Optical connection structure and method for manufacturing same

Abstract

An optical connection structure (10) according to the present invention comprises a first waveguide core (111), a second waveguide core (121), a first tapered waveguide core (131), and a second tapered waveguide core (132), and: the first and second tapered waveguide cores are configured from a photo-cured photocurable resin; an end surface of the first waveguide core is disposed facing an end surface of the second waveguide core; the base ends of the first and second tapered waveguide cores are respectively connected to the end surfaces of the first and second waveguide cores; the tip end of the first tapered waveguide core and the tip end of the second tapered waveguide core are connected; and the respective core diameters of the first and second tapered waveguide cores increase from the base ends to the tip ends thereof.　The present invention thereby provides an optical connection structure that can reduce optical loss and improve optical axis deviation tolerance.

Description

Optical connection structure and manufacturing method thereof

[0001] The present invention relates to an optical connection structure for optically connecting optical components and a method for manufacturing the same.

[0002] With the advancement of optical communication networks, there is a demand for high performance and low cost optical communication modules. Optical communication modules are modularized by electro-optical packaging, combining electrical elements such as amplifiers, switches, and electric amplification circuits, and optical elements such as semiconductor lasers, optical switches, and optical fibers.

[0003] In optical elements, the optical connection process, which optically connects each optical element discretely, is crucial. In particular, precise positioning between optical elements is crucial for achieving low-loss optical connections between optical devices operating in single mode. For this reason, general-purpose optical connectors and other devices use high-precision components with an optical axis misalignment of 1 μm or less. Thus, the manufacture of optical communication modules requires highly precise tolerance-based design and positioning of precision components and devices, and processes have been developed to achieve this.

[0004] Kagami, M., "Self-Written Optical Waveguide Technology for Optical Wiring," Optics, Japan Society of Applied Physics, February 2008, Vol. 37, No. 2, pp. 94(22)-100(28).

[0005] The positioning accuracy required for low-loss optical connections between devices in the communication wavelength band is limited by the mode-field diameter (MFD) of general-purpose optical fibers.

[0006] The positioning accuracy when performing low-loss optical connections is determined by the MFD of the waveguide end faces within the device. In order to connect optical devices with low loss, it is necessary to position the gap, angle misalignment, and optical axis misalignment of the waveguides within the device with high precision. In particular, high precision is required for the positioning accuracy of the optical axis misalignment. The coupling efficiency T due to optical axis misalignment is calculated by multiplying the MFR (Mode-field radius) of the end faces of the two waveguides by w １ , w ２and the optical axis deviation between the waveguides is d, it is expressed by the following equation (1): Here, it is assumed that the gap and angle deviation of the waveguides in the device can be ignored.

[0007]

[0008] In formula (1), w １ =w ２ And when d=0, T is maximum.

[0009] Optical communication modules are premised on the use of general-purpose single-mode optical fibers, and their connection is essential. This is because the manufacturing technology for single-mode optical fibers and related technologies (such as fusion splicing and optical connectors) are highly mature, and optical fibers offer very high performance and low cost as transmission paths between communication modules. Therefore, in optical communication modules, the connection between optical elements and general-purpose single-mode fiber (SSMF, Standard Single-Mode Fiber) is essential.

[0010] As described above, since SSMF is essential in optical communication modules, the positioning tolerance required for low-loss optical connection is determined by using SSMF as the optical fiber when connecting the transmitter / receiver of the communication module to the optical fiber.

[0011] For example, if the MFD of a transmitter connected to an SSMF is approximately the same as the MFD of the SSMF (approximately 10 μm diameter), the 1 dB optical axis misalignment tolerance is approximately 2.4 μm. Here, the 1 dB optical axis misalignment tolerance is the amount of optical axis misalignment required to increase the loss due to optical axis misalignment by 1 dB compared to when there is no optical axis misalignment, and is an index for evaluating the positioning accuracy required during optical connection. On the other hand, if the MFD of a transmitter connected to an SSMF is expanded to 20 μm, the 1 dB optical axis misalignment tolerance increases compared to when the MFD of the transmitter connected to the SSMF is approximately the same as the MFD of the SSMF.

[0012] However, from equation (1), the transmittance is w １ =w ２Therefore, in the configuration where the MFD of the transmitter is enlarged, the allowable amount of optical axis misalignment increases but the transmittance decreases. In other words, in the connection between the transmitter and receiver of the communication module and the optical fiber, the positioning accuracy improves but the optical loss increases.

[0013] In order to solve the above-mentioned problems, an optical connection structure according to the present invention is an optical connection structure through which signal light propagates, and includes a first waveguide core, a second waveguide core, a first tapered waveguide core, and a second tapered waveguide core, the first tapered waveguide core and the second tapered waveguide core are made of a photocurable resin that has been photocured, an end face of the first waveguide core is disposed opposite an end face of the second waveguide core, and a base end of the first tapered waveguide core is disposed opposite an end face of the first waveguide core. a base end of the second tapered waveguide core connected to the end face of the second waveguide core; a tip end of the first tapered waveguide core connected to the tip end of the second tapered waveguide core; a diameter of the first tapered waveguide core increasing from the base end of the first tapered waveguide core toward the tip end of the first tapered waveguide core; and a diameter of the second tapered waveguide core increasing from the base end of the second tapered waveguide core toward the tip end of the second tapered waveguide core.

[0014] Furthermore, a manufacturing method of an optical connection structure according to the present invention is a manufacturing method of an optical connection structure in which one waveguide core and another waveguide core are optically connected, and includes the steps of: arranging an end face of the one waveguide core and an end face of the other waveguide core so that they face each other; then, arranging a photocurable resin between the end face of the one waveguide core and the end face of the other waveguide core; then, irradiating the photocurable resin from the end face of the one waveguide core with light that photocures the photocurable resin; and then, irradiating the photocurable resin from the end face of the other waveguide core with light that photocures the photocurable resin.

