Patent Publication Number: US-2005117847-A1

Title: Optical waveguide module

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to an optical waveguide module,. and particularly to an optical waveguide module in which an optical waveguide element and an optical fiber array that is arranged at the end portions of optical fibers are optically and mechanically connected by adhesive.  
      2. Description of the Relate Art  
      An optical waveguide module preferably has good optical characteristics so that the optical loss that occurs when light is propagated through the connecting portion of an optical waveguide element and an optical fiber array is limited. Accordingly, it is desired that alignment of the core wires of the optical fibers and the optical waveguides of the optical waveguide element is maintained even after bonding the optical waveguide element and the optical fiber array.  
      Bonding may be one factor that disrupts the alignment of the core wires of the optical fibers and the optical waveguides of the optical waveguide element. Specifically, adhesive used for the bonding may contract upon hardening, and spreading.: states of the adhesive may differ depending on each case so that differences may occur, for example, in the shapes of the adhesive parts made of hardened adhesive. Thus, the bonding process includes an unstable factor that may affect the alignment of the optical fibers. Further, in the optical waveguide module, the area of the connecting portion between an end surface of the optical waveguide element and an end surface of the optical fiber array is relatively small, and thereby, the differences in the shapes of the adhesive parts, for example, may likely have a large influence on the alignment of the optical fibers.  
      Accordingly, a prescribed amount of adhesive is preferably arranged to settle at a prescribed position so that the shape of the adhesive part may be close to a desired shape and the bonding state of the optical waveguide element and the optical fiber array may be stabilized. Hereinafter, the act of settling a prescribed amount of adhesive to a prescribed position may be referred to as position fixing.  
       FIGS. 1 and 2  show an optical waveguide module  1  according to the prior art. As is illustrated in the drawings, the end portions of plural optical fibers  2  are aligned and fixed by an optical fiber array  10 . The optical fiber array  10  includes a base member  11  on which upper surface parallel V grooves are formed, and a cover  12 . The end portions of core wires  2   a  of the optical fibers  2  are engaged and positioned to the V grooves  11   a  formed on the base member  11 , and the cover  12  is bonded to the base member  11  by a bonding layer  13  so that the optical fibers  2  may be covered and fixed. A high polymer optical waveguide element  5  includes a substrate  6  on which upper surface a high polymer layer having optical waveguides  7  is formed. An end surface  11   b  of the base member  11  and an end surface  6   a  of the substrate  6  both correspond to flat mirror surfaces.  
      The optical fiber array  10  and the high polymer optical waveguide element  5  are bonded by an adhesive part that is made of hardened adhesive. Specifically, the core wires  2   a  and the optical waveguides  7  are aligned, and in this state, the end surface  11   b  of the base member  11  and the end surface  6   a  of the substrates are arranged to face each other so that the end surface  11   b  and the end surface  6   a  are bonded by the adhesive part  20 .  
      Preferably, the adhesive part  20  extends across the area between the end surface  11   b  and the end surface  6   a  and includes a portion sticking out along the upper edge, bottom edge, right edge, and left edge of the connecting portion of the end surfaces  11   b  and  6   a.  The portion sticking out from the connecting portion is referred to as fillet.  
      The end surface  11   b  of the base member  11  and the end surface  6   a  of the substrates correspond to flat mirror surfaces. Thereby, when the end surface  11   b  of the base member  11  and the end surface  6   a  of the substrate  6  are arranged to face each other, it is difficult to create a space between the end surface  11   b  and the end surface  6   a  in which the adhesive may be placed. In turn, even when there is a slight deviation in the loading direction of a load that is impinged upon arranging the end surfaces  11   b  and  6   a  to face each other, the position fixing of the adhesive may be disrupted and the shape of the adhesive part may be deformed. In other words, in the optical waveguide module of the prior art, it is difficult to realize accurate position fixing of the adhesive.  
