Optical connection board and optical signal transmission

Optical signal transmission system comprising optical signal transmission board having first optical waveguide, and optical connection board having second optical waveguide and inserted into opening of optical signal transmission board substantially perpendicularly thereto, opening being provided in upper surface of transmission board. The board comprises: a first board; the first optical waveguide extended on an upper surface of the first board; and a second board made parallel to the first board, the opening extended from the upper surface thereof toward the first board is provided in the optical signal transmission board. The optical connection board comprises: a third board; second optical waveguide extended on an upper surface of the third board; and reflection surface provided in end portion of second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the board.

FIELD OF THE INVENTION

The present invention relates to an optical connection board, an optical signal transmission system, and manufacturing methods thereof. In particular, the present invention relates to an optical connection board for performing optical signal transmission by means of an optical waveguide provided in an inner layer of the optical signal transmission board, an optical signal transmission system, and manufacturing methods thereof.

BACKGROUND OF THE INVENTION

As a processing speed of an electronic device has been increased, densification of signal wiring connecting the electronic device with the others with the increase in signal speed have become technical challenges. In conventional electric signal transmission technology, as the speed of signal increases, a dielectric loss and electromagnetic radiation in a periphery of the wiring are increasing. For this reason, in order to realize transmission speed equal to or more than several gigabits per second, a technical design is required for selection of a dielectric material, wiring density of transmission channels and the like, and the wiring becomes subject to physical restrictions.

In order to avoid such restrictions and to realize signal transmission at higher speed and with higher density, optical wiring by means of an optical waveguide and an optical fiber (hereinafter, collectively referred to as an “optical waveguide”) has been being studied. Here, for the purpose of supply of a power source for driving the electronic device and of low-speed signal transmission, it becomes necessary to make electric wiring coexist simultaneously with the optical wiring because the optical wiring has small economic advantage.

Japanese Patent Laid-Open No. 2000-227524 (hereinafter referred to as “Patent Document 1”) and Japanese Patent Laid-Open No. 2000-235127 (hereinafter referred to as “Patent Document 2”) disclose optical waveguide structures in each of which the electric wiring and the optical waveguide structure are mixed. In Patent Document 1, the optical waveguide is formed on a board, and on the optical waveguide, a light emitting element and a light receiving element are provided. Then, light emitted from the light emitting element is reflected on one end of the optical waveguide substantially at a right angle, propagated through the optical waveguide, reflected on the other end substantially at a right angle, and made incident onto the light receiving element. The optical waveguide structure of Patent Document 1 is constructed in a manner as described above. In Patent Document 2, while the light emitting element and the light receiving element are provided on an upper surface of the board, the optical waveguide is provided on a lower surface of the board, the light emitted from the light emitting element is guided to the lower surface of the board, and propagated through the optical waveguide. Then, the light is reflected on an end portion of the optical waveguide, and made incident onto the light receiving element located on the upper surface of the board. The optical waveguide structure of Patent Document 2 is constructed in a manner as described above.

There is a possibility that the optical waveguide, for use in the board in which the electric wiring and the optical waveguide structure are mixed, may be exposed to high temperature in a manufacturing process of an electric wiring board and an mounting process of components, and may be subjected to a mechanical impact and the like in use of the completed board. Therefore, it is preferable that the optical waveguide be mounted in an inner layer of the board to the extent possible. Furthermore, in order to avoid an influence of warp of the board, a structure is preferable, in which the optical waveguide is disposed at the center of the board, and boards on both sides of the optical waveguide, which sandwich the optical waveguide, are made of materials equal in thermal expansion coefficient and thickness so as to be arranged symmetrically to each other in a thickness direction.

More specifically, the board is heated in steps shown below in the manufacturing process of the laminated electric wiring board.

In a laminating step of the boards, the boards are stacked with adhesive resin being sandwiched therebetween, and the resin is cured for a few hours at temperature of a hundred and several ten degrees centigrade (180 to 190 degrees centigrade) with pressure. With regard to heat resistance of resin for use as a material of the optical waveguide, in general, phase transition temperature or glass transition temperature using a change of mechanical impedance as an index is conceived as a measure. However, when the resin is heated on exposure to air, a degradation in optical characteristics, such as yellowing, may sometimes be brought by a thermochemical reaction with the air though mechanical strength of the resin is maintained. Hence, in order to prevent such a degradation, it is effective to shield the optical waveguide from the air by disposing the waveguide not on a surface layer of the board but in the inner layer to the extent possible.

Moreover, in the step of mounting (assembling) components on the board, soldering process is performed in almost all the cases. In recent years, solder of lead-free type has used in consideration of the environment, and temperature of approximately 260° C. in the soldering process has become higher than the conventional temperature. Optically transparent acrylic resin and the like, which have heat resistance even to such a relatively high temperature, have been announced, and in the future, problems regarding the heat resistance will be reduced pretty much by using such resins. However, it is thought to be difficult to avoid the degradation of the optical characteristics due to the thermal reaction with the air, and also in order to solve this process problem, it is effective to dispose the optical waveguide in the inner layer of the board. Then, a time for the soldering process is relatively short, and accordingly, if the optical waveguide is disposed in the inner layer protected by resin layers in which heat conduction is relatively small, temperature increase in the inside can be restricted.

As described above, instead of adopting the structure in which the optical waveguide is exposed on the surface of the board as in Patent Documents 1 and 2, the disposition of the optical waveguide in the innermost layer of the board has a great practical advantage in terms of avoiding the problems in the manufacturing process and the assembly. However, in this structure, the optical waveguide in the laminated board and a light receiving/emitting element mounted on the surface of the board will be arranged to be spaced at a distance corresponding to the thickness of the board. For this reason, an optical component connection technology will be required. In this technology, an array of high density optical signal transmission paths is disposed in the inner layer of the laminated wiring board. Then, the light receiving/emitting element, the light receiving/emitting board, and the like, which are mounted on the board, and the array of the high density optical signal transmission paths, are optically connected to each other at a distance ranging from several ten microns to several millimeters.

Specifically, when the optical waveguide is disposed in the inner layer portion of the board, a structure for changing the direction of the light and a structure for guiding the light to the surface of the board will be required between the optical waveguide and the light receiving/emitting element which is mounted on the surface of the board. Here, when the light is propagated in the air between the optical waveguide and the light receiving/emitting element, the most part of the light does not reach the light receiving element but is dispersed in a periphery thereof, and coupling efficiency is significantly lowered. Furthermore, when the optical wiring is mounted with high density, the light is received by adjacent light receiving elements, causing a large interchannel crosstalk. Hence, in such a structure, it is difficult to realize optical connection in which, with regard to the density of the optical wiring, a wiring pitch is shorter than 250 microns realized by the current fiber ribbon, and the connection distance between the optical waveguide and the light receiving/emitting element is set in a range from several ten microns to several millimeters.

In order to avoid this problem, in Patent Document 2, a lens is used between the optical waveguide and the light receiving/emitting element. However, a divergence angle (numerical aperture: NA) of the light of the multimode fiber or optical waveguide or of the light of the light emitting element is generally 0.2 or more, and when the connection distance l is set at 1 mm, a relationship is unwillingly established as:
l·sin θ=l·NA=0.2 mm≈wiring pitch

Therefore, signal separation between the adjacent lines of wiring becomes difficult.

