Abstract:
A method of manufacturing a two-dimensional (planar) optical waveguide comprises a first step of preparing a member having a thermoplastic structure ( 102 ) formed on a substrate ( 100 ), a second step of deforming the structure by heat treatment and a third step of forming an optical waveguide section ( 112 ) on the structure and the substrate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a planar (i.e., two-dimensional) optical waveguide and a method of manufacturing the same.  
           [0003]    2. Related Background Art  
           [0004]    The quick spread of mobile phones and personal information terminals in recent years has entailed development of down-sized, lightweight and sophisticated circuit boards that are highly integrated and adapted to operate very fast. As a result, there have arisen problems including wiring delays and EMI (electromagnetic interferences).  
           [0005]    While conventional electric wiring suffers from such problems, optical wiring technologies have drawn attention as means for dissolving the problems because optical wiring is free from wiring delays and signal degradations and can reduce electromagnetic interferences caused by wires.  
           [0006]    For example, Japanese Patent Application Deposited-Open No. 9-96746 discloses an optical circuit board as described below, which exploits advantages of optical wiring. The disclosed optical circuit board has an optical wiring section and an electric wiring section separated from each other. Light that is transmitted through the optical waveguide arranged on the substrate is modulated by driving an optical switch or an optical modulator also arranged on the substrate by means of a voltage signal applied to it from an electronic device. In this way, an electric signal is converted into an optical signal and transmitted. Then, the optical signal is received by a light-receiving device arranged on the substrate or on some other substrate and converted back into an electric signal, which electric signal is then conveyed to some other electronic device or some other part of the same electronic device. While optical wiring is provided as supplementary means for avoiding problems of electric wiring in the optical circuit board of the above identified patent document, the area that can be used for electric/optical signal conversion or optical/electric signal conversion is limited because a linear transmission path (linear polymer waveguide) is used for the optical wiring.  
           [0007]    Japanese Patent Application Deposited-Open No. 2000-199827 proposes the use of a mirror that is inclined by 45° relative to the light path of an optical waveguide in order to efficiently couple rays of light entering or exiting perpendicularly relative to the light path of the optical waveguide. However, the transmission path is again linear because the 45°-inclined mirror is used in order to couple an incident light beam to the optical waveguide and also a light beam transmitted through the optical waveguide to a light-receiving device. Then, the positions that can be used for arranging the light-emitting device and the light-receiving device are limited to by turn limit freedom of design particularly when a plurality of transmission paths have to be arranged.  
         SUMMARY OF THE INVENTION  
         [0008]    In view of the above identified problem that freedom of design is limited because the transmission path of an optical signal is linear (an optical waveguide that allows transmission of light mainly in a single direction), it is therefore an object of the present invention to provide a planar optical waveguide and a method of manufacturing the same. Another object of the present invention is to provide an optical waveguide having an optical path changing section suitably adapted to converge and scatter light and a method of manufacturing the same.  
           [0009]    According to the invention, there is provided a method of manufacturing a planar optical waveguide comprising: a first step of preparing a member having a structure formed on a substrate, the structure comprising a thermoplastic material; a second step of deforming the structure by heat treatment; and a third step of forming an optical waveguide section on the structure and the substrate.  
           [0010]    The structure may be made to have a curved surface in the second step so as to make it operate as an optical path changing section.  
           [0011]    The above described method of manufacturing a planar optical waveguide according to the invention may further comprise a fourth step of forming a reflection film on a surface of the structure deformed in the second step.  
           [0012]    The third step may include a step of forming a core layer on the substrate and the structure and then forming a clad layer on the core layer.  
           [0013]    At least either a light-emitting device or a light-receiving device may be mounted on the planar optical waveguide.  
           [0014]    The structure may comprise a material selected from resists, photosensitive resins, photo-curing resins or electron beam curing resins.  
           [0015]    The structure may have a column-shaped profile and may be deformed to show a hemispherical profile in the second step.  
           [0016]    The planar optical waveguide and a printed circuit board carrying thereon an electronic device may be bonded to each by way of at least either a light-emitting device or a light-receiving device.  
           [0017]    According to the invention, there is also provided a planar optical waveguide comprising: a substrate; an optical path changing section arranged on the substrate; and an optical waveguide section formed on the substrate and the optical path changing section; the optical path changing section comprising a thermoplastic resin material.  
           [0018]    According to the invention, there is further provided a method of manufacturing a planar optical waveguide device including at least a sheet-shaped core layer and a light path converting microstructure arranged near the spot for arranging a light-emitting device or a light-receiving device, the method comprising: a first step of forming a thermoplastic first microstructure at a predetermined position on a substrate; a second step of fusing and re-solidifying the first microstructure so as to deform it and turn it into a second microstructure by heat treatment; and a third step of covering the entire substrate including the second microstructure with a core layer.  
           [0019]    A method according to the invention and comprising the above described basic steps may be carried out in various specific modes as described below.  
           [0020]    The planar optical waveguide device may have a multilayer structure of a sheet-shaped core layer and first and second clad layers sandwiching the core layer and the first microstructure may be formed in the first step at a predetermined position on the first clad layer, which is the substrate, whereas the entire substrate including the second microstructure may be covered by the core layer and the second clad layer in the third step.  
           [0021]    Furthermore, the above described method may additionally comprise a fourth step of forming a reflection film on the surface of the second microstructure. Then, the reflection film is typically formed by evaporation of a metal in the fourth step.  
           [0022]    The above described method may further comprise a fifth step of mounting at least a light-emitting device or a light-receiving device on or in the core layer or on or in the second clad layer. Typically, an optical device mounting guide is formed by photolithography or etching and the optical device is mounted in the guide in the fifth step.  
           [0023]    A plurality of first microstructures may be arranged at predetermined respective positions on the substrate in the first step and the plurality of microstructures may be simultaneously deformed and turned to second microstructures by heat treatment in the second step. More specifically, a plurality of microstructures uniformly showing a first profile may be arranged at predetermined respective positions on the substrate in the first step and the plurality of microstructures showing the first profile may be simultaneously deformed and turned to second microstructures uniformly showing a second profile in the second step. This mode of carrying out the present invention can emphatically realize the characteristic advantages of a manufacturing method according to the invention.  
