Double-layer capacitance load inclined T-type traveling wave electrode lithium niobate electro-optical modulator

Abstract

The invention relates to the technical field of electro-optical modulators, in particular to a double-layer capacitive load inclined T-type traveling wave electrode lithium niobate electro-optical modulator, which comprises a substrate, a buffer layer, a hybrid optical waveguide, an isolating layer and a metal electrode, and is characterized in that the hybrid optical waveguide comprises a rectangular Si waveguide and an LN waveguide; on the premise that the LN waveguide limits the optical mode field, the limiting effect of the hybrid optical waveguide on the optical mode field is enhanced by using the rectangular Si waveguide; the metal electrode is a double-layer capacitance load inclined T-type metal electrode, the absorption loss can be effectively reduced, the metal electrode acts on the upper part and the lower part at the same time on the photoelectric efficiency, the inclined section can increase the electric field borne by the waveguide, and the modulation efficiency is improved; the metal electrodes are periodically arranged along the Y axis of the hybrid optical waveguide; in order to reduce light absorption loss, an isolation layer is added between the upper layer of the metal electrode and the mixed optical waveguide. According to the electro-optical modulator, the half-wave voltage length product of 1.18 V * cm is realized under the light absorption loss of 0.21 dB / cm.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-optic modulators, and particularly to a dual-layer capacitive load inclined T-shaped traveling-wave electrode lithium niobate electro-optic modulator. Background Art

[0002] With the progress of optical communication technology, optoelectronic devices are developing towards high-performance, low-power consumption, low-cost, and miniaturized integrated devices.

[0003] Electro-optic modulators have become key components in modern fiber optic communication, microwave photonics systems, quantum photonics, and data center applications, etc. At the same time, thin-film lithium niobate has received extensive attention and research in recent years due to its advantages such as high integration, wide transparent band, and stable physical and chemical properties. Compared with traditional bulk material lithium niobate modulators, thin-film lithium niobate modulators have the characteristics of low power consumption, large bandwidth, small size, and relatively mature preparation technology, and are one of the effective solutions for the future development of integrated optical circuits. Summary of the Invention

[0004] The purpose of the present invention is to provide a dual-layer capacitive load inclined T-shaped traveling-wave electrode lithium niobate electro-optic modulator, aiming to improve the modulation efficiency of traditional electro-optic modulators and reduce losses.

[0005] To achieve the above object, the present invention provides a dual-layer capacitive load inclined T-shaped traveling-wave electrode lithium niobate electro-optic modulator, including a substrate, a buffer layer, a hybrid optical waveguide, an isolation layer, and a metal electrode. The hybrid optical waveguide includes a rectangular Si waveguide and an LN waveguide; the buffer layer is fixedly connected to the substrate and is located on the top of the substrate, the LN waveguide is fixedly connected to the buffer layer and is located on the side of the buffer layer away from the substrate, the rectangular Si waveguide is embedded in the buffer layer and is located on the side close to the LN waveguide, the isolation layer is fixedly connected to the LN waveguide and is located outside the LN waveguide, and the metal electrode is disposed between the isolation layer and the LN waveguide.

[0006] Wherein, the metal electrode is a gold electrode with a dual-layer capacitive load inclined T-shaped structure, which is divided into upper and lower two-layer capacitors. The lower-layer capacitor is located on both sides of the rectangular Si waveguide and the LN waveguide, and the upper-layer capacitor is located above the rectangular Si waveguide and the LN waveguide and is of a T-shaped structure. Among them, the capacitive part close to the LN waveguide side adopts an inclined design.

[0007] Wherein, the LN waveguide is a lithium niobate thin film with an X-shaped cut, which is a traditional ridge structure. The rectangular Si waveguide is much smaller than the LN waveguide, with a width of 0.2 um and a thickness of 0.15 um, and is located directly below the ridge structure.

[0008] Among them, both the isolation layer and the buffer layer are made of SiO2 material. Among them, the thickness of the isolation layer is 0.25um, and the thickness of the buffer layer is 4.7um.

