Spot size converter and optical integrated device

Abstract

A spot-size converter (11) of the present invention is a spot size converter (11) optically coupled to a semiconductor optical device, the spot size converter (11) including, sequentially on a substrate (101), a dielectric waveguide (131, 132, 133), a first cladding (141), a semiconductor waveguide (121, 122), and a second cladding (142) covering the dielectric waveguide (131, 132, 133) and the semiconductor waveguide (121, 122). The spot size converter(11) includes one end portion and another end portion, and light is coupled between the semiconductor optical device and the one end portion. The width of at least a portion of the semiconductor waveguide (121, 122) decreases from the one end portion to the other end portion. The semiconductor waveguide (121, 122) is not disposed in a partial region on a side of the other end portion, and a width of at least a portion of the dielectric waveguide (131, 132, 133) decreases from the one end portion to the other end portion. With this configuration, the present invention can provide a spot size converter that can efficiently couple light between a semiconductor optical device and a dielectric waveguide.

Description

Spot Size Converter and Optical Integrated Device

[0001] The present invention relates to a spot size converter and an optical integrated device configured to couple light between a semiconductor optical integrated device and a dielectric waveguide made of, for example, lithium niobate (LN) or lithium tantalate (LT).

[0002] Due to the rapid traffic growth in various communications networks supported by optical fibers and photonics technologies, optical components with large bandwidths and small power consumption are urgently needed. These devices are especially required to operate in the C-band telecommunications optical band as this is the most widely used band in most optical fiber systems.

[0003] Photonic integrate circuits (PICs) and heterogeneous integration enable the integration of different materials and fabrication of platforms into a single chip or PIC. These technologies are expected to support the above-described need by providing devices with large bandwidths and low power consumption, at low cost and with small form factors.

[0004] Recently, one promising technology platform for providing very high-bandwidth modulators operating at low voltages, as well as wideband nonlinear photonic devices, is the lithium niobate on insulator (LNOI) platform in which a thin film of lithium niobate (LN) is disposed at the tip (on the surface) of an insulator, typically SiO2and the like (Non-Patent Documents 1 and 2). Another promising small platform is the lithium tantalate on insulator (LTOI) platform in which a thin film of lithium tantalate (LT) instead of LN is used.

[0005] However, although LNOI and LTOI platforms can provide modulators with high performance, they cannot support lasering operations in the C-band. For that, typically, an external III-V semiconductor laser fabricated on an InP platform is used.

[0006] Another approach is the heterogeneous integration of an III-V semiconductor laser on a non-native-InP substrate such as an SiO2 / Si substrate or a silicon-on-insulator (SOI) substrate. In recent years, heterogeneous integration of a conventional III-V semiconductor laser on LNOI has been demonstrated based on a flip chip method (Non-Patent Document 3).

[0007] Another approach could be the use of a membrane III-V semiconductor laser instead of a standard III-V semiconductor laser (Non-Patent Documents 4 and 5). Owing to its very thin (typically less than 350 nm) III-V semiconductor structure cladded by low refractive index materials, a membrane III-V semiconductor laser provides a very high optical confinement factor which achieves low power consumption and high output power.

[0008] Typically, such membrane lasers have a multi-quantum well (MQW) and are composed of a buried heterostructure having a lateral p-n junction. For operation in the C-band, the MQW is typically based on an InGaAsP compound. Heterogeneous integration of the III-V semiconductor membrane with LNOI or LTOI can be performed using die or wafer bonding (Non-Patent Document 3) or using a micro-transfer printing method (Non-Patent Document 5). These methods are more suitable for lowering cost and increasing processing yield and speed when compared to the flip chip method.

[0009] However, while heterogeneous integration of the membrane III-V with LNOI or LTOI is promising, so far, no photonic structures have been discussed for efficiently coupling light between the membrane III-V having the active MQW and an LN or LT waveguide.

