Abstract:
A protective member and an optical module comprises a package for retaining an optical component, an optical fiber to be fixed to the package in such a way as to be optically coupled to the optical component and a protective member which protects the optical fiber. The protective member has a body, which covers the package and optical fiber, formed of an elastic material and a reinforcing member arranged along an inner surface of the body to cover an outer surface of the optical fiber in a contactless state with respect to the optical fiber.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a protective member and an optical module.  
         BACKGROUND OF THE INVENTION  
         [0002]    In an optical module which retains an optical component in a package, such as a semiconductor laser module, a rubber boot is provided at that portion where an optical fiber used for inputting and outputting optical signals extends from the package to protect the optical fiber against a handling-originated damage, such as breakage.  
           [0003]    There may be an event that due to miss handling an optical module, stress is applied to the optical fiber in a direction perpendicular to the longitudinal direction of the optical fiber. In such an event, if the optical fiber extends from the package via a ferrule, the applied bending stress bends the optical fiber hard at that extended portion, so that the radius of curvature of the optical fiber becomes extremely small and the optical fiber may be broken.  
           [0004]    If such breakage of the optical fiber occurs, the tensile stress resistance of the optical fiber is lower than the standard specification of the product. The breakage of the optical fiber causes another problem that a predetermined optical characteristic cannot be obtained using the optical fiber. The reduction in tensile stress resistance or the inability to acquire a predetermined optical characteristic are critical issues particularly for an optical module that is used in an optical fiber amplifier or the like for a submarine cable whose specification-requirements and reliability performances are very tight.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to provide a protective member for reducing an amount of bending stress on an optical fiber that protrudes from an exit portion of a package of an optical module.  
           [0006]    It is another object of the present invention to provide an optical module which has an improved protection for an optical fiber that protrudes from an exit portion of a package of the optical module.  
           [0007]    To achieve the first object, the protective member comprises a hollow body formed of an elastic material and having a first open end, a second open end, a reinforced hollow portion and an unreinforced hollow portion, the first open end configured to be fitted about the exit portion of the package such that the optical fiber extends through the reinforced hollow portion and unreinforced hollow portion, and exits through the second open end; and a reinforcing member disposed within the reinforced hollow portion of the hollow body and configured to reduce an amount of flexure of the reinforced hollow portion when an external force is applied in a direction orthogonal to a longitudinal axis thereof, wherein the second open end being in contact with and coaxially disposed about the optical fiber.  
           [0008]    To achieve the second object, an optical module according to the present invention comprises a package configured to retain an optical component therein, having an exit portion thereof; an optical fiber having a first portion fixed to the package so as to be optically coupled to the optical component and a second portion that extends outside of the package; and a protective member that includes a hollow body formed of an elastic material and having a first open end, a second open end, a reinforced hollow portion and an unreinforced hollow portion, the first open end configured to be fitted about the exit portion of the package such that the optical fiber extends through the reinforced hollow portion and unreinforced hollow portion, and exits through the second open end, wherein the second open end being in contact with and coaxially disposed about the optical fiber, and a reinforcing member disposed within the reinforced hollow portion of the hollow body and configured to reduce an amount of flexure of the reinforced hollow portion when an external force is applied in a direction orthogonal to a longitudinal axis thereof  
           [0009]    The aforementioned object and other objects, features and advantages of the present invention will become more apparent from the detailed description given hereinafter with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a cross-sectional view of a semiconductor laser module attached with a protective member, which illustrates the protective member and an optical module according to one embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is a cross-sectional view showing a state in which the protective member in FIG. 1 is assembled;  
         [0012]    [0012]FIG. 3 is a cross-sectional view of the assembled protective member;  
         [0013]    [0013]FIG. 4 is a cross-sectional view illustrating essential portions in enlargement when stress is applied to the protective member of the optical module in FIG. 1;  
         [0014]    [0014]FIG. 5 is an enlarged cross-sectional view of a portion A in FIG. 4;  
         [0015]    [0015]FIG. 6 is a cross-sectional view showing a protective member according to another embodiment;  
         [0016]    [0016]FIG. 7 is a cross-sectional view showing a modification of the optical module; and  
         [0017]    [0017]FIG. 8 is a cross-sectional view depicting a protective member and an optical module according to a further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    A protective member and an optical module according to one embodiment of the present invention will now be described referring to FIGS. 1 through 8.  
         [0019]    A semiconductor laser module  1  has a Peltier module  3  disposed in a metal package  2  and a base  4  placed on the Peltier module  3 , as shown in FIG. 1.  
         [0020]    As shown in FIG. 1, the package  2  has a body  2   a,  a lid  2   b  and a cylindrical portion  2   c  protruding from the body  2   a.  The cylindrical portion  2   c  is formed integrally with the body  2   a.  The cylindrical portion  2   c  fixes an optical fiber  12  to be discussed later to the package  2  via a second ferrule  13 .  
         [0021]    A semiconductor laser device  6  is provided on the top surface of the base  4  via a heat sink  5 . A monitor photodiode  7   a  is provided on a carrier  7  on one side of the base  4  and a first ferrule  11  is provided on the other side via ferrule holders  8  and  9 .  