      In the prior art, the shape of the adhesive part can vary significantly depending on circumstances of the bonding process, as is illustrated by  FIGS. 3A, 3B ,  4 A, and  4 B.  FIGS. 3A and 3B  illustrate a case in which the adhesive deviates to the upper side. In this drawing, the adhesive part  20 A has a portion  20 A 1  positioned between the end surface  11   b  and the end surface  6   a  that lacks adhesive, and a large fillet  20 A 2  sticking out from the upper surface side of the high polymer optical waveguide element  5 .  FIGS. 4A and 4B  illustrate a case in which the adhesive deviates to the lower side. In this drawing, the adhesive part B has a portion  20 B 1  positioned between the end surface  11   b  and the end surface  6   a  that lacks adhesive, and a large fillet  20 B 2  sticking out from the bottom surface side of the high polymer optical waveguide element  5 . In the case of  FIGS. 3A and 3B , the optical fiber array  10  and the high polymer optical waveguide element  5  tend to warp into a reverse V shape, and in the case of  FIGS. 4A and 4B , the optical fiber array  10  and the high polymer optical waveguide element  5  tend to warp into a V shape. It is noted that the adhesive may also deviate to the right side or to the left side. Thus, in assembling optical waveguide modules according to the prior art, a number of the optical waveguide modules assembled may have their alignment states disrupted so as to end up having large optical losses, and thereby, high yield and high reliability cannot be realized in the prior art.  
     SUMMARY OF THE INVENTION  
      The present invention has been conceived in response to the problems of the related art and its object is to provide an optical waveguide module in which accurate position fixing of adhesive may be realized.  
      The present invention according to one embodiment provides an optical waveguide module including:  
      an optical waveguide element having a roughened end surface at which end portions of optical waveguides are exposed;  
      an optical fiber array having a roughened end surface at which end portions of a plurality of core wires of optical fibers are exposed; and  
      an adhesive part for bonding the optical waveguide element and the optical fiber array that is arranged between the roughened end surface of the optical waveguide element and the roughened end surface of the optical fiber array.  
      According to one aspect of the present invention, a narrow space may be created between a roughened end surface of an optical waveguide element and a roughened end surface of an optical fiber array that face each other. The space may have predetermined dimensions and be opened to the exterior around the periphery of the connecting portion of the end surfaces. The space may provide a portion in which adhesive may be held in place so that position fixing of the adhesive may be realized. Thereby, an adhesive part having a desired shape may be stably formed.  
      The present invention according to another embodiment provides an optical waveguide module including:  
      an optical waveguide element having an end surface at which end portions of optical waveguides are exposed;  
      an optical fiber array having an end surface from which end portions of a plurality of core wires of optical fibers protrude; and  
      an adhesive part for bonding the optical waveguide element and the optical fiber array that is arranged between the end surface of the optical waveguide element and the end surface of the optical fiber array.  
      The present invention according to another embodiment provides an optical waveguide module including:  
      an optical waveguide element having an end surface at which end portions of optical waveguides are exposed;  
      an optical fiber array having an end surface at which end portions of a plurality of core wires of optical fibers are exposed, said end surface of the optical fiber array including an end surface of a bonding layer bonding the core wires, which bonding layer end surface is arranged to be recessed with respect to the end portions of the core wires; and  
      an adhesive part for bonding the optical waveguide element and the optical fiber array that is arranged between the end surface of the optical waveguide element and the end surface of the optical fiber array.  
