A ferroelectric domain electro-optic modulator with ultra-wide bandwidth

Abstract

An electro-optic modulator with ultra-wide bandwidth ferroelectric domains belongs to the field of electro-optic modulator technology. From bottom to top, it consists of a substrate, a silicon dioxide lower cladding, a ferroelectric planar layer, a ferroelectric waveguide layer, and a silicon dioxide upper cladding. The ferroelectric waveguide layer has an MZI-type structure, consisting of a 1×2 input multimode interference coupler, a first input S-bend waveguide, a second input S-bend waveguide, a first modulation straight waveguide, a second modulation straight waveguide, a first output S-bend waveguide, a second output S-bend waveguide, and a 2×1 output multimode interference coupler. The ferroelectric planar layer has a hollow structure in the middle, and ground electrodes and signal electrodes are fabricated on the exposed surface of the silicon dioxide lower cladding within and outside the hollow structure. This invention eliminates the attenuation effect of excessively high dielectric constant on microwave signals by etching away the ferroelectric material beneath the electrodes, and simultaneously ensures high modulation efficiency by reducing the distance between the electrodes and the waveguide, ultimately realizing the fabrication of an ultra-wide bandwidth electro-optic modulator.

Description

Technical Field

[0001] This invention belongs to the field of electro-optic modulator technology, specifically relating to an electro-optic modulator with ultra-large bandwidth ferroelectric domains. Background Technology

[0002] In recent years, with the rapid development of high-tech such as AI, 6G communication, big data, and the Internet of Things, the communication market's requirements for communication capacity have gradually increased. High-speed electro-optic modulators, as core components of optical modules, play a crucial role in optical communication networks. Along with the development of market demand, higher requirements have been placed on the bandwidth, transmission rate, and signal quality of optical modules.

[0003] First-order electro-optic properties (Pockels effect) are the main method for achieving high-speed linear modulation. Novel ferroelectric materials such as lithium niobate, lanthanum-modified lead zirconate titanate (Pb1-xLax(Zr yTi1-y)O3, lead zirconate titanate (PbZrxTi1-xO3, PZT), and barium titanate (BaTiO3, BTO) possess high electro-optic coefficients, making them ideal materials for electro-optic modulators. However, with the increase in electro-optic coefficient, the dielectric constant of these materials also increases rapidly. The microwave signal applied to the electrodes is quickly lost due to the increased dielectric constant, limiting further bandwidth improvements. Therefore, there is an urgent need to develop a next-generation electro-optic modulator with ultra-high bandwidth and ultra-high capacity. Summary of the Invention

[0004] To address the problems described in the background section, this invention proposes a ferroelectric domain electro-optic modulator with ultra-wide bandwidth. This invention eliminates the attenuation effect of excessively high dielectric constant on microwave signals by etching away the ferroelectric material beneath the electrodes. Simultaneously, by reducing the distance between the electrodes and the waveguide, high modulation efficiency is ensured, ultimately achieving the fabrication of an ultra-wide bandwidth electro-optic modulator.

[0005] The ferroelectric domain electro-optic modulator with ultra-wide bandwidth described in this invention is composed of, from bottom to top, a substrate (1), a silicon dioxide lower cladding layer (2), a ferroelectric planar layer, a ferroelectric waveguide layer, and a silicon dioxide upper cladding layer (6); as shown in the attached figure. Figure 1As shown, the length of the device is defined from left to right along the signal light transmission direction in the ferroelectric waveguide layer, and the width of the device is defined perpendicular to the signal light transmission direction in the ferroelectric waveguide layer within the plane of the ferroelectric flat plate layer. The ferroelectric waveguide layer is an MZI type structure, consisting of a 1×2 input multimode interference coupler (100), a first input S-bend waveguide (200), a second input S-bend waveguide (201), a first modulation straight waveguide (300), a second modulation straight waveguide (301), a first output S-bend waveguide (202), and a second output S-bend waveguide (202). The system consists of a 2×1 output multimode interference coupler (400) and a 2×1 output multimode interference coupler (203). The first input S-bend waveguide (200), the first modulation straight waveguide (300), and the first output S-bend waveguide (202) are connected sequentially. The second input S-bend waveguide (201), the second modulation straight waveguide (301), and the second output S-bend waveguide (203) are connected sequentially, forming the two output terminals of the 1×2 input multimode interference coupler (100) and the two input terminals of the 2×1 output multimode interference coupler (400), respectively. The ferroelectric flat plate layer is... The structure has a hollow center, and a signal electrode (52) is fabricated on the surface of the exposed silicon dioxide cladding (2) within the hollow structure. A first ground electrode (51) and a second ground electrode (53) are fabricated on the silicon dioxide cladding (2) outside the ferroelectric plate layer, respectively. The first ground electrode (51), the signal electrode (52), and the second ground electrode (53) together constitute a metal electrode layer. The first ground electrode (51) is located outside the first modulation straight waveguide (300), and the signal electrode (52) is located between the first modulation straight waveguide (300) and the second modulation straight waveguide (300). Between the direct waveguides (301), the second ground electrode (53) is located outside the second modulation direct waveguide (301); the first ground electrode (51), the signal electrode (52), the second ground electrode (53), the first modulation direct waveguide (300) and the second modulation direct waveguide (301) constitute the modulation area of ​​the electro-optic modulator; the first ground electrode (51), the signal electrode (52) and the second ground electrode (53) are rectangular structures, with their long sides parallel to each other and parallel to the first modulation direct waveguide (300) and the second modulation direct waveguide (301).