SUMMARY OF THE INVENTION

Consequently, it is an object of the present invention to provide an optical connection board, an optical signal transmission system, and manufacturing methods thereof, which are capable of solving the foregoing problems. This object is achieved by combinations of features described in independent claims in the claims. Moreover, dependent claims define further advantageous concrete examples of the present invention.

According to a first aspect of the present invention, provided is an optical connection board inserted into an opening of an optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board having a first optical waveguide, the optical connection board comprising: a board; a second optical waveguide extended on an upper surface of the board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the board. Moreover, a manufacturing method of the optical connection board is provided.

According to a second aspect of the present invention, provided is an optical signal transmission system comprising an optical signal transmission board having a first optical waveguide, and comprising an optical connection board having a second optical waveguide and inserted into an opening of the optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board, wherein the optical signal transmission board comprises: a first board; the first optical waveguide extended on an upper surface of the first board; and a second board made parallel to the first board so that a lower surface thereof is in contact with an upper surface of the first optical waveguide, the opening extended from the upper surface thereof toward the first board is provided in the optical signal transmission board, and the optical connection board comprises: a third board; the second optical waveguide extended on an upper surface of the third board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the third board. Moreover, a manufacturing method of the optical signal transmission system is provided.

Note that the above-described summary of the invention is not one listing all necessary features of the present invention, and sub-combinations of groups of these features can also be incorporated in the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an optical connection board, an optical signal transmission system, and manufacturing methods thereof, which are capable of solving the foregoing problems. This object is achieved by combinations of features described in independent claims in the claims. Moreover, dependent claims define further advantageous concrete examples of the present invention.

According to a first aspect of the present invention, provided is an optical connection board inserted into an opening of an optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board having a first optical waveguide, the optical connection board comprising: a board; a second optical waveguide extended on an upper surface of the board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the board. Moreover, a manufacturing method of the optical connection board is provided.

According to a second aspect of the present invention, provided is an optical signal transmission system comprising an optical signal transmission board having a first optical waveguide, and comprising an optical connection board having a second optical waveguide and inserted into an opening of the optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board, wherein the optical signal transmission board comprises: a first board; the first optical waveguide extended on an upper surface of the first board; and a second board made parallel to the first board so that a lower surface thereof is in contact with an upper surface of the first optical waveguide, the opening extended from the upper surface thereof toward the first board is provided in the optical signal transmission board, and the optical connection board comprises: a third board; the second optical waveguide extended on an upper surface of the third board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the third board. Moreover, a manufacturing method of the optical signal transmission system is provided.

Note that the above-described summary of the invention is not one listing all necessary features of the present invention, and sub-combinations of groups of these features can also be incorporated in the invention.

The present invention will be described below through an embodiment thereof. However, the embodiment below is not one limiting the invention according to the claims, and not all combinations of features described in the embodiment are always essential to the solving means of the present invention.

FIG. 1shows a configuration of an optical signal transmission system10according to this embodiment. The optical signal transmission system10according to this embodiment comprises an optical signal transmission board100having a first optical waveguide110, and an optical connection board130having a second optical waveguide150and inserted into an opening provided on an upper surface of the optical signal transmission board100substantially perpendicularly to the optical signal transmission board100. In the optical signal transmission system10, a light receiving/emitting element175located above the upper surface of the optical signal transmission board100and the first optical waveguide110are connected to each other with high coupling efficiency.

The optical signal transmission board100comprises a first board105, the first optical wave guide110, and a second board125. The first board105is, for example, a laminated wiring board such as a multilayer wiring board and a multilayer integrated board. The first optical waveguide110is an optical waveguide extended on an upper surface of the first board105, and comprises a core120propagating light therethrough, and cladding layers115aand115bcovering an outer circumference of the core120. Here, the optical signal transmission board100may comprise a plurality of the first optical waveguides110, and in this case, the plurality of first optical waveguides110may be composed of a plurality of the cores120, and of cladding layers115serving as claddings covering the respective outer circumferences of the plurality of cores120. The second board125is a board made parallel to the first board105so that a lower surface thereof is in contact with an upper surface of the first optical waveguide110. Similarly to the first board105, the second board125is, for example, a laminated wiring board such as a multilayer wiring board and a multilayer integrated board.

In the optical signal transmission board100described as above, an opening extended from the upper surface of the optical signal transmission board100toward the first board105and having a sidewall to which an end portion of the first optical waveguide110is exposed is provided.

The optical connection board130comprises a third board135, the second optical waveguide150, a reflection surface155, and a connection portion160. The third board135according to this embodiment is, for example, a single layer board, a laminated wiring board, or the like. The second optical waveguide150is an optical waveguide extended on an upper surface of the third board135. The second optical waveguide150comprises a core145propagating light therethrough, and cladding layers140aand140bcovering an outer circumference of the core145. More specifically, the optical connection board130according to this embodiment further comprises a cladding layer140being in contact with the third board135and serving as a cladding of the second optical waveguide150. Then, the second optical waveguide150may adopt a structure of comprising the core145extended parallel to the optical connection board130within the cladding layer140.

Moreover, the optical connection board130may comprise a plurality of the second optical waveguides150correspondingly to the plurality of first optical waveguides110. In this case, the plurality of second optical waveguides150may be composed of a plurality of the cores145, and of cladding layers140covering the respective outer circumferences of the plurality of cores145. In such a way, the plurality of light receiving/emitting elements and the plurality of first optical waveguides110can be optically coupled to each other by inserting the one optical connection board130into the opening of the optical signal transmission board100. Thus, the second optical waveguide150and the first optical waveguide110can be mounted with high density, and manufacturing cost thereof can be reduced. Such a structure is particularly effective in the case of transmitting a plurality of signals in parallel.

The reflection surface155is provided in an end portion of the second optical waveguide150. The reflection surface155is provided on the light emitting element-side of the optical connection board130. The reflection surface155reflects light, which is made incident from the light emitting element and travels through the second optical waveguide150, in a direction away from the third board135. Then, the reflection surface155makes the light incident onto the core120of the first optical waveguide110extended in the direction substantially perpendicular to the third board135. Moreover, the reflection surface155provided on the light receiving element-side of the optical connection board130reflects light incident from the first optical waveguide110which has an end portion exposed to a sidewall of the opening and is extended in the direction substantially perpendicular to the third board135. Then, the reflection surface155makes the light incident onto the second optical waveguide150.

The connection portion160is formed of a material of the core, and optically couples the core145of the second optical waveguide150, the reflection surface155, and the core120of the first optical waveguide110to one another by means of a function of the core material. Specifically, by means of the function of the core material, the connection portion160provided on the light emitting element-side of the optical connection board130propagates, to the reflection surface155, light incident from the core145in the end portion of the second optical waveguide150, in addition, propagates the light reflected by the reflection surface155by means of the function of the core material, and makes the light incident onto the core120in the end portion of the first optical waveguide110. On the contrary, the connection portion160provided on the light receiving element-side of the optical connection board130propagates, to the reflection surface155, light incident from the core120in the end portion of the first optical waveguide110by means of the function of the core material, in addition, propagates the light reflected by the reflection surface155by means of the function of the core material, and makes the light incident onto the core145in the end portion of the second optical waveguide150. Thus, the connection portion160can reduce an optical coupling loss between the core145of the second optical waveguide150and the core120of the first optical waveguide110.

