Patent ID: 12210191

DETAILED DESCRIPTION

In the following detailed description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

However, in the optical coupling device described in Japanese Patent No. 5571855, an end surface of the multicore fiber is formed in a direction perpendicular to an optical axis direction. Further, the optical coupling device includes self-forming optical waveguides diagonally formed from the end surface of the multicore fiber. Thus, the angle of light incidence/emission of the multicore fiber and the angle of light incidence/emission of the diagonally-formed self-forming optical waveguide do not match with each other, and therefore, a connection loss is caused.

The single-mode optical fibers and the self-forming optical waveguides connected thereto are arranged coaxially, and therefore, it is assumed that an end surface of the single-mode optical fiber is at 0° and unnecessary reflection is caused at an interface between the single-mode optical fiber and the self-forming optical waveguide.

The single-mode optical fibers need to be arranged with the angle of the optical axis direction of each single-mode optical fiber being set with respect to the optical axis of the multicore fiber. For this reason, it is difficult to arrange the single-mode optical fibers.

One object of the present disclosure is to provide the following optical coupling device and the following method for manufacturing the optical coupling device. The optical coupling device can reduce a connection loss and a return loss between an optical fiber and a self-forming optical waveguide, and can achieve reduction in a manufacturing cost and improvement in a yield by easy arrangement of the optical fibers.

An optical coupling device (the present optical coupling device) according to one aspect of the present disclosure, including: multiple optical fibers each of which includes at least one core; and a self-forming optical waveguide, wherein the optical fibers are arranged facing each other, and the self-forming optical waveguide is provided between the optical fibers, an end portion of the self-forming optical waveguide is optically connected to the core of each optical fiber, the cores of the optical fibers arranged facing each other are optically connected to each other through the self-forming optical waveguide in a linear shape, optical axis directions of the optical fibers optically connected to each other through the self-forming optical waveguide are parallel with each other, and an end portion of each core is diagonally formed with an inclination angle according to a refractive index of each core and a refractive index of the self-forming optical waveguide.

A method for manufacturing an optical coupling device (the present manufacturing method) according to one aspect of the present disclosure, including: preparing multiple optical fibers each of which includes at least one core and whose end portions are diagonally formed with an inclination angle and photo-curing resin, the inclination angle being set based on a refractive index of each core of the optical fibers and a refractive index of the photo-curing resin; arranging the optical fibers facing each other such that optical axis directions thereof are parallel with each other; arranging the photo-curing resin between the optical fibers; causing light to enter the photo-curing resin through the optical fibers to cure the photo-curing resin, thereby forming a linear self-forming optical waveguide to optically connect the diagonally-formed end portions of the cores of the optical fibers to each other through the self-forming optical waveguide; and forming a clad by curing of the photo-curing resin.

According to the optical coupling device and the manufacturing method of the present disclosure, the connection loss and the return loss between the optical fiber and the self-forming optical waveguide can be reduced. Further, reduction in the cost for manufacturing the optical coupling device and improvement in the yield by easy arrangement of the optical fibers can be also achieved.

An optical coupling device according the first aspect of the present embodiment, including: multiple optical fibers each of which includes at least one core; and a self-forming optical waveguide, wherein the optical fibers are arranged facing each other, and the self-forming optical waveguide is provided between the optical fibers, an end portion of the self-forming optical waveguide is optically connected to the core of each optical fiber, the cores of the optical fibers arranged facing each other are optically connected to each other through the self-forming optical waveguide in a linear shape, optical axis directions of the optical fibers optically connected to each other through the self-forming optical waveguide are parallel with each other, and an end portion of each core is diagonally formed with an inclination angle according to a refractive index of each core and a refractive index of the self-forming optical waveguide.

