Abstract:
An optical waveguide device includes: a waveguide core that guides light; a mirror surface that deflects light coming from the waveguide core by 90°; a main waveguide core that guides light deflected at the mirror surface; a waveguide core for monitoring that branches the light deflected at the mirror surface off from the main waveguide core, and guides the light in a different direction, the mirror surface being disposed at a branching portion of the waveguide core for monitoring; and a clad portion that surrounds the waveguide core, the main waveguide core and the waveguide core for monitoring.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-236413 filed on Sep. 12, 2007. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to an optical waveguide device which is used in a mobile apparatus or the like and guides light as a waveguide, and to a light outputting module using the optical waveguide device. 
         [0004]    2. Related Art 
         [0005]    Examples of methods of fabricating an optical waveguide film as an optical waveguide device are: (1) a method of impregnating a film with a monomer, selectively exposing a core portion so as to change the refractive index, and laminating films together (a selective polymerization method); (2) a method of coating a core layer and a clad portion, and thereafter, forming the clad portion by using reactive ion etching (RIE method); (3) a method using photolithography which carries out exposure and development by using an ultraviolet-curing resin which is obtained by adding a photosensitive material into a polymer material (a direct exposure method); (4) a method using injection molding; (5) a method of coating a core layer and a clad portion, and thereafter, exposing a core portion so as to change the refractive index of the core portion (a photobleaching method); and the like. Further, when limited to a rectilinear waveguide, there are methods such as a method of fabricating the optical waveguide including forming a core portion of the optical waveguide by locally cutting and removing, by a dicing saw or the like, the layer which becomes the core and which has a high refractive index and is obtained by laminating two layers of resin having different refractive indices, and thereafter, covering the core portion with the same polymer resin as the clad portion, and the like. 
         [0006]    However, in recent years, in IC technologies and LSI technologies, attention has focused on carrying out optical wiring between apparatuses and between the boards and between the chips within the apparatuses, instead of carrying out high density electrical wiring, in order to improve the operational speed and the degree of integration. In order to realize such optical wiring, surface emitting elements having an excellent high-speed characteristic and mass-production characteristic, and VCSEL elements in particular, are used for interconnection applications and applications for optical communications. However, differently than edge emitter elements, it is difficult to monitor the light output of a VCSEL element as a unit. 
         [0007]    Thus, in elements at which a VCSEL element is packaged, a method is usually used in which a portion of light coming from a window for output is reflected, and this reflected light is used in monitoring the light output. However, reflecting and taking-out a portion of light coming from a window for output is inefficient, and excess current must be sent to the VCSEL element so as to increase the light output. At this time, excessively complex external circuits that also are needed as temperature control is required in order to avoid the effects of heat, or the like. 
       SUMMARY 
       [0008]    An optical waveguide device of a first aspect of the present invention includes: a waveguide core that guides light; a mirror surface that deflects light coming from the waveguide core by 90°; a main waveguide core that guides light deflected at the mirror surface; a waveguide core for monitoring that branches the light deflected at the mirror surface off from the main waveguide core, and guides the light in a different direction, the mirror surface being disposed at a branching portion of the waveguide core for monitoring; and a clad portion that surrounds the waveguide core, the main waveguide core and the waveguide core for monitoring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0010]      FIG. 1  is a schematic structural diagram of a light outputting module relating to a first exemplary embodiment; 
           [0011]      FIG. 2  is a perspective view of an optical waveguide device relating to the first exemplary embodiment; 
           [0012]      FIG. 3A  is a side sectional view of the optical waveguide device relating to the first exemplary embodiment, and  FIG. 3B  is a top view thereof; 
           [0013]      FIG. 4A  is a perspective view of a modified example of the optical waveguide device relating to the first exemplary embodiment, and  FIG. 4B  is a side sectional view thereof; 
           [0014]      FIG. 5A  is a perspective view of another modified example of the optical waveguide device relating to the first exemplary embodiment, and  FIG. 5B  is a side sectional view thereof; 
           [0015]      FIG. 6  is a perspective view of yet another modified example of the optical waveguide device relating to the first exemplary embodiment; 
           [0016]      FIG. 7  is a schematic structure diagram of a light outputting module relating to a second exemplary embodiment; 
           [0017]      FIG. 8  is a perspective view of an optical waveguide device relating to the second exemplary embodiment; 
           [0018]      FIG. 9A  is a side sectional view of the optical waveguide device relating to the second exemplary embodiment, and  FIG. 9B  is a top view thereof; 
           [0019]      FIG. 10  is a perspective view of a modified example of the optical waveguide device relating to the second exemplary embodiment; and 
           [0020]      FIGS. 11A and 11B  are schematic top views of conventional optical waveguide devices. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Examples of exemplary embodiments of the present invention will be described in detail hereinafter with reference to the drawings. 
