Inverted step capacitance load type traveling wave electrode lithium niobate electro-optical modulator

Abstract

The invention relates to the technical field of electro-optical modulators, in particular to an inverted step capacitor load type traveling wave electrode lithium niobate electro-optical modulator which comprises a substrate, a buffer layer, an optical waveguide, a metal electrode, an isolation layer and a high-dielectric cladding. The metal electrode is an inverted step capacitance load type electrode which can effectively reduce electrical loss and obtain high bandwidth, the inverted step capacitance load type metal electrode enhances the effect on the optical waveguide and effectively improves the modulation efficiency on the aspect of photoelectric efficiency, and the high-dielectric cladding and the isolation layer change the electric field intensity distribution while reducing the optical loss, so that the modulation efficiency is improved. The electric field intensity in the waveguide is greatly improved, the overlapping between the electric field and the light field is enhanced, the modulation efficiency is further improved, the half-wave voltage length product of 0.99 V.cm is achieved under the light absorption loss of 0.25 dB / cm through the lithium niobate electro-optical modulator of the inverted-step capacitance load type traveling wave electrode, and important guiding significance is achieved for the design of the electro-optical modulator.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-optic modulators, and particularly to an inverted stepped-capacitance-loaded traveling-wave electrode lithium niobate electro-optic modulator. Background Art

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

[0003] Electro-optic modulators have become key components in modern fiber optic communications, microwave photonics systems, quantum photonics, and data center applications. At the same time, thin-film lithium niobate modulators have the characteristics of low power consumption, large bandwidth, small size, and relatively mature fabrication technologies, 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 an inverted stepped-capacitance-loaded traveling-wave electrode lithium niobate electro-optic modulator, aiming to improve the modulation efficiency of the electro-optic modulator.

[0005] To achieve the above purpose, the present invention provides an inverted stepped-capacitance-loaded traveling-wave electrode lithium niobate electro-optic modulator, which includes a substrate, a buffer layer, an optical waveguide, a metal electrode, an isolation layer, and a high-dielectric cladding layer; the buffer layer is fixedly connected to the substrate and is located on top of the substrate, the optical waveguide is fixedly connected to the buffer layer and is located on the side of the buffer layer away from the substrate, the isolation layer is fixedly connected to the optical waveguide and is located outside the optical waveguide, the high-dielectric cladding layer is fixedly connected to the isolation layer and is located outside the isolation layer, and the metal electrode is disposed on top of the isolation layer.

[0006] Among them, the metal electrode is an electrode with an inverted stepped-capacitance-loaded structure, which is divided into three layers, each layer widening from bottom to top in an inverted stepped shape, and the number of the metal electrodes is multiple, which are arranged periodically along the Y-axis of the optical waveguide.

[0007] Among them, the optical waveguide is an X-cut lithium niobate thin film, which is a ridge structure and is processed by etching through, and is located between the buffer layer and the isolation layer.

[0008] Among them, the high-dielectric cladding layer has a high dielectric constant and includes barium titanate or glycerol high-dielectric constant materials.

[0009] Among them, the substrate is Si or quartz, the buffer layer is made of SiO2 material, with a thickness of 4.7 um, and is located between the substrate and the optical waveguide.

[0010] A traveling-wave electrode lithium niobate electro-optic modulator with an inverted stepped capacitive load according to the present invention. The substrate provides a stable base for the optical waveguide, ensuring the mechanical strength and reliability of the device. The buffer layer can confine the optical field in the optical waveguide, reduce light leakage into the substrate, and lower the transmission loss. The optical waveguide is an X-cut lithium niobate thin film with a ridge structure and is processed by etching through. The optical waveguide is bonded to the buffer layer. The metal electrode is a gold electrode with an inverted stepped capacitive load structure, which can effectively reduce the electrical loss and obtain a high bandwidth. In terms of the optoelectronic efficiency, the inverted stepped capacitive load metal electrode enhances the effect on the optical waveguide and effectively improves the modulation efficiency. The metal electrodes are arranged periodically along the Y-axis of the optical waveguide. The high-dielectric cladding layer and the isolation layer change the electric field intensity distribution while reducing the light loss, greatly increasing the electric field intensity in the waveguide, enhancing the overlap between the electric field and the optical field, and thus improving the modulation efficiency. The lithium niobate electro-optic modulator with an inverted stepped capacitive load traveling-wave electrode achieves a half-wave voltage-length product of 0.99 V·cm at an optical absorption loss of 0.25 dB / cm, which has important guiding significance for the design of electro-optic modulators. BRIEF 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 use in 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 traveling-wave electrode lithium niobate electro-optic modulator with an inverted stepped capacitive load provided by the present invention.

[0013] Figure 2 It is a cross-sectional view of a traveling-wave electrode lithium niobate electro-optic modulator with an inverted stepped capacitive load provided by the present invention.

