Lithium niobate modulator with embedded microstructure electrode film

Abstract

The invention discloses an embedded microstructure electrode film lithium niobate modulator, which comprises an optical structure and an electrical structure, and is characterized in that the optical structure sequentially comprises a substrate layer, a lower cover layer, a film lithium niobate layer and an upper cover layer from bottom to top; a ridge waveguide is formed on the thin film lithium niobate layer, and embedded grooves are formed in the two sides of the ridge waveguide; the electrical structure is a micro-structure traveling wave electrode composed of a ground electrode, signal electrodes and a ground electrode, the ground electrode comprises a main electrode and T electrodes arranged on the inner side of the main electrode in an array mode and connected with the main electrode, and the signal electrodes comprise a main electrode and T electrodes arranged on the two sides of the main electrode in an array mode and connected with the main electrode; the T electrode comprises a transverse section and a vertical section vertically connected with the transverse section; the microstructure traveling wave electrode is arranged between the thin film lithium niobate layer and the upper cover layer, and the transverse section of the T electrode is embedded into the embedded groove. The problem that large waveguide loss is generated due to the fact that the distance between microstructural electrodes in a thin-film lithium niobate modulator is short is solved. And the modulation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronic technology, and in particular relates to an embedded microstructure electrode thin film lithium niobate modulator. Background Art

[0002] Lithium niobate material has excellent electro-optical effect and nonlinear optical properties, which makes it play a vital role in the field of optoelectronics. Lithium niobate material has a high electro-optic coefficient and fast response speed, making it an ideal choice for manufacturing key optoelectronic devices such as electro-optic modulators, optical switches, high voltage sensors and optical parametric oscillators. In addition, the physical and chemical properties of lithium niobate material are stable, which ensures the long-term reliability of the device and simplifies the processing process, making it easy to manufacture high-quality optical waveguides.

[0003] It is worth noting that electro-optic modulators based on lithium niobate materials have obvious advantages in long-distance optical fiber communication systems, including extremely low chirp effect, high modulation bandwidth, faster data transmission, and excellent extinction ratio and stability, which are key factors in ensuring communication quality. Therefore, electro-optic modulators based on lithium niobate materials are widely used in high-speed, high-bandwidth, long-distance communication systems.

[0004] However, traditional bulk lithium niobate modulators have obvious limitations, such as poor electro-optical interaction performance, low modulation efficiency, and large device size, which limit their potential in miniaturization and monolithic integration. In order to overcome these shortcomings, thin-film lithium niobate modulators came into being. This new type of modulator uses thin-film technology to achieve higher integration and better performance, thus promoting the development of optoelectronic devices towards smaller size and higher performance.

[0005] The advantages of thin-film lithium niobate modulators are not only reflected in their size, but also include higher electro-optical efficiency, lower insertion loss and better temperature stability. These characteristics make thin-film lithium niobate modulators have great application prospects in integrated optoelectronics, optical interconnection and optical computing. In addition, thin-film lithium niobate technology also provides the possibility of realizing more complex optoelectronic integrated systems, such as photonic integrated circuits and photonic neural networks. However, the existing thin-film lithium niobate modulators still have the problem of not being able to take into account both electrode spacing and waveguide loss. That is, the existing thin-film lithium niobate modulators have the problem of large waveguide loss when the electrode spacing is close. For example, the conventional modulator has a microstructure electrode with a spacing of 4μm, and its waveguide loss reaches 0.82dB / cm, which limits the miniaturization and higher performance application of thin-film lithium niobate modulators. Summary of the invention

[0006] The purpose of the present invention is to provide an embedded microstructure electrode thin film lithium niobate modulator, which solves the problem of mutual restriction between the microstructure electrode spacing and the waveguide loss in the thin film lithium niobate modulator, that is, solves the problem that the close spacing of the microstructure electrodes in the thin film lithium niobate modulator will produce large waveguide loss; and provides a new technical idea for the miniaturization of the thin film lithium niobate modulator.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] An embedded microstructure electrode thin film lithium niobate modulator includes an optical structure and an electrical structure.