[0010] C. Wang, et al., “Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages,” Nature, vol. 562, pp. 101-104, 2018.M. Jankowski, et al., “Ultrabroadband nonlinear optics in nanophotonic periodically poled lithium niobate waveguides,” Optica, vol. 7, pp. 40-46, 2020.A. Shams-Ansari, et al., “Electrically pumped laser transmitter integrated on thin-film lithium niobate,” Optica, vol. 9, no. 4, pp. 408-411, 2022.T. Aihara, et al., “Membrane III-V / Si DFB Laser Using Uniform Grating and Width-Modulated Si Waveguide,” Journal of Lightwave Technology, vol. 38, no. 11, pp. 2961-2967, 2020.B. Corbett, et al., “Transfer print techniques for heterogeneous integration of photonic components,” Progress in Quantum Electronics, vol. 52, pp. 1-17, 2017.

[0011] However, while heterogeneous integration of the membrane III-V with LNOI or LTOI is promising, so far, no photonic structures have been discussed for efficiently coupling light between the active MQW in the membrane III-V and an LN or LT waveguide.

[0012] To solve the above-described problem, a spot size converter according to the present invention is a spot size converter optically coupled to a semiconductor optical device, the spot size converter including, sequentially on a substrate, a dielectric waveguide, a first cladding, a semiconductor waveguide, and a second cladding covering the dielectric waveguide and the semiconductor waveguide, in which the spot size converter includes one end portion and another end portion, and light is coupled between the semiconductor optical device and the one end portion, the width of at least a portion of the semiconductor waveguide decreases from the one end portion to the other end portion, and the semiconductor waveguide is not disposed in a partial region on a side of the other end portion, and a width of at least a portion of the dielectric waveguide decreases from the one end portion to the other end portion.

[0013] According to the present invention, it is possible to provide a spot size converter and an optical integrated device that can efficiently couple light between a semiconductor optical device and a dielectric waveguide made of, for example LN or LT.

[0014] FIG. 1A is a schematic birds’ eye view illustrating a configuration of a spot size converter and an optical integrated device according to a first embodiment of the present invention.FIG. 1B is a schematic top view illustrating the configuration of the spot size converter and the optical integrated device according to the first embodiment of the present invention.FIG. 1C is a cross-sectional view taken along line IC-IC′, illustrating the configuration of the spot size converter and the optical integrated device according to the first embodiment of the present invention.FIG. 1D is a cross-sectional view taken along line ID-ID′, illustrating the configuration of the spot size converter and the optical integrated device according to the first embodiment of the present invention.FIG. 1E is a cross-sectional view taken along line IE-IE′, illustrating the configuration of the spot size converter and the optical integrated device according to the first embodiment of the present invention.FIG. 1F is a cross-sectional view taken along line IF-IF′, illustrating the configuration of the spot size converter and the optical integrated device according to the first embodiment of the present invention.FIG. 2A is a diagram showing operation of the spot size converter according to the first embodiment of the present invention.FIG. 2B is a diagram showing operation of the spot size converter according to the first embodiment of the present invention.FIG. 3A is a graph showing the effect of the optical integrated device according to the first embodiment of the present invention.FIG. 3B is a graph showing the effect of the optical integrated device according to the first embodiment of the present invention.FIG. 3C is a graph showing the effect of the optical integrated device according to the first embodiment of the present invention.FIG. 3D is a graph showing the effect of the optical integrated device according to the first embodiment of the present invention.FIG. 3E is a graph showing the effect of the optical integrated device according to the first embodiment of the present invention.FIG. 3F is a graph showing the effect of the optical integrated device according to the first embodiment of the present invention.

[0015] <First Embodiment> A spot size converter and an optical integrated device according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 1F.

[0016] <Configuration of Spot Size Converter and Optical Integrated Device> FIG. 1A is a schematic birds’ eye view illustrating an optical integrated device 10 according to an embodiment of the present invention. FIG. 1B is a schematic top view illustrating the optical integrated device 10. In FIG. 1B, illustration of a second cladding 142 is omitted. FIGS. 1C to 1F are each cross-sectional views of the optical integrated device 10 taken along line IC-IC′, ID-ID′, IE-IE′, IF-IF′, respectively. In FIG. 1C, illustration of electrodes 155 and 156 is omitted.

