Abstract:
An optical interconnect assembly includes an optical coupling component having a body formed of a polymer material. The body has a reflecting surface defining a first focal point and a second focal point, a first focal surface generally aligned with the first focal point, and a second focal surface generally aligned with the second focal point. The first focal surface and the second focal surface are spaced apart and at an angle to each other, and an optical path extends through the body from the first focal point to the reflecting surface and to the second focal point. An optical source from which a light signal is transmitted is positioned adjacent the first focal surface and an optical target at which the light signal is received is positioned adjacent the second focal surface.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    The Present Disclosure claims priority to prior-filed U.S. Provisional Patent Application No. 61/890,541, entitled “Athermal Optical Geometry For Fiber Coupling,” filed on 14 Oct. 2013 with the United States Patent And Trademark Office. The content of the aforementioned Patent Application is incorporated in its entirety herein. 
     
    
     BACKGROUND OF THE PRESENT DISCLOSURE 
       [0002]    The Present Disclosure relates generally to optical assemblies and, more particularly, to an optical coupling component and assembly in which changes in temperature have a reduced operational impact. 
         [0003]    A significant issue when using polymer optics is the performance of the optical system over temperature. For example, optic components made from polymers have fundamental properties inherent to the material, such as, changes in Refractive Index with temperature (dN/dT) and coefficients of thermal expansion (CTE), that are typically ten times larger than glass or electronic substrates and glass filled polymers to which they are attached. These fundamental properties limit the use of polymer optical components in many fiber optic connection applications. 
         [0004]    In some applications, the large dN/dT and CTE properties may generate a change in focused light position that results in a degradation of performance of the optical connection over temperature. This degradation of performance limits and sometimes prevents the use of polymer optic components in many fiber optic applications. In some instances, single mode fiber optic applications may be especially susceptible to degradation of performance due to the effects of changes in temperature. 
         [0005]    The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein, nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims. 
       SUMMARY OF THE PRESENT DISCLOSURE 
       [0006]    In one aspect, an optical interconnect assembly includes an optical coupling component having a body formed of a polymer material. The body has an ellipsoidal reflecting surface defining a first focal point and a second focal point, a first focal surface generally aligned with the first focal point, and a second focal surface generally aligned with the second focal point. The first focal surface and the second focal surface are spaced apart and at an angle to each other, and an optical path extends through the body from the first focal point to the reflecting surface and to the second focal point. An optical source from which a light signal is transmitted is positioned adjacent the first focal surface and an optical target at which the light signal is received is positioned adjacent the second focal surface. 
         [0007]    In another aspect, an optical coupling component for optically coupling a first optical component to a second optical component includes a body formed of a polymer material. The body has an ellipsoidal reflecting surface defining a first focal point and a second focal point, a first focal surface aligned with the first focal point and a second focal surface aligned with the second focal point. The first focal surface and the second focal surface are spaced apart and at an angle to each other and an optical path extends through the body from the first focal point to the reflecting surface and to the second focal point. 
         [0008]    In still another aspect, an optical interconnect assembly includes an optical coupling component having a body formed of a polymer material. The body has a reflecting surface defining a first focal point and a second focal point, a first focal surface generally aligned with the first focal point, and a second focal surface generally aligned with the second focal point. The first focal surface and the second focal surface are spaced apart and at an angle to each other and an optical path extends through the body from the first focal point to the reflecting surface and to the second focal point. An optical source is positioned adjacent the first focal surface and an optical target is positioned adjacent the second focal surface. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    The organization and manner of the structure and operation of the Present Disclosure, together with further objects and advantages thereof, may best be understood by reference to the following Detailed Description, taken in connection with the accompanying Figures, wherein like reference numerals identify like elements, and in which: 
           [0010]      FIG. 1  is a schematic illustration of an optical coupling system according to the disclosure; 
           [0011]      FIG. 2  is a perspective view of an optical coupling system according to the disclosure; 
           [0012]      FIG. 3  is a perspective view similar to  FIG. 2  but taken from a different perspective; 
           [0013]      FIG. 4  is a section of the optical coupling system taken generally along line  4 - 4  in  FIG. 2 ; 
           [0014]      FIG. 5  is a perspective view of an alternate embodiment of an optical coupling system with optical fibers coupled to the coupling component; 
           [0015]      FIG. 6  is a perspective view of another alternate embodiment of an optical coupling system with an emitter and a detector coupled to the coupling component; and 
           [0016]      FIG. 7  is a schematic illustration of an alternate embodiment of the coupling component of the optical coupling system. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    While the Present Disclosure may be susceptible to embodiment in different forms, there is shown in the Figures, and will be described herein in detail, specific embodiments, with the understanding that the Present Disclosure is to be considered an exemplification of the principles of the Present Disclosure, and is not intended to limit the Present Disclosure to that as illustrated. 
