass sheets produced by other methods. The fusion process is described in U.S. Pat. Nos. 3,338,696 and 3,682,609. Other suitable glass sheet forming methods include a float process, updraw and slot draw methods. 
     Methods of manufacturing flexible glass optical waveguide structures  10  will now be described.  FIG. 2  represents steps of example methods with the understanding that the illustrated steps may be carried out in a different order unless otherwise noted. Moreover, additional steps may be provided that are not illustrated unless otherwise stated. As shown in  FIG. 2 , the method can optionally begin with a step  102  of obtaining the flexible glass substrate  104  having a thickness of about 300 μm or less, such as about 200 μm or less, such as about 100 μm or less, such as about 50 μm or less. The flexible glass substrate  104  can be provided with glass selected from various families of glass including soda lime glass, borosilicate and alkaline earth boro-aluminosilicate although other glass compositions may be used in further examples. Additionally, the flexible glass substrate can be formed of either a single layer or multiple layers of a glass or glass ceramic material. 
     At step  106 , the flexible glass substrate  104  may be provided to a waveguide forming station  108  where one or more waveguide features ( FIG. 1 ) are formed in the flexible glass substrate  104 . The waveguide forming station  108  may form the waveguide features in the flexible glass substrate using any suitable process, such as ion exchange, laser inscription or any other suitable process or combination of processes. These features can be formed while the glass substrate is part of a continuous flexible glass web, or after it has been cut into discrete sections. The waveguide features can be formed single mode or multi-mode (e.g., depending at least in part on the size of the waveguide features). A relative refractive index change is used to describe refractive index increase between the waveguide features (i.e., waveguide core) and surrounding glass cladding by the waveguide forming process: 
       Δ=(( n   1   2   −n   2   2 )/2 n   2   2 )
 
     where, n 1  and n 2  are the refractive indices of the waveguide core and cladding, respectively. The A value of the waveguide features may be between about 0.1 and 10 percent The index profile of the waveguide features can be a step-like profile or a graded profile. In some embodiments, the width or diameter of the waveguides may be between about 2 μm and 100 μm. 
       FIG. 2 , for example, illustrates two example sources  120  for obtaining flexible glass substrate  104 , although other sources may be provided. For instance, the source  120  can include a down draw glass forming apparatus  122 . As schematically shown, the down draw glass forming apparatus  122  can include a forming wedge  124  at a bottom of a trough  126  , wherein glass flows down opposite sides  128  and  130  of the forming wedge  124 . The two sheets of molten glass are subsequently fused together as they are drawn off root  132  of the forming wedge  124 . As such, the flexible glass substrate  104 , in the form of a flexible glass ribbon, may be fusion drawn to traverse in a downward direction  136 , off the root  132  of the forming wedge  124  and directly into a downward zone  138  positioned downstream of the down draw glass forming apparatus. After forming, the flexible glass substrate  104  may be further processed, such as by cutting, trimming, etc. The flexible glass substrate  104 , in the form of the continuous flexible glass ribbon may then be provided to the waveguide forming station  108 . 
     Referring to  FIG. 3 , waveguide features  110  may be formed at a broad surface  112  of the flexible glass substrate  104 . In these embodiments, the waveguide features  110  may have semi-circular or semi-elliptical cross sectional shapes, or some other suitable shape. Referring to  FIG. 4 , waveguide features  114  may be at least partially buried within the flexible glass substrate  104 , spaced from both broad surfaces  112  and  116 . In these embodiments, the waveguide features  114  may have circular or elliptical cross sectional shapes, or some other suitable shape. Additionally, while the waveguide features are illustrated as being parallel, other arrangements are possible, which will be described in greater detail below (i.e., the waveguide features may extend in any or a combination of lengthwise, widthwise and/or thickness directions). For parallel waveguide features, the waveguide widthwise spacing or pitch may be between about 15 μm and 100 μm, such as between about 20 μm, 30 μm, 40 μm and 50 μm to reduce crosstalk between neighboring waveguide features. Unlike circular optical fiber, the number of waveguide features in a planar flexible glass substrate can be scaled in the width dimension. A larger number of waveguide features can be provided by a single flexible glass substrate (e.g., 4 or more, 8 or more, 10 or more, 16 or more, 20 or more, 24 or more, 48 or more, 96 or more, 100 or more, 124 or more,  150  or more, 200 or more,  300  or more, etc.). To protect the waveguide features, such as shown by  FIG. 3  at the surface  112 , a coating material  140  may be applied at step  142 . 
     The flexible glass optical waveguide structures can be a single layer of flexible glass substrate or a multi-layer composite, including multiple flexible glass substrates and/or different materials, such as non-glass materials. Individual layers of the flexible glass optical waveguide structures can be chosen specifically to perform optical, mechanical and/or electrical functions. For example, a polymeric coating can be applied to one or both surfaces  112  and  116  ( FIGS. 2 and 3 ) to serve as optical, mechanical and/or electrical layers. 
