Abstract:
An optical module box made of aluminum that has a reworkable glass-sealed fiber feedthru is disclosed. A fiber is inserted through a glass seal and a C-seal for hermetically sealing an opening in the optical module box. In a first embodiment, a module box employing a single-fiber fiber feedthru is described. In a second embodiment, a module box employing a 2-fiber feedthru is described. In a third embodiment, a module box employing a ribbon fiber feedthru is described. A module box having an opening with a single-fiber feedthru, comprising a C-seal; a glass sealed feedthru having a front tube and a back tube, the back tube of the glass sealed feedthru extending through the C-seal; and a fiber passing through the glass sealed feedthru and the C-seal, thereby hermetically sealed into the opening of the module box.

Description:
BACKGROUND INFORMATION 
   1. Field of the Invention 
   The invention relates to the field of telecommunications, and more particularly to the assembly of optical modules. 
   2. Description of Related Art 
   Fiber optics transmission is a common platform for transporting voice, data, and images. As the demand for data carrying capacity continues to increase, optical companies are seeking techniques to utilize the bandwidth of existing fiber-optic cables more efficiently while enhancing the performance. Typically, the performance of optical devices is sensitive to its operational environment, such as humidity and pressure. Optical devices generally require a tight sealing package, i.e. hermetic sealing package, in order to prevent moisture or any other gas from passing through, ensuring a reliable performance during the life span of an optical module. 
   Conventionally, sealing techniques using epoxy and aluminum ferrule have been selected for implementing fiber feedthrus. Both of these solutions, however, are insufficient in their compliance to a more stringent sealing requirement. The higher stringent sealing requirement also makes an optical module more susceptible to sensitivities. Modernly, optical companies in the telecommunication industry that make optical modules are required to use a reliable sealing method which complies with the environmental reliability specifications in designing and manufacturing optical components and modules. The epoxy sealing technique is less flexible in that it is not reworkable. An epoxy-type material fills the pore in optical fiber holes and the optical package is baked at an elevated temperature until the epoxy dries. Once the epoxy dries, the optical module is therefore not reworkable. 
   Accordingly, it is desirable to have sealing techniques for optical modules that are less sensitive to meet a more stringent sealing requirement as well as making the optical module sealing reworkable. 
   SUMMARY OF THE INVENTION 
   The invention describes an optical module box made of aluminum that employs a glass-sealed fiber feedthru which is reworkable. A fiber is inserted through a glass seal and a C-seal for hermetically sealing an opening in the optical module box. In a first embodiment, a module box employing a single-fiber fiber feedthru is described. The second embodiment describes a module box that employs a 2-fiber feedthru. In a third embodiment, a module box employing a ribbon fiber feedthru is described. 
   A module box having an opening with a single-fiber feedthru, comprising a C-seal; a glass-sealed feedthru having a front tube and a back tube, the back tube of the glass-sealed feedthru extending through the C-seal; and a fiber passing through the glass-sealed feedthru and the C-seal, thereby hermetically sealing into the opening of the module box. 
   Advantageously, the present invention allows the module box to be reworkable by using a C-seal, which provides the flexibility for replacing a fiber connection when necessary. 
   Other structures and methods are disclosed in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a pictorial diagram illustrating a cross-sectional view of a module box employing a reworkable glass-seal fiber feedthru with a C-seal in accordance with the present invention. 
       FIG. 2  is a pictorial diagram illustrating a first embodiment of a module box employing a single-fiber feedthru in accordance with the present invention. 
       FIG. 3  is a pictorial diagram illustrating a second embodiment of a module box employing a 2-fiber feedthru in accordance with the present invention. 
       FIG. 4  is a pictorial diagram illustrating a third embodiment of a module box employing a ribbon fiber feedthru in accordance with the present invention. 
       FIG. 5  is a pictorial diagram illustrating a sectional view of the module box employing the 2-fiber feedthru as described with respect to  FIG. 3  in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , there is shown a pictorial diagram illustrating a module box  100  employing a reworkable glass-seal fiber feedthru with a C-seal. Three principle elements are used in hermetically sealing this design: a module box  100  made of aluminum, a ferrule sub-assembly  110 , and a C-seal  120 . The ferrule sub-assembly  110  comprises a glass-seal  130  and a fiber  140 . The ferrule sub-assembly  110  is hermetically sealed by using the glass seal  130  and the C-seal  120  for sealing the opening where the fiber  140  extends into the module box  100 . The fiber  140  extends firstly through the glass seal  130 , extends secondly through the C-seal  120 , and subsequently hermetically seals the module box  100 . The ferrule sub-assembly  110  is preferably made of Kovar, or other similar or equivalent materials. 
