Optical connector module and method of manufacturing optical waveguide board

An optical connector module (1) according to the present disclosure includes an optical waveguide board (10) and an optical connector (20) attached to the optical waveguide board (10). The optical connector (20) includes a positioning target portion (23) that engages with the optical waveguide board (10), and the optical connector (20) is positioned relative to the optical waveguide board (10) in a state in which the positioning target portion (23) is engaged with the optical waveguide board (10). The optical waveguide board (10) includes an optical waveguide (12) including a first cladding (122a) and a core (121) stacked on the first cladding (122a), the first cladding being stacked on a substrate (11) in a stacking direction perpendicular to the substrate (11), and a positioning core (14) that is stacked on the first cladding (122a) by using a material the same as a material of the core (121) and that engages with the positioning target portion (23). The positioning core (14) protrudes further than the core (121) toward a side opposite to the substrate (11) in the stacking direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Japanese Patent Application No. 2019-010561, filed on Jan. 24, 2019, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an optical connector module and a method of manufacturing an optical waveguide board.

BACKGROUND ART

An optical connector module for optically coupling an optical waveguide included in an optical waveguide board to another optical transmission line is known. For example, PTL 1 discloses an optical connector module that includes an optical waveguide board including a positioning projection that is stacked on a lower cladding layer of an optical waveguide in parallel with a core of the optical waveguide.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

An optical connector module according to an embodiment of the present disclosure isan optical connector module including an optical waveguide board and an optical connector attached to the optical waveguide board.

The optical connector includes:a positioning target portion that engages with the optical waveguide board; andthe optical connector is positioned relative to the optical waveguide board in a state in which the positioning target portion is engaged with the optical waveguide board.

The optical waveguide board includesan optical waveguide including a first cladding and a core stacked on the first cladding, the first cladding being stacked on a substrate in a stacking direction perpendicular to the substrate, anda positioning core that is stacked on the first cladding by using a material the same as a material of the core and that engages with the positioning target portion.

The positioning core protrudes further than the core toward a side opposite to the substrate in the stacking direction.

A method of manufacturing an optical waveguide board according to an embodiment of the present disclosure isa method of manufacturing an optical waveguide board to which an optical connector is to be attached.

The method includes:a first step of stacking a cladding of an optical waveguide on a substrate in a staking direction perpendicular to the substrate; anda second step of stacking a core of the optical waveguide and a positioning core on the cladding by using materials that are the same as each other, the positioning core to be engaged with a positioning target portion of the optical connector to position the optical connector relative to the optical waveguide board.

In the second step, the positioning core is formed so as to protrude further than the core toward a side opposite to the substrate in the stacking direction.

DESCRIPTION OF EMBODIMENTS

In order to optically couple an optical waveguide to another optical transmission line efficiently, in general, it is necessary to align the positions of the optical waveguide and the other optical transmission line with each other with a precision of the order of micrometers. Accordingly, accuracy of the same order is required for positioning an optical connector of an optical connector module, which is to be connected to a connector that holds another optical transmission line, relative to an optical waveguide board. With the optical connector module including the optical waveguide board described in PTL 1, the accuracy in positioning the optical connector relative to the optical waveguide board is not sufficient.

An embodiment of the present disclosure provides an optical connector module and a method of manufacturing an optical waveguide board with which the accuracy in positioning an optical connector relative to an optical waveguide board is improved.

Hereafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The front-back, the left-right, and the up-down directions in the following description are defined as the directions of arrows in the figures. The directions of arrows in different figures are consistent with each other.

The “stacking direction” used in the following description includes, for example, the up-down direction. The “extension direction of a core” includes, for example, the front-back direction. The “direction perpendicular to the stacking direction” includes, for example, the left-right direction. The “side opposite to the substrate” includes, for example, the upper side.

First Embodiment

Referring toFIGS.1to11C, a first embodiment of the present disclosure will be mainly described.FIG.1is a perspective view of an optical connector module1according to the first embodiment.FIG.2is an exploded perspective view of the optical connector module1shown inFIG.1. The optical connector module1includes an optical waveguide board10and an optical connector20attached to the optical waveguide board10.

FIG.3is a perspective view of only the optical waveguide board10shown inFIG.2. Referring toFIG.3, the configuration of the optical waveguide board10shown inFIG.2will be mainly described.

The optical waveguide board10includes, for example, a substrate11that is constituted by a rigid printed wiring substrate and an optical waveguide12that is stacked on an upper surface of the substrate11. The optical waveguide12is formed, for example, so as to protrude from the upper surface of the substrate11. The optical waveguide12is formed, for example, in order to be optically coupled to the optical connector20, so that a front end surface thereof coincides with a front end surface of the substrate11. The front end surface of the optical waveguide12has, for example, a flat shape along the front end surface of the substrate11. The waveguide mode of the optical waveguide12is, for example, a single mode. The waveguide mode of the optical waveguide12is not limited to this, and may be a multi-mode. In the following description, it is assumed that the optical waveguide12is formed on the upper surface of the substrate11. However, the position of the optical waveguide12is not limited to this. For example, the optical waveguide12may be embedded in the substrate11. In this case, the front end surface of the optical waveguide12may be formed so that the front end surface coincides with the front end surface of the substrate11and so that end surfaces of cores121described below are exposed from the substrate11.

The optical waveguide12includes the cores121and a cladding122that are stacked on the substrate11in the stacking direction perpendicular to the substrate11. To be more specific, the optical waveguide12includes a first cladding122astacked on the upper surface of the substrate11, the cores121stacked on the first cladding122a, a second cladding122bthat is disposed so that the cores121are interposed between the second cladding122band the first cladding122ain the stacking direction and that surrounds the cores121.

