Optical devices

Abstract

To provide an optical device etc., capable of improving coupling efficiency while securing high integrability of a silicon photonics component.SOLUTION: An optical device has: a substrate: a first clad layer laminated on one surface of the substrate; and a first light guide formed in the first clad layer on the opposite side from the substrate. The optical device further has: an electro-optic crystal layer laminated on the surface of the first clad layer on the opposite side from the substrate; and a second light guide formed of the electro-optic crystal layer on the surface of the electro-optic crystal layer on the opposite side from the first clad layer. The optical device furthermore has a second clad layer laminated on the surface of the electro-optic crystal layer on the opposite side from the first clad layer.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an optical device.

Background Art

[0002] In silicon photonics components, due to the high refractive index difference between the core and the cladding, light can be strongly confined in a micro region. Therefore, it is advantageous for miniaturized integration of various silicon optical elements such as, for example, optical modulators, light receiving elements, phase control elements, polarization beam splitters, etc. However, in a general silicon optical modulator, for example, since it is a carrier control type of PN junction by doping, there is a problem in further expanding the modulation bandwidth.

[0003] Therefore, for example, in an optical modulator using an electro-optic crystal having an electro-optic effect such as LiNbO3 (LN: Lithium Niobate), the modulation bandwidth can be expanded and no absorption loss occurs, so a high-performance optical modulator can be realized. However, for example, it is difficult to integrate silicon optical elements other than optical modulators, such as light receiving elements, phase control elements, and polarization beam splitters, into an electro-optic crystal.

[0004] Therefore, in recent years, hybrid optical devices combining silicon photonics components and crystals having an electro-optic effect have attracted attention. In a hybrid optical device, it is required to be an optical device having both the high integration of silicon photonics components and the high modulation characteristics of a crystal having an electro-optic effect.

[0005] In a conventional optical device, an electro-optic crystal layer having an electro-optic effect is laminated on a buffer layer in a pre-formed silicon photonics component, an optical waveguide of the electro-optic crystal is formed on the electro-optic crystal layer, and a cladding layer is laminated on the electro-optic crystal layer. Further, by disposing an electrode on the cladding layer, an optical modulator of the electro-optic crystal can be formed.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0150467 [Patent Document 2] Japanese Patent Publication No. 2011-102891 [Overview of the project] [Problems that the invention aims to solve]

[0007] In conventional optical devices where electro-optic crystal layers are stacked on silicon photonic components, a first optical waveguide is formed on an intermediate layer within the silicon photonic component, and a second optical waveguide is formed on the electro-optic crystal layer. However, if the distance between the intermediate layer forming the first optical waveguide and the electro-optic crystal layer forming the second optical waveguide is too large, optical coupling between the first and second optical waveguides becomes difficult, resulting in optical loss due to deterioration of the optical coupling characteristics.

[0008] The disclosed technology was developed in view of these points, and aims to provide optical devices and the like that improve coupling efficiency while ensuring high integration of silicon photonic components. [Means for solving the problem]

[0009] In one embodiment, the optical device disclosed herein includes a substrate, a first cladding layer laminated on one side of the substrate, and a first optical waveguide formed in the first cladding layer on the side of the first cladding layer opposite to the substrate. Furthermore, the optical device includes an electro-optic crystal layer laminated on the side of the first cladding layer opposite to the substrate, and a second optical waveguide formed in the electro-optic crystal layer on the side of the electro-optic crystal layer opposite to the first cladding layer. Furthermore, the optical device includes a second cladding layer laminated on the side of the electro-optic crystal layer opposite to the first cladding layer. [Effects of the Invention]

[0010] According to one embodiment of the optical device, etc. disclosed in this application, it is possible to improve coupling efficiency while ensuring high integration of silicon photonics components. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic plan view showing an example of the configuration of the optical device in this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of the section along line AA shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing an example of the section of the BB line shown in Figure 1. [Figure 4] Figure 4 is a schematic cross-sectional view showing an example of the CC line section (Mach-Zehnder interferometer) shown in Figure 1. [Figure 5] Figure 5 is a schematic cross-sectional view showing an example of the DD line cross-sectional area (phase control element) shown in Figure 1. [Figure 6] Figure 6 is a schematic cross-sectional view showing an example of the EE line cross-section (photodetector) shown in Figure 1. [Figure 7] Figure 7 is a flowchart showing an example of the manufacturing process for an optical device. [Figure 8A] Figure 8A is a schematic cross-sectional view showing an example of the configuration of a silicon photonics component. [Figure 8B] Figure 8B is a schematic cross-sectional view showing an example of the bonding process. [Figure 9A] Figure 9A is a schematic cross-sectional view showing an example of the substrate removal process. [Figure 9B] Figure 9B is a schematic cross-sectional view showing an example of the thickness adjustment process and the electro-optic crystal layer formation process. [Figure 10A] Figure 10A is a schematic cross-sectional view showing an example of the second optical waveguide formation process. [Figure 10B] Figure 10B is a schematic cross-sectional view showing an example of the second cladding layer formation process, electrode formation process, and via formation process. [Figure 11A] Figure 11A is a schematic plan view showing an example of the configuration of an optical modulator. [Figure 11B]FIG. 11B is a schematic plan view showing an example of the configuration of an IQ optical modulator. [Figure 11C] FIG. 11C is a schematic plan view showing an example of the configuration of a DP-IQ optical modulator. [Figure 11D] FIG. 11D is a schematic plan view showing an example of the configuration of an optical communication device. [Figure 12] FIG. 12 is a schematic plan view showing an example of the configuration of an optical device of a comparative example. [Figure 13] FIG. 13 is a schematic cross-sectional view showing an example of the cross-sectional portion of the A1-A1 line shown in FIG. 12. [Figure 14] FIG. 14 is a schematic cross-sectional view showing an example of the cross-sectional portion of the B1-B1 line shown in FIG. 12. [Figure 15] FIG. 15 is a schematic cross-sectional view showing an example of the cross-sectional portion (Mach-Zehnder interferometer) of the C1-C1 line shown in FIG. 12. [Figure 16] FIG. 16 is a schematic cross-sectional view showing an example of the cross-sectional portion (phase control element) of the D1-D1 line shown in FIG. 12. [Figure 17] FIG. 17 is a schematic cross-sectional view showing an example of the cross-sectional portion (light receiving element) of the E1-E1 line shown in FIG. 12.