A method for manufacturing an optical coupling device according to the second aspect of the present embodiment, comprising: preparing multiple optical fibers each of which includes at least one core and whose end portions are diagonally formed with an inclination angle and photo-curing resin, the inclination angle being set based on a refractive index of each core of the optical fibers and a refractive index of the photo-curing resin; arranging the optical fibers facing each other such that optical axis directions thereof are parallel with each other; arranging the photo-curing resin between the optical fibers; causing light to enter the photo-curing resin through the optical fibers to cure the photo-curing resin, thereby forming a linear self-forming optical waveguide to optically connect the diagonally-formed end portions, that are formed with an identical angle in parallel with each other, of the cores of the optical fibers to each other through the self-forming optical waveguide; and forming a clad by curing of the photo-curing resin.

The optical coupling device according to the third aspect of the present disclosure, wherein the optical fibers, in the optical coupling device according to the first aspect, include multiple first optical fibers and one multicore fiber, a total number of cores of the multiple first optical fibers and a total number of cores of the multicore fiber are both n which is a natural number not including zero, the multiple first optical fibers and the multicore fiber are arranged facing each other, and the self-forming optical waveguide is provided among the multiple first optical fibers and the multicore fiber, the end portions of the self-forming optical waveguide are optically connected to each core of the multiple first optical fibers and each core of the multicore fiber, arrangement of the cores of the multiple first optical fibers is identical to arrangement of the cores of the multicore fiber, the cores of the multiple first optical fibers and the cores of the multicore fiber are arrayed at an equal angle and an equal interval on a circumference of a circle about a center, the cores of the multiple first optical fibers and the multicore fiber arranged facing each other are optically connected to each other through the linear self-forming optical waveguide, and end portions of the cores optically connected to each other through the self-forming optical waveguide are diagonally formed with an identical angle in parallel with each other.

The method for manufacturing the optical coupling device according to the fourth aspect of the present embodiment, further including: in the method for manufacturing the optical coupling device according to the second aspect, preparing multiple first optical fibers and a multicore fiber as the optical fibers; confirming whether or not a total number of cores of the multiple first optical fibers and a total number of cores of the multicore fiber are both n which is a natural number not including zero and the cores of the multiple first optical fibers and the cores of the multicore fiber are arrayed at an equal angle and an equal interval on a circumference of a circle about a center; arranging the multiple first optical fibers and the multicore fiber facing each other; arranging the cores of the multiple first optical fibers in a manner identical to that of the cores of the multicore fiber; arranging the photo-curing resin among the multiple first optical fibers and the multicore fiber; causing light to enter the photo-curing resin through the multiple first optical fibers and the multicore fiber to cure the photo-curing resin, thereby forming the linear self-forming optical waveguide and optically connecting end portions, which are diagonally formed with an identical angle in parallel with each other, of the cores of the multiple first optical fibers and the cores of the multicore fiber to each other through the self-forming optical waveguide; and forming the clad by curing of the photo-curing resin.

According to the configuration and the manufacturing method, the connection loss and the return loss between the optical fiber and the self-forming optical waveguide can be reduced. Further, reduction in the cost for manufacturing the optical coupling device and improvement in the yield by easy arrangement of the optical fibers can be also achieved.

The optical coupling device according to the fifth aspect of the present disclosure, wherein, in the optical coupling device according to the third aspect, cores are further arrayed at the center as another core of the multiple first optical fibers and another core of the multicore fiber, end portions of the center cores are formed in a direction perpendicular to a light propagation direction of the center cores, and the center core of the multiple first optical fibers and the center core of the multicore fiber are optically connected to each other through the self-forming optical waveguide.

The method for manufacturing the optical coupling device according to the sixth aspect of the present disclosure, further comprising: in the method for manufacturing the optical coupling device according to the fourth aspect, confirming whether or not cores are further arrayed at the center as another core of the multiple first optical fibers and another core of the multicore fiber and end portions of the center cores are formed in a direction perpendicular to a light propagation direction of the center cores; and optically connecting an end portion of the center core of the multiple first optical fibers and an end portion of the center core of the multicore fiber to each other through the self-forming optical waveguide.