         [0018]    As such, references to a feature or aspect are intended to describe a feature or aspect of an example of the Present Disclosure, not to imply that every embodiment thereof must have the described feature or aspect. Furthermore, it should be noted that the description illustrates a number of features. While certain features have been combined together to illustrate potential system designs, those features may also be used in other combinations not expressly disclosed. Thus, the depicted combinations are not intended to be limiting, unless otherwise noted. 
         [0019]    In the embodiments illustrated in the Figures, representations of directions such as up, down, left, right, front and rear, forward and rearward, used for explaining the structure and movement of the various elements of the Present Disclosure, are not absolute, but relative. These representations are appropriate when the elements are in the position shown in the Figures. If the description of the position of the elements changes, however, these representations are to be changed accordingly. 
         [0020]      FIGS. 1-4  depict an optical coupling system  10  for optically coupling two components together. As depicted, a first optical component or optical source  11  and a second optical component or optical target  12  are optically coupled by a transparent optical coupling component  20 , More specifically, coupling component  20  directs optical signals in the form of light from the first optical component  11  to the second optical component  12 . In one embodiment, the first optical component  11  may be any optical source such as a semi-conductor emitter or transmitter or an optical fiber through which an optical signal is transmitted. The second optical component  12  may be any optical target such as a semi-conductor detector or receiver or an optical fiber into which an optical signal is directed. 
         [0021]    Coupling component  20  may be a one-piece polymer or resin member that includes a reflecting surface  21  together with a first focal surface  30  spaced from and opposing the reflecting surface and a second focal surface  35  that is also spaced from and opposing the reflecting surface. The first focal surface  30  is spaced from and at an angle to the second focal surface  35 . The angle between the first focal surface  30  and the second focal surface  35  may be any desired angle provided that the other characteristics of the optical component  20  as described below are met, In sonic applications, the angle between the first focal surface  30  and the second focal surface may be between approximately 70 and 110 degrees. In other application the angle may be approximately 90 degrees. 
         [0022]    Reflecting surface  21  may have an ellipsoidal shape or surface ( FIGS. 2-3 ) to create or define a pair of optical foci or focal points  31 ,  36 , An ellipse defining a portion of the reflecting surface  21  is depicted in dashed line  38  for clarity. First focal point  31  may fall on or be aligned with first focal surface  30  and second focal point  36  may fall on or be aligned with the second focal surface  30 . By aligning the first focal point  31  in three dimensions (x, y and z) with the first optical component  11  and second focal point  36  in three dimensions with the second optical component  12 , losses within the optical coupling between the first optical component and the second optical component may be minimized. 
         [0023]    It should be noted that in some instances, it may be desirable to only generally align the focal surfaces with the respective foci. For example, this may occur when it is desirable for the beam of light being transmitted to be focused at a specified diameter rather than a specified point or in instances in which exact alignment is not required for system performance. In such case, the light enters and exits coupling component  20  at a focal plane rather than a point. 
         [0024]    As depicted in  FIG. 1 , the major axis  39  of ellipse  38  (i.e., a line through the foci) is at an angle to both the first focal surface  30  and the second focal surface  35 . The angle of the major axis  39  relative to the focal surfaces coincides with the angle of the reflecting surface relative to the focal surfaces. 
         [0025]    As depicted in  FIG. 1 , first focal surface  30  is configured as a source location aligned with first optical component  11  and second focal surface  31  is configured as a target location aligned with second optical component  12 . As such, optical signals in the form of a beam of light may enter the first focal surface  30  at an angle generally perpendicular to the first focal surface, reflect off of the reflecting surface  21 , and exit from the second focal surface  35  at an angle generally perpendicular to the second focal surface. However, the first optical component  11  and the second optical component  12  may be reversed with the coupling component  20  operating with equal effectiveness. 
