Abstract:
An optical transmission module is disclosed that comprises an optical element having an optical path formed therein, optical connection parts respectively arranged on both sides of the optical element so as to connect the optical element to plural optical fibers, and reinforcement parts. The reinforcement parts are applied to a part of or an entire circumference of respective connected portions between the optical element and the optical connection parts, and then cured to reinforce connections between the optical element and the optical connection parts.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical transmission module and a manufacturing method thereof, and particularly relates to an optical transmission module having an optical element with an optical circuit formed therein and optical connection parts adapted to connect optical fibers to the optical element.  
         [0003]     2. Description of the Related Art  
         [0004]     In recent years, with a rapid progress in optical communications, enhancement of communication speed and transmission capacity has been promoted. Wavelength-Division Multiplexing (WDM), which is a multiplexing technique using lights with various wavelengths and capable of supporting such enhancement, is gaining widespread use in optical communication systems. The WDM requires highly-accurate optical components for enabling multiplexing and demultiplexing of lights with a wavelength interval of 1 nm or less.  
         [0005]     As is commonly known in the art of optical communications, various optical elements are used in transmission channels formed by optical fibers (see, for example, Japanese Patent Laid-Open Publication No. 05-264862). Among the optical components, waveguide components are remarkable in that they are mass-producible and applicable to LSI. Especially, expectations for Planar Lightwave Circuit (PLC), which is one of the waveguide components, is high because it can be connected to optical fibers with a low optical transmission loss and can integrate a number of optical functions therein.  
         [0006]     A PLC substrate having such a PLC optically connected to optical fibers is therefore used in high-speed and large-capacity optical communications. The PLC substrate is connected to the optical fibers by fiber arrays, and the fiber arrays are connected to the PLC substrate by optical path forming resins.  
         [0007]     Conventionally, the optical elements having PLCs have been made of quartz, Pyrex™, or the like. However, with recent developments for size and weight reduction and easier production, the core and cladding of optical elements having PLCs can be formed by laminating polymer resins with different refractive indexes on a silicon substrate.  
         [0008]      FIG. 8  shows a perspective view of a related-art optical transmission module  10 , and  FIG. 9  shows side and top views of the optical transmission module  10 .  
         [0009]     The optical transmission module  10  comprises an optical element  30 , and fiber arrays  21  and  22  for connecting optical fibers  11 ,  12  and  13  to the optical element  30 .  
         [0010]     The fiber array  21  holds the optical fiber  11 , an end face of which is exposed from an end face of the fiber array  21  in the direction of an arrow X 2 . The fiber array  22  holds the optical fibers  12  and  13 , an end face of each of which is exposed from an end face of the fiber array  22  in the direction of an arrow X 1 . The fiber arrays  21  and  22  are typically made of quartz or a glass material. The end face of the fiber array  21  in the direction of the arrow X 2  is bonded to the optical element  30  through an optical path forming resin  41  so as to match the end face of the optical fiber  11  and an end face of an optical path formed in the optical element  30 . The end face of the fiber array  22  in the direction of the arrow X 1  is bonded to the optical element  30  through an optical path forming resin  42  so as to match the end faces of the optical fibers  12  and  13  and end faces of optical paths formed in the optical element  30 .  
         [0011]     The following describes the optical element  30  in detail.  
         [0012]      FIG. 10  shows a perspective view of the optical element  30 .  
         [0013]     The optical element  30  is adapted to branch an incident light output and output branched lights form a waveguide, comprising a substrate  31 , a lower cladding layer  32 , a core  33 , and an upper cladding layer  34 . The substrate  31  is, for example, a silicon (Si) substrate. The lower cladding layer  32 , the core  33 , the upper cladding layer  34  are resin laminations formed on the substrate  31 .  
         [0014]     The following describes a manufacturing method of the optical element  30 .  
         [0015]     First, the lower cladding layer  32  is formed on the substrate  31 . The lower cladding layer  32  is typically made of transparent resin such as fluorinated polyimide. The lower cladding layer  32  is formed by, for example, forming a polyamic acid layer on the substrate  31  with a spin-coating method, and imidizing the layer through a heat treatment.  