           [0024]    Typically, the first microstructure is formed by using at least a thermoplastic resin material selected from resists, photosensitive resins, photo-curing resins, or electron beam curing resins.  
           [0025]    Typically, the first microstructure formed in the first step has a column-shaped profile such as a cylindrical profile and the second microstructure has a substantially hemispherical profile. Then, the profile and the radius of curvature of the microstructure of a thermoplastic material deformed by heat treatment may be appropriately controlled by treating the substrate surface to make it water-repellent. The surface energy of the substrate is reduced by such a water-repelling treatment and the thermoplastic material is repelled more strongly. As an example, a water-repellent surface can be formed by treating the substrate surface with a silane coupling agent having a functional group containing a fluorine atom.  
           [0026]    The substrate may be made of glass and the core layer and the second clad layer may be made of an organic polymer or resin.  
           [0027]    A method of manufacturing an opto-electronic circuit board according to the invention is proposed to dissolve the above identified problems. With the method of manufacturing an opto-electronic circuit board according to the invention, a planar optical waveguide device manufactured by the method of manufacturing a planar optical waveguide device according to the invention and a printed circuit board carrying an electronic element such as LSI are bonded to each other so that all or part of the electric signal output from the electronic element on the printed circuit board is converted into an optical signal by way of a light-emitting device, planarly transmitted through the core layer as it is scattered by the light path converting microstructure and converted back into an electric signal by way of an appropriate light-receiving device as it is scattered by the light path converting microstructure near the light-receiving device and the electric signal obtained by the conversion is electrically coupled to the electronic element on the printed circuit board. The method of manufacturing an opto-electronic circuit board may comprise a step of mounting a light-emitting device on the electric signal output terminal of the electronic element and mounting a light-receiving device on the electric signal input terminal of the electronic element and a step of bonding the light-emitting device and the light-receiving device mounted on the electronic element to the mounting guides of the planar optical waveguide device when bonding the planar optical waveguide device and the printed circuit board. Alternatively, the method of manufacturing an opto-electronic circuit board may comprise a step of mounting a light-emitting device and a light-receiving device on corresponding mounting guides of the planar optical waveguide device and a step of bonding the electrodes of the light-emitting device and the light-receiving device mounted on the planar optical waveguide device respectively to the output terminal and the input terminal of the electronic element mounted on the printed circuit board when bonding the planar optical waveguide device and the printed circuit board.  
           [0028]    With the above described manufacturing method, in the step of arranging a plurality of microstructures uniformly showing a first profile at desired positions on the first clad layer, a pattern of circular cylinders can be formed easily at a time by using a photoresist (e. g., AZ9260) as a thermoplastic material of the microstructures and a photo-mask showing a pattern of circular openings (e. g., having a radius of 50 μm) and exposing the pattern to light irradiation perpendicularly from right above.  
           [0029]    It was found by experiments that a microstructure showing a cylindrical profile can be deformed and turned to a microstructure showing a hemispherical profile by subjecting the former to a predetermined heat treatment in the step of deforming a first microstructure and turning it to a second microstructure. It was also found that a plurality of microstructures showing a certain profile can be deformed simultaneously and uniformly. For example, microstructures showing a cylindrical profile can be uniformly and simultaneously turned to microstructures showing a hemispherical profile when they are heat-treated at 160° C. for 30 minutes in an oven containing a nitrogen atmosphere. What is remarkable about the heat treatment is that, even if the microstructures showing a cylindrical pattern are not highly accurately formed in the first step, they can simultaneously be deformed and turned to microstructures uniformly showing a hemispherical profile in the second step. In other words, light path converting microstructures can be formed at low cost. The hemispherical profile of the microstructures is indispensable and ideal for an opto-electronic circuit board having a planar optical waveguide to scatter light or converge light. Thus, a method of manufacturing an opto-electronic circuit board according to the invention is a very effective method. A thermoplastic material (e.g., photosensitive resins, photo-curing resins such as a UV-curing resin, electron beam-curing resins or metals having a relatively low melting point) other than resists provides similar advantages.  
           [0030]    The above described step of forming a reflection film on the surface of the second microstructure is used to raise the surface reflectivity of the microstructure for enhancing its light scattering effect. When a number of microstructures are used, a reflection film is formed on all of them at a time by for example evaporation of a metal. The use of a metal layer or a dielectric layer (multilayer film mirror) showing a reflectivity appropriate to the wavelength of light to be transmitted is effective. It may not be necessary to form a reflection film on the microstructure when the refractive index of the microstructure is smaller than that of the core layer. Alternatively, a technique of making the microstructure showing a coarse surface may be used in order to enhance its light scattering effect.  
           [0031]    The above described step of covering the entire surface of the substrate including the microstructure with a core layer (or a core layer and a second clad layer) is used to bury the microstructure and make the substrate show a flat surface. An application technique is used at least for the core layer because it can easily produce a flat surface.  
           [0032]    In the above described step of mounting a light-emitting device or a light-receiving device on or in the core layer or on or in the second clad layer, a guide is formed so as to put the light-emitting device or the light-receiving device into engagement with ease and accurately align the light-emitting device or the light-receiving device with the light path converting microstructure.  
           [0033]    As described above, a method of manufacturing a planar optical waveguide device according to the invention is characterized in that it can produce one or more than one light path converting microstructures that operate for scattering or converging light with any desired profile at low cost.  
           [0034]    A planar optical waveguide device according to the invention is characterized in that it can be deposited on a conventional printed circuit board or vice versa to form an opto-electronic circuit board. A planar optical waveguide device can be deposited on a printed circuit board either by mounting a light-emitting device or a light-receiving device on the planar optical waveguide device by way of a mounting guide and subsequently electrically connecting the planar optical waveguide device to the printed circuit board or by mounting a light-emitting device or a light-receiving device on the printed circuit board and subsequently electrically connecting the planar optical waveguide device and the printed circuit board by way of a mounting guide. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    [0035]FIGS. 1A, 1B,  1 C,  1 D,  1 E,  1 F and  1 G are schematic cross sectional views of an embodiment of the present invention.  
