Optical wiring board, optical bus system, and method of manufacturing optical wiring board

In an optical wiring board, an optical components including a planar optical waveguide, a plurality of first optical fibers optically connected via a transmissive diffusion plate to a light incident face of the waveguide, and a plurality of second optical fibers optically connected to a light emitting face of the waveguide is placed on a support board. The optical component is sealed by a sealing member made of a resin.

The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-307500 filed on Oct. 3, 2001, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical wiring board and an optical bus system through which transmission between boards or chips is conducted by means of a light signal, and a method of manufacturing such an optical wiring board, and more particularly relates to an optical wiring board and an optical bus system, which can be manufactured easily and have a high degree of freedom in arrangement of optical components, and a method of manufacturing such an optical wiring board.

2. Description of the Related Art

Conventionally, an optical wiring board in which data are optically transmitted has been proposed for a purpose of increasing the data transmission speed between boards or chips and reducing electromagnetic noise.

JP-A-2000-329962 discloses such a conventional optical wiring board.

The optical wiring board includes a planar optical waveguide, a plurality of first optical fibers optically connected to one end face of the waveguide, a plurality of second optical fibers optically connected to the other end face of the waveguide, and a support board in which grooves for accommodating the waveguide and the optical fibers are formed. The waveguide and the optical fibers are accommodated and supported in the grooves. An electro-optical conversion circuit is connected to the first optical fibers via photoelectric conversion elements. An opto-electrical conversion circuit is connected to the second optical fibers via photoelectric conversion elements. According to the configuration, many-to-many communication can be conducted between the electro-optical conversion circuit and the opto-electrical conversion circuit. Since the optical fibers can be embedded in the grooves, the optical fibers can be disposed while being bent. Moreover, devices for fixing the optical fibers are not required, and hence an apparatus can be more miniaturized than a case where the optical fibers are disposed on a surface of the support board.

In the optical wiring board disclosed in JP-A-2000-329962, the optical waveguide and the optical fibers are accommodated and positioned in the grooves formed by a cutting process, thereby causing problems in that the cost of the cutting process is increased, and that the degree of freedom in arrangement is lowered.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an optical wiring board and an optical bus system which can be easily manufactured and have a high degree of freedom in the arrangement of optical components, and a method of manufacturing such an optical wiring board.

In order to attain the objects, according to the embodiment of the invention, an optical wiring board includes a support board and an optical component. The optical component includes an optical waveguide, which has a plate shape and has at least two end faces; and an optical fiber connected to at least one of the end faces of the optical waveguide optically. The optical component is placed on the support board. The optical component is sealed by resin.

In order to attain the objects, according to the embodiment of the invention, an optical bus system includes a conversion circuit section for converting an electric signal into an optical signal and converting the optical signal into the electric signal, and an optical wiring board for transmitting and receiving the optical signal to and from the conversion circuit section. The optical wiring board includes a support board and an optical component. The optical component includes an optical waveguide, which has a plate shape and has at least two end faces, and an optical fiber connected to at least one of the end faces of the optical waveguide optically. The optical component is placed on the support board. The optical component is sealed by resin.

In order to attain the objects, according to the embodiment of the invention, A method for manufacturing an optical wiring board including a support board and an optical component having an optical waveguide, which has a plate shape and has at least two end faces, and an optical fiber connected to at least one of the end faces of the optical waveguide optically, wherein the optical component is placed on the support board, the method includes temporarily securing the optical component on the support board, and sealing the optical component by resin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2show an optical bus system of a first embodiment to which an optical wiring board of the invention is applied.FIG. 1Ais a plan view,FIG. 1Bis a section view taken along the line A—A inFIG. 1A, andFIG. 2is a perspective view. As shown inFIGS. 1 and 2, the optical bus system10includes a plurality of optical wiring boards1arranged with forming given gaps therebetween; a plurality of electro-optical conversion circuits11which, as shown inFIG. 1A, convert an electric signal into a light signal and supply the light signal to the respective optical wiring boards1; and a plurality of opto-electrical conversion circuits12which convert a light signal output from the respective optical wiring boards1into an electric signal.

Each of the electro-optical conversion circuits11and the opto-electrical conversion circuits12has a CPU, a memory, and a photoelectric conversion element and is connected to the corresponding optical wiring board1via the photoelectric conversion element.

