Optical modulation element, optical modulator using optical modulation element, and lidar

Abstract

To provide an optical modulation element for modulating light propagating through an optical waveguide according to an applied voltage.SOLUTION: An optical modulation element (1A) is provided, comprising an optical waveguide (23, 24) and a pair of electrodes (26, 27) for applying an electric field to the optical waveguide. The optical waveguide includes a ferroelectric layer (24) containing a compound represented by HfxZr1-xO2, where 0<x<1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical modulation element, an optical modulator using the optical modulation element, and a LIDAR. [Background technology]

[0002] In recent years, development has been progressing on devices that realize high-speed, energy-efficient communications by using optical signals, which have a wider operating bandwidth and less propagation loss than electrical signals. Generally, communications using optical signals are realized by optical modulation elements that convert electrical signals into optical signals.

[0003] For example, Non-Patent Document 1 discloses an optical modulation element having an optical waveguide configured by depositing a LiNbO3 film adjacent to a Si waveguide core. When a voltage is applied to an optical waveguide having ferroelectric LiNbO3, the refractive index changes due to the Pockels effect, making it possible to control the modulation of an optical signal according to the applied voltage. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] C. Wang et al., Nature, vol. 562, no. 7725, pp. 101-104, 2018. Summary of the Invention [Problem to be solved by the invention]

[0005] When manufacturing an optical modulation element using Si, it is preferable to apply a semiconductor element manufacturing process for which manufacturing methods have been established. However, since LiNbO3 disclosed in Non-Patent Document 1 is a material that is not generally used in semiconductor elements, it is not easy to manufacture it using a semiconductor element manufacturing process. Therefore, there is a need to realize an optical modulation element using a material that is highly compatible with existing semiconductor element manufacturing processes.

[0006] The present invention has been made to solve such problems, and an object thereof is to provide an optical modulation element that modulates light propagating through an optical waveguide according to an applied voltage using a material having high affinity with an existing semiconductor element manufacturing process.

Means for Solving the Problems

[0007] The optical modulation element according to one aspect of the present invention includes an optical waveguide and a pair of electrodes for applying an electric field to the optical waveguide. The optical waveguide includes a ferroelectric layer containing a compound represented by Hf , , , , , , , ,

[0009] , [Figure 3C] , [Figure 3B] , [Figure 3A] , [Figure 3E] , [Figure 2] , [Figure 3D] , [Figure 1] Zr 1-x O2 (0 < x < 1).

Effects of the Invention

[0008] According to the optical modulation element of one aspect of the present invention, when a voltage is applied to a pair of electrodes, in an optical waveguide including a ferroelectric layer made of Hf x Zr 1-x O2, the refractive index changes due to the Pockels effect, so that the light propagating through the optical waveguide can be modulated according to the applied voltage. Further, since Hf x Zr 1-x O2 is a material used in an existing semiconductor manufacturing process, an optical modulation element can be put into practical use by diverting an existing manufacturing method and manufacturing apparatus.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a schematic configuration diagram of an optical modulator using the optical modulation element of the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the optical modulation element. [Figure 3A] FIG. 3A is an explanatory diagram of the manufacturing process of the optical modulation element. [Figure 3B] FIG. 3B is an explanatory diagram of the manufacturing process of the optical modulation element. [Figure 3C] FIG. 3C is an explanatory diagram of the manufacturing process of the optical modulation element. [Figure 3D] FIG. 3D is an explanatory diagram of the manufacturing process of the optical modulation element. [Figure 3E]FIG. 3E is an explanatory diagram of a manufacturing process of the optical modulation element. [Figure 3F] FIG. 3F is an explanatory diagram of a manufacturing process of the optical modulation element. [Figure 4] FIG. 4 is a schematic diagram of a Mach-Zehnder interferometer using an optical modulation element. [Figure 5] FIG. 5 is a diagram showing the measurement results of FIG. [Figure 6] FIG. 6 is a cross-sectional view of the light modulation element according to the second embodiment. [Figure 7] FIG. 7 is a cross-sectional view of the light modulation element according to the third embodiment. [Figure 8] FIG. 8 is a cross-sectional view of the light modulation element according to the fourth embodiment. [Figure 9] FIG. 9 is a cross-sectional view of the optical modulation element according to the fifth embodiment. [Figure 10] FIG. 10 is a cross-sectional view of the light modulation element of the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] (First embodiment) FIG. 1 is a diagram showing an optical modulator using the optical modulation element of this embodiment.