[0006] like Figure 2 As shown, the 1×2 input multimode interference coupler (100) and the 2×1 output multimode interference coupler (400) are devices with the same structure and size but opposite usage. The 1×2 input multimode interference coupler (100) is composed of a first wedge waveguide (101), a multimode interference waveguide (104), a second wedge waveguide (102), and a third wedge waveguide (103). The first wedge waveguide (101), the second wedge waveguide (102), and the third wedge waveguide (103) have the same structure and size. The first wedge waveguide (101) serves as the input end of the 1×2 input multimode interference coupler (100), and the second wedge waveguide (102) and the third wedge waveguide (103) serve as the output ends of the 1×2 input multimode interference coupler (100).

[0007] like Figure 3 As shown, Figure 1 The cross-sectional view at position A-A' shows that, from bottom to top, it consists of a substrate (1), a lower silicon dioxide cladding layer (2), a first ferroelectric planar layer (31), a first ferroelectric waveguide layer (41), and an upper silicon dioxide cladding layer (6). The first ferroelectric waveguide layer (41) corresponds to... Figure 2 The input waveguide (101) of the 1×2 input multimode interference coupler (100).

[0008] like Figure 4 As shown, Figure 1 The cross-sectional view at position B-B' shows that, from bottom to top, it consists of a substrate (1), a silicon dioxide lower cladding layer (2), a ferroelectric planar layer, a ferroelectric waveguide layer, and a silicon dioxide upper cladding layer (6). The ferroelectric planar layer and ferroelectric waveguide layer in the first modulation straight waveguide (300) and the second modulation straight waveguide (301) regions are discrete structures. The ferroelectric planar layer includes a second ferroelectric planar layer (32) and a third ferroelectric planar layer (33). The ferroelectric waveguide layer includes a second ferroelectric waveguide layer (42) and a third ferroelectric waveguide layer (33). The waveguide layer (43) consists of two parts: a second ferroelectric waveguide layer (42) is located above the second ferroelectric planar layer (32), and a third ferroelectric waveguide layer (43) is located above the third ferroelectric planar layer (33); the first ground electrode (51) and the second ground electrode (53) are located outside the second ferroelectric planar layer (32) and the third ferroelectric planar layer (33), respectively; the signal electrode (52) is located between the second ferroelectric planar layer (32) and the third ferroelectric planar layer (33); the second ferroelectric waveguide layer (42) corresponds to... Figure 1 The first modulation straight waveguide (300) and the third ferroelectric waveguide layer (43) correspond to Figure 1 The second modulation straight waveguide (301), the second ferroelectric waveguide layer (42), the second ferroelectric flat plate layer (32), the third ferroelectric waveguide layer (43) and the third ferroelectric flat plate layer (33) constitute the optical waveguide core layer; the silicon dioxide cladding layer (6) has a hollow structure, and the first ground electrode (51), the signal electrode (52) and the second ground electrode (53) are exposed to form contact holes, and the second ferroelectric flat plate layer (32), the second ferroelectric waveguide layer (42), the third ferroelectric flat plate layer (33) and the third ferroelectric waveguide layer (43) are completely covered therein; the first ground electrode (51), the signal electrode (52) and the second ground electrode (53) together constitute the metal electrode layer.