Furthermore, the optical connection board130comprises a positioning portion137for determining depth of the optical connection board130inserted into the optical signal transmission board100so that, on the light emitting side, the light reflected by the reflection surface155is made incident onto the first optical waveguide110, and that, on the light receiving side, the light emitted from the first optical waveguide110is made incident onto the reflection surface155. Specifically, in a state where the optical connection board130is inserted into the opening of the optical signal transmission board100to a predetermined depth, the positioning portion137does not allow the optical connection board130to be further inserted into the optical signal transmission board100, thus determining a position of the reflection surface155with respect to the first optical waveguide110. More specifically, the positioning portion137according to this embodiment is a side surface of the third board135inserted into the opening of the optical signal transmission board100. In a state where the side surface is in contact with a bottom surface of the opening, the positioning portion137does not allow the optical connection board130to be further inserted into the optical signal transmission board100, thus determining the position of the reflection surface155with respect to the first optical waveguide110.

As described above, the depth of the opening provided in the optical signal transmission board100and the position of the reflection surface155with respect to the side surface of the third board135are set precisely, and thus the position of the reflection surface155with respect to the first optical waveguide110can be properly determined by using the positioning portion137.

An electronic device170is mounted on the upper surface of the optical signal transmission board100. The electronic device170comprises the light receiving/emitting element175that is a light emitting element for outputting optical signals by light emission and making the optical signals incident onto the second optical waveguide150and/or a light receiving element for receiving optical signals emitted from the second optical waveguide150. Moreover, the electronic device170comprises a terminal180for input and output of electric signals. Light outputted from the light emitting side of the light receiving/emitting element175is made incident onto the second optical waveguide150on the light emission side, propagated therethrough, reflected by the reflection surface155on the light emitting side, and then made incident onto the first optical waveguide110. Then, the light propagated through the first optical waveguide110is reflected by the reflection surface155on the light receiving side, made incident onto the second optical waveguide150on the light receiving side, propagated through the second optical waveguide150on the light receiving side, and then made incident onto the light receiving/emitting element175on the light receiving side.

According to the optical signal transmission system10described as above, the first optical waveguide110disposed in the inner layer portion of the optical signal transmission board100can be connected to the light receiving/emitting element175mounted on the surface of the light transmission board100by the optical connection board130with high coupling efficiency. Moreover, the optical connection board130is inserted into the optical signal transmission board100after the laminating step and the soldering step of components in the manufacturing process are finished, thus making it possible to prevent the second optical waveguide150from being affected by heat.

FIG. 2shows a configuration of the optical signal transmission system10according to a first modification example of this embodiment. The optical signal transmission system10according to the first modification example adopts a configuration modified from the optical signal transmission system10shown inFIG. 1, and accordingly, description thereof will be omitted except for the following difference.

The optical signal transmission system10according to this modification example is different from the optical signal transmission system10shown inFIG. 1in comprising an optical connection board230in place of the optical connection board130.

The optical connection board230comprises a third board235, a second optical waveguide250, and a reflection surface255. The third board235according to this modification example is an optically transparent board. Here, it is preferable that the third board235be thin as compared with the third board135shown inFIG. 1in order to transmit light exchanged between the second optical waveguide250and the first optical waveguide110. The second optical waveguide250is an optical waveguide extended on an upper surface of the third board235. The second optical waveguide250comprises a core245propagating the light therethrough, and cladding layers240aand240bcovering an outer circumference of the core245. More specifically, the optical connection board230according to this modification example further comprises a cladding layer240being in contact with the third board235and serving as a cladding of the second optical waveguide250. Then, the second optical waveguide250may adopt a structure of comprising the core245extended parallel to the optical connection board230within the cladding layer240. Moreover, the optical connection board230may comprise a plurality of the second optical waveguides250correspondingly to the plurality of first optical waveguides110. In this case, the plurality of second optical waveguides250may be composed of a plurality of the cores245, and of cladding layers240covering the respective outer circumferences of the plurality of cores245.

The reflection surface255is provided in an end portion of the second optical waveguide250. The reflection surface255is provided on the light emitting element-side of the optical connection board230. The reflection surface255reflects light, which is made incident from the light emitting element and travels through the second optical waveguide250, in a direction to the third board235. Then, the light is transmitted through the third board235, and is made incident onto the core120of the first optical waveguide110extended in the direction substantially perpendicular to the third board235. Meanwhile, the reflection surface255provided on the light receiving element-side of the optical connection board230reflects light incident from the first optical waveguide110which has an end portion exposed to a sidewall of the opening and is extended in the direction substantially perpendicular to the third board235. Then the light is transmitted through the third board235, and is made incident onto the second optical waveguide250.

Furthermore, the optical connection board230comprises a positioning portion237for determining depth of the optical connection board230inserted into the optical signal transmission board100so that, on the light emitting side, the light reflected by the reflection surface255is made incident onto the first optical waveguide110, and that, on the light receiving side, the light emitted from the first optical waveguide110is made incident onto the reflection surface255. Similarly to the positioning portion137, the positioning portion237according to this modification example is a side surface of the third board235inserted into the opening of the optical signal transmission board100. In a state where the side surface is in contact with a bottom surface of the opening, the positioning portion237does not allow the optical connection board230to be further inserted into the optical signal transmission board100, thus determining the position of the reflection surface255with respect to the first optical waveguide110.

As described above, the bottom surface of the opening provided in the optical signal transmission board100functions as a positioning plane for use in the positioning, which is parallel to the optical signal transmission board100. Then, in a state where the optical connection board230is inserted into the opening of the optical signal transmission board100to a predetermined depth, the positioning portion237is in contact with an upper surface of the positioning plane, and does not allow the optical connection board230to be further inserted into the optical signal transmission board100.

According to the optical signal transmission system10described as above, the first optical waveguide110disposed in the inner layer portion of the optical signal transmission board100can be connected to the light receiving/emitting element mounted on the surface of the light transmission board100by the optical connection board230with high coupling efficiency. Moreover, the optical connection board230is inserted into the optical signal transmission board100after the laminating step and the soldering step of components in the manufacturing process are finished, thus making it possible to prevent the second optical waveguide250from being affected by heat.

Note that, in place of the above, a structure may be adopted, in which the third board235is formed of a material serving as a cladding of the second optical waveguide250, and the core245is in contact with an upper surface of the third board235and is extended on the upper surface. In this case, the cladding layer240ais in contact with the upper surface of the third board235and an upper surface and side surface of the core245, and serves as the cladding of the second optical waveguide250.

FIGS. 3(a) to3(c) are a first group of diagrams showing a manufacturing method of the optical connection board230.FIGS. 3(a) to3(c) show mold fabrication steps of forming a negative mold350for use in forming the core245on the third board235.

As shown inFIG. 3(a), first, a metal plate is cut by means of a blade320by using, for example, precision diamond cutting, and a positive mold300provided with an optical waveguide shape310having a shape of the cores245is formed. Next, as shown inFIG. 3(b), portions to be end portions of the optical waveguide shape310are cut by means of a blade340, and a reflection surface shape330having a shape of the reflection surfaces255is formed on the end portions of the optical waveguide shape310. Next, as shown inFIG. 3(c), the negative mold350serving as a negative mold for the positive mold300on which the optical waveguide shape310and the reflection surface shape330are formed is made by using, for example, electroforming, molding or the like.