         [0026]    In other words, the coupling component  20  operates in an equally effective manner regardless of whether tight is being transmitted from the first focal surface  30  to the second focal surface  35  or if light is being transmitted from the second focal surface to the first focal surface. As an example, the first optical component  11  is depicted in  FIG. 1  as an optical fiber  13  and second optical component  12  as a detector  14 . In  FIG. 5 , both the first optical component  11  and the second optical component are depicted as optical fibers  13 . In  FIG. 6 , the first optical component  11  is depicted as an emitter  15  and the second optical component is depicted as a detector  14 . 
         [0027]    Optical component  20  may be formed of an optical grade polymer that is capable of being injection molded, formed as part of an additive process (e.g., 3-D printed) or otherwise formed, such as polycarbonate, cyclic olefin or Ultem.® By positioning optical component  20  so that the reflecting surface  21  is in contact with air, the differences in the indices of refraction between the optical component and air causes light to reflect efficiently off of the reflecting surface. That is, provided that the light engages the reflecting surface at an angle greater than the Brewster angle, the ellipsoidal shaped reflecting surface  21  operates as a total internal reflecting mirror that efficiently reflects light that enters the optical component  20  at the first focal point  31  and focuses the light at the second focal point  36 . As a result, light entering the optical component  20  from the first optical component  11  will reflect off of reflecting surface  21  and direct the light into second optical component  12 . 
         [0028]    As depicted in  FIGS. 1-6 , an optical signal transmitted through coupling component  20  may be depicted as a beam or a bundle of rays  50 . A first component of the beam is depicted at  51  entering optical component  20  at a first angle generally perpendicular to first focal surface  30  at source location  30  and reflects off of reflecting surface  21  at location  22  at a first reflecting angle  52  so that the light is reflected to second focal point  36 . In addition, a second component of the beam that represents one outer vertical boundary of the beam is depicted at  53  entering optical component  20  at a second entry angle  54  relative to surface  31  at source location  30  and reflects off of reflecting surface  21  at location  23  at a second reflecting angle  55  so that the light is reflected to second focal point  36 . Still further, a third component of the beam that represents an opposite outer vertical boundary of the beam is depicted at  56  entering optical component  20  at a third entry angle  57  relative to surface  30  at source location  30  and reflects off of reflecting surface  21  at location  24  at a third reflecting angle  58  so that the light is reflected to second focal point  36 . Thus, as the light from first optical component  11  expands as it enters optical component  20 , all of the light will be reflected to the second focal point  36 . 
         [0029]    Referring to  FIGS. 2-3 and 5-6 , it should be understood that the beam of light  50  will expand in three dimensions to form a relative conical shape and the ellipsoidal shape of the reflecting surface will reflect the light to the second focal point  36 . For example, light enters the coupling component  20  at first focal surface  30  as a relatively small collimated beam of light  59 . The beam expands in three dimensions as it travels through coupling component  20  until it reaches reflecting surface  21 , The beam of light will contact the reflecting surface  21  in a generally elliptical shape as depicted at  60  ( FIG. 2 ) and reflect off of the reflecting surface. 
         [0030]    The beam of light will taper or focus as depicted at  61  until it reaches the second focal point  36  In a manner similar to the outer vertical boundaries of the beam that are depicted at  53  and  56  (as depicted in  FIG. 1 ), the lateral or horizontal expansion of the beam of light will also be redirected by the ellipsoidal reflecting surface  21  to the second focal point  36 . One lateral outer boundary of the beam of light  50  as it expands is depicted in  FIGS. 2-3  at  62  and a lateral outer boundary as the beam of light contracts or is focused is depicted at  63 . 
         [0031]    Under ideal operating conditions, reflecting surface  21  operates as a total internal reflecting mirror due to the shape of the surface and the difference in the indices of refraction between the optical coupling component  20  (optical grade polymer) and the atmosphere (air) surrounding the reflecting surface. However, if a contaminant or foreign material (e.g., water, dirt, dust, adhesive) is in contact with the outer surface  25  of the reflecting surface  21 , such undesired material will change the difference in the indices of refraction between the optical component  20  and the air at the location of the contaminant and thus change the optical characteristics of the reflecting surface at the contaminant. 