[0015] According to the present invention, it is possible to provide an optical connection structure that can reduce optical loss in optical connections between waveguides and improve tolerance for optical axis misalignment.

[0016] FIG. 1 is a schematic top view showing the configuration of an optical connection structure according to a first embodiment of the present invention. FIG. 2 is a schematic top view showing the configuration of an optical connection structure according to the first embodiment of the present invention. FIG. 3 is a diagram for explaining the effects of the optical connection structure according to the first embodiment of the present invention. FIG. 4 is a diagram for explaining a manufacturing method of an optical connection structure according to the first embodiment of the present invention. FIG. 5 is a flowchart for explaining a manufacturing method of an optical connection structure according to the first embodiment of the present invention. FIG. 6 is a schematic top view showing an example of the configuration of an optical connection structure according to the first embodiment of the present invention. FIG. 7 is a schematic top view showing the configuration of an optical connection structure according to a second embodiment of the present invention. FIG. 8 is a flowchart for explaining a manufacturing method of an optical connection structure according to the second embodiment of the present invention. FIG. 9 is a diagram for explaining a manufacturing method of an optical connection structure according to the second embodiment of the present invention. FIG. 10 is a diagram for explaining an example of a manufacturing method of an optical connection structure according to the second embodiment of the present invention. FIG. 11 is a schematic top view showing an example of the configuration of an optical connection structure according to the second embodiment of the present invention. FIG. 12 is a schematic top view showing the configuration of an optical connection structure according to a third embodiment of the present invention. FIG. 13A is a schematic top view showing an example of the configuration of an optical connection structure according to the third embodiment of the present invention. FIG. 13B is a diagram XIIIB-XIIIB' showing an example of the configuration of an optical connection structure according to the third embodiment of the present invention. FIG. 14 is a schematic top view showing an example of the configuration of an optical connection structure according to the third embodiment of the present invention. FIG. 15A is a schematic top view showing an example of the configuration of an optical connection structure according to the third embodiment of the present invention. FIG. 15B is a diagram XVB-XVB' showing an example of the configuration of an optical connection structure according to the third embodiment of the present invention. FIG. 16 is a side view showing an example of the configuration of an optical connection structure according to the third embodiment of the present invention.

[0017] First Embodiment An optical connection structure and a method for manufacturing the same according to a first embodiment of the present invention will be described with reference to FIGS.

[0018] <Configuration of optical connection structure> As shown in FIG. 1 , the optical connection structure 10 according to this embodiment includes a first waveguide 11, a second waveguide 12, and a tapered waveguide 13 formed between the first waveguide 11 and the second waveguide 12.

[0019] The first waveguide 11 includes a first core (hereinafter also referred to as a “first waveguide core”) 111 and a first clad (hereinafter also referred to as a “first waveguide clad”) 112 .

[0020] The second waveguide 12 includes a second core (hereinafter also referred to as a “second waveguide core”) 121 and a second clad 122 .

[0021] The end face of the first waveguide 11 and the end face of the second waveguide 12 are arranged to face each other.

[0022] The tapered waveguide 13 includes a first tapered waveguide core 131 , a second tapered waveguide core 132 , and a tapered waveguide clad 133 .

[0023] The first tapered waveguide core 131 and the second tapered waveguide core 132 are formed in the gap between the first waveguide 11 and the second waveguide 12. The base end of the first tapered waveguide core 131 is connected to the end face of the first waveguide core 111. The base end of the second tapered waveguide core 132 is connected to the end face of the second core. The tip of the first tapered waveguide core 131 is connected to the tip of the second tapered waveguide core 132. The core diameters of the first tapered waveguide core 131 and the second tapered waveguide core 132 increase from the base end to the tip.

[0024] The lengths of the first tapered waveguide core 131 and the second tapered waveguide core 132 are L1 and L2, respectively. The taper angle of the tapered waveguide cores 131 and 132 is θt. The distance between the end face of the first waveguide core 111 and the end face of the second waveguide core 121 is g. Although an example has been shown in which the first tapered waveguide core 131 and the second tapered waveguide core 132 have the same shape, the present invention is not limited to this and they may have different shapes.

[0025] The tapered waveguide cladding 133 is formed around the first tapered waveguide core 131 and the second tapered waveguide core 132. The refractive index of the tapered waveguide cladding 133 is lower than the refractive index of the tapered waveguide cores 131 and 132. The tapered waveguide cladding 133 may be air.

[0026] In the optical connection structure 10, the tapered waveguide 13 can increase the mode field diameter (MFD) of light propagating through the tapered waveguide cores 131 and 132. The MFD depends on the core diameter of the waveguide in which the light is confined. In the tapered waveguide 13, when light propagates through the tapered structure in the light propagation direction (x direction in the figure), the diameter of the waveguide core that confines the light gradually increases, so the MFD can be increased as the light propagates. As described above, increasing the MFD can increase the optical axis misalignment tolerance.

[0027] Furthermore, the core sizes at the tips of the first tapered waveguide core 131 and the second tapered waveguide core 132 are larger than the first waveguide core 111 and the second waveguide core 121. As a result, in the optical connection structure 10, the tapered waveguide 13 can expand the optical axis misalignment tolerance to be greater than or equal to the optical axis misalignment tolerance determined by the MFD of each of the first waveguide core 111 and the second waveguide core 121.

[0028] Furthermore, when there is no optical axis misalignment and light is converted adiabatically within the tapered waveguide (for example, when the taper angle is sufficiently small), the coupling efficiency of light between the first waveguide core 111 and the second waveguide core 121 depends on the difference in MFD at the tips of the first tapered waveguide core 131 and the second tapered waveguide core 132 connected to the first waveguide core 111 and the second waveguide core 121, respectively (the points in the tapered waveguide cores 131 and 132 where the core diameter is maximum).

