Optical device and production method therefor

Abstract

An opening region (131) is formed in an upper cladding layer (123) of an optical circuit board (120), an element structure (100) provided with a photon pair source (101) configured from a first optical waveguide comprising a first core (101a) comprising a compound semiconductor is mounted on and integrated with the formed opening region (131), the first optical waveguide and a second optical waveguide (120a) are optically coupled in a first optical coupling region (141), and the first optical waveguide and a third optical waveguide (120b) are optically coupled in a second optical coupling region (142).

Description

Optical device and manufacturing method thereof

[0001] The present invention relates to an optical device and a method for manufacturing the same.

[0002] Toward quantum information processing, research and development into quantum manipulation and calculation using photons is actively progressing, due to the fact that photons have weak coupling with the environment, are less susceptible to decoherence, and can operate at room temperature. Furthermore, research and development of platforms for manipulating photons was initially based on optical circuits and systems using free-space optical systems and optical fibers, which have long been commercially available.

[0003] Furthermore, toward the realization of future on-chip quantum information processing devices, research and development is accelerating on photon manipulation using optical circuits based on optical waveguides as a platform, utilizing the diverse functions provided by various optical waveguide devices. In particular, with the rapid development of Si photonics technology using Si or SiN as core materials, photon sources, photon interferometers, branching and multiplexing, wavelength filtering, phase manipulation, photon detection, etc. have been demonstrated. Furthermore, by integrating these, it has been demonstrated that basic quantum operations and calculations can be performed on optical circuits whose cores are made of Si or SiN. Note that, hereinafter, optical waveguides and optical circuits whose cores are made of Si or SiN are referred to as Si optical waveguides and Si optical circuits.

[0004] Among these, photon sources are extremely important functional elements that generate photons, which serve as quantum information media. An ideal photon source would be able to deterministically emit single photons at any time. Previous attempts have been made to realize single-photon sources by utilizing quantum dots or two-level systems based on lattice defects in materials. However, these single-photon sources still have significant challenges, such as low optical coupling efficiency with optical waveguides, the need for cryogenic temperatures for operation, and high technological barriers to fabrication.

[0005] To address the above-mentioned challenges, photon pair sources (or heralded single photon sources) are widely used as photon sources on Si optical circuits as an alternative to the ideal single photon source. Photon pair sources utilize the nonlinear optical effect (four-wave mixing) in Si optical waveguides to generate correlated photon pairs through a spontaneous parametric process using externally incident pump light.

[0006] For example, a Si optical waveguide can confine light in the optical communication wavelength range in a core cross section of the submicron order by taking advantage of the high refractive index of Si, and has a small effective mode area (A eff In addition, it has been reported that the nonlinear refractive index (n2) of Si is 100 to 200 times higher than that of glass, which is the core material of optical fibers, and the nonlinear parameter γ (=n2ω / c / A eff ) has also been reported to have a high value of about 200 (1 / W / m). This has the advantage that photon pairs can be generated with low pump light power.

[0007] Furthermore, by optimizing the core size, Si optical waveguides can be made into optical waveguides with anomalous dispersion around a wavelength of 1550 nm. Therefore, if an appropriate four-wave mixing gain spectrum is obtained using a Si optical waveguide, the wavelength of the photon pairs generated by four-wave mixing can be sufficiently separated from the pump wavelength. This has the advantage that photons at the pump wavelength, which cause noise, can be cut using a wavelength filter downstream of the photon pair source, making it easier to obtain photon pairs with less noise. In other words, the high nonlinearity (γ) of Si optical waveguides and the broadband four-wave mixing spectrum due to anomalous dispersion provide strong motivation for their widespread use as photon pair sources.

[0008] Meanwhile, optical waveguides with cores made of compound semiconductors have recently attracted attention as a new photon pair source. In particular, III-V compound semiconductors such as AlGaAs have a higher n value than Si, and are expected to realize highly efficient photon pair sources. Furthermore, compound semiconductors can be configured to have a desired band gap by controlling their composition, making it possible to suppress nonlinear loss caused by two-photon absorption, which becomes particularly pronounced when high pump light power is input. Furthermore, similar to Si optical waveguides, optical waveguides with cores made of compound semiconductors can achieve high optical confinement by using SiO2 cladding, and it is also possible to impart anomalous dispersion to the optical waveguide by controlling the structural dispersion.

