Optical circuit chip

Abstract

The present invention constitutes an optical circuit chip (3) that includes an optical circuit connected to a fiber array (5). In this case, the optical chip (3) includes: a high refractive index layer (307); a low refractive index layer (306) that has a refractive index lower than the high refractive index layer (307); a substrate that encompasses the high refractive index layer (307) and the low refractive index layer (306) and includes a lower cladding layer (308) and an upper cladding layer (309) which have a refractive index lower than the low refractive index layer (306); a high refractive index core (301) that connects to an optical circuit formed in the high refractive index layer (307); low refractive index cores (302a-302d) that are formed in the low refractive index layer (306) and connect to the high refractive index core (301); and at least a pair of alignment waveguides (302e, 302f) that are formed in the low refractive index layer (306) and connect to an end surface (3E) of the substrate of which one end faces the fiber array (5).

Description

[Technical Field]

[0001] The present disclosure relates to an optical circuit chip included in an optical module. [Background technology]

[0002] To meet the demands for further miniaturization, cost reduction, and increased capacity, optical communication systems are now using integrated optical circuits to construct optical components. Integrated optical circuits can be constructed using a variety of materials, but in recent years, Si photonics, which uses silicon (Si) as its core material, has attracted attention. Silicon has a higher refractive index than known low-refractive-index materials, and Si photonics has stronger optical confinement than optical circuits made of low-refractive-index materials, allowing for a smaller allowable bending radius for optical waveguides. Furthermore, Si photonics can realize various circuit elements that make up optical circuits, such as optical couplers, multiplexers, filters, modulators, and optical receivers, and ultimately enables the miniaturization of optical circuits that integrate these elements on a single chip.

[0003] Furthermore, in order to actually use optical circuits that utilize Si photonics, terminals that can input and output light and electricity are provided on the Si photonics chip. The Si photonics chip that can input and output light and other signals is connected to the optical fibers of a fiber array to form an optical module.

[0004] It is preferable that the connection between the Si photonics chip and the optical fiber is performed so that the optical loss due to the connection is sufficiently low. The alignment when connecting the optical fiber is performed, for example, by active alignment, in which light is input into the optical fiber and the optimal alignment position is searched for while monitoring the light intensity transmitted through or reflected from the optical circuit in the Si photonics chip. Active alignment is described, for example, in Non-Patent Document 1. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Suruga Electric Co., Ltd., Optical fiber alignment, alignment system, [Retrieved April 21, 2022], Internet<https: / / jpn.surugaseiki.com / dcms_media / other / 504_Alignment-System_Web.pdf> Summary of the Invention

[0006] Here, the issue of alignment of an optical module will be explained. FIG. 1 is a top view illustrating the connection between a known Si photonics chip C and an optical fiber 21. The optical waveguide of the Si photonics chip C includes a plurality of input / output units 11. An optical fiber 23 including a core 21 and a cladding layer is fixed to a fiber array F. The optical fiber 23 is fixed by passing the optical fiber 23 through the fiber array F and applying an adhesive 22 around the optical fiber 23. Note that an SSC (Spot Size Converter) may be provided at the connection portion between the optical fiber 23 and the input / output unit 11 to increase the mode field diameter (MFD). The fiber array F comes in various assembly forms, such as a lensed fiber array.

[0007] When assembling an optical module, it is necessary to precisely align the core 21 of the optical fiber 23 with the input / output unit 11 to efficiently input light from a laser light source (not shown) into the optical waveguide. The required alignment accuracy is at least approximately 0.1 μm to 1.0 μm. Since such high-precision alignment is difficult to achieve using image processing, active alignment is performed by actually injecting light from the optical fiber 23 into the input / output unit 11 and monitoring the coupling loss. In the example configuration shown in Figure 1, the incident light is observed using a photodetector or the like installed within the Si photonics chip C to align the Si photonics chip C with the fiber array F. However, observing light using a photodetector requires driving the photodetector in the optical circuit while injecting light, which has the disadvantage of being cumbersome.