[0012] 1, an optical modulation element 1A is used in an optical modulator 2. The optical modulator 2 includes an input section 3, a branching section 4, a first branching waveguide 5, a second branching waveguide 6, a multiplexing section 7, and an output section 8, and the optical modulation element 1A is provided in the first branching waveguide 5. The optical modulation element 1A can change the refractive index of the waveguide by the Pockels effect.

[0013] The optical modulation element 1A includes an incident portion 10, an output portion 11, an optical waveguide 12 connecting the incident portion 10 to the output portion 11, and an input electrode 13 as an electrode to which a modulated electrical input signal is input. The optical modulation element 1A modulates continuous wave light (CW (Continuous Wave) light) passing through the optical waveguide 12 with the modulated electrical input signal input to the input electrode 13, and outputs the modulated optical modulated signal from the output portion 11. The detailed configuration of the optical waveguide 12 of the optical modulation element 1A will be described later using FIG. 2.

[0014] The CW light incident on the input section 3 is branched by the branching section 4 into a first branching waveguide 5 and a second branching waveguide 6. A portion of the CW light branched into the first branching waveguide 5 is incident on the optical modulation element 1A and is output from the optical modulation element 1A as an optically modulated signal modulated by a modulated electrical input signal input to the input electrode 13. The optically modulated signal is multiplexed in the multiplexing section 7 with the remaining portion of the CW light that has propagated through the second branching waveguide 6, and is output from the output section 8 as a modulated optical output signal to which a predetermined intensity modulation has been imparted.

[0015] In this way, the optical modulation element 1A, which utilizes the refractive index of light, can be applied to the optical modulator 2. A part of the input CW light is converted into an optical modulated signal by the optical modulation element 1A, and is further output as a modulated optical output signal that has been intensity-modulated by the optical modulator 2.

[0016] Fig. 2 is a cross-sectional view of the light modulation element 1A shown in Fig. 1. This figure shows a cross section perpendicular to the direction of propagation of incident light, with the light modulation element 1A extending from the front to the back of the paper and having a waveguide for incident light traveling in that direction provided inside. In the following explanation, the up, down, left, and right directions in the figure will be used, but these directions do not limit the arrangement direction of the light modulation element 1A.

[0017] In the optical modulation element 1A, a first insulating layer 22 made of an oxide film (SiO2) is laminated on a silicon substrate 21. A waveguide core 23 made of Si is formed in a portion of the upper part of the first insulating layer 22, extending in the front-to-back direction of the page. A ferroelectric film 24 is provided so as to cover the first insulating layer 22 and the waveguide core 23. A second insulating layer 25 made of an oxide film (SiO2) is further laminated on the upper part of the ferroelectric film 24. A pair of a first electrode 26 and a second electrode 27 is provided on the upper surface of the second insulating layer 25 at both ends in the left-to-right direction of the figure. The ferroelectric film 24 is one layer of the optical modulation element 1A having such a layered structure and is an example of an embodiment of a ferroelectric layer.

[0018] The ferroelectric film 24 is made of a HfO2-based ferroelectric material that mainly uses HfO2 as a material. The HfO2-based ferroelectric material may be mixed with Al, Zr, etc., and may be used as a gate insulating film of a transistor. In this embodiment, the ferroelectric film 24 is made of Hf x Zr 1-x It consists of O2.

