Optical connector and apparatus equipped therewith

Provided is an optical connector used for connecting an optical waveguide substrate and an optical-fiber connector member, where the optical connector comprises a plurality of positioning structures, each having a cylindrical hole for inserting another end of a pin which has an end inserted into the connector member, and a groove formed on a second surface perpendicular to a first surface on which an open end of the hole is located, and where the groove and the hole are continuous, the groove has an arc-shaped cross section, and a center of a circle formed by a cross section of the hole and a center of an arc formed by the cross section of the groove are identical, and when the optical connector is coupled to the optical waveguide substrate that comprises a plurality of protrusions having a rectangular cross section, in each of the plurality of positioning structures, at least two corners of a corresponding protrusion among the plurality of protrusions are supported by an inner wall of the groove.

TECHNICAL FIELD

The present disclosure relates to an optical connector and an apparatus equipped therewith.

BACKGROUND ART

In many devices, components such as processors and memory units are interconnected through electric signal paths. However, delay required for data transmission between components becomes shorter in recent years, so that it becomes difficult to meet the requirement in the data transmission using electric signal paths. As such, data transmission using optical signals is attracting attention.

For example, a method for disposing optical waveguides in components on a polymer waveguide substrate formed by a poly-chlorinated biphenyl (PCB) or the like and using the optical waveguides as a guiding portion for guiding light into the components is proposed in Richard C. A. Pitwon et. al, “Firstlight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers”, Journal of Light wave technology, vol. 30, No. 21, Nov. 1, 2012. For example, a flexible optical fiber array is used as the guiding portion for guiding light into the optical waveguides from outside thereof.

An optical connector is arranged at an end of the optical fiber array. If the optical fiber array is connected to the optical waveguides on the polymer waveguide substrate, connection between the optical waveguides and the optical fiber array may be implemented by providing another optical connector on the polymer waveguide substrate side and coupling both the optical connectors together.

However, misalignment between optical fiber cores and optical waveguide cores on the opposing surfaces causes optical connection loss. The optical connection loss increases with increase in a magnitude of axial misalignment between the opposing cores and a distance between the end surfaces of the opposing cores. For example, there exists a report describing that when the axial misalignment is 1.6 μm, an experiment in a case of connecting a single mode (SM) fiber shows the optical connection loss of 0.5 dB.

As a method to align the cores, U.S. Pat. Nos. 7,369,728, 7,447,405, and 7,889,958 propose methods for providing multiple holes in each of two optical connectors to be connected and inserting metal pins into the holes to couple the connectors together. This proposed method requires alignment between the optical connector on a optical waveguide-side (hereafter, a waveguide-side connector) having the holes and the polymer waveguide substrate.

U.S. Pat. No. 7,936,953 proposes a method for aligning the waveguide-side connector and the polymer waveguide substrate. For example, the method comprises providing positioning protrusions on a surface of the polymer waveguide substrate on which the optical waveguides are disposed and engaging the protrusions with stepped parts of the waveguide-side connector. In addition, U.S. Patent Publication No. 2012/0114280 proposes a method which comprises providing a step on a surface of the waveguide-side connector facing the polymer waveguide substrate and engaging the step with an edge of the polymer waveguide substrate to implement positioning in the depth direction.

In any of the above methods, a process for forming the holes provided in the waveguide-side connector is different from a process for forming the positioning structural portion (the stepped parts and/or the step mentioned above). Accordingly, even though a positional relationship between the holes and the cores is defined correctly, the optical waveguide cores and the optical fiber cores may be misaligned unless the cores on both sides are precisely positioned with respect to each other.

SUMMARY OF INVENTION

A possible implementation form of an embodiment according to the present disclosure provides an optical connector used for connecting an optical waveguide substrate and an optical-fiber connector member, comprising a plurality of positioning structures, each having a cylindrical hole for inserting another end of a pin which has an end inserted into the connector member, and a groove formed on a second surface perpendicular to a first surface on which an open end of the hole is located, where the groove and the hole are continuous, the groove has an arc-shaped cross section, and a center of a circle formed by a cross section of the hole and a center of an arc formed by the cross section of the groove are identical, and when the optical connector is coupled to the optical waveguide substrate that comprises a plurality of protrusions having a rectangular cross section, in each of the plurality of positioning structures, at least two corners of a corresponding protrusion among the plurality of protrusions are supported by an inner wall of the groove.

This application claims the benefit of priority to Japanese Patent Application No. 2018-053034 filed on Mar. 20, 2018, which is incorporated herein by reference in its entirety.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Throughout the specification and the drawings, elements with substantially like functions may be given like symbols and not be repeatedly described. For convenience of description, some components, as well as representations such as hatching, may be omitted in the drawings.

A mechanism for connecting an optical waveguide unit and an optical fiber array according to an embodiment of the present disclosure will be described with reference toFIG. 1.FIG. 1shows diagrams for describing the mechanism for connecting an optical waveguide unit and an optical fiber array. For convenience of description, a structural body given by connecting a polymer waveguide substrate with a waveguide-side connector will hereafter be referred to as an optical waveguide unit or an optical waveguide substrate.

FIG. 1shows an optical waveguide unit1, an optical fiber2, and metal pins3aand3b. The optical waveguide unit1has a waveguide-side connector1a(e.g. a receptacle) and a polymer waveguide substrate1b. The optical fiber2has a fiber-side connector2aand an optical fiber array2b.