   The C-seal  120  is a metal-to-metal seal that is suitable for hermetic sealing. The use of the C-seal  120  allows the ferrule sub-assembly  110  and the fiber  140  to be reworkable when it is necessary to replace with a new one. A clamp  150  is used to clamp down a rubber boot  160  for enhancing hermetically sealing of the fiber  140  into the module box  100 . At the entrance of the glass seal  130  by the fiber  140 , an epoxy overfillet  170  is placed in front of the glass seal  130 . The module box  100  can be made of aluminum or other similar materials that are suitable for hermetic sealing. 
   Turning now to  FIG. 2 , there is shown a pictorial diagram illustrating a first embodiment of a module box  200  employing a single-fiber feedthru. In this embodiment, the module box  200  has two entry openings where a first single-fiber feedthru sub-assembly  210  is hermetically sealed into a first opening of the module box  200  and where a second single-fiber feedthru sub-assembly  250  is hermetically sealed into a second opening of the module box  200 . One of ordinary skill in the art should recognize that additional single-fiber feedthrus can be added without departing from the spirits of the present invention. 
   A first fiber  220  passes through a first opening in a feedthru holder  224 , a first glass-sealed feedthru  226  and a first C-seal  228  into the first opening of the module box  200 . A second fiber  260  passes through a second opening in the feedthru holder  224 , a second glass-sealed feedthru  266 , and a second C-seal  268  into the second opening of the module box  200 . The combination of the first glassed-sealed feedthru  226  pressing through the first C-seal  228  into the first opening of the module box  200  and the second glassed-sealed feedthru  266  pressing through the second C-seal  268  into the second opening of the module box  200  hermetically seals the module box  200 . A set of screws  223 ,  243  and  263  are used, together with a set of split lock washers  222 ,  242  and  262 , respectively for pressing the feedthru holder  224  into the module box  200 , thereby mechanically sealing the module box  200 . The screw  223  passes through a split lock washer  222 , passes through a first opening of the feedthru holder  224 , and presses into the module box  200 , the screw  243  passes through a split lock washer  242 , passes through a second opening of the feedthru holder  224 , and presses into the module box  200  and the screw  263  passes through a split lock washer  262 , passes through a third opening of the feedthru holder  224 , and presses into the module box  200 . 
     FIG. 3  is a pictorial diagram illustrating a second embodiment of a module box  300  employing a 2-fiber feedthru. Two fibers, a first fiber  310  and a second fiber  311 , are used with a set of sub-assembly  305  to hermetically seal the module box  300 . The sub-assembly  305  comprises a first fiber  310 , a second fiber  311 , a glass-sealed 2-fiber feedthru with integrated holder  314 , and a C-seal  316 , a strain relief or rubber boot  315 , a first screw  320 , a first split lock washer  312 , a second screw  321  and a second split lock washer  313 . The first fiber  310  passes through a first opening  314   a  in the glass-sealed 2-fiber feedthru with integrated holder  314  and passes through the C-seal  316  into a first opening of the module box  300 . The second fiber  311  passes through a second opening  314   b  in the glass-sealed 2-fiber feedthru with integrated holder  314  and the C-seal  316  into a second opening of the module box  300 . A pair of screws  320  are used, together with a set of split lock washers  312  and  313 , respectively for pressing the glass-sealed 2-fiber feedthru with integrated holder  314  into the module box  300 , thereby hermetically seals the module box  300 . The screw  320  passes through a split lock washer  312 , passes through the glass-sealed 2-fiber feedthru with integrated holder  314  and presses into the module box  300 . The screw  321  passes through a split lock washer  313 , passes through the glass-sealed 2-fiber feedthru with integrated holder  314  and presses into the module box  300 . 