[0009] The substrate (1) can be one of quartz, silicon, or high-resistivity silicon (resistivity greater than 1000 Ω·cm), and the thickness of the substrate (1) is 500~625μm; the thickness of the silicon dioxide cladding layer (2) can be adjusted according to the actual situation, and is 2~15μm; in the same device, the ferroelectric planar layer and the ferroelectric waveguide layer are the same ferroelectric material, which can be one of lead zirconate titanate, lanthanum-modified lead zirconate titanate, or barium titanate, and the thickness of the ferroelectric planar layer is 100~300nm, and the thickness of the ferroelectric waveguide layer is 50~150nm; in the same device, the first ground electrode (51), the signal electrode (52), and the second ground electrode (53) are the same metal material, which can be one of aluminum, gold, silver, tungsten, or titanium, and the thickness is 300~500nm. m, and the thickness of the electrode is greater than the sum of the thicknesses of the ferroelectric planar layer and the ferroelectric waveguide layer. The width of the signal electrode (52) is 20~50μm. The distance between the first ground electrode (51) and the signal electrode (52) is the same as the distance between the second ground electrode (53) and the signal electrode (52), which is 4.5~6μm. The distance between the first modulation straight waveguide (300) and the second modulation straight waveguide (301) is the sum of the width of the signal electrode (52), the distance between the first ground electrode (51) and the signal electrode (52), and the distance between the second ground electrode (53) and the signal electrode (52). The thickness of the silicon dioxide cladding (6) is 1~5μm. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0011] Figure 1 This is a schematic diagram of a ferroelectric domain electro-optic modulator structure with ultra-large bandwidth according to the present invention; in the figure, dark blue represents the ferroelectric waveguide layer, light blue represents the ferroelectric planar layer, and the two together constitute the optical waveguide core layer; yellow represents the metal electrode layer, and light gray represents the silicon dioxide underlayer.

[0012] Figure 2 This is a schematic diagram of the 1×2 input multimode interference coupler described in this invention;

[0013] Figure 3 For the present invention Figure 1 Schematic diagram of the cross section at position A-A';

[0014] Figure 4 For the present invention Figure 1 Schematic diagram of the cross-section at position B-B';

[0015] Figure 5This is a flowchart illustrating the fabrication process of the non-modulation region waveguide for a ferroelectric domain electro-optic modulator with ultra-large bandwidth, as described in this invention.

[0016] Figure 6 This is a flowchart illustrating the fabrication process of the modulation region waveguide for a ferroelectric domain electro-optic modulator with ultra-large bandwidth, as described in this invention.

[0017] Figure 7 The curves showing the modulation voltage and optical transmission loss of a ferroelectric domain electro-optic modulator with ultra-wide bandwidth as described in this invention are as follows (the black curve corresponds to the voltage signal on the left vertical axis, and the red curve corresponds to the transmitted light intensity signal on the right vertical axis); this indicates that the modulator can achieve light intensity modulation as time changes.

[0018] Figure 8 The graph shows the relationship between E21 and frequency for a ferroelectric domain electro-optic modulator with ultra-large bandwidth as described in this invention.

[0019] Figure 9 This is a 200Gbaud OOK test eye diagram of a ferroelectric domain electro-optic modulator with ultra-high bandwidth as described in this invention. Detailed Implementation

[0020] To further illustrate the core technical solutions and application objectives of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Example 1

[0022] The ferroelectric domain electro-optic modulator with ultra-wide bandwidth described in this invention is composed of, from bottom to top, a substrate (1), a silicon dioxide lower cladding layer (2), a ferroelectric planar layer, a ferroelectric waveguide layer, and a silicon dioxide upper cladding layer (6); as shown in the attached figure. Figure 1As shown, the length of the device is defined from left to right along the signal light transmission direction in the ferroelectric waveguide layer, and the width of the device is defined perpendicular to the signal light transmission direction in the ferroelectric waveguide layer within the plane of the ferroelectric flat plate layer. The ferroelectric waveguide layer is an MZI type structure, consisting of a 1×2 input multimode interference coupler (100), a first input S-bend waveguide (200), a second input S-bend waveguide (201), a first modulation straight waveguide (300), a second modulation straight waveguide (301), a first output S-bend waveguide (202), a second output S-bend waveguide (203), and a 2×1 output multimode interference coupler (400). The first input S-bend waveguide (200), the first modulation straight waveguide (300), and the first output S-bend waveguide (202) are connected sequentially, and the second input S-bend waveguide (201), the second modulation straight waveguide (301), and the second output S-bend waveguide (203) are connected sequentially, forming a 1×1 multimode interference coupler. The two output terminals of the 2-input multimode interference coupler (100) and the two input terminals of the 2×1 output multimode interference coupler (400) are provided. The ferroelectric plate layer is a hollow structure in the middle. A signal electrode (52) is prepared on the surface of the exposed silicon dioxide cladding (2) in the hollow structure. A first ground electrode (51) and a second ground electrode (53) are prepared on the silicon dioxide cladding (2) on the outside of the ferroelectric plate layer. The first ground electrode (51) is located outside the first modulation straight waveguide (300), the signal electrode (52) is located between the first modulation straight waveguide (300) and the second modulation straight waveguide (301), and the second ground electrode (53) is located outside the second modulation straight waveguide (301). The first ground electrode (51), the signal electrode (52) and the second ground electrode (53) are rectangular structures with their long sides parallel to each other and parallel to the first modulation straight waveguide (300) and the second modulation straight waveguide (301).