According to these configuration and manufacturing method, the center core of the multicore fiber and the core of the center first optical fiber can be, in addition to each of the above-described advantageous effects, used for center positioning upon manufacturing of the optical coupling device. Thus, manufacturing of the optical coupling device is more facilitated, and therefore, reduction in the manufacturing cost and improvement in the yield can be more easily achieved.

Hereinafter, a first embodiment according to the present disclosure will be described with reference toFIGS.1A,1B,2A,2B,3, and4. Note that a Z-axis ofFIG.4is a direction parallel with a longitudinal direction of a multicore fiber6and a longitudinal direction of each optical fiber2ato2g. Moreover, X-axis and Y-axis directions are directions perpendicular to the Z-axis direction.

Referring toFIGS.1A,1B,2A,2B, and4, an optical coupling device5according to the first embodiment is formed with multiple optical fibers (the optical fibers2ato2gand the multicore fiber6), each of which includes at least one core, and multiple self-forming optical waveguides (only3band3care shown inFIG.4). In the embodiment ofFIGS.1A,1B,2A,2B, and4, the optical fibers include seven optical fibers2ato2gand one multicore fiber6. The optical fibers2ato2gserve as first optical fibers.

Each optical fiber2ato2gis of a type that a clad surrounds a core, is a single mode or a multimode, and is any of a step index fiber or a graded index fiber. Thus, the total number n (n: an natural number not including zero) of cores of the optical fibers2ato2gis seven. Further, each optical fiber2ato2gis made of glass or plastic. The outer diameter of the clad is 0.125 mm (125 μm) in the case of the single-mode optical fiber. Note that the mode field diameter of a single-mode fiber with a band of 1550 nm is 10.5 μm.

As shown inFIGS.2A and2B, the optical fiber2aof the optical fibers2ato2gis arranged at the center, and the remaining six optical fibers2bto2gare arrayed in a circular pattern at equal angles)(60° and equal intervals about the optical fiber2a. Thus, the cores of the optical fibers2bto2gare arrayed at equal angles)(60° and equal intervals on the circumference of a circle about the core of the center optical fiber2a. At the center among the cores of the optical fibers2bto2g, the core of the optical fiber2ais further arrayed as another core.

As shown inFIG.2B, an end portion of the core of the center optical fiber2ais formed in a direction perpendicular to a light propagation direction (the horizontal direction ofFIG.2B) of such a core (the core of the optical fiber2a). As shown inFIGS.2B and3, an end portion of each core of the optical fibers2bto2gis diagonally formed with an inclination angle φ2. The inclination angle φ2can be set to an optional angle according to the refractive index of each core of the optical fibers2bto2gand the refractive index of the self-forming optical waveguide. The inclination angle φ2can be set within a range of 30° to 60°, for example. Note that inFIG.3, only the structure of an end portion of the optical fiber2bis shown. Other optical fibers2cto2galso have similar end portion structures.

Further, as shown inFIG.2B, each optical fiber2bto2gis arrayed such that among the optical fibers2bto2garrayed about the core of the center optical fiber2a, the core end portions of the optical fibers arranged facing each other with an angle of 180° are symmetry with respect to a line. Thus, not only a sectional side view of FIG.2B along a D-D line ofFIG.2Abut also sectional side views along an E-E line and an F-F line also show sectional side structures similar to that ofFIG.2B.

The optical fibers2ato2gare arrayed such that outer peripheral surfaces of the dads of the optical fibers2ato2gcontact each other, i.e., are arranged not to be shifted from each other. Note that bundle fibers may be used as the optical fibers2ato2g.

