Optical element, optical integrated element, and method for manufacturing an optical element

Abstract

This optical element (10) connects to another optical element (10_2) through a self-written waveguide (16), the optical element comprising, in the following order: a substrate (11); first cladding (12); a waveguide core (13) which has a higher refractive index than the refractive index of the first cladding (12), and through which signal light and resin curing light propagate; and second cladding (14) having a lower refractive index than the refractive index of the waveguide core (13), wherein a tip (131) of the waveguide core (13) on the side connecting to the self-written waveguide (16) is disposed at a position separated from an end face (141) of the second cladding (14) such that the mode field diameter of the signal light and the mode field diameter of the resin curing light are the same at the end face (141) of the second cladding (14), and the second cladding (14) is disposed between the tip (131) of the waveguide core (13) on the side connecting to the self-written waveguide (16) and the end face (141) of the second cladding (14).　The foregoing makes it possible to provide an optical element that can reduce connection loss with a self-written waveguide for signal light.

Description

[Technical Field]

[0001] The present invention relates to an optical element for connecting optical elements, an optical integrated element, and a method for manufacturing optical elements. [Background technology]

[0002] With the advancement of optical communication networks, there is a growing demand for more sophisticated and cost-effective optical communication devices. Optical communication devices require electrical elements such as drivers, switches, and electrical amplification circuits, as well as optical elements such as semiconductor lasers, optical switches, and optical fibers.

[0003] In the optical connection process, where each optical element is discretely connected, precise positioning between the optical elements is crucial for achieving low-loss optical connections. Therefore, even in commonly used optical connectors, high-precision components are employed that minimize the optical axis misalignment between waveguide cores to less than 1 μm. Thus, in manufacturing optical communication devices, designs and precision components that consider strict tolerances are essential.

[0004] In particular, Silicon Photonics (SiPh) face challenges in positioning accuracy during optical packaging. SiPh is an optical device with a semiconductor material core, enabling not only the fabrication of ultra-small and cost-effective optical circuits, but also high-density integration with electrical circuit elements.

[0005] However, in SiPh, the positioning accuracy and tight tolerances required during connection are greater than those of conventional silica-based core devices such as PLCs (Planar Lightwave Circuits), which increases the process load for optical connection. This is because the smaller the mode field diameter (MFD), the stricter the tolerance requirements for optical connection. Therefore, optical connection of SiPh, a semiconductor-based optical circuit device with a minute MFD, requires more precise positioning technology.

[0006] On the other hand, increasing the MFD size can alleviate the positioning accuracy requirements. However, in SiPh, the film thickness of each layer during manufacturing is constrained, and high losses occur due to the roughness of the waveguide sidewalls caused by the high refractive index unique to semiconductor waveguides. Therefore, it is difficult to obtain an MFD with low loss and high yield comparable to that of general optical fibers, compared to optical elements such as conventional PLCs.

[0007] Therefore, a method is used for low-loss optical connections to convert the MFD of the optical element (chip) to a smaller MFD of about 4 μm, compared to the conventional MFD of about 10 μm of optical fibers. However, when using this method, because the MFD is small, high positioning accuracy of the submicron level is required, which makes the positioning accuracy during optical connection and the tolerances required for optical components stricter.

[0008] As a technique that can alleviate the positioning accuracy required for this connection, a self-written waveguide (hereinafter referred to as "SWW") has been disclosed (Non-Patent Document 1).

[0009] This technology is an optical connection technology using a photocurable resin, and can connect waveguide cores as follows. Here, light used as signal light for optical communication (hereinafter referred to as "signal light") is emitted from at least one of the waveguide core end faces.

[0010] In the formation of SWWs, first, a photocurable resin is dropped into the gap between the waveguide cores.

[0011] Next, resin curing light, which is light used to cure the photocurable resin, is irradiated from both or one of the waveguide cores. At this time, due to the property of the photocurable resin that it cures sequentially from areas with high light intensity, SWW cores (hereinafter referred to as "SWW cores") are formed sequentially from the end faces of each waveguide core. As a result, SWW cores are formed on the end faces of the waveguide cores.

[0012] Furthermore, since the SWW core is formed according to the propagation path of the resin-cured light, even if an optical axis misalignment occurs between waveguide cores, an S-shaped SWW core is formed to compensate for the optical axis misalignment, enabling low-loss optical connection.

[0013] Finally, if necessary, any uncured portions of the photocurable resin are removed by washing, etc. Then, cladding resin is dripped onto the removed area (around the SWW core) and cured as appropriate to form the SWW cladding (hereinafter referred to as "SWW cladding"), and the connection using SWW is completed.

[0014] Here, the wavelength of the resin curing light used to form SWW is mostly in the wavelength range below visible light.

[0015] To form SWW with a constant core diameter, it is necessary to lower the electric field intensity of the resin curing light below a predetermined threshold and make the light intensity distribution of the resin curing light close to a Gaussian function.