[0009] Although compound semiconductor optical waveguides are thus promising as photon pair sources, it is still desirable to use Si photonics technology as a platform for constructing optical circuits other than photon pair sources. The reasons for this include the high performance of functional elements other than photon pair sources, which have already been established in optical devices for communication, excellent manufacturability that enables the realization of large-scale optical integrated circuits, and low manufacturing costs.

[0010] Based on this concept, Non-Patent Document 1 proposes a technology for integrating Si optical circuits with compound semiconductor (AlGaAs) optical waveguides. In this technology, a compound semiconductor wafer with crystal growth of AlGaAs-based materials is bonded to a wafer with a Si optical circuit formed thereon, and then the AlGaAs layer is thinned and the optical waveguide is processed to achieve the integration of an AlGaAs optical waveguide on a Si optical circuit. In Non-Patent Document 1, as shown in Fig. 1(b) and Fig. 2(b) of Non-Patent Document 1, there is no Si layer directly below the AlGaAs optical waveguide. Instead, the AlGaAs core is covered with SiO2, and the cross-sectional shape of the AlGaAs core is appropriately designed to impart anomalous dispersion.

[0011] W. Xie et al., "Silicon-integrated nonlinear III-V photonics", Photonics Research, vol. 10, no. 2, pp. 535-541, 2022.

[0012] However, the integrated structure of compound semiconductors and Si optical circuits as shown in Non-Patent Document 1 has the following problems.

[0013] Because the area of ​​a Si optical circuit is overwhelmingly larger than the area occupied by a compound semiconductor optical waveguide, most of the compound semiconductor mounted by wafer bonding does not function as a functional element, or is removed again by etching, etc., resulting in a significant problem of wasting a lot of compound semiconductor material and increasing the manufacturing costs of integrated devices.

[0014] Furthermore, even if one were to attempt to mount a compound semiconductor material locally by small piece bonding, a Si optical circuit generally involves multilayer electrode wiring to drive the constituent functional elements and an upper cladding layer made of SiO2 to protect and insulate them, and as shown in Non-Patent Document 1, it is difficult to create a state in which the Si optical waveguide layer is exposed in most of the Si optical circuit after optical circuit fabrication. Thus, the prior art has had the significant problem of difficulty in mounting optical elements made of compound semiconductor materials on a Si optical waveguide.

[0015] The present invention has been made to solve the above problems, and has as its object to make it easier to integrate a compound semiconductor optical waveguide on a Si optical circuit.

[0016] An optical device according to the present invention comprises: an element structure having a photon pair source constituted by a first optical waveguide with a first core made of a compound semiconductor; and an optical circuit substrate having second and third optical waveguides constituted by a lower cladding layer, a semiconductor layer made of Si or SiN formed on the lower cladding layer, a second core constituted by a convex portion of the semiconductor layer, and an upper cladding layer made of silicon oxide formed on the semiconductor layer and the second core; the element structure is mounted in an opening region formed by removing the upper cladding layer and integrated into the optical circuit substrate; in a first optical coupling region where the first optical waveguide and the second optical waveguide are optically coupled, one end of the first optical waveguide is arranged overlapping on the second optical waveguide and are optically coupled to each other; and in a second optical coupling region where the first optical waveguide and the third optical waveguide are optically coupled to each other, the other end of the first optical waveguide is arranged overlapping on the third optical waveguide and are optically coupled to each other.

[0017] A method for manufacturing an optical device according to the present invention includes a first step of forming an element structure having a photon pair source formed thereon, the photon pair source being composed of a first optical waveguide with a first core made of a compound semiconductor; a second step of forming an optical circuit board including a lower cladding layer, a semiconductor layer made of Si or SiN formed on the lower cladding layer, a second core made of a convex portion of the semiconductor layer, and an upper cladding layer made of silicon oxide formed on the semiconductor layer and the second core, the second optical waveguide and a third optical waveguide having ends located on the side of a central mounting area where the element structure is integrated; and a fourth step of mounting an element structure in the opening region and integrating the element structure on the optical circuit board, wherein the element structure is integrated on the optical circuit board in such a manner that, in a first optical coupling region where the first optical waveguide and the second optical waveguide are optically coupled, one end of the first optical waveguide is arranged overlapping on the second optical waveguide and they are optically coupled to each other, and in a second optical coupling region where the first optical waveguide and the third optical waveguide are optically coupled to each other, the other end of the first optical waveguide is arranged overlapping on the third optical waveguide and they are optically coupled to each other.