In the multicore fiber6, a core diameter is about 9 μm, a clad diameter is 125 μm, and the number of cores is a plural number (n; six including6a,6cto6ginFIGS.1A and1B). Further, as one example, a cutoff wavelength is 1190 nm to 1500 nm, and a mode field diameter is 4.8 μm to 5.6 μm (a propagating light wavelength of 1310 nm) or 5.7 μm to 8.5 μm (a propagating light wavelength of 1550 nm). Moreover, as shown inFIG.1A, cores are arrayed at equal angles (60° inFIG.1A) and equal intervals on the circumference of a circle about the center of the multicore fiber6. Each core gap is 35 μm to 50 μm.

As shown inFIG.1B, an end portion of each core6a,6cto6gis diagonally formed with an inclination angle φ1. Further, as shown inFIGS.1A and1B, among the cores6a,6cto6garrayed about the center of the multicore fiber6, the core end portions arranged facing each other with 180° are symmetry with respect to a line. Thus, not only a sectional side view ofFIG.1Balong an A-A line ofFIG.1Abut also sectional side views along a B-B line and a C-C line also show sectional side structures similar to that ofFIG.1B. The inclination angle φ1is set to the same angle as the inclination angle φ2, and for example, can be set within a range of 30° to 60°.

Note that a center portion of the multicore fiber6is not diagonally formed with the inclination angle φ1, and is formed in a direction perpendicular to an axial direction (the horizontal direction ofFIG.1B) of the multicore fiber6.

Further, the self-forming optical waveguides (hereinafter referred to as optical waveguides) are provided among the optical fibers2ato2gand the multicore fiber6. The same number (six) of optical waveguides as the number of cores of the multicore fiber6is formed. Note thatFIG.4shows only two (3band3c) of the six optical waveguides. The optical waveguides are formed in a not-shown container. A clad4is formed around the optical waveguides. The clad4is also housed in the container. The clad4can be, for example, formed in a circular columnar shape, a rectangular columnar shape, or other three-dimensional shapes according to a container inner surface shape.

A dimension in the Z-axis direction between the end portion of the center portion of the multicore fiber6and the end portion of the optical fiber2acan be set according to the inclination angles φ1, φ2, each optical axis direction with respect to the end portions diagonally formed with the inclination angles φ1, φ2, the refractive index of each core of the multicore fiber6, the refractive index of each core of the optical fibers2bto2g, the refractive index of the optical waveguide, and the refractive index of photo-curing resin forming the optical waveguide. Of the inclination angles φ1, φ2, the refractive index of the photo-curing resin to be the self-forming optical waveguide, the positions of the multicore fiber6and the optical fibers2bto2gin the X-axis or Y-axis direction, and a distance between the multicore fiber6and each optical fiber2bto2gin the Z-axis direction, three parameters are determined, so that an optimal solution can be obtained.

The container is formed in a hollow three-dimensional shape forming the outer shape of the clad4. Moreover, the material of the container may be a hard material such as metal, hard synthetic resin, ceramic, or glass. As necessary, the container is provided with, e.g., a window or an opening allowing penetration of ultraviolet light (UV).

An end portion of the multicore fiber6is arranged on one end side of the container. Moreover, on the other end side of the container, the end portions of the optical fibers2ato2gare arranged. Further, the container is provided with a not-shown opening for charging the photo-curing resin forming each optical waveguide and the clad4.

Each optical fiber2ato2gand the multicore fiber6are arranged facing each other. Arrangement of each core of the optical fibers2bto2gin the Z-axis direction is set to the same arrangement as that of each core6a,6cto6gof the multicore fiber6. Further, each optical axis direction of the optical fibers2ato2gand the multicore fiber6is arranged parallel with the Z-axis direction. The six optical waveguides are linearly provided between the core of each optical fiber2bto2gand the multicore fiber6. Thus, both end portions of the optical waveguide in the Z-axis direction are each optically connected to a corresponding one of the cores of the optical fibers2bto2gand a corresponding one of the cores6a,6cto6gof the multicore fiber6. Specifically, the core6aand the core of the optical fiber2bare optically connected to each other through the optical waveguide, the core6cand the core of the optical fiber2care optically connected to each other through the optical waveguide, the core6fand the core of the optical fiber2dare optically connected to each other through the optical waveguide, the core6dand the core of the optical fiber2gare optically connected to each other through the optical waveguide, the core6gand the core of the optical fiber2fare optically connected to each other through the optical waveguide, and the core6eand the core of the optical fiber2eare optically connected to each other through the optical waveguide. Note that the optical fiber2ais not optically connected to the optical waveguide.