Embodiments for Carrying Out the Invention

[0012] [Comparative Example] FIG. 12 is a schematic plan view showing an example of the configuration of an optical device 100 of a comparative example. The optical device 100 shown in FIG. 12 includes an input unit 111, a first optical waveguide 102, a branching unit 112, two optical modulators 103, two phase control elements 104, a multiplexing unit 113, an output unit 11, and a light receiving element 105.

[0013] The input unit 111 inputs the signal light from a light source (not shown) into the first optical waveguide 102. The first optical waveguide 102 is, for example, a silicon optical waveguide through which the signal light from the input unit 111 passes.

[0014] The optical modulator 103 is, for example, an LN modulator. The optical modulator 103 has a branching section 112, two Mach-Zehnder interferometers 103A, and a multiplexing section 113, and optically modulates the signal light after optical branching from the first optical waveguide 102 according to an electrical signal, for example, it is a Mach-Zehnder modulator. The branching section 112 optically branches the signal light from the first optical waveguide 102 into two first optical waveguides 102, and outputs the optically branched signal light to each Mach-Zehnder interferometer 103A. Each Mach-Zehnder interferometer 103A has, for example, a second optical waveguide 132A of an electro-optic crystal such as LN, and an electrode 134. The electrode 134 has a signal electrode 134A and a ground electrode 134B. Each Mach-Zehnder interferometer 103A generates an electric field from the signal electrode 134A to the ground electrode 134B in response to the application of an electrical signal to the signal electrode 134A. The electric field changes the refractive index of the second optical waveguide 132A, and the phase of the light passing through the second optical waveguide 132A is adjusted in accordance with the change in the refractive index. Each Mach-Zehnder interferometer 103A outputs the phase-adjusted light to the phase control element 104. The multiplexer 113 combines the phase-shifted signal light from each phase control element 104 and outputs the combined signal light to the output unit 114 via the first optical waveguide 102.

[0015] Each phase control element 104 is a silicon component that shifts the phase of the signal light after optical modulation by the optical modulator 103. The phase control elements 104 output the phase-shifted signal light to the multiplexer 113 via the first optical waveguide 102. The multiplexer 113 combines the phase-shifted signal light from each phase control element 104 and outputs the combined signal light to the output unit 114 via the first optical waveguide 102. The output unit 114 is connected to an optical fiber (not shown) and outputs the combined signal light from the first optical waveguide 102. The photodetector 105 is a silicon component that converts a portion of the signal light output from the multiplexer 113 into an electrical signal.

[0016] For example, the silicon photonic component 120 integrates the input section 111, the first optical waveguide 102, the branching section 112, two phase control elements 104, the multiplexing section 113, the output section 114, and the photodetector 105 within the optical device 100. The silicon photonic component 120 is a pre-formed component.

[0017] Figure 13 is a schematic cross-sectional view showing an example of the A1-A1 section shown in Figure 12. The A1-A1 section shown in Figure 13 comprises a silicon photonics component 120, an electro-optic crystal layer 132, and a second cladding layer 133.

[0018] The silicon photonic component 120 includes a first substrate 121, a first cladding layer 124 laminated on the first substrate 121, and a first optical waveguide 102 formed within the first cladding layer 124. The first substrate 121 has a resistivity of, for example, less than 1000 Ωcm. The first cladding layer 124 includes an intermediate layer 122 laminated on the first substrate 121, a first optical waveguide 102 formed in the intermediate layer 122, and a buffer layer 123 laminated on the intermediate layer 122. The electro-optic crystal layer 132 is a layer having an electro-optic effect, such as LN, which is laminated on the buffer layer 123 in the silicon photonic component 120. The second cladding layer 133 is a layer such as SiO2, which is laminated on the electro-optic crystal layer 132.

[0019] Figure 14 is a schematic cross-sectional view showing an example of the B1-B1 section shown in Figure 12. The B1-B1 section shown in Figure 14 includes a first substrate 121, an intermediate layer 122, a first optical waveguide 102, a buffer layer 123, an electro-optic crystal layer 132, a second optical waveguide 132A formed on the electro-optic crystal layer 132, and a second cladding layer 133. The second optical waveguide 132A is an LN optical waveguide formed in the electro-optic crystal layer 132. The first optical waveguide 102 and the second optical waveguide 132A are optically coupled.

[0020] Figure 15 is a schematic cross-sectional view showing an example of the C1-C1 line section (Mach-Zehnder interferometer 103A) shown in Figure 12. The C1-C1 line section shown in Figure 15 is a cross-sectional view of the Mach-Zehnder interferometer 103A within the optical modulator 103. The C1-C1 line section includes a first substrate 121, an intermediate layer 122, a buffer layer 123, an electro-optic crystal layer 132, a second optical waveguide 132A, a second cladding layer 133, and an electrode 134 formed on the second cladding layer 133. The electrode 134 includes a signal electrode 134A and a ground electrode 134B. Each Mach-Zehnder interferometer 103A changes the optical refractive index of the second optical waveguide 132A in response to the application of an electrical signal to the signal electrode 134A and the electric field from the signal electrode 134A to the ground electrode 134B, and modulates the signal light passing through the second optical waveguide 132A in accordance with the change in optical refractive index.

[0021] Figure 16 is a schematic cross-sectional view showing an example of the D1-D1 section (phase control element 104) shown in Figure 12. The D1-D1 section shown in Figure 16 includes a first substrate 121, an intermediate layer 122, a first optical waveguide 102, a buffer layer 123, a phase control element 104 formed near the first optical waveguide 102 within the buffer layer 123, an electro-optic crystal layer 132, and a second cladding layer 133. Vias 135 are formed in the second cladding layer 133, the electro-optic crystal layer 132, and the buffer layer 123, exposing the metal wiring 104A2 within the phase control element 104.

