Optical connection structure

Abstract

The present invention is an optical connection structure that comprises: a substrate on which at least one optical waveguide is formed; at least one blind hole structure arranged in correspondence to each position of the at least one optical waveguide; and at least one optical fiber optically connected to the at least one optical waveguide by being inserted into the blind hole structure and fixed. The cross section of the blind hole structure of the optical connection structure is circular, and the diameter of the blind hole structure is larger than the diameter of the optical fiber. The diameter of the blind hole structure may be greater than the diameter and at least an active alignment width of the optical fiber.

Description

Optical connection structure

[0001] The present disclosure relates to an optical connection structure having a blind hole structure at the end of an optical circuit member in which an optical waveguide is formed, into which an optical fiber is inserted to optically connect the optical fiber to the optical waveguide.

[0002] An optical waveguide structure is formed from a waveguide core with a high refractive index and a waveguide cladding with a refractive index lower than that of the waveguide core. Because optical waveguide structures can be densely integrated on a wafer, they are increasingly being applied to optical communication transceivers, high-speed data transfer within microchips, sensing devices, and the like. In many cases, optical signals propagating through these optical waveguides use communication wavelength bands, and optical waveguide devices for optical communication applications in particular often involve connecting optical fibers to optical waveguides.

[0003] For example, the diameter of a single-mode fiber used to propagate optical signals in the communication wavelength band used in optical communications is approximately 125 μm, and the diameter of a small-diameter fiber is approximately 80 μm. In contrast, the dimensions of a silicon waveguide that satisfies the single-mode condition for optical signals in the communication wavelength band are several hundred nanometers, and even a quartz waveguide with a low refractive index is several μm, which is significantly different from the diameter of an optical fiber.

[0004] For this reason, a method has been used in the past to facilitate the connection between optical fibers and optical waveguides by preparing an optical fiber array block to which optical fibers are fixed separately from the optical circuit member and bonding it to the optical fiber connection end face of the optical circuit member to connect the optical fibers and optical waveguides (Patent Document 1).

[0005] Fig. 1 is a diagram showing the schematic configuration of a connection structure between optical fibers and optical waveguides using a conventional optical fiber array block. The optical fiber array block 101 shown in Fig. 1 is fabricated by aligning multiple optical fibers 104 in the V-groove on a V-groove substrate 102, which has multiple parallel V-grooves 103 with a V-shaped cross section formed at a predetermined core spacing on its surface, and then pressing them down from above with a pressing plate 105 and fixing them with an adhesive 106 or the like.

[0006] The optical circuit board 107 is an optical circuit connected to the optical fiber array block, and has a plurality of input / output waveguides 108 that transmit and receive optical signals corresponding to the optical fibers 104. The optical circuit board and the optical fiber array block are optically coupled by aligning the core end faces of the waveguides 108 with the core end faces of the optical fibers 104. For this reason, when using conventional connection methods, a process of aligning the optical axes of the optical fiber core and the optical waveguide core is required.

[0007] When an optical waveguide has a large number of input / output ports, an optical fiber array block consisting of a corresponding number of optical fibers is used. In this case, the optical axes of the many optical fibers fixed to the optical fiber array block and the waveguide cores must be aligned. This requires high precision in V-groove processing. Furthermore, the difficulty of core alignment increases, resulting in high implementation costs. Furthermore, the need to prepare the optical fiber array block as a separate component increases component procurement costs.

[0008] In particular, in the configuration shown in Figure 1, in which the optical fiber is sandwiched between the V-groove and the pressure plate 105 and fixed by filling with adhesive, the optical fiber 104 is supported at three points, which makes it susceptible to the effects of temperature changes and the like, and there is a problem that the insertion loss varies due to processing errors in the V-groove.

[0009] As another example of the prior art, a method has been proposed in which an interposer circuit is formed with an optical waveguide having an intermediate refractive index and equipped with a spot size conversion function and a pitch conversion function, as shown in Fig. 2 (Patent Document 2). By using an interposer circuit, it is possible to accommodate optical fiber connection with an optical waveguide formed of a high refractive index material with a smaller waveguide dimension.

[0010] 2 has input / output waveguides 204-1 to 204-3, which are Si waveguides consisting of a silicon core and a quartz clad. The interposer circuit 202 has interposer waveguides 205-1 to 205-3, which are quartz waveguides. Optical fibers 206-1 to 206-3 are arranged in the optical fiber block 203. SSCs 207-1 to 207-3 are arranged in the input / output waveguides 204-1 to 204-3, respectively, to match the MFDs to the interposer waveguides.

[0011] Similarly, SSCs 208-1 to 208-3 are arranged in interposer waveguides 205-1 to 205-3, respectively, to match the MFDs with optical fibers 206-1 to 206-3. In this conventional connection structure, an interposer circuit 202 is connected to an optical circuit 201, and an optical fiber block 203 is connected to the interposer circuit 202.

[0012] In this connection configuration, since an optical fiber block 203, an interposer circuit 202, and a Si optical circuit 201 are present, alignment between the optical fiber block 203 and the interposer circuit 202, and alignment between the interposer circuit 202 and the Si optical circuit 201 are required, which again poses the problem of increased implementation costs.

[0013] As a method for solving the problems of these conventional connection methods, a method has been reported in which a groove into which an optical fiber can be fixed is formed in an optical circuit board having an optical waveguide, and the optical fiber is fixed in the groove to optically connect the optical fiber and the optical waveguide (Non-Patent Document 1).

