Abstract:
A device for holding a component of a fiber optic circuit on a substrate includes two resilient arms or two series of spring fingers, one on each side of the component. Ideally, the substrate is crystalline silicon and the arms or fingers are fabricated using a DRIE etching process. The holding device is particularly suited for securing an optical fiber in a groove, but it can also be used for fixing other components, i.e. lenses.

Description:
FIELD OF INVENTION  
         [0001]    The present invention relates to a device for holding a component on a substrate, and in particular to a device for holding an optical component, such as an optical fiber, in a groove etched in a crystalline silicon substrate.  
         BACKGROUND OF THE INVENTION  
         [0002]    Recent demands in the fiber optics industry to increase durability and decrease cost have led to the use of micro-electromechanical systems (MEMS) in key optical components. However, problems arise when other components are to be connected to the substrate. In particular, the positioning of optical fibers and lenses on the substrate has led to a variety of problems.  
           [0003]    In the past these other components have been fixed to the substrate using epoxy resins. For example. U.S. Pat. No. 5.937,132 issued Aug. 10, 1999 in the name of Pierre Labeye et al discloses a process and a system for positioning and holding optical fibers in a groove using an adhesive material introduced therein. Unfortunately, there are several applications in which the use of epoxy resins is not acceptable, e.g. in 980 nm pump laser sources for fiber amplifiers, the use of organic materials such as epoxy resins is undesirable because of the damage to the laser facet.  
           [0004]    Another method of fixing components to a substrate is to solder or weld a separate holder overtop of the fiber. U.S. Pat. Nos. 5,717,803, issued Feb. 10, 1998 in the name of Isao Yoneda et al, and 5,367,140, issued Nov. 22, 1994 to Musa Jouaneh et al disclose coupling methods utilizing a separate holder requiring welding or soldering to the substrate.  
           [0005]    U.S. Pat. No 4,788,406, issued Nov. 29, 1988 to Robert Holman et al, is indicative of another approach used to attach an optical fiber to a substrate. In this approach, a metallic sleeve is coated or mounted on the end of the fiber, so that the sleeve can be welded to a plate of similar material mounted on the substrate.  
           [0006]    So far, the use of soldering or welding techniques to fix optical components to a substrate is quite labor intensive, requiring several additional steps to modify the elements, whereby they can be connected.  
           [0007]    U.S. Pat. No. 5,961,849, issued Oct. 5, 1999 to Robert Bostock et al, discloses another mounting method, in which a MEMS device is used to hold down an optical fiber in a groove. This device is also relatively complicated to manufacture, requiring the deposition of a special layer onto the substrate. Moreover, many MEMS devices require power to operate.  
           [0008]    It is an object of the present invention to avoid the shortcomings of the prior art by providing a relatively simple mounting device to hold an optical component on a substrate without the need for adhesives, solder or welds, and without the need for power consumption.  
           [0009]    Accordingly, the present invention relates to a device for holding a component on an substrate comprising first and second opposed resilient arm means extending from the substrate for holding the component therebetween. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention will be described in greater detail with reference to the accompanying drawings, which illustrate preferred embodiments of the invention, wherein:  
         [0011]    [0011]FIG. 1 is a top view of a component holding device according to the present invention;  
         [0012]    [0012]FIG. 2 is a cross-sectional view of the device of FIG. 1 taken along line A-A;  
         [0013]    [0013]FIG. 3 is a cross-sectional view of the device of FIG. 1 illustrating the spring fingers experiencing twist;  
         [0014]    [0014]FIG. 4 is a top view of a second embodiment of the component holding device according to the present invention;  
         [0015]    [0015]FIG. 5 is a cross-sectional view of the device of FIG. 4 taken along line B-B;  
         [0016]    FIGS.  6  to  11  are side views of the substrates used in the present invention at various stages during the manufacturing thereof-,  
         [0017]    [0017]FIG. 12 is an end view of a third embodiment of the component holding device according to the present invention;  
         [0018]    [0018]FIG. 13 is an end view of the device of FIG. 12 with an optical fiber in place;  
         [0019]    [0019]FIG. 14 is a top view of the device of FIGS. 12 and 13;  
         [0020]    [0020]FIG. 15 is an end view of a fourth embodiment of the component holding device according to the present invention;  
         [0021]    [0021]FIG. 16 is an end view of the device of FIG. 14 with a lens in place;  
         [0022]    FIGS.  17  to  21  illustrate a series of steps using another embodiment of the invention to lock an optical fiber on a substrate;  
         [0023]    FIGS.  22  to  25  illustrate additional steps taken to interlock the present invention with the component; and  
         [0024]    FIGS.  26  to  28  illustrate a further embodiment of the present invention in which the component is mounted in a housing. 