         [0022]    The first ferrule  11  has a distal end at which the optical fiber  12  is inserted, secured, and protruding toward the semiconductor laser device  6 . The optical fiber  12  has a lens portion  12   a  formed at its distal end, and its distal-end side surface is coated with a metal plating  12   b  of Au or the like. The lens portion  12   a  of the optical fiber  12  is arranged facing to and aligned with the semiconductor laser device  6 , and the other end of the optical fiber  12  is drawn out of the cylindrical portion  2   c  formed on the package  2 . The metal second ferrule  13  is attached to that portion of the optical fiber  12  which corresponds to the cylindrical portion  2   c.  The optical fiber  12  is secured to the first ferrule  11  and the second ferrule  13  at the distal end of the ferrule  11 ,  13  by a solder  15  of Au—Sn. The second ferrule  13  is fixed to the cylindrical portion  2   c  by soldering, welding, an adhesive, synthetic resin or a composite member or the like of an adhesive and synthetic resin.  
         [0023]    The portion of the optical fiber  12  that extends from the second ferrule  13  is a bending allowance portion  12   c  which can bend to some degree (see FIG. 5).  
         [0024]    The package  2  has a protective boot  20  for protecting the extending optical fiber  12 . The protective boot  20  is fitted over the cylindrical portion  2   c.    
         [0025]    The protective boot  20  has a body  21  and a cylindrical reinforcing member  22  shown in FIGS. 1 through 3.  
         [0026]    The body  21  is made of an elastic member, such as silicone-based nonflammable rubber, and formed into a cylinder which has openings  21   a  and  21   b  at the front and rear portion and becomes narrower rearward in a tapered shape. Formed in the inner surface of the body  21  is a recess portion  21   c  in which the reinforcing member  22  is to be fitted. The body  21  is formed in such a way that the inner shape of the end portion of the body  21  lying on the cylindrical portion ( 2   c ) side has a shape approximately identical to the outer shape of the cylindrical portion  2   c.  As the body  21  is fitted over the cylindrical portion  2   c , the end portion firmly contact the outer surface of the cylindrical portion  2   c  by the elastic force and covers the cylindrical portion  2   c,  the second ferrule  13  and the bending allowance portion  12   c  of the optical fiber  12 . The recess portion  21   c  is formed in such a way that as shown in FIGS. 1 and 5, when the reinforcing member  22  is fitted in the recess portion  21   c,  the reinforcing member  22  is placed at such a position as to cover at least the rear portion of the second ferrule  13  and a start end portion  12   d  of the bending allowance portion  12   c  of the optical fiber  12 .  
         [0027]    The reinforcing member  22  is formed of a metal, such as aluminum, engineering plastic, such as polyphenylene sulfide (PPS), phenolic resin or glass epoxy resin, or ceramic, such as zirconia, into a cylindrical shape. As shown in FIG. 2, the reinforcing member  22  is led into the body  21  through the opening side  21   a  and fitted into the recess portion  21   c.  The inside diameter of the reinforcing member  22  is set larger than the outside diameter of the second ferrule  13 .  
         [0028]    The optical fiber  12 , the second ferrule  13 , the reinforcing member  22 , the cylindrical portion  2   c  and the body  21  of the protective boot  20  are arranged concentrically with the optical fiber  12  as the center as seen from their cross sections perpendicular to the longitudinal direction of the optical fiber  12 . While it is desirable that the reinforcing member  22  is integrated, it may approximately have the shape of the alphabet C partially having a cut as seen from the end face, or may be a combination of multiple parts divided along with the center axis of the cylinder.  
         [0029]    In case where a connector which is hard to pass through the opening  21   b  is attached to the end portion of the optical fiber  12  of the semiconductor laser module  1  with the above-described structure, the protective boot  20  is put over the optical fiber  12  in advance, then the first ferrule  11  and second ferrule  13  are attached to a predetermined position of the optical fiber  12 .  
         [0030]    Next, the Peltier module  3  is placed in the body  2   a  of the package  2 , and the base  4  provided with the components from the heatsink  5  to the ferrule holders  8  and  9  is set in the body  2   a.    
         [0031]    Then, the optical fiber  12  with the first ferrule  11  and second ferrule  13  attached thereto is led into the package  2  from the cylindrical portion  2   c  and the first ferrule  11  is fixed to the ferrule holders  8  and  9  with the lens portion  12   a  at the distal end aligned with the semiconductor laser device  6 .  
         [0032]    Then, the second ferrule  13  is fixed to the cylindrical portion  2   c  as mentioned above, and the protective boot  20  is moved along the optical fiber  12  to be fitted over the cylindrical portion  2   c.  Then, the lid  2   b  is attached to the body  2   a  by soldering, YAG laser welding or the like, thus completing the assembly of the semiconductor laser module  1  with the package  2  sealed airtight.  
         [0033]    As shown in FIG. 4, bending stress may be applied to the bending allowance portion  12   c  of the optical fiber  12  when the semiconductor laser module  1  fabricated in the above-described manner is handled. Even with the bending stress applied, the action of the protective boot  20  can restrain the optical fiber  12  from being broken. This will be discussed below specifically.  
