Thin film lithium niobate differential modulator and its traveling wave electrode

Abstract

The application provides a thin film lithium niobate differential modulator and a traveling wave electrode thereof. The traveling wave electrode comprises a positive signal electrode, a bias electrode and a negative signal electrode. The positive signal electrode comprises a first electrode plate and a first connecting part. The first connecting part connects the thin film lithium niobate differential modulation structure and the first electrode plate. The negative signal electrode comprises a second electrode plate and a second connecting part. The second connecting part connects the thin film lithium niobate differential modulation structure and the second electrode plate. The bias electrode comprises a third electrode plate, a third connecting part and a fourth connecting part. The third connecting part and the fourth connecting part both connect the thin film lithium niobate differential modulation structure and the third electrode plate. The traveling wave electrode provided by the application has a modulation bandwidth greater than 100 GHz in the differential driving mode. Meanwhile, the comprehensive requirements of the differential traveling wave electrode on the consistency of characteristic impedance, low microwave loss and high electro-optic overlap integral factor are met, so that an engineering electrode solution is provided for the ultrahigh-speed thin film lithium niobate optical modulator.

Description

Technical Field

[0001] This invention relates to the field of optical communication device technology, and in particular to a thin-film lithium niobate differential modulator and its traveling wave electrode. Background Technology

[0002] With the rapid development of 5G communication, high-speed data centers, and ultra-high-speed optical transmission networks, the requirements for modulation bandwidth, transmission rate, operational stability, and integration of electro-optic modulators in optical communication systems are continuously increasing. Mach-Zehnder modulators (MZMs) are core devices in optical communication systems that perform electro-optic signal conversion, and their performance directly determines the communication capacity and transmission quality of the optical transmission system. Compared to traditional modulation materials such as silicon-based and indium phosphide-based modulators, thin-film lithium niobate possesses outstanding advantages such as excellent linear electro-optic effect, low optical loss, high electro-optic overlap efficiency, and no doping loss. It is the preferred material for fabricating ultra-high-speed, low-power electro-optic modulators and is widely used in 400G, 800G, and next-generation terabit-level ultra-high-speed optical communication scenarios.

[0003] The traveling-wave electrode is the core structure of a thin-film lithium niobate differential MZM modulator, and its design directly determines the device's microwave transmission characteristics, electro-optic matching effect, and modulation bandwidth limit. Among them, the differential drive architecture, with its strong anti-interference capability, low drive voltage, and low signal distortion, has become the mainstream driving method for ultra-high-speed thin-film lithium niobate MZM modulators. It can be adapted to high-speed RF differential drive chips, effectively improving the linearity and stability of high-speed signal modulation.

[0004] Currently, existing thin-film lithium niobate differential MZM traveling-wave electrode designs still face significant technical bottlenecks, hindering the improvement of ultra-high-speed modulation performance. Traditional traveling-wave electrodes often employ a fixed impedance and fixed loss design, making it impossible to precisely control electrode impedance and microwave loss according to the differential signal transmission characteristics. This makes it difficult to achieve high-precision speed and impedance matching between microwave signals and optical waveguide signals. In ultra-high-speed operating scenarios of 100 GHz and above, problems such as impedance mismatch, signal reflection, and speed detuning are prone to occur, leading to increased microwave transmission loss, degraded modulation bandwidth, and common-mode noise interference. Ultimately, this results in modulation signal distortion and a reduced signal-to-noise ratio of the device.

[0005] Furthermore, existing technologies cannot simultaneously achieve the three core performance indicators of impedance consistency, low microwave loss, and high electro-optic overlap integral factor for differential traveling-wave electrodes. Conventional optimization methods can only improve a single parameter, resulting in significant performance trade-offs: optimizing impedance matching increases microwave loss and reduces electro-optic coupling efficiency, while reducing transmission loss exacerbates impedance deviation and signal reflection, making it difficult to meet the comprehensive requirements of wide bandwidth, low loss, and high stability for ultra-high-speed optical communication devices. At the same time, traditional design schemes have poor engineering adaptability, hindering large-scale mass production and limiting the industrial application of thin-film lithium niobate ultra-high-speed differential modulators.

