Patent Publication Number: US-2009232465-A1

Title: Optical Waveguide Device and Method for Fabricating Optical Waveguide Device

Description:
TECHNICAL FIELD 
     The present invention relates to an optical waveguide device and a method for fabricating an optical waveguide device. 
     BACKGROUND ART 
     Recently, as a component for optical communication, an optical waveguide device which uses polymer resin material is used. In order to change a direction of optical wiring in an optical waveguide, a technique where an end of the optical waveguide forms an inclination surface by 45° and the inclination surface bends an optical path in a right angle is developed (for example, Patent Document 1). 
       FIG. 7  shows a cross-sectional view of an optical waveguide device  31 . As shown in  FIG. 7 , the optical waveguide device  31  is constituted of a light-emitting element  33  provided on a substrate  32 , a light-receiving element  35  provided on a substrate  34 , and an optical guide member  36  for guiding the light. The light-emitting element  33  and an optical guide member  36 , and the light-receiving element  35  and the optical guide member  36  are adhered to each other with optical path members  37 ,  38  respectively. 
     The optical guide member  36  includes, from the bottom, a protective layer  39 , a clad section  40 , and a protective layer  41 , and a core section  42  with a higher refractive index than the clad section  40  is formed in the clad section  40 . Mirror faces  43 ,  44  having an inclination angle of 45° are formed on both ends of the optical guide member  36 . The mirror faces  43 ,  44  are formed by cutting using an angled blade having an inclination angle on its blade edge. As shown in  FIG. 7 , light emitted from the light-emitting element  33  is reflected totally by the mirror face  43  and progresses through the core section  42 . Then, the light is reflected totally by the mirror face  44  and is received by the light-receiving element  35 . 
     Other than the total reflection mirror method shown in  FIG. 7 , a mirror block method for changing an optical path as shown in  FIG. 8  is used. In  FIG. 8 , the same reference numerals are applied to the same components as in  FIG. 7 , and description of the structure is omitted. As shown in  FIG. 8 , the light which propagated through the core section  42  is reflected by the mirror face  45  and the light is received by the light-receiving element  35 . In the mirror block method, it is preferable to coat the surface of the mirror face  45  with metal in order to increase reflection efficiency. 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2001-166167 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in  FIG. 7 , in order for the light emitted from the light-emitting element  33  to reach the core section  42 , the light needs to pass through the optical path member  37 , the protective layer  39 , and the clad section  40 , causing light loss through optical diffusion and interface reflection. Similarly, light loss occurred when the light reached the light-receiving element  35  from the core section  42 . In order to prevent light loss, highly accurate adjustment of the position in the height direction was necessary. 
     Since the mirror faces  43 ,  44  totally reflect the light with a refractive index difference between the core section  42  and air, as shown in  FIG. 9 , there was a problem of when the optical path member  37  adheres to the mirror face  43 , the light leaks. Also, the mirror faces  43 ,  44  are formed by cutting using an angled blade, in which rotary instability easily occurs due to blade thickness, and it was necessary to carefully control the accuracy of the angle. 
     The present invention has been made in consideration of the above problems of the techniques, and it is an object to reduce light loss in an optical waveguide device. 
     Means for Solving the Problem 
     In order to achieve the above object, according to a first aspect of the present invention, there is provided an optical waveguide device, comprising: 
     an optical guide member extending in an optical guide direction with a core section in a clad section, wherein 
     the core section is formed in a substantial U-shape of a two-dimensional shape including;
         a body portion; and   light inlet and exit portions which protrude from both ends of the body portion in a direction substantially orthogonal to the body portion;       

     inclined planes are formed on shoulder portions located at continuous portions of the body portion and the light inlet and exit portions; and 
     the inclined planes of the core section are exposed outside. 
     Preferably, the optical guide member is formed in a film-like shape. 
     Preferably, ends of the light inlet and exit portions of the core section are provided with photoelectric conversion elements to perform a conversion between light and electricity. 
     Preferably, one of the photoelectric conversion elements provided on one end of the light inlet and exit portions is a light-emitting element, and the other of the photoelectric conversion elements provided on the other end of the light inlet and exit portions is a light-receiving element. 