The cores121are formed so as to be separated from each other by predetermined distances in the left-right direction. The cores121and the cladding122are each made of, for example, an appropriate material such as quartz glass. The refractive index of each core121is higher than the refractive index of the cladding122. In the following description, it is assumed that the optical waveguide12is, for example, an embedded optical waveguide. However, the optical waveguide12is not limited to this. The optical waveguide12may be an optical waveguide of any appropriate type, such as a slab optical waveguide or a semi-embedded optical waveguide.

The optical waveguide board10includes heat conductors13that are embedded in the substrate11along positioning cores14described below. To be more specific, each heat conductor13is embedded in the substrate11along the entire width of a corresponding one of the positioning cores14in the front-back and left-right directions. The heat conductor13is embedded in the substrate11directly below the positioning core14so as to extend parallel to the positioning core14in the front-back direction. The heat conductor13may be a single copper plate that is embedded in the substrate11directly below the positioning core14, or may be a plurality of copper wires that are embedded in the substrate11directly below the positioning core14and that extend parallel to each other. The material of the heat conductor13is not limited to copper and may be any appropriate material having high thermal conductivity.

The optical waveguide board10further includes the positioning cores14that are stacked on the substrate11by using a material the same as the material of the core121. The positioning cores14are stacked on the first cladding122a. The positioning cores14are formed, for example, in a pair so that the optical waveguide12is interposed therebetween in the left-right direction. Each positioning core14is formed, for example, parallel to the optical waveguide12in the front-back direction. The positioning core14is each formed, for example, so as to extend by a predetermined length in the front-back direction.

Each positioning core14includes a small-width portion141that constitutes a front half part of the positioning core14and that has a rectangular shape in a top view. The positioning core14includes an engagement portion142that is formed so as to be continuous backward from the small-width portion141and that has a trapezoidal shape in a top view that gradually becomes wider from the front toward the back. The positioning core14includes a large-width portion143that is formed so as to be continuous backward from the engagement portion142, the has a larger width in the left-right direction than the small-width portion141, and that has a rectangular shape in a top view.

Each positioning core14and each core121are separated from the heat conductor13. The distance between the positioning core14and the heat conductor13is smaller than the distance between the core121and the heat conductor13. In a process of manufacturing the optical waveguide board10described below, a heat amount based on heat applied to the optical waveguide board10differs between the positioning core14and the core121due to the effect of the distance from the heat conductor13. To be more specific, when a heat amount received by the positioning core14and a heat amount received by the core121in the manufacturing process are compared, the heat amount in the positioning core14is smaller than the heat amount in the core121, because the distance the positioning core14and the heat conductor13is smaller than the distance between the core121and the heat conductor13. Thus, under the same environment in the process of manufacturing the optical waveguide board10, the temperature of the positioning core14tends to become lower than the temperature of the core121.

FIG.4is a perspective view of only the optical connector20shown inFIG.2. Referring toFIG.4, the configuration of the optical connector20shown inFIG.2will be mainly described.

The optical connector20is made of, for example, a light-transmissive resin material. For example, the optical connector20is made of a material having a refractive index that is substantially the same as the refractive index of the core121of the optical waveguide12. The optical connector20has an L-shape. The optical connector20includes a first base member21that extends in the front-back direction. The first base member21includes a recessed portion21bthat is recessed inward from a central part of a lower surface21a. The optical connector20includes a second base member22that protrudes forward from the first base member21and that is formed to be continuous from the first base member21. The second base member22is formed so as to jut out downward from the first base member21. The optical connector20includes a pair of through-holes22athat extend through the second base member22from the front surface to the back surface of the second base member22and each of which has a circular shape in a sectional view. The pair of through-holes22aare formed in left and right end portions of the second base member22in such a way that the recessed portion21bof the first base member21is interposed therebetween in the left-right direction. The optical connector20includes a recessed portion22bthat is recessed by one step inward from the front surface of the second base member22.

The optical connector20includes a pair of positioning target portions23that are formed in the lower surface21aof the first base member21on the left and right outer sides of the recessed portion21bin such a way that the recessed portion21bis interposed therebetween in the left-right direction. The positioning target portions23are, for example, recessed portions each of which has a semicircular shape in a sectional view. The positioning target portions23are formed to be continuous from the through-holes22aof the second base member22to the back end of the first base member21. The through-holes22aand the positioning target portions23have circular shapes that are concentric with each other. The positioning target portions23extend parallel to the recessed portion21bin the front-back direction.

The optical connector20includes a pair of accommodation portions24that are formed in the lower surface21aof the first base member21on the left and right outer sides of the positioning target portions23in such a way that the recessed portion21band the positioning target portions23are interposed therebetween in the left-right direction. The accommodation portions24are, for example, recessed portions each of which has a semicircular shape in a sectional view. The radius of the semicircle of each accommodation portion24in a sectional view is, for example, sufficiently smaller than the radius of the semicircle of each positioning target portion23in a sectional view. The accommodation portions24are, for example, formed to be continuous from the front end to the back end of the first base member21. The accommodation portions24extend, for example, in the extension direction of the cores121perpendicular to the stacking direction. The accommodation portions24extend, for example, parallel to the recessed portion21band the positioning target portions23in the front-back direction.

The optical connector20includes a lens portion25that is provided in a front surface A1of the recessed portion22b. The lens portion25is constituted by a plurality of lenses25aeach having a curvature. The number of the lenses25aof the lens portion25corresponds to the number of the cores121of the optical waveguide12.