[0006] In summary, the industry urgently needs to design a thin-film lithium niobate differential MZM traveling wave electrode structure that can precisely control electrode transmission characteristics, synergistically optimize multiple performance indicators, and be engineering-ready to break through the bandwidth and performance bottlenecks of existing technologies, achieve ultra-high-speed stable modulation above 100GHz, and meet the application requirements of next-generation ultra-high-speed optical communication systems. Summary of the Invention

[0007] This invention provides a thin-film lithium niobate differential modulator and its traveling-wave electrode. In differential driving mode, the traveling-wave electrode has a modulation bandwidth greater than 100 GHz and meets the comprehensive requirements of differential traveling-wave electrodes for characteristic impedance consistency, low microwave loss and high electro-optic overlap integral factor, thereby providing an engineerable electrode solution for ultra-high-speed thin-film lithium niobate optical modulators.

[0008] According to one aspect of the present invention, a traveling wave electrode of a thin-film lithium niobate differential modulator is provided, comprising a positive signal electrode, a bias electrode, and a negative signal electrode extending along a first direction and arranged along a second direction; The positive signal electrode includes a first electrode plate and a first connection portion located on the side of the first electrode plate near the bias electrode. The first end of the first connection portion is connected to the thin-film lithium niobate differential modulation structure, and the second end of the first connection portion is connected to the first electrode plate. The negative signal electrode includes a second electrode plate and a second connection portion located on the side of the second electrode plate near the bias electrode. The first end of the second connection portion is connected to the thin-film lithium niobate differential modulation structure, and the second end of the second connection portion is connected to the second electrode plate. The bias electrode includes a third electrode plate, a third connecting portion, and a fourth connecting portion. The first end of the third connecting portion is connected to the thin-film lithium niobate differential modulation structure, the second end of the third connecting portion is connected to the end of the third electrode plate near the positive signal electrode, the first end of the fourth connecting portion is connected to the thin-film lithium niobate differential modulation structure, and the second end of the fourth connecting portion is connected to the end of the third electrode plate near the negative signal electrode. The dimensions of the first connecting part and the second connecting part in the third direction are first dimensions, and the dimensions of the third connecting part and the fourth connecting part in the third direction are second dimensions, wherein the first dimension is larger than the second dimension; The first direction, the second direction, and the third direction are perpendicular to each other, and the first direction and the second direction are both parallel to the plane in which the thin-film lithium niobate differential modulation structure is located.

[0009] Optionally, the traveling wave electrode is symmetrical about a first plane, the first plane being parallel to the third direction, and the first plane passing through the center of the third electrode plate.

[0010] Optionally, both the first connecting portion and the second connecting portion include a plurality of periodically arranged hollow areas.

[0011] Optionally, the size of the hollow area in the first direction is greater than or equal to 30 μm and less than or equal to 80 μm, the size of the hollow area in the third direction is greater than or equal to 0.5 μm and less than or equal to 2 μm, and the distance between two adjacent hollow areas in the first direction is greater than or equal to 2 μm and less than or equal to 30 μm.

[0012] Optionally, the third electrode plate includes a plurality of grooves extending along the second direction and arranged along the first direction, the grooves penetrating the third electrode plate, the grooves including a first groove and a second groove, the first groove being located on the side of the third electrode plate closer to the first electrode plate, and the second groove being located on the side of the third electrode plate closer to the second electrode plate.

[0013] Optionally, the groove has a size greater than or equal to 2 μm and less than or equal to 10 μm in the first direction, and the groove has a size greater than or equal to 2 μm and less than or equal to 10 μm in the second direction.

[0014] Optionally, the first connection portion is provided with a plurality of first interruption regions on the side near the thin-film lithium niobate differential modulation structure, and in the second direction, the first interruption regions coincide with the first groove; The second connection portion has a plurality of second interruption regions on the side near the thin-film lithium niobate differential modulation structure, and in the second direction, the second interruption regions coincide with the second groove.