[0019] Hf, a mixed crystal of Hf and Zr x Zr 1-x O2 has a high dielectric property when it has a rectangular polycrystalline structure with x=0.5 (Hf:Zr=0.5:0.5), for example. In the example shown in the figure, the ferroelectric film 24 is provided on the upper surface of the first insulating layer 22, but it is sufficient that it is provided adjacent to the waveguide core 23, and it is not necessary to configure it so as to cover the entire surface of the first insulating layer 22.

[0020] The waveguide core 23 is not limited to Si, but may be made of other semiconductor materials (Ge, SiGe, SiC, InP-based materials, GaAs-based materials, GaN-based materials) or dielectric materials (SiN, SiO x ) may be configured.

[0021] An optical signal propagating within the optical modulation element 1A is mainly conducted within the waveguide core 23, with a portion of the signal seeping into the ferroelectric film 24. In other words, an optical waveguide (hereinafter referred to as "waveguide") is formed by the waveguide core 23 and a portion of the ferroelectric film 24. When a voltage is applied between the first electrode 26 and the second electrode 27, an electric field is generated in the waveguide core 23 and the ferroelectric film 24, as shown by the arrows in the figure. Then, in the optical modulation element 1A, the refractive index of the waveguide changes mainly due to the Pockels effect.

[0022] The Pockels effect is expressed by the following equation (1): where Δn is the change in the refractive index of the waveguide (medium), n is the refractive index of the medium, r is the electro-optic tensor, and E is the applied voltage.

number

[0023] As shown in equation (1), the Pockels effect causes the refractive index of the waveguide to change positively or negatively depending on whether the applied voltage is positive or negative. In addition to the Pockels effect, other known causes of refractive index change include the thermo-optic effect and the free carrier effect. The thermo-optic effect is a phenomenon in which the refractive index of a medium changes when it is heated, but the refractive index does not change in response to an electric field, making it difficult to apply to optical modulation elements. The free carrier effect causes greater optical loss than the Pockels effect. Therefore, by using an optical modulation element 1A in which the Pockels effect is dominant, an optical modulator 2 with high modulation efficiency can be constructed.

[0024] LiNbO3 is known as a material with a high Pockels effect, but it has low compatibility with existing semiconductor manufacturing processes, which may lead to increased manufacturing costs. In response to this, the inventors of the present application have developed Hf x Zr 1-x It was found that O2 exhibits the Pockels effect when the orthorhombic structure is dominant. x Zr 1-xBy using O2, it is possible to realize an optical modulation element 1A that has a high optical modulation effect and can be manufactured by applying existing semiconductor processes. A method for manufacturing the optical modulation element 1A will be described below with reference to Figures 3A to 3F.

[0025] As shown in Figure 3A, a substrate is prepared in which Si, SiO2, and Si are stacked vertically. A substrate in which an insulator (SiO2) layer is formed inside a silicon wafer (Si) is called an SOI (Silicon On Insulator) substrate. In the SOI substrate shown in the figure, the lower layer corresponds to the silicon substrate 21, and the insulator layer corresponds to the first insulating layer 22. Then, a silicon (Si) layer 31 is provided on the first insulating layer 22.

[0026] 3B, after masking the portion of the silicon layer 31 of the SOI substrate that will become the waveguide core 23 with resist, the unmasked portion of the silicon layer 31 is removed by etching. Thereafter, the resist is removed, thereby forming the waveguide core 23.

[0027] Next, as shown in FIG. 3C, Hf is deposited on the upper surfaces of the waveguide core 23 and the first insulating layer 22 by atomic layer deposition (ALD). x Zr 1-x A ferroelectric film 24 made of O2 is formed. The compounding ratio of Hf and Zr is set to x=0.4 (Hf:Zr=0.4:0.6) to 0.6 (Hf:Zr=0.6:0.4), preferably x=0.5 (Hf:Zr=1:1 (=0.5:0.5)). Then, as shown in FIG. 3D, a TiN film 32 is formed by sputtering so as to cover the upper surface of the ferroelectric film 24, and then annealed at about 400°C.