         [0016]     Then, the core  33  is formed on the lower cladding layer  32 . The core  33  as a waveguide is made of the same fluorinated polyimide as the lower cladding layer  32  and the upper cladding layer  34 . The composition of the resin of the core  33  is adjusted to have a refractive index different from that of the lower cladding layer  32  and the upper cladding layer  34 . For example, when the refractive index of the lower cladding layer  32  and the upper cladding layer  34  is n 1  and the refractive index of the core  33  is n 2 , the composition of the resin is adjusted to have 
 
n 1 &lt;n 2 . 
 
 Herein, the refractive index n 1  and n 2  are, for example, n 1 =1.525, n 2 =1.531. 
 
         [0017]     For forming the core  33 , a polyamic acid layer is formed uniformly on the lower cladding layer  32  with a spin-coating method, and the layer is imidized through a heat treatment to form a transparent resin layer. Then, the transparent resin layer is coated with a patterned resist, and is dry-etched by a RIE (Reactive Ion Etching) machine to have the lower cladding layer  32  exposed. In this process, a part coated with a photoresist remains unetched to keep the transparent resin layer thereunder. Then, the remaining photoresist is removed. In this way, the core  33  with a desired pattern is formed. The thickness of the core  33  is around 9 through 10 μm, which is substantially equal to the diameter of the optical fibers  11 ,  12  and  13 .  
         [0018]     Next, the upper cladding layer  34  is formed to cover the upper and side surfaces of the core  33 . The upper cladding layer  34  is made of the same fluorinated polyimide as the lower cladding layer  32 , and the composition thereof is adjusted to have the refractive index n 1 , which is the same refractive index as the lower cladding layer  32 . The upper cladding layer  34  is formed by, for example, forming a polyamic acid layer with a spin-coating method, and imidizing the layer through a heat treatment.  
         [0019]     In this way, the optical element  30  having a waveguide with a desired pattern is formed.  
         [0020]     The optical element  30  having polymer resins with different refractive indexes on the silicon substrate cannot have a resin material on the upper, side, and bottom surfaces thereof due to a large influence of the refractive index. If the optical element  30  has the resin material on those surfaces, a light passing through the core  33  is lost. For this reason, the optical element  30  is connected to the fiber arrays  21  and  22  only at the end faces thereof.  
         [0021]     However, the end faces of the optical element  30  are small, so that the connection areas between the optical element  30  and the fiber arrays  21  and  22  are also small. This makes connections between the optical element  30  and the fiber arrays  21  and  22  weak. Therefore, the optical transmission module  10  with a silicon substrate described above is disadvantageous in this respect.  
       SUMMARY OF THE INVENTION  
       [0022]     An object of the present invention is to provide an optical transmission module and a manufacturing method thereof to overcome at least one disadvantage described above. The specific object of the present invention is to provide an optical transmission module and a manufacturing method thereof to strengthen connections between fiber arrays and an optical element with minimum optical loss.  
         [0023]     According to an aspect of the present invention, there is provided an optical transmission module, comprising an optical element having an optical path formed therein, optical connection parts respectively arranged on both sides of the optical element so as to connect the optical element to plural optical fibers, and reinforcement parts applied to a part of or an entire circumference of respective connected portions between the optical element and the optical connection parts and cured to reinforce connections between the optical element and the optical connection parts.  
         [0024]     The reinforcement parts are preferably made of a resin material with hardness lower than the hardness of a material of the optical element, a material of the optical connection parts, and an optical path forming resin connecting the optical element and the optical connection parts.  
         [0025]     It is preferable that the Young&#39;s modulus of the resin material of the reinforcement parts be approximately 9.0×10 9  or lower.  
         [0026]     It is also preferable that the Young&#39;s modulus of the resin materials of the reinforcement parts be approximately 1.0×10 4  or higher.  
         [0027]     It is also preferable that the reinforcement parts be respectively formed as fillets on the corresponding connected portions between the optical element and the optical connection parts.  