[0017] In the optical integrated device 10 according to the present embodiment, a spot size converter is integrated on a substrate (e.g., an Si substrate, an SiO2substrate or an LNOI substrate), together with a semiconductor optical device or an optical device. As illustrated in FIGS. 1A and 1B, as one example, in the optical integrated device 10, a semiconductor optical device 15 is connected to a spot size converter 11. The semiconductor optical device 15 is an active membrane III-V device, such as a membrane III-V semiconductor laser.

[0018] The spot size converter 11 includes an LN waveguide portion 13, a first cladding 141, and an InP waveguide portion 12, in the stated order from the substrate 101 side.

[0019] The InP waveguide portion 12 is configured by InP waveguides 121, 122 and an InP slab 123.

[0020] The LN waveguide portion 13 is configured by LN waveguides 131, 132, 133 and an LN slab 134.

[0021] The optical integrated device 10 also includes the second cladding 142 which covers the spot size converter 11 and the semiconductor optical device 15. The first cladding 141 and the second cladding 142 are materials with low refractivity, such as SiO2, SiOx, or BCB.

[0022] In the spot size converter 11, light is coupled between one end face of the spot size converter 11 and the active membrane III-V device 15, and light exits from another end face of the spot size converter 11. Light is coupled between the other end face of the spot size converter 11 and a thin-film LN ridge waveguide or an LN waveguide device integrated in the optical integrated device 10, at a core width of 3 μm. The LN waveguide device is, for example, an LN Mach-Zehnder modulator, an LN waveguide circuit element, or an LN filter.

[0023] As illustrated in FIG. 1C, the active membrane III-V device 15 includes an active-layer MQW core 151 having a BH structure, and a p-type InP 153 and an n-type InP 154 on either side of the MQW core 151 in a lateral direction (direction perpendicular to the waveguide direction on the horizontal plane; y-direction). Contact layers / electrodes 155, 156 are provided at the surfaces of the p-type InP 153 and n-type InP 154, respectively (FIG. 1A). An undoped InP 152 may be disposed around the MQW core 151. For compatibility with operation in the C-band, the MQW core 151 is made of InGaAsP having a core width of approximately 600 nm, with a maximum value of the thickness of the entire membrane structure being 180 nm. With this configuration, the MQW core 151 has a high optical confinement factor.

[0024] As illustrated in FIG. 1C, the membrane III-V device 15 is integrated into a patterned LNOI substrate. The patterned substrate is configured by an LN slab 134 having a thickness of 300 nm and LN ridge waveguides 131, 132, 133 each having a thickness of 600 nm on the substrate 101 made of, for example, SiO2.

[0025] The width of the LN waveguide (ridge core) 131 below the membrane III-V device 15 is 3 μm, which makes it possible to compensate for waveguide misalignment between the MQW core and the LN core due to a transfer printing process.

[0026] The InP waveguide portion 12 is disposed such that light is coupled between the InP waveguide core 121 and the MQW core 151 of the membrane III-V device 15.

[0027] A gap (indicated by the arrow in FIG. 1D) between the InP waveguide portion 12 and the LN waveguide portion 13 is defined by a distance between a bottom face of the InP slab 123 and a front face of the LN waveguide portion 13, and is 50 nm for partial coupling of the optical mode field to the LN waveguide (described later). In other words, the thickness of the first cladding 141 between the InP waveguide portion 12 and the LN waveguide portion 13 is 50 nm.

[0028] The thickness of the InP waveguide portion 12 is approximately equal to the thickness (e.g., 180 nm at a maximum) of the membrane III-V device 15.

[0029] In the InP waveguide portion 12, the thickness of the InP slab 123 is 50 nm, which can improve mechanical stability in the transfer printing process.

[0030] Further, as illustrated in FIG. 1B, the InP waveguides 121 and 122 each have a tapered shape. The width of the InP waveguide portion 121, 122 narrows from one end face to the other end face. More specifically, the InP waveguide has a first tapered structure 121 and a second tapered structure 122 starting from one end face side, and the first tapered structure 121 and the second tapered structure 122 have different tapered shapes.