         [0036]    [0036]FIGS. 2A, 2B,  2 C,  2 D,  2 E,  2 F,  2 G and  2 H are schematic cross sectional views of a first embodiment of the manufacture of a planar optical waveguide device according to the present invention, using a resist as thermoplastic material for the microstructures thereof.  
         [0037]    [0037]FIG. 3 is a schematic cross sectional view of a planar optical waveguide device manufactured by the first embodiment of the invention, illustrating the operation of the element.  
         [0038]    [0038]FIGS. 4A, 4B,  4 C,  4 D,  4 E,  4 F,  4 G,  4 H,  4 I,  4 J and  4 K are schematic cross sectional views of a second embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide according to the invention.  
         [0039]    [0039]FIGS. 5A, 5B,  5 C,  5 D,  5 E,  5 F,  5 G,  5 H,  5 I,  5 J,  5 K and  5 L are schematic cross sectional views of a third embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide according to the invention.  
         [0040]    [0040]FIGS. 6A, 6B,  6 C,  6 D,  6 E,  6 F,  6 G and  6 H are schematic cross sectional views of a fourth embodiment of the method of manufacturing a planar optical waveguide device according to the invention.  
         [0041]    [0041]FIG. 7 is a schematic cross sectional view of a planar optical waveguide device manufactured by the fourth embodiment of the invention, illustrating the operation of the element.  
         [0042]    [0042]FIGS. 8A, 8B,  8 C,  8 D,  8 E,  8 F,  8 G,  8 H,  8 I,  8 J and  8 K are schematic cross sectional views of a fifth embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide according to the invention.  
         [0043]    [0043]FIGS. 9A, 9B,  9 C,  9 D,  9 E,  9 F,  9 G,  9 H,  9 I,  9 J,  9 K and  9 L are schematic cross sectional views of a sixth embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide according to the invention.  
         [0044]    [0044]FIGS. 10A, 10B and  10 C are schematic illustrations of a microstructure formed by a seventh embodiment of the manufacture of a planar optical waveguide device according to the invention, illustrating the profile after deformation by heat.  
         [0045]    [0045]FIGS. 11A, 11B and  11 C are schematic illustrations of microstructures obtained after heat treatment and showing different profiles produced by differences of heat treatment temperature and heat treatment time. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    Now, an embodiment of the present invention will be described by referring to FIGS. 1A through 1G.  
         [0047]    With this embodiment, firstly a member having structures  102  formed on a substrate  100  as shown in FIG. 1A is prepared (Step  1 ). The structures comprise a thermoplastic material. Then, the structures  102  are deformed by heat treatment (Step  2 ) as shown in FIG. 1B. More specifically, the structures  102  are deformed as they are fused and re-solidified. As the result of deformation, the structures  102  are turned to structures  104  having a profile (e.g., of a curved surface) adapted to operate as optical path changing sections. Subsequently, an optical waveguide section is formed on the substrate  100  and the structures  104  to produce a planar optical waveguide having optical path changing sections (not shown). If necessary, the structures are further processed to form a reflection film on each of the surfaces thereof. More specifically, a resist mask  106  is formed on the substrate  100  as shown in FIG. 1C and a reflection film material  108  is deposited on the resist mask  106  and the structures  104  (FIG. 1D). Then, the resist mask  106  is removed to produce a reflection film  110  on the respective structures  104  (FIG. 1E).  
         [0048]    The above described optical waveguide section may be formed by an alternative process as described below.  
         [0049]    A core layer  112  and a second clad layer  114  are formed by this alternative process as shown in FIG. 1F. If the material of the substrate  100  is so selected as to make the substrate  100  operate as a clad layer relative to the core layer  112 , an optical waveguide having a construction of clad layer/core layer/clad layer can be obtained.  
         [0050]    Still alternatively, a planar optical waveguide device can be formed by mounting a light-emitting device  116  and a light-receiving device  118  in the above optical waveguide as shown in FIG. 1G. Then, it is possible to provide an information processing apparatus realized by using a circuit board including such a planar optical waveguide device (opto-electronic fused substrate).  
         [0051]    According to the invention, optical path changing sections  104  are formed by deforming structures  102  by heat treatment. Therefore, when a number of structures are arranged on a substrate, they can be simultaneously deformed.  
         [0052]    A glass substrate may typically be used for the substrate  100 . However, it should be noted that a material having a refractive index lower than that of the material of the optical waveguide section is preferably used for the substrate  100 . There are no particular limitations for the selection of the material of the structures  102  so long as the material shows thermal plasticity. Examples of such a material that can be used for the structures  102  include positive resists, negative resists, photosensitive polysilane resins, relatively low melting point metals such as Sn—Ag—Cu solder and metal paste such as silver paste.  
         [0053]    Desired optical path changing sections can be produced by using structures  102  having a profile of a cylinder or a polygonal prism such as a quadrangular prism. Hemicylindrical or hemispherical optical path changing sections can be produced when the structures are made to show a rectangular or square plan view.  
         [0054]    The extent of deformation by heat of the structures can be controlled by partially exposing the structures  102  to irradiation of light or laser beams between the first step and the second step.  
         [0055]    The substrate  100  and the structures  102  may be made of a same material. For example, the member of FIG. 1A can be formed by using a substrate and structures that are equally made of photosensitive polysilane resins.  
         [0056]    Now, the present invention will be described further by referring to the accompanying drawings that illustrate specific embodiments.  
         [0057]    (First Embodiment)  
         [0058]    [0058]FIGS. 2A to  2 H are schematic cross sectional views of a first embodiment of the method of manufacturing a planar optical waveguide device according to the present invention, using a resist as the thermoplastic material of the microstructures.  
