Abstract:
An optical module with an improved coupling portion to couple an optical device with an external fiber is disclosed. The coupling portion includes a stub to secure a coupling fiber in a center thereof, a bush to support the stub, a sleeve to receive the stub in a portion thereof and an external ferrule in another portion, and a sleeve cover to cover the sleeve. The coupling portion further includes a latch put between the bush and the cover by being hooked with both the bush and the cover. The latch electrically isolates the bush from the cover even when the bush and the sleeve cover are made of metal.

Description:
TECHNICAL FIELD 
       [0001]    Various embodiments of the present application relate to an optical module. In particular, various embodiments relate to a mechanism to lath a cover for a sleeve with a bush to secure a stub. 
       BACKGROUND ART 
       [0002]    An optical transceiver installed within an optical communication system includes an optical module that has a light-emitting device or a light-receiving device coupled with an external optical fiber in the optical communication system. In order to couple the optical device above with the external optical fiber, a coupling portion is prepared in the optical module, and the coupling portion includes, for a light-emitting module, a stub securing a coupling fiber therein and a sleeve. The optical device is optically coupled with the coupling fiber, while, the external fiber with a ferrule in an end thereof also is coupled with the coupling fiber by inserting the ferrule into the sleeve and making the ferrule abut against the coupling fiber. Thus, the external fiber is optically coupled with the optical device, 
         [0003]    The optical device, which electrically couples with circuits in the optical transceiver, such as a driver for driving the light-emitting device or a pre-amplifier for amplifying a faint signal converted by the light-receiving device, is necessary to be grounded to, what is called as the signal ground. On the other hand, a housing of the optical transceiver is unavoidably grounded to, what is called as the frame or chassis ground. The latter ground, the frame or chassis ground, is strongly influenced by ambient electrical conditions, in other words, the electro-magnetic interference (EMI). Accordingly, the signal ground is strongly preferable to be isolated from the frame or chassis ground. In the optical module, a cover that secures the sleeve is grounded to the frame or chassis ground, while, a bush that secures the stub is grounded to the signal ground. Accordingly, a mechanism or a structure to isolate the cover from the bush electrically is inevitable in the optical module. 
       SUMMARY OF INVENTION 
       [0004]    An aspect of the present application relates to an optical module. The optical module includes an optical device, a stub, a metal bush, a sleeve, a metal sleeve cover, and a latch. The stub has a coupling fiber that optically couples with the optical device. The metal bush receives the first portion of the stub. The sleeve receives the second portion of the stub. The metal cover covers the sleeve. The sleeve receives an external optical fiber. Thus, the external optical fiber optically couples with the optical device by interposing the coupling fiber in the stub. A feature of the optical module according an embodiment is that the latch, which is made of electrically insulating material, typically resin, is put between the metal sleeve cover and the metal bush. Moreover, the latch is hooked with the bush, and also with the metal sleeve cover. Thus, the optical device, which is grounded to, what is called as the signal ground, may be electrically isolated from the metal sleeve cover which is grounded to, what is called as the frame or chassis ground, only by hooking the latch with the bush and the metal sleeve cover. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    The foregoing and other purposes, aspects and advantages will be better understood from the following detailed description of embodiments of the invention with reference to the drawings, in which: 
           [0006]      FIG. 1  is a side view showing an optical module according to an embodiment of the present application; 
           [0007]      FIG. 2  shows a cross section of the optical module shown in  FIG. 1 , where the cross section is taken along the optical axis Z appeared in  FIG. 1 ; 
           [0008]      FIGS. 3A and 3B  are perspective views of a latch implemented with the optical module shown in  FIG. 1 , where  FIG. 3A  views the latch from a side of an optical device; while,  FIG. 3B  views it from a side from which the cover is put; 
           [0009]      FIG. 4  is a side view of the cover, where a portion of the cover is cut away to show the cross section thereof; 
           [0010]      FIG. 5  shows a process to assemble the optical module shown in  FIG. 1 ; 
           [0011]      FIG. 6  is a perspective view showing another latch modified from the aforementioned latch shown in  FIG. 2 ; 
           [0012]      FIG. 7  shows a modified process to assemble the optical module implemented with the latch shown in  FIG. 6 ; 
           [0013]      FIGS. 8A and 8B  are perspective views showing modified cover and latch; and 
           [0014]      FIG. 9  shows a cross section of the optical coupling portion implemented with the modified cover and latch shown in  FIGS. 8A and 8B . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0015]    Next, various embodiments according to the present invention will be described. In the description of drawings, numerals or symbols same as or similar to each other will refer to elements same as or similar to each other without overlapping explanations. 