The optical connector20is to be optically coupled to the optical waveguide12included in the optical waveguide board10. To be more specific, the second base member22of the optical connector20, for example, transmits light emitted from the cores121of the optical waveguide12and guides the light to the lenses25a. The light that has passed through the lenses25ais emitted from the optical connector20and becomes coupled to another optical transmission line that is held by a connector connected to the optical connector20. Conversely, the lenses25aof the second base member22of the optical connector20transmit light emitted from the other optical transmission line that is held by the connector connected to the optical connector20. The light that has passed through the lenses25apasses through the second base member22and enters the cores121of the optical waveguide12.

As illustrated inFIGS.1and2, the optical connector20is placed, for example, on the optical waveguide12from above the optical waveguide board10. To be more specific, the optical connector20is placed on the first cladding122aas the lower surface21aof the first base member21comes into contact with the upper surface of the first cladding122aof the optical waveguide12. At this time, the small-width portion141of each positioning core14is accommodated within the width of a corresponding one of the positioning target portions23of the optical connector20in the left-right direction. The optical connector20is slightly pushed backward from this state, and a back end portion of the positioning target portions23come into contact with the engagement portions142of the positioning cores14. Thus, the positioning cores14and the positioning target portions23engage with each other.

In the state in which the positioning target portions23are engaged with the positioning cores14, the optical connector20is positioned relative to the optical waveguide board10. To be more specific, the position of the optical connector20in the up-down direction relative to the optical waveguide board10is determined based on contact of the lower surface21aof the first base member21with the upper surface of the first cladding122aof the optical waveguide12. The position of the optical connector20relative to the optical waveguide board10in the front-back and left-right directions is determined based on the engagement of the positioning target portions23of the first base member21with the positioning cores14of the optical waveguide board10.

FIG.5is a front view of the optical connector module1shown inFIG.1. As illustrated inFIG.5, when the optical connector20is positioned relative to the optical waveguide board10, front end portions of the cores121of the optical waveguide12and the second cladding122bare accommodated in the recessed portion21bof the first base member21. The optical connector20is disposed in a state in which the lower surface21aof the first base member21is in contact with the upper surface of the first cladding122aand covers a part of the optical waveguide12. The second base member22is disposed so as to protrude forward from the front end surface of the substrate11and jut out downward from the first base member21. The second base member22protrudes so that the lower surface thereof is located below the up-down position of the optical waveguide12and located above the lower surface of the substrate11. The lenses25aof the lens portion25, which is formed in the second base member22, respectively face the cores121of the optical waveguide12.

FIG.6is an enlarged view of a region surrounded by an alternate long and short dash line inFIG.5. As illustrated inFIG.6, the accommodation portion24of the optical connector20is formed outside, along the substrate11, of the positioning target portion23, which is engaged with the positioning core14. The first cladding122aof the optical waveguide12has a slightly smaller width in the left-right direction than the lower surface21aof the first base member21of the optical connector20. To be more specific, the width of the first cladding122ain the left-right direction is smaller than the distance between the pair of left and right accommodation portions24and larger than the distance between the pair of left and right positioning target portions23, which are engaged with the positioning cores14. Accordingly, the left and right ends of the lower surface21a, which respectively include the pair of left and right accommodation portions24, are not in contact with the first cladding122aand face the upper surface of the substrate11in a state of being separated from the upper surface of the substrate11. The accommodation portions24, which are formed in the lower surface21a, face the substrate11. A space S is formed between each of the left and right ends of the lower surface21a, which respectively include the pair of left and right accommodation portions24, and the upper surface of the substrate11.

FIG.7is an enlarged front sectional view schematically illustrating a part of the optical connector module1shown inFIG.1. InFIG.7, the structural relationship between each core121of the optical waveguide12and the positioning core14is illustrated. As illustrated inFIG.7, in the optical connector module1shown inFIG.1, the positioning core14is stacked on the first cladding122aso that the volume of the positioning core14is larger than that of the core121of the optical waveguide12. To be more specific, the positioning core14is stacked on the first cladding122aso that the up-down width of the positioning core14is larger than that of the core121of the optical waveguide12. The positioning core14protrudes further than the core121of the optical waveguide12toward a side opposite to the substrate11in the stacking direction. Likewise, the positioning core14is stacked on the first cladding122aso that the left-right width of the positioning core14is larger than that of the core121of the optical waveguide12.

In general, with an existing method of manufacturing an optical waveguide board, when a core and a positioning core are formed in the same manufacturing process, top end surfaces thereof, that is, upper surfaces thereof are uniformly formed to have heights that are the same as each other. However, the upper surface of the positioning core14of the optical connector module1according to the first embodiment differs from that of the common sense of existing technology, and is formed so as to be positioned further than the upper surface of the core121toward a side opposite to the substrate11in the stacking direction.

The optical waveguide board10according to the first embodiment is manufactured, for example, by using photolithography. A manufacturing process described below is repeatedly performed to sequentially form the first cladding122a, the core121and the positioning core14, and the second cladding122b. A method of manufacturing the optical waveguide board10according to the first embodiment includes a first step of stacking the first cladding122aof the optical waveguide12on the substrate11in the stacking direction perpendicular to the substrate11. The method of manufacturing the optical waveguide board10includes a second step of stacking the core121of the optical waveguide12and the positioning core14on the first cladding122aby using materials that are the same as each other. The method of manufacturing the optical waveguide board10includes a third step of stacking the second cladding122bof the optical waveguide12so that the core121is interposed between the second cladding122band the first cladding122ain the stacking direction.