[0031] The first tapered structure 121 of the InP is coupled to the MQW core 151 of the membrane III-V device 15, with a maximum core width of approximately 1.5 μm and a minimum core width of approximately 0.6 μm. The first tapered structure 121 makes it possible to focus light to ensure high tolerance to waveguide misalignment in transfer printing.

[0032] The second tapered structure 122 of the InP has a maximum core width of approximately 0.6 μm and a tip width, that is, a minimum width of 0.2 μm. The second tapered structure 122 makes it possible to efficiently couple light between the InP waveguide and the LN waveguide.

[0033] As illustrated in FIG. 1E, a short region (InP protection region) on the side of the other end face of the InP waveguide portion 12 is composed of only the InP scrub 123. The InP scrub 123 extends on the other end face side of the InP waveguide portion 12. This region makes it possible to protect the tip of the first tapered structure 121 of the InP during fabrication.

[0034] In the spot size converter 11, the LN waveguide (first portion) 131 is disposed below the membrane III-V device 15 and the InP waveguide portion 12 (substrate side) via the first cladding 141. The LN waveguide has a constant width in this region (FIG. 1C, 1D).

[0035] In the spot size converter 11, as illustrated in FIG. 1F, in a predetermined region on the other end face side, the membrane III-V device and the InP waveguide are not disposed and the LN waveguides 132, 133 are disposed covered by the second cladding 142.

[0036] As illustrated in FIGS. 1A and 1B, in this region, the LN waveguide has a second portion 132 and a third portion 133 from the one end face side.

[0037] The second portion 132 of the LN waveguide has a tapered shape. In the second portion 132, the width of the LN waveguide decreases from the one end face side to the other end face side.

[0038] Further, in the third portion 133, the width of the LN waveguide is constant.

[0039] The length of the first tapered structure 121 of the InP is approximately 10 μm, the length of the second tapered structure 122 of the InP is approximately 56 μm, and the length of the InP protection region is approximately 5 μm. The total length of these three regions is 71 μm.

[0040] The length of the second portion 132 (tapered region) of the LN waveguide is 50 μm. The length of the third portion 133 of the LN waveguide is 10 μm.

[0041] The total length of the spot size converter 11 is 121 μm.

[0042] Light exiting from the membrane III-V device 15 is input from the InP waveguide portion 121 on one end face of the spot size converter 11 and propagates through the InP waveguide portion 121, 122. Light that has leaked near the tip of the tapered structure of the InP waveguide portion 122 couples with the LN waveguide (first portion) 131 via the first cladding 141. The light propagates through the LN waveguide (first portion) 131, the size of the spot of the light is converted at the tapered shape (second portion) 132, and the light exits from the LN waveguide (third portion) 133 (other end face).

[0043] Accordingly, the spot size converter 11 according to the present embodiment includes the InP waveguides 121 and 122 each having two tapered shapes and the LN waveguide having a tapered shape.

[0044] <Operation of Spot Size Converter> Operation of the spot size converter 11 according to the present embodiment will be described with reference to FIGS. 2A and 2B.

[0045] FIGS. 2A and 2B show results of mode analysis simulation performed for the spot size converter 11. FIMMWAVE (PHOTON Design Corporation) was used for the simulation.

[0046] In a mounting process such as transfer printing, assuming a case where the InP waveguide and the LN waveguide are misaligned by 1 μm in the y-direction, a simulation was performed for a structure in which the y-axis spacing between the optical axis (central axis) of the InP waveguide and the optical axis (central axis) of the LN waveguide was 1μm. The MQW used here was based on six periods.

[0047] In FIG. 2A, the white solid line represents the entire InP, the white dashed line represents the InP taper, and the white dotted line represents the LN waveguide. FIG. 2A illustrates a region 221 in which the first tapered structure 121 of the InP waveguide is disposed, a region 222 in which the second tapered structure 122 is disposed, the InP protection region 223, and a region 232 in which the second portion (tapered portion) 132 of the LN waveguide is disposed.

[0048] For simulation purposes, the lengths of the input region 25 from the membrane III-V device and the output LN waveguide region 233 were both set to be 10 μm. Propagation of an optical mode in which light (input light) 1 is input to an end face of the region 25 and a light (output light) 2 is output from an end face of the region 233 was calculated.