InFIG. 1, dashed lines in the waveguide-side connector1aillustrate an inner structure thereof. Although the following description takes a polymer waveguide substrate as an example for convenience of description, a positioning mechanism for the optical waveguide unit according to an embodiment of the present disclosure may also be applied to an organic substrate, a ceramic substrate, and a silicon substrate, or the like. The optical waveguides may be made of other materials, such as silicon, quartz, and a compound semiconductor.

Hereafter, a surface Sa1and a surface Sb1shown inFIG. 1may be expressed as a top surface of the waveguide-side connector1aand a top surface of the polymer waveguide substrate1b, respectively. A surface Sat may denote a bottom surface of the waveguide-side connector1a. The expressions “top” and “bottom” are merely used for convenience of description and not intended to limit the orientation of the optical waveguide unit1.

Optical waveguide cores11a,11b,11c, and11dare provided on the top surface Sb1of the polymer waveguide substrate1b. Protrusions12aand12bare also formed on the top surface Sb1of the polymer waveguide substrate1b. The protrusions12aand12bare used for positioning the waveguide-side connector1awith respect to the polymer waveguide substrate1b. For example, the protrusions12aand12bmay be formed with photolithography, as in forming a cladding layer on the optical waveguide cores11a,11b,11c, and11d.

Although description herein shows a case that the number of optical waveguide cores is four for convenience of description, there may be three or fewer cores, or five or more cores. The cladding layer on the optical waveguide cores11a,11b,11c, and11dwill not be shown or described in detail (for example, see Richard C. A. Pitwon et. al, “Firstlight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers”, Journal of Light wave technology, vol. 30, No. 21, Nov. 1, 2012).

Multiple holes for inserting the metal pins3aand3bused for positioning are formed in each of the waveguide-side connector1aand the fiber-side connector2a. In an example ofFIG. 1, an end of each of the metal pins3aand3bis inserted into a corresponding one of holes22aand22bformed in the fiber-side connector2a. The other end of each of the metal pins3aand3bis inserted into a corresponding one of holes (holes13band13dto be described below) in the waveguide-side connector1a.

An end surface of a lens unit21is exposed on an end surface of the fiber-side connector2aon which the open ends of the holes22aand22bare located. A view (a) ofFIG. 1schematically shows an Ia-Ia sectional view of the fiber-side connector2acut along an X-Y plane. A view (b) ofFIG. 1schematically shows an Ib-Ib sectional view of the fiber-side connector2acut along an X-Z plane. As shown in the views (a) and (b) ofFIG. 1, the lens unit21includes multiple lenses, each connected to an end surface of a corresponding one of optical fiber cores21a,21b,21c, and21d.

In configuration in which the end surfaces of the optical fiber cores21a,21b,21c, and21dare directly connected with end surfaces of the optical waveguide cores11a,11b,11c, and11d, the lens unit21may be eliminated. Although description herein shows that the number of the optical fiber cores is four for convenience of description, there may be three or fewer cores, or five or more cores.

The holes22aand22b, into which the cylindrical metal pins3aand3bare inserted, are cylindrical and formed to have a diameter substantially the same as the diameter of the metal pins3aand3b. For example, the holes22aand22bare positioned such that the centers of the optical fiber cores21a,21b,21c, and21dare on a straight line connecting the centers of the holes22aand22bat their open ends. The distance from at least one of the centers of the holes22aand22bto each of the optical fiber cores21a,21b,21c, and21dis predetermined.

With the holes22aand22bconfigured as above, the alignment of the optical waveguide cores11a,11b,11c, and11dwith the optical fiber cores21a,21b,21c, and21dis realized by positioning the optical waveguide cores11a,11b,11c, and11dwith reference to the centers of the metal pins3aand3b. The accuracy of this alignment depends on the accuracy of the alignment between the waveguide-side connector1ainto which the metal pins3aand3bare inserted and the polymer waveguide substrate1bon which the optical waveguide cores11a,11b,11c, and11dare provided.

For example, it is assumed that an X direction is the direction from the end surface of the fiber-side connector2atoward the opposing end surface of the waveguide-side connector1a, along the axes of the metal pins3aand3b. Misalignment in the X direction creates gaps between the opposing cores, thereby causing optical connection loss. It is assumed that a Z direction is the upward direction perpendicular to the top surface Sb1of the polymer waveguide substrate1b, and a Y direction is the direction perpendicular to the X-Z plane. Misalignment in the Y-Z plane results in axial misalignment between the opposing cores, and the misalignment causes optical connection loss. For convenience of description, the following description may use a rectangular coordinate system defined by the above X, Y, and Z directions (an XYZ coordinate system).

To reduce optical connection loss, it is effective to increase the alignment accuracy for all the X, Y, and Z directions and the rotational directions in the X-Y plane, Y-Z plane, and Z-X plane. In this embodiment, positioning structures are provided on the bottom surface Sa2of the waveguide-side connector1a. The above alignment accuracy is improved by physical connection between these positioning structures and the protrusions12aand12bon the polymer waveguide substrate1b.

The above positioning structures, as well as the structure of the protrusions12aand12bon the polymer waveguide substrate1b, will further be described below with reference toFIGS. 2A to 6.