[0008] Furthermore, optical circuits using Si photonics have a very large refractive index and strong light confinement. As a result, the mode field diameter of the optical waveguide used in the optical circuit is small, at several hundred nanometers, which is significantly different from the mold diameter of the optical fiber 21, which is several micrometers to 10 micrometers. Although an SSC is provided in the input / output unit 11 to expand the mode field diameter and bring it closer to the mold field diameter of the optical fiber 21, even with this technology, it is difficult to sufficiently reduce the connection loss between the Si photonics chip C and the optical fiber 23.

[0009] The present disclosure aims to solve these problems and relates to an optical circuit chip that allows for highly accurate and easy connection between a photonics chip and an optical fiber, with little coupling loss.

[0010] In order to achieve the above object, an optical circuit chip according to one embodiment of the present disclosure is connected to a fiber array. having an end surface, An optical circuit chip including an optical circuit, a silicon substrate and a substrate positioned above the silicon substrate A first layer and a second layer having a refractive index higher than that of the first layer. is low and is located further above the first layer a second layer, and a layer including the first layer and the second layer; and a layer disposed between the first layer and the second layer. a substrate including a third layer having a refractive index lower than that of the second layer; a first optical waveguide connected to the optical circuit formed on the first layer; and a second optical waveguide formed on the second layer, One end is connected to the end face, and the other end is a second optical waveguide connected to the first optical waveguide; fruit , The first optical waveguide and the second optical waveguide constitute an optical waveguide having a spot size conversion function, in which the mode field on the side of the end face is larger than the mode field on the side of the optical circuit. .

[0011] According to the above embodiment, the photonics chip and the optical fiber can be connected with high precision and with ease, and an optical module with little coupling loss can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a top view illustrating a connection between a known Si photonics chip and an optical fiber. [Figure 2] FIG. 2(a) is a top view for explaining the substrate of the first embodiment, and FIG. 2(b) is a cross-sectional view. [Figure 3] FIG. 1A is a top view for explaining the optical module of the first embodiment, and FIG. 1B is a cross-sectional view. [Figure 4] FIG. 1(a) is a top view for explaining the effect of the first embodiment, and FIG. 1(b) is a cross-sectional view. [Figure 5] FIG. 10(a) is a top view for explaining an optical module according to a second embodiment, and FIG. 10(b) is a cross-sectional view. [Figure 6] FIG. 10(a) is a top view illustrating the configuration of an optical module according to a third embodiment, and (b) to (d) are top views illustrating alignment performed in the optical module. [Figure 7] 10(a) and 10(b) are diagrams illustrating the process of aligning the optical module according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, first to fourth embodiments of the present invention will be described with reference to the drawings. However, the drawings are intended to explain the configuration, arrangement of each part, effects, and technical concepts of the embodiments, and do not necessarily accurately show the aspect ratio or dimensions of each illustrated configuration. Furthermore, the embodiments are not limited to the specific shapes of the illustrated configurations. Furthermore, the optical module of the embodiments includes a substrate and an optical circuit mounted on this substrate. In the following description of the drawings, the direction in which the optical circuit is mounted relative to the substrate is considered to be "up."

[0014] [First embodiment] 2(a) and 2(b) are diagrams illustrating the configuration of a substrate of an optical module 10 according to a first embodiment. The optical module 10 includes an optical circuit chip 2 and a fiber array 4. FIG. 2(a) is a schematic top view showing the optical circuit chip 2 and the fiber array 4 aligned with each other, and FIG. 2(b) is a schematic cross-sectional view taken along the arrows IIb and IIb in FIG. 2(a). The optical module 10 according to the first embodiment of the present disclosure includes a high-refractive-index layer 207 as a first layer and a low-refractive-index layer 206 as a second layer having a refractive index lower than that of the high-refractive-index layer 207. The optical module 10 further includes a lower cladding layer 208 and an upper cladding layer 209 as third layers that encompass the high-refractive-index layer 207 and the low-refractive-index layer 206 and have a refractive index even lower than that of the low-refractive-index layer 206. The high refractive index layer 207, the low refractive index layer 206, the lower cladding layer 208, and the upper cladding layer 209 constitute the substrate 1 of the optical circuit chip 2, and this substrate 1 is a planar optical circuit board.