[0015] Optionally, the size of the hollow area in the first direction is P, and the distance between two adjacent grooves in the first direction is L, where 0.7≤L / P≤1.

[0016] Optionally, the first connecting portion includes a first part, a second part, and a third part arranged sequentially along the third direction, wherein the second part has a larger dimension in the second direction than the first part in the second direction, and the second part has a larger dimension in the second direction than the third part in the second direction.

[0017] Optionally, the first part has a dimension greater than or equal to 2 μm and less than or equal to 5 μm in the second direction, the second part has a dimension greater than or equal to 3 μm and less than or equal to 6 μm in the second direction, the third part has a dimension greater than or equal to 2 μm and less than or equal to 5 μm in the second direction, the first part has a dimension greater than or equal to 0.5 μm and less than or equal to 2 μm in the third direction, the second part has a dimension greater than or equal to 1 μm and less than or equal to 4 μm in the third direction, and the third part has a dimension greater than or equal to 0.5 μm and less than or equal to 2 μm in the third direction.

[0018] Optionally, the first electrode plate has a dimension in the second direction that is greater than or equal to 30 μm and less than or equal to 100 μm, the first electrode plate has a dimension in the third direction that is greater than or equal to 1 μm and less than or equal to 4 μm, and the third electrode plate has a dimension in the second direction that is greater than or equal to 10 μm and less than or equal to 30 μm.

[0019] According to another aspect of the present invention, a thin-film lithium niobate differential modulator is provided, comprising the traveling wave electrode described above.

[0020] The traveling-wave electrode of the thin-film lithium niobate differential modulator provided in this invention includes a positive signal electrode, a bias electrode, and a negative signal electrode extending along a first direction and arranged along a second direction. By providing corresponding driving signals to the positive and negative signal electrodes and a corresponding bias signal to the bias electrode, the electric field generated by the traveling-wave electrode acts on the optical waveguide of the thin-film lithium niobate differential modulator, thereby achieving differential modulation. By designing parameters such as the electrode width and spacing of each electrode, the differential impedance of the traveling-wave electrode can be controlled, while ensuring the matching of the microwave signal and the optical signal, to achieve a large bandwidth modulation of 100 GHz. This invention addresses the impedance matching and bandwidth bottleneck problem in the design of traveling-wave electrodes for differential drive modulators in thin-film lithium niobate platforms. It provides a traveling-wave electrode structure based on a controllable differential resistor. In differential drive mode, its modulation bandwidth is greater than 100 GHz, while simultaneously meeting the comprehensive requirements of differential traveling-wave electrodes for characteristic impedance consistency, low microwave loss, and high electro-optic overlap integral factor. This provides an engineerable electrode solution for ultra-high-speed thin-film lithium niobate optical modulators.

