Thin film lithium niobate electro-optical modulator with sinking stacked electrode structure

Abstract

The invention provides a thin film lithium niobate electro-optical modulator with a sinking stacked electrode structure, and belongs to the field of photoelectric integrated devices, and the thin film lithium niobate electro-optical modulator is provided with a miniature T structure. The modulator comprises a substrate layer, a buffer layer, a waveguide layer, a covering layer and a metal electrode. The substrate layer is located at the bottom, the buffer layer is located above the substrate layer, and the waveguide layer, the covering layer and the metal electrode are all arranged above the buffer layer. The metal electrode structure is a sinking stacked electrode structure, the lower electrode structure adopts a traveling wave electrode of a micro-T structure, the upper electrode adopts an inverted trapezoidal structure, and the upper electrode and the lower electrode jointly act to realize phase velocity matching of microwaves and light waves and keep a small electrode distance to effectively enhance an electric field in the waveguide, so that the modulation efficiency is improved. And by adjusting the sinking depth of the stacked electrode, the electric field of the modulation region can be further enhanced, so that higher modulation performance is obtained.

Description

A thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure Technical Field

[0001] This invention relates to the field of optoelectronic integrated devices, specifically to a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure, and more particularly to an electro-optic modulator structure that employs a sunken stacked electrode structure to achieve high modulation efficiency and large bandwidth. Background Technology

[0002] With the development of 5G communication technology and artificial intelligence, the amount of data that needs to be transmitted and processed is increasing dramatically, placing high-speed and high-capacity demands on fiber optic communication systems. As a core component of fiber optic communication systems, electro-optic modulators need to meet the ever-growing performance requirements of low power consumption, low loss, miniaturization, and high efficiency.

[0003] Lithium niobate has a wide transparency window and excellent electro-optic, piezoelectric and nonlinear properties, making it a mainstream electro-optic modulation material. Thin-film lithium niobate significantly enhances optical field confinement while maintaining its physical advantages, providing an ideal platform for realizing high-performance integrated photonic devices.

[0004] Existing thin-film lithium niobate modulators still need improvement in terms of device size, modulation efficiency, and driving voltage. These issues not only affect the device's integration density but also increase RF losses, leading to a mismatch between microwave and optical wave velocities, and consequently hindering the improvement of key performance aspects such as electro-optic bandwidth. Summary of the Invention

[0005] (I) Technical problem to be solved The purpose of this invention is to provide a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure to solve the problems existing in the background art.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure, comprising a substrate layer, a buffer layer, a waveguide layer, a capping layer and a metal electrode, wherein the substrate layer is located at the bottom, the buffer layer is located above the substrate layer, the waveguide layer, the capping layer and the metal electrode are all disposed above the buffer layer, and the capping layer is located between the waveguide layer and the metal electrode.

[0007] Furthermore, the waveguide is configured with a ridge-shaped waveguide structure, and the waveguide material is an X-cut lithium niobate thin film.

[0008] Furthermore, a Mach-Zehnder structure is adopted, with the metal electrodes including ground electrodes on both sides and a signal electrode in the middle.

[0009] Furthermore, the metal electrode has two structures, including a traveling wave electrode with a micro-T structure at the bottom and an inverted trapezoidal electrode at the top, wherein the micro-T structures are periodically arranged along the direction of the waveguide.

[0010] Furthermore, the substrate layer is made of silicon.

[0011] Furthermore, both the buffer layer and the cover layer are made of silicon dioxide.

[0012] Furthermore, the metal electrode material is gold.

[0013] Furthermore, the width of the left and right ground electrodes is 120um, the width of the lower signal electrode is 50um, the distance between the lower signal electrode and the ground electrode is 5um, the tilt of the upper signal electrode is 70 degrees, and the distance between the upper signal electrode and the ground electrode is 2.8um.

[0014] Furthermore, the thickness of the cover layer is 0.2 μm, and the thickness of the buffer layer is 3 μm.