         [0022]    [Branched Optical Waveguides] 
         [0023]    A branched waveguide is generally structured by a core portion having a high refractive index, and a clad portion which surrounds the core portion and has a lower refractive index than the core portion. The greater the difference in refractive indices between the core portion and the clad portion, the smaller the radius of curvature of a curved portion can be made without causing a loss at the time of bending. On the other hand, the greater the difference in refractive indices, the larger the spread angle of the light output and the greater the connection loss in a case of being connected to an optical fiber. Thus, the difference in refractive indices between the core portion and the clad portion is preferably made to be about 0.5 to 5%. 
         [0024]    In the case of using a branched waveguide and monitoring the light from a surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser) by using a waveguide M for monitoring, because the lower limit of the radius of curvature is prescribed, a light-receiving element R for monitoring must be placed at a surface which is different than the surface emitting laser L, as shown in  FIG. 11A . Further, if the surface emitting laser L and the light-receiving element R for monitoring are disposed on the same straight line, as shown in  FIG. 11B , the direction in which the light advances must be turned-around in the form of an arc, and the size of the waveguide device increases. 
         [0025]    Thus, in the present exemplary embodiments, optical waveguide devices having a waveguide core for monitoring are structured as follows. 
       First Exemplary Embodiment 
       [0026]      FIG. 1  is a schematic structural diagram of an optical waveguide device and a light outputting module relating to the present exemplary embodiment. As shown in  FIG. 1 , a light outputting module  10  has an optical waveguide device  20 , a surface emitting laser section  12 , and a light-receiving element section  14 . 
         [0027]    As shown in  FIG. 2 , the optical waveguide device  20  has a rectangular-plate-shaped clad portion  22 . The clad portion  22  is a portion which structures the main body of the optical waveguide device  20 , and can be formed of a transparent resin film or the like. A first mirror surface  24  and a second mirror surface  26  are structured at corner portions of the rectangle of the clad portion  22 . The first mirror surface  24  and the second mirror surface  26  are respectively structured at the upper sides of corner portions which are adjacent to one another with a short side of the rectangle of the clad portion  22  located therebetween. The first mirror surface  24  and the second mirror surface  26  are structured to form 45° angles with a top surface  22 A, a side surface  22 B at the short side, and a side surface  22 C at the long side of the clad portion  22 . The first mirror surface  24  and the second mirror surface  26  function as optical path changing surfaces which change the optical path of the light. Note that the 45° angles here may deviate, for example, ±10% in light of mechanical precision. 