         [0032]    In order to reduce the risk of such a change in the reflecting characteristics of the reflecting surface  21 , and a corresponding change in the performance of coupling component  20 , it may be desirable to add or apply a reflective coating or plating  40  ( FIG. 7 ) to the outer surface  25  of the optical component  20  along the reflecting surface  21 . The coating  40  provides additional reflectivity in case any contaminants or foreign materials come into contact with or become affixed to the outer surface of the reflecting surface. The reflective coating  40  may be any highly reflective material such as gold, silver, or any other desired material. Coating  40  may be applied to the outer surface  25  in any desired manner. Although depicted with the coating  40  extending along the entire reflecting surface  21 , the coating may be selectively applied so that it is only applied in the portion of the reflecting surface at which most of the beam of light will reflect. 
         [0033]    Upon assembling optical coupling system  10 , an index matched medium  41  may be used to fill a first gap  16  ( FIG. 1 ) between the first optical component  11  and the first focal surface  30  of coupling component  20  and a second gap  17  between the second optical component  12  and the second focal surface  35  of the optical component. It should be noted that  FIG. 1  is not to scale for purposes of illustration. The gaps  16 ,  17  may be any desired distance, In one example, the gaps  16 ,  17  may be between 25 and 50 microns. 
         [0034]    The refractive index of the medium  41  may closely match the refractive indices of the first optical component  11 , the second optical component  12 , and the coupling component  20 . The medium  41  may be an index matched adhesive such as an epoxy that not only transfers light between the first optical component  11 , the second optical component  12 , and the coupling component  20  in an efficient manner but also functions to secure the first optical component  11  and the second optical component  12  to the coupling component  20 . 
         [0035]    In an alternate embodiment, the first optical component  11  and the second optical component  12  may be secured to the coupling component  20  using some structure or mechanism other than an adhesive and the medium  41  may be an index matching gel, fluid or other material that does not have adhesive qualities. 
         [0036]    The index of refraction of the medium  41  may be any desired value. In one example, the index of refraction of silica optical fiber is approximately 1.48 and the index of refraction of the polymer coupling component  20  is approximately 1.56. In such case, the index of refraction of the medium  41  may be matched to approximate the midpoint (i.e., approximately 1.52) between the indices of refraction of the optical fibers and the coupling component  20 . In another example, the index of refraction of the medium  41  may be set to be approximately equal to the index of refraction of either the optical fibers or the coupling component  20 . In still another example, the index of refraction of the medium  41  may be set at any value between the indices of refraction of the optical fibers and the coupling component  20 . Regardless of the medium, the use of an index matched medium will generally result in improved optical characteristics within the system  10 . 
         [0037]    The coupling component  20  provides the advantage of redirecting and focusing an optical signal from the first optical component  11  to the second optical component without transmitting the signal through air and thus reduces the impact of changes in temperature on the signal transmission. More specifically, as the signal travels through the coupling component (i.e., from the first foci  31  to the reflecting surface  20  and from the reflecting surface to the second foci  36 ), it is subject to a constant index of refraction along its entire path since it is always traveling though the polymer material, Still further, the components other than the coupling component  20  that form the optical path of system  10  (i.e., first optical component  11 , second optical component  12  and medium  41 ), have very similar indices of refraction and thus changes in temperature have a relatively small impact. By closely matching the indices of refraction of the first optical component  11 , the second optical component  12 , the coupling component  20 , and the medium  41  and avoiding the transmission of the signal through air, the impact of changes in the index of refraction due to changes in temperature and resulting degradation in the optical signal may be minimized. 
         [0038]    By reducing the impact of temperature change with respect to the refractive index, the beam of light or optical signal is consistently focused on the target location. While this may be desirable in most applications, it may be especially important when one or both of the first optical component  11  and the second optical component  12  are single mode optical fibers due to their relatively small core diameter as compared to that of a multi-mode optical fiber. 
         [0039]    The shape of the coupling component  20  may also provide the benefit of compensating to some extent for changes in the physical structure of the coupling component due to expansion and contraction with changes in temperature. More specifically, due to the elliptical shape of the reflecting surface  21 , the position of the first focal point  31  and the second focal point  36  will typically follow the position of the first optical component  11  and the second optical component  12 , respectively, as the coupling component  20  changes size with changes in temperature. 
         [0040]    While a preferred embodiment of the Present Disclosure is shown and described, it is envisioned that those skilled in the art may devise various modifications without departing from the spirit and scope of the foregoing Description and the appended Claims.