     According to a second aspect of the present invention, there is provided a method for fabricating an optical waveguide device, comprising the steps of: 
     forming a first clad layer; 
     forming a core section formed in a substantial U-shape of a two-dimensional shape on the first clad layer, including a body portion and light inlet and exit portions which protrude from both ends of the body portion in a direction substantially orthogonal to the body portion, in which inclined planes are formed on shoulder portions located at continuous portions of the body portion and the light inlet and exit portions; 
     forming a second clad layer which covers the core section and has a refractive index as same as the first clad layer; and 
     exposing the inclined planes of the core section outside. 
     Preferably, the inclined planes of the core section are exposed by cutting the first clad layer and the second clad layer in a direction orthogonal to the layers. 
     Preferably, the inclined planes of the core section are exposed by etching processing performed on the first clad layer and the second clad layer. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     According to the present invention, by totally reflecting light on an inclined plane and propagating the light along the substantially U-shaped core section, the light may be directly introduced to the core section from a substantially orthogonal direction to the optical guide direction, and the light directly exits from the core section in a direction substantially orthogonal to the optical guide direction. Consequently, since the light does not pass through a portion where a refractive index is different, scattering and reflecting on an interface can be avoided, and optical loss can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an optical waveguide film cable  1  of the embodiment of the present invention; 
         FIG. 2  is a cross-sectional view showing the optical waveguide film cable  1 ; 
         FIG. 3A  is a diagram for describing a forming of a clad layer  9   a;    
         FIG. 3B  is a diagram for describing a forming of a core layer  10   a;    
         FIG. 3C  is a diagram for describing a forming of a core section  10 ; 
         FIG. 3D  is a diagram showing a shape of the core section  10 ; 
         FIG. 4A  is a diagram for describing a method of forming the clad layer  9   b  and a protective layer  12 ; 
         FIG. 4B  is a diagram showing a cross-section taken along A-A shown in  FIG. 4A ; 
         FIG. 5A  is a perspective view showing layers by cutting out in a rectangular shape to include the core section  10 ; 
         FIG. 5B  is a top view showing layers by cutting out in a rectangular shape to include the core section  10 ; 
         FIG. 6A  is a perspective view showing mirror faces  18 ,  19  in an exposed state; 
         FIG. 6B  is a top view showing the mirror faces  18 ,  19  in an exposed state; 
         FIG. 7  is a cross-sectional view showing an optical waveguide device  31 ; 
         FIG. 8  is a diagram for describing a mirror block method to change an optical path; and 
         FIG. 9  is a diagram for describing a problem in the optical waveguide device  31 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention will be specifically described with reference to the drawings. 
       FIG. 1  is a perspective view showing an optical waveguide film cable  1  of the embodiment of the present invention and  FIG. 2  is a cross-sectional view of the optical waveguide film cable  1 . As shown in  FIG. 1  and  FIG. 2 , the optical waveguide film cable  1  is constituted of a light-emitting element  3  provided on a substrate  2 , a light-receiving element  5  provided on a substrate  4  and an optical guide member  6  extending in an optical guide direction (in  FIG. 2 , right direction). The light-emitting element  3  and the optical guide member  6 , and the light-receiving element  5  and the optical guide member  6  are adhered with each other by optical path members  7 ,  8  respectively. The optical path members  7 ,  8  have a function to adhere and fix the light-emitting element  3  and the light-receiving element  5  to the optical guide member  6  and a function as a refractive medium to stabilize transmission of light. 
     The optical guide member  6  has a film-like shape and flexibility, and is constituted of a clad section  9 , a core section  10  formed in the clad section  9  and protective layers  11 ,  12 . A refractive index of the core section  10  is higher than a refractive index of the clad section  9  and a refractive index of air. Thus, the light propagated through the core section  10  is totally reflected at the interface with the clad section  9  or the air. A side face of the clad section  9  is covered with protective films  11 ,  12 . 