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

[0015] Figure 4 It is a spot diagram of the ridge waveguide during single-mode transmission of a traveling-wave electrode lithium niobate electro-optic modulator with an inverted stepped capacitive load provided by the present invention.

[0016] Figure 5 It is a comparison diagram of the structure of a traveling-wave electrode lithium niobate electro-optic modulator with an inverted stepped capacitive load and the half-wave voltage-length product (V π L) of the non-sunken rectangular electrode structure.

[0017] Figure 6 It is a comparison diagram of the light absorption loss between the structure of an inverted stepped-capacitance-loaded traveling-wave electrode lithium niobate electro-optic modulator provided by the present invention and the non-sunken rectangular electrode structure.

[0018] In the figure: 101 - substrate, 102 - buffer layer, 103 - optical waveguide, 104 - metal electrode, 105 - isolation layer, 106 - high-dielectric cladding. Detailed implementation manners

[0019] 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 denote the same or similar elements or elements with the same or similar functions throughout. 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.

[0020] Please refer to Figures 1 to 6 , the present invention provides an inverted stepped-capacitance-loaded traveling-wave electrode lithium niobate electro-optic modulator, which includes a substrate 101, a buffer layer 102, an optical waveguide 103, a metal electrode 104, an isolation layer 105, and a high-dielectric cladding 106; the buffer layer 102 is fixedly connected to the substrate 101 and is located on the top of the substrate 101, the optical waveguide 103 is fixedly connected to the buffer layer 102 and is located on the side of the buffer layer 102 away from the substrate 101, the isolation layer 105 is fixedly connected to the optical waveguide 103 and is located outside the optical waveguide 103, the high-dielectric cladding 106 is fixedly connected to the isolation layer 105 and is located outside the isolation layer 105, and the metal electrode 104 is disposed on the top of the isolation layer 105.

[0021] In an embodiment of the present invention, the substrate 101 provides a stable base for the optical waveguide 103 to ensure the mechanical strength and reliability of the device; the buffer layer 102 can confine the optical field in the optical waveguide 103, reduce the leakage of light into the substrate 101, and reduce the transmission loss; the optical waveguide 103 is an X-cut lithium niobate thin film, with a ridge structure and a through-etching process. The optical waveguide 103 is bonded to the buffer layer 102. The metal electrode 104 is a gold electrode with an inverted stepped capacitor load structure, which can effectively reduce the electrical loss and obtain a high bandwidth. In terms of optoelectronic efficiency, the inverted stepped capacitor load type metal electrode 104 enhances the effect on the optical waveguide 103 and effectively improves the modulation efficiency. The metal electrodes 104 are arranged periodically along the Y-axis of the optical waveguide 103. While reducing the optical loss, the high dielectric cladding layer 106 and the isolation layer 105 change the electric field intensity distribution, greatly increase the electric field intensity in the waveguide, enhance the overlap between the electric field and the optical field, and thus improve the modulation efficiency. The lithium niobate electro-optic modulator with an inverted stepped capacitor load traveling wave electrode achieves a half-wave voltage length product of 0.99 V·cm at an optical absorption loss of 0.25 dB / cm, which has important guiding significance for the design of electro-optic modulators.

[0022] Further, the metal electrode 104 is an electrode with an inverted stepped capacitor load structure, which is divided into three layers, each layer widening successively from bottom to top, showing an inverted stepped shape. The number of the metal electrodes 104 is multiple, and they are arranged periodically along the Y-axis of the optical waveguide 103 respectively; the optical waveguide 103 is an X-cut lithium niobate thin film, with a ridge structure and a through-etching process, and is located between the buffer layer 102 and the isolation layer 105.

[0023] In an embodiment of the present invention, the metal electrode 104 is an inverted stepped capacitor load type metal electrode 104, forming an inverted stepped electrode that widens from bottom to top near the optical waveguide 103. The lower end is far from the optical waveguide 103 to reduce the optical absorption loss; the widening of the upper end results in being close to the optical waveguide 103. At the same time, due to the tip effect of the inverted step, the electric field intensity near the optical waveguide 103 is greatly enhanced, improving the modulation efficiency; the use of a periodic capacitor T-shaped electrode can make the current evenly distributed, increase the effective conductor area, and reduce the ohmic loss; to further improve the modulation efficiency, the optical waveguide 103 is subjected to a through-etching process to make the metal electrode 104 completely sink. According to electromagnetic theory, the electric field intensity is the largest at the center position between the two electrodes. The complete sinking of the metal electrode 104 makes the optical waveguide 103 located in the middle of the metal electrode 104, further increasing the electric field near the optical waveguide 103, thereby improving the modulation efficiency.

[0024] Further, the high dielectric cladding layer 106 has a high dielectric constant and includes barium titanate or glycerol high dielectric constant materials.

[0025] Among them, the substrate 101 is Si or quartz, the buffer layer 102 is made of SiO2 material, with a thickness of 4.7 μm, and is located between the substrate 101 and the optical waveguide 103.

