Abstract:
A precision optical centering device for a passive optical element includes a first feature on a substrate which secures and centers the passive optical element in the alignment device and a second feature on the substrate which is adapted to mate the substrate to another separate substrate having another optical element to which the passive optical element is to be coupled. The first feature aligns the passive optical element to the other optical element along the y-axis when the substrates are mated. The position of the passive optical element may be altered along the x-axis and/or the z-axis before the device is secured to the separate substrate. The device may be actively or passively aligned.

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. 60/276,131 entitled “Precision Optical Centering Device” 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 interconnects, and particularly to a device and method to align the optic axes of optical elements.  
         BACKGROUND OF THE INVENTION  
         [0003]    Typically coupling between optical components has involved stack up or vertical arrangements. Stack up arrangements involve complicated assembly processes using multiple pieces, active alignments, and/or compromised optical performance. Solutions involving v-grooves for providing alignment typically require providing a v-groove in a substrate housing the optical element with which the optical element in the v-groove is to be coupled. This requires very high precision manufacturing for the depth and position of the v-groove, which must be assumed to work for a predetermined size of an optical element to be received therein.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to an optical centering device and method which overcomes at least one of the above disadvantages.  
           [0005]    It is an object of the present invention to provide a structure for aligning optical elements in a manner which reduces stack-up tolerances.  
           [0006]    To achieve the above and other objects, an alignment block includes a holding section which holds an optical element at a substantially precise position. The alignment block is located in a manner in which the holding section is substantially aligned to another optical device.  
           [0007]    By virtue of the present invention, precise alignment of the optical device held in the holding section to the other optical device is facilitated.  
           [0008]    At least one of the above and other objects of the present invention may be realized by providing an alignment device for a passive optical element including a first feature on a substrate which secures the passive optical element in the alignment device and a second feature on the substrate which is adapted to mate the substrate to another separate substrate having another optical element to which the passive optical element is to be coupled. When the substrate is mated with the another substrate, the first feature aligns the passive optical element to the another optical element along a first axis and the second feature is attached to the another substrate to align the passive optical element to the another optical element along a second axis, different from the first axis.  
           [0009]    At least one of the above and other objects of the present invention may be realized by providing a method for aligning optical elements on separate substrates, the method including securing a passive optical element in a first feature on a first substrate, aligning the first substrate to a second substrate having an optical element thereon, the first feature aligning the passive optical element with the optical element along a first axis and positioning the first substrate relative to the second substrates along a second axis, different from the first axis, and attaching aligned first and second substrates via a second feature of the first substrate to provide optical coupling between the passive optical element and the optical element.  
           [0010]    The securing of the passive optical element in the first feature may include providing the passive optical element in a groove in the first substrate, the groove serving as the first feature. The groove may be a V-groove. The mounting may include an arm in the first substrate extending, either laterally and/or longitudinally, over the second substrate when the first and second substrates are mated, the arm serving as the second feature. The securing of the passive optical element may occur before or after the securing of the aligned first and second substrates. The passive optical element may be removed after the attaching of the aligned first and second substrates. The position of the passive optical element along a third axis, different from the first and second axes, after the securing and the attaching  
           [0011]    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  
       [0012]    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.  
         [0013]    [0013]FIG. 1( a ) is a perspective front view of an alignment block according to an illustrative embodiment of the present invention.  
         [0014]    [0014]FIG. 1( b ) is a perspective rear view of an alignment block according to an illustrative embodiment of the present invention.  
         [0015]    [0015]FIG. 2( a ) is a perspective rear view of an aligmnent block according to another illustrative embodiment of the present invention.  
         [0016]    [0016]FIG. 2( b ) is a magnified view of an alignment block according to an illustrative embodiment shown in FIG. 2( a ).  
         [0017]    [0017]FIG. 2( c ) is a perspective front view of an alignment block according to an illustrative embodiment of the present invention.  
         [0018]    [0018]FIG. 2( d ) is a magnified view of an alignment block according to an illustrative embodiment shown in FIG. 2( c ).  
         [0019]    [0019]FIG. 3 is a front view of an alignment block according to an illustrative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]    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.  