[0015] The fiber array 4 has a base 405, a step portion 405a formed in the base 405, and four optical fibers 403 that penetrate the step portion 405a. The four optical fibers 403 have cores 401 and are fixed in parallel to the base 405 by adhesive 402 applied between the cores 401 and the step portion 405a.

[0016] According to the above configuration, light incident from the optical fiber 403 passes through each of the low-refractive-index cores 202a to 202d of the optical circuit chip 2 and propagates to the high-refractive-index core 201. The high-refractive-index core 201 functions as an input / output unit connected to an optical circuit (not shown).

[0017] The optical circuit chip 2 has a lower cladding layer 208 formed on a Si substrate 200 that serves as a circuit support substrate, and a high-refractive-index layer 207 formed on the lower cladding layer 208. The high-refractive-index layer 207 is processed into a high-refractive-index core 201 by known photolithography and etching. The low-refractive-index layer 206 is formed on the high-refractive-index core 201. Low-refractive-index cores 202a, 202b, 202c, and 202d, which serve as second optical waveguides, are formed in the low-refractive-index layer 206 by known photolithography and etching. The low-refractive-index cores 202a to 202d are formed by processing the low-refractive-index layer 206 by known photolithography and etching.

[0018] The above process may be performed, for example, by depositing a lower cladding layer 208 on a Si substrate 200, then depositing and etching a high-refractive-index layer 207 to form the high-refractive-index core 201. Alternatively, the lower cladding layer 208 and the upper cladding layer 209 may be deposited on the high-refractive-index core 201, and a portion of the upper cladding layer 209 may be etched and removed along with the low-refractive-index cores 202a to 202d, after which the low-refractive-index layer 206 may be deposited. An upper cladding layer 209 is further deposited on the low-refractive-index cores 202a to 202d. In the optical module 10 configured in this manner, the high-refractive-index core 201 and the low-refractive-index cores 202a, etc. are disposed with a portion of the upper cladding layer 209 sandwiched between them. Light output from an optical circuit (not shown) propagates from the high-refractive-index core 201 through the upper cladding layer 209 to the low-cladding layer 202a, etc.

[0019] In the first embodiment, the low refractive index cores 202a to 202d are SSCs, and optical coupling is achieved by changing the spot size of the light so that light output from the optical fiber side of the optical module 10 can be optically coupled with low loss to the optical waveguide formed by the high refractive index core 201, lower cladding layer 208, and upper cladding layer 209. Such a configuration in the first embodiment is effective in reducing the connection loss of the optical module 10.

[0020] The high refractive index layer 207 is a layer having a basic optical waveguide structure of Si, and its refractive index is approximately equal to that of Si. The low refractive index layer 206 may be an insulating layer having a refractive index lower than that of Si, for example, SiN, SiO x , SiNO are used. The lower cladding layer 208 and the upper cladding layer 209 may be, for example, SiO2, which is a well-known cladding layer material. Such a layer structure realizes an optical waveguide structure having a double core layer. Note that the spacing between the high refractive index layer 207 and the low refractive index layer 206 is preferably an interlayer distance that allows adiabatic coupling of light, taking into account coupling loss. Furthermore, it is preferable that the optical waveguide structure including the high refractive index core 201 and the low refractive index core 202d has a structure with low coupling loss.

[0021] The optical module of the first embodiment has a dual optical waveguide structure consisting of a high-refractive-index core 201 and a low-refractive-index core 202d. The side of the low-refractive-index layer 202d facing the optical circuit chip 4 (see FIG. 2) is designed to match the mode field diameter of the optical fiber 403, while the side of the low-refractive-index layer 202d facing the optical circuit (not shown) has a mode field diameter that allows low-loss optical coupling with the optical waveguide used in the optical circuit. Furthermore, in the first embodiment, the low-refractive-index layer 202d is made of SSC, which allows the spot size to gradually change in the direction of light propagation. This configuration avoids optical connection loss due to the difference between the mode field diameter of the optical waveguide used in the optical circuit of the optical circuit chip 2 and the mold diameter of the optical fiber 403. Furthermore, in the first embodiment, the low-refractive-index cores 202a to 202d are made of SSC, which allows the mode field diameter to be adjusted with higher precision, further reducing connection loss with the fiber array 4. Furthermore, the optical circuit chip 2 with an enlarged mode field diameter improves the connection tolerance between the low refractive index cores 202a to 202d and the optical fiber 403, significantly reducing the alignment precision required when connecting optical fibers.