[0028] Next, as shown in FIG. 3E, the TiN film 32 is removed by APM cleaning (Ammonia-hydrogen Peroxide Mixture cleaning) to expose the ferroelectric film 24. Then, as shown in FIG. 3F, a second insulating layer 25 and a metal layer 33 are formed on the ferroelectric film 24. Then, the metal layer 33 is etched according to the patterns of the first electrode 26 and the second electrode 27, thereby obtaining the optical modulation element 1A shown in FIG. 2.

[0029] The mixed crystal of Hf and Zr thus produced is Hf x Zr 1-x The ferroelectric film 24 made of HfO2 has a predominantly orthorhombic structure. A single crystal of HfO2 is a paraelectric with a monoclinic structure, and a single crystal of ZrO2 is an antiferroelectric with a tetragonal structure. x Zr 1-x O2 with a rectangular crystal structure has ferroelectric properties. Hf produced through the steps shown in Figures 3A to 3F x Zr 1-x O2 has a predominantly orthorhombic structure and exhibits ferroelectric properties.

[0030] The orthorhombic crystal is not a highly stable crystal phase. Therefore, the inventors of the present application have formed a TiN film 32 in the step of FIG. x Zr 1-x By heating the O2 layer, stress from the TiN film 32 causes the Hf 0.5 Zr 0.5 It has been found that the crystal structure of O2 can be made to be predominantly orthorhombic. x Zr 1-x O2 is sufficient, and annealing the TiN film 32 after deposition is not an essential manufacturing step.

[0031] The crystal structure of the ferroelectric film 24 can be confirmed by X-ray diffraction (XRD). x Zr 1-xWhen analyzing O2, it is possible to obtain a peak pattern of diffraction angles corresponding to the crystal structure of the object of analysis (monoclinic, orthorhombic, and tetragonal). Most of the diffraction angle peaks obtained by X-ray diffraction for the ferroelectric film 24 of the light modulation element 1A manufactured by the method of FIGS. 3A to 3F coincide with the peak pattern of orthorhombic crystals, and the peak patterns of monoclinic and tetragonal crystals do not dominate. Therefore, it can be understood that the crystal structure of the ferroelectric film 24 manufactured by the method of FIGS. 3A to 3F is dominated by the orthorhombic crystal structure.

[0032] 4 and 5, the optical modulation element 1A having the ferroelectric film 24 is applied to a Mach-Zehnder interferometer, and the results of the experiment are shown below. x Zr 1-x It will be explained that the ferroelectric film 24 made of O2 has the Pockels effect.

[0033] FIG. 4 is a diagram showing the configuration of a Mach-Zehnder interferometer 41, and FIG. 5 is a diagram showing the output from the Mach-Zehnder interferometer 41 of FIG.

[0034] As shown in Fig. 4, a Mach-Zehnder interferometer 41 includes a branching section 42 and a multiplexing section 43. The optical signals branched by the branching section 42 are guided through a first branching waveguide (left side of the figure) and a second branching waveguide (right side of the figure), respectively. The first branching waveguide has an optical path longer than the second branching waveguide by 2ΔL. An optical modulation element 1A is provided in the second branching waveguide, and when a voltage is applied between the first electrode 26 and the second electrode 27, the refractive index of the waveguide changes due to the Pockels effect.

[0035] In Fig. 5, the output light from the multiplexing section 43 is indicated by a solid line (circle plot), a dashed line (square plot), and a diamond plot. The solid line indicates the case where no voltage is applied between the first electrode 26 and the second electrode 27 of the optical modulation element 1A. The dashed line indicates the case where a voltage is applied so as to generate an electric field from the first electrode 26 to the second electrode 27. The dashed line indicates the case where a voltage is applied so as to generate an electric field from the second electrode 27 to the first electrode 26. The direction of voltage application is also indicated by the dashed line and the dashed line in Fig. 4.