FIGS. 4(a) to4(c) are a second group of diagrams showing the manufacturing method of the optical connection board230.FIGS. 4(a) to4(c) show second optical waveguide fabrication steps of forming the cores245on the third board235by using a 2P method as a molding method.

As shown inFIG. 4(a), UV curing resin400such as curing acrylic resin having a high refractive index is applied as mold resin on the negative mold350. Next, as shown inFIG. 4(b), the third board235is pressed onto the negative mold350on which the UV curing resin400is applied, and UV light is irradiated from a back surface of the third board235. Thus, the UV curing resin400is cured. In such a way, glass having a lower refractive index than the UV curing resin400may be used as the third board235, the cores245may be provided on the upper surface of the third board235so as to directly be in contact therewith, and the third board235may be used as the cladding layer of the second optical waveguide250. Instead of this, cladding resin having a low refractive index as compared with the UV curing resin400may be applied or molded on the core245-side surface of the third board235, and the cladding layer240bmay be formed in advance. Next, as shown inFIG. 4(c), the third board235in which the cores245are formed on the upper surface is released from the negative mold350.

According to the second optical waveguide fabrication steps described as above, each core245of the second optical waveguide250extended on the upper surface of the third board235is formed by using the molding, thus making it possible to form the second optical waveguide250. In addition, the photo-curing resin (UV curing resin400) is used as the mold resin, and accordingly, temperature during the molding can be set substantially the same as room temperature, and heat shrinkage of the resin can be restricted to a relatively small extent. Thus, the second optical waveguide250can be formed with high precision. Moreover, resin excellent in heat resistance can also be used as the UV curing resin400.

Instead of the above, in the second optical waveguide fabrication steps, the second optical waveguide250and the third board235may be integrally molded by using an injection or compression method.

FIGS. 5(a) to5(c) are a third group of diagrams showing the manufacturing method of the optical connection board230.

As shown inFIG. 5(a), in the second optical waveguide fabrication steps, the one or plurality of cores245which are extended on the upper surface of the third board235and have inclined surfaces serving as the reflection surfaces255on the end portions are formed on the third board235. Next, as shown inFIG. 5(b), in a reflection surface fabrication step, metal films serving as mirrors are deposited on the inclined surfaces on the end portions of the cores245by using mask deposition or the like, and the reflection surfaces255are formed on the end portions of the second optical waveguides250.

Next, as shown inFIG. 5(c), in a cladding layer fabrication step, the cladding layer240awhich is in contact with the cores245and the upper surface of the third board235and serves as the claddings of the second optical waveguides250is formed, by means of coating the resin as the cladding material on the upper surface of the third board235, by means of forming the cladding layer on the upper surface of the third board235by using the 2P mold method, or the like.

According to the above-described manufacturing method shown inFIGS. 3(a) to5(c), an optical connection board230having a similar function to that of the optical connection board230shown inFIG. 2can be fabricated.

In the case of fabricating an optical connection board230having the same structure as the optical connection board230shown inFIG. 2, the respective manufacturing steps described above are changed shown as below. First, the step of forming the reflection surface shape330, which is shown inFIG. 3(b), is not performed, but a positive mold300provided with a reflection surface shape330that does not have the shape of the reflection surfaces255on the end portions of the optical waveguide shape310is formed. Thus, inFIG. 5(a), cores245that do not have the inclined surfaces serving as the reflection surfaces255on the end portions are obtained. Next, the reflection surface fabrication step shown inFIG. 5(b) is omitted, and the cladding layer240ais formed by the cladding layer fabrication step shown inFIG. 5(c).

Thereafter, the cladding layers240aand240band the cores245to be the end portions of the second optical waveguides250are cut, and the inclined surfaces to be the reflection surfaces255are formed. Next, the metal films are deposited on the inclined surfaces by using the mask deposition, and the reflection surfaces255are formed. At this stage, spaces on the opposite of the cores245with respect to the reflection surfaces255are in a state of being cut away when the inclined surfaces are formed. The optical connection board230may be inserted into the optical signal transmission board100in this state. Alternatively, the optical connection board230may be inserted into the optical signal transmission board100, after the portions cut for forming the inclined surfaces serving as the reflection surfaces are filled with resin or the like.

According to the manufacturing process thus changed, the optical connection board230having the same structure as that shown inFIG. 2can be fabricated.

FIGS. 6(a) to6(c) are a first group of diagrams showing a manufacturing method of the optical connection board130according to this embodiment.FIGS. 6(a) to6(c) show first cladding layer fabrication steps of forming the cladding layer140bon the third board135by using the 2P method as the molding method.

First, as shown inFIG. 6(a), the UV curing resin400is applied on the positive mold300fabricated in the step ofFIG. 3(b) in a similar way to that inFIG. 4(a). Next, as shown inFIG. 6(b), the third board135is pressed onto the positive mold300on which the UV curing resin400is applied, and UV light (ultraviolet rays) is irradiated from a back surface of the third board135. In such a way, the UV curing resin400is cured. In order to perform the processing as described above, it is preferable to use an optically transparent board as the third board135. Accordingly, in a similar way to the step ofFIG. 4(b), glass having a lower refractive index than the UV curing resin400may be used, and the third board135may be used as a cladding layer of the second optical waveguide150.

Instead of this, the cladding layer140amay be formed in advance on the surface of the core145-side of the third board135. Next, as shown inFIG. 6(c), the third board135in which the cladding layer140ais formed on the upper surface is released from the positive mold300. Moreover, the third board135and the cladding layer140amay be formed integrally by using the injection method and the like.

FIGS. 7(a) to7(d) are a second group of diagrams showing the manufacturing method of the optical connection board130according to this embodiment.

As shown inFIG. 7(a), in the first cladding layer fabrication step, the cladding layer140ahaving groove portions in which inner walls are formed in a shape of the cores of the second optical waveguides150and serving as the claddings of the second optical waveguides150is formed on the upper surface of the third board135. Next, as shown inFIG. 7(b), in the reflection surface fabrication step, metal films serving as mirrors are deposited on end portions of the groove portions provided in the cladding layer140aby using the mask deposition or the like, and thus the reflection surfaces155are formed on the end portions of the second optical waveguides150.

Next, as shown inFIG. 7(c), in the second optical waveguide fabrication steps, the groove portions of the cladding layer140aare filled with a core material such as resin, and the cores145of the second optical waveguides150are formed. Then, surplus resin is removed by a squeegee and the like, optical surfaces are formed by means of surface tension of the resin, and the resin is cured by light or heat. Instead of this, an optical plane may be formed by the 2P method and the like by using a plane mold and the like. Next, as shown inFIG. 7(d), in the second cladding layer fabrication step, the cladding layer140bserving as claddings of the second optical waveguides150are formed on the upper surface of the cladding layer140ain which the groove portions are filled with the core material.