[0022] The phase control element 104 includes a thermo-optic heater 104A1, which is an electrical resistor such as TiN and is placed on the first optical waveguide 102, and a metal wiring 104A2 that is electrically connected to the thermo-optic heater 104A1 and supplies current to the thermo-optic heater 104A1. The thermo-optic heater 104A1 generates heat when current flows from the metal wiring 104A2 to the thermo-optic heater 104A1. The phase control element 104 works by changing the refractive index of the silicon in the first optical waveguide 102 due to the heat from the thermo-optic heater 104A1, thereby shifting the phase of the light passing through the first optical waveguide 102.

[0023] Figure 17 is a schematic cross-sectional view showing an example of the E1-E1 section (photodetector 105) shown in Figure 12. The E1-E1 section shown in Figure 17 includes a first substrate 121, an intermediate layer 122, a first optical waveguide 102, a buffer layer 123, a photodetector 105 formed on the first optical waveguide 102 within the buffer layer 123, an electro-optic crystal layer 132, and a second cladding layer 133. Vias 135 are formed in the second cladding layer 133, the electro-optic crystal layer 132, and the buffer layer 123, exposing the metal wiring 105A2 within the photodetector 105.

[0024] The light-receiving element 105 includes a photoelectric conversion element 105A1 made of Ge or the like, which is placed on the first optical waveguide 102, and a metal wiring 105A2 connected to the photoelectric conversion element 105A1, which outputs an electrical signal from the photoelectric conversion element 105A1. The light-receiving element 105 converts the signal light passing through the first optical waveguide 102 into an electrical signal through the photoelectric conversion element 105A1, and outputs the electrical signal to a monitor (not shown) through the metal wiring 105A2.

[0025] In the comparative example optical device 100, an electro-optic crystal layer 132 is laminated on a buffer layer 123 within a pre-formed silicon photonic component 120, a second optical waveguide 132A is formed on the electro-optic crystal layer 132, and a second cladding layer 133 is laminated on the electro-optic crystal layer 132. Furthermore, by placing electrodes 134 on the second cladding layer 133, an electro-optic crystal optical modulator 103 can be formed.

[0026] In an optical device 100 in which an electro-optic crystal layer 132 is laminated on a silicon photonic component 120, a first optical waveguide 102 is formed on an intermediate layer 122 within the silicon photonic component 120, and a second optical waveguide 132A is formed on the electro-optic crystal layer 132. However, if we focus on, for example, a photodetector 105 or a phase control element 104, and the distance L2 between the intermediate layer 122 forming the first optical waveguide 102 and the electro-optic crystal layer 132 forming the second optical waveguide 132A is too large, optical coupling between the first optical waveguide 102 and the second optical waveguide 132A becomes difficult, resulting in optical loss due to deterioration of the optical coupling characteristics.

[0027] Furthermore, in the optical modulator 103, the resistivity of the first substrate 121 within the silicon photonic component 120 is less than 1000 Ωcm, which degrades the modulation bandwidth of the optical modulator 103.

[0028] Therefore, there is a need to provide an optical device of this embodiment that stabilizes optical coupling by reducing the distance between the electro-optic crystal layer forming the second optical waveguide and the first optical waveguide formed on the intermediate layer, and that can also suppress the degradation of the modulation bandwidth of the optical modulator.

[0029] The embodiments of the optical devices and the like disclosed in this application will be described in detail below with reference to the drawings. However, the present invention is not limited by these embodiments. [Examples]

[0030] Figure 1 is a schematic plan view showing an example of the configuration of the optical device 1 in this embodiment. The optical device 1 shown in Figure 1 includes an input section 11, a first optical waveguide 2, a branching section 12, two optical modulators 3, two phase control elements 4, a multiplexing section 13, an output section 14, and a photodetector 5.

[0031] The input unit 11 inputs signal light from a light source (not shown) to the first optical waveguide 2. The first optical waveguide 2 is, for example, a silicon optical waveguide through which the signal light from the input unit 11 passes.

[0032] The optical modulator 3 is an LN optical modulator of a crystal having an electro-optic effect, for example, an LN. The optical modulator 3 has a branching section 12, two Mach-Zehnder interferometers 3A, and a multiplexing section 13, and is a Mach-Zehnder modulator, for example, that optically modulates the signal light after optical branching from the first optical waveguide 2 according to an electrical signal. The branching section 12 optically branches the signal light from the first optical waveguide 2 into two first optical waveguides 2, and outputs the optically branched signal light to each Mach-Zehnder interferometer 3A. Each Mach-Zehnder interferometer 3A has a second optical waveguide 32A and an electrode 34. The second optical waveguide 32A is, for example, an LN optical waveguide. The electrode 34 has a signal electrode 34A and a ground electrode 34B. Each Mach-Zehnder interferometer 3A generates an electric field from the signal electrode 34A to the ground electrode 34B in response to the application of an electrical signal to the signal electrode 34A. The electric field changes the refractive index of the second optical waveguide 32A, and the phase of the light passing through the second optical waveguide 32A is adjusted in accordance with the change in the refractive index. Each Mach-Zehnder interferometer 3A outputs the phase-adjusted light to the phase control element 4. The multiplexing unit 13 combines the phase-shifted signal light from each phase control element 4 and outputs the combined signal light to the output unit 14 via the first optical waveguide 2.

[0033] Each phase control element 4 is a silicon component that shifts the phase of the signal light after phase modulation by the optical modulator 3. The phase control element 4 outputs the phase-shifted signal light to the multiplexer 13 via the first optical waveguide 2. The output unit 14 is connected to an optical fiber (not shown) and outputs the signal light after multiplexing from the first optical waveguide 2. The photodetector 5 is a silicon component that converts a portion of the signal light output from the multiplexer 13 into electrical signals.

[0034] For example, the silicon photonic component 20 integrates the input section 11, the first optical waveguide 2, the branching section 12, two phase control elements 4, the multiplexing section 13, the output section 14, and the photodetector 5 within the optical device 1. The silicon photonic component 20 is a pre-formed component.