         [0059]    In FIGS. 2A through 2H, there are shown a first clad layer  200  operating as a substrate, a microstructure material  202 , a photo-mask  204  for forming a desired shading pattern that is aligned with the arrangement of light path converting microstructures, a plurality of microstructures  206  showing a first profile, a plurality of microstructures  208  showing a second profile, a resist mask  210  formed on the first clad layer  200 , a reflection film material  212  deposited on the first clad layer  200  and the microstructures  208 , reflection films  214  formed on the respective microstructures  208 , a core layer  216 , a second clad layer  218 , light-emitting devices  220  and light-receiving devices  222 .  
         [0060]    Firstly as shown in FIG. 2A, a resist (AZ9260)  202  is applied to (i.e., used to coat therewith) the surface of a glass substrate (Corning 7059)  200  that operates as a first clad layer by means of a spin coater and the applied resist  202  is selectively exposed to UV light by using a photo-mask  204  (having a plurality of round shading patterns with a radius of 50 μm).  
         [0061]    Subsequently, as shown in FIG. 2B, microstructures  206  showing a cylindrical first profile with a radius of 50 μm and a height of 35 μm are formed by way of a developing process. Then, the work is put in the inside of an oven filled with a nitrogen atmosphere and heated to 160° C. for 30 minutes in order to fuse and re-solidify the microstructures  206  of resist by heat treatment. As a result, the microstructures  206  showing the above described first profile are turned to microstructures  208  showing a hemispherical second profile with a radius of 50 μm as illustrated in FIG. 2C. The aspect ratio of the cylindrical profile may be freely selected depending on the circumstances.  
         [0062]    Then, a photoresist is applied to the entire surface of the work by means of a spin coater and subsequently subjected to exposure and development processes in order to form a resist mask  210  so as to expose only the surfaces of the microstructures  208  showing a hemispherical second profile as shown in FIG. 2D. Thereafter, as shown in FIG. 2E, a reflection film material  212 , which is Cr/Au (the thickness of Cr: 50 nm, the thickness of Au: 200 nm), is deposited on the entire surface of the work by means of an electron beam evaporation system (Cr takes the role of adhesive for firmly bonding the reflection film of Au and the surfaces of the microstructures  208 ). The reflection film shows a reflectivity of not lower than 90% to light having a wavelength not shorter than 600 nm. Thereafter, the substrate of FIG. 2E is immersed into a remover solution that is heated to 80° C. and subjected to an ultrasonic cleaning operation. As a result of the lift-off process, the reflection film  214  is formed only on the surfaces of the microstructures  208  having the hemispherical profile as shown in FIG. 2F.  
         [0063]    Then, as shown in FIG. 2G, a core layer  216  is formed to a thickness of 100 μm by applying a polymeric material (polycarbonate resin, refractive index: 1.58) having a refractive index higher than that of the glass substrate  200  and curing it. Thereafter, a 40 μm thick second clad layer  218  is formed by applying another polymeric material (norbornene resin, refractive index: 1.51) having a refractive index lower than that of the core layer  216  and curing it. In the case of this embodiment, since the reflection film  214  is formed on the microstructures  208 , the relationship of the values between the refractive index of the microstructures  208  and that of the core layer  216  is not particularly important.  
         [0064]    Subsequently, a resist mask (not shown) are formed for the purpose of forming grooves in which optical devices are to be mounted right above the respective microstructures  208  having the hemispherical second profile as shown in FIG. 2H. Then, the work is put in a reactive ion etching (RIE) system in order to selectively etch the second clad layer  218  under etching conditions of RF power: 500 W, pressure: 2 Pa and O 2  gas flow rate: 20 sccm. As a result of the etching process, optical device mounting guides are formed. Then, a complete planar optical waveguide device is produced by mounting light-emitting devices  220  and light-receiving devices  222 .  
         [0065]    Since the microstructures  208  showing a hemispherical second profile as a result of deformation and having the respective reflection films  214  are arranged in the produced planar optical waveguide device as shown in FIG. 3, rays of light striking the hemispherical microstructures  208  from above (which are preferably caused to strike the entire surfaces of the microstructures  208 ) are efficiently scattered by the microstructures  208  having the respective reflection films  214  so as to propagate through the entire core layer  216  in all directions. Additionally, rays of light propagated through the core layer  216  are scattered again by the microstructures  208  showing the hemispherical second profile and having the respective reflection films  214  so as to go out from the microstructures  208  showing the hemispherical second profile and move upward. In this way, light from the light-emitting device  220  is reliably transmitted to the light-receiving device  222 .  
         [0066]    While a glass substrate, polycarbonate resin and norbornene resin are used respectively as materials of the first clad layer  200 , the core layer  216  and the second clad layer  218  in the above description of the embodiment, materials that can be used for the above components are by no means limited to them. A combination of polyimide resin, acrylic resin, fluorinated polyimide resin and photosensitive polysilane resin may alternatively be used so long as the material of the core layer shows a refractive index higher than those of the materials of the first and second clad layers. Such an appropriate combination of materials can also be used for the other embodiments that will be described hereinafter.  
         [0067]    Additionally, while a glass substrate is used as the material of the first clad layer  200 , the latter may be made of some other appropriate material. For example, it may be made of a resin film having a refractive index lower than that of the material of the core layer  216 . Then, the produced planar optical waveguide can be bent. Furthermore, the planar optical waveguide may comprise only a core layer. If such is the case, the core layer may be peeled off from the substrate on which it was formed and optical devices may be mounted on or in the core layer.  
         [0068]    While the core layer  216  and the second clad layer  218  have respectively thicknesses of 100 μm and 40 μm in the above description of the embodiment, their thicknesses are by no means limited thereto. They may have appropriate thicknesses so long as they operate properly for their desired respective functions.  
         [0069]    While the microstructures  206  showing the first profile are cylindrical and have a radius of 50 μm and a height of 35 μm in the above description of the first embodiment, their profile is by no means limited thereto. They may alternatively show a profile of a column having an elliptic or polygonal cross section and different dimensions.  
         [0070]    While the optical device mounting guides are formed by etching in the above description of the embodiment, they may alternatively be formed by using a photosensitive resin material for the second clad layer  218  and subjecting the photosensitive resin material to exposure and development processes.  