[0014] 3 is a diagram showing the schematic configuration of an optical connection portion in which an optical fiber fixing groove is formed in an optical waveguide substrate. An optical fiber connection portion 301 of the optical circuit board is formed with an optical waveguide 302 and a groove 303 for fixing the optical fiber. By fixing the optical fiber 304 directly to the optical circuit board using the groove 303, the core of the optical fiber and the core of the optical waveguide can be optically coupled.

[0015] This method fixes the optical fiber by forming a groove in the optical circuit board itself, eliminating the need for optical fiber blocks or interposer circuits, and reducing the number of parts required. Therefore, using this method makes it possible to reduce procurement costs and implementation costs.

[0016] However, this method has the problem that because the optical fiber is fixed by a groove, it is difficult to align the height of the optical fiber core with the optical waveguide core, resulting in high mounting costs.

[0017] Furthermore, since the optical fiber is fixed by the dimensions and shape of the groove formed in the optical circuit board, it is difficult to perform active alignment after the optical fiber is installed.

[0018] Japanese Patent No. 7244788 Japanese Patent Application Laid-Open No. 2020-126128

[0019] Y. Yamada et al. , JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. LT-5. No. 12, pp. 1716-1720, DECEMBER 1987.

[0020] The present disclosure has been made in view of the above points, and an object of the present disclosure is to provide an optical connection structure that facilitates vertical positioning of an optical fiber and an optical waveguide without the need for separate components such as an optical fiber block or an interposer circuit. Another object of the present disclosure is to provide an optical connection structure that eliminates variations in optical connection loss by enabling the optical fibers to be individually aligned and then fixed.

[0021] To achieve this objective, one embodiment of the present disclosure is an optical connection structure comprising a substrate on which at least one optical waveguide is formed, at least one blind hole structure arranged corresponding to the position of each of the at least one optical waveguide, and at least one optical fiber optically connected to the at least one optical waveguide by being inserted into and fixed in the blind hole structure, wherein the cross section of the blind hole structure is circular.

[0022] In another embodiment, the diameter of the blind hole structure may be set larger than the diameter of the optical fiber by at least the width required for active alignment, or even by a width α that allows for the fine alignment step while omitting the coarse alignment step.

[0023] According to the present disclosure, an optical fiber is inserted into a hollow blind hole structure formed directly in an optical connection structure including a substrate on which an optical waveguide is formed, and the core of the optical fiber and the core of the optical waveguide can be aligned and fixed, eliminating the need for a separate component such as an optical fiber block and making vertical positioning easier.

[0024] Furthermore, since the optical fiber can be actively aligned while inserted into the hollow blind hole structure and then fixed after active alignment, it is possible to suppress variations in optical loss due to processing errors during the manufacturing of the blind hole structure. Furthermore, active alignment can be achieved without the need for a rough alignment process.

[0025] Furthermore, since the refractive index matching material can be filled at least in the tip portion of the blind hole structure, it is also possible to reduce optical connection loss.

[0026] FIG. 1 is a diagram showing a schematic configuration of a connection structure between an optical fiber and an optical waveguide using a conventional optical fiber array block. FIG. 2 is a diagram showing a schematic configuration of a connection structure between an optical fiber and an optical waveguide using a conventional interposer circuit. FIG. 3 is a diagram showing a schematic configuration of an optical connection portion in which an optical fiber fixing groove is formed in an optical waveguide substrate. FIG. 4 is a schematic configuration diagram showing an optical connection structure constituting an input / output port of an optical circuit member to which an optical fiber according to a first embodiment of the present disclosure is connected, where (a) is a top view, (b) is a cross-sectional view, and (c) is a side view seen from the connection side. FIG. 5 is a schematic configuration diagram showing a cross-sectional structure when a blind hole structure of the optical connection structure according to the first embodiment is fabricated by cutting using a drill. FIG. 6 is a diagram showing the relationship between excess loss and axial misalignment during active alignment of a single-mode optical fiber and a quartz waveguide. FIG. 7 is a flowchart showing the steps of a method for connecting and fixing an optical fiber to an optical waveguide in the optical connection structure according to the first embodiment. 8 is a diagram showing a schematic configuration of an optical connection structure of an optical circuit member according to a first embodiment, where (a) is a cross-sectional view showing the schematic configuration when applied to a single-layer optical circuit member, and (b) is a cross-sectional view showing the schematic configuration when applied to a laminated optical circuit member. Fig. 9 is a diagram showing the schematic configuration of an optical connection structure of an optical circuit member according to a second embodiment. Fig. 10 is a diagram showing the schematic configuration of an optical connection structure of an optical circuit member according to a third embodiment. Fig. 11 is a diagram showing the schematic configuration of an optical connection structure of an optical circuit member according to a fourth embodiment. Fig. 12 is a schematic configuration diagram showing an optical connection structure constituting an input / output port of an optical circuit member to which an optical fiber according to a second embodiment of the present disclosure is connected. Fig. 13 is a diagram showing the schematic configuration of an optical connection structure according to a third embodiment of the present disclosure, where (a) is a perspective view showing the entire structure, and (b) is a perspective view seen from the surface on the single-mode optical fiber side so that the pitch relationship between optical waveguides can be easily understood.

[0027] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the following description is an example, and some configurations may be modified without departing from the spirit of the present disclosure. The same or similar reference numerals indicate the same or similar elements, and repeated description may be omitted.