[0016] In detail, since photocurable resins harden from areas with high intensity of resin-curing light, if the intensity distribution of the resin-curing light is close to a Gaussian distribution, the resin-curing reaction proceeds rapidly in the center of that distribution. As a result, the tip of the SWW becomes lens-shaped. This lens-shaped tip of the SWW focuses the resin-curing light emitted from the tip of the SWW, curing the resin. Since the SWW is formed by the repetition of this phenomenon, the SWW is formed while maintaining its core diameter approximately constant by resin-curing light with an intensity distribution close to a Gaussian function (Non-Patent Literature 1).

[0017] Furthermore, increasing the intensity of the resin curing light causes the resin curing rate (= monomer polymerization rate) to saturate at a certain intensity. When this saturation occurs across the entire beam cross-section, the polymerization rate becomes almost constant across the beam cross-sectional area. As a result, the tip of the SWW does not become lens-shaped, and a tapered SWW is formed in which the core diameter of the SWW gradually increases with respect to the propagation direction of the resin curing light. Therefore, in order to form an SWW with a constant core diameter, the intensity of the resin curing light must be lower than a predetermined threshold that depends on the resin.

[0018] The SWW technology has an axial misalignment compensation effect and can achieve low-loss connection regardless of the gap between cores or the optical axis misalignment, which are the causes of connection loss between cores. Therefore, the optical connection technology using SWW can relax the tolerance requirements in optical connection and achieve simple optical integration and high-yield and low-loss implementation.

[0019] SWW is formed on the SiPh chip end face by resin-cured light (visible light) using a known specific waveguide structure. At this time, the waveguide structure needs to be transparent to visible light in the wavelength band of the resin-cured light and light in the long wavelength band of the communication wavelength band. Here, materials such as SiN and SiON are transparent to light from visible light to the communication wavelength band, so they are used for the waveguide structure for SWW.

[0020] As shown in FIGS. 10A and 10B, for a conventional optical element 40 for forming SWW, a lower cladding 42 and a waveguide core 43 are sequentially formed on an SOI (Silicon-on-insulator) substrate (not shown), and the waveguide core 43 is covered by an upper cladding 44. Here, the upper cladding 44 and the lower cladding 42 are made of silicon oxide, and the waveguide core 43 is made of SiN. The waveguide core 43 may be made of SiON.

[0021] The width of the waveguide core 43 decreases toward the end of the optical element 40 (in the direction of arrow x in FIG. 10A), and has a function of expanding the MFD as a SSC (Spot-size converter). Thereby, the MFD of the end face of the optical element 40 can be expanded according to another optical element (not shown) to be connected, and the optical connection loss between the optical element 40 and another optical element can be reduced.

Prior Art Documents

Non-Patent Documents

[0022]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0023] However, when forming the SWW using the conventional optical element 40, there is a problem that connection loss occurs when the signal light propagates through the boundary between the end face of the optical element 40 and the SWW. Details will be described below.

[0024] Figures 11A and B show the calculation results of the modes of the signal light and the resin curing light in the conventional optical element. The x-axis represents the light propagation direction (arrow x direction in Figure 10A), and the y-axis represents the direction perpendicular to the light propagation direction (arrow y direction in Figure 10A). Here, in Figures 11A and B, the waveguide structure 431 used in the calculation is shown by a thin solid line.

[0025] The calculation was performed for a two-dimensional waveguide structure by the FDTD method (product name: "ANSYS Lumerical FDTD").

[0026] Also, the waveguide structure is composed of a tapered SiN. The width of one end (base end) is 800 nm, the width of the other end (tip) is 100 nm, and the length of the tapered structure is 350 μm. The parts other than the waveguide structure were assumed to be composed of silicon oxide.

[0027] Also, in the structure used for the calculation, the base end of the tapered structure has a waveguide with a constant width (width 800 nm) and a length of 10 μm, and the tip has a waveguide with a constant width (width 100 nm) and a length of 20 μm. In this constant-width waveguide, the signal light and the resin curing light propagate without changing the MFD.

[0028] [[ID=,27]]Also, the light source was placed on the central axis of the waveguide structure, at a position 1 μm inside the waveguide from the base end of the waveguide structure (position x = 1 μm, y = 0 μm in the coordinates of Figure 11A), and the calculation was performed assuming that the light emitted from the light source propagates in the fundamental propagation mode with respect to the cross section of the waveguide.

[0029] Also, the wavelength of the signal light was set to 1550 nm, and the wavelength of the resin curing light was set to 532 nm.

[0030] In the case of signal light, as shown in Figure 11A, the MFD gradually expands as it propagates through the waveguide and leaks out of the waveguide.

[0031] On the other hand, the resin curing light is confined throughout the entire waveguide, as shown in Figure 11B. This is because the wavelength of the resin curing light is shorter than that of the signal light.

[0032] In conventional optical elements, for signal light (long-wavelength light), the waveguide at the tip of a tapered SSC is narrowed, allowing the signal light to gradually leak out of the waveguide and expanding the MFD (Multi-Function Display). In this case, the core size of the waveguide at the tapered tip is smaller than the core size in which the signal light can exist as a propagation mode within the waveguide.

[0033] On the other hand, resin curing light (short-wavelength light) is confined as a propagation mode within the core, even in smaller cores. As a result, as shown in Figure 11B, the resin curing light propagates within the waveguide without leaking out of the core in a waveguide of a size that functions as a SSC.