[0009] The optical structure includes, from bottom to top, a substrate layer, a low-refractive index lower cover layer, a thin-film lithium niobate layer, and a low-refractive index upper cover layer; a ridge waveguide is formed on the thin-film lithium niobate layer, and two sides of the ridge waveguide are provided with embedded grooves arranged parallel to the ridge waveguide;

[0010] The electrical structure is a microstructure traveling wave electrode composed of a ground electrode-signal electrode-ground electrode, wherein the ground electrode comprises a main electrode and T electrodes arranged in an array inside the main electrode and connected to the main electrode, and the signal electrode comprises a main electrode and T electrodes arranged in an array on both sides of the main electrode and connected to the main electrode; the T electrode comprises a horizontal segment and a vertical segment vertically connected thereto;

[0011] The microstructure traveling wave electrode is arranged between the thin film lithium niobate layer and the upper cover layer, and the transverse section of the T electrode is embedded in the embedded groove.

[0012] By optimizing the embedded groove depth, the waveguide loss of the modulator reaches stability after the embedded groove depth reaches 0.17 μm, which is defined as the embedded groove depth of 0.17-0.25 μm. As an optimal solution, the embedded groove depth is 0.2 μm.

[0013] By optimizing the embedded groove depth, after the embedded groove width reaches 3.7, the waveguide loss of the modulator is very small, which is defined as the embedded groove width of 3.7-5.0 μm. As an optimal solution, the embedded groove width is 4.0 μm.

[0014] Preferably, the thickness of the microstructure traveling wave electrode is 0.88-0.90 μm, that is, the thickness of the main electrode and the T electrode are the same. As an optimal solution, the thickness of the main electrode and the T electrode are both 0.89 μm.

[0015] Preferably, the distance between the ground electrode and the signal electrode is 4 μm.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. Based on the microstructure traveling wave electrode, the present invention embeds the embedded groove of the lithium niobate waveguide in the transverse section of the T electrode. Due to the embedded design formed by the embedded groove, a structure similar to a large trapezoid is formed on both sides of the lithium ridge waveguide. Such a structure can play an effect similar to that of an optical isolator. The effect of the optical isolator can significantly reduce the loss of the waveguide under the same spacing, and the part of the embedded T electrode can make the central ridge waveguide more strongly controlled by the electric field, and the waveguide loss of the entire modulator can be further reduced.

[0018] 2. Through the optimization of the embedded groove, it was found that when the distance between the ground electrode and the signal electrode is kept constant, the overall impact on the waveguide loss tends to be stable after the width of the embedded groove reaches 4μm. When the depth of the embedded groove is optimized, it is found that when the depth reaches 0.2μm, the overall waveguide loss is very small.

[0019] 3. When the distance between the ground electrode and the signal electrode of a conventional microstructure electrode is 4μm, the waveguide loss is 0.82dB / cm; when the electrode distance is 4μm, the embedded groove width is 4μm, and the depth is 0.2μm, the waveguide loss of the structure of the present invention is as low as 0.068dB / cm. Compared with the conventional microstructure electrode, the waveguide loss of the embedded microstructure electrode is reduced by about 12 times. This also means that the modulator using the embedded microstructure electrode structure can further reduce the electrode distance of the modulator, while reducing the half-wave voltage, it is not troubled by the large waveguide loss caused by the electrode distance, and due to the reduction in the metal electrode distance, the device can be designed to be more compact and compact, which is more in line with the current characteristics of miniaturization and microminiaturization of devices.

[0020] 4. Compared with conventional sunken electrodes, the present invention uses segmented microstructure electrodes and adopts an embedded method, which can reduce waveguide losses while making the modulator longer and having better performance. Compared with the design of completely embedding the microstructure electrode into the waveguide (sunken electrode), the present invention only embeds the transverse section of the T electrode into the waveguide, which ensures the effect of reducing waveguide losses and reduces the complexity of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a schematic diagram of the three-dimensional structure of the present invention;

[0023] Figure 3 It is a top view of the signal electrode, ground electrode and ridge waveguide of the present invention;

[0024] Figure 4 The waveguide loss diagram with and without embedded electrodes at different spacings;

[0025] Figure 5 It is the half-wave voltage-length product diagram under different spacing;

[0026] Figure 6 is the waveguide loss diagram corresponding to the change of embedded slot width;

[0027] Figure 7 Waveguide loss plot for varying embedded groove depth.