[0049] As illustrated in FIG. 2A, the light input from the membrane III-V device to the InP waveguide leaked at the InP tapered waveguide, coupled with the LN waveguide disposed from the InP waveguide at an interval of 1 μm in the y-direction, and was output from the end face of the LN waveguide.

[0050] As illustrated in FIG. 2B, the optical mode is satisfactorily confined at the InP waveguide (201 in FIG. 2B), couples with (moves to) the LN waveguide disposed below the InP waveguide disposed above (202, 203 in FIG. 2B), and propagates after being satisfactorily confined at the LN waveguide (204 in FIG. 2B).

[0051] Accordingly, with the spot size converter according to the present invention, the optical mode is efficiently and satisfactorily coupled from the MQW core on the input side to the LN core on the output side even when the InP waveguide and the LN waveguide are misaligned by 1 μm.

[0052] <Effects> Effects of the spot size converter 11 according to the present invention will be described with reference to FIGS. 3A to 3F.

[0053] FIGS. 3A to 3F illustrate parameter dependency of light transmission characteristics of the spot size converter 11. Unless otherwise specified, the parameters are the same as stated above. Herein, a transmittance T is the intensity of light output from the LN waveguide / the intensity of light input to the InP waveguide from the MQW core.

[0054] FIG. 3A illustrates length dependence of the first tapered structure 121 of InP of the transmission characteristics. A maximum InP taper length was defined as around 66 μm and the length of the first tapered structure 121 of the InP was varied. A length LInP2of the second tapered structure of the InP was 66 - LInP1. In the first tapered structure 121 of the InP, the width of one end was defined as 1.5 μm and the width of the other end was defined as 0.6 μm for a width variation ΔWInP1of 0.9 μm. In the second tapered structure 122 of the InP, the width of one end was defined as 0.6 μm and the width of the other end was defined as 0.2 μm for a width variation ΔWInP2of 0.4 μm.

[0055] LInP1is 10 to 50 μm (LInP2= 56 to 16 μm) and the transmittance is 90%. With this configuration, LInP1is preferably 10 to 50 μm (LInP2= 56 to 16 μm). At this time, LInP1 / LInP2is approximately 0.18 to 3.1. The rate of narrowing of the waveguide width (rate of change), that is, the slope of the taper shape (0.5 × ΔW / L) is ΔWInP1 / LInP1= 0.045 to 0.0035 for the first tapered structure 121 of the InP, and ΔWInP2 / LInP2= 0.0045 to 0.006 for the second tapered structure 122 of the InP.

[0056] To compensate for misalignment in transfer printing, LInP1is preferably short, and is desirably LInP1approximately 10 μm (LInP2is 56 μm).

[0057] FIG. 3B illustrates length dependence of LN taper of transmission characteristics. The length of the LN taper is 30 to 150 μm and transmittance is 90% or greater than or equal to 90%. According to this configuration, the length of the LN taper is desirably 30 to 150 μm. Further, to reduce the chip size, the length of the LN taper is desirably about 50 μm.

[0058] FIG. 3C illustrates interval dependency of the transmittance characteristics between the InP waveguide portion 12 and the LN waveguide. In the InP waveguide portion 12 and the LN waveguide, the thickness of the first cladding 141 disposed between the InP waveguide portion 12 and the LN waveguide is the same. This interval is from 50 to 250 μm and transmittance is 90% or greater than or equal to 90%. With this configuration, the interval between the InP waveguide portion 12 and the LN waveguide is desirably 50 to 250 μm. In other words, the thickness of the first cladding between the InP waveguide portion 12 and the LN waveguide portion 13 is desirably 50 to 250 μm. More preferably, the interval is 50 nm because the confinement factor of the LN waveguide increases as the interval decreases.

[0059] FIG. 3D illustrates C-band wavelength dependence of the transmittance characteristics. Transmittance is 90% or greater than or equal to 90% in the entire C band (1530 to 1565 nm). Accordingly, the spot size converter 11 is compatible with wavelength division multiplexing (WDM) in the C-band.