[0018] As described above, according to the present invention, an opening region is formed in the upper cladding layer in the mounting region of the optical circuit board, and an element structure is mounted in this opening region, in which a first optical waveguide is formed using a first core made of a compound semiconductor. This makes it easier to integrate a compound semiconductor optical waveguide on a Si optical circuit.

[0019] FIG. 1 is a perspective view showing a configuration of an optical device according to an embodiment of the present invention. FIG. 2 is a plan view (a) and a cross-sectional view (b) showing a configuration of an optical device according to an embodiment of the present invention. FIG. 3A is a cross-sectional view showing a partial configuration of an optical device according to an embodiment of the present invention. FIG. 3B is a cross-sectional view showing a partial configuration of an optical device according to an embodiment of the present invention. FIG. 3C is a cross-sectional view showing a partial configuration of an optical device according to an embodiment of the present invention. FIG. 3D is a cross-sectional view showing a partial configuration of an optical device according to an embodiment of the present invention. FIG. 3E is a cross-sectional view showing a partial configuration of an optical device according to an embodiment of the present invention. FIG. 4 is a configuration diagram showing an application example of an optical device according to an embodiment of the present invention. FIG. 5 is a characteristics diagram showing characteristics of an optical device according to an embodiment of the present invention. FIG. 6 is a characteristics diagram showing characteristics of an optical device according to an embodiment of the present invention. FIG. 7 is a characteristics diagram showing characteristics of an optical device according to an embodiment of the present invention.

[0020] An optical device according to an embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3A to 3E. FIG. 2B shows a cross section taken along line AA' in FIG. 2A. FIG. 3A shows a cross section taken along line BB' in FIG. 2A. FIG. 3B shows a cross section taken along line CC' in FIG. 2A. FIG. 3C shows a cross section taken along line DD' in FIG. 2A. FIG. 3D shows a cross section taken along line EE' in FIG. 2A. FIG. 3E shows a cross section taken along line FF' in FIG. 2A.

[0021] This optical device comprises an element structure 100 and an optical circuit substrate 120, with the element structure 100 being integrated on the optical circuit substrate 120. The element structure 100 can be integrated by transferring it to a predetermined location on the optical circuit substrate 120 using a transfer stamp by a well-known micro transfer printing method. In the transfer printing method, the element structure to be transferred is called a coupon.

[0022] The device structure 100 includes a photon pair source 101 configured as a first optical waveguide with a first core 101a made of a compound semiconductor. A cladding layer 102 made of silicon oxide is formed on the first core 101a. The device structure 100 is configured using the cladding layer 102 as a substrate (base). The first optical waveguide is a channel-type optical waveguide.

[0023] The first core 101a can be made of, for example, AlGaAs (Al composition 20%). The first core 101a can also be made of a III-V group compound semiconductor such as InP, GaAs, or InGaP, or a II-VI group compound semiconductor such as ZnSe. The material and composition of the first core 101a can be adjusted appropriately according to the desired nonlinearity.

[0024] The optical circuit board 120 includes a second optical waveguide 120a and a third optical waveguide 120b. The optical circuit board 120 includes a lower cladding layer 121, a semiconductor layer 122 made of Si or SiN formed on the lower cladding layer 121, and an upper cladding layer 123 made of silicon oxide formed on the semiconductor layer 122. The lower cladding layer 121, the semiconductor layer 122, and the upper cladding layer 123 are formed over the entire area of ​​the optical circuit board 120.

[0025] The second optical waveguide 120a and the third optical waveguide 120b are optical waveguides with a second core 125 formed from a convex portion of the semiconductor layer 122. The portions of the second optical waveguide 120a and the third optical waveguide 120b are so-called rib-type waveguides, in which slabs 126 are formed by forming recesses in the semiconductor layer 122 so as to sandwich the portion that will become the second core 125. A peripheral portion 127 around the rib-type waveguide formed by the second core 125 and the slab 126 has the same thickness as the second core 125.

[0026] The device structure 100 is mounted in an opening region 131 where the upper cladding layer 123 has been removed, and is integrated into an optical circuit substrate 120 .