         [0028]    A waveguide core  30 , a main waveguide core  32  and a waveguide core  34  for monitoring, which guide light, are formed at the clad portion  22  so as to be covered by the clad portion  22 . The waveguide core  30 , the main waveguide core  32 , and the waveguide core  34  for monitoring are structured of a material having a higher refractive index than the clad portion  22 . As shown in  FIG. 3A  and  FIG. 3B  as well, the waveguide core  30  is disposed in the direction of thickness (thickness direction) of the clad portion  22  such that the one end of the waveguide core  30  is disposed at a bottom surface  22 D of the clad portion  22  and the other end thereof is disposed at the first mirror surface  24 . The main waveguide core  32  is disposed in the longitudinal direction (length direction) of the clad portion  22  along the top surface  22 A, such that one end of the main waveguide core  32  is connected to the first mirror surface  24  side end portion of the waveguide core  30 , and the other end of the main waveguide core  32  reaches a side surface  22 E which opposes the side surface  22 B. The waveguide core  34  for monitoring is structured by a waveguide core  34 A for monitoring which is disposed in the short-side direction (width direction) of the clad portion  22 , and a waveguide core  34 B for monitoring which is disposed in the direction of thickness of the clad portion  22 . The waveguide core  34 A for monitoring is disposed in the short-side direction of the clad portion  22  such that one end of the waveguide core  34 A for monitoring is connected to the first mirror surface  24  side end portion of the waveguide core  30 , and the other end of the waveguide core  34 A for monitoring is disposed at the second mirror surface  26 . The waveguide core  34 B for monitoring is disposed in the direction of thickness of the clad portion  22  such that one end of the waveguide core  34 B for monitoring is connected to the second mirror surface  26  side end portion of the waveguide core  34 A for monitoring, and the other end of the waveguide core  34 B for monitoring is disposed at the bottom surface  22 D. The light, which is incident from the bottom surface  22 D side of the waveguide core  30 , reaches the first mirror surface  24 , and, at the first mirror surface  24 , is branched toward the longitudinal direction main waveguide core  32  side and the short-side direction waveguide core  34  for monitoring side, which run along the top surface  22 A of the clad portion  22 . Then, the branched-off light of the main waveguide core  32  side reaches the side surface  22 E and is used as light output. The branched-off light of the waveguide core  34  for monitoring side reaches the second mirror surface  26  via the waveguide core  34 A for monitoring, and is reflected toward the bottom surface  22 D, and is outputted from the bottom surface  22 D side of the waveguide core  34 B for monitoring and used for monitoring the output. 
         [0029]    The optical waveguide device  20  of the present exemplary embodiment can be fabricated by using any of various methods, such as, for example, a reproducing method utilizing a mold which uses a silicone resin, a method using a stamper, a method utilizing cutting which uses a dicing saw, a direct exposure method, or the like. 
         [0030]    Further, ultraviolet-curing or thermosetting (heat-curing) epoxy resins or acrylic resins can be used as the materials of the clad portion  22 , the waveguide core  30 , the main waveguide core  32 , and the waveguide core  34  for monitoring. 
         [0031]    The first mirror surface  24  and the second mirror surface  26  can be structured by cutting by using a dicing saw having a 45° blade. Note that, in order to ensure the reflecting precision of the first mirror surface  24  and the second mirror surface  26 , the first mirror surface  24  and the second mirror surface  26  are preferably flat surfaces whose surface roughnesses are greater than or equal to 1 nm and less than or equal to 50 nm. 
         [0032]    In the present exemplary embodiment, as described above, by structuring the first mirror surface  24  at the branching portion of the main waveguide core  32  and the waveguide core  34  for monitoring, the waveguide core  34  for monitoring which has little loss can be structured, and further, the output end portion of the waveguide core  34  for monitoring can be disposed at a corner portion which is adjacent to the corner portion at which the input end portion of the waveguide core  30  is disposed. 
         [0033]    As shown in  FIG. 1 , the surface emitting laser section  12  has a base material  12 A and a surface emitting element  12 B. The surface emitting element  12 B is a surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser) at which plural light-emitting points, which emit laser light, are arrayed two-dimensionally. The surface emitting laser section  12  is disposed at the first mirror surface  24  side corner portion of the bottom surface  22 D of the clad portion  22 , such that the surface emitting element  12 B is disposed in a vicinity of the end portion of the waveguide core  30  and the laser light from the surface emitting element  12 B exits toward the waveguide core  30 . 
         [0034]    The light-receiving element section  14  has a substrate  14 A and a light-receiving element  14 B. The light-receiving element  14 B is structured by a photodiode. The light-receiving element section  14  is disposed at the second mirror surface  26  side corner portion of the bottom surface  22 D of the clad portion  22 , such that the light-receiving element  14 B is disposed at the end portion of the waveguide core  34  for monitoring and can receive the laser light from the waveguide core  34  for monitoring. 