[0036] When no voltage is applied between the first electrode 26 and the second electrode 27, the refractive index of the second branch waveguide in which the optical modulation element 1A is provided does not change, but an optical path difference (2ΔL) exists between the first branch waveguide and the second branch waveguide. Therefore, when the light that has passed through the first branch waveguide and the second branch waveguide is combined by the combining section 43, constructive or destructive interactions occur between the two lights at a predetermined wavelength. As a result, as shown by the solid line, peaks that increase and decrease in intensity depending on the wavelength occur, and these peaks are observed at a predetermined wavelength period.

[0037] As shown by the dashed-dotted line, when an electric field is applied from the first electrode 26 to the second electrode 27, the refractive index of the second branch waveguide decreases. As a result, the optical path length of the second branch waveguide decreases, and the peak wavelength of the output light from the multiplexing section 43 decreases. On the other hand, as shown by the dashed-dotted line, when an electric field is applied from the second electrode 27 to the first electrode 26, the refractive index of the second branch waveguide increases. As a result, the optical path length of the second branch waveguide increases, and the peak wavelength of the output light from the multiplexing section 43 increases. It can be observed that the positive and negative changes in the amount of change in the refractive index are reversed depending on the direction of the electric field, which indicates that the Pockels effect is occurring in the optical modulation element 1A.

[0038] Thus, Hf, which has a predominantly orthorhombic structure, x Zr 1-xSince the Pockels effect can be obtained by the optical modulation element 1A having the ferroelectric film 24 of O2, the optical modulator 2 can be configured using the optical modulation element 1A. x Zr 1-x O2 is a material that is used in existing semiconductor manufacturing processes, and therefore has the advantage that the optical modulation element 1A can be easily manufactured using existing manufacturing processes.

[0039] The optical modulation element 1A can be applied to the optical modulator 2 as shown in Fig. 1, but is not limited to this. The optical modulation element 1A may also be applied to a LiDAR (Light Detection and Ranging) to modulate laser measurement light. In the LiDAR, an optical signal obtained by modulating CW light with a predetermined modulation pattern using the optical modulation element 1A is irradiated onto an object, and the reflected signal from the object is compared with the irradiated signal to measure the distance to the object.

[0040] (Second embodiment) In the first embodiment, the ferroelectric film 24 is a single layer of Hf x Zr 1-x Although an example in which the ferroelectric film is made of O2 has been described, the present invention is not limited to this. x Zr 1-x An example in which O2 and Al2O3 are laminated will be described.

[0041] 6 is a cross-sectional view of the optical modulation element 1B of the second embodiment, and corresponds to FIG. 2. The ferroelectric film 61 is made of, for example, three Hf x Zr 1-x A first layer 62 of O2 is laminated via a second layer 63 of Al2O3, and further second layers 63 of Al2O3 are provided above and below. x Zr 1-x The thickness of the first layer 62 of O2 is approximately 10 nm, the thickness of the second layer 63 of Al2O3 is approximately 1 nm, and the total thickness of the ferroelectric film 61 is approximately 30 nm.

[0042] The inventors of the present application have reported that Hf produced by the method shown in FIGS. 3A to 3Fx Zr 1-x It has been found that the dielectric properties of O2 are relatively high when the film thickness is about 5 nm to 20 nm (preferably 10 nm). However, in order to increase the overlap with the waveguide light in the waveguide of the optical modulation element 1A, a certain film thickness is necessary. Therefore, as in this embodiment, Hf x Zr 1-x By stacking the first layer 62 of O2 and the second layer 63 of Al2O3, a ferroelectric film 61 having a constant film thickness can be formed.