[0034] Thus, when the resin curing light propagates through the waveguide of the optical element, curing occurs from the areas with higher intensity of the resin curing light, forming an SWW. As shown in Figure 12, an SWW core 461 with a width approximately the same as the width of the tapered waveguide core 43 is formed on the end face of the optical element 40. Subsequently, an SWW cladding 462 is formed around the SWW core 461.

[0035] On the other hand, as shown in Figure 11A, the signal light has an expanded MFD due to its tapered structure, resulting in an MFD larger than the width of the waveguide core. As a result, loss occurs in the signal light propagating within the optical element when it is connected to the SWW.

[0036] Typically, in the case of single-mode waveguides such as SiPh, the connection loss of light transitioning between optically different waveguides is determined by the difference in the MFD (Multi-Function Diameter) of the propagation modes of each waveguide. While the MFD is slightly affected by the refractive index difference between the waveguide core and cladding, it is generally of a similar magnitude to that of the waveguide core during propagation.

[0037] In SWW46, as shown in Figure 12, the MFD of the propagation mode of the signal light propagating through the SWW core 461 is approximately equal to the diameter of the SWW core 461. On the other hand, the MFD of the signal light at the end face of the optical element 40 is greater than that of the waveguide core 43. Thus, because the MFD of the signal light at the SWW core 461 and the MFD at the waveguide core 43 are different, connection losses occur between the respective waveguides.

[0038] As described above, when an SWW is formed using visible light in an optical element having an SSC where the waveguide narrows towards the end face of the conventional optical element, connection loss occurs due to the difference between visible light and signal light. As a result, optical communication devices that use conventional optical elements to form an SWW and connect them optically have the problem of connection loss. [Means for solving the problem]

[0039] To solve the problems described above, the optical element according to the present invention is combined with other optical elements. , in photocurable resins, the part that hardens upon irradiation with resin-curing light. Connected via self-forming waveguides The device comprises, in order, a substrate, a first cladding, a waveguide core having a refractive index higher than that of the first cladding and through which signal light and resin curing light propagate, and a second cladding having a refractive index lower than that of the waveguide core. It is an optical element ,before The tip of the waveguide core that connects to the self-forming waveguide has a mode field diameter of the signal light at the end face of the second cladding. The aforementioned The second cladding is positioned at a distance from the end face of the second cladding such that its mode field diameter is approximately the same as that of the resin curing light, and is characterized in that the second cladding is positioned between the tip of the waveguide core that connects to the self-forming waveguide and the end face of the second cladding.

[0040] Furthermore, the method for manufacturing an optical element according to the present invention is compatible with other optical elements. , in photocurable resins, the part that hardens upon irradiation with resin-curing light. Connected via a self-forming waveguide, the substrate, the first cladding, and the signal light having a refractive index higher than that of the first cladding. The aforementionedA method for manufacturing an optical element comprising a waveguide core through which resin-cured light propagates, and a second cladding having a refractive index lower than that of the waveguide core, comprising the steps of: determining the structures of the waveguide core, the first cladding, and the second cladding, and determining the wavelengths of the signal light and the resin-cured light; calculating the mode field diameters of the signal light and the resin-cured light propagating through and emitting from the waveguide core in the structure; determining the position of the end face of the second cladding at which the mode field diameters of the signal light and the resin-cured light emitting from the waveguide core are approximately the same; depositing the material of the first cladding and the material of the waveguide core in order on the substrate; processing the material of the waveguide core into the waveguide core based on the structure and the position of the end face of the second cladding; and forming the second cladding so as to cover the waveguide core. [Effects of the Invention]

[0041] According to the present invention, it is possible to provide an optical element that can reduce connection losses with a self-forming waveguide (SWW) of signal light. [Brief explanation of the drawing]