         [0021]    Turning to FIGS.  1 ( a ) and  1 ( b ), the alignment block  101  is shown. A holding section  102  is shown having a substantially precisely located passive optical element  103 . The alignment block  101  also includes a mating section  108  which mates the alignment block  101  to another substrate having an optical element thereon. In FIGS.  1 ( a ) and  1 ( b ), the mating section  108  includes two arms which extend longitudinally from the alignment block  101 .  
         [0022]    In the illustrative embodiment of FIGS.  1 ( a ) and  1 ( b ), the passive optical element  103  is a lens element. This lens element could be a spherical lens, a gradient refractive index (GRIN) lens, or other lens element well within the purview of one having ordinary skill in the art. Although not shown in FIGS.  1 ( a ) and  1 ( b ), this passive optical element  103  could also be an optical fiber. The alignment block  101  provides accurate registration of the optical axis of the optical element  103 . To this end, in the illustrative embodiment shown in FIG. 1( a ), the optical axis of the passive optical element  103  would be along the z-direction. As would be readily apparent to one having ordinary skill in the art, it is important to assure that the x-y registration, again see FIG. 1( a ), of the optical element is precisely located, as well. Accordingly, the holding section  102  is designed such that precise placement/alignment of the passive optical element  103  is fostered. This placement enables coupling of the passive optical element  103  to another optical element, for example an active optical element  104  shown in FIGS.  1 ( a ) and  1 ( b ).  
         [0023]    In the illustrative embodiment shown in FIGS.  1 ( a ) and  1 ( b ), a submount  105  may be an optical subassembly or other type of optical bench or substrate. The submount  105  may include an active optical device  104 , illustratively a laser or light emitting diode (LED), or other active device including an optical detector. If an active optical device  104  is provided on the submount  105 , the submount  105  may include contact pads  106  to provide electrical connection to the active optical device  104 . Moreover, the submount  105  may include other passive optical devices. In either case, the passive optical element  103  may be precisely aligned to various optical elements on the submount  105 .  
         [0024]    The holding section  102  of the alignment block  101  provides centering. The alignment block  101  could be fabricated via a number of well known technique such that the holding section, which resembles “V”-shape is precisely located to a mounting surface. Illustratively, the mounting surface is the submount  105 . In the illustrative embodiment shown in FIGS.  1 ( a ) and  1 ( b ), the “V”-shaped holding section  102  is slightly undersized to provide a clamping or friction force on the passive optical element  103 .  
         [0025]    The provision of the passive optical element  103  in the alignment block  101  separate from the submount  105  allows the relative positioning of the alignment block  101  and the optical element  104  on the submount  105 . In particular, the holding section  102 , in conjunction with the mating section  108 , positions the passive optical element  103  in the Y-direction. Before the alignment block  101  is secured to the submount  105 , but while mated to the submount  105 , the alignment block  101  may be moved along the X-axis and/or the Z-axis to more precisely align the optical elements  103 ,  104 . This alignment may be active, i.e., while the active optical element  104  is on, or passive. If passive alignment is employed, the contact pads  106  may be used as passive alignment features. Of course, other passive alignment features may be provided on the submount  105  as needed.  
         [0026]    During alignment, the alignment block  101  may be held by some tooling attached to the alignment system, e.g., a robot or translational stages. This holding may be realized using a vacuum or a mechanical clamp. Any conventional attachment manner may be used to attach the alignment block  101  to the submount  105 . For example, epoxy or other bonding material may be used. Additionally, the submount  105  and the alignment block  101  could be metalized and then soldered together. The alignment block  101  may be made of a material having a coeffecient thermal expansion which matches that of the submount  105  for performance reliability. The alignment block  101  may be made of a mechanically stable material, so that the alignment block  101  does not change shape over time, thus affecting the coupling.  
         [0027]    Turning to FIG. 2( a ), another illustrative embodiment of the present invention is shown. In the illustrative embodiment shown in FIG. 2( a ), an alignment structure  201  is mounted to a surface of a substrate  205 . The substrate  205  may include an active optical device  204 , e.g., a laser or a detector. In the illustrative embodiment in which the active optical device  204  is coupled to a passive optical device  203 , such as an optical fiber, the active optical device  204  is disposed over the substrate  205  such that its active area is substantially in the same plane as the top surface of the substrate  205 .  