         [0016]    Referring to  FIGS. 1 and 2  first,  FIG. 1  is a side view of an optical module  10  according to an embodiment; while  FIG. 2  shows a cross section of the optical module taken along the line II-II appeared in  FIG. 1 . The optical module  10  primarily includes an optical device  12 , a jointer  24 , and a coupling portion  23 . 
         [0017]    The optical device  12  provides a package with a cylindrical shape in which a semiconductor light-emitting device, typically, a semiconductor laser diode (hereafter denoted as LD) is enclosed. The package comprises a stem  28 , a cap  30  with a lens  40 , and a plurality of leads  34 . 
         [0018]    The stem  28 , which is made of metal, for instance, stainless steel, has a disk shape. The leads  34  pass through the stem  28  and extend from one of surfaces  28   a,  the inner surface, of the stem  28 . Some of leads  34  pass through holes provided in the stem  28 . The holes are filled with sealant; that is, the leads  34  passing the holes are electrically isolated from the metal stem  28  by the sealant. At least one of leads  34 , the lead  34   a,  is integrally formed with the stem  28  or directly and electrically connected to the stem  28 , where this lead  34   a  is the ground lead. Also the stem  28  provides a sub-mount  28   b  extending from the inner surface  28   a  of the stem  28 . The LD  26  is mounted on a side surface  28   c  of the sub-mount  28   b,  where the side surface  28   c  extends substantially in parallel to the optical axis Z of the optical module  10 . 
         [0019]    The LD  26 , according to the present embodiment, is a type of, what is called as the edge-emitting type. Light emitted from one facet of the LD  26 , which becomes signal light, is output from the optical module  10 ; while, light emitted from another facet opposite to the former facet is utilized as monitored light to control the operation of the LD  26 . The stem  28  in the inner surface  28   a  thereof also provides a photodiode (hereafter denoted as PD) mounted on another sub-mount  36  for detecting the monitored light emitted from the other facet of the LD  26 . An area placing this sub-mount  36  for the PD makes a substantial angle, or inclined, with respect to the optical axis Z. The PD  38  mounted on the inclined surface effectively prevents light emitted from the other facet of the LD  26  and reflected at the surface of the PD  38  from returning the LD  26 . 
         [0020]    The stem  28  also provides the cap  30  made of metal, typically Kovar, with a cylindrical shape. One ends of the cap  30  is fixed on the inner surface  28   a  of the stem  28 , while, the other end of the cap  30 , which is the ceiling thereof, has an opening in which the lens  40  is held by a sealant  42 . 
         [0021]    The jointer  24  includes a cap  32  and a cover  44 , each of which is made of metal, for instance, stainless steel and has the cylindrical shape. The cap  32  in one ends thereof is fixed to the surface  28   a  of the stem  28  by, for instance, the YAG laser welding; while, the other end thereof provides an opening  32   a  to pass the light emitted from the LD  28  in the optical device  12  and condensed by the lens  40 . Thus, the cap  32  fully covers the cap  30  of the optical device  12 . 
         [0022]    The cover  44  is also made of metal, typically, stainless steel and has a cylindrical shape. The cover  44  includes a skirt  44   a  forming a bore, into which the cap  32  is fitted, and a ceiling  44   b  with a flat outer surface. Adjusting an overlapping length between the cover  32  in the end thereof and the bore of the skirt  44   a,  the optical alignment of the optical module  10  along the optical axis Z thereof, namely, adjustment of a distance from the lens  40  and the coupling portion  23  is carried out. While, sliding the coupling portion  23  on the flat outer surface of the ceiling  44   b,  the optical alignment is carried out along directions perpendicular to the optical axis Z. Thus, the cover  44  is often called as a joint sleeve. The cover  44  is fixed with the cap  32  by piercing welding at several points of the skirt  44   a.    