[0042] [Figure 1A] Figure 1A is a top-view schematic diagram showing the configuration of an optical element according to the first embodiment of the present invention. [Figure 1B] Figure 1B is a schematic cross-sectional diagram of the IB-IB' section showing the configuration of the optical element according to the first embodiment of the present invention. [Figure 1C] Figure 1C is a schematic cross-sectional diagram of an IC-IC' showing the configuration of an optical element according to the first embodiment of the present invention. [Figure 2] Figure 2 is a top-view schematic diagram showing an example of the configuration of an optical element according to the first embodiment of the present invention. [Figure 3A] Figure 3A is a top-view schematic diagram showing the configuration of an optical integrated element according to the first embodiment of the present invention. [Figure 3B] Figure 3B is a schematic cross-sectional diagram of IIIB-IIIB' showing the configuration of an optical integrated element according to the first embodiment of the present invention. [Figure 4A] Figure 4A is a schematic diagram of a waveguide structure illustrating the mode field diameter (MFD) of the signal light and resin curing light propagating through the optical element according to the first embodiment of the present invention. [Figure 4B] Figure 4B is a diagram illustrating the mode field diameter (MFD) of the signal light and resin curing light propagating through the optical element according to the first embodiment of the present invention. [Figure 4C] Figure 4C is an enlarged view illustrating the mode field diameter (MFD) of the signal light and resin curing light propagating through the optical element according to the first embodiment of the present invention. [Figure 5] Figure 5 is a flowchart illustrating the method for manufacturing an optical element according to the first embodiment of the present invention. [Figure 6A] Figure 6A is a top-view schematic diagram showing the configuration of an optical element according to a second embodiment of the present invention. [Figure 6B] Figure 6B is a schematic cross-sectional view of VIB-VIB' showing the configuration of an optical element according to a second embodiment of the present invention. [Figure 7A] Figure 7A is a top-view schematic diagram showing the configuration of an optical integrated element according to a second embodiment of the present invention. [Figure 7B] Figure 7B is a schematic cross-sectional diagram of VIIB-VIIB' showing the configuration of an optical integrated element according to a second embodiment of the present invention. [Figure 8] Figure 8 is a top-view schematic diagram showing the configuration of an optical element and a self-formed waveguide according to a third embodiment of the present invention. [Figure 9] Figure 9 is a schematic top view showing the configuration of a mode filter in an optical element according to a third embodiment of the present invention. [Figure 10A] Figure 10A is a top-view schematic diagram showing the configuration of a conventional optical element. [Figure 10B] Figure 10B is a schematic XB-XB' cross-sectional diagram showing the configuration of a conventional optical element. [Figure 11A] Figure 11A is a diagram illustrating the light intensity distribution of signal light in a conventional optical device. [Figure 11B]Figure 11B is a diagram illustrating the light intensity distribution of resin curing light in a conventional optical device. [Figure 12] Figure 12 is a top-view schematic diagram showing the configuration of a conventional optical element and a self-formed waveguide. [Modes for carrying out the invention]

[0043] <First Embodiment> An optical element according to the first embodiment of the present invention will be described with reference to Figures 1 to 5B.

[0044] <Configuration of optical elements> As shown in Figures 1A to C, the optical element according to this embodiment comprises, in order, a substrate 11, a first cladding 12, a waveguide core 13, and a second cladding 14.

[0045] The substrate 11 is a Si substrate.

[0046] The first cladding layer 12 is silicon oxide (SiO2).

[0047] The waveguide core 13 is made of silicon nitride and is placed on the first cladding 12. The waveguide core 13 has a tapered shape that narrows towards the tip 131 of the waveguide core 13 (the tip on which the self-forming waveguide is formed). Here, for example, the length of the waveguide core 13 is 350 μm, and the width varies from 800 nm to 100 nm. Alternatively, the waveguide core 13 may be made of silicon nitride.

[0048] The second cladding 14 is silicon oxide and is positioned to cover the waveguide core 13.

[0049] The waveguide core 13 is not positioned near the end face 141 of the second cladding 14. That is, there is a gap (hereinafter referred to as the "MFD control gap") 15 between the end face 131 of the waveguide core 13 and the end face 141 of the second cladding 14, and the second cladding 14 is positioned in this gap.

[0050] In this embodiment, an example is shown in which the waveguide core 13 has a tapered shape, but it is not limited to this. The waveguide core 13 may have a waveguide 132 of a constant width at its tip 131. For example, as shown in Figure 2, the waveguide core 13 may have a shape of a constant width on the tip 131 side of the waveguide core 133 from the dotted line 133 in the figure, and a tapered shape on the opposite side. In this case, the waveguide 132 of the waveguide core 13 of a constant width propagates without changing the MFD.

[0051] <Configuration of an optical integrated device> In the optical integrated element 1 according to this embodiment, as shown in Figures 3A and 3B, the optical element 10 is connected to other optical elements 10_2 via SWW16.

[0052] SWW16 has an SWW cladding 162 around an SWW core 161.

[0053] Other optical elements 10_2 include waveguide elements and optical fibers, and for example, comprises a substrate 11_2, a first cladding 12_2, a waveguide core 13_2, and a second cladding 14_2.

[0054] Light propagating through the waveguide core 13 of the optical element 10 is optically coupled with the waveguide core 13_2 of another optical element 10_2 via the SWW core 161.

[0055] Next, the MFD control gap 15 in the optical element according to this embodiment will be explained based on the calculation results with reference to Figures 4A to C.

[0056] Figure 4A shows a schematic diagram of the waveguide structure used in the calculations.

[0057] The waveguide (shaded area in the figure) is made of SiN, and the waveguide at the base end has a constant width (width 800 nm) (x=0~x T1 ) and a tapered waveguide (x=x T1 ~x T2 ) and a waveguide with a constant width (width 100 nm) at the tip (x=x T2 ~x L) and is composed of. In the tapered waveguide, the width at the base end (x = x T1 ) is 800 nm, the width at the tip end (x = x T2 ) is 100 nm, and the length (x = x T1 ~x T2 ) is 350 μm. Here, the length of the waveguide with a constant width on the base end side (x = 0 to x T1 ) is 10 μm, and the length of the waveguide with a constant width on the tip end side (x = x T2 ~x L ) is 20 μm. Thus, the total length of the waveguide (x = 0 to x L ) is 380 μm.

[0058] From the tip end of the waveguide to the external region (x = x L ~x1), the part other than the waveguide structure is composed of silicon oxide.