      According to an aspect of the present invention, a narrow space may be created between an end surface of an optical waveguide element and an end surface of an optical fiber array. The space may provide a portion in which adhesive may be held in place so that position fixing of the adhesive may be realized. Thereby, an adhesive part having a desired shape may be stably formed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an optical waveguide module according to the prior art;  
       FIG. 2  is a perspective view of a connecting portion between an optical fiber array and a high polymer optical waveguide element of the optical waveguide module shown in  FIG. 1 ;  
       FIGS. 3A and 3B  are diagrams showing an exemplary defect occurring in the optical waveguide module of  FIG. 1 ;  
       FIGS. 4A and 4B  are diagrams showing another exemplary defect occurring in the optical waveguide module of  FIG. 1 ;  
       FIG. 5  is a perspective view of an optical waveguide module according to a first embodiment of the present invention;  
       FIG. 6  is a perspective view of a connecting portion between an optical fiber array and a high polymer optical waveguide element of the optical waveguide module of  FIG. 5 ;  
       FIG. 7  is cross-sectional elevation view of the optical waveguide module of  FIG. 5 ;  
       FIG. 8  is a perspective view of an adhesive part of the optical waveguide module of  FIG. 5 ;  
       FIG. 9  is a perspective view of an optical waveguide module according to a second embodiment of the present invention;  
       FIGS. 10A and 10B  respectively show a connecting portion between an optical fiber array and a high polymer optical waveguide element of the optical waveguide module of  FIG. 9 , and a surface configuration of the optical fiber array;  
       FIG. 11  is a cross sectional view of the optical waveguide module of  FIG. 9 ;  
       FIG. 12  is a perspective view of an adhesive part of the optical waveguide module of  FIG. 9 ;  
       FIG. 13  is a perspective view of an optical waveguide module according to a third embodiment of the present invention;  
       FIG. 14  is a perspective view of a connecting portion between an optical fiber array and a high polymer optical waveguide element of the optical waveguide module of  FIG. 13 ;  
       FIG. 15  is a cross-sectional view of the optical waveguide module of  FIG. 13 ; and  
       FIG. 16  is a perspective view of an adhesive part of the optical waveguide module of  FIG. 13 .  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In the following, principles and embodiments of the present invention will be described with reference to the accompanying drawings.  
       FIGS. 5 through 7  illustrate an optical waveguide module  30  according to a first embodiment of the present invention.  FIG. 5  is a perspective view of the optical waveguide module  30 ;  FIG. 7  is a cross-sectional elevation view of the optical waveguide module  30 ; and  FIG. 6  shows the connecting portion between an optical waveguide element and an optical fiber array. In the drawings, directions Z 1 -Z 2  represent length directions, directions X 1 -X 2  represent width directions, and directions Y 1 -Y 2  represent height directions.  
      The optical waveguide module  30  according to the present embodiment includes an optical fiber array  40  and a high polymer optical waveguide element  50 . End portions of plural optical fibers  2  are aligned and fixed by the optical fiber array  40 . The optical fiber array  40  includes a base member  41  on which upper surface parallel V grooves  41   a  are formed, and a cover  42 . The ends of core wires  2   a  corresponding to the end portions of the optical fibers  2  are engaged and positioned to the V grooves  41   a  formed on the base member  41 , and the cover  42  is bonded to the base member  41  by a bonding layer  43  so that the core wires  2   a  of the optical fibers  2  may be covered and fixed.  
      The high polymer optical waveguide element  50  includes a substrate  51  on which upper surface a high polymer layer made of resin material and having optical waveguides  52  is formed.  
      According to the present embodiment, an end surface  41   b  of the base member  41  of the optical fiber array  40  and an end surface  51   a  of the substrate  51  of the high polymer optical waveguide element  50  correspond to flat roughened surfaces with an average roughness Ra of 0.2 μm±0.1 μm. An end surface  42   a  of the cover  42  may also be arranged into a roughened surface. These roughened surfaces may be formed by conducting mechanical processes of lapping and polishing, for example. Alternatively, instead of conducting the mechanical processes, the rough surfaces may be formed by conducting a dry etching process such as ion milling, or plasma etching, for example. Also, the roughened surfaces may be formed by conducting a chemical wet etching process using NF or NH4F, for example.  
      The optical fiber array  40  and the high polymer optical waveguide element  50  are bonded by an adhesive part  70 . Specifically, the core wires  2   a  and the optical waveguides  52  are aligned, and in this state, the end surface  41   b  of the base member  41  and the end surface  51   a  of the substrate  51  are arranged to face each other so that the end surface  41   b  and the end surface  51   b  may be connected and fixed by the adhesive part  70 . In one embodiment, ultraviolet cure adhesive with a relatively low viscosity of approximately 30 cp may be used for the adhesive part  70 , and this adhesive in its hardened state may have optical transparency, a predetermined refraction index, and a predetermined Young&#39;s modulus.  