[0035] Figure 2 is a schematic cross-sectional view showing an example of the AA line cross-sectional area shown in Figure 1. The AA line cross-sectional area shown in Figure 2 includes a second substrate 31, a silicon photonics component 20A, an electro-optic crystal layer 32, and a second cladding layer 33. The silicon photonics component 20A is the silicon photonics component 20 after the first substrate 21 has been removed.

[0036] The second substrate 31 is a substrate with a resistivity of, for example, 1000 Ωcm or more. The thickness L of the second substrate 31 is, for example, 1000 μm. The second substrate 31 is also a substrate of, for example, silicon, LN, or quartz. The silicon photonics component 20 has a first substrate 21, a first cladding layer 24 laminated on the first substrate 21, and a first optical waveguide 2 formed within the first cladding layer 24. The material of the first cladding layer 24 is, for example, SiO2. The first optical waveguide 2 is, for example, a silicon waveguide. The first optical waveguide 2 is, for example, a rib-type waveguide. The first optical waveguide 2 is an optical waveguide formed within the first cladding layer 24 on the side of the first cladding layer 24 opposite to the second substrate 31.

[0037] The first cladding layer 24 includes an intermediate layer 22 laminated on the first substrate 21, a first optical waveguide 2 formed in the intermediate layer 22, and a buffer layer 23 laminated on the intermediate layer 22. The buffer layer 23 is a layer laminated on one side of the second substrate 31. The intermediate layer 22 is a layer laminated on the side of the buffer layer 23 opposite to the second substrate 31.

[0038] The buffer layer 23 from the silicon photonics component 20A is bonded to the second substrate 31. In other words, the cross-sectional area along line AA shown in Figure 2 has the second substrate 31, the buffer layer 23 laminated on the second substrate 31, the intermediate layer 22 laminated on the buffer layer 23 and on which the first optical waveguide 2 is formed, the electro-optic crystal layer 32 laminated on the intermediate layer 22, and the second cladding layer 33 laminated on the electro-optic crystal layer 32. The material of the second cladding layer 33 is, for example, SiO2. The second cladding layer 33 is a layer laminated on the side of the electro-optic crystal layer 32 opposite to the first cladding layer 24.

[0039] The first optical waveguide 2 is formed on the second substrate 31 side of the intermediate layer 22. The electro-optic crystal layer 32 is, for example, a layer of X-cut LN. LN is an anisotropic material whose refractive index changes when an electric field is applied, for example, with a Pockels coefficient of approximately 30 pm / V. The electro-optic crystal layer 32 is a layer laminated on the side of the first cladding layer 24 opposite to the second substrate 31. The second optical waveguide 32A is an optical waveguide formed by the electro-optic crystal layer 32 on the side of the electro-optic crystal layer 32 opposite to the first cladding layer 24. The first optical waveguide 2 and the second optical waveguide 32A have a trapezoidal shape with their long sides facing each other via the intermediate layer 22.

[0040] The intermediate layer 22 is a layer of material with a lower refractive index than LN, for example, SiO2. The thickness dimension of the intermediate layer 22 between the first optical waveguide 2 and the second optical waveguide 32A is, for example, 2 μm~ 6 The thickness is approximately μm. The buffer layer 23 is provided to prevent light propagating through the first optical waveguide 2 from being absorbed by the electrode 34, and is, for example, a layer of SiO2. The thickness of the electro-optic crystal layer 32 is, for example, approximately 0.5 to 3 μm.

[0041] Figure 3 is a schematic cross-sectional view showing an example of the BB line cross-section shown in Figure 1. The BB line cross-section shown in Figure 3 includes a second substrate 31, a buffer layer 23, a first optical waveguide 2, an intermediate layer 22, an electro-optic crystal layer 32, a second optical waveguide 32A formed on the electro-optic crystal layer 32, and a second cladding layer 33. Optical coupling is performed between the first optical waveguide 2 and the second optical waveguide 32A. The first optical waveguide 2 and the second optical waveguide 32A are located close to each other vertically. For example, by making the width of the first optical waveguide 2 adiabatically narrower, the confinement of light is weakened, and it is gradually coupled to the second optical waveguide 32A. The thickness of the intermediate layer 22 between the first optical waveguide 2 formed in the intermediate layer 22A and the second optical waveguide 32A formed on the electro-optic crystal layer 32 is shortened, that is, the distance L between the first optical waveguide 2 and the second optical waveguide 32A is shortened.

[0042] Figure 4 is a schematic cross-sectional view showing an example of the CC line section (Mach-Zehnder interferometer 3A) shown in Figure 1. The CC line section shown in Figure 4 is a cross-sectional view of the Mach-Zehnder interferometer 3A within the optical modulator 3. The CC line section includes a second substrate 31, a buffer layer 23, an intermediate layer 22, an electro-optic crystal layer 32, a second optical waveguide 32A, a second cladding layer 33, and an electrode 34 formed on the second cladding layer 33.

[0043] The electrode 34 has a signal electrode 34A and a ground electrode 34B. The signal electrode 34A is made of a metal material such as gold or copper, and has a width of 2 to 10 μm and a thickness of 1 to 20 μm. The ground electrode 34B is made of a metal material such as gold or copper, and has a thickness of 1 μm or more.

[0044] If the electro-optic crystal layer 32 is an X-cut LN, the refractive index changes when an electric field is applied horizontally, and an electric field is applied from the signal electrode 34A to the ground electrode 34B in the left-right direction of the second optical waveguide 32A. Each Mach-Zehnder interferometer 3A changes the optical refractive index of the second optical waveguide 32A in response to the electric field from the signal electrode 34A to the ground electrode 34B in response to the application of an electrical signal to the signal electrode 34A, and modulates the signal light passing through the second optical waveguide 32A in accordance with the change in optical refractive index.

[0045] Figure 5 is a schematic cross-sectional view showing an example of the DD line section (phase control element 4) shown in Figure 1. The DD line section shown in Figure 5 includes a second substrate 31, a buffer layer 23, a first optical waveguide 2, an intermediate layer 22, a phase control element 4 formed near the first optical waveguide 2 within the buffer layer 23, an electro-optic crystal layer 32, and a second cladding layer 33. Vias 35 are formed in the second cladding layer 33, the electro-optic crystal layer 32, the intermediate layer 22, and the buffer layer 23, exposing the metal wiring 4A2 within the phase control element 4.