[0059] Also, the light source is arranged at a position 1 μm inward from the base end on the central axis C of the waveguide structure (x R = 1 μm), and the emitted light from the light source is calculated assuming that it propagates in the fundamental propagation mode with respect to the cross section of the waveguide.

[0060] The calculation was performed for the two-dimensional waveguide structure by the finite difference time domain method (FDTD: Finite Difference Time Domain Method) (product name: "ANSYS Lumerical FDTD"). In addition to the FDTD method, the eigenmode expansion (EME) method may be used for the calculation.

[0061] Regarding the fundamental mode of the propagating light (signal light and resin curing light), the wavelength of the signal light was set to 1550 nm and the wavelength of the resin curing light was set to 532 nm for the calculation.

[0062] For each of the signal light and the resin curing light, the MFD at each x coordinate was calculated by performing Gaussian fitting on the function f(y) showing the intensity distribution of the light at each coordinate x in the propagation direction. Here, y indicates the direction perpendicular to the propagation direction (x direction) (in the figure, arrow y).

[0063] Figures 4B and 4C show the calculated MFD results for the propagation direction of the signal light and resin curing light, respectively. Figure 4A shows the beam diameters of the signal light and resin curing light at position (coordinate) x in the region from the base end of the waveguide to the outside (x=0 to x1=0 μm to 400 μm). Figure 4B shows a magnified view in the region x=350 μm to 400 μm.

[0064] As shown in Figures 4A and 4B, the signal light expands in its MFD as it propagates through the SSC of the waveguide and is emitted from the tip of the waveguide (x=380μm). The emitted signal light expands in its MFD as it propagates through the cladding (silicon oxide).

[0065] On the other hand, as the resin curing light propagates within the SSC, its MFD gradually decreases and is emitted from the tip of the waveguide (x=380μm). As the emitted resin curing light propagates through the cladding (silicon oxide), its MFD expands.

[0066] Here, with resin curing light, the MFD expands more rapidly than with signal light. This is because, as mentioned above, shorter wavelength light spreads more per unit propagation distance than longer wavelength light.

[0067] As a result, as shown in Figures 4A and 4B, the beam diameters of the propagating signal light and the resin curing light coincide at a predetermined position (coordinate x', here x' = 384 μm).

[0068] Therefore, by designating a predetermined position (coordinate x') as the output end face of the optical element and forming the SWW from this end face, the size of the SWW at the output end face will be approximately the same as the MFD of the resin curing light, and the MFD of the signal light will be approximately the same.

[0069] In other words, the MFD control gap 15 in the optical element 10 is x L By setting the length to ~x' (4 μm in this case), the MFD of the signal light emitted from the optical element 10 becomes approximately the same as the size of the SWW, thereby reducing the connection loss of the signal light.

[0070] Thus, in the optical element 10 according to this embodiment, by setting the MFD control gap 15 at the output end face 101 of the optical element 10 so that the beam diameters of the signal light and the resin curing light are approximately the same, the connection loss of the signal light to the SWW caused by the difference in wavelength between the signal light and the resin curing light can be reduced.

[0071] Here, the range of similar beam diameters includes cases where the beam diameters are the same, and also includes cases where there is a difference of, for example, 1 to 2 μm. It is sufficient if the connection loss of the signal light between the optical element and the SWW is within a range that does not hinder the propagation of the signal light in optical communication, etc.

[0072] In this embodiment, calculation results for a two-dimensional waveguide structure are shown, but similar calculations can be performed for a three-dimensional waveguide structure using the FDTD method (product name: "ANSYS Lumerical FDTD"). By varying the waveguide core structure (thickness of 2 μm or less), the wavelength of the signal light, and the wavelength of the resin curing light, calculations were performed, and the results showed that the beam diameters of the propagating signal light and the resin curing light coincided at a predetermined position (MFD control gap: corresponding to 1 to 20 μm).

[0073] <Manufacturing method for optical elements> A method for manufacturing an optical element according to this embodiment will be described with reference to Figure 5.

[0074] First, the MFD control gap 15 in the optical element is determined.

[0075] First, the structures of the waveguide core 13 and the first and second claddings 12 and 14 are determined. Also, the wavelengths of the signal light and the resin curing light are determined (step S1).

[0076] Next, in the determined structure, the MFD diameters of the signal light and resin curing light propagating through and emitting from the waveguide core 13 are calculated (step S2).

[0077] Next, the position on the end face of the second cladding is determined such that the MFD diameters of the signal light and the resin curing light emitted from the waveguide core 13 are approximately the same. That is, the MFD control gap 15 is determined (step S3).

[0078] Next, based on the above calculation results, the optical element is manufactured.

[0079] First, the material for the lower cladding (first cladding) 12 is deposited on the substrate. Subsequently, the material for the waveguide core 13 is deposited on top of the lower cladding (first cladding) 12 (step S4). Here, the substrate material is Si, the lower cladding material is SiO2, and the waveguide core 13 material is SiN x These can be used.

[0080] Next, using photolithography, SiN x The material is processed into a waveguide core 13 (step S5). The mask pattern used for photolithography is fabricated based on the shape of the waveguide core 13 obtained by calculation and the MFD control gap 15.