         [0035]    In the present exemplary embodiment, as described above, the input end portion of the waveguide core  30  and the output end portion of the waveguide core  34  for monitoring are respectively disposed at corner portions which are adjacent to one another along a short-side direction end side of the clad portion  22 . Therefore, the surface emitting laser section  12  and the light-receiving element section  14  can together be disposed at one side of the clad portion  22 . Accordingly, the light outputting module  10  can be designed to be compact. 
         [0036]    Note that the present exemplary embodiment describes, as an example, providing the second mirror surface  26  which is for deflecting, downward in the direction of thickness, the light which is guided by the waveguide core  34  for monitoring. However, the second mirror surface  26  is not absolutely necessary, and the waveguide core  34 A for monitoring may be made to pass-through toward a side surface  22 F of the clad portion  22 . 
         [0037]    Further, a third mirror surface  28 , which is for deflecting light by 90° in the direction of thickness, may be provided at the side surface  22 E side of the clad portion  22 . The third mirror surface  28  may be structured at a 45° angle in the direction deflecting toward the bottom surface  22 D as shown in  FIG. 4A  and  FIG. 4B , or may be structured at a 45° angle in the direction deflecting toward the top surface  22 A as shown in  FIG. 5A  and  FIG. 5B . By deflecting toward the bottom surface  22 D at the third mirror surface  28 , the output direction of the light can be returned toward the surface emitting element  12 B side. By deflecting toward the top surface  22 A at the third mirror surface  28 , the output direction of the light can be made to be the same direction as the output direction from the surface emitting element  12 B. 
         [0038]    Further, as shown in  FIG. 6 , the above-described first mirror surface  24 , second mirror surface  26  and third mirror surface  28  may be structured such that metal films  25  are disposed at the outer sides. By providing the metal films  25  in this way, the light outputting module  10  can be easily packed. 
         [0039]    Note that gold, silver, copper, or an alloy of any of these can be used as the metal films  25 . In consideration of cost and the reflectance, silver or a silver alloy is preferable. Further, the formation of the metal films  25  can be carried out by depositing by sputtering, vapor deposition, or the like. 
       Second Exemplary Embodiment 
       [0040]    A second exemplary embodiment of the present invention will be described next. In the present exemplary embodiment, portions which are the same as in the first exemplary embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. 
         [0041]      FIG. 7  is a schematic structural diagram of an optical waveguide device and a light outputting module relating to the present exemplary embodiment. As shown in  FIG. 7 , a light outputting module  40  has an optical waveguide device  50 , the surface emitting laser section  12 , and the light-receiving element section  14 . 
         [0042]    As shown in  FIG. 8 , the optical waveguide device  50  has the rectangular-plate-shaped clad portion  22 . The first mirror surface  24  and the second mirror surface  26  are structured at corner portions of the rectangle of the clad portion  22 . 