[0043] Hf x Zr 1-x When the ferroelectric film 61 is formed by laminating a first layer 62 of O2 and a second layer 63 of Al2O3, Hf x Zr 1-x By configuring the first layer 62 of O2 to be thicker than the second layer 63 of Al2O3, the Pockels effect of the ferroelectric film 61 is enhanced. x Zr 1-x A high Pockels effect can be obtained by forming the ferroelectric film 61 by stacking a second layer 63 of Al2O3 with a thickness of 0.5 nm to 2 nm on a first layer 62 of O2. x Zr 1-x By laminating the first layer 62 of O2 and the second layer 63 of Al2O3 with a thickness of 1 nm, a ferroelectric film 61 can be formed that can obtain a higher Pockels effect.

[0044] Furthermore, it is generally known that when oxygen is taken from a ferroelectric film, oxygen vacancies are formed, resulting in an increase in dielectric properties. The inventors of the present application have found that by providing the second layer 63 (Al2O3), the Al component is reduced in the first layer 62 (Hf x Zr 1-x O2), the dielectric properties of the ferroelectric film 61 are increased.

[0045] These findings suggest that Hf x Zr 1-xBy using the ferroelectric film 61 made up of a laminate of O2 (first layer 62) and Al2O3 (second layer 63) in the light modulation element 1B, higher light modulation efficiency can be obtained.

[0046] (Third embodiment) In the first embodiment, an example has been described in which the waveguide core 23 made of Si is configured in a part of the upper part of the first insulating layer 22, but this is not limitative. In the third embodiment, another configuration of the waveguide core 23 will be described.

[0047] FIG. 7 is a cross-sectional view of an optical modulation element 1C according to a third embodiment, corresponding to FIG. 2. According to this figure, a waveguide core 71 made of Si is configured to have a convex cross section by providing a protrusion extending from the center of the top surface of a plate-like member toward the front and rear of the page. The top surface of the waveguide core 71 is covered with a ferroelectric film 24. The waveguide core 71 with a convex cross section is formed by leaving a portion of the silicon layer 31 as a slab in the process shown in FIG. 3A, and is called a rib waveguide. Even such a waveguide core 71 can be applied to the optical modulator 2 because the Pockels effect occurs when the ferroelectric film 24 is provided. Note that if the ferroelectric film 24 itself is used as a waveguide, this can be achieved by forming the waveguide core 71 from a ferroelectric material instead of Si.

[0048] (Fourth embodiment) In the third embodiment, an example in which the first electrode 26 and the second electrode 27 are provided on both ends of the upper surface of the light modulation element 1C has been described, but this is not limitative. In the fourth embodiment, other forms of electrode configurations will be described.

[0049] Fig. 8 is a cross-sectional view of an optical modulation element 1D of the fourth embodiment, and corresponds to Fig. 7. First electrodes 81A and 81B are provided at both ends of the upper part of the optical modulation element 1D, and one second electrode 82 is provided in the center. The first electrodes 81A and 81B at both ends extend downward through the second insulating layer 25 and the ferroelectric film 24 and are electrically connected to the waveguide core 71. The waveguide core 71 is made conductive by doping impurities into Si.

[0050] When the positive terminal of a power supply is connected to the first electrodes 81A and 81B and the negative terminal of the power supply is connected to the second electrode 82, the voltage applied to the first electrodes 81A and 81B is conducted inside the waveguide core 71, and an electric field is generated from the top surface of the central protrusion of the waveguide core 71 toward the second electrode 82 at the center of the optical modulation element 1D.

[0051] In this configuration, compared to the first to third embodiments, a higher Pockels effect can be obtained because a voltage can be applied directly to the ferroelectric film 24. As a result, an optical modulator 2 that achieves high optical modulation efficiency can be configured using the optical modulation element 1D.

[0052] (Fifth embodiment) In the fifth embodiment, an example in which an electric field is applied to a ferroelectric film in a different manner will be described.