[0081] Finally, an upper cladding (second cladding) 14 is formed to cover the waveguide core 13 (step S6). For example, SiO2 is used as the material for the upper cladding (second cladding) 14.

[0082] <Manufacturing method for optically integrated devices> An example of a method for manufacturing an optical integrated element 1 in which the optical element 10 according to this embodiment and another optical element (waveguide element) 10_2 are connected via SWW16 is described below.

[0083] First, the end face 101 of the optical element 10 and the end face of the other optical element (waveguide element) 10_2 are placed facing each other with a predetermined distance between them.

[0084] Next, SWW material (photocurable resin) is filled (dropped) between the end face 141 of the second cladding 14 of the optical element and the end face of the other optical element (waveguide element) 10_2. By using a photocurable resin with high viscosity, the photocurable resin can be held in place.

[0085] Next, the resin curing light is propagated to the waveguide core 13 and emitted from the tip 131 of the waveguide core 13, and then propagated to the second cladding 14 and emitted from the end face 141 of the second cladding 14.

[0086] Next, the resin curing light is irradiated onto the photocurable resin. As a result, the area of ​​the photocurable resin irradiated with the resin curing light hardens and becomes the SWW core 161.

[0087] Finally, after removing the uncured photocurable resin, SWW cladding 162 is formed around it.

[0088] As a result, the optical element 10 according to this embodiment and another optical element (waveguide element) 10_2 are optically connected via SWW16 to manufacture the optical integrated element 1 (Figures 3A and 3B).

[0089] In the optical integrated element according to this embodiment, the SWW16 functions as a waveguide if the refractive index of the core 161 is higher than the refractive index of the cladding 162. Therefore, the area around the SWW core 161 may be air, for example, and an SWW cladding may not be provided. In this case, the SWW cladding may not be formed in the final step of the manufacturing method of the optical integrated element described above.

[0090] <Effects> According to the optical element of this embodiment, the size of the SWW and the MFD of the signal light can be made to be approximately the same, thereby reducing the connection loss of the signal light between the waveguide of the optical element and the SWW.

[0091] The MFD of the signal light propagating through an actual SWW is affected by the refractive index difference between the SWW cladding and core. Therefore, the refractive index of the SWW cladding may be adjusted so that the MFD of the signal light matches the propagation mode of the signal light within the SWW, thereby reducing losses that occur at the boundary between the SWW and the end face of the optical element (chip).

[0092] Furthermore, the core diameter of the SWW depends somewhat on the intensity of the resin curing light. Therefore, the loss of signal light transitioning from the optical element to the SWW can be reduced by changing the intensity of the resin curing light.

[0093] Here, SWWs can only be formed at an intensity of resin curing light above a predetermined level. On the other hand, if the intensity of the resin curing light is too high, bubbles will form due to the heat generated by the resin, which will negatively affect SWW formation. Therefore, it is necessary to form SWWs at an intensity of resin curing light lower than the intensity that would negatively affect SWW formation.

[0094] Furthermore, in this embodiment, it is necessary to control the length of the MFD control gap 15. The optimal value for the MFD control gap 15 can be determined in advance by numerical calculations during the design of the optical element. Based on this design value, polishing marks can be created on the optical element (chip) using a waveguide pattern or the like, along with a dicing marker, in order to adjust the MFD control gap 15 of the fabricated optical element (chip). This allows for efficient control of the length of the MFD control gap 15 by polishing the end face of the optical element while checking the polishing marks with an optical microscope or the like.

[0095] Furthermore, the optical element according to this embodiment can improve yield in the manufacturing process and reduce waveguide loss.

[0096] In more detail, conventional optical elements require a narrower tip width to increase the MFD (Multi-Function Display) width. However, narrowing the waveguide width makes it difficult to control the waveguide width during the manufacturing process, and also increases optical loss due to the roughness of the waveguide sidewalls.

[0097] On the other hand, in the optical element according to this embodiment, the MFD expands when not only resin curing light but also signal light propagates through the MFD control gap. Therefore, even if the width of the waveguide tip of the optical element (width of SSC) is set wider than the width of the waveguide tip in a normal optical element, the MFD at the end face of the optical element can be made equivalent.

[0098] Thus, with the optical element according to this embodiment, the waveguide width can be set to be wider, which improves the yield in the manufacturing process and reduces optical loss due to the roughness of the side walls of the manufactured waveguide.

[0099] In this embodiment, an example is shown in which the length of the MFD control gap in the optical element is set to 4 μm. However, the length of the MFD control gap depends on the shape of the waveguide core, the wavelength of the signal light, and the wavelength of the resin curing light. For example, when the wavelength of the signal light is 1550 nm and the wavelength of the resin curing light is 532 nm, the length of the MFD control gap is 2 to 10 μm when the length of the tapered structure of the waveguide core is 200 to 500 μm, the width of the base end is 500 to 1000 nm, and the width of the tip is 50 to 200 nm. Also, when the length of the tapered structure of the waveguide core is 350 μm or more, the width of the base end is 500 to 1000 nm, the width of the tip is 500 nm or less, and the thickness of the waveguide core is 2 μm or less, the length of the MFD control gap is 1 to 150 μm when the wavelength of the signal light is 1250 to 1350 nm and the wavelength of the resin curing light is 385 to 1550 nm.