[0027] Here, in a first optical coupling region 141 where the first optical waveguide and the second optical waveguide 120a are optically coupled, one end 103 of the first optical waveguide is arranged overlapping the second optical waveguide 120a, and they are optically coupled to each other. In the first optical coupling region 141, the first core 101a of the one end 103 of the first optical waveguide is arranged overlapping the second core 125 of the second optical waveguide 120a. In the first optical coupling region 141, the one end 103 of the first optical waveguide and the second optical waveguide 120a have the same waveguiding direction.

[0028] In addition, in a second optical coupling region 142 where the first optical waveguide and the third optical waveguide 120b are optically coupled, the other end 104 of the first optical waveguide is arranged to overlap the third optical waveguide 120b and are optically coupled to each other. In the second optical coupling region 142, the first core 101a of the other end 104 of the first optical waveguide is arranged to overlap the second core 125 of the third optical waveguide 120b. In the second optical coupling region 142, the other end 104 of the first optical waveguide and the third optical waveguide 120b have the same waveguiding direction.

[0029] Furthermore, in the first optical coupling region 141, the first core 101a at one end 103 of the first optical waveguide can have a tapered shape with a diameter that becomes smaller toward the end. Also, in the second optical coupling region 142, the first core 101a at the other end 104 of the first optical waveguide can have a tapered shape with a diameter that becomes smaller toward the end.

[0030] In the first optical coupling region 141, the second core 125 of the second optical waveguide 120a may have a tapered shape with a diameter that becomes smaller toward the end. In the second optical coupling region 142, the second core 125 of the third optical waveguide 120b may have a tapered shape with a diameter that becomes smaller toward the end.

[0031] In the first optical coupling region 141, one end 103 of the first optical waveguide is arranged to overlap the second optical waveguide 120a where each core is tapered, thereby forming a mode conversion structure. Similarly, in the second optical coupling region 142, the other end 104 of the first optical waveguide is arranged to overlap the third optical waveguide 120b where each core is tapered, thereby forming a mode conversion structure.

[0032] Here, the waveguide length of the first optical waveguide can be appropriately designed so that sufficient photon pairs can be generated with an appropriate pump light input power, taking into account the nonlinearity and dispersion characteristics of the first optical waveguide. In order to minimize the area of ​​the device structure 100 and improve manufacturability, the first optical waveguide can be arranged in a spiral shape when viewed in a plan view normal to the plane of the cladding layer 102. Furthermore, in order to improve the alignment accuracy between the second optical waveguide 120 a and the third optical waveguide 120 b and one end 103 and the other end 104 of the first optical waveguide in the optical circuit board 120, it is desirable to arrange the one end 103 and the other end 104 as close to each other as possible.

[0033] For example, as shown in Fig. 4, an element structure including a photon-pair source configured with a first optical waveguide having a first core 101a made of a compound semiconductor can be disposed at a location serving as a photon pair source on an optical circuit substrate including an optical circuit (Si-PIC) fabricated based on a Si optical waveguide. The optical circuit (Si-PIC) formed on the optical circuit substrate can include an optical unitary circuit.

[0034] As an example, the cross-sectional size of the optical waveguide defined by the second core 125 can be such that the core width of the second core 125 is 600 nm and the tapered tip width of the tapered portion is 250 nm. The thickness of the slab 126 can be 110 nm and the core height of the second core 125 can be 220 nm.

[0035] The cross-sectional size of first core 101a of first optical waveguide can be set so that the core width in the region serving as photon pair source 101 is 700 nm and the tapered tip width of the tapered portion at one end 103 and the other end 104 of first optical waveguide is 150 nm. Also, the core height of first core 101a of first optical waveguide can be set to 400 nm.

[0036] Next, the dispersion of the first optical waveguide in the photon pair source 101 will be described. FIG. 3E shows the structural parameters that are important for dispersion control. The core width of the first core 101a is w, the core height is h, and the total thickness of the semiconductor layer 122 made of Si is h. Si , and the layer thickness of the slab 126 is h SiSlab In addition, the width of the slab 126 in the direction perpendicular to the waveguide direction in the region where the second core 125 is not present on the line FF′ in FIG. SiRm The thickness of the cladding layer 102 on the first core 101a is set to 200 nm, and the cladding layer 102 is formed uniformly to cover the first core 101a.