First, the above positioning structures formed on the bottom surface Sa2of the waveguide-side connector1awill be described with reference toFIGS. 2A to 3.

FIG. 2Ashows diagrams (a bottom view and side views) for describing the structure of the waveguide-side connector.FIG. 2Bshows diagrams (X-Z sectional views) for describing the structure of the waveguide-side connector.FIG. 3shows diagrams (Y-Z sectional views) for further describing the geometries of grooves and holes in the waveguide-side connector. Dashed lines in the polymer waveguide substrate1bin a view (b) ofFIG. 2Aillustrate an inner structure.

A view (a) ofFIG. 2Ashows the geometry of a side surface (the surface not facing the fiber-side connector2a) of the waveguide-side connector1aviewed along the −X direction. A view (b) ofFIG. 2Ashows the geometry of the bottom surface Sa2of the waveguide-side connector1a. A view (c) ofFIG. 2Ashows the geometry of a side surface (the surface facing the fiber-side connector2a) of the waveguide-side connector1aviewed along the X direction.

As shown in the view (b) ofFIG. 2A, grooves13aand13cand a recess13eare formed on the bottom surface Sa2of the waveguide-side connector1a. As shown in the views (a) and (b) ofFIG. 2A, the recess13eis disposed between the grooves13aand13c. The grooves13aand13care connected to respective holes13band13dshown in the view (c) ofFIG. 2A.

Here, reference will be made toFIG. 3. A view (a) ofFIG. 3is a sectional view of the waveguide-side connector1acut along a line IIIc-IIIa in the view (b) ofFIG. 2A. A view (b) ofFIG. 3is a sectional view of the waveguide-side connector1acut along a line IIIb-IIIb in the view (b) ofFIG. 2A. A view (c) ofFIG. 3is a sectional view of the waveguide-side connector1acut along a line IIIc-IIIc in the view (b) ofFIG. 2A.

As shown in the view (a) ofFIG. 2Aand the views (a) and (b) ofFIG. 3, the grooves13aand13care arc-shaped in cross section (Y-Z cross section). As shown in the view (b) ofFIG. 2Aand a view (d) ofFIG. 2B, the holes13band13dpenetrate through the waveguide-side connector1awhile connected to the respective grooves13aand13cat the line IIIb-IIIb. The holes13band13dhave a size corresponding to the size of the metal pins3aand3b.

As shown in the views (a)-(c) ofFIG. 3, the arc corresponding to the groove13cis concentric with the circle corresponding to the hole13d. That is, the positioning structure is coaxially produced. Coaxially producing the positioning structure realizes high positioning accuracy and further provides advantages such as a simple and convenient product test.

The groove13cand the hole13dmay be coaxially formed without relying on the height h from the top surface Sa1of the waveguide-side connector1ato the axis, or the distance u from a side surface of the waveguide-side connector1ato the axis. Then, high positioning accuracy is realized, and advantages such as a simple and convenient product test are further provided. The groove13aand the hole13bare also structured in a similar manner.

Here, reference will be made to the view (d) ofFIG. 2B. The view (d) ofFIG. 2Bis a sectional view of the waveguide-side connector1acut along a line IIBd-IIBd in the view (b) ofFIG. 2A. As shown in the view (d) ofFIG. 2B, the hole13dconnects to the groove13cat the IIIb-IIIb line and penetrates through the waveguide-side connector1a. The hole13bis also structured in a similar manner.

As shown in the view (b) ofFIG. 2Aand the view (d) ofFIG. 2B, the groove13cincludes a section in which the width and the depth are constant (a section with a constant arc radius; hereafter referred to as a uniform-width section). The groove13calso includes a section in which the width and the depth increase to form a tapered shape from the uniform-width section to a connecting portion to be connected with the hole13d(a section with an increasing arc radius; hereafter referred to as a tapered section). The groove13ais also structured in a similar manner.

The grooves13aand13cand the holes13band13dhave the structures as described above.

The recess13eis a structural portion for avoiding the optical waveguide cores11a,11b,11c, and11dfrom contacting the bottom surface Sa2of the waveguide-side connector1awhen the waveguide-side connector1aand the polymer waveguide substrate1bare connected. The depth of the recess13eis set to be equal to or greater than the height of the optical waveguide cores11a,11b,11c, and11dplus the height of the cladding layer on the cores (the height in the Z direction from the top surface Sb1of the polymer waveguide substrate1b).

A view (e) ofFIG. 2Bis a sectional view of the waveguide-side connector1acut along a line IIBe-IIBe in the view (b) ofFIG. 2A. As shown in the view (c) ofFIG. 2Aand the view (e) ofFIG. 2B, in this example, a lens unit14is provided near the end surface of the waveguide-side connector1afacing the fiber-side connector2a. The lens unit14includes lenses at positions corresponding to the ends of the optical waveguide cores11a,11b,11c, and11d, and adjusts the paths of light that is input to the ends or output from the ends.

As shown in the views (d) and (e) ofFIG. 2B, the waveguide-side connector1ahas different thicknesses (heights in the Z direction) in a section X1corresponding to the grooves13aand13cand in a section X2corresponding to the holes13band13d. This forms a step at the boundary between the sections X1and X2.