[0029] 1 , when the diameters of the first tapered waveguide core 131 and the second tapered waveguide core 132 are the same and the refractive indices of the first tapered waveguide core 131 and the second tapered waveguide core 132 are the same, the MFDs at the tips of the tapered waveguide cores 131 and 132 are the same. As a result, the optical coupling efficiency between the first waveguide core 111 and the second waveguide core 121 in the optical connection structure 10 is 1.

[0030] Furthermore, by controlling the refractive indexes of the first tapered waveguide core 131 and the second tapered waveguide core 132, the refractive index of the tapered waveguide clad 133, and the diameters of the base and tip ends of the tapered waveguide cores 131 and 132 so that the MFDs between the first waveguide core 111 and the first tapered waveguide core 131 and / or between the second waveguide core 121 and the second tapered waveguide core 132 are consistent, it is possible to reduce optical loss in the optical connection structure 10.

[0031] In this way, in the optical connection structure 10, the first waveguide 11 and the second waveguide 12 can be optically connected with low optical loss, and the tolerance for optical axis misalignment can be improved.

[0032] <Effects> The effects of the optical connection structure 10 according to this embodiment will be described with reference to FIGS.

[0033] The coupling efficiency with respect to the optical axis misalignment in the optical connection structure 10 was calculated.

[0034] For the calculation, the "FDTD solution" of the analysis software "Ansys Lumerical" (ANSYS) was used.

[0035] The calculation domain was two-dimensional, and the structure used in the calculation was optically the same as the structure shown in Fig. 1. The parameters were: the width (y direction in the figure) of the first waveguide core 111 and the second waveguide core 121 was 10 µm; the refractive index of the first waveguide clad 112, the second waveguide clad 122, and the tapered waveguide clad 133 was 1.47; and the refractive index of the first waveguide core 111, the second waveguide core 121, and the tapered waveguide cores 131 and 132 was 1.5. The diameter of the base end of the first tapered waveguide core 131 and the second tapered waveguide core 132 was 10 µm, and the diameter of the tip end was 20 µm. The gap between the first waveguide 11 and the second waveguide 12 was set to 350 μm, and the length of each of the first tapered waveguide core 131 and the second tapered waveguide core 132 disposed in this gap was set to 175 μm.

[0036] The fundamental mode propagation mode in the first waveguide core obtained by calculation was set as the light source. The wavelength of the light source was set to 1.55 μm. The light was assumed to propagate from the first waveguide 11 to the second waveguide 12, and the coupling rate (coupling efficiency) of the propagating light to the fundamental mode in the second waveguide core 121 was calculated.

[0037] In the optical connection structure 10, an optical axis misalignment was set as shown in Fig. 2. The amount of optical axis misalignment d is the distance between the optical axis of the first waveguide core 111 and the optical axis of the second waveguide core 121. In this configuration, a discontinuous portion 135 caused by the optical axis misalignment is present at the connection portion of each tapered waveguide. The width of the exposed portion of the discontinuous portion 135 is d. Fig. 3 shows the calculation results of the change in the coupling efficiency of the propagating light with respect to the change in the amount of optical axis misalignment d.

[0038] When the optical axis misalignment varies from approximately -5 μm to +5 μm, the coupling efficiency varies from approximately -2.3 dB to approximately 0.3 dB. When there is no optical axis misalignment (zero), the coupling efficiency is approximately 0.3 dB. The 1 dB optical axis misalignment tolerance is between -3.7 μm and +3.7 μm. In this case, the optical axis misalignment between the first waveguide 11 and the second waveguide 12 is within 3.7 μm. This 1 dB optical axis misalignment tolerance value is greater than the 1 dB optical axis misalignment tolerance value of ±2.4 μm, which is determined by the MFD of the SSMF (the MFD of the first waveguide core 111 and the second waveguide core 121). In this way, the optical connection structure 10 allows for low optical loss connection between waveguides even when using SSMF. The optical loss of about 0.4 dB when the optical axis misalignment is zero can be reduced by optimizing the length of the tapered waveguide core, the shape of the base end of the tapered waveguide core, and the refractive index of the waveguide.

[0039] Similar calculations were also performed for a configuration in which the width of the first waveguide core 111 and the second waveguide core 121 was 3 μm (the MFD was approximately 3 to 4 μm in this case). As an example, the calculations were performed with the refractive index of the first waveguide clad 112, the second waveguide clad 122, and the tapered waveguide clad 133 set to 1.47, the refractive index of the first waveguide core 111, the second waveguide core 121, and the tapered waveguide cores 131 and 132 set to 1.5, the diameter of the base end of the first tapered waveguide core 131 and the second tapered waveguide core 132 set to 3 μm, the diameter of the tip end of the first tapered waveguide core 131 and the second tapered waveguide core 132 set to 20 μm, and the length of each of the first tapered waveguide and the second tapered waveguide set to 300 μm. As a result, it is possible to obtain an optical axis misalignment tolerance equivalent to that when the width of the first waveguide core 111 and the second waveguide core 121 is 10 μm.

[0040] The diameter of each of the base ends of the first tapered waveguide core 131 and the second tapered waveguide core 132 may be 1 μm to 10 μm, and the diameter of each of the tip ends may be 10 μm to 40 μm. The length of each of the tapered waveguide cores 131 and 132 may be 50 μm to 600 μm. The taper angle of each of the tapered waveguide cores 131 and 132 may be 1 degree to 30 degrees. The refractive index of each of the first tapered waveguide core 131 and the second tapered waveguide core 132 may be approximately 1.4 to 1.6.

[0041] According to this embodiment, in the optical connection structure, the first waveguide and the second waveguide can be optically connected with low optical loss, and the tolerance for optical axis misalignment can be improved.

[0042] <Method for Manufacturing Optical Connection Structure> A method for manufacturing the optical connection structure 10 according to this embodiment will be described below.

[0043] First, a case where SWWs (tapered waveguide cores) are simultaneously formed from both opposing waveguides will be described with reference to FIG.