      According to the present embodiment, the end surface  41   b  and the end surface  51   a  correspond to roughened surfaces, and thereby, convex portions of the end surface  41   b  and the end surface  51   a  may be faced with each other and concave portions of the end surface  41   b  and the end surface  51   a  may be faced opposite to each other. A narrow space (gap) may be formed in the connecting portion between the end surface  41   b  and the end surface  51   a  that are facing each other. This narrow space may be opened to the exterior along the upper side, bottom side, right side, and left side of the end surfaces  41   b  and  51   a  facing each other. From the interior-portion of the connecting portion between the end surfaces  41   b  and  51   a,  plural paths leading to the exterior periphery of the end surfaces  41   b  and  51   a  may be formed.  
      When a loading direction of a load impinged upon arranging the end surfaces  41   b  and  51   a  to face each other corresponds to a desired direction, accurate position fixing of the adhesive may be realized. However, according to the present embodiment, even when the loading direction of the load impinged upon arranging the end surfaces  41   b  and  51   a  to face each other deviates from the desired direction, the adhesive may penetrate through and spread across the connecting portion between the end surfaces  41   b  and  51   a  owing to the capillary effect, and surplus adhesive may stick out evenly around the periphery of the end surfaces  41   b  and  51   a.  In this embodiment, the narrow space between the end surfaces  41   b  and  51   a  may enable position fixing of the adhesive, and the adhesive may be hardened in this state to be formed into the adhesive part  70 . It is noted that, through testing, the inventors of the present invention have discovered that the capillary effect may occur in the adhesive when the average roughness Ra of the end surfaces  41   b  and  51   a  is 0.1 μm or greater.  
      The adhesive part  70  may be arranged to have a configuration as is illustrated in  FIG. 8 , for example. As is shown in  FIG. 8 , the adhesive part  70  includes a layer portion  70   a  that extends across the connecting portion between the end surfaces  41   b  and  51   a,  and a fillet  70   b  that evenly surrounds the periphery of the end surfaces  41   b  and  51   a.    
      According to the present embodiment, layer portion  70   a  extends across the connecting portion between the end surfaces  41   b  and  51   a,  and thereby, the optical fiber array  40  and the high polymer optical waveguide element  50  may be bonded with sufficient strength. Further; the end surface  41   b  and the end surface  51   a  correspond to roughened surfaces, and thereby, the area of the connecting portion at which the layer portion  70   a  connects the end surfaces  41   b  and  51   a  may be increased compared to the case in which the end surfaces correspond to mirror surfaces, and the so-called anchor effect may occur so that the bonding may be further strengthened.  
      The fillet  70   b  may be evenly arranged around the periphery of the end surfaces  41   b  and  51   a,  including the upper side, the bottom side, the right side and left side of the end surfaces. In turn, a contraction force generated by this fillet  70   b  along the periphery of the end surfaces  41   b  and  51   a  may be uniformly distributed so that the force may not act in a direction that can cause the optical fiber array  40  and the high polymer optical waveguide element  50  to warp into a V shape, for example, to disrupt the alignment of the core wires  2   a  of the optical fibers  2  and the optical waveguides  52  of the optical waveguide element  50 . In this way, the alignment of the optical fiber array  40  and the high polymer optical waveguide element  50  may be maintained.  
       FIGS. 9 through 11  illustrate an optical waveguide module  30 A according to a second embodiment of the present invention.  FIG. 9  is a perspective view of the optical waveguide-module  30 A;  FIG. 11  is a cross-sectional elevation view of the optical waveguide module  30 A; and  FIGS. 10A and 10B  show-respectively show a connecting portion between an-optical waveguide element and a band-shaped optical fiber array, and a surface configuration of the optical fiber array.  