[0028] 4 is a schematic diagram showing an optical connection structure 401 constituting an input / output port of an optical circuit element to which an optical fiber according to a first embodiment of the present disclosure is connected. The optical connection structure 401 is a part of a substrate 400 constituting an optical circuit element made of a substrate on which a waveguide, an optical functional element, and the like are formed. The optical connection structure 401 is, for example, near an end of a substrate on which an input / output optical waveguide constituting the input / output port of the optical circuit element is formed. This optical connection structure 401 connects the input / output optical waveguide to an optical fiber, thereby inputting and outputting signals to and from the outside of the optical circuit element.

[0029] The optical circuit component may be a high-density optical integrated circuit composed of a silicon waveguide, a silicon nitride waveguide, an indium phosphide waveguide, a lithium diisopropyltide waveguide, a quartz waveguide, or the like, but may also include an optical waveguide composed of other materials.

[0030] The optical connection structure 401 according to this embodiment includes a substrate 402 on which at least one optical waveguide 406 is formed, and a fixing member 403 adhesively fixed to the upper surface of the substrate 402. The substrate 402 and fixing member 403 of the optical connection structure 401 form an end surface 408 on the connection side of the optical connection structure 401. At least one blind hole structure 407 is formed in the substrate 402 and the fixing member 403, respectively, at a position corresponding to the optical waveguide 406, extending from the end surface 408 on the connection side in the optical axis direction of the optical waveguide. An optical fiber 409 is inserted into and fixed in the blind hole structure 407.

[0031] 4(a) is a top view of an optical circuit member 400 having an optical connection structure 401 formed thereon, as viewed from the Y-axis direction of the figure, and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb. The optical connection structure 401 of this embodiment includes a substrate 402 having optical waveguides 406-1 to 406-3 formed thereon, and a support member 403 adhesively fixed to the upper surface of the substrate 402. The portion to which the support member 403 is adhesively attached is defined as the optical connection structure 401 of this embodiment, which, together with the substrate, optically connects the optical fiber and the optical waveguide.

[0032] The optical fiber array block 403 of this embodiment can be a conventional optical fiber array block attached to a substrate, with the aim of increasing the bonding area and ensuring mechanical strength (adhesion strength) when bonding the optical fiber array block to an optical circuit board. The optical fiber array block 403 can be made of synthetic quartz, fused silica, soda glass, etc., as with conventional optical fiber array blocks. However, other materials may also be used. Note that in FIG. 4, only the core of the optical waveguide is shown for ease of understanding, with cladding layers and other elements omitted as appropriate. The blind hole structure 407 formed including the boundary between the optical fiber array block 403 and the substrate, the optical fiber, and the optical fiber array block 403 are also shown in a see-through state as appropriate to facilitate understanding of their relative positions. This also applies to the following drawings.

[0033] 4(c) is a side view of the optical circuit element of FIG. 4(a) as viewed from the connection-side end face 408. As shown in FIG. 4(c), the substrate 402 and the gate member 403 of the optical connection structure 401 form the connection-side end face 408. The substrate 402 and the gate member 403 have blind hole structures 407-1 to 407-3 formed in positions corresponding to each of the optical waveguides 406-1 to 406-3 in the optical axis direction of the optical waveguide from the connection-side end face 408. In this embodiment, the blind hole structures 407-1 to 407-3 are formed as hollow holes that include the boundary between the substrate 402 and the gate member 403.

[0034] In the optical connection structure 401 of this embodiment, optical fibers 409-1 to 409-3 are roughly positioned by inserting them into this hollow blind hole structure. Then, the optical fibers and the optical waveguide are connected by aligning the positions of the optical fiber cores and the optical waveguide cores and then fixing them in place. At this time, because the blind hole structure has a circular shape, it can be easily positioned relative to the optical waveguide cores, including in the vertical direction.

[0035] As mentioned above, the diameter of an optical fiber used at a frequency used in communication is significantly larger than the dimensions of the waveguide. The optical waveguides 406-1 to 406-3 of the optical connection structure 401 have their waveguide cores located near the surface of the substrate 402, with an upper core layer formed on top of the cores. Therefore, the substrate 402 alone cannot be used to form the blind hole structure 407 so that its central axis corresponds to the position of the optical waveguide core. Therefore, in this embodiment, the optical connection structure 401 is formed using a substrate and a bracket member 403 adhesively fixed to the substrate, thereby enabling the blind hole structure to have its central axis corresponding to the position of the optical waveguide core.

[0036] The blind hole structure of this embodiment can be formed by etching or cutting. When a blind hole is formed by cutting using a drill, the shape of the blind hole reflects the shape of the tip of the drill. In this case, it is desirable to process the shape of the tip of the optical fiber to match the shape of the blind hole. If the tip of the optical fiber is not processed, the distance between the core and the waveguide becomes large, resulting in increased radiation loss.

[0037] Fig. 5 is a schematic diagram showing the cross-sectional structure of an optical connection structure 501 when the blind hole structure of this embodiment is fabricated by cutting using a drill. Fig. 5 is a cross-sectional view taken along the line IVb-IVb, similar to Fig. 4(b). Components in Fig. 5 denoted by the same reference numerals as in Fig. 4 are the same as the components denoted by the same reference numerals in Fig. 4, including their arrangement, and therefore will not be described here.

[0038] 5 reflects the shape of the tip of a drill, and the tip of the optical fiber 509 is tapered to match this shape. Therefore, the distance between the optical fiber 509 and the core of the optical waveguide 406 does not increase, and an increase in radiation loss can be prevented.

[0039] In addition, instead of using a yatai member as in the optical connection structure of this embodiment, as in the second and third embodiments described below, the substrate included in the optical connection structure may be a bulk substrate having a thickness that allows it to be formed at a position where the optical waveguide core and the central axis of the blind hole structure correspond, and the waveguide core may be formed at a deep position from the surface of the bulk substrate.