[0015] (III) Beneficial Effects As can be seen from the above technical solutions, the present invention provides a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure, which has the following beneficial effects: Compared with traditional traveling wave electrodes without sunken electrodes or without microstructures, the present invention achieves overall optimization of the electro-optic modulator performance by introducing "electrode sunken structure", "electrode T-shaped microstructure" and "inverted trapezoidal structure" on the thin-film lithium niobate sheet.

[0016] (1) The electrode recessed structure effectively reduces the longitudinal overlap between the metal top surface and the optical waveguide mode, keeping the optical field away from the high-loss metal region and fundamentally weakening the optical power attenuation caused by metal absorption. Therefore, while maintaining the electrode driving efficiency, the insertion loss of the modulator can be significantly reduced, and the optical signal-to-noise ratio of the overall link can be improved.

[0017] (2) By using periodic micro-T structures at the electrode edge, the local distribution of the microwave electric field can be finely controlled. On the one hand, more accurate microwave phase velocity compensation can be achieved, so that microwaves and light waves can maintain velocity matching in a wider frequency range; on the other hand, the microstructure can effectively adjust the local characteristic impedance of the electrode, which helps to suppress impedance mismatch and electromagnetic reflection at high frequencies, thereby broadening the effective bandwidth of the electrode.

[0018] (3) The synergistic effect of the inverted trapezoidal structure, electrode sinking and micro-T structure design improves the electro-optic overlap efficiency, enhances the transverse electric field component near the waveguide core layer, thereby effectively reducing the driving voltage of the modulator and improving the modulation efficiency without increasing the device size. Attached Figure Description

[0019] Figure 1 is a three-dimensional structural schematic diagram of a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure according to the present invention.

[0020] Figure 2 is a schematic cross-sectional view of a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure according to the present invention.

[0021] Figure 3 is a graph showing the relationship between the electrode sinking depth and the half-wave voltage length product of a thin-film lithium niobate electro-optic modulator with a sinking stacked electrode structure according to the present invention.

[0022] Figure 4 is a graph showing the relationship between the electrode sinking depth and light absorption loss of a thin-film lithium niobate electro-optic modulator with a sinking stacked electrode structure according to the present invention.

[0023] Figure 5 shows the microwave loss curve of a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure according to the present invention as a function of frequency.

[0024] Figure 6 shows the curve of microwave effective refractive index as a function of frequency for a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure according to the present invention.

[0025] Figure 7 shows the curve of S11 reflection coefficient as a function of frequency for a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure according to the present invention.

[0026] Figure 8 shows the electro-optic coefficient of a thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure according to the present invention as a function of frequency.

[0027] (1) Substrate layer, (2) Buffer layer, (3) Waveguide layer, (4) Cover layer, (5) Metal electrode. Detailed Implementation

[0028] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0029] First, the structure includes a substrate layer (1), a buffer layer (2), a waveguide layer (3), a capping layer (4), and a metal electrode (5). The substrate is located at the bottom, the buffer layer is located above the substrate layer, the waveguide layer, the capping layer, and the metal electrode are all disposed above the buffer layer, and the capping layer is located between the waveguide layer and the metal electrode.

[0030] Secondly, the substrate layer (1) is made of silicon, the buffer layer (2) and the cover layer (4) are both made of silicon dioxide, the waveguide layer (3) is an X-cut lithium niobate film, and the metal electrode (5) is made of gold.

[0031] Then, as shown in Figure 2, the thickness of the substrate layer (1) is 550 μm. The thickness of the buffer layer (2) is 3 μm. The thickness of the waveguide layer (3) is 0.6 μm, wherein the width of the ridge waveguide is 1 μm, the height of the ridge waveguide is 0.3 μm, and the angle is 73°. The thickness of the buffer layer (2) is 0.2 μm. The thickness of the capping layer (4) is 1.2 μm.

[0032] Meanwhile, the waveguide layer adopts a traditional ridge structure, the modulator adopts a Mach-Zehnder structure, the metal electrode includes ground electrodes on both sides and a signal electrode in the middle, the lower signal electrode is 5 μm apart from the lower ground electrode, the upper signal electrode is 2.8 μm apart from the lower ground electrode, the metal electrode (5) is 1.2 μm thick, including a micro T-shaped structure at the bottom, the short strip electrode of the micro T structure is 19 μm long and 6 μm wide, the long strip electrode is 45 μm long and 3 μm wide, the two upper micro Ts are 5 μm apart; the upper part adopts an inverted trapezoidal structure with an inclination of 70°, and the electrodes are formed by stacking.