[0022] Next, an optical module 20 according to a first embodiment will be described, which further includes an alignment mechanism in addition to the optical module 10 described above. FIGS. 3(a) and 3(b) are diagrams illustrating the optical module 20 according to the first embodiment. FIG. 3(a) is a top view of the optical module 20, and FIG. 3(b) is a cross-sectional view taken along the arrows IIIb and IIIb in FIG. 3(a). The optical module according to the first embodiment includes an optical circuit chip 3 and a fiber array 5. The optical circuit chip 3 includes a Si substrate 300, a high-refractive-index core 301 formed by a high-refractive-index layer 307, and low-refractive-index cores 302a to 302d formed by a low-refractive-index layer 306. The optical circuit chip 3 further includes a pair of alignment cores 302e and 302f, which are aligned waveguides, in the low-refractive-index layer 306, a lower cladding layer 308 that encompasses the high-refractive-index core 301 and the low-refractive-index cores 302a to 302d, and an upper cladding layer 309. One end eE1 of the aligning core 302e is connected to the end face 3E facing the fiber array 5 of the optical circuit chip 3, and the other end eE2 is connected to one end fE2 of the aligning core 302f. The other end fE1 of the aligning core 302f is connected to the end face 3E. The connection between the end eE2 and the end fE2 is made by an optical waveguide 305. The aligning cores 302e, 302f and the optical waveguide 305 are all formed in the low-refractive-index layer 306, and the connection is made within the low-refractive-index layer 306.

[0023] The fiber array 5 also has a step portion 505a in the base 505, and six optical fibers 503 corresponding to the low refractive index cores 302a to 302d and the alignment cores 302e and 302f of the optical circuit chip. Each optical fiber 503 has a core 501, passes through the step portion 505a, and is fixed to the base 505 with adhesive 502.

[0024] The alignment of the optical module 20 of the first embodiment is performed by inputting light from a light source (not shown), such as a laser, into the optical fiber 503 connected to the alignment core 302e. The light input to the optical fiber 503 propagates to the alignment core 302e, passes through the optical waveguide 305, and then enters the alignment core 302f. The light is output from the alignment core 302f through the optical fiber 503 and is monitored, for example, by an optical power meter. The alignment is performed by adjusting the relative positions of the optical fiber 503 and the optical circuit chip 3 so that the intensity of the monitored light is maximized. The pitch of the optical fiber 503 corresponds to the pitch of the low-refractive-index cores 302a to 302d, and the low-refractive-index cores 302a to 302d and the optical fiber 503 are connected so that their optical axes are aligned by the alignment using the alignment cores 302e and 302f. This adjustment is hereinafter referred to as "alignment."

[0025] Next, the effect of forming such alignment cores 302e, 302f and optical waveguide 305 in low-refractive-index layer 306 will be described. FIGS. 4(a) and 4(b) are diagrams for explaining an optical module in which alignment cores are formed in a high-refractive-index layer. FIG. 4(a) is a top view, and FIG. 4(b) is a cross-sectional view of this optical module taken along arrows IVb and IVb shown in FIG. 4(a). In the optical circuit chip 3' shown in FIG. 4, the alignment cores 302e, 302f, and optical waveguide 305, along with the high-refractive-index core 301, are all formed in the high-refractive-index layer. In this way, the high-refractive-index core 301 and the optical waveguide 305 intersect, causing a large optical loss in the high-refractive-index core 301.

[0026] In contrast, the optical module 20 of the first embodiment has a dual core structure consisting of a high-refractive-index core 301 and low-refractive-index cores 302a to 302d. In the optical module 20, the low-refractive-index cores 302a to 302d, the alignment cores 302e and 302f, and the optical waveguide 305 are formed in a low-refractive-index layer 306, thereby avoiding intersection of the optical waveguide 305 with the high-refractive-index core 301. With this configuration, the first embodiment can prevent optical loss in the high-refractive-index core 301.