[0009] Among them, the substrate includes Si material or quartz.

[0010] A double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator of the present invention, the substrate provides a stable base for the LN waveguide, ensuring the mechanical strength and reliability of the device; the buffer layer can confine the optical field in the LN waveguide, reduce light leakage to the substrate, and reduce transmission loss; the rectangular Si waveguide is embedded in the buffer layer, and the LN thin film is bonded thereto. On the premise that the LN waveguide confines the optical mode field, the rectangular Si waveguide is used to further strengthen the confinement of the optical mode field; the metal electrode is a double-layer capacitive load tilted T-shaped metal electrode, which can effectively reduce the absorption loss. In terms of optoelectronic efficiency, the double-layer capacitive load tilted T-shaped metal electrode acts on both the upper and lower parts at the same time, and the tilted cross-section can increase the electric field received by the waveguide, effectively improving the modulation efficiency; the metal electrodes are arranged periodically along the Y-axis of the hybrid optical waveguide; in order to further reduce the optical absorption loss, the isolation layer is added between the upper layer of the metal electrode and the hybrid optical waveguide. The double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator achieves a half-wave voltage length product of 1.18 V·cm under an optical absorption loss of 0.21 dB / cm, which has important guiding significance for the design of electro-optic modulators. Description of the Drawings

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0012] Figure 1 It is a top view of a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator provided by the present invention.

[0013] Figure 2 It is a cross-sectional view of a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator provided by the present invention.

[0014] Figure 3 It is an electric field distribution diagram of the cross-section of a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator provided by the present invention.

[0015] Figure 4It is the spot pattern of the ridge waveguide during single-mode transmission of a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator provided by the present invention.

[0016] Figure 5 It is a comparison diagram of the product of half-wave voltage length (V π L) between the structure of a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator and a single-layer rectangular electrode structure provided by the present invention.

[0017] Figure 6 It is a comparison diagram of the light absorption loss between a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator with and without an Si waveguide provided by the present invention.

[0018] Figure 7 It is a relationship diagram between the lower electrode spacing (gap) and the product of half-wave voltage length (V π L) of a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator provided by the present invention.

[0019] In the figure: 101 - substrate, 102 - rectangular Si waveguide, 103 - buffer layer, 104 - LN waveguide, 105 - isolation layer, 106 - metal electrode. Detailed implementation manners

[0020] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0021] Please refer to Figures 1 to 7 , the present invention provides a double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator, including a substrate 101, a buffer layer 103, a hybrid optical waveguide, an isolation layer 105, and a metal electrode 106. The hybrid optical waveguide includes a rectangular Si waveguide 102 and an LN waveguide 104; the buffer layer 103 is fixedly connected to the substrate 101 and is located on the top of the substrate 101. The LN waveguide 104 is fixedly connected to the buffer layer 103 and is located on the side of the buffer layer 103 away from the substrate 101. The rectangular Si waveguide 102 is embedded in the buffer layer 103 and is located on the side close to the LN waveguide 104. The isolation layer 105 is fixedly connected to the LN waveguide 104 and is located outside the LN waveguide 104. The metal electrode 106 is disposed between the isolation layer 105 and the LN waveguide 104.

[0022] In an embodiment of the present invention, the substrate 101 provides a stable base for the LN waveguide 104 to ensure the mechanical strength and reliability of the device; the buffer layer 103 can confine the optical field in the LN waveguide 104, reduce the light leakage into the substrate 101, and lower the transmission loss. The rectangular Si waveguide 102 is embedded in the buffer layer 103, and the LN thin film is bonded thereto. On the premise that the LN waveguide 104 confines the optical mode field, the rectangular Si waveguide 102 is further used to strengthen the confinement effect on the optical mode field; the metal electrode 106 is a double-layer capacitive load inclined T-shaped metal electrode 106, which can effectively reduce the absorption loss. In terms of optoelectronic efficiency, the double-layer capacitive load inclined T-shaped metal electrode 106 acts on both the upper and lower parts at the same time. The inclined cross-section can increase the electric field received by the waveguide, effectively improving the modulation efficiency; the metal electrodes 106 are arranged periodically along the Y-axis of the hybrid optical waveguide; to further reduce the optical absorption loss, the isolation layer 105 is added between the upper layer of the metal electrode 106 and the hybrid optical waveguide. The double-layer capacitive load inclined T-shaped traveling-wave electrode lithium niobate electro-optic modulator achieves a half-wave voltage length product of 1.18 V·cm at an optical absorption loss of 0.21 dB / cm, which has important guiding significance for the design of electro-optic modulators.