In the method of manufacturing the optical waveguide board10according to the first embodiment, in the second step, the positioning core14is formed so as to protrude further than the core121toward the side opposite to the substrate11in the stacking direction. For example, in the second step, the core121and the positioning core14are formed by manufacturing processes that are the same as each other. For example, in a predetermined manufacturing process in the second step, the amount of exposure light with which the core121is irradiated and the amount of exposure light with which the positioning core14is irradiated differ from each other. For example, when a photoresist liquid used for photolithography is of a negative type, in the predetermined manufacturing process in the second step, the amount of exposure light with which the positioning core14is irradiated may be larger than the amount of exposure light with which the core121is irradiated. By adjusting the amount of exposure light irradiated in the predetermined manufacturing process between the positioning core14and the core121, it is possible to form the positioning core14in such a way that the height of the positioning core14becomes larger than the height of the core121. A method of forming the positioning core14and the core121is not limited to this. For example, in a predetermined manufacturing process in the second step, the positioning core14and the core121are each stacked on the first cladding122aso that a heat amount based on heat applied to the positioning cores14and a heat amount based on heat applied to the core121differ from each other.

FIG.8is a schematic view illustrating an example of the method of manufacturing the optical waveguide board10shown inFIG.2. Hereafter, referring toFIG.8, a method of forming the positioning core14of the optical connector module1according to the first embodiment will be described in further detail. For convenience of description, the first cladding122ais omitted, and a case where the core121and the positioning core14are stacked on the substrate11will be described. A description similar to the following description also applies to forming of the cladding122.

In a first process, pretreatment for cleaning the upper surface of the substrate11is performed.

In a second process, a photoresist liquid is ejected, and, for example, while the substrate11is rotated by a spin coater, the photoresist liquid is uniformly applied to the entire area of the upper surface of the substrate11due to a centrifugal force. Thus, a base for the core121of the optical waveguide12and the positioning core14is uniformly formed. A coating method used in the second process is not limited to spin coating, and may be any appropriate method. For example, the coating method may be bar coating, spray coating, or the like. When all manufacturing processes are finished, the heights of the core121and the positioning core14are smaller than or equal to the heights of corresponding parts of the photoresist liquid applied in the second process.

At the time when the second process is finished, the amount of photoresist liquid on the outer periphery of the upper surface of the substrate11is large. Accordingly, in a third process, edge rinsing is performed to wipe out the outer peripheral edge by using a needle. Thus, the thickness of the entirety of the photoresist liquid becomes uniform.

In a fourth process, pre-baking is performed to apply heat to the entirety at a temperature in the range of 90° C. to 120° C. Thus, the photoresist liquid becomes slightly solidified. At this time, due to the heat conductor13embedded in the substrate11, a heat amount transferred to the positioning core14is smaller than a heat amount transferred to the core121of the optical waveguide12. For example, due to the heat conductor13, the temperature of the positioning core14becomes lower than the temperature of the core121of the optical waveguide12. Because the temperature of the core121is higher than the temperature of the positioning core14, organic solvents, such as a binder, in the core121evaporate easier than those in the positioning core14. As a result, when all manufacturing processes are finished, the volume of the core121tends to become smaller than the volume of the positioning core14. In the finished optical waveguide board10, the positioning core14protrudes further than the core121of the optical waveguide12toward the side opposite to the substrate11in the stacking direction.

In a fifth process, a mask is placed on a part of the photoresist excluding parts that are to be left as the core121and the positioning core14in the finished optical waveguide board10, and exposure is performed by irradiating the photoresist with ultraviolet radiation. Thus, only the parts of the photoresist irradiated with ultraviolet radiation are solidified. At this time, a photosensitizer mixed in the photoresist solidifies in accordance with the exposure light amount. The larger the exposure light amount and the larger the number of chemical bonds in the photosensitizer that are formed due to light, corresponding photoresist parts are left unremoved in a phenomenon described below. Accordingly, the exposure light amount of ultraviolet radiation with which the positioning core14is irradiated is made larger than the exposure light amount of ultraviolet radiation with which the core121of the optical waveguide12is irradiated. Thus, the positioning core14solidifies more solidly than the core121of the optical waveguide12and becomes more unlikely to be removed in development. As a result, in the finished optical waveguide board10, the positioning core14protrudes further than the core121of the optical waveguide12toward the side opposite to the substrate11in the stacking direction. The method of adjusting the exposure light amount may be, for example, a method related to adjustment of light amount, such as a method of reducing the light amount of ultraviolet radiation by attaching an ultraviolet radiation filter only at a position directly in front to the core121of the optical waveguide12. The method of adjusting the exposure light amount may be, for example, a method related to adjustment of exposure time, such as a method of making the exposure time for which the positioning core14is irradiated with ultraviolet radiation longer.

In a sixth process, post-exposure baking (PEB) of applying heat to the entirety at a temperature in the range of 50° C. to 90° C. may be performed. In this case, the irregularity of a side surface of a photoresist part irradiated with ultraviolet radiation in the fifth process is smoothed. PEB in the sixth process may be omitted, if not necessary.

In a seventh process, by using a developing liquid, development is performed to remove the part of photoresist excluding the parts to be left as the core121and the positioning core14in the finished optical waveguide board10. Due to the development, adjustment between the positioning core14and the core121, which is represented by the fifth process described above, is reflected, and the height of the core121becomes smaller than the height of the positioning core14.

In an eighth process, post-baking it performed to apply heat to the entirety in a drying oven. Thus, the parts of photoresist to be left as the core121and the positioning core14become harder and strongly adhere to the substrate11.