[0060] Lastly, the tolerance of the spot size converter 11 to waveguide misalignment caused by transfer printing was tested. FIGS. 3E and 3F show dependency of the transmittance characteristic relative to axis misalignment. Axis misalignment was defined as the distance between the InP waveguide core to the LN waveguide core. FIG. 3E shows a case in which the total thickness of the III-V semiconductor layer including the six period MQW is 180 nm, and FIG. 3F shows a case in which the total thickness of the III-V semiconductor layer including a three period MQW is 135 nm.

[0061] As it can be seen from both of these figures, a transmittance of more than 80% could be achieved for axis misalignment values up to + / -1 μm, which is within the typical specifications range of advanced micro transfer printing methods.

[0062] Accordingly, with the spot size converter 11, even if an error of + / -1 μm occurs in the mounting process such as transfer printing, light can be efficiently coupled between the InP waveguide and the LN waveguide. As a result, light can be efficiently coupled between the LN waveguide and the semiconductor optical device optically coupled to the InP waveguide.

[0063] With the spot size converter according to the present embodiment, light can be efficiently coupled between a semiconductor optical device and a dielectric waveguide such as LN.

[0064] In the embodiments of the present invention, an example is given in which the membrane III-V semiconductor laser is optically connected to one end face of the spot size converter, with light input from one end face (InP waveguide) and output from the other end face (LN waveguide), but no limitation is intended. Light may be input from the other end face (LN waveguide) and output from the one end face (InP waveguide). In this case, the semiconductor optical device optically connected to the one end face may be a light-receiving device or converter.

[0065] In the embodiments of the present invention, an example is given in which an LN waveguide based on an LNOI platform is used as the dielectric waveguide, but an LT waveguide based on an LTOI platform may be used.

[0066] In the embodiments of the present invention, an example is given in which the pn junction is disposed in the lateral direction (direction parallel to the substrate surface), and a membrane device that injects current in the lateral direction is used. However, the pn junction may be disposed in a longitudinal direction (direction perpendicular to the substrate surface) and a device that injects current in the longitudinal direction may be used. Since a membrane device has high light confinement due to its ultra-thin active layer cladded with a low refractive index material, a membrane device is preferable to achieve high-speed operation at low power consumption.

[0067] In the embodiments of the present invention, an example is given in which the present invention applies to an optical communication wavelength band within the C-band, but the present invention may also be applied to another optical communication wavelength band, for example, from 1.26 μm to 1.625 μm. Further, the present invention is not limited to optical communication wavelength bands and may be used on other wavelengths.

[0068] In the embodiments of the present invention, an example is given in which InP is used in the semiconductor waveguide, but InGaAsP, AlInGaAs, or the like that is lattice-matched to InP may be used. Further, other semiconductor materials may be used depending on the applicable wavelength.

[0069] In the embodiments of the present invention, an example is given in which the semiconductor waveguide is configured by two tapered structures, but the semiconductor waveguide may be configured by one tapered structure or three or more tapered structures. Further, the semiconductor waveguide need only include a tapered structure in at least a part of the waveguide.

[0070] In the embodiments of the present invention, an example is given in which the dielectric waveguide includes a single tapered structure, but the dielectric waveguide may include multiple tapered structures.

[0071] In the embodiments of the present invention, for the configurations and manufacturing methods of the spot size converter and the optical integrated device, examples are given for the structure, dimensions, material and the like of each component, but not limitation is intended. Any configuration may be used provided that the functions of the spot size converter and the optical integrated device can be performed to achieve the effects of the present invention.

[0072] Note that the present invention is not limited to the embodiments described above, and it will be obvious that a person having ordinary skill in the art can change or combine the embodiments in various ways to implement the present invention without departing from the technical concept of the present invention.

[0073] Some or all of the above embodiments or examples may also be regarded as the following notes, but no limitation is intended.