[0023] Further, the metal electrode 106 is a gold electrode with a double-layer capacitive load inclined T-shaped structure, which is divided into upper and lower two-layer capacitors. The lower-layer capacitor is located on both sides of the rectangular Si waveguide 102 and the LN waveguide 104, and the upper-layer capacitor is located above the rectangular Si waveguide 102 and the LN waveguide 104 and is of a T-shaped structure. Among them, the capacitive part close to the LN waveguide 104 is designed in an inclined manner.

[0024] In an embodiment of the present invention, the metal electrode 106 is a double-layer capacitive load inclined T-shaped electrode. The double-layer capacitors act on the upper and lower parts respectively. The lower layer keeps a relatively large distance from the optical waveguide to reduce the optical absorption loss, and the upper layer keeps a relatively small electrode spacing. At the same time, the inclination angle of the inclined electrode and the tip effect of the extended part will cause the electric field to concentrate, increasing the electric field strength received by the optical waveguide and effectively improving the modulation efficiency; adopting a periodic capacitive T-shaped electrode can make the current evenly distributed, increase the effective conductor area, and reduce the ohmic loss.

[0025] Further, the LN waveguide 104 is a lithium niobate thin film with X-cut, having a conventional ridge structure. The rectangular Si waveguide 102 is much smaller than the LN waveguide 104, with a width of 0.2 μm and a thickness of 0.15 μm, and is located directly below the ridge structure. Both the isolation layer 105 and the buffer layer 103 are made of SiO2 material. Among them, the thickness of the isolation layer 105 is 0.25 μm, and the thickness of the buffer layer 103 is 4.7 μm. The substrate 101 includes Si material or quartz.

[0026] The half-wave voltage-length product of the lithium niobate electro-optic modulator with a double-layer capacitive load tilted T-type traveling-wave electrode provided by the present invention has more advantages, and the optical absorption loss also remains at a relatively low value, which has important guiding significance for the design of electro-optic modulators.

[0027] To better understand the technical solution, the following embodiments are provided for further illustration:

[0028] Using COMSOL simulation software, study the half-wave voltage-length product and optical absorption loss of the electro-optic modulator at different electrode spacings;

[0029] The environmental settings are as follows:

[0030] Modeling process: In the software, create a two-dimensional model of the cross-sectional structure of the modulation region of the electro-optic modulator according to the design, including the substrate 101, the buffer layer 103, the hybrid optical waveguide, the isolation layer 105, and the metal electrode 106. Among them, the thickness of the buffer layer 103 is 4.7 μm; the LN waveguide 104 of the hybrid optical waveguide has a ridge structure, with an upper surface width of 1.5 μm, a sidewall inclination angle of 70°, and an etching depth of 0.25 μm; the metal electrode 106 is a double-layer capacitive load tilted T-type electrode structure, with an upper layer inclination angle of 25° and a lower layer inclination angle of 20°, and the thickness of the isolation layer 105 is 0.25 μm.

[0031] Material settings: Set the relative permittivity and refractive index corresponding to the waveguide direction of the model anisotropically according to the properties of the x-cut lithium niobate material. The diagonal elements of the refractive index matrix are set to (2.1376, 2.2111, 2.2111), and the diagonal elements of the relative permittivity matrix are set to (27.9, 44.3, 44.3) respectively.

[0032] Physical field settings: Use the electrostatic field and the electromagnetic wave frequency domain field. In the electrostatic field, the ground electrode and the signal electrode are given voltage terminal types, where the voltage of the ground electrode is 0 V and the voltage of the signal electrode is 1 V.