         [0071]    Finally, while the microstructures  206  showing the first profile are formed by way of exposure and development processes in the above description of the embodiment, they may alternatively be formed by applying a thermoplastic material and etching the applied material or by dropping a thermoplastic material to form a desired pattern of the material. In short, an appropriate technique of forming the microstructures may be selected depending on the material and the function of changing an optical path.  
         [0072]    (Second Embodiment)  
         [0073]    [0073]FIGS. 4A to  4 K are schematic cross sectional views of a second embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide device according to the invention. In FIGS. 4A through 4K, there are shown a first clad layer  300 , a microstructure material  302 , a photo-mask  304 , microstructures  306  showing a first profile, microstructures  308  showing a second profile, a resist mask  310  formed on the first clad layer  300 , a refection film material  312 , reflection films  314 , a core layer  316 , a second clad layer  318 , a planar optical waveguide device  320 , a resist mask  322 , optical device mounting guides  324 , LSI chips  326 , a printed circuit board  328 , light-emitting devices  330 , light-receiving devices  332  and an opto-electronic circuit board  334 .  
         [0074]    Firstly as shown in FIG. 4A, a resist (AZ9260)  302  is applied to the surface of a glass substrate (Corning 7059)  300  that operates as a first clad layer by means of a spin coater and the applied resist  302  is exposed to UV light by using a photo-mask  304  (having a pattern of round shades with a radius of 50 μm). Subsequently, as shown in FIG. 4B, microstructures  306  showing a cylindrical first profile with a radius of 50 μm and a height of 35 μm are formed by way of a developing process. Then, the work is put in the inside of an oven filled with a nitrogen atmosphere and heated to 160° C. for 30 minutes in order to fuse. and re-solidify the microstructures  306  of resist by heat treatment. As a result, the microstructures  306  showing the above described first profile are turned to microstructures  308  showing a hemispherical second profile with a radius of 50 μm as shown in FIG. 4C.  
         [0075]    Then, a photoresist is applied to the entire surface of the work by means of a spin coater and subsequently subjected to exposure and development processes in order to form a resist mask  310  so as to expose only the surfaces of the microstructures  308  showing a hemispherical second profile as shown in FIG. 4D. Thereafter, as shown in FIG. 4E, a reflection film material  312 , which is Cr/Au (the thickness of Cr: 50 nm, the thickness of Au: 200 nm), is deposited on the entire surface of the work by evaporation by means of an electron beam vacuum evaporation system. The reflection film shows a reflectivity of not lower than 90% to light having a wavelength of 660 nm. Thereafter, the substrate is immersed into a remover solution that is heated to 80° C. and subjected to an ultrasonic cleaning operation. As a result, the reflection film  314  is formed only on the surfaces of the microstructures  308  having the hemispherical second profile as shown in FIG. 4F.  
         [0076]    Then, as shown in FIG. 4G, a core layer  316  is formed to a thickness of 100 μm by applying a polymeric material (polycarbonate resin, refractive index: 1.58) having a refractive index higher than that of the glass substrate  300  and curing it. Thereafter, a 40 μm thick second clad layer  318  is formed by applying another polymeric material (norbornene resin, refractive index: 1.51) having a refractive index lower than that of the core layer  316  and curing it to obtain a planar optical waveguide device  320 .  
         [0077]    Subsequently, a resist mask  322  is formed for the purpose of forming grooves in which optical devices are to be mounted right above the respective microstructures  308  having the hemispherical second profile as shown in FIG. 4H. Then, the work is put in a reactive ion etching (RIE) system in order to etch the second clad layer  318  under etching conditions of RF power: 500 W, pressure: 2 Pa and O 2  gas flow rate: 20 sccm. As a result of the etching process, optical device mounting guides  324  are formed as shown in FIG. 4I. The above operation is substantially the same as the corresponding operation of forming the first embodiment.  
         [0078]    Then, a printed circuit board  328  is prepared as shown in FIG. 4J. The printed circuit board  328  has LSI chips  326  mounted thereon and provided on the top surface of the package with electric signal input/output terminals. Subsequently, light-emitting devices  330  and light-receiving devices  332  are mounted on the LSI chips  326  arranged on the printed circuit board  328 . Then, the light-emitting devices  330  and the light-receiving device  332  on the LSI chips  326  arranged on the printed circuit board  328  are fitted into the respective optical device mounting guides  324 . Then, the printed circuit board  328  is bonded to the planar optical waveguide device  320  by way of an optical adhesive to obtain an opto-electronic circuit board  334  as shown in FIG. 4K.  
         [0079]    An opto-electronic circuit board  334  prepared in this way effectively suppresses EMI if compared with an instance where logic signals are transmitted from the LSI chips  326  as electric signals because logic signals are transmitted as optical signals that is basically free from electromagnetic induction. Additionally, an opto-electronic circuit board  334  prepared in this way is advantageous in terms of cost because it can be prepared without changing the design of the printed circuit board  328 . Furthermore, any undesired increase of the surface area of the printed circuit board  328  that may be required for mounting components can be suppressed because light-emitting devices and light-receiving devices for converting electric signals into optical signals do not need to be directly arranged on the printed circuit board  328  when LSI chips  326  having electric signal input/output terminals arranged on the top surfaces of the packages are used.  
         [0080]    The alternative arrangements described above for the first embodiment can also be used for this embodiment.  
         [0081]    (Third Embodiment)  
         [0082]    [0082]FIGS. 5A to  5 L are schematic cross sectional views of a third embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide device according to the invention. In FIGS. 5A through 5L, there are shown a first clad layer  400 , a microstructure material  402 , a photo-mask  404 , microstructures  406  showing a first profile, microstructures  408  showing a second profile, a resist mask  410 , a reflection film material  412 , reflection films  414 , a core layer  416 , a second clad layer  418 , a planar optical waveguide device  420 , a resist mask  422 , optical device mounting guides  424 , light-emitting devices  426 , light-receiving devices  428 , LSI chips  430 , a printed circuit board  432  and an opto-electronic circuit board  434 .  
