Thin film lithium niobate modulator based on zigzag electrode structure

Abstract

The invention discloses a thin-film lithium niobate modulator based on a zigzag electrode structure, and belongs to the technical field of electro-optical modulation. The modulator sequentially comprises a silicon substrate layer, a silicon dioxide lower cladding, a lithium niobate waveguide layer, a ridge-shaped optical waveguide layer formed by etching the upper surface of the lithium niobate layer, a silicon dioxide thin cover layer, a zigzag electrode structure and a main ground-signal-ground traveling wave electrode, and a silicon dioxide upper cladding covers the upper surface. The ground-signal-ground traveling wave electrode is composed of a first ground transmission electrode, a signal transmission electrode and a second ground transmission electrode. The zigzag electrode structure is periodically arranged, and the overlook structure of the zigzag electrode structure is composed of a plurality of triangles side by side. The invention provides a novel zigzag electrode structure, a periodic zigzag electrode is designed by utilizing a point effect, electro-optical modulation efficiency is enhanced and loss is reduced through electric field concentration, and meanwhile, the electrode structure is simple to manufacture.

Description

Technical Field

[0001] The present invention provides a thin-film lithium niobate modulator based on a zigzag electrode structure, belonging to the technical field of electro-optic modulation. Background Art

[0002] With the in-depth integration of 5G with technologies such as AI, big data, Internet of Things, and artificial intelligence, the data traffic has increased significantly. Data centers need to continuously expand their scale to meet the growing communication needs. An optical modulator is an important part of optical communication. Among them, an electro-optic modulator is the core component of the current communication industry. The electro-optic modulator is located in the optical emission link, which converts the high-speed electronic signal in the communication device into an optical signal, and then realizes the long-distance high-speed transmission of information in the optical fiber. Compared with traditional lithium niobate, the thin-film lithium niobate (LNOI) technology has enhanced the binding ability of optical signals. The formed thin-film lithium niobate electro-optic modulator has significant characteristics of low loss, small size, and high bandwidth.

[0003] In the traditional CPW electrode structure, it is impossible to break the voltage-bandwidth trade-off limitation of the thin-film lithium niobate electro-optic Mach-Zehnder modulator, especially impossible to achieve impedance matching. Therefore, in order to break this limitation, we have made innovations in the waveguide structure, electrode structure, and material process. In recent years, we have proposed new structures such as ridge waveguides, heterogeneous integrated waveguides, microring resonator waveguides, and fishbone waveguides in the waveguide structure, innovated designs such as T electrodes, L electrodes, cascaded electrodes, and composite double-capacitance electrodes in the electrode aspect, and also applied Smart-cut technology, dry etching technology, and heterogeneous integration technology in the process aspect. These structural innovations have further reduced the transmission loss and improved the modulation efficiency. Summary of the Invention

[0004] The present invention provides a lithium niobate thin-film electro-optic modulator with a zigzag electrode structure, which maintains a high modulation efficiency, reduces electrode loss while maintaining speed matching and impedance matching conditions, and breaks the voltage-bandwidth trade-off limitation of the thin-film lithium niobate electro-optic Mach-Zehnder modulator.

[0005] To achieve the above object, the present invention provides a thin-film lithium niobate modulator based on a zigzag electrode structure, which includes a substrate layer, a lower cladding layer, a lithium niobate thin film layer, a ridge waveguide layer with a Mach-Zehnder structure, a thin capping layer, a metal traveling-wave electrode, and an upper cladding layer; the silicon dioxide lower cladding layer (2) is located above the silicon substrate layer (1), the lithium niobate waveguide layer (3) is located above the silicon dioxide lower cladding layer (2), the ridge waveguide layer (301, 302) with a Mach-Zehnder structure is located on the lithium niobate waveguide layer (3) for optical signal transmission, the silicon dioxide thin capping layer (4) covers the lithium niobate waveguide layer (3), and the metal traveling-wave electrode is located between the silicon dioxide thin capping layer (4) and the silicon dioxide upper cladding layer (6), including a zigzag electrode structure (501) and a main ground-signal-ground traveling-wave electrode (502, 503, 504), and the ground-signal-ground traveling-wave electrode is composed of a first ground transmission electrode, a signal transmission electrode, and a second ground transmission electrode.

[0006] Among them, a periodic traveling-wave electrode structure is adopted, which is composed of a metal main electrode and a periodic micro-structure electrode. The periodic micro-structure electrode is the zigzag electrode structure with a thickness of 1.4 μm. By adjusting the parameters of the zigzag structure, characteristic impedance matching and velocity matching are achieved.

[0007] Among them, the zigzag electrode structure (501) is that multiple triangles are regularly distributed in the transmission direction of the traveling-wave electrode in a periodic manner, forming a periodic capacitance between the signal transmission electrode and the ground transmission electrode. The triangles are not limited to equilateral triangles, isosceles triangles, obtuse or acute triangles.