[0037] It is also assumed that the region where the semiconductor layer 122 is removed between the lower part of the photon pair source 101 configured as the first optical waveguide with the first core 101a covered with the cladding layer 102 and the slab 126 is air. The wavelength of the light used is 1550 nm. The total thickness of the semiconductor layer 122 is 220 nm, which is the thickness supplied by a general Si photonics foundry.

[0038] In (a), (b), and (c) of FIG. SiSlab The relationship between w and h and dispersion is shown when the wavelengths are set to 60 nm, 110 nm, and 160 nm, respectively. To broaden the photon pair generation spectrum by four-wave mixing, it is important that the dispersion is positive (anomalous dispersion). SiSlabWhen h is set to 60 nm, as shown in FIG. 5A, it can be seen that anomalous dispersion can be obtained in a wide range of w when h is 300 to 450 nm.

[0039] On the other hand, h SiSlab When h is set to 110 nm, it is difficult to obtain anomalous dispersion at h=300 and 350 nm, as shown in FIG. 5B. However, by setting h>400 nm, it is possible to obtain anomalous dispersion at various w. SiSlab When w is set to 160 nm, it is difficult to obtain anomalous dispersion for any value of w when h is between 300 and 450 nm, as shown in FIG. 5(c).

[0040] From the above results, h SiSlab It can be seen that anomalous dispersion can be obtained by making the thickness of the slab 126 thinner than 110 nm. Si This is half the value of the conventional method, and is generally provided as a half-etching process in the process rules of Si photonics foundries, so the manufacturing barrier is low.

[0041] Next, w = 700 nm, h = 400 nm, h SiSlab = 110 nm, the effective refractive index (n eff ), group refractive index (n g ), keep it distributed lol SiRm The influence of is shown in Figure 6 (a), (b), and (c), respectively. eff , n g In both cases, w SiRm changes significantly from 1 μm to 2 μm, and w SiRm It can be seen that there is almost no fluctuation when w is 2 μm or more. SiRm However, in practice, n eff , n g It is desirable to have a design that is tolerant to dispersion controllability, manufacturing errors of the structure, and positional deviation errors when mounting the element structure 100 on the optical circuit board 120. SiRmIt is desirable to set it so that various errors are allowed.

[0042] As shown in Figure 5, it is easier to obtain anomalous dispersion by making the slab 126 as thin as possible, but in Si photonics foundries, the thickness of the slab 126 other than half-etching generally has special specifications, and it is desirable to avoid this from the standpoint of manufacturability.

[0043] If the slab 126 is completely removed, the influence of Si, which has a higher refractive index than compound semiconductors such as AlGaAs, can be suppressed. eff , n g This results in a structure that is tolerant to dispersion controllability, fabrication errors in the structure, and misalignment errors when mounting the element structure 100 on the optical circuit board 120. However, a structure without the slab 126 is inferior in manufacturability, as will be described later. By adopting a configuration in which the slab 126 is present, this optical device has the advantages of being able to obtain excellent characteristics as a photon pair source and also being excellent in manufacturability.

[0044] Next, the calculation results of the optical coupling efficiency between the first optical waveguide and the second optical waveguide 120a in the first optical coupling region 141 are shown in Figure 7. The tapered length of the first core 101a at one end 103 of the first optical waveguide and the tapered length of the second core 125 of the second optical waveguide 120a were set to 280 µm. In Figure 7, the horizontal axis (offset) represents the positional deviation between the tapered portion of the first core 101a and the tapered portion of the second core 125 in a direction parallel to the surface of the lower cladding layer 121 and perpendicular to the waveguiding direction, and the vertical axis represents the optical coupling efficiency. It can be seen that there is no excess loss up to an offset of 200 nm, and optical coupling is achieved with a loss of approximately 0.02 dB.

[0045] Next, a method for manufacturing an optical device according to an embodiment of the present invention will be described.

[0046] First, a device structure 100 is formed in which a photon pair source 101 is formed, the photon pair source 101 being configured as a first optical waveguide with a first core 101a made of a compound semiconductor (first step).