[0033] Research settings: Add an electrostatic field solution project, set the modeled electrode part as the signal electrode and the ground electrode, and apply the corresponding voltage.

[0034] Add solution settings: Solve the effective mode refractive index of the waveguide and the electric field distribution in the corresponding optical waveguide region.

[0035] Parameter sweep settings: While fixing other parameters, sweep the lower electrode spacing gap from 2 μm to 5 μm to obtain calculation results at different electrode spacings.

[0036] Results: As Figure 4 shown, verify that the fundamental mode of the waveguide is the TE mode, determine the feasibility of the structure, and optimize the electrode spacing between the signal electrode and the ground electrode through parameter sweep.

[0037] Formula calculation: Refer to the calculation formula of the half-wave voltage-length product and calculate the half-wave voltage-length product at different electrode spacings. The calculation results of the half-wave voltage-length product and the optical absorption loss are as Figure 5 , Figure 6 and Figure 7 shown.

[0038]

[0039] In formula (1), n e is the optical refractive index of the lithium niobate crystal in the z direction, γ 33 is the electro-optic coefficient of the lithium niobate crystal in the z direction, E0(x, z) is the electric field strength of the TE mode, and E z (x, z) is the electric field along the z-axis direction.

[0040] Simulate the modulation efficiency and loss of the structure of the present invention through software. Compared with the traditional electro-optic modulator, a smaller half-wave voltage-length product can be obtained under the same optical absorption loss. This electro-optic modulator can achieve a half-wave voltage-length product of 1.18 V·cm at an optical loss of 0.21 dB / cm, with excellent performance.

[0041] The above-disclosed is only a preferred embodiment of a double-layer capacitor-loaded tilted T-type traveling-wave electrode lithium niobate electro-optic modulator of the present invention. Of course, the scope of the rights of the present invention cannot be limited by this. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A double-layer capacitive load tilted T-type traveling-wave electrode lithium niobate electro-optic modulator, characterized in that ； It includes a substrate, a buffer layer, a hybrid optical waveguide, an isolation layer and a metal electrode. The hybrid optical waveguide includes a rectangular Si waveguide and an LN waveguide; The buffer layer is fixedly connected to the substrate and is located on top of the substrate. The LN waveguide is fixedly connected to the buffer layer and is located on the side of the buffer layer away from the substrate. The rectangular Si waveguide is embedded in the buffer layer and is located on the side close to the LN waveguide. The isolation layer is fixedly connected to the LN waveguide and is located outside the LN waveguide. The metal electrode is disposed between the isolation layer and the LN waveguide.

2. The double-layer capacitive load inclined T-type traveling-wave electrode lithium niobate electro-optic modulator according to claim 1, characterized in that ； The metal electrode is a gold electrode with a double-layer capacitor load inclined T-shaped structure, which is divided into upper and lower capacitors. The lower capacitor is located on both sides of the rectangular Si waveguide and the LN waveguide. The upper capacitor is located above the rectangular Si waveguide and the LN waveguide and is in a T-shaped structure. Among them, the capacitor part close to the LN waveguide side adopts an inclined design.

3. The lithium niobate electro-optic modulator with a double-layer capacitor load inclined T-shaped traveling wave electrode according to claim 1, characterized in that; The LN waveguide is a lithium niobate thin film cut in an X shape and has a traditional ridge structure. The rectangular Si waveguide is much smaller than the LN waveguide, with a width of 0.2 um and a thickness of 0.15 um, and is located directly below the ridge structure.

4. The double-layer capacitive load tilted T-shaped traveling-wave electrode lithium niobate electro-optic modulator according to claim 1, characterized in that ； Both the isolation layer and the buffer layer are made of SiO2 material. Among them, the thickness of the isolation layer is 0.25 um, and the thickness of the buffer layer is 4.7 um.

5. The double-layer capacitive load inclined T-shaped traveling-wave electrode lithium niobate electro-optic modulator according to claim 1, characterized in that ； The substrate includes Si material or quartz.

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