         [0043]    As shown in  FIG. 9A  and  FIG. 9B  as well, the waveguide core  30 , a main waveguide core  52  and a waveguide core  54  for monitoring, which guide light, are formed at the clad portion  22  so as to be covered by the clad portion  22 . The waveguide core  30  is disposed in the direction of thickness of the clad portion  22  such that one end of the waveguide core  30  is disposed at the bottom surface  22 D of the clad portion  22  and the other end thereof is disposed at the first mirror surface  24 . One end of the main waveguide core  52  is connected to the first mirror surface  24  side end portion of the waveguide core  30 , and, as seen from the top surface  22 A side, extends out in a perpendicular direction from the first mirror surface  24 , and is bent gradually such that the orientation thereof is changed to the longitudinal direction of the clad portion  22 . The other end of the main waveguide core  52  is disposed at the side surface  22 E which opposes the side surface  22 B. The waveguide core  54  for monitoring is structured by a waveguide core  54 A for monitoring which is disposed in the short-side direction of the clad portion  22 , and a waveguide core  54 B for monitoring which is disposed in the direction of thickness of the clad portion  22 . The waveguide core  54 A for monitoring is disposed in the short-side direction of the clad portion  22  such that one end of the waveguide core  54 A for monitoring is branched-off from the first mirror surface  24  side end portion of the main waveguide core  52 , and the other end of the waveguide core  54 A for monitoring is disposed at the second mirror surface  26 . The waveguide core  54 B for monitoring is disposed in the direction of thickness of the clad portion  22  such that one end of the waveguide core  54 B for monitoring is connected to the second mirror surface  26  side end portion of the waveguide core  54 A for monitoring, and the other end of the waveguide core  54 B for monitoring is disposed at the bottom surface  22 D. Namely, the light, which is incident from the bottom surface  22 D side of the waveguide core  30 , reaches the first mirror surface  24 , and, at the first mirror surface  24 , is branched toward the main waveguide core  52  side, which is bent so as be directed in the longitudinal direction along the top surface  22 A of the clad portion  22 , and the waveguide core  54  for monitoring side which is directed in the short-side direction. Then, the branched-off light of the main waveguide core  52  side reaches the side surface  22 E and is used as light output. The branched-off light of the waveguide core  54  for monitoring side reaches the second mirror surface  26  via the waveguide core  54 A for monitoring, and, at the second mirror surface  26 , is reflected toward the bottom surface  22 D, and is outputted from the bottom surface  22 D side of the waveguide core  54 B for monitoring and used for monitoring the output. 
         [0044]    In the present exemplary embodiment, the first mirror surface  24  is formed at a corner portion of the rectangle as described above. Therefore, the main waveguide core  52  can be extended from the corner portion of the rectangle toward the inner side without a loss of light, and can be bent toward the output end portion. Further, the waveguide core  54  for monitoring can be easily branched toward the short-side direction of the clad portion  22  from the main waveguide core  52  which extends toward the inner side from the corner portion of the rectangle of the clad portion  22 . The output end portion of the waveguide core  54  for monitoring can be disposed at a corner portion which is adjacent to the corner portion at which the input end portion of the waveguide core  30  is disposed. 
         [0045]    Note that the optical waveguide device  50  of the present exemplary embodiment can be fabricated in the same way as the optical waveguide device  20  of the first exemplary embodiment. 
       EXAMPLE 1 
       [0046]    (Fabrication of Optical Waveguide Device) 
         [0047]    A thick-film resist (SU-8 manufactured by Microchemical KK) is coated by spin coating onto an Si substrate. Thereafter, pre-baking is carried out at 80° C., exposure and development are carried out through a photomask, and a convex portion (width: 50 μm, height: 50 μm), which has a square cross-section and at which two straight lines intersect at 90° (see  FIG. 3B ) is formed. 
         [0048]    Next, after a mold releasing agent is coated on this original plate, a mixture of a thermosetting (heat-curing) liquid dimethylsiloxane rubber (SYLGARD 184 manufactured by Dow Corning Asia Ltd., viscosity: 5000 mPa·s) and a curing agent thereof is made to flow in, and is heated at 120° C. for 30 minutes so as to be cured. Thereafter, peeling is carried out, and a mold (mold thickness: 5 mm), which has a concave portion corresponding to a convex portion having a rectangular cross-section, is prepared. 
         [0049]    Further, through-holes, whose planar configurations are circular and whose cross-sectional configurations in the direction of thickness of the mold are taper-shaped, are formed by punching at one end and at the other end of the concave portion so as to communicate with the concave portion, and the mold is prepared. 
         [0050]    This mold and a film base material for cladding (ARTON film manufactured by JSR Corporation, refractive index: 1.510), which has a film thickness of 100 μm and is slightly larger than the mold, are fit tightly together. Next, when several drops of an ultraviolet-curing resin of a viscosity of 500 mPa·s are placed into the entry side through-hole of the mold, and reduced-pressure suctioning is carried out from the discharging side (reduced-pressure suctioning side) through-hole, the ultraviolet-curing resin is filed within the concave portion in 10 minutes. Then, UV light of 50 mW/cm 2  is illuminated for 5 minutes from above the mold, and ultraviolet curing is carried out. When the mold is peeled-off from the ARTON film, a core of the same shape as the convex portion of the original plate is formed on the ARTON film. 
