JP-2026074644-A - Optical waveguide medium, optical modulation element, and method for manufacturing an optical modulation element

JP2026074644AJP 2026074644 AJP2026074644 AJP 2026074644AJP-2026074644-A

Abstract

[Problem] To provide a hybrid optical waveguide medium, an optical modulation element, and a method for manufacturing an optical modulation element that are highly productive and low-cost. [Solution] The optical waveguide medium 1 comprises a substrate 10, an ABX3 type ferroelectric thin film 11 formed on the substrate 10, a first dielectric thin film 12 formed on the ABX3 type ferroelectric thin film 11, a second dielectric thin film 13 formed on the first dielectric thin film 12, and a third dielectric thin film 14 formed on the first dielectric thin film 12 and the second dielectric thin film 13. The first dielectric thin film 12, the second dielectric thin film 13, and the third dielectric thin film 14 constitute an embedded optical waveguide structure in which the second dielectric thin film 13 is embedded by the first dielectric thin film 12 and the third dielectric thin film 14. The refractive indices of the first dielectric thin film 12 and the third dielectric thin film 14 are lower than the refractive indices of the ABX3 type ferroelectric thin film 11 and the second dielectric thin film 13. [Selection Diagram] Figure 1

Inventors

吉成次郎
三枝慈
原裕貴
福澤英明

Assignees

ＴＤＫ株式会社

Dates

Publication Date: 20260507
Application Date: 20241021

Claims (13)

circuit board and An ABX- 3 type ferroelectric thin film formed on the substrate, A first dielectric thin film formed on the aforementioned ABX- 3 type ferroelectric thin film, A second dielectric thin film formed on the first dielectric thin film, The invention comprises a first dielectric thin film and a third dielectric thin film formed on the second dielectric thin film, The first dielectric thin film, the second dielectric thin film, and the third dielectric thin film constitute an embedded optical waveguide structure in which the second dielectric thin film is embedded by the first dielectric thin film and the third dielectric thin film. An optical waveguide medium characterized in that the refractive indices of the first dielectric thin film and the third dielectric thin film are lower than the refractive indices of the ABX3 type ferroelectric thin film and the second dielectric thin film.
The optical wave guide medium according to claim 1, wherein the ABX- 3 type ferroelectric thin film is a lithium niobate film or a lithium tantalate film.
The optical waveguide medium according to claim 2, wherein the ABX- 3 type ferroelectric thin film is a sputtered thin film.
The optical waveguide medium according to claim 2 or 3, wherein the substrate is a sapphire single crystal substrate.
The optical waveguide medium according to claim 1, wherein the first dielectric thin film and/or the third dielectric thin film is made of silicon dioxide or aluminum oxide.
The optical waveguide medium according to claim 1, wherein the second dielectric thin film is made of silicon nitride.
circuit board and An ABX- 3 type ferroelectric thin film formed on the substrate, A first dielectric thin film formed on the aforementioned ABX- 3 type ferroelectric thin film, A second dielectric thin film formed on the first dielectric thin film, A third dielectric thin film formed on the first dielectric thin film and the second dielectric thin film, The device comprises a traveling wave electrode, consisting of a signal electrode and a ground electrode, formed on the third dielectric thin film, for applying an electric field to the ABX3 type ferroelectric thin film. The first dielectric thin film, the second dielectric thin film, and the third dielectric thin film are arranged such that the second dielectric thin film is embedded by the first dielectric thin film and the third dielectric thin film, forming adjacent first and second embedded optical waveguide structures. An optical modulation element characterized in that the refractive indices of the first dielectric thin film and the third dielectric thin film are lower than the refractive indices of the ABX3 type ferroelectric thin film and the second dielectric thin film.
The optical modulation element according to claim 7, wherein the ABX3 type ferroelectric thin film is a lithium niobate film or a lithium tantalate film.
The optical modulation element according to claim 8, wherein the ABX3 type ferroelectric thin film is a sputtered thin film.
The optical modulation element according to claim 8 or 9, wherein the substrate is a sapphire single crystal substrate.
The optical modulation element according to claim 7, wherein the first dielectric thin film and/or the third dielectric thin film is made of silicon dioxide or aluminum oxide.
The optical modulation element according to claim 7, wherein the second dielectric thin film is made of silicon nitride.
A process for forming an ABX- 3 type ferroelectric thin film on a substrate by sputtering, The process of forming a first dielectric thin film on the aforementioned ABX- 3 type ferroelectric thin film, A step of forming a second dielectric thin film on the first dielectric thin film, A step of forming a third dielectric thin film on the first dielectric thin film and the second dielectric thin film, The process includes forming a traveling wave electrode, consisting of a signal electrode and a ground electrode, on the third dielectric thin film for applying an electric field to the ABX- 3 type ferroelectric thin film, The first dielectric thin film, the second dielectric thin film, and the third dielectric thin film are arranged such that the second dielectric thin film is embedded by the first dielectric thin film and the third dielectric thin film, forming adjacent first and second embedded optical waveguide structures. A method for manufacturing an optical modulation element, characterized in that the refractive indices of the first dielectric thin film and the third dielectric thin film are lower than the refractive indices of the ABX3 type ferroelectric thin film and the second dielectric thin film.