The optical wiring board1includes a support board2; a planar optical waveguide3placed on the support board2; a plurality of (for example, eight) first optical fibers5in which tip ends5aare optically connected via a transmissive diffusion plate4to a light incident face3athat is one end face of the waveguide3; a plurality (for example, eight) of second optical fibers6in which tip ends6aare optically connected to a light emitting face3bthat is the other end face of the waveguide3; and a positioning member8in which rear ends5band6bof the optical fibers5and6are passed through positioning holes8ato position the rear ends5band6b. The optical components including the waveguide3, the transmissive diffusion plate4, and the optical fibers5and6are sealed by a sealing member7made of a resin. InFIGS. 1A and 2, the sealing member7is shown as a transparent member.

The support board2is made of a metal such as aluminum, a resin such as polymethyl methacrylate (PMMA), glass, or ceramics. The material of the support board2is not particularly limited to these examples so long as the positioning and fixation of the optical components are not adversely affected. Alternatively, a flexible board made of polyimide may be used.

The waveguide3includes a planar core and a clad. The planar core has a plate-like shape and has, for example, a thickness of 0.5 mm, a width of 4 mm, and a length of 20 mm. The planar core is made of a transparent material. The clad is formed on the upper, lower, and right and left side faces of the core except the light incident face3aand the light emitting face3b. The clad is lower in refractive index than the core. The core is made of, for example, a plastic material such as polymethyl methacrylate (PMMA), polycarbonate, or amorphous polyolefin, or inorganic glass. The clad is made of a fluoroploymer. In the case where the sealing member7functions also as a clad, the clad may be omitted.

The transmissive diffusion plate4may be formed in a such a manner that an epoxy layer is formed on a substrate of a resin such as an acrylic resin, polycarbonate, or polyester and then cured by ultraviolet rays, and a concave and convex pattern for diffusing light is formed on a light incident face (diffusing portion)4a. Alternatively, the transmissive diffusion plate4may be formed in such another manner that a concave and convex pattern is formed directly on the light incident face (diffusing portion)4aby injection molding. The diffusion plate may be of a type in which particles of different refractive indices are dispersed in an inner portion thereof so that the inner portion functions as a diffuser.

Each of the first and second optical fibers5and6includes a core having an outer diameter of, for example, 0.5 mm, and having a circular section shape, and a clad disposed around the core. The rear ends5band6bare bent at curved portions5cand6cso as to be perpendicular to the long edge of the support board2and slightly exposed from the long edge of the support board2. In the case where the sealing member7also functions as a clad, the clads of the optical fibers5and6may be omitted.

A resin such as a silicone resin or an epoxy resin may be used as the sealing member7. Such a resin can be cured by cold curing, heat curing, UV curing, or another curing process. The method of applying the resin to the sealing member7is not limited to a particular method, and may be any one of methods including pouring, application by a roller, and application by a blade which will be described later, and a screen printing method, and a spin coating method so long as the resin can be applied in a desired thickness. Alternatively, a member such as a heat-fusible resin film described later, which is melted by heating and is returned to its original state at ordinary temperature, may be used as the sealing member7.

FIGS. 3A to 3Dshow steps of manufacturing the optical wiring board1of the first embodiment. As shown inFIG. 3A, the optical components including the waveguide3, the transmissive diffusion plate4, and the first and second optical fibers5and6are placed on the support board2. As shown inFIG. 3B, the optical components are temporarily secured by a temporarily securing member, which will be described later. Then, as shown inFIG. 3C, a resin7ain a fluid state is poured from a syringe58onto the support board2, and cured to form the sealing member7as shown inFIG. 3D. The optical wiring board1is manufactured in this way. In the case of pouring the resin7a, a frame surrounding the support board2may be preferably disposed so as to prevent the resin7afrom flowing down from the support board2. If the resin7ais highly viscous, the surrounding frame may not be disposed.

FIGS. 4A to 4Dshow methods of temporarily securing the optical components. In the specification, the term “temporary securing” means positioning or fixation of the optical components, and the term “fixation” means both fixation in which the optical components are fixed so as to be immovable, and that in which the optical components are fixed so as to be slightly movable.

The optical components may be positioned in one of the following manners. As shown inFIG. 4A, positioning pins52may be disposed so that a part of the positioning pins52upstand and butt against corners of the waveguide3and the transmissive diffusion plate4, and other positioning pins52upstand inside the curved portions5cand6cof the optical fibers5and6and outside the rear ends5band6b.

As shown inFIG. 4B, the waveguide3and the transmissive diffusion plate4are fixed by a positioning adhesive agent53such as a silicone resin ejected from a tube59, so that the curved portions5cand6cand the rear ends5band6bof the optical fibers5and6are fixed. In this case, an adhesive agent having a refractive index equivalent to those of the optical fiber6and the waveguide3may be used as the positioning adhesive agent53to fill the gap between the end face of the tip end6aof the optical fiber6and the end face of the waveguide3. In the case where the transmissive diffusion plate4is of the type in which particles of different refractive indices are dispersed in the inner portion thereof, an adhesive agent having a refractive index equivalent to those of the optical fibers5and6and the waveguide3may be used as the positioning adhesive agent53, and the gaps between the end face of the tip end5aof the optical fiber5and the transmissive diffusion plate4, and between the end face of the tip end6aof the optical fiber6and the end face of the waveguide3may be filled with the positioning adhesive agent53.