Now, the geometry of the protrusions12aand12bformed on the top surface Sb1of the polymer waveguide substrate1bwill be described with reference toFIG. 4.FIG. 4shows diagrams (a top view and a side view) for describing the geometries of the polymer waveguide substrate and the protrusions formed thereon.

A view (a) ofFIG. 4shows the geometry of the top surface Sb1of the polymer waveguide substrate1b. A view (b) ofFIG. 4shows the geometry of a side surface of the polymer waveguide substrate1bviewed along the X direction. As shown in the view (a) ofFIG. 4, the protrusions12aand12bare formed on the top surface Sb1of the polymer waveguide substrate1b, and the optical waveguide cores11a,11b,11c, and11dare provided between the protrusions12aand12b.

For example, the protrusions12aand12bare formed along the X direction. The protrusions12aand12bare formed to be spaced apart at the same distance as the grooves13aand13c. The protrusions12aand12bare formed with a height (a height in the Z direction from the top surface Sb1of the polymer waveguide substrate1b) that is the same as the optical waveguide cores11a,11b,11c, and11d.

The protrusions12aand12bare formed with a width (a length in the Y direction) substantially the same as the opening width of the arcs formed by the cross sections of the grooves13aand13c. For example, the opening width of the arcs corresponds to the distance between the two points at which the bottom surface Sa2of the waveguide-side connector1aand the arc of the groove13cshown in the view (a) ofFIG. 3intersect. The width of the protrusions12aand12bmay be determined based on the opening width of the arcs of the grooves13aand13cin the uniform-width section.

For convenience of description, the protrusions and their corresponding grooves are shown with the same width. However, the width of the protrusions and the width of their corresponding grooves may be different due to an error occurring in a production process or due to a clearance allowed for the groove width in order to facilitate fitting. Such a difference in width is to be expected by those skilled in the art and is within the technical scope of this embodiment.

As shown in the view (a) ofFIG. 4, a tip part of each of the protrusions12aand12bcloser to the surface in the view (b) ofFIG. 4is tapered so that the width gradually decreases. Tapering the tip part of each of the protrusions12aand12bfacilitates the fitting of the protrusions12aand12binto the grooves13aand13cin connecting the waveguide-side connector1aand the polymer waveguide substrate1b.

Connecting the waveguide-side connector1aand the polymer waveguide substrate1bresults in a state as shown in a view (a) ofFIG. 5.FIG. 5shows diagrams (a top view, a Y-Z sectional view, and enlarged sectional views) for describing the structure of the optical waveguide unit in which the polymer waveguide substrate and the waveguide-side connector are connected together.

The view (a) ofFIG. 5is a top view of the optical waveguide unit1in which the polymer waveguide substrate1band the waveguide-side connector1aare connected together. Dashed lines in the top surface Sa1of the waveguide-side connector1ain the view (a) ofFIG. 5illustrate an inner structure.

An exemplary method of connection is as follows. While the top surface Sb1of the polymer waveguide substrate1bis kept in contact with the bottom surface Sat of the waveguide-side connector1a, the waveguide-side connector1ais slid in the X direction so that the tip parts of the protrusions12aand12b(see the view (b) ofFIG. 4) is slipped into the openings of the grooves13aand13c(see the view (a) ofFIG. 2A). According to this method, the tapered tip parts of the protrusions12aand12ballow easier connection between the waveguide-side connector1aand the polymer waveguide substrate1b.

A view (b) ofFIG. 5shows a cross sectional geometry of the optical waveguide unit1cut along a line Vb-Vb in the view (a) ofFIG. 5. As shown in the view (b) ofFIG. 5, the protrusions12aand12bare fitted into the respective grooves13aand13cin the waveguide-side connector1a. The optical waveguide cores11a,11b,11c, and11dare disposed inside the recess13ein the waveguide-side connector1a.

Here, the geometries of the protrusion12band the groove13cwill further be described with reference to a view (c) ofFIG. 5. The view (c) ofFIG. 5an enlarged view of the area around the groove13cwith the protrusion12bfitted therein. For ease of viewing, the view (c) ofFIG. 5is not hatched.

For convenience of description, the view (c) ofFIG. 5shows the center C0of the arc formed by the cross section of the groove13c, and contact points C1, C2, C3, and C4at which the groove13ccontacts the protrusion12b. The contact points C3and C4are the end points of the arc. For convenience of description, the view (c) ofFIG. 5shows parameters such as the height of the protrusion12b(d1×2), the radius of the arc (d2), space between the protrusion12band the side wall of the groove13c(d3), and the width of the protrusion12b(d4×2).

As shown in the view (c) ofFIG. 5, the protrusion12bsupports the inner wall of the groove13cat the two contact points C1and C2at least. Similarly, the protrusion12a, which is rectangular in cross section, supports the inner wall of the groove13aat the two corners corresponding to the contact points C1and C2among the four corners of the protrusion12a. The protrusions12aand12b, therefore, support the waveguide-side connector1aat four corners at least.

Because the protrusions12aand12bsupport the grooves13aand13cat four corners at least, the positional relationship between the grooves13aand13cand the protrusions12aand12bcan be fixed for the Y and Z directions and for the rotational directions in the X-Y plane, Y-Z plane, and Z-X plane.

As shown in the view (c) ofFIG. 5, when the two points on the rectangle (the contact points C1and C2) contact the inner wall of the arc, the center of the rectangle coincides with the center C0of the arc. The distance from the base of the rectangle to its center is half the height of the rectangle.

