EP-4737999-A1 - WAVELENGTH CONVERSION ELEMENT, OPTICAL CIRCUIT USING SAME, AND LIGHT SOURCE DEVICE

Abstract

To provide a wavelength conversion element that can use a high-quality crystal part with a simple configuration. The wavelength conversion element includes: a substrate having a main surface; and an optical waveguide disposed on the main surface of the substrate. A core of the optical waveguide includes a polar member having a second-order nonlinear optical constant, and a first nonpolar member adjacent to the polar member in a direction parallel to the main surface of the substrate. In a cross section orthogonal to an optical axis of the optical waveguide, one or both of lateral surfaces of the polar member and the first nonpolar member are in contact with each other.

Inventors

• TANIKAWA, Tomoyuki
• KATAYAMA, Ryuji
• UEMUKAI, Masahiro
• HONDA, HIROTO
• OKADA, MASANORI

Assignees

• The University of Osaka
• NICHIA CORPORATION

Dates

Publication Date

20260506

Application Date

20240626

Claims (15)

1. A wavelength conversion element comprising: a substrate having a main surface; and an optical waveguide disposed on the main surface of the substrate, wherein a core of the optical waveguide comprises a polar member having a second-order nonlinear optical constant, and a first nonpolar member adjacent to the polar member in a direction parallel to the main surface of the substrate, and in a cross section orthogonal to an optical axis of the optical waveguide, one or both of lateral surfaces of the polar member are in contact with the first nonpolar member.
2. The wavelength conversion element according to claim 1, wherein the first nonpolar member is in contact with both of the lateral surfaces of the polar member in the cross section orthogonal to the optical axis of the optical waveguide.
3. The wavelength conversion element according to claim 2, wherein the core further comprises a second nonpolar member located outside the first nonpolar member when seen from the polar member in the cross section orthogonal to the optical axis, the second nonpolar member being in contact with a lateral surface of the first nonpolar member, and a refractive index of the second nonpolar member is greater than a refractive index of the first nonpolar member.
4. The wavelength conversion element according to claim 1, wherein the core further comprises a third nonpolar member disposed on an upper surface of the polar member and an upper surface of the first nonpolar member, and a refractive index of the third nonpolar member is equal to or greater than a refractive index of the polar member.
5. The wavelength conversion element according to any one of claims 1 to 4, wherein the polar member comprises a first polar member and a second polar member in a direction normal to the main surface of the substrate, the first polar member is located between the substrate and the second polar member, and a refractive index of the second polar member is greater than a refractive index of the first polar member.
6. The wavelength conversion element according to any one of claims 1 to 4, wherein, in the cross section orthogonal to the optical axis of the optical waveguide, a width of the core is a width in which the number of modes that can be present for a first frequency component with a first angular frequency is three or less, and is a width in which the number of modes that can be present for a second frequency component with a second angular frequency greater than the first angular frequency is two or more.
7. The wavelength conversion element according to any one of claims 1 to 4, wherein, in the cross section orthogonal to the optical axis, a width of the core is in a range from 200 nm to 2000 nm.
8. The wavelength conversion element according to any one of claims 1 to 4, wherein, in the cross section orthogonal to the optical axis, a width of the core is in a range from 1.5 times to 4 times a width of the polar member.
9. The wavelength conversion element according to any one of claims 1 to 4, wherein the polar member is made of a wurtzite crystal having polarization along a c-axis direction.
10. The wavelength conversion element according to claim 9, wherein a c-axis of the polar member is perpendicular to the main surface of the substrate.
11. The wavelength conversion element according to claim 9, wherein the polar member is made of Al x Ga 1 - x N (0 ≤ x ≤ 1).
12. The wavelength conversion element according to any one of claims 1 to 4, wherein the first nonpolar member is an amorphous layer.
13. The wavelength conversion element according to any one of claims 1 to 4, wherein the first nonpolar member is one selected from the group consisting of Nb 2 O 5 , Ta 2 O 5 , TiO 2 , HfO 2 , ZrO 2 , and Si 3 N 4 .
14. An optical circuit comprising: a laser element; a mode converter optically coupled to the laser element; and the wavelength conversion element according to any one of claims 1 to 4, the wavelength conversion element being optically coupled to the mode converter.
15. A light source device comprising: a laser element; and the wavelength conversion element according to any one of claims 1 to 4, the wavelength conversion element being optically coupled to the laser element.