Based on each parameter described above, the dimension in the Z-axis direction between the end portion of the center portion of the multicore fiber6and the end portion of the optical fiber2ais set according to the Snell's law (the law of refraction) so that the linear optical waveguides can be formed. The inclination angle φ1and the inclination angle φ2are set to the same angle, and accordingly, the end portions of the cores6a,6cto6gof the multicore fiber6and the end portions of the cores of the optical fibers2bto2gare, as shown inFIG.4, diagonally formed with the same angle in parallel with each other, the end portions of the cores6a,6cto6gof the multicore fiber6and the end portions of the cores of the optical fibers2bto2gbeing optically connected to each other through the optical waveguides.

Note that in the present embodiment, even if there is a height difference in the X-axis direction between each optical fiber2bto2gand the multicore fiber6, in a case where the optical waveguides are formed among the cores, such a state is taken as each optical fiber2bto2gand the multicore fiber6being arranged facing each other.

Next, the method for manufacturing the optical coupling device5will be described. First, multiple optical fibers each of which includes at least one core and whose end portions are diagonally formed and photo-curing resin are prepared. As the optical fibers, optical fibers2ato2gand a multicore fiber6are prepared. Further, the optical fibers2ato2gand the multicore fiber6are arranged facing each other, and arrangement of the cores of the optical fibers2bto2gand arrangement of the cores of the multicore fiber6are the same as each other. Note that the fiber end portions can be diagonally formed with an inclination angle φ1and an inclination angle φ2by, e.g., CO2laser processing.

The photo-curing resin is prepared in such a manner that the photo-curing resin is charged into a not-shown container through an opening thereof. The photo-curing resin is charged into the container, and accordingly, is arranged among the optical fibers2ato2gand the multicore fiber6.

The photo-curing resin is of a clad selective polymerization type. The material of the photo-curing resin is a solution containing a liquid mixture of two or more types of monomer and a photopolymerization initiator added to such a liquid mixture. The photo-curing resin is polymerized and cured into polymer by incident light with such a wavelength band that the photopolymerization initiator has a sensitivity.

It is confirmed whether or not the total number of cores of the optical fibers2bto2gother than the optical fiber2anot optically connected to an optical waveguide is n (n: a natural number not including zero, and6) and the total number of cores of the multicore fiber6is n (n: a natural number not including zero, and6). Further, it is confirmed whether or not the cores of the optical fibers2bto2gand the cores6a,6cto6gof the multicore fiber6are, as described above, arrayed at equal angles and equal intervals on the circumferences of circles about the centers.

Note that after the photo-curing resin has been charged into the container, the optical fibers2ato2gand the multicore fiber6may be arranged facing each other at both ends of the container.

Next, light enters the photo-curing resin through each optical fiber2bto2gand each core6a,6cto6gof the multicore fiber6to polymerize and cure the photo-curing resin. Accordingly, six linear optical waveguides are formed. Each optical waveguide is formed based on the Snell's law. The wavelength λw of the light for polymerizing and curing the photo-curing resin can be set as necessary according to the photopolymerization initiator. The wavelength of such light is, as one example, 365 nm to 1675 nm.

The inclination angle φ1and the inclination angle φ2are set to the same angle so that the end portions, which are diagonally formed with the same angle in parallel with each other, of the optical fibers2bto2gand the cores6a,6cto6gof the multicore fiber6can be optically connected to each other through the optical waveguides as shown inFIG.4.