[0033] Furthermore, the lower electrode structure effectively reduces the effective refractive index of the microwave signal, improving microwave phase velocity matching while reducing microwave loss; the upper electrode structure, with its small spacing, greatly enhances the electric field strength within the waveguide, effectively improving modulation efficiency. Additionally, using a 0.2µm silicon dioxide capping layer to separate the metal electrodes and the waveguide reduces optical absorption loss caused by the metal electrodes. Finally, adjusting the sink depth further increases the electric field strength within the waveguide, effectively improving modulation efficiency and reducing optical absorption loss.

[0034] To illustrate the benefits of recessed stacked electrodes in improving modulation efficiency, in this embodiment, the electrodes are recessed so that the waveguide is positioned as close as possible to the middle of the two electrodes. This allows the waveguide to be in a position with higher electric field strength, thereby improving modulation efficiency. Furthermore, recessing the electrodes allows for greater flexibility in electrode design. Figures 3 and 4 show the relationship between electrode recess depth, half-wave voltage-length product, and optical absorption loss. As shown in Figures 3 and 4, with increasing recess depth, the half-wave voltage-length product gradually decreases, while the optical absorption loss first increases and then decreases. At a recess depth of 300 nm, the half-wave voltage-length product is more advantageous than when not recessed, and the optical absorption loss remains at a relatively low value. Additionally, the recessed stacked electrode structure has three different spacings, and the spacing ratio affects the magnitude of the half-wave voltage, thus affecting the modulation efficiency. Flexible design of parameters affecting electromagnetic wave propagation speed, such as period, duty cycle, electrode spacing, and electrode width, allows for the achievement of higher modulation bandwidth.

[0035] Using COMSOL optical simulation software, a two-dimensional model of the cross-section of the thin-film lithium niobate modulator was performed to study the half-wave voltage-length product and optical absorption loss of the electro-optic modulator at different sink depths.

[0036] The thin-film lithium niobate modulator was modeled and simulated in three dimensions using HFSS software. Parameters such as microwave loss, effective microwave refractive index, S11 reflection coefficient, and electro-optic coefficient of the submerged stacked thin-film lithium niobate modulator were calculated.

[0037] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure, characterized in that: It includes a substrate layer (1), a buffer layer (2), a waveguide layer (3), a capping layer (4), and a metal electrode (5); the substrate is located at the bottom, the buffer layer is located above the substrate, the waveguide layer, the capping layer and the metal electrode are all disposed above the buffer layer, and the capping layer is located between the waveguide layer and the metal electrode.

2. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 1, characterized in that: The waveguide is configured with a ridge-shaped waveguide structure, and the waveguide material is an X-cut lithium niobate thin film.

3. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 1, characterized in that: Employing a Mach-Zehnder structure, the metal electrodes include ground electrodes on both sides and a signal electrode in the middle.

4. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 1, characterized in that: The metal electrode includes two electrode structures: a traveling wave electrode with a lower micro-T structure and an upper inverted trapezoidal electrode. The micro-T structures are arranged periodically along the direction of the waveguide.

5. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 1, characterized in that: The substrate is made of silicon.

6. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 1, characterized in that: The materials of the buffer layer and the cover layer are silicon dioxide.

7. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 5, characterized in that: The width of the left and right ground electrodes is 120um, the width of the lower signal electrode is 50um, the distance between the lower signal electrode and the ground electrode is 5um, the tilt of the upper signal electrode is 70 degrees, and the distance between the upper signal electrode and the ground electrode is 2.8um.

8. The thin-film lithium niobate electro-optic modulator with a sunken stacked electrode structure as described in claim 1, characterized in that: The thickness of the overcoating layer is 0.2 μm, and the thickness of the buffer layer is 3 μm.

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