[0047] Next, an optical circuit board 120 is formed (step 2), which includes a lower cladding layer 121, a semiconductor layer 122 made of Si or SiN formed on the lower cladding layer 121, a second core 125 formed from a convex portion of the semiconductor layer 122, and an upper cladding layer 123 made of silicon oxide formed on the semiconductor layer 122 and the second core 125, and includes a second optical waveguide 120a and a third optical waveguide 120b whose ends are located on the side of the central mounting area where the device structure 100 is integrated. For example, the optical circuit board 120 manufactured by a well-known Si photonics foundry can be used. Note that when the optical circuit board 120 is made of SiN, the optical circuit board 120 provided by a similar commercial foundry can be used.

[0048] Next, the upper cladding layer 123 in the mounting area is removed by etching under conditions that selectively etch silicon oxide relative to Si or SiN, thereby forming an opening area 131 (third step).

[0049] In the aperture region 131, an optical circuit is formed so that a layer of Si or SiN is present throughout the entire region. For example, as described above, by providing the slab 126, it is possible to achieve a state in which a layer of Si is present throughout the entire aperture region 131. The aperture region 131 can be formed by selectively etching the upper cladding layer 123 made of silicon oxide using a mask pattern formed using a known photolithography technique. This etching can be performed by wet etching using hydrogen fluoride as an etchant, for example.

[0050] This wet etching etches silicon oxide but not Si, so that only the upper cladding layer 123 is selectively removed and the etching stops at the semiconductor layer 122 where the optical circuit is formed. Wet etching can suppress the problem of roughening the Si surface that occurs in dry etching.

[0051] Next, the element structure 100 is mounted in the formed opening region 131, and the element structure 100 is integrated on the optical circuit substrate 120 (step 4). For example, the element structure 100 can be integrated by transferring it to the opening region 131 on the optical circuit substrate 120 using a transfer stamp by the well-known transfer printing method. When transferring by the transfer printing method, it is extremely important that the surface roughness of the surfaces that join the element structure 100 and the optical circuit in the opening region 131 is sufficiently suppressed. As described above, the surface of the optical circuit made of Si that is exposed in the opening region 131 formed by the wet etching method is an extremely smooth surface.

[0052] On the other hand, if there is a region in the opening region 131 where Si (or SiN) is not present, there will be a region where the lower cladding layer 121 made of silicon oxide is exposed. Therefore, the selective etching of silicon oxide to form the opening region 131 may etch the exposed surface of the lower cladding layer 121. In this state, there is a serious problem that the desired optical coupling cannot be obtained in the first optical coupling region 141 and the second optical coupling region 142. To address this problem, it is effective to have the semiconductor layer 122 made of Si or SiN, such as the slab 126 and the peripheral portion 127, present throughout the entire opening region 131.

[0053] It should be noted that the slab 126 does not need to be present outside the opening region 131, and the Si optical waveguides constituting the optical circuit of the optical circuit substrate 120 can be of the channel type. In this configuration, the rib-type Si optical waveguide in the opening region 131 can be optically coupled to other channel-type Si optical waveguides using a well-known channel-to-rib conversion structure.

[0054] By integrating the element structure 100 on the optical circuit board 120 as described above, in a first optical coupling region 141 where the first optical waveguide and the second optical waveguide 120a are optically coupled, one end 103 of the first optical waveguide is arranged to overlap the second optical waveguide 120a and they are optically coupled to each other, and in a second optical coupling region 142 where the first optical waveguide and the third optical waveguide 120b are optically coupled to each other, the other end 104 of the first optical waveguide is arranged to overlap the third optical waveguide 120b and they are optically coupled to each other.

[0055] In the first optical coupling region 141, the first core 101a at one end 103 of the first optical waveguide has a tapered shape with a diameter that becomes thinner toward the end, and in the second optical coupling region 142, the first core 101a at the other end 104 of the first optical waveguide has a tapered shape with a diameter that becomes thinner toward the end.

[0056] In the first optical coupling region 141, the second core 125 of the second optical waveguide 120a has a tapered shape with a diameter that becomes thinner toward the end, and in the second optical coupling region 142, the second core 125 of the third optical waveguide 120b has a tapered shape with a diameter that becomes thinner toward the end, and in the first optical coupling region 141, one end 103 of the first optical waveguide is arranged to overlap on the second optical waveguide 120a at the location where each core is tapered, and in the second optical coupling region 142, the other end 104 of the first optical waveguide is arranged to overlap on the third optical waveguide 120b at the location where each core is tapered.