[0027] Furthermore, the optical module 20 allows for light incidence and monitoring using only the light source and optical power meter of the alignment device. This simplifies the alignment between the optical circuit chip 3 and the fiber array 5. Furthermore, the optical module 20 of the first embodiment does not require a photodetector in the optical circuit, which is effective in miniaturizing and simplifying the optical circuit of the optical circuit chip 3.

[0028] [Second embodiment] Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that alignment is performed using an optical fiber 703 that inputs and outputs light to and from the optical circuit chip 6, rather than separately forming an optical fiber for alignment in the fiber array. FIGS. 5(a) and 5(b) are diagrams showing an optical module 30 according to the second embodiment. FIGS. 5(a) and 5(b) are top views showing the optical circuit chip 6 and the fiber array 7 during alignment. The optical circuit chip 6 includes a high-refractive-index core 601 and low-refractive-index cores 602a, 602b, 602c, and 602d. In the second embodiment, the low-refractive-index cores 602a to 602d also have an SSC structure. Furthermore, the optical circuit chip 6 includes alignment cores 602e and 602f, which are connected by an optical waveguide 601.

[0029] The fiber array 7 includes a substrate 705 having a step portion 705a, and optical fibers 703 arranged in parallel and penetrating the step portion 705a. The optical fibers 703 include cores 701 and are fixed to the substrate 705 with an adhesive 702. In the second embodiment, the spacing between the pair of alignment cores 602e and 602f is equal to the spacing between any two of the multiple optical fibers 703.

[0030] The optical circuit chip 6 and fiber array 7 configured as described above are aligned as follows. As shown in Fig. 5(a), first, the optical circuit chip 6 and fiber array 7 are aligned using the alignment cores 602e and 602f and the optical fiber 703. After the alignment is complete, the fiber array 7 is moved in the -X direction shown in Fig. 5(a), and the low-refractive-index cores 602a to 602d are connected to the optical fiber 703 as shown in Fig. 5(b).

[0031] In Si photonics, the optical circuit chip and fiber array are manufactured with high precision, and the error in the relative positions of the low-refractive-index cores 602a to 602d and the alignment cores 602e and 602f, and the optical fiber 703, is sufficiently small, at about 1 nm. For this reason, in the second embodiment, the fiber array 7 is moved a known length after alignment, and the low-refractive-index cores 602a to 602d and the optical fiber 703 can be connected so that their optical axes coincide. Note that the known length may be, for example, the design value of the distance between the alignment core 602e and the low-refractive-index core 602a of the optical circuit chip 6.

[0032] In the second embodiment described above, it is not necessary to provide optical fibers for alignment in the fiber array 7, and therefore the cost of the fiber array 7 can be reduced compared to the first embodiment.

[0033] [Third embodiment] Next, an optical module 40 according to a third embodiment will be described. FIGS. 6(a), 6(b), 6(c), and 6(d) are all top views illustrating the optical module 40 according to the third embodiment. FIG. 6(a) illustrates the configuration of the optical module, and FIGS. 6(b) to 6(d) illustrate alignment performed in the optical module 40. The third embodiment makes it possible to perform alignment with higher accuracy than the second embodiment, without providing an optical fiber for alignment on the side of the fiber array 7, as in the second embodiment.

[0034] As shown in FIGS. 6(b) to 6(d), the optical module 40 includes an optical circuit chip 8 and a fiber array 7. As shown in FIG. 6(a) and other figures, the optical circuit chip 8 has four high-refractive-index cores 801 and four low-refractive-index cores 802a to 802d. Furthermore, the optical circuit chip 8 has two pairs of alignment cores 802e and 802f and alignment cores 802g and 802h. The alignment cores 802e and 802f are connected by an optical waveguide 805A, and the alignment cores 802g and 802h are connected by an optical waveguide 805B. Note that in the third embodiment as well, the low-refractive-index cores 802a to 802d form an SCC.