         [0028]    Shown in magnified view in FIG. 2( b ), the alignment structure  201  includes a holding section  202  which holds a passive optical device  203  in the alignment structure  201  and a mating section  208  which mates the alignment structure  201  to the substrate  205 . In FIGS.  2 ( a )- 2 ( d ), the passive optical element  203  is illustratively an optical fiber. The optical fiber  203  is optically coupled to an active optical device  204 , illustratively a laser. Of course, the illustrative embodiment of FIGS.  2 ( a ) and  2 ( b ) could be used to facilitate alignment of a passive optical element  203  to other devices. Illustratively, other devices could include active devices such as light emitting devices, as well as detecting devices. Moreover, the alignment structure  201  could be used to precisely align passive optical elements (not shown) disposed on the substrate  205  to other passive optical elements, such as optical fiber  203 .  
         [0029]    Turning to FIG. 2( c ), a perspective front view according to an illustrative embodiment of the present invention is shown. The optical fiber  203  is passively aligned in the alignment structure  201 . Again, the active optical device  204  is disposed over a substrate  205 . Shown in a magnified view in FIG. 2( d ), the optical fiber  203  is precisely aligned and held in holding section  202 . The holding section  202  constrains the fibers  203  such that the only the z-axis of the fiber can be adjusted once the alignment structure  201  is attached to the substrate  205 . This embodiment of the invention could be used as a fiber receptacle. Once the alignment structure  201  is aligned to the active optical device  204 , a fiber could be inserted or removed until ultimately required. The alignment of the alignment structure  201  to the active optical device  204  in the passive alignment case may use machine vision. The V&#39;s of the holding section  202  or additional features on the top  201  may be used to determine the x-axis position, where the x-axis is orthogonal to fiber axis and parallel to the top of  205 . Further, passive alignment features may be provided on the top of the submount  205  and/or in a face of a notch  210  in the submount  205  to facilitate passive alignment. If active alignment is used, a fiber may be provided in the holding section  202  during x-axis alignment.  
         [0030]    As can be seen in FIGS.  2 ( a ) and  2 ( c ), the submount  205  provides further structural support to the alignment structure  201 . In FIGS.  2 ( a )- 2 ( d ), the mating section  208  includes arms laterally extending from the alignment structure  201 , so placement of the alignment structure  201  effectively mounts the alignment structure  201  on the substrate  205 . However, the notch  210  in the substrate  206  allows the alignment structure  201  to be moved in the X-direction and/or Z-direction prior to securing the alignment structure  201  to the submount  205 . The securing of the alignment block  201  to the submount  205  may be realized in any of the manners noted above regarding the first embodiment.  
         [0031]    Finally, turning to FIG. 3, a front view of the alignment block  201  according to an illustrative embodiment of the present invention is shown. The alignment block includes a holding section  202  which precisely aligns an passive optical device (not shown in FIG. 3) to another optical device. As described briefly above, the alignment block  201  precisely centers and aligns the optic axis of the passive optical component to the optic axis another optical device, such as the active optical device  204 .  
         [0032]    In both of these configurations, the passive optical element may either be secured in an alignment device, and then this alignment device is secured to a separate submount having another optical element thereon, or the alignment device may be aligned and attached to the submount and the passive optical element inserted thereafter. Further, either configuration could align any desired passive optical element if appropriately formed. If the passive optical element has an elongated shape, i.e., extends beyond the clamping section of the alignment structure, such as a GRIN or a fiber, z-axis alignment may be altered even after the alignment structure has been secured to the submount.  
         [0033]    The securing section as shown in all of the embodiments is a pair of facing opposed V-grooves. This configuration allows optical elements of different sizes to be centered in the securing section, obviously as long as the optical element can be accommodated in the securing section. While the provision of an optical element in the securing section having a smaller diameter than the optical element for which the securing section was designed will not be as precisely centered as the designed for element, for many applications this centering is sufficient and increases the application flexibility of the alignment device. Any configuration which allows centering of differently sized optical elements, particularly those allowing optical elements to be removed and inserted from a secured alignment device, may be employed. For example, a number of differently shaped grooves may be employed, the opposing grooves do not need to have the same shape, and there may only be one groove opposite a flat surface.  
         [0034]    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.