[0008] Among them, the first ground transmission electrode (502), the signal transmission electrode (503), and the second ground transmission electrode (504) are arranged in parallel, and the zigzag electrode structure is aligned left and right in space.

[0009] Among them, the thickness of the lithium niobate waveguide layer (3, 301, 302) is 0.5 μm, and the height of the lithium niobate ridge waveguide (301, 302) is 0.25 μm, the upper width is 1.5 μm, and the angle is 67°.

[0010] Among them, the gap between two opposite zigzag electrodes is 3 - 5 μm.

[0011] Among them, the thickness of the silicon dioxide lower cladding layer (2) between the silicon substrate layer (1) and the lithium niobate waveguide layer (3) is 4.7 μm.

[0012] Among them, the silicon dioxide thin capping layer (4) covers between the lithium niobate waveguide layer (3, 301, 302) and the ground-signal-ground traveling-wave electrode, and the thickness is 0.2 μm.

[0013] Among them, the upper part of the ground-signal-ground traveling wave electrode is covered with the silicon oxide upper cladding layer (6), and the thickness is 0.8 um.

[0014] A thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention has the following significant advantages and technical effects:

[0015] The electrode uses a zigzag electrode structure, and the tip effect causes the electric field to be highly concentrated in the waveguide region, enhancing the electro-optic effect (Pockels effect) of the lithium niobate material. At the same time, it also increases the effective conductor area, reducing the microwave transmission loss and improving the modulation efficiency.

[0016] Flexibly design various parameters that affect the electromagnetic wave propagation speed, such as the period, duty cycle, electrode spacing, and electrode width, to achieve a higher modulation bandwidth. Brief Description of the Drawings

[0017] Figure 1 is a three-dimensional view of a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention.

[0018] Figure 2 is a side view of a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention.

[0019] Figure 3 is another side view of a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention.

[0020] Figure 4 is a top view of a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention.

[0021] Figure 5 is a top view of a thin-film lithium niobate modulator based on an interleaved zigzag electrode structure according to the present invention.

[0022] Figure 6 is a comparison diagram of the microwave loss versus frequency response between a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention and a conventional electro-optic modulator.

[0023] Figure 7 is a comparison diagram of the microwave refractive index versus frequency response between a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention and a conventional electro-optic modulator.

[0024] Figure 8 is a comparison diagram of the impedance versus frequency response between a thin-film lithium niobate modulator based on a zigzag electrode structure according to the present invention and a conventional electro-optic modulator. Detailed Embodiments

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will, in conjunction with the accompanying drawings, clearly and completely describe the technical solutions of the present invention. Any modifications, equivalent replacements, improvements, etc., made without departing from the spirit and scope of the present invention defined by the appended claims shall be included within the protection scope of the present invention.

[0026] The present invention provides a thin-film lithium niobate modulator based on a zigzag electrode structure, which includes a substrate layer, a lower cladding layer, a lithium niobate thin film layer, a ridge waveguide layer with a Mach-Zehnder structure, a thin capping layer, a metal traveling-wave electrode, and an upper cladding layer. The silicon dioxide lower cladding layer (2) is located above the silicon substrate layer (1), the lithium niobate waveguide layer (3) is located above the silicon dioxide lower cladding layer (2), the ridge waveguide layer (301, 302) with a Mach-Zehnder structure is located on the lithium niobate waveguide layer (3) for optical signal transmission, the silicon dioxide thin capping layer (4) covers the lithium niobate waveguide layer (3), and the metal traveling-wave electrode is located between the silicon dioxide thin capping layer (4) and the silicon dioxide upper cladding layer (6), and includes a zigzag electrode structure (501) and a ground-signal-ground traveling-wave electrode (502, 503, 504). The ground-signal-ground traveling-wave electrode is composed of a first ground transmission electrode, a signal transmission electrode, and a second ground transmission electrode.

[0027] In this embodiment, as Figure 1-4 shown, the zigzag electrode structure includes a periodic metal electrode with a sawtooth-shaped top view structure. The electrode thickness h4 = 1.4 um, the thickness of the lithium niobate waveguide layer (3, 301, 302) is 0.5 um, the height h1 of the lithium niobate ridge waveguide (301, 302) is 0.25 um, the upper width w1 is 1.5 um, and the angle is 67°. The gap GAP between two opposite zigzag electrodes is 3 um. The thickness of the silicon dioxide lower cladding layer (2) between the silicon substrate layer (1) and the lithium niobate waveguide layer (3) is 4.7 um. The silicon dioxide thin capping layer (4) covers the space between the lithium niobate waveguide layer (3, 301, 302) and the ground-signal-ground traveling-wave electrode, and the thickness is h3 = 0.2 um. The silicon dioxide capping layer (6) covers the ground-signal-ground traveling-wave electrode, and the thickness h6 = 0.8 um. In the zigzag electrode structure (501), θ = 60°, j1 = 3 um, The number of triangular electrodes is multiple and arranged periodically. The distance between two electrodes is jgap = 0.5 um. The width of the signal electrode is 20 um, the widths of the left and right ground electrodes are set to 150 um, and the length of the device is 1000 um.