         [0034]    The protective boot  20  is fitted over the cylindrical portion  2   c  of the package  2  of the semiconductor laser module  1 . As the reinforcing member  22  is placed in the body  21  of the protective boot  20 , as shown in FIG. 5, the reinforcing member  22  covers the optical fiber  12  by a predetermined length L (e.g., a length nearly equivalent to the diameter of the second ferrule  13 ) with respect to the longitudinal direction of the optical fiber  12  in the diagram over the outer surface of the start end portion  12   d  of the bending allowance portion  12   c  of the optical fiber  12  extending from the second ferrule  13 . What is more, as the inside diameter of the reinforcing member  22  is larger than the outside diameter of the second ferrule  13 , the reinforcing member  22  does not contact the optical fiber  12 .  
         [0035]    Even if bending stress is applied to the optical fiber  12 , therefore, bending stress does not act on the start end portion  12   d  of the bending allowance portion  12   c  of the optical fiber  12  and the start end portion  12   d  is held straight. Therefore, the radius of curvature of the optical fiber  12  is prevented from becoming extremely smaller and the optical fiber  12  is protected against breakage.  
         [0036]    The protective boot  20  may be designed in such a way that as shown in FIG. 6, the reinforcing member  22  placed in the body  21  is made longer to extend to the cylindrical portion  2   c.  With this structure, the reinforcing member  22  of the protective boot  20  covers around the outer surface of the cylindrical portion  2   c  in addition to the end portion of the body  21 . This stabilizes the fixing position of the reinforcing member  22 , rather than the semiconductor laser module  1  shown in FIGS.  1  to  4 . Also, this makes the laser module more resistive to the applied bending stress and facilitates the fitting of the protective boot  20 , which is preferable. As a result, the function of the protective boot  20  to protect the optical fiber  12  extending from the second ferrule  13  is enhanced further At this time, the protective boot  20  and reinforcing member  22  may be securely adhered to the cylindrical portion  2   c  by an adhesive or synthetic resin.  
         [0037]    The semiconductor laser module  1  is likewise protected by the protective boot  20  even if the optical fiber  12  is directly fixed to the cylindrical portion  2   c  in an airtight fashion by, for example, a solder  16  of Au—Sn or the like without using the second ferrule  13  as shown in FIG. 7.  
         [0038]    A protective member and an optical module according to another embodiment of the present invention will be discussed below in detail by referring to FIG. 8.  
         [0039]    An optical module  30  has a package  31 , an optical fiber  32  inserted in ferrules  32   a , slide rings  33  and a protective boot  40 , as shown in FIG. 8.  
         [0040]    As illustrated, the package  31  is a cylindrical member which holds an optical isolator  34  and lens holders  35  and  36  and has steps  31   a  formed on the outer surface of the respective ends. The lens holders  35  and  36  hold lenses  35   a  and  36   a,  respectively.  
         [0041]    The optical fiber  32  is fixed to the slide rings  33  secured to the respective sides of the package  31 , via the ferrules  32   a  by YAG welding. To reduce reflection of lights which have been transmitted from the lenses  35   a  and  36   a,  the end faces of the ferrules  32   a  that face the lens holders  35  and  36  are formed obliquely with respect to the optical axis and the rear portion from which the optical fiber  32  extends is sealed with an adhesive  32   b.    
         [0042]    The slide rings  33  are cylindrical portions that fix the optical fiber  32  to the package  31  via the ferrules  32   a,  and are fixed to the respective sides of the package  31  by YAG welding.  
         [0043]    The protective boot  40  has a body  41  and a reinforcing pipe  42  which are formed by the same materials as those of the protective boot  20 . To avoid a detailed description of the protective boot  40 , therefore, like reference numerals are used for the constituting portions of the protective boot  40  in FIG. 8 which correspond to those of the protective boot  20 .  
         [0044]    As mentioned above, the optical fiber  32  of the optical module  30  is fixed to the slide rings  33  fixed to the respective sides of the package  31  via the respective ferrules  32   a . The reinforcing pipe  42  is placed in the body  41  of the protective boot  40 . Even if bending stress is applied to the optical fiber  32  due to the handling-originated stress acting on the optical fiber  32 , therefore, the portion of the optical fiber  32  that extends from the ferrules  32   a,  i.e., a start end portion  32   d  of a bending allowance portion  32   c,  is held straight, thus preventing the optical fiber  32  from being broken.  
         [0045]    The foregoing description of the embodiment has been given of an optical module which has a semiconductor laser or an optical isolator retained in the package. The optical component to be retained in the package of the optical module of the present invention is not however limited to that particular type.  
         [0046]    Needless to say, the package, the cylindrical portion and the body and reinforcing member of the protective boot can take arbitrary cross-sectional shapes, such as a circle, a polygon, such as a rectangle.  
         [0047]    Further, the protective boot may be adhered to the package by an adhesive or synthetic resin in the embodiments.  
         [0048]    Furthermore, the optical fiber may be of any type, such as a single mode fiber, a multi-mode fiber or a polarization-maintaining fiber.