     As shown in  FIG. 2 , the core section  10  includes a body portion  13  extending in an optical guide direction, and a light inlet portion  14  and a light exit portion  15  protruding from both ends of the body portion  13  in a direction substantially orthogonal to the body portion  13 , and is formed in a substantial U-shape. The light inlet portion  14  and the light exit portion  15  are the light inlet and exit portions described in the claims. Mirror faces  18 ,  19  which are inclined planes having an inclination angle of 45° are formed on a shoulder portion  16  located at the continuous portion of a body portion  13  and a light inlet portion  14 , and on a shoulder portion  17  located at the continuous portion of the body portion  13  and a light exit portion  15 , respectively. The core section  10  is exposed outside the clad section  9  and in contact with the outside air at these mirror faces  18 ,  19 . A cross-section of the core section  10  in a direction perpendicular to the direction light propagates through the core section  10  is formed in a square shape. 
     The light-emitting element  3  is provided on an end of the light inlet section  14 . The light-emitting element  3  is constituted of, for example, a surface emitting semiconductor laser (VCSEL: Vertical Cavity Surface Emitting Laser), and according to an electrical signal supplied externally, emits light in a direction perpendicular to the contact face with the optical guide member  6  (in  FIG. 2 , upward). 
     The light-receiving element  5  is provided on an end of the light exit portion  15 . The light-receiving element  5  is constituted of, for example, PD (PhotoDiode) and receives light in a direction perpendicular to the contact face with the optical guide member  6  (in  FIG. 2 , downward) to convert to an electrical signal. 
     As shown in  FIG. 2 , the light emitted from the light-emitting element  3  propagates through the light inlet portion  14  of the core section  10  and is reflected totally by the mirror face  18 . Light subjected to optical path change by 90° on the mirror face  18  propagates through the body portion  13  of the core section  10  and is reflected totally by the mirror surface  19 . Light subjected to optical path change by 90° on the mirror surface  19  propagates through the light exit portion  15  of the core section  10  and is received by the light-receiving element  5 . 
     Next, a method for fabricating an optical waveguide film cable  1  will be described with reference to  FIG. 3A ,  FIG. 3B ,  FIG. 3C ,  FIG. 3D ,  FIG. 4A ,  FIG. 4B ,  FIG. 5A ,  FIG. 5B ,  FIG. 6A  and  FIG. 6B . 
     First, as shown in  FIG. 3A , a resin thin film in a liquid state is formed on the protective film  11  with a rotating film formation method, etc., and the film is heated to form a clad layer  9   a . The protective film  11  is constituted of a resin film, for example, polyimide, PET, etc. The clad layer  9   a  includes polymeric resin material with optical transparency, and is constituted of, for example, epoxy resin, acrylic resin, imide resin, etc. 
     Then, as shown in  FIG. 3B , a resin thin film in a liquid state is formed on the clad layer  9   a  with a rotating film formation method, etc., and the film is heated to form a core layer  10   a  with a higher refractive index than the clad layer  9   a . The core layer  10   a  includes polymeric resin material with optical transparency and is constituted of, for example, epoxy resin, acrylic resin, imide resin, etc. 
     Next, a mask is applied to the core layer  10   a , and as shown in  FIG. 3C , a core pattern of the core section  10  is formed in a two-dimensional state with photolithography and etching processing. “Formed in a two-dimensional state” means to form a two-dimensional pattern with a plane parallel to an XY plane including arrows X, Y shown in  FIG. 3C . In short, the core section  10  is formed along a plane of the clad layer  9   a . As shown in  FIG. 3D , the core section  10  is substantially U-shaped, includes the body portion  13 , the light inlet portion  14  and a light exit portion  15  and includes mirror faces  18 ,  19  on a shoulder portion  16  located at the continuous portion of a body portion  13  and a light inlet portion  14 , and on a shoulder portion  17  located at the continuous portion of the body portion  13  and a light exit portion  15 , respectively. 
     Next, as shown in  FIG. 4A , a resin thin film in a liquid state is formed with a rotating film formation method, etc., and the film is heated to cover the core section  10  with a material which has a refractive index as same as the clad layer  9   a  to form a clad layer  9   b . It is preferable that the clad layer  9   b  is formed with a material with a same composition as the clad layer  9   a . As shown in  FIG. 4   a , a protective film  12  is formed on the clad layer  9   b . The protective film  12  is constituted of a resin film, for example, polyimide, PET, etc.  FIG. 4B  shows a cross-section taken along A-A shown in  FIG. 4A . 