[0028] Reference numerals:

[0029] 1. Substrate layer, 2. Lower cover layer, 3. Thin film lithium niobate layer, 4. Ridge waveguide, 5. Upper cover layer, 6. Ground electrode, 7. Signal electrode, 8. Main electrode, 9. T electrode, 10. Horizontal section, 11. Vertical section, 12. Embedded groove. DETAILED DESCRIPTION

[0030] In order to make the purpose and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0031] like Figure 1 , Figure 2 ( Figure 2 Only the left half is drawn, and the right half is symmetrical with the left half. The right half is not drawn to better reflect the structure of the traveling wave electrode and the thin film lithium niobate layer 3. Figure 2 As shown in the figure (not shown in the figure), the present invention discloses an embedded microstructure electrode thin film lithium niobate modulator, including an optical structure and an electrical structure. The optical structure is a waveguide made of an X-cut thin film lithium niobate material, and the electrical structure is a microstructure traveling wave electrode composed of ground-signal-ground electrodes. The microstructure traveling wave electrode enables the thin film lithium niobate modulator to achieve low modulation voltage and low waveguide loss when the electrode spacing is reduced by embedding, providing a new solution for the miniaturization and high integration of the modulator.

[0032] like Figure 1 As shown, the optical structure is based on an X-cut thin-film lithium niobate material, which includes, from bottom to top, a substrate layer 1, a low-refractive index lower cover layer 2, a thin-film lithium niobate layer 3, and a low-refractive index upper cover layer 5; the direction perpendicular to the thin-film lithium niobate layer 3 is the x direction, and the directions in the plane are the z direction and the y direction. The substrate layer 1 is silicon, with a refractive index of 3.49, a relative dielectric constant of 11.9, and a thickness of 500μm. The lower cover layer 2 is an isolation layer, which is silicon dioxide, with a thickness of 5um, a refractive index of 1.44, and a relative dielectric constant of 3.9. The thin-film lithium niobate layer 3 adopts a ridge waveguide structure, with an internal angle of 75°, an upper width of 1.5μm, and a lower width of 1.65μm. The thickness of the thin-film lithium niobate layer 3 is 0.6μm, the etching depth is 0.3μm, and the extraordinary light refractive index is n. e=2.1376, ordinary light refractive index n o =2.2111, relative dielectric constant is ε e =27.9,ε o =44.3; two ridge waveguides 4 are formed on the thin film lithium niobate layer 3, and both sides of the two ridge waveguides 4 are provided with embedded grooves 12 arranged parallel to the ridge waveguides 4. The upper cover layer 5 is silicon dioxide, with a refractive index of 1.44, a relative dielectric constant of 3.9, and a thickness of 0.8μm.

[0033] like Figure 3 As shown, the electrical structure is a microstructure traveling wave electrode composed of a ground electrode-signal electrode-ground electrode, which is a gold electrode. The ground electrode-signal electrode-ground electrode structure is distributed on both sides of the ridge waveguide 4. The ground electrode 6 includes a main electrode 8 and a T electrode 9 arranged in an array inside the main electrode 8 and connected to the main electrode 8. The signal electrode 7 includes a main electrode 8 and a T electrode 9 arranged in an array on both sides of the main electrode 8 and connected to the main electrode 8. The T electrode 9 includes a horizontal section 10 and a vertical section 11 vertically connected thereto.

[0034] The microstructure traveling wave electrode is arranged between the thin film lithium niobate layer 3 and the upper cover layer 5, and the transverse section 10 of the T electrode 9 is embedded in the embedded groove 12, as shown in FIG. Figure 2 shown.