         [0051]    Next, an ultraviolet-curing resin, whose refractive index after curing is 1.510 which is the same as the ARTON film, is coated on the surface of the ARTON film at which the core is formed. Thereafter, a film base material for cladding of 100 μm is laminated. By illuminating UV light of 50 mW/cm 2  for 5 minutes and carrying out ultraviolet curing, the two films are adhered together, such that a waveguide sheet having a branched waveguide of a film thickness of 270 μm is prepared. 
         [0052]    Then, by using a dicing saw having a 45° angle blade, two of the transverse direction corner portions of the waveguide sheet are cut-off at an angle of 45° with respect to the optical axis. The rectilinear waveguides, which are orthogonal to one another and are shown in  FIG. 2  and have 45° surfaces (the first mirror surface  24  and the second mirror surface  26 ) at the corner portions, are formed. 
         [0053]    The optical waveguide device  20  of the first exemplary embodiment is prepared in this way. 
         [0054]    (Formation of Metal Mirrors) 
         [0055]    Silver alloy films of a film thickness of 100 nm are formed by sputtering on the first mirror surface  24  and the second mirror surface  26 . 
       EXAMPLE 2 
       [0056]    (Fabrication of Optical Waveguide Device) 
         [0057]    A waveguide sheet having a branched waveguide of a thickness of 270  82  m is prepared in the same way as in Example 1, except that the master pattern of the SU-8 formed on the Si substrate has the structure shown in  FIG. 9B . 
         [0058]    Then, by using a dicing saw having a 45° angle blade, two of the transverse direction corner portions of the waveguide sheet are cut-off at an angle of 45° with respect to the optical axis. The branched waveguide, which is shown in  FIG. 8  and has 45° surfaces (the first mirror surface  24  and the second mirror surface  26 ) at the corner portions, is formed. 
         [0059]    The optical waveguide device  50  of the second exemplary embodiment is prepared in this way. 
         [0060]    (Formation of Metal Mirrors) 
         [0061]    Silver alloy films of a film thickness of 100 nm are formed by sputtering on the first mirror surface  24  and the second mirror surface  26 . 
       EXAMPLE 3 
       [0062]    (Fabrication of Optical Waveguide Device) 
         [0063]    A waveguide sheet having a branched waveguide of a thickness of 270 μm is prepared in the same way as in Example 2. 
         [0064]    Next, by using a dicing saw having a 45° angle blade, two of the transverse direction corner portions of the waveguide sheet are cut-off at an angle of 45° with respect to the optical axis, so as to form 45° surfaces (the first mirror surface  24  and the second mirror surface  26 ) at the corner portions. Then, the waveguide sheet is turned upside-down, and the end side portion at the side opposite the first mirror surface  24  and the second mirror surface  26  is cut-off at a 45° angle with respect to the optical axis so as to form the third mirror surface  28  as shown in  FIG. 10 . A branched waveguide which is 3 mm square and has a thickness of 270 μm, such as shown in  FIG. 10 , is thereby formed. 
         [0065]    An optical waveguide device  51  which is a modified example of the second exemplary embodiment is prepared in this way. 
         [0066]    (Formation of Metal Mirrors) 
         [0067]    Silver alloy films of a film thickness of 100 nm are formed by sputtering at the optical path changing portions formed at 45° angles. 
       EXAMPLE 4 
       [0068]    (Fabrication of Optical Waveguide Device, and Packaging of VCSEL Element and Photodiode) 
         [0069]    An optical waveguide device which is 3.0 mm square and has a thickness of 270 μm is prepared in the same way as in Example 3. 
         [0070]    A VCSEL element and a photodiode for monitoring are disposed at the light incident portion and the light exiting portion of the above-described optical waveguide device  51 , respectively, so as to form a light outputting module. This is packaged at a TO-46 CAN, so as to form a TOSA module. 
         [0071]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.