[0044] The optical connection structure 10 can be manufactured based on the self-written waveguide (SWW) technology (see Non-Patent Document 1). In the SWW technology, a photo-curable resin is mainly used to connect the cores of the waveguides as follows.

[0045] First, a photocurable resin is dropped into the gap between two waveguides arranged opposite each other. Signal light for optical communication is emitted from the core end face of at least one of the waveguides.

[0046] Next, light for curing the photocurable resin (hereinafter referred to as "resin curing light") is irradiated from the core end face of one of the waveguides or from the core end faces of both waveguides. At this time, the photocurable resin is cured sequentially from the part where the intensity of the irradiated light (resin curing light) is high, so that the core of the SWW is formed sequentially from the core end face of each waveguide. As a result, the SWW is always formed on the core end face of the waveguide.

[0047] In particular, when resin curing light is irradiated from the core end faces of both waveguides, even if there is an optical axis misalignment between the cores of both waveguides, a SWW with a bend is formed to compensate for the misalignment, thereby realizing low-loss optical connection. In this case, since the SWW is formed sequentially from the part where the intensity of the resin curing light is high, it is desirable that the intensity of the resin curing light irradiated from the end faces of the two waveguides be approximately the same.

[0048] Finally, if necessary, the uncured portion of the photocurable resin after the SWW formation is removed, and then a cladding resin is dripped onto the removed portion and cured appropriately. This forms a cladding around the SWW core, completing the optical connection by the SWW. The wavelength of the resin curing light used to form the SWW is mainly in the wavelength range below visible light. Resin curing light in the wavelength range of near-infrared light may also be used.

[0049] When the optical field strength of the resin curing light is lower than a predetermined threshold and the light intensity distribution of the resin curing light is close to a Gaussian function, the core diameter of the resin curing light is maintained approximately constant and the SWW is formed. The photocurable resin is cured sequentially from the portion where the intensity of the resin curing light is high. When the intensity distribution of the resin curing light is close to a Gaussian distribution, the resin curing reaction is faster toward the center of the light intensity distribution. As a result, the tip of the SWW becomes lens-shaped. The resin curing light is focused at the tip of the lens-shaped SWW, causing the curing of the photocurable resin to progress. This curing of the photocurable resin is repeated to form the SWW, so the core diameter of the SWW is maintained approximately constant and the SWW is formed.

[0050] When forming the SWW using a resin curing light having an intensity sufficiently greater than that required to maintain a constant core diameter of the SWW, the SWW will have a shape in which the width or diameter increases from the base end to the tip end (a forward tapered shape). This allows two tapered waveguides to be formed by forming the SWW from each of the desired waveguide cores.

[0051] As an example of forming a SWW, after dropping a photocurable resin between two waveguide cores arranged opposite each other, if both waveguide cores are simultaneously irradiated with resin curing light under conditions that cause the SWW to tapered, the resin curing light emitted from the tip of the SWW formed from the end face of one waveguide core also contributes to the formation of the other SWW. As a result, the core 141 of the tapered waveguide 14 has a bend and has a structure that is continuous from the end face of one waveguide core to the end face of the other waveguide core, as shown in Figure 4.

[0052] In this way, when resin curing light is irradiated from both waveguide cores simultaneously to form a SWW, the tapered waveguide has a bent structure. In this bent tapered waveguide structure, multimode light is likely to occur in the guided signal light. Since multimode light is likely to be radiated to the outside at the bent portion, optical loss increases. As a result, the optical axis misalignment tolerance decreases.

[0053] Therefore, in the manufacturing method of the optical connection structure 10 according to the present embodiment, resin curing light is not irradiated from both waveguide cores simultaneously when forming the SWW. The manufacturing method of the optical connection structure 10 will be described in detail with reference to Fig. 5. Fig. 5 shows a flowchart for explaining the manufacturing method of the optical connection structure 10.

[0054] First, the first waveguide core and the second waveguide core are arranged to face each other (step S11).

[0055] Next, a photocurable resin is dropped between the first waveguide core and the second waveguide core (step S12).

[0056] Next, resin curing light is irradiated from one of the waveguide cores (for example, the first waveguide core 111) to form a SWW as one of the tapered waveguide cores (for example, the first tapered waveguide core 131) (step S13).

[0057] At this time, the SWW formation conditions, such as the intensity of the resin curing light, irradiation time, and photocurable resin, are set so that the SWW shape can convert the MFD with low loss and has a tapered shape that can achieve the desired optical axis misalignment tolerance.

[0058] For example, by setting the intensity of the resin curing light higher than the intensity of the resin curing light when forming the SWW while maintaining the core diameter of the SWW constant, it is possible to form a shape (a forward tapered shape) in which the width or diameter increases from the base end (the side where the resin curing light is incident) of the SWW to the tip. As the intensity of the resin curing light increases, the taper angle θ can be increased.

[0059] For example, the length of the tapered waveguide can be increased as the irradiation time of the resin curing light increases, and the taper angle θ can be controlled by the combination of the intensity and irradiation time of the resin curing light.

[0060] For example, it is desirable to use a material as the photocurable resin whose reaction stops immediately after the light irradiation is stopped, and an acrylic resin may be used.

[0061] Next, resin curing light is irradiated from the other waveguide core (e.g., the second waveguide core 121) to form a SWW as the other tapered waveguide core (e.g., the second tapered waveguide core 132) (step S14). At this time, the SWW is formed under predetermined conditions so that the shape of the SWW becomes a tapered shape that can achieve a desired optical axis misalignment tolerance.

[0062] After the tapered waveguide cores 131 and 132 of the optical connection structure 10 are fabricated, a tapered waveguide clad 133 may be formed around the tapered waveguide (SWW).

[0063] In this way, SWWs (tapered waveguide cores) are formed independently from the end faces of one waveguide core and the other waveguide core, respectively. As a result, the first tapered waveguide core (SWW) 131 and the second tapered waveguide core (SWW) 132 do not have a bent shape, as shown in Figure 2, and have discontinuous portions 135 at the tips of the respective tapered waveguides due to misalignment of the optical axes.