[0040] The diameter Dh of the blind hole structure formed in the optical connection structure is set to be larger than the diameter Df of the bare optical fiber or the optical fiber including the protective layer. In this case, it is desirable to set the diameter Dh of the blind hole structure to be larger than the diameter Df of the optical fiber by at least the width required for active alignment.

[0041] Active alignment usually consists of a coarse alignment process and a fine alignment process. The coarse alignment process is a process in which the optical fiber or optical circuit component is roughly scanned to search for a position where the transmitted light of the connection structure can be detected, and the fine alignment process is a process in which the optical fiber or optical circuit component is scanned with high resolution to search for the peak of the transmission intensity of the transmitted light.

[0042] Therefore, the diameter Dh of the blind hole structure may be set to be larger than the diameter Df of the optical fiber so that the positional deviation between the position of the optical fiber core and the position of the corresponding optical waveguide core is within a range that allows the fine alignment process to be performed.

[0043] That is, when the width for which active alignment is possible using only the fine alignment process without the coarse alignment process is α, it is desirable to set Dh and Df so as to satisfy the relationship of the following equation (1): Dh=Df+α (1)

[0044] Figure 6 shows the relationship between excess loss and axial misalignment during active alignment of a single-mode optical fiber and a silica waveguide (assuming no angular misalignment). For example, in a mounting device equipped with a typical photodetector, the excess loss range within which transmitted light through an optical connection structure can be detected is 0 to 40 dB. When mounting a single-mode optical fiber with a mode field diameter of approximately 10 μm used in optical communication wavelength bands using this mounting device, active alignment without the coarse alignment process is possible if the axial misalignment is in the range of 0 to 24 μm. Therefore, the width α within which active alignment without the coarse alignment process is possible is in the range of 0 to 48.0 μm. Because it is difficult to insert an optical fiber into a blind hole structure when α = 0, α is typically set to 1 μm or greater. In this case, the maximum value of α is 4.8 times the mode field diameter. Furthermore, when connecting an optical waveguide to an optical fiber, single-mode optical fiber or a polarization-maintaining optical fiber with a mode field diameter similar to that of a single-mode optical fiber is generally used.

[0045] When a small-diameter fiber with a higher numerical aperture NA and a mode field diameter of approximately 4 μm in the communication wavelength band is used, the value of α is limited to a range of 1 μm to 19.2 μm, which is a range of 1 μm to 4.8 times the mode field diameter, which is narrower than the range for single-mode optical fiber. That is, in the optical connection structure of this embodiment, α is in the range of 1 μm to 4.8 × the mode field diameter of the optical fiber.

[0046] In the optical connection structure of this embodiment, the diameter Dh of the blind hole structure is set larger by the width required for the fine alignment process, so that in the process of fixing the optical fiber to the optical connection structure, by inserting the optical fiber into the blind hole structure, it is possible to omit the coarse alignment process and achieve rough alignment to the extent that active alignment can be performed, and then the fine alignment process can be proceeded to as is.

[0047] In this way, in the optical connection structure of this embodiment, each optical fiber is adhesively fixed to its respective blind hole structure after active alignment, so that optical connections with no variation in individual connection loss are realized.

[0048] To insert and bond an optical fiber into a blind hole structure, for example, an adhesive may be applied to the optical fiber before insertion. For example, a UV-curable or heat-curable optical adhesive may be used as the adhesive. When a UV-curable adhesive is used, it is desirable that the substrate 402 on which the blind hole structure is formed and the support member 403 be made of a UV-transparent material such as quartz. The adhesive and refractive index adjusting material within the blind hole structure are omitted in Figures 4 and 5 .

[0049] (Method of fixing optical fibers to the optical connection structure of the first embodiment) As described above, the optical connection structure of this embodiment has blind hole structures 407-1 to 407-3 into which optical fibers are inserted and fixed. The optical connection structure of this embodiment is completed by inserting and fixing the optical fibers in these blind hole structures and connecting them to the optical waveguides.

[0050] The steps of the method for connecting and fixing an optical fiber to an optical waveguide in the optical connection structure of this embodiment will be described below. Fig. 7 is a flowchart showing the steps of this method.

[0051] In the first step 701, an adhesive is applied to the optical fiber as a pre-process before the optical fiber is inserted into the hollow blind hole structure. Note that, when filling the tip of the blind hole structure with a refractive index matching material as in the second embodiment described later, the tip of each blind hole structure is filled with the refractive index matching material before inserting the optical fiber.

[0052] The second step 702 is to insert the optical fiber into a hollow blind hole structure with an active alignment diameter larger than the diameter of the optical fiber.

[0053] The third step 703 is to perform active alignment of the optical fiber inserted into the blind hole structure. This active alignment can be performed using a device that is typically used as an alignment device. As described above, when the diameter Dh of the blind hole structure is larger than the diameter Df of the optical fiber by α, it is possible to perform active alignment without the rough alignment step.

[0054] The fourth step 704 is a step of curing the adhesive to fix the optical fiber. As described above, the adhesive for adhering the optical fiber to the blind hole structure is an ultraviolet-curable or heat-curable adhesive, and the optical fiber is fixed by curing it in a normal manner.

[0055] The above procedure is repeated until the optical fibers are fixed in all the blind hole structures, thereby completing the connection between the optical waveguides of the optical connection structure and the optical fibers and the fixing of the optical fibers.

