Abstract:
An optical subsystem includes a passive optical element having a lens element eccentric therein. The passive optical element is provided adjacent to an optical element on a submount and orthogonal to the submount. The alignment of the passive optical element and the optical element on the submount may be realized by rotating the passive optical element. The alignment may be further enhanced by translating the passive optical element and the optical element on the submount relative to one another. Once desired alignment is achieved, the passive optical element is secured to the submount.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/276,133 entitled “Method and Apparatus to Optimize Optical Coupling in an Axis Orthogonal to the Optical Axis” filed Mar. 16, 2001, which is hereby incorporated by reference in its entirety for all purposes 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to optical assemblies and subassemblies, and particularly to a device which fosters precision alignment of an optical device to another optical device.  
         BACKGROUND OF THE INVENTION  
         [0003]    When aligning an active optical element and a passive optical element, manufacturing tolerances often add to the axial misalignment between the passive and active optical elements. Previous attempts to correct for this axial misalignment include use of multiple piece parts, active alignment and/or compromised optical designs attempting to mitigate y-axis alignment problems.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to an optical coupling alignment method and apparatus which overcomes at least one of the above disadvantages.  
           [0005]    It is an object of the present invention to substantially precisely align optical axes of devices.  
           [0006]    To achieve this and other objects, according to an exemplary embodiment of the present invention, a coupling device is disposed in an alignment slot to locate a passive optical element which has an optical axis and an outside diameter that are not concentric.  
           [0007]    At least one of the above and other objects may be realized by providing a method for aligning an optical element on a substrate with a passive optical element orthogonal to the substrate including providing a lens element in the passive optical element which is eccentric in the passive optical element, rotating the passive optical element until optical coupling between the lens element and the optical element is optimized, and securing the lens element in an optimized position.  
           [0008]    At least one of the above and other objects may be realized by providing an optical subsystem including an optical element on a submount, a passive optical element including a lens element eccentric therein, the passive optical element being provided adjacent to the optical element and orthogonal to the submount, and a securing mechanism which maintains an optimized position of the lens element and the optical element  
           [0009]    These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion.  
         [0011]    [0011]FIG. 1( a ) is an elevational perspective view of a submount assembly including a passive optical element according to an illustrative embodiment of the present invention.  
         [0012]    [0012]FIG. 1( b ) is a perspective top view of a submount assembly including a passive optical element according to an illustrative embodiment of the present invention.  
         [0013]    [0013]FIG. 1( c ) is a side view of a submount assembly including a passive optical element according to an illustrative embodiment of the present invention.  
         [0014]    [0014]FIG. 2( a ) is a perspective view of a passive optical element according to an illustrative embodiment of the present invention.  
         [0015]    [0015]FIG. 2( b ) is a side view of a passive optical element according to an illustrative embodiment of the present invention.  
         [0016]    [0016]FIG. 2( c ) is a front view of a passive optical element according to an illustrative embodiment of the present invention.  
         [0017]    [0017]FIG. 3( a ) is a front view of a passive optical element according to an illustrative embodiment of the present invention.  
         [0018]    [0018]FIG. 3( b ) is a perspective view of the passive optical element shown in FIG. 3( a ) mounted on a substrate  
         [0019]    [0019]FIG. 4( a ) is an exploded perspective view of a passive optical element according to another illustrative embodiment of the present invention.  
         [0020]    [0020]FIG. 4( b ) is an assembled perspective view of a passive optical element according to another illustrative embodiment of the present invention 
     
    
     DETAILED DESCRIPTION  
       [0021]    In the following detailed description, for purposes of explanation and not limitation, exemplary embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure, that the present invention 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 to not obscure the description of the present invention.  
         [0022]    Turning to FIG. 1( a ), a perspective view according to an exemplary embodiment of the present invention is shown. A submount  101  has a passive optical element  102  disposed in a slot  104 . As shown in FIG. 1( b ), the passive optical element  102  couples optically to another optical element  103 . In the illustrative embodiment shown in FIG. 1( b ), optical element  103  is an active optical device. Optical element  103  may be a light emitting device, such as a laser. Of course, optical element  103  could be an optical detector, such as a PIN detector. Moreover, optical element  103  could be passive optical devices such as a refractive or diffractive optical element. Finally, while not shown in the illustrative embodiment of FIG. 1( b ), a passive optical device (e.g. an optical waveguide) could also be disposed over the submount  101 , and could optically couple to the passive optical element  103 .  
         [0023]    As shown in FIG. 1( a )- 1 ( c ), the passive optical element  102  includes a lens portion  110  having power, i.e., shapes the beam by other than due to the change in refractive index at the interfaces of the passive optical element  102 . According to the illustrative embodiment shown in FIGS.  1 ( a )- 1 ( c ), the properties of eccentricity are used in the fabrication of the passive optical element  102 . As used herein, eccentricity does not refer to the lens properties themselves, but to the position of the lens portion  110  having power in the overall passive optical element  102 . The incorporation of the eccentricity into the passive optical element  102  fosters precise alignment of the optic axes of optical devices. To this end, the optic axes of the passive optical element and that of the active optical device may be precisely aligned. Moreover, this fosters precise optical alignment to another optical device, such as an optical fiber or other waveguide (not shown), which may then be coupled to the active optical element  103  by way of the passive optical device  102 . If the active optical element  103  is a detector, typically the lens portion  110  would face the detector.  