         [0083]    Firstly as shown in FIG. 5A, a resist (AZ9260)  402  is applied to the surface of a glass substrate (Corning 7059)  400  that operates as a first clad layer by means of a spin coater and the applied resist  402  is exposed to UV light by using a photo-mask  404  (having a pattern of round shades with a radius of 50 μm). Subsequently, as shown in FIG. 5B, microstructures  406  showing a cylindrical first profile with a radius of 50 μm and a height of 35 μm are formed by way of a developing process. Then, the work is put in the inside of an oven filled with a nitrogen atmosphere and heated to 160° C. for 30 minutes in order to fuse and re-solidify the microstructures of resist by heat treatment. As a result, the microstructures  406  showing the above described first profile are turned to microstructures  408  showing a hemispherical second profile with a radius of 50 μm as shown in FIG. 5C.  
         [0084]    Then, a photoresist is applied to the entire surface of the work by means of a spin coater and subsequently subjected to exposure and development processes in order to form a resist mask  410  so as to expose only the surfaces of the microstructures  408  showing a hemispherical second profile as shown in FIG. 5D. Thereafter, as shown in FIG. 5E, a reflection film material  412 , which is Cr/Au (the thickness of Cr: 50 nm, the thickness of Au: 200 nm), is deposited on the entire surface of the work by evaporation by means of an electron beam vacuum evaporation system. The reflection film shows a reflectivity of not lower than 90% to light having a wavelength not shorter than 600 nm. Thereafter, the substrate is immersed into a remover solution that is heated to 80° C. and subjected to an ultrasonic cleaning operation. As a result; the reflection film  414  is formed only on the surfaces of the microstructures  408  having the hemispherical second profile as shown in FIG. 5F.  
         [0085]    Then, as shown in FIG. 5G, a core layer  416  is formed to a thickness of 100 μm by applying a polymeric material (polycarbonate resin, refractive index: 1.58) having a refractive index higher than that of the glass substrate  400  and curing it. Thereafter, a 40 μm thick second clad layer  418  is formed by applying another polymeric material (norbornene resin, refractive index: 1.51) having a refractive index lower than that of the core layer  416  and curing it to obtain a planar optical waveguide device  420 .  
         [0086]    Subsequently, a resist mask  422  is formed for the purpose of forming grooves in which optical devices are to be mounted right above the respective microstructures  408  having the hemispherical second profile as shown in FIG. 5H. Then, the work is put in a reactive ion etching (RIE) system in order to etch the second clad layer  418  under etching conditions of RF power: 500 W, pressure: 2 Pa and O 2  gas flow rate: 20 sccm. As a result of the etching process, optical device mounting guides  424  are formed as shown in FIG. 5I. Then, light-emitting devices  426  and light-receiving devices  428  are mounted in the optical device mounting guides  424  by way of an optical adhesive as shown in FIG. 5J. The above operation is substantially the same as the corresponding operation of forming the first embodiment.  
         [0087]    Then, a printed circuit board  432  is prepared. The printed circuit board  432  has LSI chips  430  mounted thereon and provided on the top surface of the package with electric signal input/output terminals as shown in FIG. 5K. Subsequently, light-emitting devices  426  and light-receiving devices  428  are mounted on the LSI chips  430  arranged on the printed circuit board  432 . Then, the planar optical waveguide device  420  and the printed circuit board  432  are bonded to each other so as to connect the electrode pads of the light-emitting devices  426  and the light-receiving devices  428  to the corresponding input/output terminals of the LSI chips  430  and obtain an opto-electronic circuit board  434  as shown in FIG. 5L.  
         [0088]    An opto-electronic circuit board  434  prepared in this way effectively suppresses EMI if compared with an instance where logic signals are transmitted from the LSI chips  430  as electric signals because logic signals are transmitted as optical signals that is basically free from electromagnetic induction. The opto-electronic circuit board  434  provides additional advantages similar to those of the second embodiment.  
         [0089]    The alternative arrangements described above for the first embodiment can also be used for this embodiment.  
         [0090]    (Fourth Embodiment)  
         [0091]    [0091]FIGS. 6A to  6 H are schematic cross sectional views of a fourth embodiment of the method of manufacturing a planar optical waveguide device according to the present invention, using a UV-curing resin as a microstructure material. In FIGS. 6A through 6H, there are shown a first clad layer  500 , a microstructure material  502 , a photo-mask  504 , microstructures  506  showing a first profile, microstructures  508  showing a second profile, a resist mask  510 , a reflection film material  512 , reflection films  514 , a core layer  516 , a second clad layer  518 , a light-emitting devices  520  and light-receiving devices  522 .  
         [0092]    Firstly as shown in FIG. 6A, a UV-curing resin  502  is applied to the surface of a glass substrate (Corning 7059)  500  that operates as a first clad layer by means of a spin coater and the applied resist  502  is exposed to light by using a photo-mask  504  (having a pattern of round UV transmitting sections with a radius of 30 μm). Subsequently, as shown in FIG. 6B, microstructures  506  showing a cylindrical first profile with a radius of 30 μm and a height of 50 μm are formed by removing parts of the UV-curing resin that are not exposed to UV. Then, the work is put in the inside of an oven filled with a nitrogen atmosphere and heated to 200° C. for 60 minutes in order to fuse and re-solidify the microstructures  506  having the first profile and made of a UV-curing resin by heat treatment. As a result, the microstructures  506  showing the above described first profile are turned to microstructures  508  having a radius of 50 μm and showing a hemispherical second profile as illustrated in FIG. 6C.  