         [0023]    The coupling portion  23  includes a stub,  14 , a bush  16 , a sleeve  18 , a sleeve cover  20 , and a latch  22 , all of which have a substantially cylindrical shape. The stub  14 , which is made of ceramics, secures a coupling fiber  46  in a center thereof. One end of the coupling fiber  46  couples with the LD  26  through the lens  40 . The coupling fiber  46  and the stub  14  in one end thereof facing the lens  40  makes a substantial angle with respect to the optical axis Z, namely, the end surface of the coupling fiber  46  and that of the stub  14  are inclined with respect to the optical axis Z to prevent light reflected at these end surfaces from returning the LD  26 . On the other hand, the other end of the coupling fiber  46  and that of the stub  14  have a convex shape, or are rounded in a semi-spherical shape. This convex surface is to be butted against a ferrule secured in an external optical connector coupled with the coupling portion  23 . Thus, the ferrule of the external connector and the other end of the stub  14  and the coupling fiber  46  realize the physical contact. 
         [0024]    Also, the stub  14  provides first and second portions,  14   a  and  14   b,  respectively, disposed along the optical axis Z. The first portion  14   a  is secured with the metal bush  16 , typically, made of stainless steel, or the first portion  14   a  is inserted into a bore of the bush  16 . While, the second portion  14   b  is inserted into the sleeve  18 , or the sleeve  18  secures the second portion  14   b.  Assembling the coupling portion  23 , the bush  16  secured with the stub  14  slides on the ceiling  44   b  of the cover  44  to align optically in a plane perpendicular to the optical axis Z. Accordingly, the end of the stub  14  facing the cover  44  stands back from the end of the bush  16 . The bush  16  in the end thereof is fixed to the ceiling  44   b  by, for instance, the YAG laser welding after the alignment. Thus, the metal bush  16  is secured by the jointer  24  and electrically connected to the optical device  12  through the jointer  24 . 
         [0025]    The sleeve  18 , which is made of ceramics, is a type of, what is called, the split sleeve with a slit extending in parallel to the optical axis Z. However, sleeve  18  may be a rigid sleeve without any slits and finely processed in a bore thereof depending on an outer diameter of the stub  14 . The stub  14  in the second portion thereof  14   b  is inserted into a root portion of the bore of the sleeve  18  and secured thereby. The sleeve  18  receives an optical ferrule held in an external optical connector in a vacant portion not securing the stub  14 . The external ferrule provides an optical fiber in a center thereof and this optical fiber optically couples with the coupling fiber  46  in the stub  14 . Then, the optical device  12 , or the LD  26  in the optical device  12  optically couples with the external fiber. 
         [0026]    The sleeve cover  20 , which is made of metal, typically, stainless steel, covers an end portion of the sleeve  18  and the bush  16 . The end of the sleeve cover  20  provides a tapered opening to facilitate the insertion of the external ferrule into the sleeve  18 . The optical module  10  of the present embodiment has a feature to provide, in addition to components described above, the latch  22  made of resin. 
         [0027]      FIGS. 3A and 3B  are perspective views showing details of the latch  22 , where  FIG. 3A  views the latch  22  from a side of the optical device  12 ; while,  FIG. 3B  views the latch  22  from a side of the opening of the sleeve cover  20 . The latch  22  provides first and second portions,  22   a  and  22   b,  respectively, disposed along the optical axis Z. The first portion  22   a  surrounds the bush  16 ; while, the second portion  22   b  is surrounded by the sleeve cover  20 . 
         [0028]    The first portion  22   a  is latched with the bush  16 . Specifically, the first portion  22   a  provides a plurality of projections  22   c  in inner surfaces thereof extending into the bore of the first portion  22   a.  The embodiment shown in  FIGS. 3A and 3B  provides three projections  22   c  formed in the inner surface and evenly arranged around the optical axis Z. However, the number of projections  22   c  is not restricted to that of the embodiment. Projections more or less than three (3) show the same function described below. 
         [0029]    On the other hand, the bush  16  provides a flange  16   f  in the outer surface thereof Inserting the bush  16  into the bore of the first portion  22   a  of the latch  22 , the projection  22   c  of the latch  22  hooks the flange  16   f.  Then, assembling the bush  16  with the latch  22 , the bush  16  is blocked to be slip out from the latch  22 . 