With the optical connector module1and the method of manufacturing the optical waveguide board10according to the first embodiment described above, the accuracy in positioning the optical connector20relative to the optical waveguide board10is improved. To be more specific, because the positioning core14of the optical waveguide board10protrudes further than the core121toward the side opposite to the substrate11, the protruding amount of the positioning core14becomes larger. Thus, engagement of the positioning core14with the positioning target portion23of the optical connector20becomes more reliable. For example, if the waveguide mode of the optical waveguide12is a single mode, the up-down width of the core121is smaller than or equal to about 10 μm, which is very small. In such a case, if, as in the existing technology, the positioning core14is formed through the same manufacturing process to have the same up-down width as the core121, the positioning core14and the positioning target portion23do not engage with each other, and the position of the optical connector20may become displaced. As the protruding amount of the positioning core14becomes larger, the sensitivity in positioning the optical connector20relative to the optical waveguide board10is improved, and such displacement is suppressed. Because forming of the positioning core14and the core121completes in the same manufacturing process, increase in cost is also suppressed.

Because the positioning core14is stacked on the first cladding122a, the positioning core14can be stacked on the stacking surface the first cladding122a, which is smoother than the stacking surface of the substrate11. Thus, the positioning core14is formed with higher accuracy.

Because the amount of exposure light with which the core121of the optical waveguide12is irradiated and the amount of exposure light with which the positioning core14is irradiated differ from each other, it is possible to adjust the degree of solidification of the photosensitizer mixed in the photoresist to differ between the core121and the positioning core14. For example, when the amount of exposure light with which the positioning core14is irradiated is larger than the amount of exposure light with which the core121is irradiated, it is possible to make the positioning core14solidify more firmly than the core121to enable the positioning core14to be more unlikely to be removed in development.

Because the distance between the positioning core14and the heat conductor13is smaller than the distance between the core121and the heat conductor13, the temperature of the positioning core14is lower than the temperature of the core121when heat is applied to the entirety in the process of manufacturing the optical waveguide board10. Accordingly, the vaporization amount of organic solvent is smaller for the positioning core14, and, as a result, it is possible to form the positioning core14so as to protrude upward further than the core121.

The accommodation portion24of the optical connector20is formed outside the positioning target portion23along the substrate11. Thus, for example, even in a case where, after positioning the optical connector20on the optical waveguide board10, an adhesive is applied to the left and right side surfaces the optical connector20to fix the optical connector20to the optical waveguide board10, it is possible to prevent the adhesive from flowing into the positioning target portion23.

For example, due to a capillary action, the adhesive flows from the outside to the inside through the space S between the optical connector20and the substrate11. If the accommodation portion24is not formed in the lower surface21aof the optical connector20, the adhesive may flow into the positioning target portion23due to a capillary action. If the adhesive flows into the positioning target portion23, the positioning target portion23and the positioning core14may not become engaged appropriately, and the optical connector20may become displaced relative to the optical waveguide board10.

The accommodation portion24can accommodate an adhesive that flows from the outside to the inside and can suppress the adhesive from reaching the positioning target portion23, which is formed further inside. Accordingly, the accommodation portion24can suppress the aforementioned displacement of the optical connector20due to the adhesive.

Because the accommodation portion24is formed in the lower surface21afacing the substrate11in the optical connector20and the accommodation portion24extends in the front-back direction, flow of the adhesive to the inside is suppressed over the front-back width where the accommodation portion24is formed. Accordingly, the accommodation portion24can more effectively suppress the aforementioned displacement of the optical connector20due to the adhesive.

The accommodation portion24not only can suppress the aforementioned flow of the adhesive to the inside of the optical connector20, but also can suppress spreading of the adhesive to the outside of the optical connector20. Thus, for example, even if a plurality of optical waveguides12are formed in the optical waveguide board10with small distances therebetween, when fixing the optical connector20to each optical waveguide12by using an adhesive, it is possible to reduce the risk that parts of the adhesive applied to adjacent optical connectors20interfere with each other.

FIG.9Ais a schematic top view illustrating a first modification of the optical waveguide board10shown inFIG.2. In the first embodiment, the first cladding122ahas a width that is smaller than the distance between the pair of left and right accommodation portions24of the optical connector20. However, the configuration of the optical connector module1is not limited to this. The optical connector module1may have any appropriate configuration in which spaces S are formed below the left and right end portions of the lower surface21aincluding the accommodation portions24of the optical connector20.

For example, as illustrated inFIG.9A, the first cladding122amay be stacked on the entirety of the substrate11, and the spaces S may be formed by removing the first cladding122aat positions respectively near the left and right end portions of the lower surface21aincluding the accommodation portions24of the optical connector20. InFIG.9A, regions A2from which the first cladding122ais removed each have, for example, a rectangular shape, and each have a width that is wider in the front-back direction than the front-back width of the first base member21of the optical connector20.

FIG.9Bis a schematic top view illustrating a second modification of the optical waveguide board10shown inFIG.2. InFIG.9B, only the shape of the region A2on the right side ofFIG.9Ais illustrated. InFIG.9B, the shape of the region A2is, for example, a rectangular shape, and the width of the region A2in the front-back direction is smaller than the front-back width of the first base member21of the optical connector20.

FIG.9Cis a schematic top view illustrating a third modification of the optical waveguide board10shown inFIG.2. InFIG.9C, only the shape of the region A2on the right side ofFIG.9Ais illustrated. InFIG.9C, the shape of the region A2is, for example, a convex shape having a tip with a rounded edge. The width of the region A2in the front-back direction may be larger than the front-back width of the first base member21of the optical connector20, or may be smaller than the front-back width of the first base member21.

FIG.9Dis a schematic top view illustrating a fourth modification of the optical waveguide board10shown inFIG.2. InFIG.9D, only the shape of the region A2on the right side ofFIG.9Ais illustrated. InFIG.9D, the shape of the region A2is, for example, a trapezoidal shape having a front-back width that increases from the outside toward the inside. The width of the region A2in the front-back direction may be larger than the front-back width of the first base member21of the optical connector20, or may be smaller than the front-back width of the first base member21.