[0035] In the following description, in the third embodiment, a circuit configured with alignment cores 802e and 802f and optical waveguide 805A will also be referred to as alignment circuit A, and a circuit configured with alignment cores 802g and 802h and optical waveguide 805B will also be referred to as alignment circuit B. In the optical circuit chip 8 shown in FIG. 6( a), the optical input / output circuit including low-refractive-index cores 802a to 802d and alignment circuit B are arranged so that they are shifted by a distance L in the −X direction, and alignment circuit B is shifted by a distance L in the X direction. In the third embodiment, as will be described in detail later, alignment circuit A is used to align the optical circuit chip 8 and the fiber array 7, and then alignment circuit B is used to align the optical circuit chip 8 and the fiber array 7. Then, the optical circuit chip 8 and the fiber array 7 are connected at the center of the optimal positions determined by the two alignments.

[0036] Note that the optical waveguides 805A and 805B may cross each other because they are both formed in the low refractive index layer. The optical waveguides 805A and 805B do not affect the connection loss unless they cross the high refractive index core 801. Furthermore, the optical loss caused by the crossing of the optical waveguides 805A and 805B does not affect the alignment accuracy with the optical circuit chip 8 and the fiber array 7.

[0037] Since the fiber array 7 uses existing optical fibers 703 for alignment, the spacing between any two of the optical fibers 703 matches the spacing between the alignment cores of the optical circuit chip 8 .

[0038] As shown in FIG. 6(b), the optical circuit chip 8 and the fiber array 7 are aligned using an alignment circuit A. The alignment is performed by monitoring the light incident and emitted through the low-refractive-index core 802e, the optical waveguide 805A, and the low-refractive-index core 802f. Next, as shown in FIG. 6(c), the optical circuit chip 8 and the fiber array 7 are aligned using an alignment circuit B. To switch between alignment circuits A and B, the fiber array 7 is moved in the -X direction in FIG. 6(a) using a stage (not shown).

[0039] Alignment by the alignment circuit B is performed by monitoring the light incident and emitted through the low-refractive-index core 802g, the optical waveguide 805B, and the low-refractive-index core 802h. At this time, as is clear from FIGS. 6(b) and 6(c), the optimal position of the fiber array 7 determined by the alignment circuit A relative to the optical circuit chip 8 is different from the optimal position of the fiber array 7 determined by the alignment circuit B. In the third embodiment, the fiber array 7 is connected to the optical circuit chip 8 at the center of the optimal alignment positions determined by two alignments. The optimal position determined by the alignment using the alignment circuits A and B is based on the relative positions of the optical circuit chip 8 and the fiber array 7. When the optimal position is expressed, for example, only on the X-axis, the center of the optimal position may be the center point of two optimal positions expressed, for example, by the coordinates of the stage.

[0040] According to the third embodiment described above, the connection position between the optical circuit chip 8 and the fiber array 7 can be determined based on the relative positional relationship between them. Therefore, even if the absolute accuracy of the movement amount of the stage that moves the fiber array 7 is not sufficiently high, the third embodiment can properly align the optical circuit chip 8 and the fiber array 7 and achieve connection with low optical loss. The third embodiment can improve alignment accuracy compared to the second embodiment, in which the fiber array is moved from a position determined by alignment based on the absolute movement distance of the stage. Many known stages have higher accuracy of relative position than absolute position, and therefore the third embodiment is effective in achieving an optical module 40 with low coupling loss.

[0041] [Fourth embodiment] Next, a fourth embodiment of the optical module 10 will be described. The fourth embodiment differs from the first embodiment in that the alignment cores 112e and 112f are each composed of one SSC and a reflecting circuit. A suitable reflecting circuit, for example, is a loopback mirror. When using a reflecting circuit for alignment, it is necessary to form the reflecting circuit sufficiently separated from the main circuit to avoid crossing with the circuit that inputs and outputs light. However, since the reflecting circuit is a relatively large circuit, separating it from the main circuit increases the size of the optical circuit chip. Furthermore, the greater the distance between the alignment circuit and the main circuit, the greater the final movement amount of the fiber array, resulting in reduced alignment accuracy. To address this issue, in the fourth embodiment, the alignment circuit including the reflecting circuit is formed in a low-refractive-index layer, and the main circuit is formed in a high-refractive-index layer.