Description

The present invention relates to an optical waveguide medium, an optical modulation element, and a method for manufacturing an optical modulation element, and more particularly to an optical waveguide medium, an optical modulation element, and a method for manufacturing an optical modulation element using a ferroelectric ABX3 crystal. With the widespread adoption of the internet, data traffic has increased dramatically, making fiber optic communication extremely important. Fiber optic communication converts electrical signals into optical signals and transmits them through optical fibers, offering characteristics such as high bandwidth, low loss, and strong noise resistance. Two methods for converting electrical signals into optical signals are known: direct modulation using semiconductor lasers and external modulation using optical modulators. Direct modulation does not require an optical modulator and is low-cost, but it has limitations in high-speed modulation. For high-speed, long-distance applications, external modulation is used. As for optical modulators, Mach-Zehnder type optical modulators using ferroelectric ABX3 crystals, such as lithium niobate film ( LiNbO3 ), have been put into practical use (see, for example, Patent Document 1). A Mach-Zehnder type optical modulator uses an optical waveguide (Mach-Zehnder optical waveguide) that has the structure of a Mach-Zehnder interferometer, which splits light emitted from one light source into two, passes them through different paths, and then superimposes them again to cause interference. Patent Document 1 describes a ridge-type optical modulation element comprising a waveguide layer made of a lithium niobate film formed on a substrate, wherein the waveguide layer has a slab portion having a predetermined thickness and a ridge portion protruding from the slab portion. Ferroelectric ABX3 crystals are excellent electro-optic materials with low-loss optical propagation characteristics, large electro-optic coefficients, linear modulation response, and large modulation bandwidth. However, most conventional optical modulation elements using ferroelectric ABX3 crystals are manufactured using non-standard etching techniques or partially etched ridge waveguides, resulting in poor waveguide shape reproducibility compared to silicon photonic optical modulation elements. Therefore, as an alternative to optical modulation elements using ridge waveguides, hybrid devices combining a lithium niobate thin film and a waveguide made of silicon nitride ( Si₃N₄ ) have been developed (see, for example, Patent Document 2). The hybrid device disclosed in Patent Document 2 has a structure in which a substrate with a cladding layer containing an embedded waveguide structure is bonded to an electro-optical modulation layer containing a lithium niobate thin film. Patent No. 7538209U.S. Patent No. 10788689 This is a schematic cross-sectional view of an optical waveguide medium according to the first embodiment of the present invention.This is a schematic plan view of an optical modulation element according to a second embodiment of the present invention.This is a cross-sectional view along line A-A in Figure 2.This figure schematically illustrates the manufacturing process of an optical modulation element according to a second embodiment of the present invention.This is a schematic plan view of an optical modulation element according to a third embodiment of the present invention.This is a cross-sectional view along the line B-B in Figure 5.This figure schematically illustrates the manufacturing process of an optical modulation element according to a third embodiment of the present invention.(a) A figure showing a simulation model of the optical waveguide medium in Example 1 and (b) A figure showing the electric field distribution of light.This figure shows a simulation model of the optical modulation element in Example 2.This graph shows the total width at half maximum and the field efficiency of the light intensity when the thickness and width of the second dielectric thin film are changed in the optical modulation element of Example 3.This graph shows the propagation loss and electric field efficiency when the distance between the electrode and the ABX3 type ferroelectric thin film is varied in the optical modulation element of Example 4.This figure shows a simulation model of the optical modulation element in Example 5.In the optical modulation element of Example 5, (a) is a graph showing the full width at half maximum of the light intensity when the width of the second dielectric thin film is changed, and (b) is a graph showing the electric field efficiency when the material of the cladding layer and the width of the second dielectric thin film are changed.This graph shows the full width at half maximum of the light intensity and the electric field efficiency when the thickness of the first dielectric thin film is changed in the optical modulation element of Example 6.(a) A f