[0021] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a top view schematic diagram of the traveling wave electrode of a thin-film lithium niobate differential modulator according to an embodiment of the present invention; Figure 2 For along Figure 1 A schematic diagram of the cross-sectional structure along the central section line A1A2; Figure 3 This is a top view schematic diagram of a thin-film lithium niobate differential modulation structure provided in an embodiment of the present invention; Figure 4 A schematic diagram illustrating the driving principle of a traveling wave electrode provided in an embodiment of the present invention; Figure 5 A top view schematic diagram of the traveling wave electrode of another thin-film lithium niobate differential modulator provided in an embodiment of the present invention; Figure 6 For along Figure 5 Schematic diagram of the cross-sectional structure along the center section line A3A4; Figure 7 For along Figure 5 Schematic diagram of the cross-sectional structure along the center section line A5A6; Figure 8 for Figure 5 The diagram shows a three-dimensional structure of the traveling wave electrode. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0025] It should be noted that the terminology used in the embodiments of this invention is for the purpose of describing specific embodiments only and is not intended to limit the invention. It should be noted that directional terms such as "above," "below," "left," and "right" described in the embodiments of this invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this invention. Furthermore, in the context, it should be understood that when referring to an element being formed "above" or "below" another element, it can be formed not only directly "above" or "below" the other element, but also indirectly "above" or "below" the other element through an intermediate element. The terms "first," "second," etc., are used for descriptive purposes only and do not indicate any order, quantity, or importance, but are only used to distinguish different components. It should be understood that such terms can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0026] Figure 1 This is a top view schematic diagram of the traveling wave electrode of a thin-film lithium niobate differential modulator according to an embodiment of the present invention. Figure 2 For along Figure 1 A schematic diagram of the cross-sectional structure along section line A1A2, for reference. Figure 1 and Figure 2The traveling wave electrode includes a positive signal electrode 10, a bias electrode 20, and a negative signal electrode 30 extending along a first direction x and arranged along a second direction y. The positive signal electrode 10 includes a first electrode plate 11 and a first connecting portion 12 located on the side of the first electrode plate 11 near the bias electrode 20. The first end of the first connecting portion 12 is connected to the thin-film lithium niobate differential modulation structure 100, and the second end of the first connecting portion 12 is connected to the first electrode plate 11. The negative signal electrode 30 includes a second electrode plate 31 and a second connecting portion 32 located on the side of the second electrode plate 31 near the bias electrode 20. The first end of the second connecting portion 32 is connected to the thin-film lithium niobate differential modulation structure 100, and the second end of the second connecting portion 32 is connected to the second electrode plate 31. The bias electrode 20 includes a third electrode plate 21, a third connecting portion 22, and a fourth connecting portion 23. The first end of the third connecting part 22 is connected to the thin-film lithium niobate differential modulation structure 100, the second end of the third connecting part 22 is connected to the end of the third electrode plate 21 near the positive signal electrode 10, the first end of the fourth connecting part 23 is connected to the thin-film lithium niobate differential modulation structure 100, and the second end of the fourth connecting part 23 is connected to the end of the third electrode plate 21 near the negative signal electrode 30. The dimensions of the first connecting part 12 and the second connecting part 32 in the third direction z are the first dimension h1, and the dimensions of the third connecting part 22 and the fourth connecting part 23 in the third direction z are the second dimension h2. The first dimension h1 is greater than the second dimension h2, that is, h1>h2. The first direction x, the second direction y and the third direction z are perpendicular to each other, and the first direction x and the second direction y are both parallel to the plane where the thin-film lithium niobate differential modulation structure 100 is located.

[0027] Among them, the thin-film lithium niobate differential modulation structure 100 is an optical structure in a thin-film lithium niobate differential modulator, for example, Figure 3 This is a top view schematic diagram of a thin-film lithium niobate differential modulation structure provided in an embodiment of the present invention, with reference to... Figure 3The thin-film lithium niobate differential modulation structure 100 includes a thin-film lithium niobate optical waveguide. The thin-film lithium niobate optical waveguide includes a 1×2 beamsplitter 101, a Mach-Zehnder structure 102, and a 2×1 beam combiner 103 arranged along a first direction x. The 1×2 beamsplitter 101 and the 2×1 beam combiner 103 are located on both sides of the Mach-Zehnder structure 102. The input end of the 1×2 beamsplitter 101 is used to input optical signals. The two output ends of the 1×2 beamsplitter 101 are connected through the two input ends of the Mach-Zehnder structure 102 and the 2×1 beam combiner 103. The output end of the 2×1 beam combiner 103 is used to output optical signals. The Mach-Zehnder structure 102 includes two branch arms. The two output ends of the 1×2 beamsplitter 101 are connected through one of their respective branch arms and the two input ends of the 2×1 beam combiner 103. The light is split into two beams by a 1×2 beam splitter 101, which then pass through the upper and lower branches of the Mach-Zehnder structure 102, respectively, and finally combined into a single beam by a 2×1 beam combiner 103. Positive and negative signal electrodes are respectively arranged on both sides above the Mach-Zehnder structure 102. The Mach-Zehnder structure 102 includes two waveguides, one located between the first and third connecting parts, and the other located between the second and fourth connecting parts.