[0064] In a tapered waveguide core without a bent shape, signal light is mainly guided in single mode. Even if the signal light is guided in multimode, the absence of a bent portion suppresses light radiation to the outside. Thus, in the tapered waveguide 13 of the optical connection structure 10, the effects of radiation are suppressed compared to a structure with a bent shape, and excess loss is suppressed, thereby improving the optical axis misalignment tolerance.

[0065] According to this embodiment, it is possible to manufacture an optical connection structure that can optically connect the first waveguide and the second waveguide with low optical loss and improve the tolerance for optical axis misalignment.

[0066] 6, the tips of the first tapered waveguide core (SWW) 151 and the second tapered waveguide core (SWW) 152 may have a curved shape when viewed from above. This shape can increase the MFD and improve the optical axis misalignment tolerance.

[0067] Second Embodiment An optical connection structure and a manufacturing method thereof according to a second embodiment of the present invention will be described with reference to FIGS.

[0068] 7, the optical connection structure 20 according to this embodiment includes an insertion wall 24 between one tapered waveguide (e.g., the first tapered waveguide 13_1) and the other tapered waveguide (e.g., the second tapered waveguide 13_2). The first tapered waveguide 13_1 includes a first tapered waveguide core 131 and a first tapered waveguide clad 133. The second tapered waveguide 13_2 includes a second tapered waveguide core 132 and a second tapered waveguide clad 134. The other configurations are the same as those of the first embodiment.

[0069] In the optical connection structure 20, the resin curing light can be absorbed by the insertion wall 24, so that the influence of the resin curing light emitted when forming one tapered waveguide core (e.g., the first tapered waveguide core 131) on the formation of the other tapered waveguide core (e.g., the second tapered waveguide core 132) can be suppressed.

[0070] This allows one tapered waveguide core (SWW) and the other tapered waveguide core (SWW) to be formed independently even when the resin curing light is irradiated at the same time, thereby reducing the manufacturing process and shortening the time required to form the SWW.

[0071] Furthermore, by providing the insertion wall 24, one tapered waveguide core and the other tapered waveguide core are fixed (connected) to the first waveguide core 111 and the second waveguide core 121 at their base ends, respectively, and are also fixed (connected) to the insertion wall 24 at their tip ends, thereby improving the mechanical strength of the SWW.

[0072] A material that can absorb the resin curing light and is transparent to the signal light is used as the material of the insertion wall 24. Here, the signal light is light that propagates between the first waveguide core and the second waveguide core 121 and is used in the application field of a device having the first waveguide core 111 and the second waveguide core 121, and is, for example, light in the communication wavelength band.

[0073] The insertion wall 24 may be made of a glass material such as SiO2. The glass material is transparent in the communication wavelength band and absorbs visible light, particularly light in the wavelength band from short wavelength to ultraviolet. Since the resin curing light is in the short wavelength band from ultraviolet to visible light (500 nm or less), the resin curing light can be absorbed by the glass material.

[0074] A photocurable resin may be used as the material for the insertion wall 24. The photocurable resin may be the same as or different from the photocurable resin used to form the tapered waveguide. The photocurable resin insertion wall can be fabricated using a photo-3D printing device. The photo-3D printing device can fabricate with a manufacturing resolution of sub-micron accuracy by curing the photocurable resin through two-photon absorption. Photocurable resin absorbs short-wavelength light and is transparent in the communication wavelength band, so it meets the requirements for the insertion wall described above.

[0075] Alternatively, the insertion wall 24 may be made of a polyimide film.

[0076] The thickness of the insertion wall 24 must be such that it can sufficiently absorb the resin curing light used to form the SWW. It must also be such that it can sufficiently suppress diffraction loss when signal light propagates between the tip of one tapered waveguide core and the tip of the other tapered waveguide core. The thickness of the insertion wall 24 that satisfies these requirements depends on the absorption (wavelength) of the resin curing light in the photocurable resin, the signal light, and the MFD at the tip of the tapered waveguide core. For example, the thickness of the insertion wall 24 may be approximately several tens of μm to 100 μm.

[0077] When forming the insertion wall 24 using a photo 3D printing device, a structure that induces reflection of the resin curing light may be formed in the insertion wall 24 using sub-micron structural precision. For example, a structure that reflects in the wavelength band of the resin curing light, similar to a dielectric multilayer film mirror, may be formed. Alternatively, a structure that increases absorption of the resin curing light may be formed using the photo 3D printing device.

[0078] Furthermore, since the optical 3D printing device can form three-dimensional structures, it may also form a positioning structure that achieves fixed or passive alignment of a device having the first waveguide core 111 and the second waveguide core 121.

[0079] <Method of Manufacturing Optical Connection Structure> A method of manufacturing the optical connection structure 20 according to this embodiment will be described with reference to Figures 8 and 9. Figure 8 shows a flowchart for explaining the method of manufacturing the optical connection structure 20.

[0080] First, a device having a first waveguide core and a device having a second waveguide core 121 are positioned and arranged (step S21). At this time, the positioning accuracy between the waveguide cores may be determined based on the optical axis misalignment tolerance obtained by the tapered waveguide configuration at the time of design.

[0081] Next, the insertion wall 24 is disposed between the first waveguide core and the second waveguide core (step S22). The distance between the insertion wall 24 and the end face of the first waveguide core and the distance between the insertion wall 24 and the end face of the second waveguide core 121 are each determined within an error range of about ±10 to 20 μm.

[0082] Next, photocurable resin 230 is dropped between the insertion wall 24 and the end face of the first waveguide core 111, and between the insertion wall 24 and the end face of the second waveguide core 121 (FIG. 9, step S23). Surface tension may be used to hold the photocurable resin between the insertion wall 24 and the end faces of the respective waveguide cores 111, 121. Alternatively, a structure may be used in which grooves for holding the resin are provided, the respective waveguide cores are placed in the grooves, and the insertion wall 24 is placed in part of the grooves.