[0046] The phase control element 4 includes a thermo-optic heater 4A1, which is an electrical resistor such as TiN and is placed in close proximity to the first optical waveguide 2, and a metal wiring 4A2 that is electrically connected to the thermo-optic heater 4A1 and supplies current to the thermo-optic heater 4A1. The thermo-optic heater 4A1 generates heat when current flows from the metal wiring 4A2 to the thermo-optic heater 4A1. The phase control element 4 works by changing the refractive index of the silicon in the first optical waveguide 2 due to the heat from the thermo-optic heater 4A1, thereby shifting the phase of the light passing through the first optical waveguide 2.

[0047] Figure 6 is a schematic cross-sectional view showing an example of the EE line section (photodetector 5) shown in Figure 1. The EE line section shown in Figure 6 includes a second substrate 31, a buffer layer 23, a first optical waveguide 2, an intermediate layer 22, a photodetector 5 formed near the first optical waveguide 2 within the buffer layer 23, an electro-optic crystal layer 32, and a second cladding layer 33. Vias 35 are formed in the second cladding layer 33, the electro-optic crystal layer 32, the intermediate layer 22, and the buffer layer 23, exposing the metal wiring 5A2 within the photodetector 5.

[0048] The light-receiving element 5 includes a photoelectric conversion element 5A1 made of Ge or the like, positioned close to the first optical waveguide 2, and a metal wiring 5A2 connected to the photoelectric conversion element 5A1, which outputs an electrical signal from the photoelectric conversion element 5A1. The light-receiving element 5 converts the signal light passing through the first optical waveguide 2 into an electrical signal through the photoelectric conversion element 5A1, and outputs the electrical signal to a monitor (not shown) through the metal wiring 5A2.

[0049] Figure 7 is a flowchart showing an example of the manufacturing process for the optical device 1. The manufacturing process involves a preparation step (step S11) to prepare a pre-formed silicon photonic component 20. Then, a bonding step (step S12) is performed in which the silicon photonic component 20 is inverted and the second substrate 31 is bonded to the surface of the buffer layer 23 inside the silicon photonic component 20. The second substrate 31 has a higher resistivity of 1000 Ωcm or more compared to the first substrate 21.

[0050] After bonding the second substrate 31, a removal process is performed to remove the first substrate 21 from within the silicon photonic component 20 (step S13). A thickness adjustment process is performed to adjust the thickness of the intermediate layer 22 within the silicon photonic component 20A from which the first substrate 21 has been removed (step S14). By adjusting the thickness of the intermediate layer 22, the distance L between the second optical waveguide 32A and the first optical waveguide 2 of the electro-optic crystal layer 32 can be shortened upon completion, thereby achieving highly efficient optical coupling.

[0051] Step S15 is performed to form an electro-optic crystal layer, which involves stacking an electro-optic crystal layer 32 on the intermediate layer 22 within the silicon photonic component 20A after adjusting the thickness of the intermediate layer 22. Step S16 is performed to form a second optical waveguide 32A on the electro-optic crystal layer 32.

[0052] Step S17 is performed to form a second cladding layer 33 on the electro-optic crystal layer 32 on which the second optical waveguide 32A is formed. Step S18 is performed to form an electrode 34 on the second cladding layer 33. Step S19 is performed to form vias 35 in the second cladding layer 33, the electro-optic crystal layer 32, and the buffer layer 23 so that the metal wiring 4A2 of the phase control element 4 and the metal wiring 5A2 of the photodetector 5 in the buffer layer 23 are exposed. As a result, the optical device 1 is formed as shown in Figure 10B.

[0053] In the optical device 1 shown in Figure 10B, a second substrate 31 with higher resistivity is used compared to the first substrate 21, thus avoiding situations such as degradation of the modulation bandwidth of the optical modulator 3. Furthermore, in the optical device 1, the thickness of the intermediate layer 22 is adjusted, thereby shortening the distance L between the second optical waveguide 32A and the first optical waveguide 2 in the electro-optic crystal layer 32, and thus improving the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A.

[0054] Figure 8A is a schematic cross-sectional view showing an example of the configuration of a silicon photonics component 20. The silicon photonics component 20 includes a first substrate 21, an intermediate layer 22, a plurality of first optical waveguides 2, and a buffer layer 23. Within the buffer layer 23, a phase control element 4 and a photodetector element 5 are embedded on any of the first optical waveguides 2. The silicon photonics component 20 is a pre-formed component.

[0055] Figure 8B is a schematic cross-sectional view showing an example of the bonding process. After reversing the front and back sides of the silicon photonic component 20 shown in Figure 8A, the second substrate 31 is bonded onto the buffer layer 23 of the silicon photonic component 20.

[0056] Figure 9A is a schematic cross-sectional view showing an example of the substrate removal process. By removing the first substrate 21 from within the silicon photonic component 20 to which the second substrate 31 is attached, the silicon photonic component 20A shown in Figure 9A is formed.

[0057] Figure 9B is a schematic cross-sectional view showing an example of the thickness adjustment process and the electro-optic crystal layer formation process. The thickness of the intermediate layer 22 in the silicon photonic component 20A from which the first substrate 21 has been removed is adjusted. By adjusting the thickness of the intermediate layer 22, the distance between the first optical waveguide 2 and the second optical waveguide 32A is adjusted. After adjusting the thickness of the intermediate layer 22, the electro-optic crystal layer 32 is laminated onto the intermediate layer 22 of the silicon photonic component 20A.

[0058] Figure 10A is a schematic cross-sectional view showing an example of the second optical waveguide formation process. After laminating an electro-optic crystal layer 32 on the intermediate layer 22 of the silicon photonics component 20A, the second optical waveguide 32A is formed on the electro-optic crystal layer 32.