In the example in the view (c) ofFIG. 5, the center C0of the arc is located at the height d1, which is half the height of the protrusion12b(d1×2). That is, if the cross-sectional center of the protrusion12band the center (hereafter referred to as a core center) of each of the optical waveguide cores11a,11b,11c, and11dhave the same height d1(see the views (c) and (d) ofFIG. 5), the distance from the top surface Sb1of the polymer waveguide substrate1bto the core center is equal to the distance from the top surface Sb1to the cross-sectional center (the center of the arc) of the groove13c.

The cross-sectional centers of the grooves13aand13calign with the respective cross-sectional centers of the holes13band13dcorresponding to the respective central axes of the metal pins3aand3b. Therefore, the positional relationship of the central axes of the metal pins3aand3bwith the core centers can be readily aligned. Using photolithography for forming the protrusions12aand12ballows alignment of the core centers with the cross-sectional centers of the protrusions12aand12bwith a accuracy of less than 0.1 μm.

As an example, evaluation was performed under the conditions of the height 7 μm of the optical waveguide cores11a,11b,11c, and11d, d1=3.5 μm, d2=40 μm, d3=0.2 μm, d4=39.8 μm, and θ=5° (see the view (c) ofFIG. 5for the angle θ). According to the result of the evaluation, applying the positioning mechanism in this embodiment is expected to provide a desirable accuracy. The above numerical conditions are exemplary, and the numerical ranges may be appropriately changed according to implementations. The technical scope of this embodiment is not limited to this example.

Positioning in the X direction is achieved using the step provided between the sections X1and X2in the waveguide-side connector1a. The positioning in the X direction will be described here with reference toFIG. 6.FIG. 6shows diagrams (X-Z sectional views) for further describing the structure of the optical waveguide unit in which the polymer waveguide substrate and the waveguide-side connector are connected together.

A view (a) ofFIG. 6shows a cross-sectional geometry of the optical waveguide unit1cut along a line VIa-VIa in the view (a) ofFIG. 5. A view (b) ofFIG. 6shows a cross-sectional geometry of the optical waveguide unit1cut along a line VIb-VIb in the view (a) ofFIG. 5.

As described above, if the waveguide-side connector1ais connected to the polymer waveguide substrate1b, the protrusion12ais disposed inside the groove13a(see the view (a) ofFIG. 6), and the optical waveguide cores11a,11b,11c, and11dare disposed inside the recess13e(see the view (b) ofFIG. 6). The section X2includes the hole13bcontinuing to the groove13a(see the view (a) ofFIG. 6), and the lens unit14(see the view (b) ofFIG. 6).

While the substrate and the connector are connected as above, in the section X1, the bottom surface Sa2of the waveguide-side connector1acontacts the top surface Sb1of the polymer waveguide substrate1b. In the section X2, which is thicker than the section X1, the step at the boundary between the sections X1and X2abuts against and engages with an edge part of the polymer waveguide substrate1b(the part corresponding to the surface facing the fiber-side connector2a). This restricts movements of the waveguide-side connector1ain the X direction.

The end surfaces of the optical waveguide cores11a,11b,11c, and11dmay be aligned with the edge part of the polymer waveguide substrate1b(see the view (a) ofFIG. 4), and the lens unit14may be designed to be located near the step (see the view (e) ofFIG. 2B). Then, the alignment in the X direction can be readily achieved as shown in the view (b) ofFIG. 6. The lens unit14may be eliminated in a variation, which will be described below. For the mechanism for achieving the alignment in the X direction, different variations are possible. These variations will now be described.

(First variation) First, reference will be made toFIG. 7.FIG. 7shows diagrams (a top view and a side view) for describing the geometries of the polymer waveguide substrate and the protrusions formed thereon, according to a first variation. A view (a) ofFIG. 7shows the geometry of the top surface Sb1of the polymer waveguide substrate1b. A view (b) ofFIG. 7shows the geometry of the side surface of the polymer waveguide substrate1bviewed along the X direction.

As shown in the view (a) ofFIG. 7, protrusions121aand121bare formed on the top surface Sb1of the polymer waveguide substrate1b, and the optical waveguide cores11a,11b,11c, and11dare provided between the protrusions121aand121b. A difference from the positioning mechanism shown in the view (a) ofFIG. 4is in the shape of the protrusions121aand121b.

As shown in the view (a) ofFIG. 7, each of the protrusions121aand121bhas its tip part (the end closer to the side surface in a view (b) ofFIG. 7) tapered as with the protrusions12aand12bshown in the view (a) ofFIG. 4. Each of the protrusions121aand121balso has a uniform-width section in which the width is constant (a section that fits into the uniform-width section of the corresponding one of the grooves13aand13c). Further, each of the protrusions121aand121bhas, in its terminal part, a section wider than the uniform-width section (hereafter referred to as a wider section), thereby having a T-shape as a whole.

Assume that the positioning mechanism inFIG. 7is applied and the waveguide-side connector1ais connected to the polymer waveguide substrate1bas in the example inFIG. 5. The side surface of the waveguide-side connector1acorresponding to the view (a) ofFIG. 2A(the surface not facing the fiber-side connector2a) abuts against side surfaces of the wider sections, thereby restricting movements of the waveguide-side connector1ain the X direction.