According to the above-described manufacturing method shown inFIGS. 6(a) to7(d), similarly to the optical connection board130shown inFIG. 1, the optical connection board130adopting the structure in which the light traveling through the second optical waveguide is reflected by the reflection surface155in the direction away from the third board135can be fabricated. More specifically, an optical connection board130shown inFIG. 14can be fabricated by the manufacturing method shown inFIGS. 6(a) to7(d). The optical connection board130shown inFIG. 14comprises a third board135, a cladding layer140awhich is in contact with the upper surface of the third board135and serves as the cladding of the second optical waveguide150, a core145formed in the groove portion provided on the cladding layer140a, a reflection surface155formed on an end portion of the groove portion provided on the cladding layer140a, and a cladding layer140bformed on upper surfaces of the cladding layer140aand core145. In this feature, the light traveling through the second optical waveguide150is reflected by the reflection surface155, transmitted through the cladding layer140b, and made incident onto the first optical waveguide110. Meanwhile, the light incident from the first optical waveguide110onto the second optical waveguide150is transmitted through the cladding layer140b, is reflected by the reflection surface155, and travels through the second optical waveguide150.

Instead of the above, in the case of fabricating an optical connection board130having the same structure as the optical connection board130shown inFIG. 1, the respective manufacturing steps described above are changed shown as below. First, the step of forming the reflection surface shape330, which is shown inFIG. 3(b), is not performed, but the positive mold300provided with the reflection surface shape330that does not have the shape of the reflection surfaces155on the end portions of the optical waveguide shape310is formed. Thus, inFIG. 7(a), a cladding layer140athat does not have the inclined surfaces to be the reflection surfaces155on the end portions is obtained. Next, the reflection surface fabrication step shown inFIG. 7(b) is omitted, and the cladding layer140is formed by the second optical waveguide fabrication step shown inFIG. 7(c) and the second cladding layer fabrication step shown inFIG. 7(d).

Thereafter, the cladding layers140aand140band the cores145in the portions to be the end portions of the second optical waveguides150are cut, and the inclined surfaces to be the reflection surfaces155and spaces to be provided with the connection portions160are formed. Next, the metal films are deposited on the inclined surfaces by using the mask deposition, and the reflection surfaces155are formed. Then, the spaces to be provided with the connection portions160are filled with the core material, and the connection portions160are formed.

According to the manufacturing process thus changed, the optical connection board130having the same structure as that shown inFIG. 1can be fabricated.

FIGS. 8(a) to8(c) are a first group of diagrams showing a manufacturing method of the optical signal transmission board100according to this embodiment.FIGS. 8(a) to8(c) show a first cladding layer fabrication step, a core fabrication step, and a second cladding layer fabrication step in optical signal transmission board fabrication process of the optical signal transmission board100, respectively.

First, as shown inFIG. 8(a), in the first cladding layer fabrication step, the cladding layer115ais formed on the upper surface of the first board105. Next, as shown inFIG. 8(b), in the core fabrication step, the core120extended on the upper surface of the cladding layer115ais formed. Next, as shown inFIG. 8(c), in the second cladding layer fabrication step, the cladding layer115bis formed so as to cover the upper surface of the cladding layer115aand the upper and side surfaces of the core120.

FIGS. 9(a) and9(b) are a second group of diagrams showing the manufacturing method of the optical signal transmission board100according to this embodiment. Next, as shown inFIG. 9(a), in an upper board laminating step in the optical signal transmission board fabrication process, the second board125is stacked on the upper surface of the cladding layer115b. Next, as shown inFIG. 9(b), in an opening fabrication step, an opening900extended from the upper surface of the optical signal transmission board100toward the first board105and having a sidewall to which the end portion of the first optical waveguide110is exposed, is formed.

As described above, according to the manufacturing process shown inFIGS. 8(a) to9(b), the optical signal transmission board100can be fabricated. Thereafter, in an optical connection board insertion step, the optical connection board130or the optical connection board230is inserted into the opening900of the optical signal transmission board100. Then, on the light emitting side, the reflection surface155and the like are arranged at the positions where the light traveling through the second optical waveguide150and the like and reflected by the reflection surface155and the like is incident onto the core120extended in the direction substantially perpendicular to the third board135and the like. Moreover, on the light receiving side, the reflection surface155and the like are arranged at the positions where the light emitted from the first optical waveguide110extended in the direction substantially perpendicular to the third board135and the like and reflected by the reflection surface155and the like is incident onto the second optical waveguide150.

In the above description, the laminating of boards for the optical signal transmission board100may be performed after the upper board laminating step shown inFIG. 9(a) and before the opening fabrication step shown inFIG. 9(b). Thus, the first optical waveguide110can be prevented from being damaged by heat treatment in the laminating step. Moreover, the soldering process of the electronic components on the upper or lower surface of the optical signal transmission board100may be performed after the opening fabrication step shown inFIG. 9(b) and before the optical connection board insertion step. Thus, the second optical waveguide150or the second optical waveguide250can be prevented from being affected by heat due to the soldering process.

Moreover, prior to the above-described optical connection board insertion step, as a transparent resin injection step, transparent resin filling a gap between the optical signal transmission board100and the second optical waveguide150or the second optical waveguide250may be injected into the opening900of the optical signal transmission board100. Then, after the second optical waveguide150or the second optical waveguide250is inserted into the opening900, curing treatment for this transparent resin may be performed. As a result of this, the optical signal transmission system10is configured by further comprising the transparent resin injected into the opening900of the optical signal transmission board100and filling the gap between the optical signal transmission board100and the second optical waveguide150or the second optical waveguide250.

In such away, the gap between the optical signal transmission board100and the second optical waveguide150or the second optical waveguide250is filled with the transparent resin having substantially the same refractive index as those of the core145and core120. Thus, even in the case where the surface of the sidewall of the opening900is not optically smooth (uniform) in the opening fabrication step, irregularities on the surface can be smoothed, and the core120and the core145can be connected with each other with high optical coupling efficiency. Hence, even in the case where the opening900is formed by machining in the opening fabrication step, sufficient coupling efficiency can be obtained.

FIG. 10shows a connection structure of optical waveguides according to a second modification example of this embodiment. InFIG. 10, the first optical waveguide110, a second optical waveguide1050, a reflection surface1055and a connection portion1060are illustrated, and for example, illustration of members inFIG. 1, such as the first board105, the second board125and the third board135, is omitted.

The second optical waveguide1050according to the second modification example comprises cladding layers1040aand1040bcorresponding to the cladding layers140aand140bofFIG. 1, and a core1045corresponding to the core145ofFIG. 1, and has a similar structure to that of the second optical waveguide150ofFIG. 1except for the following point. The second optical waveguide1050in the second modification example adopts a structure in which the cladding layer1040bin an end portion of the second optical waveguide1050is partially stripped off and a side surface of an end portion of the cladding layer1040bis in contact with an upper surface of the cladding layer115b. Thus, a structure can be adopted, in which the cladding layer1040b-side of the core1045and a cladding layer115b-side of the core120are in contact with each other substantially. Then, a centerline of the core1045can be made close to the end portion of the core120.