         [0024]    In the illustrative embodiment shown in FIGS.  1 ( a )- 1 ( c ), the passive optical device is a lens element. The alignment slot  104  is used to position the passive optical element  102 . The passive optical element  102  has been fabricated such that the optical axis of the lens portion  110  and outside diameter of the passive optical element  102  are not concentric. As a function of the rotation of the passive optical element  102  about its outside diameter, the optical axis of the lens portion  110  may be positioned in the Y-axis to match the “Y” optical axis of optical element  103 . In the event that optical element  103  is an active device, the height of the active area of the active device could be measured with respect to the surface of the lens to which it is bonded. The passive optical element  102  would then be rotated such that the optical centerline of the lens element  110  would be matched to the height of an active region of the optical element  103 , i.e., so that light may be coupled between the optical elements. In other words, this rotation is not to alter the functioning of the passive optical element  102 , but to have the same functioning regardless of the position of the optical element  103  along the Y-axis within some predetermined range.  
         [0025]    As can be readily appreciated, the rotation of the passive optical element  102  in the alignment slot  104  compensates for variation in Y-axis alignment between the passive optical element  102  and the active optical element  103 . However, when the lens  110  is rotated to adjust the Y-axis alignment, there is also a translation in the X-axis. In other words, as the lens is rotate, there is a translation of the lens in both the Y (Vertical) and X (Horizontal) axes. The X-axis translation may be taken into account. In the embodiment depicted in FIGS.  1 ( a )- 1 ( c ), the optical device  103  would need to be bonded at an offset in the X-axis as a function of the translation caused by the phase angle of  102 . Alternatively, the passive optical element  102  could be offset in the X-axis.  
         [0026]    Alignment of the passive optical element  102  and the optical device  103  may be done in a number of ways, e.g., machine vision. A system could be constructed that has cameras looking down the appropriated axes, either manually or automatically. Alternatively, active alignment could be used. When the elements  102 ,  103  are satisfactorily aligned, they are secured in position in a conventional manner. Once the desired alignment is obtained, the passive optical element may be secured to the submount in any conventional manner.  
         [0027]    Tuning to FIGS.  2 ( a )- 2 ( c ), a variety of views of the passive optical element  102  are shown. According to the illustrative embodiment of FIG. 2( b ), the passive optical element  102  includes a lens element  110 . The eccentricity of the lens element  110  is shown in front view in FIG. 2( c ). As can be seen, the outside circle  202  in FIG. 2( c ) is not concentric with the optic axis of the lens element  110 . The eccentricity, i.e., the difference between the center of the outer circle  202  and the optical axis of the lens element  110 , is indicated at e in FIG. 2( c ). The eccentricity is the delta between the centerline of the optical axis  110  and the outside diameter of  102 . Increasing this delta provides a greater range of adjustment. The degree of adjustment that is possible according to the illustrative embodiment of the present disclosure is approximately two times the amount of the eccentricity of the passive optical element  102 . The round outside diameter provides continuous height adjustment within a defined range.  
         [0028]    While the passive optical element  102  in the above illustrative embodiments is substantially cylindrical, other shapes could be incorporated to provide discrete adjustments in y-axis alignment. One such example may be a polygonal element  301 , shown in FIG. 3( a ). Here, the lens element  110  is still not aligned with the center of the polygonal element  301  and the eccentricity e allows for discrete alterations to the y-axis alignment. Of course, the more surfaces in the polygon, i.e., the more the polygon approximates a circle, the more continuous the rotation of the polygonal element  301  becomes. In the event that the polygonal element  301  is used, it could be attached to a flat surface, for example a surface of the submount  101 , thus eliminating the need for the alignment slot  104  of FIGS.  1 ( a )- 1 ( b ). Such attachment is shown in FIG. 3( b ), in which the polygonal passive optical element  301  is mounted on the same surface of the submount  101  as the optical element  103 .  
         [0029]    Either passive optical element including lens element  110  could be manufactured with standard processes, such as grinding/polishing and molding. The passive optical elements including lens element  110  may be fabricated from known materials, such as Corning BCD C2060 or Schott SK16.  
         [0030]    The passive optical element shown in the previous embodiments was an integral passive optical element. According to another illustrative embodiment shown in FIGS.  4 ( a ) and  4 ( b ), a passive optical element  402  includes a lens element  410  placed eccentrically in a hole or other receptacle  406  in a housing  404  or in an eccentric housing. The housing  404  and the lens element  410  could now be made of different materials.  
         [0031]    It will be obvious that the invention may be varied in a plurality of ways. For example, the alignment slot does not have to be through the substrate, but may extend underneath the passive optical element to provide support thereto. Such variations are not to be regarded as a departure from the scope of the invention. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the appended claims.