[0074] Note 1 A spot size converter optically coupled to a semiconductor optical device, the spot size converter including, sequentially on a substrate, a dielectric waveguide, a first cladding, a semiconductor waveguide, and a second cladding covering the dielectric waveguide and the semiconductor waveguide, in which the spot size converter includes one end portion and another end portion, and light is coupled between the semiconductor optical device and the one end portion, the width of at least a portion of the semiconductor waveguide decreases from the one end portion to the other end portion, and the semiconductor waveguide is not disposed in a partial region on a side of the other end portion, and a width of at least a portion of the dielectric waveguide decreases from the one end portion to the other end portion.

[0075] Note 2 The spot size converter according to Note 1, further including a semiconductor slab on a face of the semiconductor waveguide, on a side of the dielectric waveguide.

[0076] Note 3 The spot size converter according to Note 2, in which the semiconductor slab extends near an end portion of the partial region on a side of the semiconductor waveguide.

[0077] Note 4 The spot size converter according to any one of Notes 1 to 3, in which the semiconductor waveguide includes a region in which a rate at which the width of the semiconductor waveguide decreases from the one end portion to the other end portion is different.

[0078] Note 5 The spot size converter according to Note 4, in which the semiconductor waveguide includes a first tapered region and a second tapered region, and when a ratio of a length of the second tapered region to a length of the first tapered region is from 0.18 or more to 3.1 or less, the rate in the first tapered region is from 0.045 to 0.0035 and the rate in the second tapered region is from 0.0045 to 0.006.

[0079] Note 6 The spot size converter according to any one of Notes 1 to 5, in which a thickness of the first cladding is from 50 μm or more to 250 μm or less.

[0080] Note 7 The spot size converter according to any one of Notes 1 to 6, in which the dielectric waveguide is LN or LT.

[0081] Note 8 An optical integrated device including the spot size converter described in any one of Notes 1 to 7, and a semiconductor optical device optically coupled to the spot size converter.

[0082] Note 9 The optical integrated device according to Note 8, wherein the semiconductor optical device has a membrane structure.

[0083] The present invention relates to a spot size converter and optical integrated device that can be applied to optical communications components and optical communications systems.

[0084] 101 Substrate 11 Spot size converter 121 Semiconductor waveguide (first tapered structure) 122 Semiconductor waveguide (second tapered structure) 131 Dielectric waveguide (first portion) 132 Dielectric waveguide (second portion) 133 Dielectric waveguide (third portion) 14 Cladding

Claims

1. A spot size converter optically coupled to a semiconductor optical device, the spot size converter comprising, sequentially on a substrate: 　　　　a dielectric waveguide; 　　　　a first cladding; 　　　　a semiconductor waveguide; and 　　　　a second cladding covering the dielectric waveguide and the semiconductor waveguide, wherein 　　　　the spot size converter includes one end portion and another end portion, and light is coupled between the semiconductor optical device and the one end portion, 　　　　the width of at least a portion of the semiconductor waveguide decreases from the one end portion to the other end portion, and 　　　　the semiconductor waveguide is not disposed in a partial region on a side of the other end portion, and a width of at least a portion of the dielectric waveguide decreases from the one end portion to the other end portion.

2. The spot size converter according to claim 1, further comprising a semiconductor slab on a face of the semiconductor waveguide, on a side of the dielectric waveguide.

3. The spot size converter according to claim 2, wherein the semiconductor slab extends near an end portion of the partial region on a side of the semiconductor waveguide.

4. The spot size converter according to claim 1 or 2, wherein the semiconductor waveguide includes a region in which a rate at which the width of the semiconductor waveguide decreases from the one end portion to the other end portion is different.

5. The spot size converter according to claim 4, wherein 　　　　the semiconductor waveguide includes a first tapered region and a second tapered region, and 　　　　when a ratio of a length of the second tapered region to a length of the first tapered region is from 0.18 or more to 3.1 or less, the rate in the first tapered region is from 0.045 to 0.0035 and the rate in the second tapered region is from 0.0045 to 0.006.

6. The spot size converter according to claim 1 or 2, wherein a thickness of the first cladding is from 50 μm or more to 250 μm or less.

7. The spot size converter according to claim 1 or 2, wherein the dielectric waveguide is LN or LT.

8. An optical integrated device comprising: 　　　　the spot size converter described in claim 1 or 2; and 　　　　a semiconductor optical device optically coupled to the spot size converter.

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