[0056] In this way, the optical connection structure according to the first embodiment of the present disclosure can directly connect an optical fiber to an optical waveguide without using a separate component. Furthermore, since the optical fibers can be individually aligned and fixed by active alignment, the variation in optical loss between the optical fibers can be reduced.

[0057] (First Example) In the first example, the optical connection structure of the first embodiment is applied to an optical circuit member in which a weak-guiding optical waveguide and a strong-guiding optical waveguide are formed. Here, the weak-guiding optical waveguide refers to an optical waveguide in which the core is made of SiO2 or SiN and the refractive index difference between the core and the cladding is small, resulting in a weak light confinement effect, while the strong-guiding optical waveguide refers to an optical waveguide in which the core is made of Si, InP, or LN and the refractive index difference between the core and the cladding is large, resulting in a strong light confinement effect.

[0058] As in the first embodiment, the optical waveguide connected to the optical fiber is a weakly guiding type optical waveguide, and the optical circuit formed in the optical circuit member is formed of a strongly guiding type optical waveguide. This reduces the connection loss with the optical fiber, and realizes a high-density optical circuit, thereby making it possible to make the optical circuit member smaller.

[0059] 8A and 8B are diagrams showing the schematic configuration of an optical connection structure constituting an input / output port of an optical circuit element according to a first embodiment. Fig. 8A is a cross-sectional view showing the schematic configuration when applied to a single-layer optical circuit element in which a weakly guiding optical waveguide and a strongly guiding optical waveguide of the optical circuit element are directly coupled, and Fig. 8B is a cross-sectional view showing the schematic configuration when applied to a stacked optical circuit element in which a weakly guiding optical waveguide and a strongly guiding optical waveguide of the optical circuit element are connected by an adiabatic coupler such as a directional coupler. Components in Fig. 8 designated with the same reference numerals as those in Fig. 4 are the same as those designated with the same reference numerals in Fig. 4, including their arrangement, and therefore will not be described here. Also, Figs. 8A and 8B are cross-sectional views taken along the line IVb-IVb, as in Fig. 4B.

[0060] A weakly guiding optical waveguide 806 and a strongly guiding optical waveguide 807 are formed on the substrate 402 of the single-layer optical circuit component 801 in FIG. 8( a), and these two optical waveguides are formed at the same height and are directly coupled to each other.

[0061] A weak guiding type optical waveguide 806 and a strong guiding type optical waveguide 807 are formed on the substrate 402 of the laminated type optical circuit member 802 of Fig. 8(b), and these two optical waveguides are formed at different heights and are optically connected by an adiabatic coupler 808 such as a directional coupler. In the laminated type of Fig. 8(b), the weak guiding type optical waveguide and the strong guiding type optical waveguide are connected by an adiabatic coupler or the like, which makes it possible to further reduce optical loss compared to the single-layer type.

[0062] Second Example The second example is an optical connection structure in which the tip portion of the blind hole structure in the first embodiment is formed in a convex lens shape. By forming the tip portion of the blind hole structure in a convex lens shape, the optical connection loss of the optical connection portion can be reduced by the lens action.

[0063] 9 is a schematic diagram of an optical connection structure 901 that constitutes an input / output port of an optical circuit member to which an optical fiber according to the second embodiment is connected, viewed from the X-axis direction, similar to FIG. 4(b). Components denoted by the same reference numerals as in FIG. 4 are the same as the components denoted by the same reference numerals in FIG. 4, including their arrangement, etc.

[0064] The optical connection structure 901 of Figure 9 comprises a substrate 402 on which at least one optical waveguide 406 is formed, and a fixing member 403 adhesively fixed to the upper surface of the substrate 402. The substrate 402 and fixing member 403 of the optical connection structure 901 form the connection-side end face 408 of the optical connection structure 901. At least one blind hole structure 907 is formed in the substrate 402 and the fixing member 403, respectively, at a position corresponding to the optical waveguide 406, extending from the connection-side end face 408 in the optical axis direction of the optical waveguide. An optical fiber 409 is inserted into and fixed in the blind hole structure 907.

[0065] The optical connection structure 901 of the second embodiment differs from the optical connection structure 401 shown in Fig. 4 in that the tip portion 908 of the blind hole structure 907 has a convex lens shape. In the second embodiment, it is desirable to fill at least the convex lens-shaped tip portion 908 of the blind hole structure 907 with a refractive index matching material 909. The refractive index matching material here is, for example, a material having a refractive index n clad A larger refractive index can be used.

[0066] As in the first embodiment, the optical fiber 409 is inserted into the blind hole structure 907 and fixed therein by adhesive 910. Since adhesive is applied to the optical fiber 409 when it is inserted, the optical fiber 409 is fixed therein by the adhesive 910 filled in the blind hole structure 907, as shown in FIG.

[0067] When fixing an optical fiber by filling at least the tip portion of the blind hole structure 907 with a refractive index matching material 909, the tip portion of the blind hole structure is filled with the refractive index matching material 909 in advance, and an optical fiber coated with adhesive 910 is inserted and adhesively fixed.

[0068] According to this embodiment, it is possible to further reduce optical loss at the optical connection portion between the optical fiber and the optical waveguide. Note that this embodiment may also be applied to an optical circuit component in which a strong guiding type optical waveguide and a weak guiding type optical waveguide are formed, as in the first embodiment.

[0069] 10 is a diagram showing a schematic configuration of an optical connection structure 1001 of an optical circuit member according to a third example of the first embodiment. While the blind hole structure in the first embodiment has a cylindrical shape, the blind hole structure in the third example has a truncated cone shape.