FIG.9Eis a schematic top view illustrating a fifth modification of the optical waveguide board10shown inFIG.2. InFIG.9E, only the shape of the region A2on the right side ofFIG.9Ais illustrated. InFIG.9E, the shape of the region A2is, for example, a trapezoidal shape having a front-back width that decreases from the outside toward the inside. The width of the region A2in the front-back direction may be larger than the front-back width of the first base member21of the optical connector20, or may be smaller than the front-back width of the first base member21.

FIG.10Ais a schematic front view illustrating a first modification of the optical connector20shown inFIG.6.FIG.10Aillustrates the shape of the right-side surface of the first base member21. InFIG.10A, the left and right side surfaces of the first base member21of the optical connector20each include an inclined surface that is inclined inward and downward from a substantially central part thereof in the up-down direction.

FIG.10Bis a schematic front view illustrating a second modification of the optical connector20shown inFIG.6.FIG.10Billustrates the shape of the right side surface of the first base member21. InFIG.10B, the left and right side surfaces of the first base member21of the optical connector20each include an inclined surface that is inclined inward and downward from an upper part thereof.

FIG.11Ais a schematic front view illustrating a third modification of the optical connector20shown inFIG.6.FIG.11Aillustrates the shape of a part near the right end of the lower surface21a, including the accommodation portion24. InFIG.11A, the accommodation portion24has a rectangular shape in a sectional view.

FIG.11Bis a schematic front view illustrating a fourth modification of the optical connector20shown inFIG.6.FIG.11Billustrates the shape of a part the right end of the lower surface21a, including the accommodation portion24. InFIG.11B, the lower surface21aprotrudes further downward at a position inside the accommodation portion24. In this case, the accommodation portion24may face, instead of the upper surface of the substrate11, the upper surface of the first cladding122a. A space S may be formed between a corresponding part of the lower surface21aand the first cladding122a.

FIG.11Cis a schematic front view illustrating a fifth modification of the optical connector20shown inFIG.6.FIG.11Cillustrates the shape of a part near the right end of the lower surface21a. InFIG.11C, the optical connector20does not have the accommodation portion24, and the lower surface21aof the optical connector20includes an inclined surface that is inclined inward and downward.

In the first embodiment, it has been described that the accommodation portion24continuously extends from the front end to the back end of the first base member21. However, the configuration of the accommodation portion24is not limited to this. The accommodation portion24may be formed, as one or more concave portions that extend by a predetermined length within the front-back width of the first base member21, at any appropriately position outside the positioning target portion23.

In the first embodiment, it has been described that the accommodation portion24is a recessed portion. However, the configuration of the accommodation portion24is not limited to this. The accommodation portion24may have any appropriate configuration that enables the accommodation portion24to accommodate the adhesive applied to the optical connector20. For example, the accommodation portion24may be formed as a through-hole.

In the first embodiment, it has been described that the positioning target portion23is a recessed portion. However, the configuration of the positioning target portion23is not limited to this. The positioning target portion23may have any appropriate configuration that enables the positioning target portion23to be engaged with the positioning core14. For example, the positioning target portion23may be formed as a through-hole.

In the first embodiment, it has been described that the core121of the optical waveguide12and the positioning core14are formed by manufacturing processes that are the same as each other. However, the manufacturing processes are not limited to these. The core121of the optical waveguide12and the positioning core14may be formed by different manufacturing processes. For example, in the light exposure in the fifth process described above, first, only the positioning core14may be irradiated with ultraviolet radiation by using a mask for the positioning core14, and then only the core121may be irradiated with ultraviolet radiation by using a mask for the core121.

In this case, if the photosensitizer solidifies slowly over time, by first irradiating the positioning core14with ultraviolet radiation, the solidification time of the positioning core14becomes longer than that of the core121. Accordingly, the positioning core14solidifies more firmly than the core121, and the positioning core14becomes less likely to be removed during development. In this way, adjustment of the heights of the positioning core14and the core121may be performed based on the difference in solidification time.

In the first embodiment, it has been described that the photoresist liquid used for photolithography is of a negative type. However, the photoresist liquid it not limited to this. The photoresist liquid may be of a positive type. In this case, for example, by irradiating only the core121of the optical waveguide12with a small amount of ultraviolet radiation while maintaining the amount of exposure light with which the positioning core14is irradiated to be zero, the height of the core121after development may be reduced.

In the first embodiment, it has been described that the heat conductor13is embedded in the substrate11along the positioning core14. However, the position of the heat conductor13is not limited to this. The heat conductor13may be disposed on the lower surface of the substrate11, which is on the side opposite to the upper surface on which the positioning core14is formed, at a position facing the positioning core14. In this case, heat near the positioning core14is discharged to the outside the substrate11through the heat conductor13, and the temperature of the positioning core14decreases more effectively than the temperature of the core121.

In the first embodiment, it has been described that, by improving the heat dissipation effect near the positioning core14by using the heat conductor13, the temperature of the positioning core14decreases to a level below the temperature of the core121. However, the configuration of the optical connector module1is not limited to this. Instead of or in addition to the configuration such that the heat conductor13is embedded in the substrate11along the positioning core14, the optical connector module1may have a configuration such that a heat insulator, which does not easily conduct heat, is embedded in the substrate11along the core121of the optical waveguide12.

In the first embodiment, it has been described that the cladding122includes the first cladding122aand the second cladding122b. However, the configuration of the cladding122is not limited to this. The cladding122need not have the second cladding122b, if, by using an air layer instead of the second cladding122b, it is possible to form a predetermined waveguide mode with the core121and the first cladding122aof the optical waveguide12and to sufficiently realize the function of the optical waveguide12.