The reflection surface1055and the connection portion1060correspond to the reflection surface155and connection portion160ofFIG. 1, respectively. The reflection surface1055according to the second modification example is an inclined plane of which both ends are connected to an end portion on the cladding layer1040a-side of the core1045and an end portion on the cladding layer115b-side of the core120. Thus, a distance in which light exchanged between the core1045and the core120passes through the connection portion1060can be suppressed to be short. For this reason, the coupling efficiency of the light between the core1045and the core120can be increased, and crosstalk between a plurality of the cores1045and a plurality of the cores120can be restricted.

InFIG. 10, when the core1045and the core120have the same dimension, a traveling distance of the light between end surfaces of the core1045and core120, that is, a distance in which the light passes through the connection portion1060between the core1045and the core120, can be represented by the following Expression (1)

l=l1+l2=tcore2+tcore2=tcore⁢
where tcoreis heights of the core1045and core120, l1is a distance between the center of the end portion of the core120and the reflection surface1055in a direction parallel to the core120, and l2is a distance between the center of the end portion of the core1045and the reflection surface1055in a direction parallel to the core1045.

FIG. 11shows a connection structure of optical waveguides according to a third modification example of this embodiment. InFIG. 11, the first optical waveguide110, a second optical waveguide1150, a reflection surface1155and a connection portion1160are illustrated, and for example, illustration of members inFIG. 1, such as the first board105, the second board125and the third board135, is omitted.

The second optical waveguide1150according to the third modification example comprises cladding layers1140aand1140bcorresponding to the cladding layers140aand140bofFIG. 1, and a core1145corresponding to the core145ofFIG. 1. The second optical waveguide1150according to the third modification example adopts a structure, in which an end surface of the second optical waveguide1150is located on an extension of a lower surface of the cladding layer115b, and the cladding layer1140bis located between the core1145and the cladding layer115b.

The reflection surface1155and the connection portion1160correspond to the reflection surface155and connection portion160ofFIG. 1, respectively. The reflection surface1155according to the third modification example is an inclined plane of which both ends are connected to an end portion on the cladding layer1140a-side of the core1145and a lower end portion of the cladding layer115a. Moreover, the connection portion1160is provided to be in contact with end surfaces of the core1145and cladding layer1140band on end surfaces of the core120and cladding layer115a.

InFIG. 11, when the core1145and the core120have the same dimension, a traveling distance of the light between end surfaces of the core1145and core120can be represented by the following Expression (2).

At present, in general, the height tcoreof the cores is set at several ten microns in the multimode optical waveguide. When the thickness tcladdingof the cladding layer is set at several ten microns to a similar extent, the traveling distance l of the light between the end surfaces of the cores becomes approximately 100 microns. In this case, divergence of the light is represented as:
l·sin θ=l·NA=0.02 mm

Hence, even if the distance between the optical waveguides is reduced to less than 0.25 mm that is a pitch of a current optical fiber array, a crosstalk between the optical waveguides can be suppressed to be sufficiently small.

As described above, according to the connection structure of the optical waveguides, which is shown inFIG. 11, though the traveling distance of the light between the end surfaces of the cores becomes somewhat long as compared with that of the connection structure shown inFIG. 10, the crosstalk between the optical waveguides can be suppressed to be sufficiently small. Furthermore, step of stripping off a part of the end portion of the cladding layer1040bcan be eliminated, and a structure easy to manufacture and assemble can be obtained.

FIG. 12shows a connection structure of optical waveguides according to a fourth modification example of this embodiment. InFIG. 12, the first optical waveguide110, a second optical waveguide1250, a reflection surface1255and a connection portion1260are illustrated, and for example, illustration of members inFIG. 1, such as the first board105, the second board125and the third board135, is omitted.

In the third modification example, though the crosstalk between the optical waveguides can be made sufficiently small, a part of the light emitted from one optical waveguide is not incident onto the other optical waveguide, and a coupling loss occurs therebetween. In order to reduce this coupling loss, in the fourth modification example, the reflection surface provided between the two optical waveguides is made as a light collecting optical system.

The second optical waveguide1250according to the fourth modification example comprises cladding layers1240aand1240bcorresponding to the cladding layers140aand140bofFIG. 1, and a core1245corresponding to the core145ofFIG. 1. The second optical waveguide1250according to the fourth modification example adopts a structure, in which an end surface of the second optical waveguide1250is located on an extension of an upper surface of the cladding layer115b.

The reflection surface1255and the connection portion1260correspond to the reflection surface155and connection portion160ofFIG. 1, respectively. The reflection surface1255according to the fourth modification example has a concave shape, and more specifically, has a spheroidal surface shape C in which approximate center points of an end portion of the reflection surface1255and of an end portion of the core120, that is points A and B inFIG. 12, are set as focal points. Thus, light emitted from one optical waveguide is collected and made incident onto the approximate center point of the core in the end portion of the other optical waveguide. As a result of this, the coupling efficiency of the light can be increased.

InFIG. 12, when the core1245and the core120have the same dimension, a traveling distance of the light between end surfaces of the core1245and core120can be represented by the following Expression (3).

l=l1+l2=2×(tcore2+tcladding)=tcore+2·tcladding⁢⁢…⁢
where tcoreis heights of the core1245and core120, l1is a distance between the center of the end portion of the core120and the reflection surface1255in a direction parallel to the core120, l2is a distance between the center of the end portion of the core1245and the reflection surface1255in a direction parallel to the core1245, and tcladdingis thicknesses of the cladding layer1240band cladding layer115b.

As described above, according to the connection structure shown inFIG. 12, though the traveling distance of the light between the end surfaces of the cores becomes long as compared with that of the connection structures shown inFIGS. 10 and 11, the reflection surface1255is made as the light collecting optical system, thus making it possible to obtain high coupling efficiency.

The reflection surface described above can be fabricated by a method shown as below. First, in the mold fabrication step shown inFIG. 3(b), the portion to be the end portion of each optical waveguide310is cut by means of the blade340, and the reflection surface shape330having a convex shape corresponding to the reflection surface155or the reflection surface255is formed on the end portion of the optical waveguide shape310. Then, in the second optical waveguide fabrication steps shown inFIGS. 4(a) to4(c), the UV curing resin400is molded by the negative mold350for the reflection surface shape330. Alternatively, in the second optical waveguide fabrication steps shown inFIGS. 6(a) to6(c), the UV curing resin400is molded into the reflection surface shape330. Thus, the reflection surface having the concave shape on each end portion of the second optical waveguide250or second optical waveguide150can be formed.

FIG. 13shows a configuration of an optical signal transmission system10according to a fifth modification example of this embodiment. The optical signal transmission system10according to this modification example adopts a structure modified from the optical signal transmission system10shown inFIG. 1, and accordingly, description thereof will be omitted except for the following difference.

An optical connection board130according to this modification example further comprises a light receiving/emitting element1320, a pair of a reflection surface155band a connection portion160b, an electronic device1300, and wiring1310. The light receiving/emitting element1320is mounted on the optical connection board130, and functions as a light emitting unit and/or a light receiving unit. The light receiving/emitting element1320according to this modification example is mounted on the upper surface of the cladding layer140b. However, instead of this, the light receiving/emitting element1320may be mounted on a surface of the third board135, which is opposite with the second optical waveguide150.