      The optical waveguide module  30 A of the present embodiment includes an optical fiber array  40 A and a high polymer optical waveguide element  50 . The optical fiber array  40 A has an end surface  40 Aa on a side at which the ends of core wires  2   a  of optical fibers  2  are exposed. The end surface  40 Aa includes an end surface  41 Aa of a base member  41 A, an end surface  42 Aa of a cover  42 A, end surfaces of the core wires  2   a,  and an end surface  43 Aa of a bonding layer  43 A. The end surface  40 Aa has a surface configuration as is illustrated by line  80  in  FIG. 10B . The line  80  in  FIG. 10B  represents a relative measurement result obtained by tracing the end surface  40 Aa of the optical fiber array  40 A in the direction from Y 1  to Y 2  along line  81  shown in  FIG. 10A  using a needle point of a surface roughness measurement apparatus. It is noted that line  82  in  FIG. 10B  represents the surface configuration of the conventional optical fiber array shown in  FIG. 2 .  
      According to the present embodiment, the end surfaces of the core wires  2   a  of the end surface  40 Aa are arranged to protrude the farthest. The end surface  41 Aa of the base member  41 A and the end surface  42 Aa of the. cover  42 A correspond to slightly tilting surfaces that tilt from the core wire side in the Z 1  direction at a rate of −0.1˜−0.2 μm/mm with respect to the position of the end surfaces of the core wires  2   a.  The end surfaces of the core wires  2   a  protrude by dimension A (e.g., approximately 0.2 μm) in the Z 2  direction with respect to the portions of the end surface  41 Ab positioned around the core wires  2   a.    
      The end surface  40 Aa ( 41 Aa and  42 Aa) may be formed by controlling the load that is impinged on the optical fiber array  40 A upon conducting a polishing process, and the fixing method of the optical fiber array.  
      The optical fiber array  40 A and the high polymer optical waveguide element  50  are connected by an adhesive part  70 A. Specifically, the core wires  2   a  and the optical waveguides  52  are aligned, and in this state, the end surface  41 Aa of the base member  41 A and an end surface  51  of a substrate  51  of the high polymer optical waveguide element  50  are connected by-the adhesive part  70 A.  
      In the present embodiment, the end surface  41 Aa corresponds to a tilting surface that tilts from the core wire side in the Z 1  direction with respect to the position of the end surface of the core wires  2   a,  and thereby, a narrow space may be formed between the end surfaces  41 Aa and  51   a.  In turn, the adhesive part  70 A may be arranged to have a configuration as is shown in  FIG. 12 , for example. In this drawing, the adhesive part  70 A includes a layer portion  70 Aa that extends across the connecting portion between the end surfaces  41 Aa and  51   a,  and a fillet  70 Ab that evenly surrounds the periphery of the end surfaces  41 Aa and  51   a.    
      In the present embodiment, the layer portion  70 Aa extends across the connecting portion between the end surfaces  41 Aa and  51   a,  and the fillet  70 Ab is formed around the periphery of the end surfaces  41 Aa and  51   a,  and thereby, the optical fiber array  40 A and the high polymer optical waveguide element  50  may be bonded with sufficient strength. Also, the fillet  70 Ab is evenly formed around the periphery of the end surfaces  41 Aa and  51   a,  and thereby, a contraction force generated by this fillet  70 Ab may be generated uniformly throughout the periphery of the end surfaces  41 Aa and  51   a  so that the force may not act in a direction that may cause the optical fiber array  40 A and the high polymer optical waveguide element  50  to warp into V shapes, for example, to disrupt the alignment of the core wires  2   a  of the optical fibers  2  and the optical waveguides  52  of the high polymer optical waveguide element  50 . Thereby, the alignment of the optical fiber array  40 A and the high polymer optical waveguide element  50  may be maintained.  