Second Embodiment

Referring toFIGS.12to180, a second embodiment of the present disclosure will be mainly described.FIG.12is a perspective view of an optical connector module1according to the second embodiment.FIG.13is an exploded perspective view of the optical connector module1shown inFIG.12.FIG.14is a perspective view illustrating only an optical waveguide board10shown inFIG.13.FIG.15is a front view of the optical connector module1shown inFIG.12.FIG.16is an enlarged view of a region surrounded by an alternate long and short dash line inFIG.15.FIG.17is an enlarged front sectional view schematically illustrating a part of the optical connector module1shown inFIG.12.

FIGS.12to17respectively correspond toFIGS.1to3and5to7in the first embodiment. The optical connector module1according to the second embodiment differs from that of the first embodiment in the shape of the positioning core14. Other configurations, functions, effects, modifications, and the like are similar to those of the first embodiment, and the corresponding descriptions apply also to the optical connector module1according to the second embodiment. In the following, constituent elements that are similar to those of the first embodiment will be denoted by the same numerals and descriptions of such constituent elements will be omitted. Differences from the first embodiment will be mainly described.

In the second embodiment, the upper surface of the positioning core14of the optical waveguide board10may be at the same up-down position as the core121of the optical waveguide12, or may be at a different up-down position. For example, as in the first embodiment, the upper surface of the positioning core14may be positioned above the upper surface of the core121. Referring toFIG.14, the positioning core14of the optical connector module1according to the second embodiment includes cutout portions144that are linearly cut out at two positions over the entire length the front-back direction. For example, the pair of cutout portions144are formed at positions that are line-symmetrical about the center line of the positioning core14in the left-right direction.

Referring toFIGS.15and16, the through-hole22aof the optical connector20faces the positioning core14in the extension direction of the core121perpendicular to the stacking direction and enables an end surface of the positioning core14to be observed in the extension direction of the core121. Referring toFIG.17, the positioning core14has four reference surfaces A3, A4, A5, and A6that appear due to the pair of cutout portions144. The reference surfaces A3, A4, A5, and A6are formed as inner surfaces of the positioning core14in the left-right direction, which are different from outer surfaces of the positioning core14in the left-right direction.

For example, when the positioning core14is observed through the through-hole22ain the extension direction of the core121, a pair of reference surfaces A3and A6are separated from each other in a state in which the positioning core14is not interposed in a direction perpendicular to the stacking direction and extend in the stacking direction. The pair of reference surfaces A3and A6face each other in a direction that is perpendicular to the extension direction of the core121and to the stacking direction. Two cutout portions144are formed between the pair of reference surfaces A3and A6. Likewise, when the positioning core14is observed through the through-hole22ain the extension direction of the core121, a pair of reference surfaces A4and A5are separated from each other in the direction perpendicular to the stacking direction and extend in the stacking direction. One of the two cutout portions144is formed between the pair of reference surfaces A3and A4, and the other cutout portion144is formed between the pair of reference surfaces A5and A6.

When the positioning core14is observed through the through-hole22ain the extension direction of the core121, each pair of reference surfaces are formed at positions that are line-symmetrical to each other with respect to the center line of the through-hole22aparallel to the stacking direction. Each pair of reference surfaces extend from the stacking surface of the first cladding122aon which the positioning core14is stacked. To be more specific, the cutout portion144is cut out to the upper surface of the first cladding122aover the entire up-down width of the positioning core14, and the lower ends of each pair of reference surfaces and the upper surface of the first cladding122aare disposed at the same up-down position.

With the optical connector module1according to the second embodiment described above, the accuracy in positioning the optical connector20relative to the optical waveguide board10is improved. For example, with the positioning core14in the first embodiment, which does not have the cutout portion144and in which each reference surface is not formed, when the positioning core14is attempted to be observed from the front side by using a measuring device or the like, the image of the positioning core14may be out of focus because the up-down width of the positioning core14is too small relative to the diameter of the through-hole22a. With the optical connector module1according to the second embodiment, because the pair of reference surfaces are formed, it is possible to accurately measure the distance between the pair of reference surfaces when the positioning core14is observed through the through-hole22ain the extension direction of the core121.

By defining the distance between the pair of reference surfaces, it is possible to grasp the relationship between the position of the through-hole22aand the position of the positioning core14in a front view. Thus, it is possible to easily measure the displacement between the through-hole22aand the positioning core14in each direction and in each rotation direction. It is possible to easily measure the displacement between the optical connector20and the optical waveguide board10. To be more specific, if the pair of reference surfaces are displaced parallelly in the left-right direction in the through-hole22ain a front view, it is possible for a measuring device, an operator, and the like to recognize that the optical connector20and the optical waveguide board10are displaced in the left-right direction. If the pair of reference surfaces are displaced parallelly the up-down direction in the through-hole22ain a front view, it is possible for a measuring device, an operator, and the like to recognize that the optical connector20and the optical waveguide board10are displaced in the up-down direction. If the pair of reference surfaces are out of focus in a front view, it is possible for a measuring device, an operator, and the like to recognize that the optical connector20and the optical waveguide board10are displaced in the front-back direction. If the observed shape of the positioning core14changes from the shape when the optical connector20and the optical waveguide board10are accurately positioned or if the observed shape of the positioning core14differs between the left and right through-holes22ain a front view, it is possible for a measuring device, an operator, and the like to recognize that the optical connector20is displaced relative to the optical waveguide board10due to rotation around at least one of the axes extending in the front-back direction, the left-right direction, and the up-down direction.