[0059] Figure 10B is a schematic cross-sectional view showing an example of the second cladding layer formation process, electrode formation process, and via formation process. After forming the second optical waveguide 32A, the second cladding layer 33 is laminated on the electro-optic crystal layer 32. Furthermore, after laminating the second cladding layer 33, the signal electrode 34A and ground electrode 34B are placed on the second cladding layer 33 on which the second optical waveguide 32A of the Mach-Zehnder interferometer 3A is located. Furthermore, vias 35 are formed in the second cladding layer 33, electro-optic crystal layer 32, intermediate layer 22, and buffer layer 23 so that the metal wiring 4A2 of the phase control element 4 and the metal wiring 5A2 of the photodetector 5 in the silicon photonics component 20A are exposed from the second cladding layer 33, thereby forming the optical device 1.

[0060] In the optical device 1 of this embodiment, a second substrate 31 with higher resistivity is used compared to the first substrate 21, so that, for example, the modulation bandwidth of the optical modulator 3 does not deteriorate. Furthermore, in the optical device 1, the thickness of the intermediate layer 22 is adjusted, so the distance L between the electro-optic crystal layer 32 and the first optical waveguide 2 is shortened, so that the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A can be improved.

[0061] The optical device 1 includes a first optical waveguide 2 formed in the first cladding layer 24 on the side of the first cladding layer 24 opposite to the second substrate 31, an electro-optic crystal layer 32 laminated on the side of the first cladding layer 24 opposite to the second substrate 31, and a second optical waveguide 32A formed in the electro-optic crystal layer 32 on the side of the electro-optic crystal layer 32 opposite to the first cladding layer 24. As a result, the distance L between the electro-optic crystal layer 32 and the first optical waveguide 2 is shortened, thereby improving the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A. Moreover, it is possible to realize a low-loss, mass-producible optical device while simultaneously utilizing the high integration capabilities of silicon photonics and the high modulation characteristics of crystals with electro-optic effects.

[0062] Even if the optical device 1 employs a silicon photonic component 20 that incorporates a phase control element 4 and a photodetector 5, the LN optical modulator 3 will be integrated into the silicon photonic component 20. Therefore, the optical device 1 can provide different functions depending on the integrated silicon element.

[0063] The first optical waveguide 2 is formed on the surface of the intermediate layer 22 that is in contact with the buffer layer 23, while the electro-optic crystal layer 32 is laminated on the surface of the intermediate layer 22 opposite to the buffer layer 23. As a result, the distance L between the electro-optic crystal layer 32 and the first optical waveguide 2 is shortened, thereby improving the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A.

[0064] The system further includes at least one silicon component 4, 5 disposed within the first cladding layer 24 between the first optical waveguide 2 and the second substrate 31. As a result, high integration can be ensured.

[0065] The optical modulator 3 has an electrode 34 that applies an electrical signal to the second optical waveguide 32A, which is located on the side of the second cladding layer 33 opposite to the electro-optic crystal layer 32, and the second substrate 31 is a substrate having a resistivity of 1000 Ωcm or more. As a result, by using the second substrate 31 which has a higher resistivity compared to the first substrate 21, it is possible to avoid situations such as deterioration of the modulation bandwidth of the optical modulator 3.

[0066] The signal electrode 34A and the ground electrode 34B are positioned on the side of the second cladding layer 33 opposite to the electro-optic crystal layer 32, so as to apply an electrical signal horizontally to the second optical waveguide 32A when the electro-optic crystal layer 32 is X-cut. As a result, this can also be applied to an optical modulator 3 equipped with an X-cut electro-optic crystal layer 32.

[0067] For the sake of explanation, an X-cut LN electro-optic crystal layer 32 is used as an example, but this is also applicable to an optical device 1 using a Z-cut LN electro-optic crystal layer 32. The optical device 1 has a Z-cut LN electro-optic crystal layer 32 and a second optical waveguide 32A formed in the electro-optic crystal layer 32 along the X or Y direction of the crystal axis of the electro-optic crystal layer 32. In the case of an electro-optic crystal layer 32 whose refractive index changes when an electric field is applied in the vertical (Z) direction, an electric field is applied in the vertical direction of the second optical waveguide 32A by placing a signal electrode 34A directly above the second optical waveguide 32A. In this case, the ground electrode 34B may be embedded in the second cladding layer 33. A buffer layer 23 may also be formed between the second optical waveguide 32A and the signal electrode 34A. For example, by forming an SiO2 buffer layer 23, the electrode absorption loss of the propagating optical signal can be reduced even if the signal electrode 34A is located directly above the second optical waveguide 32A.

[0068] Furthermore, although the electro-optic crystal layer 32 is shown as an example, the material of the electro-optic crystal is not limited to LN, but any electro-optic crystal will suffice. For example, perovskite-type oxides such as PZT (lead zirconate titanate), PLZT (lanthanum-doped lead zirconate titanate), or BaTiO3 (barium titanate) may be used and can be changed as appropriate. Note that the Pockels coefficient of PZT is approximately 110 pm / V, the Pockels coefficient of PLZT is approximately 700 pm / V, and the Pockels coefficient of BaTiO3 is approximately 1850 pm / V. Therefore, the Pockels coefficient of the electro-optic crystal applied to this invention is within the range of 10 to 2000 pm / V.

[0069] Furthermore, although the first optical waveguide 2 and the second optical waveguide 32A are exemplified as ridge-type waveguides, the method is not limited to ridge-type waveguides and can also be applied to channel-type waveguides, for example.

[0070] Figure 11A is a schematic plan view showing an example of the configuration of an optical device 1A incorporating an optical modulator 3. Components identical to those in the optical device 1 of Example 1 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1A shown in Figure 11A includes an optical modulator 3 and two phase control elements 4. The optical modulator 3 includes a branching section 12, two Mach-Zehnder interferometers 3A, and a multiplexing section 13. For example, the Mach-Zehnder interferometer 3A includes a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, an electro-optical crystal layer 32, a second optical waveguide 32A, a second cladding layer 33, and an electrode 34. The phase control element 4 portion comprises a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, a phase control element 4, an electro-optic crystal layer 32, and a second cladding layer 33. Therefore, in the optical device 1A incorporating the optical modulator 3A shown in Figure 11A, high integration of silicon photonics can be ensured while improving the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A, and further suppressing the degradation of the modulation bandwidth.