[0100] <Second Embodiment> A second embodiment of the present invention, an optical element, will be described with reference to Figures 6A to 7B.

[0101] <Configuration of optical elements> In the optical element 20 according to this embodiment, as shown in Figures 6A and 6B, the end faces 121 and 141 of the first cladding 12 and the second cladding 14 are located inward from the end face 111 of the substrate 11 (towards the tip 131 of the waveguide core 13). That is, the end of the optical element 20 has a step, and the surface of the step is the surface of the substrate 11. Hereinafter, this region 21 will be referred to as the "SWW region". The other configurations are the same as in the first embodiment.

[0102] <Configuration of an optical integrated device> In the optical integrated element 2 according to this embodiment, as shown in Figures 7A and 7B, the optical element 20 and the other optical element 10_2 are connected via SWW16. Thus, SWW16 is formed in the region enclosed by the end face 121 of the first cladding 12, the end face 141 of the second cladding 14, the upper surface of the substrate 11, and the end face of the other optical element 10_2, i.e., the SWW region 21.

[0103] The SWW region 21 of the optical element 20 according to this embodiment can be fabricated by protecting the areas other than the SWW region 21 with a mask pattern fabricated by a wafer process, for example, and then etching it. This mask pattern is fabricated using a high-precision (1 μm or less) positioning technique used in wafer processes.

[0104] Therefore, the gap 15 for MFD control can be controlled with higher precision than dicing or marker processing in the first embodiment, and the MFD can be controlled with a higher yield.

[0105] Furthermore, on the surface of the substrate 11 in the SWW region 21 of the optical element 20 according to this embodiment, SWW material (resin) can be filled into the gap between the end face 101 of the optical element 10 (the end face 121 of the first cladding 12 and the end face 141 of the second cladding 14) and the end face of the other optical element 10_2 that is connected.

[0106] As a result, compared to structures without SWW regions, the SWW material (resin) can be easily filled and held in the gap between the end face of the optical element 20 and the end face of the other optical element 10_2 during the formation of the SWW16.

[0107] In this embodiment, the step in the SWW region is shown as being located on the surface of the substrate, but it may also be located inside the substrate or inside the first cladding.

[0108] <Third Embodiment> A third embodiment of the present invention, an optical element, will be described with reference to Figures 8 and 9.

[0109] <Configuration of optical elements> As shown in Figure 8, the optical element 30 according to this embodiment has a mode filter 31 that functions with respect to resin curing light on the proximal end side (opposite the tip 131) of the waveguide core 13. Here, the mode filter 31 can be placed on the waveguide core 13.

[0110] Furthermore, in the optical integrated element 3 according to this embodiment, the optical element 30 is connected to other optical elements (not shown) via the SWW16.

[0111] The mode filter 31 includes, for example, a width modulation structure of a Bragg grating on both sides of the waveguide core 13, as shown in Figure 9. The grating configuration is, for example, a waveguide width of 800 nm and a grating depth of 45 nm. The grating period is 320 nm and the duty cycle (ratio of the length of the protrusion to the period) is 0.5.

[0112] <Effects> In the optical element 10 according to the first embodiment, when forming SWW, the multimode effect of the resin curing light may adversely affect the conditions for forming SWW.

[0113] The structure of the optical element 10 is the same as that used in SiPh and other materials, and the waveguide core 13 is single-mode under signal light conditions. Therefore, the waveguide core 13 behaves as a multimode waveguide with respect to resin curing light, which has a shorter wavelength than the signal light.

[0114] In the case of a multimode waveguide, multiple transverse modes of light are emitted from the edge of the optical element (chip). In this case, resin curing light of different modes propagates, compared to the case where only single-mode resin curing light propagates.

[0115] As a result, the length of the MFD control gap differs between single-mode and multi-mode applications. Therefore, even if the MFD control gap is formed based on the value designed for single-mode, the SWW is formed by the resin curing light in multi-mode applications. This makes it impossible to match the size of the SWW to the MFD of the signal light, and thus the connection loss of the signal light cannot be reduced.

[0116] Furthermore, perturbations such as differences in the roughness of the waveguide sidewalls and refractive index distribution caused by manufacturing errors can alter the generation of transverse modes in multimode waveguides. Therefore, it is difficult to control the MFD control gap with high yield in multimode waveguides.

[0117] Furthermore, when forming SWWs, resin curing light with a unimodal Gaussian intensity distribution allows for the formation of long SWWs (approximately mm in length) that grow with a constant core diameter. Therefore, in order to form long SWWs, it is necessary to suppress the multimode nature of the resin curing light.

[0118] On the other hand, in the optical element according to this embodiment, the effects of multimode amplification can be suppressed by using a mode filter.

[0119] In the optical element according to this embodiment, the higher-order transverse modes of the resin-cured light propagating through the waveguide core 13 are strongly scattered by the mode filter. This makes it possible to make the light intensity of the resin-cured light at the exit end face of the waveguide core 13 a Gaussian distribution or close to a Gaussian distribution (single-mode emission).