As described above, movements of the waveguide-side connector1ain the X direction can be restricted using the step provided on the waveguide-side connector1a. The protrusions121aand121bcan be finely produced with, for example, photolithography. Applying the mechanism in the first variation shown inFIG. 7can therefore increase the positioning accuracy in the X direction.

(Second variation) Now, reference will be made toFIG. 8.FIG. 8shows diagrams (a top view and a side view) for describing the geometries of the polymer waveguide substrate and the protrusions formed thereon, according to a second variation. A view (a) ofFIG. 8shows the geometry of the top surface Sb1of the polymer waveguide substrate1b. A view (b) ofFIG. 8shows the geometry of the side surface of the polymer waveguide substrate1bviewed along the X direction.

As shown in the view (a) ofFIG. 8, protrusions122aand122bare formed on the top surface Sb1of the polymer waveguide substrate1b, and the optical waveguide cores11a,11b,11c, and11dare provided between the protrusions122aand122b. A difference from the positioning mechanism shown in the view (a) ofFIG. 7is in the shape of the protrusions122aand122b.

The protrusion122ahas its terminal part structured in the same manner as the protrusion121a. The protrusion122ais different from the protrusion121ain the shape of the uniform-width section and tip part. The uniform-width section of the protrusion122ahas a structure such that approximately half of the uniform-width section of the protrusion121acloser to the optical waveguide core11ais eliminated.

Similarly, the protrusion122bhas its terminal part structured in the same manner as the protrusion121b. The protrusion122bis different from the protrusion121bin the shape of the uniform-width section and tip part. The uniform-width section of the protrusion122bhas a structure such that half of the uniform-width section of the protrusion121bcloser to the optical waveguide core11dis eliminated. Eliminating half of the uniform-width section in this manner facilitates inserting the protrusions122aand122binto the grooves13aand13c.

Assume that the positioning mechanism inFIG. 8is applied and the waveguide-side connector1ais connected to the polymer waveguide substrate1bas in the example inFIG. 5. The protrusions122aand122bcontact the inner walls of the grooves13aand13cat fewer contact points. For example, the protrusion122bcontacts the inner wall of the groove13cat the contact points C2and C3.

As above, applying the mechanism of the second variation shown inFIG. 8reduces the number of contact points at which the protrusions122aand122bcontact the grooves13aand13c. However, sufficient positioning accuracy is provided because the corners on the top surfaces of the protrusions122aand122bsupport the respective grooves13aand13c. Further, the connection of the waveguide-side connector1ato the polymer waveguide substrate1bis advantageously facilitated.

(Third variation) Now, reference will be made toFIG. 9.FIG. 9shows diagrams (a top view, a Y-Z sectional view, and a connected-state view) for describing the geometries of the polymer waveguide substrate and the protrusions formed thereon, according to a third variation.

A view (a) ofFIG. 9shows the geometry of a cross section of the polymer waveguide substrate1b(a cross section of the polymer waveguide substrate1bcut along a line IXa-IXa in a view (b) ofFIG. 9) viewed along the −X direction. The view (b) ofFIG. 9shows the geometry of the top surface Sb1of the polymer waveguide substrate1b. A view (c) ofFIG. 9is a top view of the optical waveguide unit1in which the polymer waveguide substrate1bin the views (a) and (b) ofFIG. 9and the waveguide-side connector1aare connected together. Dashed lines in the top surface Sa1of the waveguide-side connector1ain the view (c) ofFIG. 9illustrate an inner structure.

As shown in the view (b) ofFIG. 9, protrusions123aand123bare formed on the top surface Sb1of the polymer waveguide substrate1b, and the optical waveguide cores11a,11b,11c, and11dare provided between the protrusions123aand123b. A difference from the positioning mechanism shown in the view (a) ofFIG. 4is in the shape of the protrusions123aand123b.

As shown in the view (b) ofFIG. 9, each of the protrusions123aand123bis isosceles-triangular with its vertex oriented in the X direction, when viewed from above (when viewed along the −Z direction). The protrusions123aand123bhave the same height as the protrusions12aand12bshown in the view (a) ofFIG. 4(a uniform thickness in the Z direction) (see the view (a) ofFIG. 9). Therefore, the cross section of each of the protrusions123aand123bcut along the Y-Z plane is rectangular.

Each of the protrusions123aand123bhas a tip part corresponding to the vertex of the isosceles triangle, and a terminal part corresponding to the base of the isosceles triangle. The width of the terminal part, corresponding to the length of the base, is wider than the width of the uniform-width sections of the grooves13aand13c. Therefore, if the waveguide-side connector1ais slid in the −X direction to fit the protrusions123aand123binto the grooves13aand13c, the protrusions123aand123bengage with the respective tapered sections of the grooves13aand13c, as shown in the view (c) ofFIG. 9.

Because the protrusions123aand123bengage with the respective tapered sections of the grooves13aand13c, movements of the waveguide-side connector1ain the −X direction are restricted. In applying the mechanism shown inFIG. 9, the protrusions123aand123b, which are rectangular in Y-Z cross section, still abut against the respective inner walls of the grooves13aand13cat the contact points C1, C2, C3, and C4(see the view (c) ofFIG. 5) and support the waveguide-side connector1a.