      Also, in the present embodiment, the end surfaces of the core wires  2   a  and the end surfaces of the optical waveguides are arranged to be closer to each other compared to the conventional art, and thereby, optical losses maybe reduced.  
       FIGS. 13 through 15  illustrate an optical waveguide module  30 B according to a third embodiment of the present invention.  FIG. 13  is a perspective view of the optical waveguide module  30 B;  FIG. 15  is a cross-sectional elevation view of the optical waveguide module  30 B; and  FIG. 14  shows a connecting portion between an optical waveguide element and a band-shaped optical fiber array.  
      The optical waveguide module  30 B includes an optical fiber array  40 B and a high polymer optical waveguide element  50 . The optical fiber array  40 B includes an end surface  40 Ba on a side at which the ends of core wires  2   a  of optical fibers  2  are exposed. The end surface  40 Ba includes an end surface  41 Bb of a base member  41 B, an end surface  42 Ba of a cover  42 B, end surfaces of the core wires  2   a,  and an end surface  43 Ba of a bonding layer  43 B. The end surfaces  41 Bb and  42 Ba correspond to flat mirror surfaces. The end surface  40 Ba differs from that of the conventional optical waveguide module of  FIG. 2  in that the end surface  43 Ba of the bonding layer  43 B is arranged to recede from the end surfaces of the core wires  2   a.  For example, the end surface  43 Ba of the bonding layer  43 B may recede by 0.1 0˜0.3 μm in the Z 1  direction with respect to the position of the end &#39;surfaces of the core wires  2   a.    
      In the present embodiment, the end surfaces  41 Bb and  42 Ba correspond to flat mirror surfaces. The state in which the end surface  43 Ba of the bonding layer  43 B is recessed from the end surfaces of the core wires  2   a  may be realized by arranging the polishing rate for the bonding layer  43 B to be higher than that for the base member  41 B, the cover  42 B, and the core wires  2   a  so that the bonding layer may be excessively polished. In other words, special processing may not have to be conducted to form the recessed state of the end surface  43 Ba.  
      The optical fiber array  40 B and the high polymer optical waveguide module  50  are connected by an adhesive part  70 B. Specifically, the core wires  2   a  and the optical waveguides  52  are aligned, and in this state, the end surface  41 Bb of the base member  41 B and the end surface  51   a  of the substrate  51  of the optical waveguide module  50  are connected by the adhesive part  70 B.  
      When the optical fiber array  40 B: and the high polymer optical waveguide module  50  are arranged to face each other to align the core wires  2   a  and the optical waveguides  52 , a narrow space  90  may be formed between the end surface  43 Ba of the bonding layer  43 B and the end surface  51   a  of the substrate  51 . Further, this space may be opened to the exterior at the Y 1  side, the X 1  side, and the X 2  side.  
      The space may be able to hold the adhesive in place, and thereby, position fixing of the adhesive may be realized by the space  90 .  
      The adhesive part  70 B may be arranged to have a configuration as is shown in  FIG. 16 , for example. In this drawing, the adhesive part  70 B includes a layer portion  70 Ba that extends across the area between the end surfaces  41 Bb and  51   a,  and a fillet  70 Bb of which a large portion sticks out along the upper side of the periphery of the end surfaces  41 Bb and  51   a,  that is, around the end surface  43 Ba of the bonding layer  43 B.  
      According to the present embodiment, the optical fiber array  40 B and the high polymer optical waveguide module  50  may be bonded with sufficient strength, and the alignment of the optical fiber array  40 B and the high polymer optical waveguide module  50  may be maintained.  
      It is noted that the roughened end surface configuration according to the first embodiment, the protruding configuration of the end surfaces of the core wires according to the second embodiment, and the recessed configuration of the end surface of the bonding layer according to the third embodiment may be combined as necessary or desired.  
      Further, the present invention is not limited to these embodiments, and variations and modifications may be made without departing from the scope of the present invention.  
      The present application is based on Japanese Patent Application No. 2003-397469 filed on Nov. 27, 2003, the entire contents of which are hereby incorporated by reference.