     Referring to  FIGS. 5 and 6 , schematic, simplified views of optical waveguide devices  144  and  146  are illustrated that include flexible glass optical waveguide structure  149  and  151 . Both the optical waveguide devices  144  and  146  include their own electrical, optical and/or opto-electrical devices  148 ,  150  and  152  located on a surface  154  and  158  of their respective flexible optical waveguide structures  149  and  151 . As used herein, the term “optical device” includes optical and opto-electrical devices. In  FIG. 5 , a single waveguide feature  158  is illustrated that is buried within a flexible glass substrate  160 . In  FIG. 6 , multiple waveguide features  158  are illustrated that are buried within a flexible glass substrate  162 . While the waveguide features  158  are illustrated at different thickness levels within the flexible glass substrate  160 , the waveguide features  158  may be arranged at different width locations within the flexible glass substrate  160  (see  FIGS. 3 and 4 ). 
     Referring to  FIG. 7 , an optical waveguide device  161  is illustrated including a flexible glass optical waveguide structure  163 . The flexible glass optical waveguide structure  163  includes a flexible glass substrate  164  having devices  148 ,  150  and  152  located on a surface  166  thereof. In this embodiment, a waveguide feature  168  is buried within the flexible glass substrate  164  that has a waveguide portion  170  that splits from a waveguide portion  172  in a vertical or thickness direction. Such an arrangement can allow for splitting (or combining) optical signals within the waveguide feature  168 . 
     The devices  148 ,  150  and  152  can be integrated onto the surface  166  in any suitable fashion, such as by connecting the device  148  to the surface  166  using an intermediate substrate  174 . In some embodiments, one or more of the devices  148 ,  150  and  152  may be at least partially or completely buried within the flexible glass substrate  164  as represented by dashed line  167 . In some embodiments, the device  150  may be built directly on the surface  166  (e.g., by a deposition process). For example, silicon may be used in building an active device on the surface  166  of the flexible glass optical waveguide structure  163 . Such an arrangement can allow for formation of lasers, optical detectors and optical modulators on the flexible glass optical waveguide structure  163 . Electrical components such as electrical vias, conductor traces or electrical components can also exist on the flexible glass optical waveguide structure  163 . For example, hole formation and metal filling may be used to facilitate placement and use of electrical components. Conductor trace patterning and pick-and-place features may also be provided. 
       FIG. 8  illustrates schematically operation of an exemplary optical waveguide device  180  that includes a flexible glass optical waveguide structure  182  formed of a flexible glass substrate  184  having a waveguide feature  186  extending therethrough. In this example, electrical and/or opto-electrical devices  188  and  190  are illustrated on opposite surfaces  192  and  194  of the flexible glass optical waveguide structure  182 . As indicated above, the devices  188  and  190  may be formed separately and attached to the flexible glass optical waveguide structure  182  or they may be built directly on the surfaces  192  and  194 , or some combination thereof. Use of the flexible glass substrate  184  can facilitate interaction between the various devices located thereon and even to separate devices located elsewhere (e.g., on a nearby PCB). For example, an electrical interconnect  196  may provide an electrical connection between the devices  188  and  190  to allow communication therebetween with the devices  188  and  190  at opposite surfaces  192  and  194  of the flexible glass optical waveguide structure  182 . While the electrical interconnect  196  is illustrated as extending through the thickness of the flexible glass substrate  184  in a direction generally perpendicular to surfaces  192  and  194 , the electrical interconnect  196  can extend in any of thickness, lengthwise and/or widthwise directions. Additionally, optical and physical properties of the flexible glass substrate  184  can be utilized to facilitate optical interaction between devices. For example, a through hole  200  or other passageway may be formed through the flexible glass substrate  184 . Such a hole  200  can allow for passage of conductor traces or other electrical or optical connections between the surfaces  192  and  194 . Such holes  200  may also serve as alignment features to facilitate a pick-and-place operation. As another example, the optical properties of the flexible glass substrate  184  can allow optical interaction through the flexible glass substrate  184  as represented by light beam  202  from device  204 . In some embodiments, the devices may interact with optical signals provided by the waveguide features. 