[0042] 7(a) and 7(b) are top views for explaining an optical module 50 according to a fourth embodiment, each showing an alignment process. The optical module 50 includes an optical circuit chip 12 and a fiber array 7. The optical circuit chip 12 has a high-refractive-index core 111 formed in a high-refractive-index layer, low-refractive-index cores 112a to 112d formed in a low-refractive-index layer, alignment cores 112e and 112f, and reflection circuits 121 and 122. In the fourth embodiment, the alignment core 112e and the reflection circuit 121, and the alignment core 112f and the reflection circuit 122 each constitute an alignment circuit.

[0043] As shown in Figures 7(a) and 7(b), alignment between the optical circuit chip 12 and the fiber array 7 is performed by first inputting light from the optical fiber 703 to the alignment core 112f and monitoring the light intensity of the reflected light. Once the position where the light intensity is greatest has been determined, the optical fiber 7 is moved a known distance in the X direction by a stage (not shown) or the like. The position after the movement is a position where the optical axes of the alignment core 112e and the optical fiber 703, i.e., the core 201, are thought to roughly coincide. Here, in the fourth embodiment, alignment is performed by inputting light from the optical fiber 703 to the alignment core 112e and monitoring the reflected light.

[0044] According to the fourth embodiment, the alignment circuit and the main circuit are separated in both the plane direction and thickness direction of the optical circuit chip 12, thereby preventing an increase in the area of ​​the optical circuit chip 12. Furthermore, as shown in Figures 7(a) and 7(b), by providing at least two alignment circuits, each including an alignment core and a reflection circuit, for alignment, it becomes possible to grasp the tilt and position of the fiber array 7, and the connection loss with the optical circuit chip 12 can be reduced. [Explanation of symbols]

[0045] 1 board 2, 3, 6, 8, 12 Optical circuit chip 3E End face 4, 5, 7 Fiber array 10, 20, 30, 40, 50 optical modules 111, 201, 301, 601, 801 High refractive index core 112a-112d, 202a-202d, 302a-302d, 602a-602d, 802a-802d Low refractive index core 112e, 112f, 202e, 202f, 302e, 302f, 602e, 602f, 802e, 802f, 802g, 802h alignment core 121, 122 Reflection circuit 200, 300 Si substrate 206, 306 low refractive index layer 207, 307 High refractive index layer 208, 308 Lower cladding layer 209, 309 Upper cladding layer 305, 805A, 805B optical waveguide 401, 501, 701 cores 403, 503, 703 optical fiber 402, 502 Adhesive 405, 505, 705 base 405a, 505a, 705a Steps

Claims

1. An optical circuit chip having an end face to be connected to a fiber array and including an optical circuit, a substrate including a silicon substrate, a first layer located above the silicon substrate, a second layer having a lower refractive index than the first layer and located further above the first layer, and a third layer including the first layer and the second layer and located between the first layer and the second layer, the third layer having a lower refractive index than the second layer; a first optical waveguide connected to the optical circuit formed on the first layer; a second optical waveguide formed in the second layer, one end of which is connected to the end face and the other end of which is connected to the first optical waveguide; the first optical waveguide and the second optical waveguide constitute an optical waveguide having a spot size conversion function, in which a mode field on the end face side is larger than a mode field on the optical circuit side.

2. An optical circuit chip as described in claim 1, further comprising at least one pair of alignment waveguides formed in the second layer, one end of which is connected to the end face.

3. The optical circuit chip according to claim 2 , wherein the other ends of the pair of aligned waveguides are connected to each other on the second layer.

4. 3. The optical circuit chip according to claim 2, wherein the other end of the alignment waveguide is connected to a reflection circuit.

5. 4. The optical circuit chip according to claim 3, comprising two pairs of the aligning waveguides, and the fiber array is connected at the center between a relative position determined for one pair of the aligning waveguides with respect to the fiber array and a relative position determined for the other pair of the aligning waveguides with respect to the fiber array.

6. 4. The optical circuit chip according to claim 3, wherein the fiber array has a plurality of optical fibers, and the spacing between the pair of the aligning waveguides is equal to the spacing between any two of the plurality of optical fibers.

7. The optical circuit chip of claim 1 , wherein the first layer comprises silicon.

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