[0026] In the embodiment of the present invention, the high-dielectric cladding layer 106 and the isolation layer 105 form a hybrid cladding layer. The isolation layer 105 separates the metal electrode 104 from the optical waveguide 103, which can effectively reduce the optical absorption loss, but will cause the electric field strength near the optical waveguide 103 to weaken. To avoid this phenomenon, the high-dielectric cladding layer 106 is added. The high-dielectric cladding layer 106 can effectively increase the electric field strength in the optical waveguide 103, enhance the overlap between the electric field and the optical field, and thus improve the modulation efficiency.

[0027] The half-wave voltage-length product of the inverted stepped-capacitance load traveling-wave electrode lithium niobate electro-optic modulator of 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.

[0028] To better understand the technical solution, the following embodiments are provided for further illustration:

[0029] Using COMSOL simulation software, study the half-wave voltage-length product and optical absorption loss of the electro-optic modulator at different electrode spacings;

[0030] The environmental settings are as follows:

[0031] Modeling process: In the software, a two-dimensional model of the cross-sectional structure of the modulation region of the electro-optic modulator is created according to the design, including the buffer layer 102, the optical waveguide 103, the metal electrode 104, the isolation layer 105, and the high-dielectric cladding layer 106. Among them, the thickness of the buffer layer 102 is 4.7 μm; the optical waveguide 103 is a ridge structure, with a width of 1.5 μm on the upper surface, a sidewall inclination angle of 70°, and an etching depth of 0.25 μm; the metal electrode 104 is a three-layer inverted stepped-capacitance load electrode structure, with the thickness of the first layer and the second layer being 0.5 μm, and the thickness of the third layer being 0.2 μm, and the thickness of the isolation layer 105 is 0.25 μm.

[0032] Material settings: According to the properties of the x-cut lithium niobate material, the relative permittivity and refractive index are set anisotropically corresponding to the waveguide direction of the model. 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.

[0033] Physical field setting: An electrostatic field and an electromagnetic wave frequency domain field are adopted. In the electrostatic field, the ground electrode and the signal electrode are of the voltage terminal type, where the voltage of the ground electrode is 0V and the voltage of the signal electrode is 1V.

[0034] Research setting: Add a project for solving the electrostatic field, set the modeled electrode part as the signal electrode and the ground electrode, and apply the corresponding voltages.

[0035] Add solution setting: Solve the effective mode refractive index of the waveguide and the electric field distribution in the corresponding region of the optical waveguide 103.

[0036] Parameter sweep setting: While fixing other parameters, sweep the overall electrode spacing gap from 4μm to 6μm to obtain the calculation results at different electrode spacings.

[0037] 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 sweeping.

[0038] 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 shown.

[0039]

[0040] 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.

[0041] The modulation efficiency and loss of the structure of the present invention are simulated by 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 0.99V·cm at an optical loss of 0.25dB / cm, with excellent performance.

[0042] The above-disclosed is only a preferred embodiment of a reverse stepped capacitor load 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 reverse stepped capacitance-loaded traveling-wave electrode lithium niobate electro-optic modulator, characterized in that ； It includes a substrate, a buffer layer, an optical waveguide, a metal electrode, an isolation layer and a high-dielectric cladding; The buffer layer is fixedly connected to the substrate and located on top of the substrate. The optical waveguide is fixedly connected to the buffer layer and located on the side of the buffer layer away from the substrate. The isolation layer is fixedly connected to the optical waveguide and located outside the optical waveguide. The high-dielectric cladding is fixedly connected to the isolation layer and located outside the isolation layer. The metal electrode is disposed on top of the isolation layer.

2. The inverted stepped capacitance load type traveling wave electrode lithium niobate electro-optic modulator according to claim 1, characterized in that ； The metal electrode is an electrode with an inverted stepped capacitance load structure, which is divided into three layers, each layer widening from bottom to top in an inverted stepped shape. The number of the metal electrodes is multiple, and they are arranged periodically along the Y-axis of the optical waveguide.

3. The inverted stepped capacitance load type traveling wave electrode lithium niobate electro-optic modulator according to claim 1, wherein; The optical waveguide is a lithium niobate thin film with an X-type cut, having a ridge structure and being processed by etching through, and is located between the buffer layer and the isolation layer.

4. The inverted stepped-capacitance load traveling-wave electrode lithium niobate electro-optic modulator according to claim 1, wherein ； The high-dielectric cladding has a high dielectric constant and includes barium titanate or a glycerol high-dielectric constant material.

5. The inverted stepped-capacitance load traveling-wave electrode lithium niobate electro-optic modulator according to claim 1, characterized in that ； The substrate is Si or quartz, the buffer layer is made of SiO2 material with a thickness of 4.7 um, and is located between the substrate and the optical waveguide.

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