[0083] Next, resin curing light is simultaneously irradiated from both end faces of the first waveguide core 111 and the second waveguide core 121 to form a first tapered waveguide core (SWW) 131 and a second tapered waveguide core (SWW) 132 (step S24). The SWW formation conditions, such as the irradiation time and irradiation intensity of the resin curing light, are set so that a desired tapered waveguide can be formed.

[0084] In this manner, the optical connection structure 20 can be fabricated.

[0085] In this way, in the manufacturing method of the optical connection structure 20, by disposing the insertion wall 24 between one tapered waveguide 13_1 and the other tapered waveguide 13_2, even if they are simultaneously irradiated with resin curing light, the first tapered waveguide core (SWW) 131 and the second tapered waveguide core (SWW) 132 can be formed independently. This allows one manufacturing step to be reduced compared to the first embodiment, and shortens the time required to form the SWW.

[0086] After fabricating the tapered waveguide core of the optical connection structure 20, the uncured resin in the cladding region of the tapered waveguide (SWW) may be washed with a cleaning liquid such as acetone, and another resin may be dripped and cured. The resin used for the cladding of the tapered waveguide (SWW) is a material that has a refractive index that satisfies the function of the tapered waveguide as a waveguide and that is reliable after curing. Alternatively, a method of solidifying the cladding without washing the uncured resin may be used to form the cladding of the tapered waveguide (SWW).

[0087] When a photo 3D modeling device is used, a groove may be formed to fit the insertion wall 24. Also, a structure for holding the resin may be formed between the insertion wall 24 and the end face of the waveguide core.

[0088] Furthermore, when using a photo 3D printing device, the insertion wall 24 and the SWW may be formed using a single photocurable resin. Because the resin for photo 3D printing and the resin for forming the SWW are both photocurable resins, the same material may be used. In this case, each waveguide core is positioned, resin is dripped into the gap between the cores, and the insertion wall 24 and other components are fabricated using the photo 3D printing device. Then, resin-curing light is irradiated from each waveguide core to form the SWW. This reduces the number of processes compared to using multiple resins.

[0089] In the manufacturing method of the optical connection structure 20, a first resin 231 and a second resin 232 that cure at two different wavelengths may be used. Specifically, the resin 231 that cures at a wavelength λ1 is used to form one tapered waveguide core (e.g., the first tapered waveguide core 131), and the resin 232 that cures at a wavelength λ2 is used to form the other tapered waveguide core (e.g., the second tapered waveguide core 132). That is, the refractive index of one tapered waveguide core differs from the refractive index of the other tapered waveguide core. In this case, the first resin 231 has low sensitivity to the wavelength λ2, and the second resin 232 has low sensitivity to the wavelength λ1. This allows the optical connection structure 20 to be manufactured even if the insertion wall 24 absorbs less resin curing light than when a SWW is formed using a single photocurable resin. That is, a thin insertion wall 24 can be used in manufacturing the optical connection structure 20.

[0090] When manufacturing the optical connection structure 20, if the insertion wall 24 absorbs and blocks the resin curing light, the amount of absorption depends on (is proportional to) the thickness of the insertion wall 24. Therefore, in order to absorb light sufficiently, it is better for the insertion wall 24 to be thick. On the other hand, in the optical connection structure 20, the insertion wall 24 causes diffraction loss of the signal light. Therefore, in order to reduce the diffraction loss, it is better for the insertion wall 24 to be thin. As described above, determining the thickness of the insertion wall 24 requires a trade-off between the absorption of the resin curing light and the diffraction loss of the signal light.

[0091] On the other hand, the above-described method using the first resin 231 and the second resin 232 that are cured at two different wavelengths does not require absorption of the resin curing light in the insertion wall 24, and therefore does not require a trade-off between absorption of the resin curing light and diffraction loss of the signal light in determining the thickness of the insertion wall 24, making it possible to use a thin insertion wall 24. In this way, by using the first resin 231 and the second resin 232 that are cured at two different wavelengths, it is possible to suppress the influence of the formation of one SWW on the formation of the other SWW, and to reduce the diffraction loss of the signal light.

[0092] The method for manufacturing the optical connection structure 20 using the first resin 231 and the second resin 232 that are cured at two different wavelengths will be described in detail with reference to FIG.

[0093] First, similarly to the manufacturing method of the optical connection structure 20 described above, the waveguide cores 111 and 121 and the insertion wall 24 are arranged.

[0094] 10, a first resin 231 and a second resin 232 are filled between the insertion wall 24 and the end faces of the respective waveguide cores 111, 121. The first resin 231 is a resin that can be cured with a resin curing light of λ1, and the second resin 232 is a resin that can be cured with a resin curing light of λ2.

[0095] Next, resin curing light of λ1 is emitted from the first waveguide core 111, and resin curing light of λ2 is emitted from the second waveguide core 121.

[0096] In this manner, the optical connection structure 20 shown in FIG. 6 can be manufactured.

[0097] Furthermore, when using a photo 3D printing device, if the insertion wall 24 is thin relative to its height (z direction in the drawing), the insertion wall 24 may collapse under its own weight. Therefore, as shown in Fig. 11, a structure 25 for supporting the insertion wall 24 may be provided in a location that does not affect the path of light. This improves the mechanical stability of the insertion wall 24.

[0098] Third Embodiment An optical connection structure and a manufacturing method thereof according to a third embodiment of the present invention will be described with reference to FIGS.

[0099] 12 , in the optical connection structure 30 according to this embodiment, the size of the first waveguide core 311 is different from the size of the second waveguide core 321. Accordingly, the shapes of the tapered waveguide cores 331 and 332 are different. The other configurations are the same as those in the second embodiment.

[0100] In conventional optical connection structures, since different core sizes have different MFDs, even if alignment (positioning for optical connection) is performed with high precision, loss occurs due to the difference in MFD.