As above, applying the mechanism of the third variation shown inFIG. 9allows the inner walls of the grooves13aand13cto be supported at the contact points C1, C2, C3, and C4as in the mechanism shown inFIG. 5. The engagement of the protrusions123aand123bwith the tapered sections also allows the positioning in the X direction, so that high positioning accuracy is realized for all the directions. Further, the connection of the waveguide-side connector1ato the polymer waveguide substrate1bis advantageously facilitated.

(Fourth variation) Now, reference will be made toFIG. 10.FIG. 10shows diagrams (a top view, a Y-Z sectional view, and a connected-state view) for describing the geometries of the polymer waveguide substrate and the protrusions formed thereon, according to a fourth variation.

A view (a) ofFIG. 10shows the geometry of a cross section of the polymer waveguide substrate1b(a cross section of the polymer waveguide substrate1bcut along a line Xa-Xa in a view (b) ofFIG. 10) viewed along the −X direction. The view (b) ofFIG. 10shows the geometry of the top surface Sb1of the polymer waveguide substrate1b. A view (c) ofFIG. 10is a top view of the optical waveguide unit1in which the polymer waveguide substrate1bin the views (a) and (b) ofFIG. 10and the waveguide-side connector1aare connected together. Dashed lines in the top surface Sa1of the waveguide-side connector1ain the view (c) ofFIG. 10illustrate an inner structure.

As shown in the view (b) ofFIG. 10, protrusions124aand124bare formed on the top surface Sb1of the polymer waveguide substrate1b, and the optical waveguide cores11a,11b,11c, and11dare provided between the protrusions124aand124b. A difference from the positioning mechanism shown in the view (a) ofFIG. 4is in the shape of the protrusions124aand124b.

As shown in the view (b) ofFIG. 10, each of the protrusions124aand124bis isosceles-triangular with its vertex oriented in the −X direction, when viewed from above (when viewed along the −Z direction). The protrusions124aand124bhave the same height as the protrusions12aand12bshown in the view (a) ofFIG. 4(a uniform thickness in the Z direction) (see the view (a) ofFIG. 10). Therefore, the cross section of each of the protrusions124aand124bcut along the Y-Z plane is rectangular.

Each of the protrusions124aand124bhas a tip part corresponding to the vertex of the isosceles triangle, and a terminal part corresponding to the base of the isosceles triangle. The width of the terminal part, corresponding to the length of the base, is wider than the width of the uniform-width sections of the grooves13aand13c. Therefore, if the waveguide-side connector1ais slid in the X direction to fit the protrusions124aand124binto the grooves13aand13c, the protrusions124aand124bengage with the respective openings of the uniform-width sections of the grooves13aand13c, as shown in the view (c) ofFIG. 10.

Because the protrusions124aand124bengage with the respective openings of the uniform-width sections of the grooves13aand13c, movements of the waveguide-side connector1ain the X direction are restricted. In applying the mechanism shown inFIG. 10, the protrusions124aand124b, which are rectangular in Y-Z cross section, still abut against the respective inner walls of the grooves13aand13cat the contact points C1, C2, C3, and C4(see the view (c) ofFIG. 5) and support the waveguide-side connector1a.

As above, applying the mechanism of the fourth variation shown inFIG. 10allows the inner walls of the grooves13aand13cto be supported at the contact points C1, C2, C3, and C4as in the mechanism shown inFIG. 5. The engagement of the protrusions124aand124bwith the openings of the uniform-width sections also allows the positioning in the X direction, so that high positioning accuracy is realized for all directions. Further, the connection of the waveguide-side connector1ato the polymer waveguide substrate1bis advantageously facilitated.

(Fifth variation) Now, reference will be made toFIG. 11.FIG. 11shows diagrams (a bottom view, side views, and X-Z sectional views) for describing the structure of the waveguide-side connector according to a fifth variation. For convenience of description, the waveguide-side connector and the polymer waveguide substrate according to the fifth variation will be denoted as a waveguide-side connector101aand a polymer waveguide substrate101b, respectively.

A view (a) ofFIG. 11Ato a view (e) ofFIG. 11Bcorresponds to the view (a) ofFIG. 2Ato the view (e) ofFIG. 2Bshowing the structure of the waveguide-side connector1a, respectively. Dashed lines in the waveguide-side connector1ain the view (b) ofFIG. 11Aillustrate an inner structure. The main differences between the waveguide-side connector101aand the waveguide-side connector1aare that the waveguide-side connector101ahas a recess131ewhereas the waveguide-side connector1ahas the recess13e, and that the waveguide-side connector101adoes not have the lens unit14.

As shown in the views (a)-(c) ofFIG. 11Aand the view (e) ofFIG. 11B, the recess131eforms a rectangular groove of a constant width (Y2) and a constant depth (a groove that is rectangular in Y-Z cross section). The waveguide-side connector101atherefore does not have a step in the area of the recess131e(the step at the boundary between the sections X1and X2in the waveguide-side connector1a).

However, in the waveguide-side connector101a, a step (see the view (d) ofFIG. 11B) is still formed in each of the areas where the grooves13aand13cand the holes13band13dare formed (the areas corresponding to Y1and Y3in the view (a) ofFIG. 11A). Consequently, in applying the waveguide-side connector101a, the step can still restrict movements of the waveguide-side connector101ain the X direction and enable the positioning in the X direction, as in the structure shown inFIG. 5.