         [0028]     According to another aspect of the present invention, there is provided a manufacturing method of an optical transmission module including an optical element having an optical path formed therein, and optical connection parts respectively arranged on both sides of the optical element so as to connect the optical element to plural optical fibers. The method comprises a connecting step of connecting the optical element to the optical connection parts by an optical path forming resin, and a reinforcing step of applying a resin to a part of or an entire circumference of connected portions between the optical element and the optical connection parts and curing the resin to reinforce connections between the optical element and the optical connection parts, after the connecting step in which the optical element and the optical connection parts are connected by the optical path forming resin.  
         [0029]     According to the present invention, since there are reinforcement parts applied to a part of or an entire circumference of the respective connected portions between the optical element and the optical connection parts and cured to reinforce connections between the optical element and the optical connection parts, the connections between the optical element and the optical connection parts can be reinforced with minimum optical loss. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]      FIG. 1  shows a perspective view of an optical transmission module according to a first embodiment of the present invention;  
         [0031]      FIG. 2  shows side and top views of the optical transmission module according to the first embodiment of the present invention;  
         [0032]      FIG. 3  is a graph showing characteristics of optical loss at reinforcement portions in relation to Young&#39;s modulus;  
         [0033]      FIG. 4  shows a perspective view of an optical transmission module according to a second embodiment of the present invention;  
         [0034]      FIG. 5  shows side and top views of the optical transmission module according to the second embodiment of the present invention;  
         [0035]      FIG. 6  shows a perspective view of an optical transmission module according to a third embodiment of the present invention;  
         [0036]      FIG. 7  shows side and top views of the optical transmission module according to the third embodiment of the present invention;  
         [0037]      FIG. 8  shows a perspective view of a related-art optical transmission module;  
         [0038]      FIG. 9  shows side and top views of the related-art optical transmission module; and  
         [0039]      FIG. 10  shows a perspective view of an optical element. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     First Embodiment  
       [0040]      FIG. 1  shows a perspective view of an optical transmission module  100  according to a first embodiment of the present invention, and  FIG. 2  shows side and top views of the optical transmission module  100 . In  FIGS. 1 and 2 , elements same as those in  FIGS. 8 and 9  are denoted by the same reference numbers, and they are not further described here.  
         [0041]     The optical transmission module  100  according to the first embodiment has a fillet-like reinforcement portion  111  around a connected portion between the fiber array  21  and the optical element  30 , and a reinforcement portion  112  around a connected portion between the fiber array  22  and the optical element  30 . The fiber arrays  21  and  22  correspond to optical connection parts in the following claims.  
         [0042]     The reinforcement portion  111  is made of a resin material, such as a silicon-based resin material, with hardness lower than the resin material of the optical element  30 , the resin material of the fiber array  21 , and the optical path forming resin  41  connecting the optical element  30  to the fiber array  21 .  
         [0043]      FIG. 3  is a graph showing characteristics of optical loss at the reinforcement portions  111  and  112  relative to the Young&#39;s modulus.  
         [0044]     The optical loss has the characteristic as shown in  FIG. 3  in relation to Young&#39;s modulus of the reinforcement portions  111  and  112 . For example, it was found from experiment that the optical loss at the connected portions between the optical element  30  and the fiber arrays  21  and  22  is reduced when a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9  is used as the resin material of the reinforcement portions  111  and  112 .  
         [0045]     According to the first embodiment, the connection between the fiber arrays  21  and  22  and the optical element  30  is strengthened by forming the fillet-like reinforcement portions  111  and  112  around the connected portions between the fiber arrays  21  and  22  and the optical element  30 . Especially, the optical loss is minimized when a silicon-based resin with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9  is used as the reinforcement portions  111  and  112 .  
         [0046]     The following describes a manufacturing method of the optical transmission module  100  of the first embodiment.  
         [0047]     First, the end face of the optical element  30  in the direction of the arrow X 1  and the fiber array  21  are connected through the optical path forming resin  41  so as to match the optical paths thereof, and the optical path forming resin  41  is cured. Likewise, the end face of the optical element  30  in the direction of the arrow X 2  and the fiber array  22  are connected through the optical path forming resin  42  so as to match the optical paths thereof, and the optical path forming resin  42  is cured. The fiber arrays  21  and  22  are thus bonded to the optical element  30  respectively at the end faces in the directions of the arrow X 1  and the arrow X 2 .  