         [0030]    The latch  22  of the embodiment further provides a plurality of rectangular openings  22   d  each disposed immediate neighbor to respective projections  22   c.  Specifically, the opening  22   d  is formed between the projection  22   c  and the boundary between the first portion  22   a  and the second portion  22   b,  and continuous to the projection  22   e.  The rectangular opening  22   d  provides a room for removing molds to form the projection when the latch  22  is formed by resin molding. The latch  22  further provides slits  22   s.    FIGS. 3A and 3B  show three slits  22   s  formed in the first portion  22   a  and evenly arranged around the optical axis Z as putting the projections therebetween. The slits  22   s  extend in parallel to the optical axis Z from the boundary to the second portion  22   b  to the end  22   e  of the first portion  22   a.  Inserting the bush  16  into the bore of the first portion  22   a,  the first portion  22   a  is easily bent outwardly, which facilitates the insertion of the bush  16 . 
         [0031]    The second portion  22   b  is inserted into a bore of the sleeve cover  20 . Further specifically, the second portion  22   b  is set into a space formed between the sleeve  18  and the sleeve cover  20 . The second portion  22   b  hooks the sleeve cover  20 . That is, the second portion  22   b  provides a plurality of posts  22   p  each extending from the boundary to the first portion  22   a  and providing a hook  22   f  protruding outwardly in a tip thereof. The embodiment shown in  FIGS. 3A and 3B  provides three posts  22   p  evenly arranged around the optical axis Z. Also the second portion  22   b  provides the inner rib  22   g  in the end thereof. As shown in  FIG. 2 , the inner rib  22   g  is sandwiched between the sleeve cover  20  and the bush  16 . 
         [0032]      FIG. 4  is a side view of the sleeve cover  20 , a portion of which is cut away to show the cross section thereof The sleeve cover  20  includes first and second portions,  20   a  and  20   b,  respectively. The first portion  20   a  provides a bore whose diameter is greater than that of the second portion  20   b.  Referring to  FIG. 2 , the first portion  20   a  receives the second portion  22   b  of the latch  22  and the root portion of the sleeve  18  into which the second portion of the stub  14   b  is fitted. On the other hand, the second portion  20   b  receives only the sleeve  18 . The first portion  20   a  in the bore thereof provides an axial hollow  20   h,  where the post  22   p  in the hook  22   f  thereof is set therein. The hollow  20   h  forms a step  20   s  in the edge thereof, on which the hook  22   f  of the latch  22  is to be hooked. 
         [0033]    Installing the optical module  10  above described in an optical transceiver, the jointer  24  and the optical device  12  are connected to the signal ground of the optical transceiver; while, the sleeve cover  20  is electrically connected to the frame ground, or the chassis ground. Because the latch  22  is made of resin, namely, electrically insulating material, the latch  22  isolates the signal ground of the jointer  24 , or the bush  16  in the coupling portion  23  from the frame ground of the sleeve cover  20 . In an electronic apparatus not restricted to an optical transceiver, the signal ground is usually isolated from the frame ground, because the frame ground or the outermost case is exposed in ambient radiation conditions. Many electro-magnetic interference (EMI) noises radiate in the environment. When an electronic apparatus has the signal ground common to the frame ground, such radiation noises easily penetrate into the apparatus through the ground. The optical module  10  of the embodiment effectively prevents such penetration of the EMI noise because the latch  22  made of electrically insulating material isolates the signal ground from the frame ground or the chassis ground. 
         [0034]    Next, referring to  FIG. 5 , a method to assemble the optical module  10  according to an embodiment of the invention will be described. The assembly of the optical module  10  first prepares an intermediate product  10   a  including the stub  14 , the sleeve  18 , and the bush  16 , where the stub  14  in the first portion  14   a  thereof is inserted into the bush  16 , while, in the second portion  14   b  thereof is received by the sleeve  18 . Next, adjusting the penetration depth of the cap  32  in the bore of the skirt  44   a  of the cover  44 , and sliding the root flange of bush  16  on the ceiling  44   b  of the cover  44 , the optical alignment between the coupling portion  23  and the optical device  12 , namely, the LD  26  in the optical device  12  is carried out, where the former adjustment corresponds to the Z-alignment and the latter corresponds to the XY alignment. After the optical alignment, the root flange of the bush  16  is welded to the ceiling  44   b,  while, the skirt  44   a  is welded to the cap  32 , which completes the second intermediate assembly  10   b.    