Description

Technical Field The present disclosure relates to a wavelength conversion element, an optical circuit using the same, and a light source device. Background Art When light of a high intensity is incident on a substance having a nonlinear optical effect, nonlinear polarization proportional to the square or cube of an optical electric field is generated. The second-order nonlinear optical effects include sum frequency generation and difference frequency generation, and are used for second harmonic generation (SHG), optical parametric amplification, and the like. Wavelength conversion is performed by using these nonlinear optical effects. As a wavelength converter, a wavelength conversion waveguide configured by periodic reverse polarization of a ferroelectric of lithium niobate (LN), lithium tantalate (LT), or the like is generally known. The microfabrication of such a waveguide is difficult and a damage threshold is low in a visible light band. A method has been proposed in which GaN layers are grown in opposing directions from both sidewalls of a groove formed in a substrate, and a waveguide element for wavelength conversion is manufactured by a first crystal region and a second crystal region having c-axes opposite to each other (for example, see Patent Document 1). In addition, a quasi-phase matching waveguide has been proposed in which an AlN thin film having a second-order nonlinear optical constant and HfO2 with no polarization are sequentially layered on a surface of a substrate (for example, see Non-Patent Documents 1 and 2). Citation List Patent Literature Patent Document 1: JP 2018-194617 A Non-Patent Literature Non-Patent Document 1: Design of Lateral Quasi-Phase Matched HfO2/AlN Waveguides for 230 nm Far-Ultraviolet Second Harmonic Generation, Proceedings of the 82nd Autumn Meeting of the Japan Society of Applied Physics, 2021, Lecture No. 12p-N101-7Non-Patent Document 2: Manufacturing of HfO2/AlN Lateral Quasi-Phase Matched Channel Waveguides for 230 nm Far-Ultraviolet Second Harmonic Generation, Proceedings of the 69th Spring Meeting of the Japan Society of Applied Physics, 2022, Lecture No. 26p-E203-6 Summary of Invention Technical Problem In the method of growing the GaN layers having the c-axes in the opposite directions in the groove, the manufacturing process is complicated, and the quality of a crystal in the vicinity of an interface with the substrate is insufficient. In the configuration in which the AlN thin film and the HfO2 are layered, the thickness of the AlN thin film is small, and a high-quality crystal thin film is difficult to grow. According to one aspect of the present disclosure, a wavelength conversion element that can use a high-quality crystal part with a simple configuration can be provided. Solution to Problem In an embodiment, a wavelength conversion element includes: a substrate having a main surface; andan optical waveguide disposed on the main surface of the substrate,in which a core of the optical waveguide includes a polar member having a second-order nonlinear optical constant, and a first nonpolar member adjacent to the polar member in a direction parallel to the main surface of the substrate, andin a cross section orthogonal to an optical axis of the optical waveguide, one or both of lateral surfaces of the polar member and the first nonpolar member are in contact with each other. Advantageous Effects of Invention A wavelength conversion element that can use a high-quality crystal part with a simple configuration is implemented. Brief Description of Drawings FIG. 1 is a schematic perspective view of a wavelength conversion element of a first embodiment.FIG. 2 is a cross-sectional view orthogonal to an optical axis in FIG. 1.FIG. 3 is a diagram schematically illustrating a waveguide mode propagating through an optical waveguide of the wavelength conversion element.FIG. 4 is a schematic diagram of a first modified example of the wavelength conversion element.FIG. 5A is a diagram illustrating a process for manufacturing an optical waveguide of the wavelength conversion element of FIG. 4.FIG. 5B is a diagram illustrating the process for manufacturing the optical waveguide of the wavelength conversion element of FIG. 4.FIG. 5C is a diagram illustrating the process for manufacturing the optical waveguide of the wavelength conversion element of FIG. 4.FIG. 5D is a diagram illustrating the process for manufacturing the optical waveguide of the wavelength conversion element of FIG. 4.FIG. 6A is a schematic diagram of a second modified example of the wavelength conversion element.FIG. 6B is a schematic diagram of a third modified example of the wavelength conversion element.FIG. 6C is a schematic diagram of yet another modified example of the wavelength conversion element.FIG. 7 is a model diagram for calculating a core width for phase matching.FIG. 8A is a diagram illustrating an electromagnetic distribution of a TM00 mode of an optical waveguide.FIG. 8B is a diagram ill