[0053] Fig. 9 is a cross-sectional view of an optical modulation element 1E of the fifth embodiment, and corresponds to Fig. 8. According to this figure, the waveguide cores 91 and 92 provided on the first insulating layer 22 are plate-like members having protruding ends extending in the direction toward the front and rear of the page, formed by increasing the layer thickness at one end of the upper surface, and are arranged so that the end faces of the protruding ends face each other. A groove (slot) is formed between the end faces of the protruding ends of the waveguide cores 91 and 92, exposing a part of the first insulating layer 22. The waveguide cores 91 and 92 face each other across the groove, and have a film thickness portion that is thicker in the height direction than other portions.

[0054] A ferroelectric film 93 is provided to fill the groove between the waveguide cores 91, 92 and to cover the opposing protruding ends via the groove. Furthermore, a first electrode 94 and a second electrode 95 are provided on both ends of the upper part. The first electrode 94 and the second electrode 95 extend downward inside the second insulating layer 25 and are connected to the waveguide cores 91, 92. The waveguide cores 91, 92 are made conductive by doping impurities into Si.

[0055] When an optical signal is incident on the waveguide cores 91 and 92, the guided light is concentrated in the groove. When a voltage is applied between the first electrode 94 and the second electrode 95, an electric field is generated, particularly in the ferroelectric film 93 between the opposing protruding ends of the waveguide cores 91 and 92. Here, by configuring the end faces of the protruding ends of the waveguide cores 91 and 92 via the groove to have a relatively large area and a short groove width, a high voltage can be applied to the ferroelectric film 93, and as a result, a high Pockels effect can be obtained.

[0056] Furthermore, in order to obtain a high Pockels effect, the spontaneous polarization in the ferroelectric film 93 must be uniform, and it is therefore preferable to apply an electric field in advance. In this embodiment, it is relatively easy to apply a high voltage to the ferroelectric film 93 between the waveguide cores 91 and 92, which makes the polarization process easier and makes it easier to obtain high spontaneous polarization. As a result, an optical modulator 2 with high optical modulation efficiency can be realized using the optical modulation element 1E.

[0057] (Sixth embodiment) In the sixth embodiment, an example will be described in which a plasmon waveguide that confines light in a gap between metals is used.

[0058] Fig. 10 is a cross-sectional view of an optical modulation element 1F of the sixth embodiment, and corresponds to Fig. 2 etc. According to this figure, metal layers 101 and 102 provided on the first insulating layer 22 are spaced apart laterally near the center to form a groove (slot) extending in the direction toward the front and rear of the page between them, exposing a part of the first insulating layer 22.

[0059] A ferroelectric film 103 is provided to fill the groove between the metal layers 101 and 102 and to cover the entire upper surfaces of the metal layers 101 and 102. Furthermore, a first electrode 104 and a second electrode 105 are provided on both ends of the upper portion. The first electrode 104 and the second electrode 105 extend downward through the second insulating layer 25 and the ferroelectric film 103, respectively, and are connected to the metal layers 101 and 102. That is, the first electrode 104 and the metal layer 101 constitute one electrode, and the second electrode 105 and the metal layer 102 constitute the other electrode.

[0060] When a voltage is applied between the first electrode 104 and the second electrode 105, an electric field is generated between the opposing end faces of the metal layers 101 and 102, and the refractive index of the ferroelectric film 103 changes due to the Pockels effect.

[0061] In such a structure, the ferroelectric film 103 itself serves as an optical waveguide, and a plasmon waveguide is formed in which light is tightly confined in the groove (gap) between the metal layers 101 and 102. Furthermore, surface plasmon polariton resonance occurs on the surfaces of the metal layers 101 and 102, resulting in high waveguiding characteristics. Therefore, the ferroelectric film 103 can be used as an optical waveguide.