[0071] Figure 11B is a schematic plan view showing an example of the configuration of an optical device 1B incorporating an IQ optical modulator 3B. Components identical to those in the optical device 1A shown in Figure 11A are denoted by the same reference numerals, and the explanation of the redundant components and operations is omitted. The IQ optical modulator 3B in the optical device 1B shown in Figure 11B has a first branching section 12A, an I (Inphase) component optical modulator 3B1, a Q (Quadrature) component optical modulator 3B2, two first phase control elements 4A, and a first multiplexing section 13A. The I component optical modulator 3B1 phase modulates the I component optical signal. The Q component optical modulator 3B2 phase modulates the Q component optical signal. The I component optical modulator 3B1 has a branching section 12, two Mach-Zehnder interferometers 3A1 (3A2), and a multiplexing section 13. The Q-component optical modulator 3B2 includes a branching section 12, two Mach-Zehnder interferometers 3A1 (3A2), and a multiplexing section 13.

[0072] The first branching section 12A optically splits the signal light from the first optical waveguide 2 and outputs the split signal light to each optical modulator 3B. The I-component optical modulator 3B1 outputs the phase-modulated signal light of the I-component from the multiplexing section 13 within the optical modulator 3B1 to the first phase control element 4A. The first phase control element 4A phase-shifts the phase-modulated signal light of the I-component and outputs the phase-shifted signal light of the I-component to the first multiplexing section 13A.

[0073] Furthermore, the Q component optical modulator 3B2 outputs the phase-modulated signal light of the Q component from the multiplexer 13 within the optical modulator 3B2 to the first phase control element 4A. The first phase control element 4A phase-shifts the phase-modulated signal light of the Q component and outputs the phase-shifted Q component signal light to the first multiplexer 13A. The first multiplexer 13A combines the I component signal light and the Q component signal light and outputs the combined IQ component signal light to the output unit 14.

[0074] For example, the Mach-Zehnder interferometer 3A1 (3A2) comprises a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, an electro-optic crystal layer 32, a second optical waveguide 32A, a second cladding layer 33, and an electrode 34. The phase control element 4 (first phase control element 4A) comprises a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, a phase control element 4 (first phase control element 4A), an electro-optic crystal layer 32, and a second cladding layer 33. Therefore, in the optical device 1B incorporating the IQ optical modulator 3B shown in Figure 11B, it is possible to improve the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A, and further suppress the degradation of the modulation bandwidth, while ensuring the high integration of silicon photonics.

[0075] Figure 11C is a schematic plan view showing an example of the configuration of the DP-IQ optical modulator 3C. Components identical to those in the optical device 1B shown in Figure 11B are denoted by the same reference numerals, and the explanation of the redundant components and operations is omitted. The DP-IQ optical modulator 3C in the optical device 1C shown in Figure 11C includes a second branching section 12B, an IQ optical modulator 3C1 for the X-polarization component, an IQ optical modulator 3C2 for the Y-polarization component, a PR (Polarization Rotator) 15, and a PBC (Polarization Beam Combiner) 16.

[0076] The second branching section 12B optically splits the signal light from the first optical waveguide 2 and outputs the signal light after optical splitting to the respective IQ optical modulators 3C1 and 3C2. The X-polarized IQ optical modulator 3C1 has an I component optical modulator 3B1 of the X-polarized component and a Q component optical modulator 3B2 of the X-polarized component.

[0077] The first multiplexer 13A in the X-polarized component IQ optical modulator 3C1 combines the I component signal light of the X-polarized component from the multiplexer 13 in the I component optical modulator 3B1 with the Q component signal light of the X-polarized component from the multiplexer 13 in the Q component optical modulator 3B2, and outputs the IQ component signal light of the X-polarized component to the PBC 16.

[0078] The first multiplexer 13A in the Y-polarized IQ optical modulator 3C2 combines the I component signal light of the Y-polarized component from the multiplexer 13 in the I component optical modulator 3B2 with the Q component signal light of the Y-polarized component from the multiplexer 13 in the Q component optical modulator 3B2, and outputs the IQ component signal light of the Y-polarized component to PR15. PR15 polarizes the IQ component signal light of the Y-polarized component and outputs the polarized IQ component signal light of the Y-polarized component after polarization rotation to PBC16. PBC16 combines the IQ component signal light of the X-polarized component with the polarized IQ component signal light of the Y-polarized component after polarization rotation, and outputs the combined XY-polarized component signal light to the output unit.

[0079] For example, the Mach-Zehnder interferometer 3A1 (3A2) portion within the DP-IQ optical modulator 3C includes a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, an electro-optic crystal layer 32, a second optical waveguide 32A, a second cladding layer 33, and an electrode 34. The phase control element 4 (first phase control element 4A) portion includes a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, a phase control element 4 (first phase control element 4A), an electro-optic crystal layer 32, and a second cladding layer 33. Furthermore, the PR15 and PBC16 portions also include the second substrate 31, the buffer layer 23, the intermediate layer 22, the first optical waveguide 2, PR15, PBC16, the electro-optic crystal layer 32, and the second cladding layer 33. Therefore, in the optical device 1C incorporating the DP-IQ optical modulator 3C shown in Figure 11C, while ensuring the high integration of silicon photonics, it is possible to improve the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A, and further suppress the degradation of the modulation bandwidth.

[0080] Figure 11D is a schematic plan view showing an example of the configuration of the optical communication device 1D. Components identical to those in the DP-IQ optical modulator 3C shown in Figure 11C are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical communication device 1D shown in Figure 11D includes a DP-IQ optical modulator 3C, a third branching section 12C, a light receiving input section 41, a PBS (Polarization Beam Splitter) 42, a PR 43, a first optical hybrid circuit 44A (44), a second optical hybrid circuit 44B (44), and four light receiving elements 5A and four light receiving elements 5B.