     
    
     DETAILED DESCRIPTION  
       [0025]    With reference to FIGS.  1  to  5 , the device of the present invention is formed in a substrate  1 , typically crystalline silicon, comprised of an upper wafer  2  and a lower wafer  3  with a silicon dioxide layer  4  therebetween. The device holds an optical fiber  6  in a rectangular groove  7  in alignment with an opening  8 . The opening  8  allows the fiber  6  to be optically coupled with another component, e.g. a laser alignment platform (not shown). The holding device includes a first series of elongated rectangular spring fingers  9  extending outwardly and laterally from one side of the groove  7 , and a second series of elongated rectangular spring fingers  1 I 1  extending outwardly and laterally from the other side of the groove  7 . The second series of spring fingers  1 I 1  are generally opposed to the first series of spring fingers  9 , each series of fingers applying an equal and opposite lateral force onto the fiber  6  to prevent lateral movement thereof. In the preferred arrangement, illustrated in FIGS.  1  to  5 , the first and second series of spring fingers  9  and  11  extend outwardly in opposite directions and laterally in the same general direction, towards the end of the groove with the opening  8 . Typically, the spring fingers extend from the walls of the groove at approximately a 60° angle, although any angle is possible as long as the resulting force of the spring fingers is sufficient to hold the fiber in place. This arrangement makes withdrawal of the fiber  6  much more difficult than insertion. In practice, the fiber  6  is inserted between the two sets of spring fingers  9  and  11 , which causes them to deform (FIGS. 1 and 4), until the end of the fiber  6  abuts a shoulder  12  of the opening  8 , thereby locking the fiber  6  in place.  
         [0026]    To increase the downward force on the optical fiber the spring fingers  9  and  11  are adapted to contact the fiber  6  above the horizontal central axis thereof. In the aforementioned basic arrangement, the spring fingers  9  and  11  twist slightly about their longitudinal axis, due to the fact that they contact the fiber below their midline (See FIG. 3). This twisting raises the point of contact of the finger on the fiber, thereby providing the downward force. Alternatively, having an upper portion of the spring fingers  9  and  11  sloped inwardly towards each other, also accomplishes this objective. As best seen in FIG. 5, the entire inner surfaces  13  and  14  of the spring fingers  9  and  11 , respectively, can be sloped inwardly, resulting in wedge-shaped fingers.  
         [0027]    The number of springs and their dimensions is a function of the overall package requirement and is determined from fiber insertion and location force requirements. If we assume that each spring finger has a width b and a length L, and that the upper wafer has a thickness t, we can calculate the spring constant K from:  
       K   =       3   ×   E   ×   I       L   3                 where                 I     =           b   3                   t     12                   and                 E                 is                   Young   &#39;        s                 Modulus                           
 
         [0028]    Deep reactive ion etch (DRIE) processes, such as those offered by Surface Technology Systems Ltd., are highly anisotropic and capable of machining mechanical structures within silicon which cannot be realized with wet etch techniques. In particular, the ability to produce features with vertical side walls, enables low stress micro-mechanical systems to be manufactured. Accordingly, if the DRIE process is already being used on the substrate in the fabrication process, the component holding device according to the present invention can be machined at the same time using this process by adding the features to the appropriate etch mask.  
         [0029]    A silicon-on-insulator (SOI) structure or a silicon wafer annodically bonded to glass are two of the possibilities for manufacturing the device so that the springs are suspended above the bottom of the groove. The use of the SO 1  is often preferable because of the superior thermal conductivity properties of silicon relative to glass. FIGS.  6  to  11  illustrate an example of a series of steps using an SOI structure in the manufacture of the embodiment of the present invention illustrated in FIGS.  1  to  5 .  
         [0030]    Initially, a masking layer  16  is applied to the upper surface of lower silicon wafer  3  (FIG. 6), and shallow channels  17  are etched therefrom (FIG. 7). Subsequently, upper wafer  2 , with intermediate oxidized layer  4 , is fusion bonded on top of lower wafer  3  (FIG. 8). An appropriate mask  18  is applied to the top layer of upper wafer  2  (FIG. 9), and grooves  7  with spring fingers  9  and  11  are etched out down to intermediate layer  4  (FIG. 10). Lastly, an appropriate amount of the intermediate layer  4  is removed, freeing the spring fingers  9  and  11  (FIG. 11).  
