Abstract:
A method of aligning an optical fiber to a light source (e.g., a laser diode) in an optical assembly includes inserting a weld clip over a ferrule holding the optical fiber so that there is no gap between the ferrule and the weld clip, initially aligning the optical fiber to the laser diode, fixedly attaching the weld clip to a platform, realigning the optical fiber to the laser diode, and fixedly attaching the weld clip to the ferrule.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1) Field of the Invention  
           [0002]    This invention pertains to the field of optical modules, and more particularly, a method for fabricating an optical module by fixedly attaching an optical fiber to a platform such that the input aperture of the optical fiber remains in alignment with a light output of a light source (e.g., a laser diode) after attachment.  
           [0003]    2) Description of the Related Art  
           [0004]    [0004]FIG. 1 shows an exemplary optical module  100 . The optical module  100  is a so-called “butterfly module,” so named because it has a plurality of electrical leads  105  (e.g., seven) extending from first and second sides  102 ,  104  on opposite sides of the optical module  100 , and an output optical fiber  110  extending from a third side  106  generally perpendicular to the first and second sides  102 ,  104 . The optical module  100  also includes platform  120  on which is mounted a light source (e.g., a laser diode  130 ) which outputs and supplies light to an input aperture  112  of the optical fiber  110 .  
           [0005]    A critical characteristic of the optical module  100  is the alignment of the light output of the laser diode  130  and the input aperture  112  of the optical fiber  110 . Especially in the case of a single mode fiber, it is critically important that the light output of the laser diode  130  be precisely aligned with the input aperture  112  of the optical fiber  110 . However, in the prior art, after the laser diode  130  and the optical fiber  110  are precisely aligned, they are subject to significant misalignment during the process of attaching the optical fiber  110  (and/or the laser diode  130 ) to the platform  120  of the optical module  110 .  
           [0006]    Accordingly, it would be advantageous to provide an improved method of fabricating an optical module. In particular, it would be advantageous to provide such a method including an improved method of fixedly attaching an optical fiber to a platform of the optical module such that the optical fiber and a light source remain precisely aligned even after they are both attached to the platform. Other and further objects and advantages will appear hereinafter.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention comprises a method for fabricating an optical module, including a method of fixedly attaching an optical fiber to a platform of the optical module such that the input aperture of the optical fiber remains in alignment with a light output of a light source (e.g., a laser diode) after attachment.  
           [0008]    In one aspect of the invention, a method is provided for fabricating an optical module including a laser diode producing light, an optical fiber having an input aperture aligned to receive the light, a ferrule fit around an exterior of the optical fiber, and a platform. A weld clip is provided having a pair of vertical walls each connected to a corresponding base wall formed at an angle of less than  90  degrees with respect to the corresponding vertical wall. The weld clip is inserted over the ferrule so that there is no gap between the ferrule and the vertical walls of the weld clip. The optical fiber is initially aligned to the laser diode to substantially optimize (e.g., to substantially maximize) coupling of light into the input aperture of the optical fiber. Next, the weld clip is fixedly attached to the platform via the base walls, creating a gap between the optical fiber and the vertical walls of the weld clip. Subsequently, the optical fiber is realigned to the laser diode to substantially optimize coupling of light into the input aperture of the optical fiber. Finally, the weld clip is fixedly attached to the ferrule.  
           [0009]    In another aspect of the invention, a method is provided for fabricating an optical module including a light source producing light, an optical fiber having an input aperture aligned to receive the light, a ferrule fit around an exterior of the optical fiber, and a platform. The method comprises inserting a weld clip over the ferrule so that there is no gap between the ferrule and the weld clip, initially aligning the optical fiber to the light source to substantially optimize coupling of light into the input aperture, attaching the weld clip to the platform, realigning the optical fiber to the light source to substantially optimize coupling of light into the input aperture; and attaching the weld clip to the ferrule. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a diagram of an exemplary “butterfly” type optical module.  
         [0011]    [0011]FIG. 2 is a side view of a portion of an optical module, illustrating a method of attaching the optical fiber to a platform while maintaining alignment between the optical fiber and a light source;  
         [0012]    [0012]FIG. 3 is a flowchart illustrating steps of a method of attaching the optical fiber to a platform while maintaining alignment between the optical fiber and a light source;  
         [0013]    [0013]FIG. 4 is an end view diagram illustrating one step of a method of attaching the optical fiber to a platform while maintaining alignment between the optical fiber and a light source;  
         [0014]    [0014]FIG. 5 is an end view diagram illustrating another step of a method of attaching the optical fiber to a platform while maintaining alignment between the optical fiber and a light source. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    [0015]FIG. 2 shows a side view of a portion of an optical module  200 . Portions of the optical module  200 , such as electrical leads, having no bearing on the present invention are not shown so as not to obscure the present invention. In relevant part, the optical module  200  includes an optical fiber  210 , a platform  220 , and a light source (e.g., a laser diode  230 ). The optical fiber  210  has an input aperture  212 , which is to be precisely aligned for optimally receiving light from the light source  230 . A ferrule  214  is fit around the exterior of a portion of the optical fiber  210 . The ferrule  214  is adapted to be grasped and thereby permit the optical fiber  210  to be held in place or moved, as desired.  
         [0016]    A weld clip  240  holds and attaches the optical fiber  210  to the platform  220 . Beneficially, the weld clip  240  includes a pair of base walls  242  each connected to a corresponding one of a pair of substantially vertical walls  244 . In on embodiment, the substantially vertical walls  244  include a longer, lower vertical wall portion and a shorter, upper vertical wall portion. An arching bridge beneficially connects the upper vertical walls. Advantageously, as can be seen from FIG. 4, the weld clip  240  is configured such that an angle formed between each substantially vertical wall  244  and the corresponding base wall is less than 90 degrees (i.e., an acute angle).  