[0062] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of the present invention. [Explanation of symbols]

[0063] 1A, 1B, 1C, 1D, 1E, 1F Optical modulation element 2 Optical Modulator 21 Silicon substrate 22 First insulating layer 23, 71, 91, 92 Waveguide core 24, 61, 93, 103 Ferroelectric film (ferroelectric layer) 25 Second insulating layer 26, 81A, 81B, 94, 104 First electrode 27, 82, 95, 105 2nd electrode 62 1st layer (Hf x Zr 1-x O2) 63 2nd layer (Al2O3) 101, 102 metal layer

Claims

1. an optical waveguide; a pair of electrodes for applying an electric field to the optical waveguide, The optical waveguide is made of Hf ｘ Zr １－ｘ O ２ a ferroelectric layer containing a compound represented by (0<x<1), the optical waveguide includes a waveguide core made of Si; The ferroelectric layer is provided so as to cover at least a portion of the surface of the waveguide core.

2. 2. The light modulation element according to claim 1, The Hf ｘ Zr １－ｘ O ２ The compound represented by (0<x<1) is a light modulation element in which the crystal structure is dominated by orthorhombic crystals.

3. 3. The light modulation element according to claim 2, A light modulation element, wherein x is a value in the range of 0.4 to 0.

6.

4. 3. The light modulation element according to claim 2, An optical modulation element in which the refractive index of the optical waveguide increases or decreases depending on the direction in which a voltage is applied to the pair of electrodes.

5. An optical waveguide; a pair of electrodes for applying an electric field to the optical waveguide, the optical waveguide comprises a ferroelectric layer containing a compound represented by Hf x Zr 1-x O 2 (0<x<1); The ferroelectric layer is made of Hf ｘ Zr １－ｘ O ２ and a second layer which is an oxide film of Al.

6. 6. The light modulation element according to claim 5, A light modulation element, wherein the first layer has a thickness greater than the thickness of the second layer.

7. An optical waveguide; a pair of electrodes for applying an electric field to the optical waveguide, the optical waveguide comprises a ferroelectric layer containing a compound represented by Hf x Zr 1-x O 2 (0<x<1); The optical waveguide is a plate-like member having a protrusion on one surface thereof extending in a waveguiding direction, The optical modulation element, wherein the ferroelectric layer is formed so as to cover at least a part of one surface of the optical waveguide including the protruding portion.

8. 8. The light modulation element according to claim 7, one of the pair of electrodes is connected to the optical waveguide; The other electrode of the pair of electrodes is provided so as to face the protruding portion of the optical waveguide in the protruding direction with an insulating layer interposed therebetween.

9. 2. The light modulation element according to claim 1, the optical waveguide is a pair of plate-like members each having a protruding end portion protruding from one surface at an end thereof, and the end surfaces of the protruding end portions are arranged to face each other with a gap interposed between them, the ferroelectric layer is provided in the groove portion, one of the pair of electrodes is connected to one of the optical waveguides; The other electrode of the pair of electrodes is connected to the other of the optical waveguide.

10. 6. The light modulation element according to claim 5, the optical waveguide is formed by the ferroelectric layer having a protrusion on one surface thereof extending in a waveguiding direction; The light modulation element, wherein one electrode and the other electrode of the pair of electrodes are provided so as to face each other across the protrusion.

11. A Mach-Zehnder optical modulator that outputs an optical signal having a predetermined modulation pattern obtained by combining continuous wave light through two branched optical paths, An optical modulator, wherein one of the branched optical paths is provided with the optical modulation element according to any one of claims 1, 5, 7 and 9, and a voltage according to the modulation pattern is applied to the pair of electrodes.

12. A lidar that measures the distance to an object by irradiating an object with an optical signal obtained by modulating continuous wave light with a predetermined modulation pattern using the optical modulation element described in any one of claims 1, 5, 7 and 9, and comparing the reflected signal from the object with the optical signal irradiated to the object.

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