As shown inFIG. 4C, the waveguide3and the transmissive diffusion plate4are fixed by positioning jigs54A, and the rear ends5band6bof the optical fibers5and6are fixed by a positioning jig54B. The shapes and numbers of the positioning jigs54A and54B are not particularly limited so long as the same effects can be attained.

As shown inFIG. 4D, the waveguide3and the transmissive diffusion plate4are fixed by a fixing tape55A, and the rear ends5band6bof the optical fibers5and6are fixed by a fixing tape55B.

The optical components, which are in the fixed state shown inFIGS. 4A to 4D, may be sealed by the sealing member7, and the positioning pins52or the positioning jigs54A and54B may be then removed away.

Next, an operation example of the optical bus system10will be described. When the CPU in one of the electro-optical conversion circuits11outputs an electric signal such as a clock signal, the clock signal is converted into a light signal by one of the photoelectric conversion elements of the electro-optical conversion circuits11, and the light signal is input into corresponding one of the first optical fibers5in the optical wiring board1. The light signal input to the first optical fiber5is diffused by the transmissive diffusion plate4, passed through the waveguide3to be output from the second optical fibers6, and then input to the opto-electrical conversion circuit12. The light signal input to the opto-electrical conversion circuit12is converted into an electric signal by the photoelectric conversion element of the opto-electrical conversion circuit12, and the electric signal is transmitted to the memory of the opto-electrical conversion circuit12.

In the thus configured first embodiment, since the support board2has no grooves for positioning the optical components, the support board can be manufactured easily. The optical components can be changed in configuration freely. The degree of freedom in the arrangement of the optical components can be enhanced. Since the plural first optical fibers5are optically connected to the plural second optical fibers6via the waveguide3, many-to-many communication is enabled.

In the case where the difference in thermal expansion coefficient between the support board2and the other optical components is relatively large, a resin cured at ordinary temperature or at a relatively low temperature (for example, 40.C. or lower) is preferably used as the resin for the sealing member7. An example of such a resin is a two-component silicone resin, which is cured at ordinary temperature. When such a resin is used, warp of the support board2and positional deviations of the optical components due to the difference in thermal expansion coefficient can be prevented from occurring.

In the case where the difference in thermal expansion coefficient between the support board2and the other optical components is relatively small, not only a resin which is cured at ordinary temperature or at a relatively low temperature, but also a resin which is cured at a relatively high temperature (for example, 80 to 120.C. for 30 to 60 minutes) may be used as the resin for the sealing member7. When the support board2, the waveguide3, and the transmissive diffusion plate4are made of an acrylic resin, for example, a configuration in which the difference in thermal expansion coefficient between the support board2and the other optical components is relatively small can be attained. In this example, a silicone resin which is cured at 100.C. for 30 minutes may be used as the resin for the sealing member7. When such a resin is used, the resin curing time can be shortened, and the productivity can be enhanced.

FIGS. 5A to 5Cshow other sealing methods by a resin. As shown inFIG. 5A, the resin7amay be applied onto the support board2while rotating a roller50. As shown inFIG. 5B, the resin7amay be applied onto the support board2while sliding a blade51. As shown inFIG. 5C, the sealing member7may be formed with using a heat-fusible resin film. The heat-fusible resin film may be hydrocarbon plastic such as polyethylene and polystyrene; polar vinyl plastic such as polyvinyl chloride and polymethyl methacrylate; linear plastic such as polycarbonate and polyimide; cellulosic plastic such as cellulose acetate and celluloid; and thermo plastic resin such as styrene-butadiene or polyolefin thermoplastic elastomer.

FIGS. 6A to 6Dshow steps of manufacturing an optical wiring board of a second embodiment of the invention. As shown inFIG. 6A, the optical components including the waveguide3, the transmissive diffusion plate4, and the first and second optical fibers5and6are placed on the support board2. As shown inFIG. 6B, a protective seal56is applied so that the resin7adoes not flow between the light incident face4aof the transmissive diffusion plate4and the first optical fibers5, and the optical components are temporarily secured by the temporarily securing member as described above. Then, as shown inFIG. 6C, the resin7ais poured onto the support board2, and cured to form the sealing member7. In this way, the optical wiring board1shown inFIG. 6Dis manufactured. According to the second embodiment, since the resin7adoes not flow between the light incident face4aof the transmissive diffusion plate4and the first optical fibers5, the light scattering property is stabilized. As a result, uniform light signals can be transmitted to the second optical fibers6.