[0081] The third branching section 12C optically splits the local light from a light source (not shown) from the input section 11 and outputs the split light to the DP-IQ optical modulator 3C and each hybrid circuit 44. The light receiving input section 41 receives received light from an optical fiber (not shown). The PBS 42 splits the received light from the light receiving input section 41 into X-polarized and Y-polarized light, outputs the X-polarized light to the first optical hybrid circuit 44A, and outputs the Y-polarized light to the PR 43. The PR 43 rotates the Y-polarized light by 90 degrees and outputs the rotated Y-polarized light to the second optical hybrid circuit 44B.

[0082] The first optical hybrid circuit 44A acquires I and Q component optical signals by interfering the X-polarization component of the received light with local light emission. The first optical hybrid circuit 44A outputs the I component optical signal of the X-polarization component to the photodetector 5A. The first optical hybrid circuit 44A outputs the Q component optical signal of the X-polarization component to the photodetector 5A.

[0083] The second optical hybrid circuit 44B interferes with the Y-polarization component of the received light by local emission to acquire the I and Q component optical signals. The second optical hybrid circuit 44B outputs the I component optical signal of the Y-polarization component to the photodetector 5B. The second optical hybrid circuit 44B outputs the Q component optical signal of the Y-polarization component to the photodetector 5B.

[0084] The photodetector 5A converts the I component optical signal of the X-polarized component from the first optical hybrid circuit 44A into electrical signals and outputs the electrical signal of the I component after the electrical conversion. The photodetector 5A also converts the Q component optical signal of the X-polarized component from the first optical hybrid circuit 44A into electrical signals and outputs the electrical signal of the Q component after the electrical conversion. The photodetector 5B converts the I component optical signal of the Y-polarized component from the second optical hybrid circuit 44B into electrical signals and outputs the electrical signal of the I component after the electrical conversion. The photodetector 5B also converts the Q component optical signal of the Y-polarized component from the second optical hybrid circuit 44B into electrical signals and outputs the electrical signal of the Q component after the electrical conversion.

[0085] For example, the Mach-Zehnder interferometer 3A1 (3A2) portion within the DP-IQ optical modulator 3C includes a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, an electro-optic crystal layer 32, a second optical waveguide 32A, a second cladding layer 33, and an electrode 34. The phase control element 4 (first phase control element 4A) portion includes a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, a phase control element 4 (first phase control element 4A), an electro-optic crystal layer 32, and a second cladding layer 33. Furthermore, the PR15 and PBC16 portions also include the second substrate 31, the buffer layer 23, the intermediate layer 22, the first optical waveguide 2, PR15, PBC16, the electro-optic crystal layer 32, and the second cladding layer 33.

[0086] The photodetector 5 portion comprises a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, the photodetector 5, an electro-optic crystal layer 32, and a second cladding layer 33. Similarly, the PR43 and PBS42 portions also consist of a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, PR43, PBS42, an electro-optic crystal layer 32, and a second cladding layer 33. Likewise, the hybrid circuit 44 portion also consists of a second substrate 31, a buffer layer 23, an intermediate layer 22, a first optical waveguide 2, a hybrid circuit 44, an electro-optic crystal layer 32, and a second cladding layer 33. Therefore, the optical communication device 1D shown in Figure 11D can improve the optical coupling efficiency between the first optical waveguide 2 and the second optical waveguide 32A, and further suppress the degradation of the modulation bandwidth, while ensuring high integration of silicon photonics. [Explanation of symbols]

[0087] 1 Optical devices 2. First optical waveguide 3,3B1,3B2 Optical modulators 3B, 3C1, 3C2 IQ optical modulator 3C DP-IQ Optical Modulator 3A Mach-Zehnder Interferometer 4 Phase control elements 5. Photodetector 21 First substrate 22 Middle Class 23 Buffer Layer 24. First cladding layer 31 Second substrate 32 Electro-optic crystal layer 32A Second Optical Waveguide 33. Second cladding layer

Claims

1. circuit board and A buffer layer within a first cladding layer, which is laminated on one side of the substrate, An intermediate layer within the first cladding layer, which is laminated on the side of the buffer layer opposite to the substrate, A first optical waveguide formed on the surface of the buffer layer that is in contact with the intermediate layer, An electro-optic crystal layer laminated on the surface of the intermediate layer opposite to the buffer layer, A second optical waveguide formed in the electro-optic crystal layer is provided on the surface of the electro-optic crystal layer opposite to the intermediate layer, The electro-optic crystal layer comprises a second cladding layer laminated on the side opposite to the intermediate layer, An optical device characterized in that an optical signal guiding the first optical waveguide transitions to the second optical waveguide via the intermediate layer.

2. The optical device according to claim 1, further comprising at least one silicon component disposed within the buffer layer between the first optical waveguide and the substrate.

3. The aforementioned silicon component is The optical device according to claim 2, characterized in that it is a photodetector that converts an optical signal passing through the first optical waveguide into an electrical signal.

4. The aforementioned silicon component is The optical device according to claim 2, characterized in that it is a phase control element that controls the refractive index of the first optical waveguide with a heater that heats the first optical waveguide.

5. The second cladding layer further comprises an electrode disposed on the surface opposite to the electro-optic crystal layer for applying an electrical signal to the second optical waveguide, The aforementioned substrate is The optical device according to any one of claims 1 to 4, characterized in that it is a substrate having a resistivity of 1000 Ωcm or more.

6. The electrode is It has a signal electrode and a ground electrode, The signal electrode and the ground electrode are, The optical device according to claim 5, characterized in that, when the axis in which the electro-optic effect of the electro-optic crystal layer is most strongly expressed is in the horizontal direction, the second optical waveguide is arranged on the side of the second cladding layer opposite to the electro-optic crystal layer so as to apply the electrical signal in the horizontal direction.

7. The electrode is It has a signal electrode and a ground electrode, Either the signal electrode or the ground electrode is The optical device according to claim 5, characterized in that the second optical waveguide is located on the portion of the second cladding layer where it is arranged, when the axis in which the electro-optic effect of the electro-optic crystal layer is most strongly expressed is in the vertical direction.

8. The optical device according to any one of claims 1 to 7, characterized in that the Pockels coefficient of the electro-optic crystal layer is in the range of 10 to 2000 pm / V.

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