[0070] 10, the same reference numerals as those in FIG. 4 denote the same elements as those in FIG. 4, including their arrangement, and therefore detailed description thereof will be omitted here.

[0071] 10, the blind hole structure of the third example has a truncated cone shape with an opening diameter D1 larger than a diameter D2 of the tip of the blind hole structure 1007 and tapered from the opening to the tip. In the third example, too, the diameters D1 and D2 of the blind hole structure are set larger than the diameter Df of the optical fiber, as in the first embodiment.

[0072] In the third embodiment, the optical fiber can be guided by the taper from the opening of the blind hole structure to the tip, so that the diameter D2 of the tip allows for rough positioning and simplifies the insertion of the optical fiber into the blind hole structure 1007.

[0073] In the third example, similarly to the first embodiment, in order to insert an optical fiber into the blind hole structure and fix it after active alignment, the diameter D2 of the tip of the blind hole structure 1007 is set to be larger than the diameter Df of the bare optical fiber or the optical fiber including the protective layer. In this case, it is desirable to set the diameter D2 of the blind hole structure to be larger than the diameter Df of the optical fiber by at least the width required for active alignment.

[0074] Furthermore, in order to enable active alignment using only the fine alignment process without the coarse alignment process, when the width necessary for active alignment using only the fine alignment process without the coarse alignment process is α, it is desirable to set D1, D2, and Df in a relationship that satisfies the following equation (2): D1>D2=Df+α (2)

[0075] In this example, as described above, α is in the range of 1 μm to 4.8 times the mode field diameter of the optical fiber. Specifically, in the case of a single-mode optical fiber with a mode field diameter of approximately 10 μm, α is in the range of 1 μm to 48 μm. In the case of a small-diameter fiber with a mode field diameter of approximately 4 μm, α is in the range of 1 μm to 19.2 μm.

[0076] This embodiment may also be applied to an optical circuit component in which a strong optical waveguide and a weak optical waveguide are formed, as in the first embodiment, and the tip portion of the blind hole structure may be formed in a convex lens shape, and the tip portion may be filled with a refractive index adjusting material, as in the second embodiment.

[0077] 11 is a diagram showing a schematic configuration of an optical connection structure 1101 of an optical circuit member according to a fourth example of the first embodiment. In the first embodiment, the pitch (the distance between the optical waveguide cores) of the optical waveguides 406 of the optical connection structure was the same as the pitch (the distance between the central axes of the blind hole structures 407) into which optical fibers are inserted. In contrast, in the fourth example, a pitch conversion portion is provided in the optical waveguides of the optical connection structure, thereby enabling connection to optical waveguides formed at a pitch smaller than the pitch of the blind hole structures into which optical fibers are inserted.

[0078] 11, the same reference numerals as those in FIG. 4 are used to denote the same components as those in FIG. 4, including their arrangement, and therefore detailed description thereof will be omitted here.

[0079] In the optical connection structure 1101 of the fourth embodiment, optical waveguides 1106-1 to 1106-3 have pitch conversion sections 1110, in which the pitch of the optical waveguides is converted from d1 to d2. In this case, the pitch d1 is larger than the diameter Df of the optical fiber.

[0080] Therefore, in the fourth embodiment, even if the optical waveguide array is formed at a pitch smaller than the pitch at which the blind hole structures 407 can be formed, the optical fiber array can be connected using the blind hole structures.

[0081] In this embodiment, an example in which the pitch d2 is smaller than the pitch d1 is described, but similar connection is possible when d2 is larger than d1. This embodiment may also be applied to an optical circuit component in which a strong guiding type optical waveguide and a weak guiding type optical waveguide are formed, as in the first embodiment, and the tip of the blind hole structure may be formed in a convex lens shape and filled with a refractive index adjusting material, as in the second embodiment. Furthermore, the shape of the blind hole structure may be a truncated cone, as in the third embodiment.

[0082] (Second Embodiment) In the first embodiment, the blind hole structures for inserting optical fibers to be connected to optical waveguides were arranged in the X-axis direction in accordance with the arrangement of the optical waveguides, but in this embodiment, they are arranged two-dimensionally in the X-axis and Y-axis directions. This makes it possible to miniaturize an optical connection structure for connecting optical fibers to a large number of input / output waveguides. Note that the X-axis, Y-axis, and Z-axis here are coordinate axes that are orthogonal to each other, as shown in the figure, and the blind hole structures for inserting optical fibers to be connected to waveguides are arranged in the Z-axis direction with the optical axis of the waveguide.

[0083] 12 is a schematic diagram showing an optical connection structure 1201 that constitutes an input / output port of an optical circuit member to which an optical fiber according to a second embodiment of the present disclosure is connected. In FIG. 12, the same reference numerals as in FIG. 4 are the same as those in FIG. 4 except for their arrangement, and therefore detailed description thereof will be omitted here.

[0084] The optical connection structure 1201 of this embodiment is a part of an optical circuit member made of a substrate on which a waveguide, an optical functional element, etc. are formed, as in the first embodiment. As in the first embodiment, the waveguide 1206 formed in the bulk substrate 1202 is extended up to the substrate portion on which the optical functional element, etc. of the optical circuit member is formed, and the optical functional element, etc. is connected, but for ease of understanding, the substrate portion on which the optical circuit, such as the optical functional element to which the waveguide is connected, is formed is omitted in Fig. 12.