[0028] The equivalent circuit of the traveling wave electrode provided in this embodiment of the invention can be decomposed into an RLGC model. The RLGC model is a distributed parameter equivalent circuit model used in transmission line theory to describe the propagation characteristics of high-frequency / high-speed signals along a conductor. It considers the transmission line as a series of countless tiny segments cascaded together. Each micro-element is characterized by a series resistance R (conductor loss), a series inductance L (magnetic field energy storage), a parallel conductance G (dielectric loss), and a parallel capacitance C (electric field energy storage) per unit length. Its characteristic impedance is... The propagation constant of microwave signals is Under high-frequency, low-loss conditions, the impedance is mainly determined by L and C, and the differential impedance can be simplified to... The propagation constant can be simplified to To achieve an electro-optic bandwidth exceeding 100 GHz, special methods are needed to adjust the refractive index n of the microwave signal. RF With the group refractive index n of light g The difference between them should be minimized. L and C are determined by the structure of the electrodes themselves, such as electrode width, spacing, and coupling region ratio. In this embodiment, the differential impedance is controlled by adjusting the electrode parameters. By precisely controlling the equivalent series or parallel resistance network in the differential signal path, the characteristic impedance and loss factor of the electrodes can be controlled. This controllable differential resistance design can not only effectively suppress common-mode noise and reflection in differential signal transmission, but also optimize the speed matching and impedance matching characteristics between the traveling wave electrode and the lithium niobate optical waveguide.

[0029] Figure 4This is a schematic diagram of the driving principle of a traveling wave electrode provided in an embodiment of the present invention, with reference to... Figure 4 The traveling wave electrode includes two ground terminals GND, a positive signal electrode terminal S+, and a negative signal electrode terminal S-. All four terminals are electrically connected to the Optical Digital Signal Processor (ODSP). The ODSP provides the drive signal. The positive and negative signal electrodes are simplified to L1 and L2, the first and third connection parts are simplified to C1, and the second and fourth connection parts are simplified to C2. L1 and L2 are connected to Vdd. The bias electrodes (the third and fourth connection parts, corresponding to one end of C1 and C2) are connected to the bias voltage Vb. The specific values ​​of Vdd and Vb depend on the actual driving conditions and must meet the following conditions: , where Vpp is the peak-to-peak value of the drive signal voltage.

[0030] Optionally, the traveling wave electrode is symmetrical about a first plane, the first plane is parallel to the third direction z, and the first plane passes through the center of the third electrode plate 21.

[0031] Among them, continue to refer to Figure 1 and Figure 2 The first plane is through Figure 1 The middle dashed lines B1B2 and Figure 2 The plane of the dashed line B3B4.

[0032] Figure 5 This is a top view schematic diagram of the traveling wave electrode of another thin-film lithium niobate differential modulator provided in an embodiment of the present invention. Figure 6 For along Figure 5 Schematic diagram of the cross-sectional structure along the center section line A3A4. Figure 7 For along Figure 5 Schematic diagram of the cross-sectional structure along the central section line A5A6. Figure 8 for Figure 5 The schematic diagram of the three-dimensional structure of the traveling wave electrode is shown below. (Refer to...) Figures 5-8 Optionally, the first connecting portion 12 includes a plurality of periodically arranged hollow areas 121. Since the traveling wave electrode has a symmetrical structure, the second connecting portion ( Figure 8 (Not shown) also includes multiple cutout areas.

[0033] The purpose of the cutout area is to reduce the energy coupling between the positive signal electrode 10 and the negative signal electrode 30, thereby reducing the equivalent capacitance and improving the differential impedance. (Reference) Figure 7 The dimension P of the hollow area 121 in the first direction x is greater than or equal to 30 μm and less than or equal to 80 μm. The dimension h_via of the hollow area 121 in the third direction z is greater than or equal to 0.5 μm and less than or equal to 2 μm. The distance L_via between two adjacent hollow areas 121 in the first direction x is greater than or equal to 2 μm and less than or equal to 30 μm.