Because it is easy to measure the displacement between the optical connector20and the optical waveguide board10, it is easy to position the optical connector20relative to the optical waveguide board10. In addition, the accuracy in positioning is improved. For example, with existing technology, after roughly positioning an optical connector and an optical waveguide board and connecting another optical transmission line to the optical connector, light is caused to propagate through the optical waveguide board and the optical transmission line, and, while monitoring the intensity of output light, the positioning of the optical connector and the optical waveguide board relative to each other is performed so that the optical coupling loss becomes the minimum. In such a case, it takes a very long time to perform the positioning operation. With the optical connector module1according to the second embodiment, it is possible to position the optical connector20relative to the optical waveguide board10without causing light to propagate. In addition, for example, it is possible to directly position the optical connector20relative to the optical waveguide board10while observing images of the positioning core14and the through-hole22a.

Because the pair of reference surfaces are formed at positions that are line-symmetrical to each other about the center line L of the through-hole22a, it is possible to grasp the relationship between the position of the center line L of the through-hole22aand the position of the pair of reference surfaces by comparing these positions. Thus, it is possible to easily measure the displacement between the through-hole22aand the positioning core14in each direction and in each rotational direction. It is possible to easily measure the displacement between the optical connector20and the optical waveguide board10.

Because the pair of reference surfaces extend from the stacking surface of the first cladding122a, the up-down width of each reference surface is large, and the visibility of each reference surface is improved. Thus, it is possible to more accurately measure the displacement between the optical connector20and the optical waveguide board10.

Because each reference surface is formed as an inner surface of the positioning core14in the left-right direction, which differs from the outer surfaces of the positioning core14in the left-right direction, even when the positioning target portion23of the optical connector20engages with the positioning core14, the positioning target portion23and each reference surface do not contact each other. Accordingly, each reference surface is not damaged by the positioning target portions23, and the smoothness of each reference surface is maintained. Thus, the visibility of each reference surface is maintained, and the accuracy in positioning the optical connector20relative to the optical waveguide board10is maintained.

In the second embodiment, it has been, described that the pair of reference surfaces are formed at positions that are line-symmetrical to each other with respect to the center line L of the through-hole22a. However, the positions of the pair of reference surfaces are not limited to these. The pair of reference surfaces need not be line-symmetrical to each other with respect to the center line L of the through-hole22a.

In the second embodiment, it has been described that the four reference surfaces A3, A4, A5, and A6are formed. However, the number of reference surfaces is not limited to this. The positioning core14may have any appropriate number of reference surfaces, as long as the positioning core14has at least a pair of reference surfaces that are separated from each other in a state in which the positioning core14is not interposed therebetween in the left-right direction.

In the second embodiment, it has been described that the pair of reference surfaces extend from the stacking surface of the first cladding122aon which the positioning core14is stacked. However, the pair of reference surfaces are not limited to these. For example, the cutout portion144may be cut out in a part of the positioning core14in the up-down direction to a central part of the positioning core14, and the pair of reference surfaces may be formed with an up-down width corresponding to the part in the up-down direction.

For example, inFIG.17, the sectional shapes of protruding portions of the positioning core14formed by the cutout portions144are all rectangular. However, the sectional shapes are not limited to these. The sectional shapes of the protruding portions may be any appropriate shape. For example, the sectional shapes of each protruding portion may be semicircular. The sectional shapes of the protruding portion may be the same as each other or may be different from each other.

For example, inFIG.17, the protruding portions of the positioning core14formed by the cutout portions144all have the same height. However, the protruding portions are not limited to these. The protruding portions may have heights that differ from each other.

FIG.18Ais a schematic top view of a first modification of the positioning core14of the optical waveguide board10shown inFIG.13. For example, the positioning core14may have a shape shown inFIG.18A. For example, in the positioning core14, the front end surface of a protruding portion at the center may be located behind the front end surfaces of protruding portions on the left and right sides. The protruding portion at the center may extend continuously backward in parallel with the protruding portions on the left and right sides.

FIG.18Bis a schematic top view illustrating a second modification of the positioning core14of the optical waveguide board10shown inFIG.13. For example, the positioning core14may have a shape shown inFIG.18B. For example, in the positioning core14, the front end surface of a protruding portion at the center may be located behind the front end surfaces of protruding portions on the left and right sides. The protruding portion at the center may extend by a predetermined length in the front-back direction in the positioning core14.

FIG.18Cis a schematic top view illustrating a third modification of the positioning core14of the optical waveguide board10shown inFIG.13. For example, the positioning core14may have a shape shown inFIG.18C. For example, in the positioning core14, the front end surface of a protruding portion at the center may be located in front of the front end surfaces of protruding portions on the left and right sides.

It should be clear for a person having ordinary skill in the art that the present disclosure can be carried out in predetermined embodiments other than the embodiments described above without departing from the spirit and essential features thereof. Accordingly, the foregoing descriptions are exemplary, and the present disclosure is not limited to these. The scope of the disclosure is defined not by the foregoing descriptions but by the claims. Some of all modifications that are within the range of the equivalents thereof are included therein.

For example, the shape, the arrangement, the orientation, the number, and the like of each constituent element described above are not limited to those in the forgoing descriptions and the drawings. The shape, the arrangement, the orientation, the number, and the like of each constituent element may be set in any appropriate manner, as long as the function thereof can be realized.

For example, functions and the like included in each step and each manufacturing process in the method of manufacturing the optical waveguide board described above may be rearranged while avoiding physical contradiction, and a plurality of steps or a plurality of manufacturing processes may be combined or may be divided.

REFERENCE SIGNS LIST