Patent Publication Number: US-2005135754-A1

Title: Clamshell ferrule to avoid fiber threading

Description:
FIELD OF THE INVENTION  
      Embodiments of the present invention are directed to optical modules and, more particularly, to ferrule designs to avoid the fiber threading.  
     BACKGROUND INFORMATION  
      Fiber optics are used for a great number of applications. Everything from communication and computing systems, test and measurement systems, and medical systems and devices make use of optical technology. Optical devices are becoming increasingly smaller and more fragile.  
      In particular, fiber optic telecommunications are continually subject to demand for increased bandwidth. One way that bandwidth expansion has been accomplished is through dense wavelength division multiplexing (DWDM) wherein multiple separate data streams exist concurrently in a single optical fiber, with modulation of each data stream occurring on a different channel. Each data stream is modulated onto the output beam of a corresponding semiconductor transmitter laser operating at a specific channel wavelength, and the modulated outputs from the semiconductor lasers are combined onto a single fiber for transmission in their respective channels.  
      Optical modules are the critical components for the optic communication system. To keep the module reliability over service life, hermetic optical modules are required to keep away the moisture migration and other contaminant, which degrade the optic module performance.  
      A typical hermetic module is a Kovar can with all electrical and optical parts inside and with a Kovar lid that is resistance welded by seam sealer. A hermetic fiber feedthrough is a common way to passing light through a hermetic optic module.  
      A hermetic fiber feedthrough is created by the glass or metallic solder sealed to the fiber. A ferrule is used in solder reflow process to maintain the fiber concentricity and to avoid the fiber bending.  
      The cylindrical ferrule is manually threaded through the fiber. After the placement of solder, a seal is formed coaxial with the fiber and the feed-through aperture thus hermetically sealing the package.  
      It may be desirable to provide a hermetically fiber feedthrough, which does not require fiber threading.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram of an optical module having a fiber feed-through and traditional threading ferrule;  
       FIG. 2  is a diagram of a the bottom portion of the clamshell ferrule according to one embodiment of the invention; and  
       FIG. 3 a  diagram of an optical module and clamshell ferrule according to an embodiment of the invention for avoiding fiber threading.  
    
    
     DETAILED DESCRIPTION  
      In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.  
      Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.  
       FIG. 1  shows an optical module  10  which may contain optical and electrical components. The module  10  may be hermetically sealed to protect the contents for outside contaminants. The module  10  may comprise a bottom portion  12  which is essentially a container having a bottom and vertical sides. Electrical leads  14  are shown extending from the bottom  12  of the module  10  to provide electrical inputs and/or outputs to the various components in the module  10 . A lid  16  fits over the bottom  12  and may be hermetically sealed such as by laser welding or a solder process.  
      A generally cylindrical fiber feed through or “snout”  17  projects from the front of the module  10  to provide an opening for inserting an optical fiber  18  to provide an optical input/output to the module  10 . The optical fiber  18  is generally a thin, relatively fragile strand that must be threaded through snout  17  and aligned with optics in the module  10 . Normally, the lid  16  would be off during the alignment process to gain access to the components inside.  
      In order to maintain the concentricity of the fiber  18  in the snout  17  during solder reflowing process, a ferrule  20  may be used. The ferrule  20  may also be generally cylindrical in shape and sized to fit within the snout  17 . A front end  24  of the fiber  18  is threaded through the ferrule  20  and protrudes from the ferrule  20  to be aligned with optics within the module  10 . The ferrule  20  may then be inserted into the snout  17  and the end of the fiber  18  aligned and secured within the module  10 . A stop  22  limits the length of the ferrule  20  that may be inserted into the snout  17 . Since this threading process is usually done by hand, the stop  22  also provides a convenient grip for handling the ferrule  20 . After the solder reflowing process, the ferrule  20  must be removed by reverse threading it all the way along the entire length of the fiber  18 . Since the fiber is fragile, it may be prone to damage during reverse threading. Further, threading tends to be more difficult for longer fibers  18 . Thereafter, the lid  16  may be placed on the bottom  12  of the module  10  and a hermetic seal made there between. The snout  17  further comprises an opening  26  through which a hermetic seal may be made by, for example, glass or metallic solder reflow, to seal the area between the fiber  18  and the inner diameter of the snout  17 .  
       FIG. 2  shows the bottom portion of the clamshell ferrule  30  according to an embodiment of the invention. The clamshell ferrule  30  may comprise a base or bottom portion  32  having a narrower flange portion  34  at one end. The bottom portion may comprise a generally flat top surface having a groove  36  that runs the length of the bottom portion  32  and the flange  34 . The groove  36  may be sized to accommodate and optical fiber  36 . Unlike the ferrule  10  shown in  FIG. 1 , no threading is necessary with the clamshell design since the optical fiber may simply be laid inside of the groove.  
      Referring now to  FIG. 3 , the clamshell ferrule  30  further comprises a lid  40  which may be a mirror image of the bottom portion  32 . The lid  40  may be simply fitted over the bottom  32  or optionally may be hinged with hinges  33  for easier handling. The optical fiber  38  may be laid in the groove  36  and sandwiched between the bottom portion  32  and the lid portion  40 . The optical module  10  shown for illustration may be the same as that shown and described with reference to  FIG. 1  with like reference numerals indicating like features. As shown, the ferrule  30  may be substantially rectangular in shape and provides a convenient grip for handling the fiber  38 . Of course, while a rectangular ferrule  30  is shown, the body of the ferrule  30  may be any convenient shape. The leading edge  42  of the ferrule  30  acts as a stop allowing the flange  34  to penetrate the snout  17  only as far as prior to the opening  26 . The leading edge of the fiber  38  may then be aligned and secured within the module  10 . The lid  40  may then be placed on the bottom  32  and sealed such as by laser welding or with solder. Similarly, the opening  26  may be used through which a hermetic seal may be made by, for example, glass or metallic solder reflow, to seal the area between the fiber  38  and the inner diameter of the snout  17 .  
      The ferrule  30  may then be pulled backward slightly so that the flange  34  slips out of the snout  17 . The lid  40  of the ferrule  30  may then be lifted from the bottom  32  of the ferrule  30  to release the fiber  38 . This avoids the need to reverse thread the ferrule  30  all the way down the length of the fiber  38 . In addition, unlike the ferrule  20  shown in  FIG. 1 , a pre-connectorized fiber may be used (e.g., a fiber having a connector  46  at its terminal end) according to embodiments of the invention. This is not possible with the ferrule  20  of  FIG. 1  since the ferrule  20  can not be threaded past the connector  46 .  
      The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.  
      These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.