Now, the structure of the polymer waveguide substrate101bconnected with the waveguide-side connector101awill be described with reference toFIG. 12.FIG. 12shows diagrams (a top view, a connected-state view, a side view, and an X-Z sectional view) for describing the structures of the polymer waveguide substrate and the optical waveguide unit in which the polymer waveguide substrate and the waveguide-side connector are connected together, according to the fifth variation.

A view (a) ofFIG. 12is a top view of the polymer waveguide substrate101b. A view (b) ofFIG. 12is a top view of the optical waveguide unit1in which the waveguide-side connector101aand the polymer waveguide substrate101bare connected together. Dashed lines in the top surface Sa1of the waveguide-side connector1ain the view (b) ofFIG. 12illustrate an inner structure.

A view (c) ofFIG. 12is a side view of the optical waveguide unit1viewed along the X direction, according to the fifth variation. A view (d) ofFIG. 12is a sectional view of the optical waveguide unit1cut along a line XIId-XIId in the view (b) ofFIG. 12, according to the fifth variation.

A difference between the polymer waveguide substrate101bshown in the view (a) ofFIG. 12and the polymer waveguide substrate1bshown in the view (a) ofFIG. 4is the presence or absence of cutouts15aand15b. As shown in views (b) and (d) ofFIG. 12, the cutouts15aand15baccommodate parts defined by the areas Y1and Y3shown in the view (a) ofFIG. 11and by the section X2(parts thicker in the Z direction). That is, in the example inFIG. 12, the cutouts15aand15bhave the same depth in the X direction as the section X2and substantially the same width in the Y direction as the respective areas Y1and Y3.

Providing the above cutouts15aand15bcan bring about a substantially coplanar relationship between the side surface of the waveguide-side connector101aon which the openings of the holes13band13dare located and the side surface of the polymer waveguide substrate101bfacing the fiber-side connector2a.

The cutouts15aand15bmay have a depth different from the depth of the section X2. For example, the depth of the cutouts15aand15bmay be designed such that the side surface of the waveguide-side connector101ais positioned to be protruded or recessed relative to the side surface of the polymer waveguide substrate101b.

The cutouts15aand15bmay be wider than the respective areas Y1and Y3. This creates space between the waveguide-side connector101aand the cutouts15aand15b. In practice, such space may be created due to an error occurring during production or due to clearances allowed in the design, and is therefore to be expected by those skilled in the art. Intentional or accidental creation of such space should fall within the technical scope of this embodiment.

According to the above configuration, if the end surfaces of the optical waveguide cores11a,11b,11c, and11dare aligned with the side surface of the polymer waveguide substrate101b, the end surface of the optical waveguide unit1is aligned with the end surfaces of the optical waveguide cores11a,11b,11c, and11d. Consequently, when the optical waveguide unit1and the fiber-side connector2aare connected, the end surfaces of the optical fiber cores21a,21b,21c, and21dexposed on the end surface of the fiber-side connector2aare closely connected with the end surfaces of the optical waveguide cores11a,11b,11c, and11d.

The positioning mechanisms according to this embodiment and its variations have been described above. According to these positioning mechanisms, highly precise positioning can be realized with a simple structure in which the grooves that are arc-shaped in cross section are combined with the protrusions that are rectangular in cross section.

(Method for forming the grooves and the holes) Lastly, a method of forming the grooves13aand13cand the holes13band13dwill be described. The above-described positioning accuracy is based on the assumption that the cross-sectional centers of the grooves13aand13cto be coupled with the protrusions12aand12balign with the respective cross-sectional centers of the holes13band13dreceiving the metal pins3aand3b. As such, the alignment of these cross-sectional centers is important for ensuring the positioning accuracy.

In this embodiment, a method of forming the grooves13aand13cand the holes13band13dusing a mold4shown inFIG. 13will be illustrated.FIG. 13shows diagrams showing the structure of a mold used for forming the grooves and the holes. The mold4shown inFIG. 13is exemplary, and any mold having similar structural portions is applicable.

As shown in the view (a) ofFIG. 13, the mold4has a tip part41, a groove forming part42, a tapered-structure forming part43, and a hole forming part44. Parts other than the groove forming part42and the hole forming part44may be appropriately altered in shape according to implementations.

The groove forming part42is cylindrical, and has a circular cross section as shown in the view (b) ofFIG. 13. The distance from the central axis to the periphery of the groove forming part42(the radius of the circle formed by the cross section) is the same as the radius of the arcs formed by the cross sections of the grooves13aand13c(d2in the example inFIG. 5).

The hole forming part44is cylindrical, and has a circular cross section as shown in the view (c) inFIG. 13. The distance from the central axis to the periphery of the hole forming part44(the radius of the circle formed by the cross section) is the same as the radius of the circles formed by the cross sections of the holes13band13d(d5). The central axis of the groove forming part42aligns with the central axis of the hole forming part44.

Using the above mold4enables precisely forming the coaxial and continuous groove13aand hole13b, and the coaxial and continuous groove13cand hole13d.

While a preferred embodiment of the present disclosure has been described above with reference to the accompanying drawings, the present disclosure is not limited to the above examples. It is apparent that various changes or modifications within the scope of the claims may occur to those skilled in the art, and such changes and modifications should fall within the technical scope of the present disclosure.