         [0035]    Concurrently with the assembly of the second intermediate assembly  10   b,  another intermediate assemble  10   c  is prepared independent of the second assembly  10   b  by inserting the second portion  22   b  of the latch  22  into the bore of the sleeve cover  20 . Then, the top portion of the second intermediate assembly  10   b  is inserted into the bore of the first portion  22   a  of the latch  22 . Thus, the optical module  10  shown in  FIG. 1  is completed. 
         [0036]    In the optical module  10 , the first portion  22   a  of the latch  22  hooks the flange  16   f  of the bush  16 ; while, the second portion  22   b  thereof is hooked with the sleeve cover  20 . Thus, the bush  16  and the sleeve cover  20  are assembled with each other through the latch  22  provided therebetween. Moreover, the latch  22  is made of electrically insulating material; accordingly, even when the bush  16  and the sleeve cover  20  are made of metal, the signal ground electrically connected to the bush  16  and the frame or chassis ground electrically connected to the sleeve cover  20  are electrically isolated from each other. 
         [0037]      FIG. 6  is a perspective view showing another latch  22 A according to a modified embodiment, and  FIG. 7  shows a process to assemble the optical module  10 A implementing with this latch  22 A. The modified latch  22 A shown in  FIG. 6  provides only the openings  22   h  but omits the projections  22   c  prepared in the latch  22  with a basic structure shown in  FIGS. 3A and 3B . On the other hand, the bush  16 A omits the flange  16   f  but provides the projections  16   p  in positions of the outer surface thereof around the optical axis Z. The projections  16   p  of the bush  16  mate with the openings  22   h  of the latch  22 A when the intermediate product  10   c  is assembled with the other intermediate product  10   b.    
         [0038]      FIGS. 8A and 8B  are still another modification of the optical module  10 B, and  FIG. 9  shows a cross section taken along the optical axis Z thereof. The modified optical module  10 B provides another sleeve cover  20 B and another latch  22 B. The sleeve cover  20 B of the modified embodiment provides a plurality of holes  20   o  arranged around the optical axis Z but omits the steps  20   s  formed by the axial hollow  20   h.  The holes  20   o  have a circular shape. On the other hand, the modified latch  22 B also provides the hook  22   f  but the shape thereof is circular. The sleeve cover  20 B is assembled with the latch  22 B by hooking the circular hook  22   f  with the circular holes  20   o.    
         [0039]      FIG. 9  shows a cross section of modified sleeve cover  20 B hooked with the latch  22 B each shown in  FIGS. 8A and 8B . As described above, the sleeve cover  20 B has not any step  20   s  in the inner hollow  20   k  it is difficult to from structures within bore, in particular, a structure like the hollow  20   h  with a wider diameter compared with an inlet diameter of the bore. The cover,  20  or  20 B, is made of metal, typically stainless steel, in the present embodiment. Such inner structures are necessary to be processed by lathing or casting. Because the bore of the sleeve  20 B has a diameter of only a few millimeters, the lathing is extremely complex. For the casting, specific structures are necessary to remove the casting die whose diameter gradually increases as closing the tip end thereof. Moreover, the latch  22  once fitted with the sleeve cover  20  is impossible to detach therefrom without breaking the latch  22 . The embodiment shown in  FIGS. 8A to 9  provides the hook  22   f  shaped into the circular button and the sleeve cover  20 B with the circular holes  20   o  without any specific structure in the bore thereof; accordingly, the process to form the sleeve cover  20 B becomes far simplified. 
         [0040]    While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. For instance, the optical module  10  is the type of the light-emitting module implemented with the LD  26 . However, the mechanism of the bush  16 , the latch  22  and the sleeve cover  20  is applicable to other types of the optical module such as the light-receiving module implemented with a photodiode instead of the LD  26 . Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.