         [0017]    [0017]FIG. 3 illustrates steps of a method  300  of attaching the optical fiber  210  to the platform  220  while insuring alignment between the optical fiber  210  and the light source  230 .  
         [0018]    In a first step  310 , the weld clip  240  is inserted over the ferrule  214 . At this time, the weld clip  240  is rather forcefully inserted over the ferrule  214  such that the ferrule is in contact with the inside surfaces of the substantially vertical walls  244  of the weld clip  240 . That is, no gap exists between the ferrule  214  and the inside surfaces of the substantially vertical walls  244  of the weld clip  240 , and there exists friction between the ferrule  214  and the inside surfaces of the substantially vertical walls  244  of the weld clip  240 . Moreover, beneficially, the weld clip  240  is inserted in such a way that it creates friction between the weld clip  240  and the platform  220  during the subsequent alignment. Such friction is only apparent at the beginning of the alignment process.  
         [0019]    In a step  320 , the ferrule  214  is grasped, beneficially by a mechanical arm of a robot (not shown). The mechanical arm may optionally grasp the ferrule  214  before the weld clip  240  is inserted over the ferrule  214  in the step  310 . The mechanical arm thereby moves the optical fiber  210  until it achieves a substantially optimal (e.g., a substantial maximum) coupling of light from the laser diode  230  input the input aperture  212  of the optical fiber  210 . Beneficially, a feedback system is used to control the mechanical arm. To optimally align the optical fiber  210  and the laser diode  230 , an output end of the optical fiber  210  is connected to a measurement apparatus for measuring an intensity of light emerging from the optical fiber  210 . Based on the measured light intensity, the measurement apparatus produces a feedback signal that is used to control the mechanical arm to achieve substantially optimal coupling of light from the laser diode  230  into the input aperture  212  of the optical fiber  210 . The mechanical arm continues to move the ferrule  214  and the optical fiber  210  until substantially optimal light coupling into the optical fiber  210  is achieved.  
         [0020]    Typically, at the end of the alignment step  320 , the base walls  242  of the weld clip  240  hover or float a couple of microns above the platform  220 , as shown in FIG. 4. Also, beneficially, the base walls  242  of the weld clip  240  are not quite parallel with the top surface of the platform  220 . Instead, as illustrated in FIG. 4, the base walls  242  of the weld clip  240  extend at a small, acute angle with respect to the top surface of the platform  220 .  
         [0021]    After the optical fiber  210  is aligned to the light from the laser diode  230 , then in a step  330  the weld clip  240  is fixedly attached to the platform  220 , preferably by means of a first set of welds  250 , shown in FIG. 2. Upon welding the weld clip  240  to the platform  220 , the base walls  242  of the weld clip  240  are pulled against the platform  220  due to shrinking of the melted metal as it cools down. As shown in FIG. 5, this in turn opens up the substantially vertical walls  244  of the weld clip  240 , drawing them apart and away from the ferrule  214 , thus releasing the ferrule  214  from being gripped by the weld clip  240  which is now attached to the platform  220 . In other words, when the base walls  242  of weld clip  240  are welded to the platform  220 , the substantially vertical walls  244  of the weld clip  240  are drawn away from the ferrule  214 , opening up to produce a gap between the ferrule  214  and the inside surfaces of the substantially vertical walls  244  of the weld clip  240 . This gap allows for virtually frictionless movement of the ferrule  214  in the vertical direction, while keeping the gap at a minimum.  
         [0022]    Beneficially, the gap allows for a very small or even no weld shift of the ferrule  214  and optical fiber  210  in the horizontal direction after the weld clip  240  is attached to the platform  220 .  
         [0023]    The gap greatly simplifies the subsequent realignment &amp; bending steps  340 - 370 . In the step  340 , the mechanical arm again moves the ferrule  214  to realign the optical fiber  210  until a substantially optimal (e.g., a substantial maximum) coupling of light from the laser diode  230  into the input aperture  212  of the optical fiber  210  is again achieved. As in the step  320 , beneficially a feedback arrangement is employed to determine the optimal position of the optical fiber  210 .  
         [0024]    Next, in a step  350 , the optical fiber  210  is moved vertically with respect to the optical platform  220  by a predetermined amount to account for a settling of the optical fiber  210  that will occur after cooling of the welds produced during a subsequent welding step  360 . In a preferred embodiment, the cooling of the welds will produce a negative vertical displacement of the optical fiber  210  of 6-9 μm with respect to the optical platform  220 . Accordingly, before the welding step  360 , the optical fiber  210  is moved vertically with respect to the optical platform  220  by 6-9 μm, beneficially 7.5 μm.  
         [0025]    Next, in a step  360 , the weld clip  240  is fixedly attached to the ferrule  214 , preferably by means of a second set of welds  260 , as shown in FIG. 2.  
         [0026]    Beneficially, in a final step  370 , the optical fiber  210  attached to the optical platform  220  via the weld clip  240  is bent slightly to optimize alignment with the laser diode  230 .  
         [0027]    Disclosed above is a method for attaching an optical fiber to an optical module such that the input aperture of the optical fiber remains in alignment with a light output of a light source after attachment. The method insures that the optical fiber and light source will remain precisely aligned even after they are both attached to a platform of the optical module.  
         [0028]    While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.