[0085] The optical connection structure 1201 of this embodiment is composed of a bulk substrate 1202 having optical waveguides 1206-1 to 1206-6 including three-dimensional optical waveguides that connect a planar optical waveguide array formed in the X-axis direction and optical fibers arranged two-dimensionally in the X-axis and Y-axis directions on a substrate constituting an optical circuit member, and blind hole structures 407-1 to 407-6 formed corresponding to the two-dimensionally arranged optical waveguides 1206-1 to 1206-6 on the connection side end face 408. The bulk substrate 1202 has a thickness that allows the blind hole structures 407 to be formed by arranging them two-dimensionally.

[0086] 12 shows only six optical waveguides 1206, blind hole structures 407, and optical fibers 409, but multiple numbers may be arranged in the X-axis direction and the Y-axis direction. The number of optical waveguides, optical fibers, and blind hole structures arranged may be, for example, 128 or 64. The number of arrangements in the X-axis direction and the Y-axis direction is determined appropriately according to the dimensional design of the optical connection portion. Each optical waveguide 1206 including a three-dimensional waveguide in the bulk substrate 1202 can be fabricated by drawing a waveguide core using, for example, an ultrashort pulse laser or the like.

[0087] In this embodiment, as in the first embodiment, the diameter Dh of the blind hole structure formed in the optical connection structure is set to be larger than the diameter Df of the bare optical fiber or the optical fiber including the protective layer. In this case, it is desirable that the diameter Dh of the blind hole structure is set to be larger than the diameter Df of the optical fiber by at least the width required for active alignment.

[0088] Furthermore, in order to enable active alignment using only the fine alignment process without the coarse alignment process, when the width at which active alignment is possible using only the fine alignment process without the coarse alignment process is α, it is desirable to set Dh and Df in a relationship that satisfies the following equation (1): Dh = Df + α (1)

[0089] As described above, α is in the range of 1 μm to 4.8 × the mode field diameter of the optical fiber. For example, in the case of a single-mode optical fiber with a mode field diameter of approximately 10 μm used in the optical communication wavelength band, the width α required for active alignment without the coarse adjustment step is 1 μm to 48 μm.

[0090] After active alignment, the optical fiber is adhesively fixed in the blind hole structure, completing the optical connection structure of the embodiment of the present disclosure. To insert and adhere the optical fiber into the blind hole structure, for example, an adhesive may be applied to the optical fiber before insertion. For example, a UV-curable or heat-curable optical adhesive may be used as the adhesive. When a UV-curable adhesive is used, it is desirable that the material of the bulk substrate 1202 in which the blind hole structure is formed be a UV-transparent material such as quartz.

[0091] In this embodiment, as in the first example of the first embodiment, it may be applied to an optical circuit component in which a strong guiding type optical waveguide and a weak guiding type optical waveguide are formed, and the tip portion of the blind hole structure may be formed in a convex lens shape as in the second example, and at least the tip portion of the blind hole structure may be filled with a refractive index matching material. Furthermore, as in the third example, the shape of the blind hole structure may be formed in a truncated cone shape.

[0092] 12, optical waveguides 1206-1 to 1206-6, which are arranged one-dimensionally at a pitch d2, are arranged two-dimensionally on the end face 408 on the optical fiber connection side, and the pitch is the arrangement pitch d1 of the blind hole structures 407. In this manner, in this embodiment as well, as in the fourth embodiment, an optical fiber array can be connected to optical waveguides formed at a pitch smaller than the pitch at which the blind hole structures 407 can be formed.

[0093] 12 illustrates an example in which the pitch d1 is larger than the pitch d2, but the pitch d1 and the pitch d2 may be the same, or the pitch d2 may be larger than the pitch d1. Furthermore, the blind hole structure and the optical waveguide do not have to be formed at a constant pitch.

[0094] Third Embodiment Next, a third embodiment will be described in which the optical connection structure of the present disclosure is applied as a fan-in / fan-out device. Here, fan-in / fan-out refers to a configuration in which each core of a multicore fiber is connected to a single-mode optical fiber.

[0095] Fig. 13 is a perspective view showing an optical connection structure 1301 according to a third embodiment of the present disclosure. Fig. 13(a) is a perspective view showing the entire structure, and Fig. 13(b) is a perspective view seen from the surface on the single-mode optical fiber side, particularly to make it easier to understand the pitch relationship between the optical waveguides. In Fig. 13 as well, only the core of the optical waveguide is shown in a transparent manner, and cladding layers and the like are omitted as appropriate, so that the positional relationship of each component can be easily understood. Also, blind hole structures formed in a bulk substrate and optical fibers inserted into the blind hole structures are shown in a transparent manner.

[0096] 13 has a blind hole structure 1304 formed on one of two opposing surfaces of a bulk substrate 1302, into which a multicore fiber 1303 is inserted and fixed, and blind hole structures 1306-1 to 1306-4 formed on the other surface, into which single-mode optical fibers 1305-1 to 1305-4 are inserted and fixed, and optical waveguides 1307-1 to 1307-4 including three-dimensional waveguides that connect the multicore fiber 1303 inserted and fixed in each blind hole structure to the single-mode optical fibers 1305-1 to 1305-4 are formed. Each optical waveguide 1307 including a three-dimensional waveguide in the bulk substrate 1302 can be fabricated by drawing a waveguide core using, for example, an ultrashort pulse laser or the like.

[0097] In this embodiment, as in the first embodiment, the diameter Dh of the blind hole structures 1304 and 1306-1 to 1306-4 is set to be larger than the diameter Df of the bare optical fiber or the optical fiber including the protective layer to be inserted into each blind hole structure. In this case, it is desirable that the diameter Dh of the blind hole structure is set to be larger than the diameter Df of the optical fiber by at least the width required for active alignment.