[0120] The mode filter in the optical element according to this embodiment can impose a large loss on all modes except the lowest-order transverse mode of the resin curing light propagating through the waveguide core 13. Therefore, even if the resin curing light becomes multimode due to manufacturing errors, only the lowest-order transverse mode can be emitted from the tip 131 of the waveguide core 13 with a high yield. In other words, it is possible to provide an optical element that emits resin curing light having a distribution in which the light intensity is high at the center of the core and decreases towards the sides of the core.

[0121] According to the optical element of this embodiment, in addition to the effects of the first embodiment, the light intensity distribution of the resin curing light can be made to be a Gaussian distribution or close to a Gaussian distribution, so that SWW can be formed with high precision, and a low-loss SWW core can be formed in a long shape with a constant core diameter. Therefore, the connection loss of signal light between the waveguide of the optical element and the SWW can be further reduced.

[0122] In this embodiment, an example is shown where the grating is formed on the side surface of the waveguide core as a mode filter, but it may also be formed on the top surface of the waveguide core.

[0123] Furthermore, a grating made of a material other than the waveguide core 12, such as a metal diffraction grating made of aluminum (Al), may also be used.

[0124] Furthermore, in the grating, the bumps and dips do not have to be arranged periodically; the bumps and dips may be arranged randomly, and the waveguide width may be randomly modulated. Also, instead of bumps and dips, the shape may be a waveform.

[0125] Alternatively, a bent waveguide may be used as a mode filter. In a bent waveguide, the radiation loss of higher-order modes of the propagating light is large, so multimode propagation can be suppressed. In addition, a structure that suppresses multimode propagation of resin-cured light propagating through the waveguide may be used.

[0126] The optical element according to the embodiment of the present invention can be applied to a structure in which an optical waveguide made of a material transparent to resin-cured light is formed on a substrate. For example, it can be applied to a planar lightwave circuit (PLC).

[0127] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc., of each component in the configuration and manufacturing method of the optical element are shown, but the invention is not limited to these examples. Any configuration that allows the optical element to perform its function and produce the desired effect is acceptable. [Industrial applicability]

[0128] The present invention relates to an optical element for connecting optical elements, an optical integrated element, and a method for manufacturing an optical element, and can be applied to optical communication devices and optical communication network systems. [Explanation of Symbols]

[0129] 10 Optical elements 10_2 Other optical elements 11 circuit boards 12 The First Clad 13 Waveguide core 131 The tip of the waveguide core, 14. The Second Clad 141 End face of the second cladding 16 Self-formed waveguide

Claims

1. An optical element connected to another optical element via a self-formed waveguide, which is a portion of a photocurable resin that is cured by irradiation with resin curing light, comprising, in order, a substrate, a first cladding, a waveguide core having a refractive index higher than that of the first cladding and through which signal light and the resin curing light propagate, and a second cladding having a refractive index lower than that of the waveguide core, The tip of the waveguide core that connects to the self-forming waveguide is positioned away from the end face of the second cladding such that the mode field diameter of the signal light and the mode field diameter of the resin curing light are approximately the same at the end face of the second cladding. The second cladding is positioned between the end of the waveguide core that connects to the self-forming waveguide and the end face of the second cladding. An optical element characterized by the following features.

2. The end face of the first cladding and the end face of the second cladding are located on the tip side of the waveguide core relative to the end face of the substrate. The self-forming waveguide is formed in the region enclosed by the end face of the first cladding, the end face of the second cladding, the upper surface of the substrate, and the end face of the other optical element. The optical element according to feature 1.

3. The waveguide core includes a mode filter. The optical element according to feature 1.

4. The waveguide core includes a mode-field conversion unit. The optical element according to feature 1.

5. The optical element according to claim 1, The other optical element connected via the self-forming waveguide An optical integrated element equipped with the following features.

6. A method for manufacturing an optical element, comprising a substrate, a first cladding, a waveguide core having a refractive index higher than that of the first cladding and through which signal light and the resin curing light propagate, and a second cladding having a refractive index lower than that of the waveguide core, wherein the optical element is connected to another optical element via a self-formed waveguide, which is a portion of a photocurable resin that is cured by irradiation with resin curing light, and the optical element comprises a substrate, a first cladding, a waveguide core having a refractive index higher than that of the first cladding and through which signal light and the resin curing light propagate, A step of determining the structure of the waveguide core, the first cladding, and the second cladding, and determining the wavelengths of the signal light and the resin curing light, In the above structure, the steps include calculating the mode field diameters of the signal light and the resin curing light propagating through the waveguide core and being emitted, A step of determining the position on the end face of the second cladding where the mode field diameters of the signal light and the resin curing light emitted from the waveguide core are approximately the same, The process involves sequentially depositing the material for the first cladding and the material for the waveguide core onto the substrate, A step of processing the material for the waveguide core into the waveguide core based on the above structure and the position of the end face of the second cladding, The steps include forming the second cladding so as to cover the waveguide core, A method for manufacturing an optical element equipped with the above.

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