       FIG. 5A  and  FIG. 5B  are a perspective view and a top view showing layers shown in  FIG. 4A  by cutting out in a rectangular shape to include core section  10 . By processing the layers perpendicular to the layers at the position of B-B, C-C shown in  FIG. 5A  and  FIG. 5B , the mirror faces  18 ,  19  of the core section  10  are exposed to the outside. In this way, an optical guide member  6  shown in  FIG. 6A  and  FIG. 6B  is completed. The clad layer  9   a  and the clad layer  9   b  shown in  FIG. 6A  correspond to the clad section  9  shown in  FIG. 1  and  FIG. 2 . 
     The protective layer  11 , the clad layer  9   a , the clad layer  9   b  and the protective layer  12  may be cut in a direction perpendicular to the layers with a dicer or a laser as a method of processing for exposing the mirror faces  18 ,  19 . The unnecessary portions may also be dissolved by liquid phase etching or gas phase etching processing on the layers, protective layer  11 , the clad layer  9   a , the clad layer  9   b  and the protective layer  12 . 
     As shown in  FIG. 1  and  FIG. 2 , by adhering the light-emitting element  3  and the light-receiving element  5  to the optical guide member  6  with optical path members,  7 ,  8 , the optical waveguide film cable  1  is completed. 
     As described above, according to the present embodiment, by totally reflecting light by mirror faces  18 ,  19  and propagating the light along a core section  10  substantially U-shaped, the light may be directly introduced to the core section  10  from a substantially orthogonal direction to the optical guide direction, and the light may directly exit from the core section  10  in a substantially orthogonal direction to the optical guide direction. Consequently, since the light does not pass through a portion where a refractive index is different, scattering and reflecting on an interface may be avoided, and optical loss may be reduced. Also, the length of the light inlet portion  14  and the light exit portion  15  of the core section  10  may be set freely. 
     When the mirror faces  18 ,  19  are exposed by cutting with a dicer, since the processing may be performed with the same thin blade as used in cutting the external form of the optical guide member  6 , processing with high accuracy may be easily performed, and a number of steps such as changing blades, etc. may be reduced compared to the method of processing using an angled blade. 
     The above-described embodiment is an example of the optical waveguide device of the present invention, and thus is not limited to the embodiments shown. Details of the components constituting the optical waveguide film cable  1  may be modified without leaving the scope of the invention. 
     For example, in the above-described embodiment, the angle of the mirror faces  18 ,  19  are formed at 45°, however, the angle of the mirror faces  18 ,  19  are not limited to this angle, and the angle may be adjusted to an angle so that the light loss becomes a minimum according to a characteristic of the light-emitting element  3  or the light-receiving element  5 . In the above-described embodiment, the substantially U-shaped core section  10  is formed in a two-dimensional shape, however, the shape is not limited to a U-shape, and a V-shaped, M-shaped, N-shaped, etc. two-dimensional pattern may be formed. 
     The method of forming the core pattern is not limited to photolithography and etching processing, and direct lithography may also be used. 
     In the above-described embodiment, the light-emitting element  3  and the light-receiving element  5  are respectively provided on different substrates  2 ,  4 , however, the light-emitting element  3  and the light-receiving element  5  may be provided on the same substrate. 
     INDUSTRIAL APPLICABILITY 
     The optical waveguide device and the method for fabricating the optical waveguide device of the present invention may be applied to the field of optical communication. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  optical waveguide film cable (optical waveguide device) 
           3  light-emitting element 
           5  light-receiving element 
           6  optical guide member 
           7 ,  8  optical path members 
           9  clad section 
           9   a  clad layer (first clad layer) 
           9   b  clad layer (second clad layer) 
           10  core section 
           10   a  core layer 
           11 ,  12  protective layers 
           13  body portion 
           14  light inlet portion (light inlet and exit portion) 
           15  light exit portion (light inlet and exit portion) 
           16 ,  17  shoulder portions 
           18 ,  19  mirror faces (inclined planes) 
           31  optical waveguide device 
           33  light-emitting element 
           35  light-receiving element 
           36  optical guide member 
           37 ,  38  optical path member 
           39  protective layer 
           40  clad section 
           41  protective layer 
           42  core section 
           43 ,  44  mirror faces 
           45  mirror face