[0101] 12, the optical connection structure 30 according to this embodiment can correct the MFD and increase the optical axis misalignment tolerance by using the first tapered waveguide core 331 and the second tapered waveguide core 332. For example, it is possible to connect a general-purpose optical fiber (MFD=10 μm) and a silicon photonics chip (MFD=3 μm) with low loss and increase the optical axis misalignment tolerance (described later).

[0102] When the MFD of the second waveguide core 321 is smaller than the MFD of the first waveguide core 311, it is desirable that the second tapered waveguide core 332 connected to the second waveguide core 321 be longer than the first tapered waveguide core 331 connected to the first waveguide core 311. This is because, when the MFD is adiabatically converted in the tapered structure, the length of the tapered waveguide in the light propagation direction (x direction in the figure) increases as the amount of change in MFD increases.

[0103] When forming a SWW by simultaneously irradiating resin curing light from both waveguide cores (bidirectional simultaneous irradiation) and forming a tapered waveguide (SWW) between waveguide cores of different MFDs, it is difficult to increase the optical axis misalignment tolerance. This is because, as described above, the tapered structure formed by bidirectional simultaneous irradiation of resin curing light has a curved structure, and the radiation loss of this structure is higher than that of a waveguide without a curved structure.

[0104] As described above, it is difficult to convert the MFD and increase the optical axis misalignment tolerance by simultaneously irradiating the resin curing light in both directions.

[0105] According to this embodiment, by forming SWWs independently as the first tapered waveguide and the second tapered waveguide and realizing connection using two tapered waveguides, it is possible to reduce optical loss due to the difference in MFD and to increase the optical axis misalignment tolerance.

[0106] As an example of the optical connection structure 30, an optical connection structure between a silicon phononix (SiPh) chip 31 and an optical fiber 32 will be described. Fig. 13A is a top view of the optical connection structure 30 between the SiPh chip 31 and the optical fiber 32. Fig. 13B shows a cross-sectional view of the optical connection structure 30 taken along line XIIIB-XIIIB'.

[0107] The optical connection structure 30 includes, for example, a SiPh chip 31 , an optical fiber 32 , and a tapered waveguide 33 .

[0108] The SiPh chip 31 has a SiPh waveguide core 311 on a substrate 310. A groove 313 adjacent to the SiPh waveguide core 311 is formed in the substrate 310. The surface around the groove 313 is covered with SiO ２ is formed.

[0109] The optical fiber 32 has a fiber core 321. The optical fiber 32 is placed in the groove 313 of the substrate 310 with its end face facing the end face of the SiPh waveguide core 311.

[0110] The tapered waveguide 33 includes a first tapered waveguide core 331 and a second tapered waveguide core 332. The tapered waveguide 33 has a configuration in which the first tapered waveguide core 331 and the second tapered waveguide core 332 are asymmetrically arranged, thereby compensating for the MFD difference between the SiPh chip 31 and the optical fiber 32 and enabling low-loss optical connection between the SiPh chip 31 and the optical fiber 32.

[0111] The optical fiber 32 is disposed in a groove 313 formed on a substrate 310 of the SiPh 31 .

[0112] The groove 313 in which the optical fiber 32 is disposed may be a V-groove fabricated by processing a silicon substrate with wet etching. Because the V-groove is anisotropically etched, the depth direction of the V-groove can be determined with high precision. This allows for the positioning precision (±1 μm precision) required for low-loss optical connections. However, this places a heavy burden on the wafer process, such as the need to form a high-quality protective film to prevent other circuit elements from being etched during wet etching.

[0113] The groove 313 in which the optical fiber 32 is disposed may be a U-groove fabricated by dry etching. The U-groove 313 has a U-shaped cross section and a curved bottom. Alternatively, the U-groove 313 may have a flat bottom and a curved bottom ridge. The groove 313 may also have a rectangular cross section. While a U-groove can reduce the process load, it is difficult to process with high precision and to position with high precision, making it difficult to use it as a positioning structure in an optical connection structure. On the other hand, in the optical connection structure 30 according to this embodiment, the optical axis misalignment tolerance between the SiPh chip 31 and the optical fiber 32 can be increased, so a U-groove structure can be used for the groove 313 in which the optical fiber 32 is disposed, thereby reducing the process load.

[0114] <Method for Manufacturing Optical Connection Structure> A method for manufacturing the optical connection structure 30 according to this embodiment will be described below.

[0115] First, the SiPh 31 is fabricated by a wafer process, and a U-shaped groove 313 is formed in the substrate 310 .

[0116] Next, the optical fiber 32 is placed in the U-groove 313, and a photocurable resin is dropped into the U-groove 313. When placing the optical fiber 32, a lid may be used to press the optical fiber 32 from above, or the lid may be bonded in the optical connection process. Alternatively, the optical fiber 32 may be fixed to the U-groove 313 with an adhesive.

[0117] Next, similarly to the first embodiment, a SWW is formed as a first tapered waveguide core 331 and a second tapered waveguide core 332. At this time, the optical fiber 32 may be bonded to the U-groove 313 by using a photocurable resin for the SWW that has an adhesive function.

[0118] Here, an example has been shown in which a U-groove is used as the groove 313 in which the optical fiber 32 is arranged, but a V-groove may also be used.

[0119] 14, the U-groove 313 may be formed by a wafer process so that the width of the region where the optical fiber 32 is disposed is wider than the width of the region where the tapered waveguide is formed. That is, the U-groove 313 may have a step 314 in the width direction (y direction in the drawing) at the boundary between the region where the optical fiber 32 is disposed and the region where the tapered waveguide is formed.

[0120] In the optical connection structure 30, it is important to control the length of the tapered structure for adiabatically converting the MFD, as well as the distance between the waveguide cores to be optically connected. In the optical connection structure 30, by forming a step 314 in the width direction, the position of the optical fiber 32 can be defined, and the distance between the optical fiber 32 and the SiPh chip 31 can be determined with wafer process precision. In addition, by fabricating the step 314 during processing, it is also possible to easily prepare a groove for arranging the insertion wall.