Next, the clad4is formed. The clad4is of a clad selective polymerization type. In each optical waveguide, at least one type of monomer is in polymerization reaction with the wavelength λw. As a result, in the cured core region, a non-polymerization-reacted monomer component is, at the same level of concentration as that in the liquid mixture, dispersed as unreacted monomer. At the same time, only one type of monomer is consumed and polymerized in the core region. Thus, at a boundary surface between the core and the clad, a monomer concentration gradient is caused, and interdiffusion progresses. Accordingly, the function of the clad can be obtained. Finally, the entirety of the photo-curing resin is irradiated with ultraviolet light (UV irradiation), and accordingly, the cores and the entirety of the clad4are cured and formed and the optical waveguides are obtained.

When the six optical waveguides are formed, the six optical waveguides may be sequentially formed one by one with a time lag. Alternatively, the six optical waveguides may be simultaneously formed with no time lag in such a manner that light simultaneously enters the photo-curing resin through the optical fibers2bto2gand the cores6a,6cto6gof the multicore fiber6. Note that in a case where the light enters simultaneously, a time lag of 2 to 3 seconds is within an acceptable range at manufacturing steps.

As described above, according to the optical coupling device5and the method for manufacturing the optical coupling device5in the first embodiment, the core end surface of the multicore fiber6is diagonally formed with the inclination angle φ1with respect to the optical axis direction (the Z-axis direction ofFIG.4). Moreover, the optical coupling device5includes the self-forming optical waveguides diagonally formed with respect to the optical axis direction of the multicore fiber6. Thus, the angle of light emission from the core end surface of the multicore fiber6can match the diagonally-formed self-forming optical waveguide. With this configuration, a connection loss among the multicore fiber6and the self-forming optical waveguides can be reduced.

The end surfaces of the optical fibers2bto2gare diagonally formed with the inclination angle φ2according to the refractive index of each core and the refractive index of the self-forming optical waveguide. Thus, a return loss at the end surfaces of the optical fibers2bto2gcan be reduced.

The end surface of the multicore fiber6and each end surface of the optical fibers2bto2gare diagonally formed with these inclination angles φ1, φ2, so that the optical axis direction of each optical fiber (6and2bto2g) can be, as shown inFIG.4, arranged parallel with the Z-axis direction. Thus, there is no need to arrange each optical fiber (6and2bto2g) with the angle of each optical fiber in the optical axis direction being set. Consequently, arrangement of the optical fibers (6and2bto2g) is facilitated, and therefore, reduction in a cost for manufacturing the optical coupling device5and improvement in the yield of the optical coupling device5can be achieved.

In the optical coupling device5, the cores of the optical fibers (each optical fiber2bto2gand the multicore fiber6) arranged facing each other are optically connected to each other through the linear optical waveguides. Further, arrangement of the cores of the optical fibers2bto2gand arrangement of the cores6a,6cto6gof the multicore fiber6are the same as each other. Thus, when the optical waveguides are formed, crossing of adjacent ones of the optical waveguides can be reduced. Consequently, erroneous connection to an adjacent core is reduced. As a result, reduction in the connection loss of the optical coupling device5and improvement of the yield of the optical coupling device5can be achieved.

Further, the end portions of the cores of the optical fibers (6and2bto2g) optically connected to each other through the optical waveguides are diagonally formed with the same angle, such as φ1=φ2, in parallel with each other. Thus, processing of each optical fiber tip end is facilitated. As a result, the cost for manufacturing the optical coupling device5can be reduced.

Note that as a modification of the first embodiment, a multicore fiber8whose end surface is formed in a conical shape with the inclination angle φ1as shown inFIGS.7A and7Bmay be used instead of the multicore fiber6. The multicore fiber8also includes six cores8a,8cto8g. Not only a sectional side view ofFIG.7Balong an A-A line ofFIG.7Abut also sectional side views along a B-B line and a C-C line also show sectional side structures similar to that ofFIG.7B.