The reflection surface155band the connection portion160bhave similar functions and configurations to those of the reflection surface155aand connection portion160a. The reflection surface155band the connection portion160bfunction as a light guide unit for making an optical signal outputted by the light receiving/emitting element1320incident onto an end portion of the second optical waveguide150, which is opposite with the first optical waveguide110, and for inputting an optical signal incident from the second optical waveguide150to the light receiving/emitting element1320. The reflection surface155band the connection portion160bexchange the optical signals between the light receiving/emitting element1320mounted on an upper surface of the cladding layer140band the second optical waveguide150. However, instead of this, the optical signals may be exchanged with a light receiving/emitting element1320mounted on a surface of the third board135, which is opposite with the second optical waveguide150.

The reflection surface155ais provided in an end portion on the first optical waveguide110-side of the second optical waveguide150. The reflection surface155areflects the optical signal traveling through the second optical waveguide150and makes the reflected optical signal incident onto the first optical waveguide110. Meanwhile, the reflection surface155areflects the optical signal incident from the first optical waveguide110and makes the reflected optical signal incident onto the second optical waveguide150.

The electronic device1300is mounted on the optical connection board130. The electronic device1300according to this modification example is mounted on the surface of the third board135, which is opposed with the second optical waveguide150. However, instead of this, the electronic device1300may be mounted on the upper surface of the cladding layer140b. The wiring1310connects the electronic device1300and the light receiving/emitting element1320to each other. In this modification example, the wiring1310is provided so as to pass on the surface of the third board135or through an inner layer thereof. The wiring1310connected to the light receiving/emitting element1320for use as the light emitting unit inputs, to the light receiving/emitting element1320, an electric signal outputted from the electronic device1300, and the inputted electric signal is converted into an optical signal by the light receiving/emitting element1320. Moreover, the wiring1310connected to the light receiving/emitting element1320for use as the light receiving unit inputs, to the electronic device1300, an electric signal outputted based on the optical signal received by the light receiving/emitting element1320.

In the above description, when the electronic device1300has a plurality of terminals for use in parallel transmission, a plurality of the light receiving/emitting elements1320may convert a plurality of electric signals outputted from the plurality of terminals into a plurality of optical signals, and a plurality of the second optical waveguides150and a plurality of the first optical waveguides110may transmit the plurality of optical signals so as to make the optical signals incident onto the plurality of light receiving elements, respectively. In this case, for the purpose of densification, it is desirable that the plurality of second optical waveguides150and the plurality of first optical waveguides110adopt structures of being extended parallel to one another in the optical connection board130and the optical signal transmission board100, respectively.

In a similar way to the above, the electronic device1300, the wiring1310and the light receiving/emitting element1320can also be mounted on the optical connection board230. Specifically, for example, the electronic device1300and the light receiving/emitting element1320may be mounted on the surface of the third board235, which is opposite with the second optical waveguide250, a reflection surface for exchanging the light between the light receiving/emitting element1320and the second optical waveguide250may be provided similarly to the reflection surface255, and the wiring1310may be provided on the surface of the third board235or in the inner layer thereof.

According to the optical signal transmission system10described above, the first optical waveguide110disposed in the inner layer portion of the optical signal transmission board100and the light receiving/emitting element mounted on the surface-side of the optical signal transmission board100can be connected to each other with high coupling efficiency by the optical connection board130or the optical connection board230. Here, the light receiving/emitting element may be mounted after completing the board by inserting the optical connection board130or the optical connection board230into the opening provided in the optical signal transmission board100. Alternatively, it is also possible to provide the light receiving/emitting element with the optical connection board130or the optical connection board230, and to insert it into the opening of the optical signal transmission board100at the stage of mounting components.

Moreover, the reflection surface155and the like are molded integrally with a light guiding optical system such as the optical connection board130, and thus the reflection surface155and the like can be formed more easily and precisely as compared with the case of forming the reflection surface155and the like in the inner layer of the optical signal transmission board100having large size and thickness. Moreover, for the optical signal transmission board100, it is necessary to perform, in the laminating step of the boards, many heat and solvent treatment processes such as a thermal curing process and thermal annealing process for the resin configuring the boards, an UV light irradiation process for printed wiring, an alkaline treatment for resist development, and a cleaning process. According to the manufacturing method of the optical signal transmission system10in accordance with this embodiment, it is satisfactory if the opening for inserting the optical connection board130or the like thereinto may be provided by performing a drilling process after the above-described processes, and thus the first optical waveguide110can be prevented from being broken or damaged.

Moreover, the opening of the optical signal transmission board100is filled with the transparent resin, and the optical connection board130or the like is inserted therethrough. Accordingly, even if irregularities occur on the sidewall of the opening to some extent, the optical coupling efficiency can be prevented from being lowered. Therefore, the drilling process for the optical signal transmission board100can be performed not by a highly precise process such as a laser beam machining but by machining controlled so as not to cause a burr.

Moreover, the optical connection board130and the optical connection board230are small in size as compared with the optical signal transmission board100, and accordingly, processes such as the molding and the diamond cutting can be easily performed therefor. Moreover, also in the deposition process for the reflection surface155and the reflection surface255, the reflection films can be deposited by use of a compact evaporation apparatus, and thus the manufacturing cost can be reduced.

Although the present invention has been described above by use of the embodiments, the technical scope of the present invention is not limited to the scope described in the embodiments. It is apparent to those skilled in the art that it is possible to add various alterations or modifications to the above-described embodiments. It is apparent from description in the claims that modes added with such alterations or modifications as described above can be incorporated in the technical scope of the present invention.