[0028] Secondly, a zigzag electrode structure is used for the electrode. The tip effect causes the electric field to be highly concentrated in the waveguide region, enhancing the electro-optic effect (Pockels effect) of the lithium niobate material. At the same time, it also increases the effective conductor area, reducing the microwave transmission loss while improving the modulation efficiency.

[0029] Figure 5 For a thin-film lithium niobate modulator derived from an interleaved zigzag electrode structure, in addition, the toothed electrode structure can be thinned into a thin-film lithium niobate modulator with a double-capacitance zigzag electrode structure. By flexibly designing various parameters that affect the electromagnetic wave propagation speed, such as the period, duty cycle, electrode spacing, and electrode width, a higher modulation bandwidth can be achieved.

[0030] The HFSS software is used to perform three-dimensional modeling and simulation on this thin-film lithium niobate modulator. As Figures 6-8 shown, in the relationship diagram of the thin-film lithium niobate modulator with a zigzag electrode structure and a conventional zigzag electrode modulator, by comparing several parameters such as microwave loss, radio frequency refractive index, and impedance, it is found that the radio frequency refractive index of the present invention is closer to the optical group refractive index of 2.26. At the same time, the loss is reduced, and the impedance mismatch problem is solved, thereby obtaining a higher modulation bandwidth.

[0031] The above-disclosed is only a preferred embodiment of the present application, and it cannot be used to limit the scope of rights of the present application. 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 application still fall within the scope covered by the present application.

Claims

1. A thin-film lithium niobate modulator based on a zigzag electrode structure, characterized in that It includes a silicon substrate layer, a lower cladding layer, a lithium niobate thin film layer, a ridge waveguide layer of a Mach-Zehnder structure, a thin capping layer, metal traveling wave electrodes, and an upper cladding layer; the silicon dioxide lower cladding layer is located above the silicon substrate layer, the lithium niobate waveguide layer is located above the silicon dioxide lower cladding layer, the ridge waveguide layer of the Mach-Zehnder structure is located on the lithium niobate waveguide layer for optical signal transmission, the silicon dioxide thin capping layer covers the lithium niobate waveguide layer, and the metal traveling wave electrodes are located between the silicon dioxide thin capping layer and the silicon dioxide upper cladding layer, including a zigzag electrode structure and a ground-signal-ground traveling wave electrode, and the ground-signal-ground traveling wave electrode is composed of a first ground transmission electrode, a signal transmission electrode, and a second ground transmission electrode.

2. The thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, wherein A periodic traveling wave electrode structure is adopted, which is composed of a metal main electrode and a periodic microstructured electrode. The periodic microstructured electrode is the zigzag electrode structure with a thickness of 1.4 μm. By adjusting the parameters of the zigzag structure, characteristic impedance matching and velocity matching are achieved.

3. The thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, wherein The zigzag electrode structure is that multiple triangles are regularly distributed in the traveling direction of the traveling wave electrode in a period, forming a periodic capacitance between the signal transmission electrode and the ground transmission electrode. The triangles are not limited to equilateral triangles, isosceles triangles, obtuse or acute triangles.

4. The thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 2, characterized in that, The first ground transmission electrode, the signal transmission electrode, and the second ground transmission electrode are arranged in parallel, and the zigzag electrode structure is aligned left and right in space.

5. A thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, characterized in that, The thickness of the lithium niobate waveguide layer is 0.5 μm, the height of the lithium niobate ridge waveguide is 0.25 μm, the upper width is 1.5 μm, and the angle is 67°. The extraordinary light refractive index of the lithium niobate material is ne = 2.1376, and the ordinary light refractive index is no = 2.2111.

6. The thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, characterized in that: The gap between two opposite zigzag electrodes is 3 - 5 μm.

7. A thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, characterized in that The thickness of the silicon dioxide lower cladding layer between the silicon substrate layer and the lithium niobate waveguide layer is 4.7 μm.

8. A thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, characterized in that, The silicon dioxide thin capping layer with a thickness of 0.2 μm covers between the lithium niobate waveguide layer and the ground-signal-ground traveling wave electrode.

9. A thin-film lithium niobate modulator based on a zigzag electrode structure according to claim 1, characterized in that, The silicon dioxide upper cladding layer with a thickness of 0.8 μm covers above the ground-signal-ground traveling wave electrode.

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