         [0093]    Then, a photoresist is applied to the entire surface of the work by means of a spin coater and subsequently subjected to exposure and development processes in order to form a resist mask  510  so as to expose only the surfaces of the microstructures  508  showing a hemispherical second profile as shown in FIG. 6D. Thereafter, as shown in FIG. 6E, a reflection film material  512 , which is Cr/Au (the thickness of Cr: 50 nm, the thickness of Au: 200 nm), is deposited on the entire surface of the work by evaporation by means of an electron beam vacuum evaporation system. The reflection film shows a reflectivity of not lower than 90% to light having a wavelength not shorter than 600 nm. Thereafter, the substrate is immersed into a remover solution that is heated to 80° C. and subjected to an ultrasonic cleaning operation. As a result, the reflection film  514  is formed only on the surfaces of the microstructures  508  having the hemispherical second profile as shown in FIG. 6F.  
         [0094]    Then, as shown in FIG. 6G, a core layer  516  is formed to a thickness of 100 μm by applying a polymeric material (polycarbonate resin, refractive index: 1.58) having a refractive index higher than that of the glass substrate  500  and curing it. Thereafter, a 40 μm thick second clad layer  518  is formed by applying another polymeric material (norbornene resin, refractive index: 1.51) having a refractive index lower than that of the core layer  516  and curing it.  
         [0095]    Subsequently, a resist mask (not shown) is formed for the purpose of forming grooves in which optical devices are to be mounted right above the respective microstructures  508  having the hemispherical second profile as shown in FIG. 6H. Then, the work is put in a reactive ion etching (RIE) system in order to etch the second clad layer  518  under etching conditions of RF power: 500 W, pressure: 2 Pa and O 2  gas flow rate: 20 sccm. As a result of the etching process, optical device mounting guides (not shown) are formed. Then, a complete planar optical waveguide device is produced by mounting light-emitting devices  520  and light-receiving devices  522  on the optical device mounting guides.  
         [0096]    Since the microstructures  508  showing a hemispherical second profile as a result of deformation and having the respective reflection films  514  are arranged in the produced planar optical waveguide device as shown in FIG. 7, rays of light striking the hemispherical microstructures  508  from the light-emitting device  520  that is located above the microstructures are efficiently scattered so as to propagate through the entire planar optical waveguide. Additionally, rays of light propagated through the core layer  516  are scattered again by the microstructures  508  showing the hemispherical second profile so as to go out from the microstructures  508  showing the hemispherical profile and become transmitted to the light-receiving device  522  that is located above the microstructures  508  having the hemispherical second profile.  
         [0097]    While the microstructures  506  showing the first profile are cylindrical and have a radius of 30 μm and a height of 50 μm in the above description of the fourth embodiment, their profile is by no means limited thereto. They may alternatively show a profile of a column having an elliptic or polygonal cross section and different dimensions. Additionally, the alternative arrangements described above for the first embodiment can also be used for this embodiment.  
         [0098]    (Fifth Embodiment)  
         [0099]    [0099]FIGS. 8A to  8 K are schematic cross sectional views of a fifth embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide device according to the invention. In FIGS. 8A through 8K, there are shown a first clad layer  600 , a microstructuure material  602 , a photo-mask  604 , microstructures  606  showing a first profile, microstructures  608  showing a second profile, a resist mask  610 , a reflection film material  612 , reflection films  614 , a core layer  616 , a second clad layer  618 , a planar optical waveguide device  620 , a resist mask  622 , optical device mounting guides  624 , LSI chips  626 , a printed circuit board  628 , light-emitting devices  630 , light-receiving devices  632  and an opto-electronic circuit board  634 .  
         [0100]    Firstly as shown in FIG. 8A, a UV-curing resin  602  is applied to the surface of a glass substrate (Corning 7059)  600  that operates as a first clad layer by means of a spin coater and the applied resist  602  is exposed to UV light by using a photomask  604  (having a pattern of round UV transmitting sections with a radius of 30 μm). Subsequently, as shown in FIG. 8B, microstructures  606  showing a cylindrical first profile with a radius of 30 μm and a height of 35 μm are formed by removing parts of the UV-curing resin that are not exposed to UV. Then, the work is put in the inside of an oven filled with a nitrogen atmosphere and heated to 200° C. for 60 minutes in order to fuse and re-solidify the microstructures  606  having the first profile and made of UV-curing resin by heat treatment. As a result, the microstructures  606  showing the above described first profile are turned to microstructures  608  showing a hemispherical second profile with a radius of 50 μm as illustrated in FIG. 8C.  
         [0101]    Then, a photoresist is applied to the entire surface of the work by means of a spin coater and subsequently subjected to exposure and development processes in order to form a resist mask  610  so as to expose only the surfaces of the microstructures  608  showing a hemispherical second profile as shown in FIG. 8D. Thereafter, as shown in FIG. 8E, a reflection film material  612 , which is Cr/Au (the thickness of Cr: 50 nm, the thickness of Au: 200 nm), is deposited on the entire surface of the work by evaporation by means of an electron beam vacuum evaporation system. The reflection film shows a reflectivity of not lower than 90% to light having a wavelength not shorter than 600 nm. Thereafter, the substrate is immersed into a remover solution that is heated to 80° C. and subjected to an ultrasonic cleaning operation. As a result, the reflection film  614  is formed only on the surfaces of the microstructures  608  having the hemispherical second profile as shown in FIG. 8F.  
         [0102]    Then, as shown in FIG. 8G, a core layer  616  is formed to a thickness of 100 μm by applying a polymeric material (polycarbonate resin, refractive index: 1.58) having a refractive index higher than that of the glass substrate  600  and curing it. Thereafter, a 40 μm thick second clad layer  618  is formed by applying another polymeric material (norbornene resin, refractive index: 1.51) having a refractive index lower than that of the core layer  616  and curing it. As a result, a planar optical waveguide device  620  is obtained.  
         [0103]    Subsequently, a resist mask  622  is formed for the purpose of forming grooves in which optical devices are to be mounted right above the respective microstructures  608  having the hemispherical second profile as shown in FIG. 8H. Then, the work is put in a reactive ion etching (RIE) system in order to etch the second clad layer  618  under etching conditions of RF power: 500 W, pressure: 2 Pa and O 2  gas flow rate: 20 sccm. As a result of the etching process, optical device mounting guides  624  are formed as shown in FIG. 8I.  