       FIGS. 9-15  illustrate exemplary interconnect options for parallel optical links utilizing one or more flexible glass optical waveguide structures. Referring first to  FIG. 9 , a device assembly  210  includes devices  212  and  214  (e.g., optical or electro-optical devices) that are attached to a substrate  216  (e.g., a PCB). An optical connector  218  (e.g., a ferrule) optically connects a flexible glass optical waveguide structure  220  to, for example, an array of optical fibers of an optical fiber cable that deliver optical signals to the device assembly  210 . In this example, the optical connector  218  is connected to an edge  222  of the substrate  216  and the flexible glass optical waveguide structure  220  extends along and may be connected to and extend contiguously with a surface  224  of the substrate  216 . The flexible glass optical waveguide structure  220  is also optically connected to device  212 . Another flexible glass optical waveguide structure  226  extends along and may be connected to and extend contiguously with the surface  224  of the substrate  216  to connect the devices  212  and  214 .  FIG. 10  illustrates an alternative embodiment of a device assembly  230  where flexible glass optical waveguide structures  232  and  234  are both on and off of substrate  236  to facilitate optical connection to devices  238  and  240  at locations spaced from the substrate  236 .  FIG. 11  illustrates another embodiment where a flexible glass optical waveguide structure  242  is connected to substrate facing surfaces  244  and  246  of devices  248  and  250 , yet a central portion  252  of the flexible glass optical waveguide structure  242  is spaced from substrate  254 . Referring to  FIG. 12 , another embodiment of a device assembly  260  includes an off substrate arrangement where optical connector  262  and flexible glass optical waveguide structures  264  and  266  are spaced from substrate  268  and optically connected to devices  270  and  272 . 
     Not only can the above-described flexible glass optical waveguide structures facilitate optical connections on a single side of a substrate, they can also facilitate optical connections between opposite sides of the substrate. For example, referring to  FIG. 13 , another embodiment of a device assembly  280  includes a flexible glass optical waveguide structure  282  that delivers optical signals to a lens array  284 , which delivers the optical signals through a substrate  286  to an optical device  288  that receives the optical signals and, in turn, delivers optical signals to another flexible glass optical waveguide structure  290 . As can be seen, the flexibility of the flexible glass optical waveguide structure  290  allows the flexible glass optical waveguide structure  290  to be routed through an opening  292  in the substrate  286 . The flexible glass optical waveguide structure  290  is also optically connected with an optical device  294  that receives the optical signals from the flexible glass optical waveguide structure  290 .  FIG. 14  illustrates an alternative embodiment of a device assembly  300  having a flexible glass optical waveguide structure  302  that is at least partially encapsulated within a multi-layer substrate  304 . The flexible glass optical waveguide structure  302  is routed from optical device  305  and surface  306  and through an opening  308  that extends through only layer  310 . The flexible glass optical waveguide structure  302  is then routed between the layer  310  and layer  312  and then through another opening  314  that extends only through layer  312  to allow an optical connection with optical device  315  located at an opposite surface  318  of the substrate  304 . Flexible glass optical waveguide structures  320  and  322  can also facilitate connection between substrates  324  and  326  having non-parallel arrangements and provide access to either or both surfaces  328  and  329  the substrate  326  (and/or substrate  324 ) as shown by  FIG. 15 . 
     Referring to  FIG. 16 , the above-described flexible glass optical waveguide structures can facilitate pluggable connections between devices. An exemplary pluggable optical board interconnection system  340  is shown by  FIG. 16 . Optical adapters  342  and  344  may be connected to a backplane board  346  that are each configured to releasably receive optical board assemblies  348  and  350 . A flexible glass optical waveguide structure  352  is provided that extends on or within the backplane board turning perpendicular into the optical adapters  342  and  344  to optically couple to waveguides  354  and  356  carried by the optical board assemblies  348  and  350  to allow optical communications therebetween. 
     While many of the flexible glass optical waveguide structures described above illustrate parallel waveguide features ( FIG. 1 ), other arrangements are possible. For example,  FIG. 17  illustrates a Y-branch waveguide feature  360  that can be used for splitting optical signals from one waveguide portion into multiple waveguide portions or combine optical signals from multiple waveguide portions into one waveguide portion if used reversely.  FIG. 18  illustrates a star-coupler waveguide arrangement  362  for performing splitting/combining functions.  FIG. 19  illustrates a directional coupler arrangement  364  for coupling optical signals from one waveguide feature  366  to another waveguide feature  368 .  FIG. 20  illustrates a Mach-Zehnder interferometer arrangement  370  for signal processing. 
     The above-described flexible glass optical waveguide structures can facilitate a variety of connection arrangements of different optical components due to the flexibility of the flexible glass substrate. A large number of waveguide features (e.g., hundreds) can be formed in the flexible glass substrate. The flexible glass optical waveguide structures can support device forming temperatures of several hundred degrees Celsius, which is suitable for high temperature PCB processing. The flexible glass substrates can be compatible with via hole processing and electronic component assembly to enable full integration between optical and electrical components. The flexible glass optical waveguide structures can enable efficient fiber end-face coupling. The waveguide features can be formed at one or both surfaces, as well as buried internally within the flexible glass substrate. Optical and electronic active components can be integrated using the flexible glass optical waveguide structures. 
     It should be emphasized that the above-described embodiments of the present disclosure, including any embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of various principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and various principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present disclosure and protected by the following claims.