   The glass-sealed 2-fiber feedthru with integrated holder  314  has a fiber retention tubing  314   c  at a first end and a glass sealing tubing  314   d  on a second end. On the first end, the glass-sealed 2-fiber feedthru with integrated holder  314  has the fiber retention tubing  314   c  for holding the rubber boot  315  in place. On the second end, the glass-sealed 2-fiber feedthru with integrated holder  314  has the glass sealing tubing  314   d  for avoiding stress from imposing on the glass seal area, such as the area shown in the glass seal  130  in FIG.  1 . The glass sealing tubing  314   d  is preferably designed with some length so that the sealing area nearing the module box  300  is distant away from the stress area nearing the glass-sealed 2-fiber feedthru with integrated holder  314 . 
   In  FIG. 4 , there is shown a pictorial diagram illustrating a third embodiment of a module box  400  employing a ribbon fiber feedthru sub-assembly  405 . The ribbon fiber sub-assembly  405  comprises a ribbon fiber  410 , a glass-sealed ribbon feedthru with integrated holder  414 , a C-seal  416 , a strain relief or rubber boot  415 , a first screw  420 , a first split lock washer  412 , a second screw  421  and a second split lock washer  418 . The ribbon fiber  410  passes through the glass-sealed ribbon feedthru with integrated holder  414  and the C-seal  416  into the module box  400  for hermetic sealing. A pair of screws  420  and  421  are used, together with a set of split lock washers  412  and  418 , respectively for pressing the glass sealed ribbon feedthru with integrated holder  414  into the module box  400 , thereby mechanically seals the module box  400 . The first screw  420  passes through the first split lock washer  412 , passes through a first opening  414   a  in the glass sealed 2-fiber feedthru with integrated holder  414 , and presses into the module box  400 , and the second screw  421  passes through the second split lock washer  418 , passes through a second opening  414   b  in the glass sealed 2-fiber feedthru with integrated holder  414 , and presses into the module box  400 . 
   The glass-sealed ribbon feedthru with integrated holder  414  has a fiber retention tubing  414   c  at a first end and a glass sealing tubing  414   d  on a second end. On the first end, the glass-sealed ribbon feedthru with integrated holder  414  has the fiber retention tubing  414   c  for holding the rubber boot  415  in place. On the second end, the glass-sealed ribbon feedthru with integrated holder  414  has the glass sealing tubing  414   d  for avoiding stress from imposing on the glass seal area, such as the area shown in the glass seal  130  in FIG.  1 . The glass sealing tubing  414   d  is preferably designed with some length so that the sealing area near the module box  400  is distant away from the stress area near the glass-sealed ribbon feedthru with integrated holder  414 . 
     FIG. 5  is a pictorial diagram illustrating a cross-sectional view of the module box  300  employing the 2-fiber feedthru as described with respect to  FIG. 3  that shows the glass seal  130  and the epoxy fill  170 . The glass sealed 2-fiber feedthru with integrated holder  314  holds the first fiber  310  and the second fiber  311  in place, with the glass seal  130  presses into the module box  300  with the epoxy fill  170  surrounding the entry into the module box  300  and the glass seal  130 . The C-seal  316  wraps around the glass sealed 2-fiber feedthru with integrated holder  314 . The first screw  320  passes through the first split lock washer  312  and presses the first split lock washer  312  into the module box  300 . The second screw  321  passes through the split lock washer  313  and presses the second split lock washer  313  into the module box  300 . The split lock washers  312  and  313  are used to maintain the tightness of the screws  320  and  321 , preventing the first and second screws  320  and  321  from becoming loose. 
   With respect to  FIGS. 3 and 5  for the 2-fiber feedthru, during the assembly of the feedthru with integrated holder  314 , areas surrounding the feedthru  314  and module box  300  that make contacts with the C-seal  316  are wiped and cleaned using alcohol to remove any potential oil residual and contaminants on these sealing surfaces. Screws  320  and  321  are evenly tightened using a torque wrench to avoid any deformation of the feedthru  314 . Similar practices are applicable to the single-fiber feedthru embodiment as described with respect to FIG.  2  and the ribbon fiber feedthru embodiment as described with respect to FIG.  4 . 
   The above embodiments are only illustrative of the principles of this invention and are not intended to limit the invention to the particular embodiments described. For example, each of the module boxes described above can be made of aluminum or other similar materials that are suitable for hermetic sealing. Moreover, it is apparent to one of ordinary skill in the art that other types of glass seal designs may be used without departing from the spirit of the present invention. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the appended claims.