FIGS. 7A to 7Dshow steps of manufacturing an optical wiring board of a third embodiment of the invention. As shown inFIG. 7A, the optical components including the waveguide3, the transmissive diffusion plate4, and the first and second optical fibers5and6are temporarily secured onto the support board2by the temporarily securing member as described above. A high viscosity resin57is applied so that the resin7adoes not flow between the light incident face4aof the transmissive diffusion plate4and the first optical fibers5, and then the high viscosity resin57is cured as shown inFIG. 7B. The resin57has a desired viscosity so long as the resin57keeps an applied shape thereof for several tens minutes after applying the resin57. Preferably, the resin57has 5,000 cps or higher in viscosity. More preferably, the resin57further has thixotropic characteristic. If the resin57has high viscosity and thixotropic characteristic as described above, shape stability thereof after applying the resin57is further improved. As a result, the workability is also improved.

Then, as shown inFIG. 7C, the resin7ais poured onto the support board2, and cured to form the sealing member7. In this way, the optical wiring board1shown inFIG. 7Dis produced. According to the third embodiment, as with the second embodiment, the light scattering property is stabilized, and uniform light signals can be transmitted to the second optical fibers6. Alternatively, a low viscosity resin may be applied and cured as an inflow preventing member for the resin7a.

Incidentally, a resin (such as the resin57) used for preventing the resin7afrom flowing into may be a low viscosity resin having 5,000 cps or lower. Even in a case of using such a low viscosity resin, no problem occurs so long as the low viscosity resin has a short cure time after applying or the low viscosity resin can be cured by exposing UV radiation while applying so that the low viscosity resin can prevent the resin7afrom flowing into the diffusion member.

FIG. 8shows an optical wiring board of a fourth embodiment of the invention. The optical wiring board1includes a support board2; a planar optical waveguide3placed on the support board2; a plurality of (for example, eight) optical fibers26optically connected to one end face3cof the waveguide3; a reflective diffusion plate14placed on the other end face3dof the waveguide3; and a positioning member8in which rear ends26bof the optical fibers26are passed through positioning holes8ato position the rear ends26b. The optical components including the waveguide3, the reflective diffusion plate14, and the optical fibers26are sealed by the sealing member7made of a resin. Alternatively, the reflective diffusion plate14may not be used, and only reflected light may be used. InFIGS. 8, and9and10which will be described later, the sealing member7is shown as a transparent member.

In the fourth embodiment, an electro-optical circuit section which can convert an electric signal into a light signal and a light signal into an electric signal is optically connected to the optical fibers26. When a light signal output from the electro-optical circuit section enters one of the optical fibers26, the light signal is passed through the waveguide3and diffused and reflected by a diffusion face14aof the reflective diffusion plate14. The reflected light signal is again passed through the waveguide3and enters the optical fibers26to be transmitted to the electro-optical circuit section.

FIG. 9shows an optical wiring board of a fifth embodiment of the invention. The optical wiring board1is configured so that, in the first embodiment, the transmissive diffusion plate4is not used, and a concave and convex pattern (diffusion face) for diffusing light is formed in the light incident face3aof the waveguide3. In the case where the light diffusion is not requested to be provided with high uniformity, the diffusion face may not be disposed.

FIG. 10shows an optical wiring board of a sixth embodiment of the invention. The optical wiring board1is configured so that, as the optical fibers in the first embodiment, optical fibers15and16having a covering material such as vinyl are used. The optical fibers15and16are protected by the covering material. Even when the resin7afor the sealing member7is applied by the roller50or the blade51shown inFIG. 5Aor5B, therefore, the clads and cores of the optical fibers15and16can be prevented from being damaged.

The invention can be applied also to an optical wiring board in which one optical fiber is connected to one end face of an optical waveguide, and a plurality of optical fibers are connected to the other end face of the waveguide. According to the configuration, one-to-many communication can be conducted.

The invention can be applied also to an optical wiring board in which optical fibers are connected to the end faces of an optical waveguide, and which transmits and receives a light signals so as to conduct bidirectional communication between CPUs. In this case, an electro-optical circuit section which can convert an electric signal to a light signal and a light signal to an electric signal is optically connected to the optical fibers.

As described above, according to the embodiments of the invention, grooves for positioning optical components are not required in an optical wiring board. Therefore, the optical wiring board can be manufactured easily, and the degree of freedom in the arrangement of the optical components is enhanced.