[0121] In the optical connection structure 30, as shown in FIGS. 15A and 15B , by disposing the insertion wall 34 between the first tapered waveguide core 331 and the second tapered waveguide core 332, the mechanical stability of the tapered waveguide (SWW) can be improved. A groove (mating groove) for mating the insertion wall 34 may be formed by dry etching or dicing to form the U-groove 313 described above. This allows the insertion wall 34 to be easily positioned and fixed, improving workability. In this case, as in the second embodiment, the first tapered waveguide core (SWW) 331 and the second tapered waveguide core (SWW) 332 may be formed by simultaneously irradiating the resin curing light from both end faces of the first waveguide core 311 and the second waveguide core 321.

[0122] In this embodiment, as shown in FIG. 16, a cladding resin 333 may be formed around the tapered waveguide cores 331 and 332 .

[0123] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration of the optical connection structure and the manufacturing method thereof are shown, but the present invention is not limited to these examples. Any material may be used as long as it can exhibit the functions and effects of the optical connection structure and the manufacturing method thereof.

[0124] It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0125] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0126] (Supplementary Note 1) An optical connection structure through which signal light propagates, comprising a first waveguide core, a second waveguide core, a first tapered waveguide core, and a second tapered waveguide core, wherein the first tapered waveguide core and the second tapered waveguide core are made of a photocurable resin that has been photocured, an end face of the first waveguide core is disposed opposite an end face of the second waveguide core, a base end of the first tapered waveguide core is connected to the end face of the first waveguide core, and the second tapered waveguide core is connected to the end face of the first waveguide core. a base end of the tapered waveguide core connected to an end face of the second waveguide core, a tip end of the first tapered waveguide core connected to a tip end of the second tapered waveguide core, a diameter of the first tapered waveguide core increasing from the base end of the first tapered waveguide core toward the tip end of the first tapered waveguide core, and a diameter of the second tapered waveguide core increasing from the base end of the second tapered waveguide core toward the tip end of the second tapered waveguide core.

[0127] (Appendix 2) An optical connection structure as described in Appendix 1, further comprising an insertion wall between the tip of the first tapered waveguide core and the tip of the second tapered waveguide core, the insertion wall absorbing the light that photo-cures the photo-curable resin and transmitting the signal light.

[0128] (Supplementary Note 3) The optical connection structure described in Supplementary Note 1 or Supplementary Note 2, wherein a mode field diameter of the second waveguide core is smaller than a mode field diameter of the first waveguide core, and the second tapered waveguide core is longer than the first tapered waveguide core.

[0129] (Appendix 4) A method for manufacturing an optical connection structure in which one waveguide core and another waveguide core are optically connected, the method comprising the steps of: arranging an end face of the one waveguide core and an end face of the other waveguide core so as to face each other; then, arranging a photocurable resin between the end face of the one waveguide core and the end face of the other waveguide core; then, irradiating the photocurable resin from the end face of the one waveguide core with light that photocures the photocurable resin; and then, irradiating the photocurable resin from the end face of the other waveguide core with light that photocures the photocurable resin.

[0130] (Supplementary Note 5) The optical connection structure according to Supplementary Note 2, wherein the refractive index of the first tapered waveguide core is different from the refractive index of the second tapered waveguide core.

[0131] (Appendix 6) An optical connection structure according to Appendix 3, comprising a substrate and a groove disposed in the substrate, the first waveguide core being disposed on the substrate, the groove being disposed adjacent to the first waveguide core, the second waveguide core being a core of an optical fiber, and the optical fiber being disposed in the groove.

[0132] (Supplementary Note 7) An optical connection structure described in any one of Supplementary Notes 1 to 3, Supplementary Notes 5, and 6, wherein the distance between the optical axis of the first waveguide core and the optical axis of the second waveguide core is greater than 0 and not greater than 3.7 μm.

[0133] The present invention relates to an optical connection structure, and can be applied to optical communication devices and optical communication systems.

[0134] 10 Optical connection structure 111 First waveguide core 121 Second waveguide core 131 First tapered waveguide core 132 Second tapered waveguide core

Claims

1. An optical connection structure through which signal light is propagated, comprising: a first waveguide core; a second waveguide core; a first tapered waveguide core; and a second tapered waveguide core; the first tapered waveguide core and the second tapered waveguide core are made of photocurable resin; an end face of the first waveguide core is disposed opposite an end face of the second waveguide core; a base end of the first tapered waveguide core is connected to the end face of the first waveguide core; a base end of the second tapered waveguide core is connected to the end face of the second waveguide core; a tip end of the first tapered waveguide core is connected to a tip end of the second tapered waveguide core; the diameter of the first tapered waveguide core increases from the base end of the first tapered waveguide core toward the tip end of the first tapered waveguide core; An optical connection structure in which the diameter of the second tapered waveguide core increases from the base end of the second tapered waveguide core toward the tip end of the second tapered waveguide core.

2. The optical connection structure according to claim 1, further comprising an insertion wall between the tip of the first tapered waveguide core and the tip of the second tapered waveguide core, said insertion wall absorbing the light that photo-cures the photo-curable resin and transmitting the signal light.

3. An optical connection structure according to claim 1 or claim 2, wherein the mode field diameter of the second waveguide core is smaller than the mode field diameter of the first waveguide core, and the second tapered waveguide core is longer than the first tapered waveguide core.

4. A method for manufacturing an optical connection structure in which one waveguide core and another waveguide core are optically connected, comprising the steps of: arranging an end face of one waveguide core and an end face of the other waveguide core so that they face each other; then, arranging a photocurable resin between the end face of one waveguide core and the end face of the other waveguide core; then, irradiating the photocurable resin from the end face of the one waveguide core with light that photocures the photocurable resin; and then, irradiating the photocurable resin from the end face of the other waveguide core with light that photocures the photocurable resin.

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