[0034] refer to Figure 5 and Figure 8 The third electrode plate 21 includes a plurality of grooves 211 extending along the second direction y and arranged along the first direction x. The grooves 211 penetrate the third electrode plate 21. The grooves 211 include a first groove 2111 and a second groove 2112. The first groove 2111 is located on the side of the third electrode plate 21 closer to the first electrode plate 11, and the second groove 2112 is located on the side of the third electrode plate 21 closer to the second electrode plate 31.

[0035] The groove 211 has the same function as the hollow area 121. In specific implementation, the size w_slot of the groove 211 in the first direction x is greater than or equal to 2μm and less than or equal to 10μm, and the size h_slot of the groove 211 in the second direction y is greater than or equal to 2μm and less than or equal to 10μm.

[0036] Continue to refer to Figure 7 and Figure 8 Optionally, the first connecting portion 12 is provided with a plurality of first interruption regions 122 on the side near the thin film lithium niobate differential modulation structure (i.e. below the hollow area), and in the second direction y, the first interruption region 122 coincides with the first groove 2111; the second connecting portion is provided with a plurality of second interruption regions on the side near the thin film lithium niobate differential modulation structure, and in the second direction, the second interruption region coincides with the second groove.

[0037] Optionally, the dimension of the hollow area 121 in the first direction x is P, and the distance between two adjacent grooves in the first direction x (i.e. the distance between two adjacent first interruption areas 122) is L, 0.7≤L / P≤1.

[0038] refer to Figure 6 Optionally, the first connecting portion 12 includes a first portion 12a, a second portion 12b, and a third portion 12c arranged sequentially along the third direction z. The second portion 12b has a larger dimension in the second direction y than the first portion 12a in the second direction y, and the second portion 12b has a larger dimension in the second direction y than the third portion 12c in the second direction y.

[0039] The width of the second part 12b is set to be wider than that of the upper and lower layers mainly to consider the tolerance of the process. In specific implementation, the dimensions of the first part 12a in the second direction y, w_ct, are greater than or equal to 2μm and less than or equal to 5μm; the dimensions of the second part 12b in the second direction y, w_m1, are greater than or equal to 3μm and less than or equal to 6μm; the dimensions of the third part 12c in the second direction y, w_via, are greater than or equal to 2μm and less than or equal to 5μm; the dimensions of the first part 12a in the third direction z, h_ct, are greater than or equal to 0.5μm and less than or equal to 2μm; the dimensions of the second part 12b in the third direction z, h_m1, are greater than or equal to 1μm and less than or equal to 4μm; and the dimensions of the third part 12c in the third direction z, h_via, are greater than or equal to 0.5μm and less than or equal to 2μm.

[0040] Optionally, the dimension w1 of the first electrode 11 in the second direction y is greater than or equal to 30 μm and less than or equal to 100 μm, the dimension h_m2 of the first electrode 11 in the third direction z is greater than or equal to 1 μm and less than or equal to 4 μm, and the dimension w2 of the third electrode 21 in the second direction y is greater than or equal to 10 μm and less than or equal to 30 μm.

[0041] It is understandable that the positive signal electrode and the negative signal electrode have symmetrical structures and the same size.

[0042] By optimizing the combination of various parameters of the traveling wave electrode, the design goals of differential impedance control and large electro-optic bandwidth can be achieved.

[0043] This invention also provides a thin-film lithium niobate differential modulator, including the traveling-wave electrode provided in the above embodiments. Since the thin-film lithium niobate differential modulator provided in this invention includes the traveling-wave electrode provided in the above embodiments, it has the same and corresponding technical effects.