[0035] The depth of the embedded groove 12 is 0.17-0.25 μm. Figure 7 As shown in FIG. 1 , after the width of the embedded groove 12 reaches 3.7 μm, the waveguide loss of the modulator reaches stability. The width of the embedded groove 12 is 3.7-5.0 μm. Figure 6 As shown in the figure, after the width of the embedded groove 12 reaches 3.7μm, the waveguide loss of the modulator is very small. Through further optimization of the embedded groove 12, it is found that when the electrode spacing is kept constant, the width of the embedded groove 12 reaches 4μm, and its overall impact on the waveguide loss tends to be stable. When the depth of the embedded groove 12 is optimized, it is found that its depth reaches 0.2μm, and the overall waveguide loss is very small.

[0036] Preferably, the thickness of the microstructure traveling wave electrode is 0.88-0.90 μm, that is, the thickness of the main electrode 8 and the T electrode 9 are the same. As an optimal solution, the thickness of the main electrode 8 and the T electrode 9 are both 0.89 μm.

[0037] In the conventional microstructure electrode, when the spacing between the ground electrode 6 and the signal electrode 7 is 4 μm, the waveguide loss is 0.82 dB / cm. In the present invention, when the spacing between the ground electrode 6 and the signal electrode 7 is 4 μm, the width of the embedded groove 12 is 4 μm, and the depth is 0.2 μm, the waveguide loss is as low as 0.068 dB / cm, which is about 12 times smaller than that of the conventional microstructure. Figure 4 This also means that the structure of the present invention can further reduce the distance between the ground electrode 6 and the signal electrode 7 of the modulator. Figure 5 While reducing the half-wave voltage, it is not troubled by the large waveguide loss caused by the electrode spacing. In addition, due to the reduction in the electrode spacing, the device can be designed to be more compact, which is more in line with the current characteristics of miniaturization and micro-miniaturization of devices.

[0038] The above embodiments are only specific examples for further describing the purpose, technical solutions and beneficial effects of the present invention, and the present invention is not limited thereto. Any modification, equivalent replacement, improvement, etc. made within the scope of the disclosure of the present invention are included in the protection scope of the present invention.

Claims

1. An embedded microstructure electrode thin film lithium niobate modulator, comprising an optical structure and an electrical structure, characterized in that: The optical structure comprises, from bottom to top, a substrate layer (1), a low-refractive index lower cover layer (2), a thin-film lithium niobate layer (3), and a low-refractive index upper cover layer (5); a ridge waveguide (4) is formed on the thin-film lithium niobate layer (3), and embedded grooves (12) arranged parallel to the ridge waveguide (4) are provided on both sides of the ridge waveguide (4); The electrical structure is a microstructure traveling wave electrode composed of a ground electrode, a signal electrode and a ground electrode. The ground electrode (6) comprises a main electrode (8) and T electrodes (9) arranged in an array inside the main electrode (8) and connected to the main electrode (8). The signal electrode (7) comprises a main electrode (8) and T electrodes (9) arranged in an array on both sides of the main electrode (8) and connected to the main electrode (8). The T electrode (9) comprises a horizontal section (10) and a vertical section (11) vertically connected thereto. The microstructure traveling wave electrode is arranged between the thin-film lithium niobate layer (3) and the upper cover layer (5), and the transverse section (10) of the T electrode (9) is embedded in the embedded groove (12).

2. The embedded microstructure electrode thin film lithium niobate modulator according to claim 1, characterized in that: The depth of the embedded groove (12) is 0.17-0.25 μm.

3. The embedded microstructure electrode thin film lithium niobate modulator according to claim 2, characterized in that: The depth of the embedded groove (12) is 0.2 μm.

4. The embedded microstructure electrode thin film lithium niobate modulator according to any one of claims 1, 2 and 3, characterized in that: The width of the embedded groove (12) is 3.7-5.0 μm.

5. An embedded microstructure electrode thin film lithium niobate modulator according to claim 4, characterized in that: The width of the embedded groove (12) is 4.0 μm.

6. The embedded microstructure electrode thin film lithium niobate modulator according to claim 1, characterized in that: The thickness of the microstructure traveling wave electrode is 0.88-0.90 μm.

7. The embedded microstructure electrode thin film lithium niobate modulator according to any one of claims 1, 2, 3, 5, and 6, characterized in that: The distance between the ground electrode (6) and the signal electrode (7) is 4 μm.

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