Next, an optical coupling device7and the method for manufacturing the optical coupling device7according to a second embodiment of the present disclosure will be described with reference toFIGS.2A,2B,5A,5B, and6. Note that the same numerals are used to represent the same elements as those of the optical coupling device5of the first embodiment and overlapping description thereof will be simplified or omitted.

Differences of the optical coupling device7from the optical coupling device5are that cores1bto1gare, as each core of a multicore fiber1, arrayed at equal angles (60° inFIG.5A) and equal intervals on the circumference of a circle about the center of the multicore fiber1and another core1ais further arrayed at the center. Thus, in addition to optical connection among the cores1bto1gand each core of optical fibers2bto2gthrough optical waveguides, a core of a center optical fiber2aand the center core1bat the center are optically connected to each other through a linear optical waveguide3a.

When the optical coupling device7is manufactured, it is confirmed whether or not an end portion of the core1bis formed in a direction perpendicular to a light propagation direction of the core1b. Next, it is confirmed whether or not the total number of cores of the optical fibers2ato2gand the total number of cores1ato1gof the multicore fiber1are the same as each other (inFIGS.2A,2B,5A, and5B, the total number is an identical number of 7).

According to the optical coupling device7and the method for manufacturing the optical coupling device7according to the second embodiment, the center core1aat the multicore fiber1and the core of the optical fiber2acan be used for center positioning upon manufacturing of the optical coupling device7. Thus, in addition to the advantageous effects of the optical coupling device5of the first embodiment, manufacturing of the optical coupling device7is more facilitated. Consequently, reduction in a manufacturing cost and improvement in a yield can be more easily achieved.

Next, an optical coupling device according to a third embodiment of the present disclosure will be described with reference toFIGS.8A and8B. Note that the same numerals are used to represent the same elements as those of each of the above-described embodiments and overlapping description thereof will be simplified or omitted.

A difference of the optical coupling device according to the third embodiment from the optical coupling device5is that a fiber including four cores9ato9dis used instead of the multicore fibers1,6,8. Further, each end surface of the cores9ato9dis formed in a planar shape with an inclination angle φ1. Thus, an end surface of a multicore fiber9is formed in a quadrangular pyramid shape.

Thus, multiple optical fibers (first optical fibers) optically connected to the multicore fiber9through self-forming optical waveguides form a fiber group in which the optical fibers shown inFIG.3are arranged in the same manner as that of the cores9ato9d, i.e., arranged in two rows and two cores. As this fiber group, a bundle fiber with two-row two-core arrangement may be used.

Note that not only a sectional side view ofFIG.8Balong an A-A line ofFIG.8Abut also a sectional side view along a B-B line also show sectional side structures similar to that ofFIG.8B.

Note that as a modification of the third embodiment, a multicore fiber10whose end surface is formed in a conical shape with the inclination angle φ1as shown inFIGS.9A and9Bmay be used instead of the multicore fiber9. The multicore fiber10also includes four cores10ato10d. Not only a sectional side view ofFIG.9Balong an A-A line ofFIG.9Abut also a sectional side view along a B-B line also show sectional side structures similar to that ofFIG.9B.

Note that the technique of the present disclosure can be changed to various forms based on the technical idea of the technique of the present disclosure. For example, the following optical coupling device may be formed. The optical coupling device includes multiple single-core optical fibers, each of which includes one core, instead of the optical fibers2ato2gand the multicore fiber (1,6). These single-core optical fibers are arranged facing each other. Further, optical axis directions of the optical fibers are arranged parallel with each other. Moreover, each end portion of the optical fibers is diagonally formed with an angle according to the refractive index of each core and the refractive index of a self-forming optical waveguide, and these end portions are connected to each other through linear optical waveguides.

The optical fibers arranged facing each other may be optical fibers made of different materials.

The foregoing detailed description has been presented for the purposes of illustration and description. Many modifications and variations are possible in light of the above teaching. It is not intended to be exhaustive or to limit the subject matter described herein to the precise form disclosed. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims appended hereto.