According to the above-described embodiments, optical connection boards, optical signal transmission systems, and methods for manufacturing the optical signal transmission systems, which are described in the following respective items, are realized.(Item1) An optical connection board inserted into an opening of an optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board having a first optical waveguide, the optical connection board comprising: a board; a second optical waveguide extended on an upper surface of the board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the board.(Item2) The optical connection board according to Item1, further comprising: a cladding layer being in contact with the board and serving as a cladding of the second optical waveguide, wherein the second optical waveguide has a core extended parallel to the board within the cladding layer.(Item3) The optical connection board according to Item2, wherein the reflection surface reflects the light traveling through the second optical waveguide in a direction away from the board, and makes the light incident onto the first optical waveguide.(Item4) The optical connection board according to Item2, wherein the reflection surface reflects the light traveling through the second optical waveguide in a direction toward the board, transmits the light through the board, and makes the light incident onto the first optical waveguide.(Item5) The optical connection board according to Item1, wherein the second optical waveguide has a core extended on an upper surface of the board, the board is formed of a material serving as a cladding of the second optical waveguide, and the optical connection board further comprises a cladding layer being in contact with the upper surface of the board and an upper surface and side surface of the core and serving as a cladding of the second optical waveguide.(Item6) The optical connection board according to Item1, wherein the first optical waveguide and the second optical wave guide have cores and claddings covering outer circumferences of the cores, and the optical connection board further comprises a connection portion formed of a core material and for propagating, to the reflection surface by the core material, light emitted from the core in the end portion of the second optical waveguide, and propagating, by the core material, the light reflected by the reflection surface, to make the light incident onto the core in an end portion of the first optical waveguide.(Item7) The optical connection board according to Item6, wherein the reflection surface has a spheroidal surface shape in which approximate center points of the cores in the end portion of the first optical waveguide and the end portion of the second optical waveguide are set as focal points.(Item8) The optical connection board according to Item1, wherein the reflection surface has a concave shape.(Item9) The optical connection board according to Item1, further comprising: a positioning portion for determining depth of the optical connection board inserted into the optical signal transmission board so that the light reflected by the reflection surface is made incident onto the first optical waveguide.(Item10) The optical connection board according to Item9, wherein the positioning portion does not allow the optical connection board to be further inserted into the optical signal transmission board in a state where the optical connection board is inserted into the opening of the optical signal transmission board to a predetermined depth, thus determining a position of the reflection surface with respect to the first optical waveguide.(Item11) The optical connection board according to Item9, wherein a positioning plane parallel to the optical signal transmission board is provided in an inside of the opening of the optical signal transmission board, and the positioning portion is in contact with an upper surface of the positioning plane in a state where the optical connection board is inserted into the opening of the optical signal transmission board to a predetermined depth.(Item12) The optical connection board according to Item9, wherein the positioning portion is a side surface of the board inserted into the opening, and does not allow the optical connection board to be further inserted into the optical signal transmission board in a state where the side surface is in contact with a bottom surface of the opening, thus determining a position of the reflection surface with respect to the first optical waveguide.(Item13) The optical connection board according to Item1, comprising: a plurality of the second optical waveguides; and cladding layers being in contact with the board and serving as claddings of the plurality of second optical waveguides.(Item14) The optical connection board according to Item1, further comprising: a light emitting unit mounted on the optical connection board; and a light guide unit for making an optical signal outputted by the light emitting unit onto a first end portion of the second optical waveguide, wherein the reflection surface is provided in a second end portion of the second optical waveguide, reflects the optical signal traveling through the second optical waveguide, and makes the optical signal incident onto the first optical waveguide.(Item15) The optical connection board according to Item14, further comprising: an electronic device mounted on the optical connection board; and wiring for inputting, to the light emitting unit, an electric signal outputted from the electronic device, wherein the light emitting unit converts the electric signal inputted from the electronic device into the optical signal.(Item16) An optical connection board inserted into an opening of an optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board having a first optical waveguide, the optical connection board comprising: a board; a second optical waveguide extended on an upper surface of the board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light incident from the first optical waveguide extended in a direction substantially perpendicular to the board, and making the light incident onto the second optical waveguide.(Item17) An optical signal transmission system comprising an optical signal transmission board having a first optical waveguide, and comprising an optical connection board having a second optical waveguide and inserted into an opening of the optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board, wherein the optical signal transmission board comprises: a first board; the first optical waveguide extended on an upper surface of the first board; and a second board made parallel to the first board so that a lower surface thereof is in contact with an upper surface of the first optical waveguide, the opening extended from the upper surface thereof toward the first board is provided in the optical signal transmission board, and the optical connection board comprises: a third board; the second optical waveguide extended on an upper surface of the third board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light traveling through the second optical waveguide, and making the light incident onto the first optical waveguide extended in a direction substantially perpendicular to the third board.(Item18) The optical signal transmission system according to Item17, further comprising: transparent resin injected into the opening of the optical signal transmission board and filling a gap between the optical signal transmission board and the optical connection board.(Item19) An optical signal transmission system comprising an optical signal transmission board having a first optical waveguide, and comprising an optical connection board having a second optical waveguide and inserted into an opening of the optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board, wherein the optical signal transmission board comprises: a first board; the first optical waveguide extended on an upper surface of the first board; and a second board made parallel to the first board so that a lower surface thereof is in contact with an upper surface of the first optical waveguide, the opening extended from the upper surface thereof toward the first board is provided in the optical signal transmission board, and the optical connection board comprises: a third board; the second optical waveguide extended on an upper surface of the third board; and a reflection surface provided in an end portion of the second optical waveguide, reflecting light incident from the first optical waveguide extended in a direction substantially perpendicular to the third board, and making the light incident onto the second optical waveguide.(Item20) A method for manufacturing an optical signal transmission system comprising an optical signal transmission board having a first optical waveguide, and comprising an optical connection board having a second optical waveguide and inserted into an opening of the optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board, the method comprising: an optical signal transmission board fabrication step of forming the optical signal transmission board comprising a first board, the first optical waveguide extended on an upper surface of the first board, and a second board made parallel to the first board so that a lower surface thereof is in contact with an upper surface of the first optical waveguide; a second optical waveguide fabrication step of forming the second optical waveguide extended on an upper surface of a third board; a reflection surface fabrication step of forming a reflection surface reflecting light traveling through the second optical waveguide in an end portion of the second optical waveguide; an opening fabrication step of forming the opening extended from the upper surface of the optical signal transmission board toward the first board; and an optical connection board insertion step of inserting the optical connection board into the opening of the optical signal transmission board, and disposing the reflection surface at a position where the light traveling through the second optical waveguide and reflected by the reflection surface is made incident onto the first optical waveguide extended in a direction substantially perpendicular to the third board.(Item21) The method according to Item20, wherein the second optical waveguide fabrication step further comprises a cladding layer fabrication step of forming a core of the second optical waveguide extended on the upper surface of the third board and forming a cladding layer being in contact with the upper surface of the third board and the core and serving as a cladding of the second optical waveguide.(Item22) The method according to Item20, further comprising: a first cladding layer fabrication step of forming, on the upper surface of the third board, a first cladding layer having a groove portion in which an inner wall is formed into a shape of a core of the second optical waveguide and serving as a cladding of the second optical waveguide, wherein the second optical waveguide fabrication step further comprises a second cladding layer fabrication step of filling a core material in the groove portion of the first cladding layer, forming the core of the second optical waveguide, and then forming a second cladding layer serving as a cladding of the second optical waveguide on an upper surface of the first cladding layer in which the groove portion is filled with the core material.(Item23) The method according to Item20, further comprising: a transparent resin injection step of injecting, into the opening of the optical signal transmission board, transparent resin filling a gap between the optical signal transmission board and the optical connection board.(Item24) A method for manufacturing an optical signal transmission system comprising an optical signal transmission board having a first optical waveguide, and comprising an optical connection board having a second optical waveguide and inserted into an opening of the optical signal transmission board substantially perpendicularly thereto, the opening being provided in an upper surface of the optical signal transmission board, the method comprising: an optical signal transmission board fabrication step of forming the optical signal transmission board comprising a first board, the first optical waveguide extended on an upper surface of the first board, and a second board made parallel to the first board so that a lower surface thereof is in contact with an upper surface of the first optical waveguide; a second optical waveguide fabrication step of forming the second optical waveguide extended on an upper surface of a third board; a reflection surface fabrication step of forming a reflection surface reflecting light incident from the first optical waveguide in an end portion of the second optical waveguide; an opening fabrication step of forming the opening extended from the upper surface of the optical signal transmission board toward the first board; and an optical connection board insertion step of inserting the optical connection board into the opening of the optical signal transmission board, and disposing the reflection surface at a position where light emitted from the first optical waveguide extended in a direction substantially perpendicular to the third board and reflected by the reflection surface is made incident onto the second optical waveguide.

According to the present invention, the optical waveguide disposed in the inner layer portion of the board and the light receiving/emitting element can be connected to each other with high coupling efficiency.

Although the preferred embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and alternations can be made therein without departing from spirit and scope of the inventions as defined by the appended claims.