         [0104]    Then, a printed circuit board  628  is prepared. The printed circuit board  628  has LSI chips  626  mounted thereon and provided on the top surface of the package with electric signal input/output terminals as shown in FIG. 8J. Subsequently, light-emitting devices  630  and light-receiving devices  632  are mounted on the LSI chips  626  arranged on the printed circuit board  628 . Then, light-emitting devices  630  and a light-receiving device  632  which are formed on the LSI chips  626  that are mounted on the printed circuit board  628  are fitted into the respective optical device mounting guides  624 . Then, the printed circuit board  628  is bonded to the planar optical waveguide device  620  by way of an optical adhesive to produce an opto-electronic circuit board  634  as shown in FIG. 8K.  
         [0105]    An opto-electronic circuit board  634  prepared in this way effectively suppresses EMI if compared with an instance where logic signals are transmitted from the LSI chips  626  as electric signals because logic signals are transmitted as optical signals that is basically free from electromagnetic induction. The opto-electronic circuit board  634  provides additional advantages similar to those of the second embodiment.  
         [0106]    While the microstructures  606  showing the first profile are cylindrical and has a radius of 30 μm and a height of 50 μm in the above description of the fifth embodiment, their profile is by no means limited thereto. They may alternatively show a profile of a column having an elliptic or polygonal cross section and different dimensions.  
         [0107]    The alternative arrangements described above for the first embodiment can also be used for this embodiment.  
         [0108]    (Sixth Embodiment)  
         [0109]    [0109]FIGS. 9A to  9 L are schematic cross sectional views of a sixth embodiment of the method of manufacturing an opto-electronic circuit board realized by using a planar optical waveguide device of the fourth embodiment of the invention. In FIGS. 9A through 9L, there are shown a first clad layer  700 , a microstructure material  702 , a photo-mask  704 , microstructures  706  showing a first profile, microstructures  708  showing a second profile, a resist mask  710 , a reflection film material  712 , reflection films  714 , a core layer  716 , a second clad layer  718 , a planar optical waveguide device  720 , a resist mask  722 , optical device mounting guides  724 , light-emitting devices  726 , light-receiving devices  728 , LSI chips  730 , a printed circuit board  732 , and an opto-electronic circuit board  734 .  
         [0110]    The steps to the one of mounting light-emitting devices  726  or light-receiving devices  728  in the respective optical device mounting guides  724  as shown in FIG. 9J are the same as those described above for the fourth embodiment. Then, a printed circuit board  732  is formed. The printed circuit board  732  has LSI chips  730  mounted thereon and provided on the top surface of the package with electric signal input/output terminals as shown in FIG. 9K. Then, the planar optical waveguide device  720  and the printed circuit board  732  are bonded to each other so as to connect the electrode pads of the light-emitting devices  726  or the light-receiving devices  728  to the corresponding input/output terminals of the LSI chips  730  and obtain an opto-electronic circuit board  734  as shown in FIG. 9L.  
         [0111]    An opto-electronic circuit board  734  prepared in this way effectively suppresses EMI if compared with an instance where logic signals are transmitted from the LSI chips  730  as electric signals because logic signals are transmitted as optical signals that is basically free from electromagnetic induction. The opto-electronic circuit board  734  provides additional advantages similar to those of the second embodiment.  
         [0112]    While the microstructures  706  showing the first profile are cylindrical and have a radius of 30 μm and a height of 50 μm in the above description of the sixth embodiment, their profile is by no means limited thereto. They may alternatively show a profile of a column having an elliptic or polygonal cross section and different dimensions. Additionally, the alternative arrangements described above for the first embodiment can also be used for this embodiment.  
         [0113]    (Seventh Embodiment)  
         [0114]    Microstructures having a first profile (not shown) are formed by subjecting a resist to exposure and development processes as in the first embodiment. However, instead of the microstructures showing a cylindrical profile and having a radius of 50 μm and a height of 35 μm, the microstructures of this embodiment show a box-shaped first profile with a width of 100 μm, a length of 1,500 μm and a height of 35 μm (not shown). The microstructures having the first profile are heated to 150° C. for 5 minutes on a hot plate in order to fuse and re-solidify the microstructures by heat treatment. As a result, the microstructures showing the above described first profile are deformed and turned to microstructures showing a hemicylindrical profile (obtained by cutting a circular cylinder along the axis thereof) with a semicircular cross section whose radius is 50 μm as shown in FIGS. 10A through 10C. Note that FIG. 10A is a plan view of a microstructure after the thermal deformation and FIGS. 10B and 10C are cross sectional views taken along lines  10 B- 10 B and  10 C- 10 C respectively.  
         [0115]    It will be appreciated that microstructures having the first profile as described above by referring to the first through third embodiments can also be deformed and turned to microstructures having the hemispherical second profile by heating them to 150° C. for 5 minutes on a hot plate in place of heat-treating them in an oven. The second profile of the microstructures can be modified appropriately by controlling the heat treatment temperature and/or the heat treatment time.  
         [0116]    In an experiment, microstructures having a first profile as shown in FIG. 11A, which are similar to those illustrated for the first embodiment, were heated to 135° C. for 5 minutes on a hot plate in order to fuse and re-solidify. As a result, the microstructures showing the above described first profile are deformed and turned to microstructures showing a hemispherical second profile as illustrated in FIG. 11B. Additionally, microstructures having a first profile as shown in FIG. 11A were heated to 150° C. for 7 minutes on a hot plate in order to fuse and re-solidify. As a result, the microstructures showing the above described first profile are deformed and turned to microstructures showing a hemispherical second profile as illustrated in FIG. 11C. FIG. 11A is a lateral view of a semi-sphere having a radius of 50 μm. FIG. 11B is a lateral view of a slightly deformed half-sphere having a circular bottom with a radius of 50 μm and a height of 40 μm. FIG. 11C is a lateral view of a slightly deformed half-sphere having a circular bottom with a radius of 50 μm and a height of 65 μm.  
         [0117]    As described above in detail, the present invention provides a planar optical waveguide having optical path changing sections and a method of manufacturing such a planar optical waveguide.