[0098] Furthermore, in order to enable active alignment using only the fine alignment process without the coarse alignment process, when the width at which active alignment is possible using only the fine alignment process without the coarse alignment process is α, it is desirable to set Dh and Df in a relationship that satisfies the following equation (1): Dh = Df + α (1)

[0099] For example, even when a multi-core optical fiber with a diameter of 900 μm including a protective layer is inserted, as described above, α is in the range of 1 μm to 4.8× the mode field diameter of the optical fiber, and when the mode field diameter of a multi-core optical fiber used in the optical communication wavelength band is approximately 10 μm, α is 1 μm to 48 μm.

[0100] After active alignment, each optical fiber is adhesively fixed in its corresponding blind hole structure, completing the optical connection structure of the embodiment of the present disclosure. To insert and adhere the optical fiber into the blind hole structure, for example, an adhesive may be applied to the optical fiber before insertion. For example, a UV-curable or heat-curable optical adhesive may be used as the adhesive. When a UV-curable adhesive is used, it is desirable that the material of the bulk substrate 1302 in which the blind hole structure is formed be a UV-transparent material such as quartz.

[0101] In this embodiment, as in the second example of the first embodiment, the tip portions of the blind hole structures 1306-1 to 1306-4 into which the single-mode optical fibers are inserted may be formed in a convex lens shape. Furthermore, a refractive index-matching material may be filled into at least the tip portion of the blind hole structure 1306. Furthermore, as in the third example, the shape of the blind hole structures 1304 and 1306 may be formed in a truncated cone shape.

[0102] In this embodiment, as shown in Fig. 13(b), the arrangement pitches of the optical waveguides 1307-1 to 1307-4 on the multicore fiber side are formed as d1 and d2 corresponding to the arrangement pitch of the cores of the multicore fiber. In contrast, the arrangement pitches d3 and d4 on the single-mode optical fiber connection side are set to be larger than the arrangement pitches d1 and d2 of the cores of the multicore optical fiber and to be equal to or larger than the diameter Dh of the blind hole structure into which the single-mode optical fiber is inserted. This relationship can be expressed by the following formula (3): d3, d4 ≥ Dh > d1, d2 (3)

[0103] In this embodiment, the multi-core optical fiber 1303 has been described as having four cores, but the number of cores of the multi-core optical fiber may be other than four, for example, seven. Furthermore, although the blind-hole structures 1306 into which the single-mode optical fibers 1305 are inserted are arranged two-dimensionally in accordance with the core arrangement of the multi-core optical fiber, they may also be arranged one-dimensionally. Furthermore, the single-mode blind-hole structures do not need to be formed at a constant pitch.

[0104] According to the present disclosure, it is possible to provide an optical connection structure to which an optical fiber can be connected without using a separate member such as an optical fiber block, etc. Furthermore, it is possible to provide an optical connection structure in which the optical fiber is aligned and fixed in a state where it is inserted into the blind hole structure, thereby suppressing variations in optical loss due to processing errors during the manufacturing of the blind hole structure.

[0105] Optical connection structure 401, 501, 601, 901, 1001, 1101, 1201, 1301 Substrate 402 Component 403 Optical waveguide 406, 806, 807, 1106, 1206, 1307 Blind hole structure 407, 507, 907, 1007, 1304, 1306 End face of connection side 408 Optical fiber 409, 509 Tip portion 908 Refractive index adjusting material 909 Adhesive 910 Pitch conversion portion 1110 Bulk substrate 1202, 1302 Multicore fiber 1303 Single-mode optical fiber 1305

Claims

1. An optical connection structure comprising: a substrate on which at least one optical waveguide is formed; at least one blind hole structure arranged corresponding to the position of each of the at least one optical waveguide; and at least one optical fiber optically connected to the at least one optical waveguide by being inserted into and fixed in the blind hole structure, wherein the cross section of the blind hole structure is circular.

2. The optical connection structure according to claim 1, wherein the substrate is a part of an optical circuit member on which an optical functional element connected to the at least one optical waveguide is formed.

3. The optical connection structure described in claim 1, characterized in that when the diameter of the tip end of the blind hole structure is Dh and the diameter of the optical fiber is Df, Dh is larger than Df by at least the width that allows active alignment.

4. The optical connection structure according to claim 3, wherein Dh=Df+α, where α is the width that allows active alignment without requiring a rough alignment process.

5. An optical connection structure according to any one of claims 1 to 4, characterized in that the diameter of the opening of said blind hole structure is larger than the diameter of the tip end side of said blind hole structure.

6. An optical connection structure described in any one of claims 1 to 4, characterized in that a stopper member is adhered to the substrate, and the blind hole structure is formed including the interface between the substrate and the stopper member.

7. The optical connection structure according to any one of claims 1 to 4, characterized in that the blind hole structures are arranged two-dimensionally.

8. An optical connection structure as described in claim 1, 3 or 4, characterized in that the blind hole structure is formed on each of two opposing surfaces of the substrate, and the core of the optical fiber inserted into the blind hole structure formed on one of the two surfaces is connected to the core of the optical fiber inserted into the blind hole structure formed on the other surface by the optical waveguide.

9. The optical connection structure according to any one of claims 1 to 4, wherein the substrate is transparent to ultraviolet light.

10. An optical connection structure according to any one of claims 1 to 4, characterized in that the tip of the blind hole structure is shaped like a convex lens.

11. An optical connection structure according to claim 9, characterized in that at least the tip of the blind hole structure is filled with a refractive index matching material having a refractive index higher than the refractive index of the clad of the at least one optical waveguide.

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