[0044] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A traveling-wave electrode for a thin-film lithium niobate differential modulator, characterized in that, It includes a positive signal electrode, a bias electrode, and a negative signal electrode that extend along a first direction and are arranged along a second direction; The positive signal electrode includes a first electrode plate and a first connection portion located on the side of the first electrode plate near the bias electrode. The first end of the first connection portion is connected to the thin-film lithium niobate differential modulation structure, and the second end of the first connection portion is connected to the first electrode plate. The negative signal electrode includes a second electrode plate and a second connection portion located on the side of the second electrode plate near the bias electrode. The first end of the second connection portion is connected to the thin-film lithium niobate differential modulation structure, and the second end of the second connection portion is connected to the second electrode plate. The bias electrode includes a third electrode plate, a third connecting portion, and a fourth connecting portion. The first end of the third connecting portion is connected to the thin-film lithium niobate differential modulation structure, the second end of the third connecting portion is connected to the end of the third electrode plate near the positive signal electrode, the first end of the fourth connecting portion is connected to the thin-film lithium niobate differential modulation structure, and the second end of the fourth connecting portion is connected to the end of the third electrode plate near the negative signal electrode. The dimensions of the first connecting part and the second connecting part in the third direction are first dimensions, and the dimensions of the third connecting part and the fourth connecting part in the third direction are second dimensions, wherein the first dimension is larger than the second dimension; The first direction, the second direction, and the third direction are perpendicular to each other, and the first direction and the second direction are both parallel to the plane in which the thin-film lithium niobate differential modulation structure is located.

2. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 1, characterized in that, The traveling wave electrode is symmetrical about a first plane, which is parallel to the third direction and passes through the center of the third electrode plate.

3. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 2, characterized in that, Both the first connecting portion and the second connecting portion include a plurality of periodically arranged hollow areas.

4. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 3, characterized in that, The size of the hollow area in the first direction is greater than or equal to 30 μm and less than or equal to 80 μm, the size of the hollow area in the third direction is greater than or equal to 0.5 μm and less than or equal to 2 μm, and the distance between two adjacent hollow areas in the first direction is greater than or equal to 2 μm and less than or equal to 30 μm.

5. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 3, characterized in that, The third electrode plate includes a plurality of grooves extending along the second direction and arranged along the first direction. The grooves penetrate the third electrode plate. The grooves include a first groove and a second groove. The first groove is located on the side of the third electrode plate closer to the first electrode plate, and the second groove is located on the side of the third electrode plate closer to the second electrode plate.

6. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 5, characterized in that, The groove has a dimension greater than or equal to 2 μm and less than or equal to 10 μm in the first direction, and the groove has a dimension greater than or equal to 2 μm and less than or equal to 10 μm in the second direction.

7. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 5, characterized in that, The first connection portion is provided with a plurality of first interruption regions on the side near the thin-film lithium niobate differential modulation structure, and in the second direction, the first interruption regions coincide with the first groove; The second connection portion has a plurality of second interruption regions on the side near the thin-film lithium niobate differential modulation structure, and in the second direction, the second interruption regions coincide with the second groove.

8. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 5, characterized in that, The size of the hollow area in the first direction is P, and the distance between two adjacent grooves in the first direction is L, where 0.7≤L / P≤1.

9. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 2, characterized in that, The first connecting portion includes a first part, a second part, and a third part arranged sequentially along the third direction. The second part has a larger dimension in the second direction than the first part in the second direction, and the second part has a larger dimension in the second direction than the third part in the second direction.

10. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 9, characterized in that, The first part has a dimension greater than or equal to 2 μm and less than or equal to 5 μm in the second direction; the second part has a dimension greater than or equal to 3 μm and less than or equal to 6 μm in the second direction; the third part has a dimension greater than or equal to 2 μm and less than or equal to 5 μm in the second direction; the first part has a dimension greater than or equal to 0.5 μm and less than or equal to 2 μm in the third direction; the second part has a dimension greater than or equal to 1 μm and less than or equal to 4 μm in the third direction; and the third part has a dimension greater than or equal to 0.5 μm and less than or equal to 2 μm in the third direction.

11. The traveling wave electrode of the thin-film lithium niobate differential modulator according to claim 2, characterized in that, The first electrode plate has a dimension in the second direction that is greater than or equal to 30 μm and less than or equal to 100 μm, the first electrode plate has a dimension in the third direction that is greater than or equal to 1 μm and less than or equal to 4 μm, and the third electrode plate has a dimension in the second direction that is greater than or equal to 10 μm and less than or equal to 30 μm.

12. A thin-film lithium niobate differential modulator, characterized in that, Includes the traveling wave electrode as described in any one of claims 1 to 11.

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