         [0031]    FIGS.  12  to  14  illustrate another embodiment of the present invention, in which spring fingers  20  extend upwardly from the bottom of a groove  21 , formed in silicon wafer  22 . Preferably, the inner wall  23  of the upper end of each spring finger  20  is angled inwardly, thereby applying a downward force on the fiber  6  and/or restricting upward movement of the fiber  6 .  
         [0032]    [0032]FIGS. 15 and 16 illustrate a third embodiment of the present invention, in which L-shaped spring arms  31  extend downwardly into groove  32 , etched into substrate  33 . In FIG. 15, the spring arms  31  are in a relaxed position. In FIG. 16, the spring arms  31  are slightly bent and a lens  34  is held therebetween, suspended in the groove  32  by the opposed spring forces of the spring arms  31 . The lens  34  is mounted in a trench  36 , formed in each spring arm  31 , to prevent any vertical movement thereof. Ideally, the groove  32  is made wide enough to enable the spring arm  31  to be spread apart wide enough to receive the lens  34 . Alternatively, the sides of the trench  36  are resilient enough to allow the lens  34  to be mounted therein.  
         [0033]    In certain applications, the substrate is not provided with a shoulder  12  to halt the insertion of fiber  6 . FIGS.  17  to  21  illustrate an alternative means to prevent insertion and/or withdrawal of the fiber  6 . Initially, a locking cleat  41  is mounted on an optical fiber  6  at a distance down the fiber  6  greater than the distance that the fiber  6  is to be inserted. The locking cleat  41  includes a first series of spring fingers  42  and a second series of spring fingers  43  extending into a groove  44 , formed in a silicon substrate  45 . A special MEMS tool (not shown) is used to open the spring fingers  42  and  43  so that the locking cleat  41  can be slid onto the fiber  6  in a direction opposite to the normal insertion direction. In this position the locking cleat  41  is prevented from sliding any further down the fiber  6 , but is able to slide back towards the end  46  of the fiber. With reference to FIGS.  19  to  21 , the fiber  6  is inserted into a normal holding device  47 , which includes spring fingers  48  and  49  extending into a groove  50  formed in a substrate  51 , until the end of the fiber  46  is correctly positioned proximate component  52 . At which time, the locking cleat  41  is slid back towards the end of the fiber  46  until abutting an edge  53  of the substrate  51 . In this position (FIG. 21) the fiber  6  is locked in both axial directions, unable to be inserted because of spring fingers  42  and  43 , unable to be withdrawn because of spring fingers  48  and  49 .  
         [0034]    With reference to FIGS.  22  to  25 , additional steps can be made to more securely interlock the spring fingers  9  and  11  to the component, which in the illustrated example is optical fiber  6 . Initially, one or more glass pre-forms  61 , made of low melting-point glass material, are positioned in the gaps between the upper portion of the spring fingers  9  or  11  and the upper portion of the component  6 . The pre-forms  61  can be in any suitable form, including rods, balls or powder. In the second step, the pre-forms  61  are melted, causing the material to flow around the fiber  6  and in between the spring fingers  9  and  11 . A CO 2  laser, generally indicated by arrows  62 , is preferably used to melt the pre-forms  61 , creating melt zones  63  (FIG. 25). The resulting melt zones  63  increase the contacting surface area between the fiber  6  and the fingers  9  and  11 , providing added stability therebetween. In most cases it is preferable to form the pre-forms  61  out of glass, which has a melting point below that of the fiber  6  and the substrate  1 , so that when the pre-forms  61  are melted neither the fiber  6  nor the substrate  1  undergo any localized melting. Moreover, it is preferable that the selected glass wets to the substrate to form a bond therebetween. A suitable coating can be added to the fiber and substrate to facilitate this bonding.  
         [0035]    When the optical component  70  (FIG. 26) is too small, too fragile or has an incompatible shape, a housing  71  is provided for mounting the component  70  therein. In its simplest form, the housing  71  has a rectangular body  72  with first and second rectangular channels  73  and  74  formed in opposite sides thereof. The channels  73  and  74  are adapted to be engaged by the first and second spring fingers  76  and  77 , respectively, for holding the housing  71  in the groove  7 . Alternatively, one side of the groove  7  can be formed with a projection  78  for engaging the first channel  73 , while one of the spring fingers  77  engages the second channel  74  (see FIG. 28). With reference to FIG. 29, spring finger  77  can be in any one of a variety of forms including a baffle spring  79 . If the housing  71  is mounted in a recess in the substrate instead of a groove, the channels  73  and  74  can be formed in any of the sides of the housing  71 . Similarly, the spring fingers  76  and  77 , and/or the projection  78  would then be formed accordingly. The projection  78  can also take any one of a variety of forms other than the illustrated form, including a plurality of fingers.