         [0048]     Next, a reinforcement resin material is applied to the entire circumference of the connected portion between the end face of the optical element  30  in the direction of the arrow X 1  and the fiber array  21 , and cured through addition/condensation reactions by, for example, a heat treatment and an ultraviolet radiation to form the reinforcement portion  111 . Likewise, a reinforcement resin material is applied to the entire circumference of the connected portion between the end face of the optical element  30  in the direction of the arrow X 2  and the fiber array  22 , and is cured through addition/condensation reactions by, for example, a heat treatment and an ultraviolet radiation to form the reinforcement portion  112 . In this way, the reinforcement portions  111  and  112  are respectively formed on the entire circumferences of the connected portions between the end faces of the optical element  30  in the directions of the arrows X 1  and X 2  and the fiber arrays  21  and  22 .  
         [0049]     Since the reinforcement portions  111  and  112  formed on the connected portions between the optical element  30  and the fiber arrays  21  and  22  are made of the resin material with hardness that minimizes the optical loss, i.e., with the Young&#39;s modulus of approximately 1.0×10 4  through 9.0×10 9 , the connections between the optical element  30  and the fiber arrays  21  and  22  are strengthened while minimizing the optical loss at the connected portions between the optical element  30  and the fiber arrays  21  and  22  and therearound.  
       Second Embodiment  
       [0050]      FIG. 4  shows a perspective view of an optical transmission module  200  according to a second embodiment of the present invention, and  FIG. 5  shows side and top views of the optical transmission module  200 . In  FIGS. 4 and 5 , elements the same as those in  FIGS. 8 and 9  are denoted by the same reference numbers, and they are not further described here.  
         [0051]     The optical transmission module  200  of the second embodiment is different from that of the first embodiment in the position of reinforcement portions  211 ,  212 ,  221  and  222 .  
         [0052]     The reinforcement portion  211  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  21  in the direction of an arrow Z 1 . The reinforcement portion  212  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  21  in the direction of an arrow Z 2 .  
         [0053]     The reinforcement portion  221  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  22  in the direction of the arrow Z 1 . The reinforcement portion  222  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  22  in the direction of the arrow Z 2 .  
         [0054]     According to the second embodiment, since the reinforcement portions  211 ,  212 ,  221  and  222  are formed only on the edges of the optical element  30  and the fiber arrays  21  and  22  in the directions of the arrows Z 1  and Z 2 , the optical loss at the connected portions between the optical element  30  and the fiber arrays  21  and  22  is reduced.  
       Third Embodiment  
       [0055]      FIG. 6  shows a perspective view of an optical transmission module  300  according to a third embodiment of the present invention, and  FIG. 7  shows side and top views of the optical transmission module  300 . In  FIGS. 6 and 7 , elements the same as those in  FIGS. 8 and 9  are denoted by the same reference numbers, and they are not further described here.  
         [0056]     The optical transmission module  300  of the third embodiment is different from those of the first and second embodiments in the position of reinforcement portions  311 ,  312 ,  321  and  322 .  
         [0057]     The reinforcement portion  311  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  21  in the direction of an arrow Y 1 . The reinforcement portion  312  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  21  in the direction of an arrow Y 2 .  
         [0058]     The reinforcement portion  321  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  22  in the direction of the arrow Y 1 . The reinforcement portion  322  is made of a resin material with the Young&#39;s modulus in a cured state of approximately 1.0×10 4  through 9.0×10 9 , which is applied and cured like a fillet on the edges of the optical element  30  and the fiber array  22  in the direction of the arrow Y 2 .  
         [0059]     According to the third embodiment, since the reinforcement portions  311 ,  312 ,  321  and  322  are formed only on the edges of the optical element  30  and the fiber arrays  21  and  22  in the directions of the arrows Y 1  and Y 2 , the optical loss at the connected portions between the optical element  30  and the fiber arrays  21  and  22  is reduced.  
       Others  
       [0060]     While the optical element  30  that branches a light into two is exemplified in the above embodiments, the present invention is applicable to other types of optical elements without being limited to the above specific optical element  30 .  
         [0061]     The present application is based on Japanese Priority Application No. 2004-325087 filed on Nov. 9, 2004, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.