[0057] As described above, according to the embodiment of the present invention, an opening region is formed in the upper cladding layer in the mounting region of the optical circuit board, and an element structure in which a first optical waveguide is formed using a first core made of a compound semiconductor is mounted in this opening region. This makes it possible to more easily realize the integration of a compound semiconductor optical waveguide on a Si optical circuit.

[0058] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0059] 100...element structure, 101...photon pair source, 101a...first core, 102...cladding layer, 103...one end, 104...other end, 120...optical circuit substrate, 120a...second optical waveguide, 120b...third optical waveguide, 121...lower cladding layer, 122...semiconductor layer, 123...upper cladding layer, 125...second core, 126...slab, 127...surrounding portion, 131...opening region, 141...first optical coupling region, 142...second optical coupling region.

Claims

1. A method for manufacturing an optical circuit board comprising: a first step of forming a device structure having a photon pair source formed thereon, the photon pair source being composed of a first optical waveguide with a first core made of a compound semiconductor; a second step of forming an optical circuit board having a lower cladding layer, a semiconductor layer made of Si or SiN formed on the lower cladding layer, a second core made of a convex portion of the semiconductor layer, and an upper cladding layer made of silicon oxide formed on the semiconductor layer and the second core, the second optical waveguide and a third optical waveguide having ends disposed on the side of a central mounting area where the device structure is integrated; a third step of removing the upper cladding layer in the mounting area by etching under conditions that selectively etch silicon oxide relative to Si or SiN to form an opening area; and a fourth step of mounting the device structure in the opening area and integrating the device structure on the optical circuit board. a first optical coupling region where the first optical waveguide and the second optical waveguide are optically coupled, with one end of the first optical waveguide overlapping the second optical waveguide and optically coupled to each other, and a second optical coupling region where the first optical waveguide and the third optical waveguide are optically coupled, with the other end of the first optical waveguide overlapping the third optical waveguide and optically coupled to each other, 2. A method for manufacturing an optical device as defined in claim 1, wherein, in the first optical coupling region, the first core at one end of the first optical waveguide is tapered so that its diameter becomes smaller towards the end; in the second optical coupling region, the first core at the other end of the first optical waveguide is tapered so that its diameter becomes smaller towards the end; in the first optical coupling region, the second core of the second optical waveguide is tapered so that its diameter becomes smaller towards the end; in the second optical coupling region, the second core of the third optical waveguide is tapered so that its diameter becomes smaller towards the end; in the first optical coupling region, one end of the first optical waveguide is arranged to overlap on the second optical waveguide at a location where each core is tapered; and in the second optical coupling region, the other end of the first optical waveguide is arranged to overlap on the third optical waveguide at a location where each core is tapered.

3. An optical device comprising: an element structure having a photon pair source composed of a first optical waveguide with a first core made of a compound semiconductor; and an optical circuit board having second and third optical waveguides composed of a lower cladding layer, a semiconductor layer made of Si or SiN formed on the lower cladding layer, a second core composed of a convex portion of the semiconductor layer, and an upper cladding layer made of silicon oxide formed on the semiconductor layer and the second core, wherein the element structure is mounted in an opening area formed by removing the upper cladding layer and integrated into the optical circuit board; in a first optical coupling area where the first optical waveguide and the second optical waveguide are optically coupled, one end of the first optical waveguide is placed overlapping on the second optical waveguide and optically coupled to each other; and in a second optical coupling area where the first optical waveguide and the third optical waveguide are optically coupled to each other, the other end of the first optical waveguide is placed overlapping on the third optical waveguide and optically coupled to each other.

4. An optical device according to claim 3, wherein in the first optical coupling region, the first core at one end of the first optical waveguide is tapered so that its diameter becomes smaller towards the end; in the second optical coupling region, the first core at the other end of the first optical waveguide is tapered so that its diameter becomes smaller towards the end; in the first optical coupling region, the second core of the second optical waveguide is tapered so that its diameter becomes smaller towards the end; in the second optical coupling region, the second core of the third optical waveguide is tapered so that its diameter becomes smaller towards the end; in the first optical coupling region, one end of the first optical waveguide is arranged overlapping on the second optical waveguide at a location where each core is tapered; and in the second optical coupling region, the other end of the first optical waveguide is arranged overlapping on the third optical waveguide at a location where each core is tapered.

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