[0023] In this embodiment, the substrate is silicon with a thickness of 550 μm, the silicon dioxide lower cladding (2) has a thickness of 3 μm, the first ferroelectric plate layer (31), the first ferroelectric waveguide layer (41), the second ferroelectric plate layer (32), the second ferroelectric waveguide layer (42), the third ferroelectric plate layer (33), and the third ferroelectric waveguide layer (43) are all made of the same ferroelectric material with the same refractive index and dielectric constant. In this embodiment, it is lanthanum-modified lead zirconate titanate. The thickness of the first ferroelectric plate layer (31), the second ferroelectric plate layer (32), and the third ferroelectric plate layer (33) is the same at 200 nm, and the thickness of the first ferroelectric waveguide layer (41), the second ferroelectric waveguide layer (42), and the third ferroelectric waveguide layer (43) is the same at 100 nm. The first ground electrode (51), the signal electrode (52), and the second ground electrode (53) are aluminum with a thickness of 400 nm. The thickness of the silicon dioxide upper cladding (6) is 1 μm.

[0024] The first input S-bent waveguide (200), the second input S-bent waveguide (201), the first output S-bent waveguide (202), and the second output S-bent waveguide (203) are two 90° bent waveguides with a radius of 150μm connected together. The first modulation straight waveguide (300) and the second modulation straight waveguide (301) have the same length of 0.5cm. The first ground electrode (51), the signal electrode (52), and the second ground electrode (53) have the same length of 0.5cm. The first ground electrode (51) and the second ground electrode (53) have the same width of 30μm. The signal electrode (52) has the same width of 50μm. The distance between the first ground electrode (51) and the signal electrode (52) is 5μm. The distance between the second ground electrode (53) and the signal electrode (52) is 5μm. The distance between the first modulation straight waveguide (300) and the second modulation straight waveguide (301) is the sum of the width of the signal electrode (52), the distance between the first ground electrode (51) and the signal electrode (52), and the distance between the second ground electrode (53) and the signal electrode (52), which is 50μm+5μm+5μm=60μm.

[0025] The structures of the 1×2 input multimode interference coupler (100) and the 2×1 output multimode interference coupler (400) are as follows: Figure 2 As shown, devices with the same structure and size but opposite usage are used. In this embodiment, the 1×2 input multimode interference coupler (100) and the 2×1 output multimode interference coupler (400) are composed of a first wedge waveguide (101), a multimode interference waveguide (104), a second wedge waveguide (102), and a third wedge waveguide (103). The first wedge waveguide (101), the second wedge waveguide (102), and the third wedge waveguide (103) have the same structure and size, and the same length of 12μm. Along the direction of light transmission, the width of the first wedge waveguide (101) is linearly widened from 1.6μm to 2μm, the width of the second wedge waveguide (102) and the third wedge waveguide (103) is linearly narrowed from 2μm to 1.6μm, and the width of the multimode interference waveguide (104) is 6μm and the length is 30.75μm.

[0026] When the device is working, light enters the 1×2 input multimode interference coupler (100). Due to the self-image principle of the multimode interference coupler, the light is split into two parts of completely equal power in the 1×2 input multimode interference coupler (100), which are output from the first input S-bend waveguide (200) and the second input S-bend waveguide (201), respectively. Then the light enters the first modulation straight waveguide (300) and the second modulation straight waveguide (301), respectively. The first ground electrode (51) and the second ground electrode (53) are grounded simultaneously. A signal voltage is applied to the signal electrode (52), and the electric field strength changes. The first modulation... The polarization directions of the straight waveguide (300) and the second modulation straight waveguide (301) are opposite. Due to the Pockels effect, the refractive index of the first modulation straight waveguide (300) and the second modulation straight waveguide (301) changes, and a refractive index difference is generated between the two modulation straight waveguides. This results in a phase difference between the light in the two modulation straight waveguides. The light then enters the 2×1 output multimode interference coupler (400) and is output after interference. Since there is a phase difference between the two beams, the output power is the maximum when the phase difference is 0 and the output power is the minimum when the phase difference is π, thereby achieving intensity modulation of the beam. During the above operation, the light field is confined to the vicinity of the second ferroelectric waveguide layer (42) and the third ferroelectric waveguide layer (43). The second ferroelectric plate layer (32) and the third ferroelectric plate layer (33) are wider than the second ferroelectric waveguide layer (42) and the third ferroelectric waveguide layer (43), which can prevent the light field from spreading to the edges of the second ferroelectric plate layer (32) and the third ferroelectric plate layer (33) and avoid absorption loss caused by metal.

[0027] Figure 3 This is a cross-sectional view of the waveguide in the non-modulation region, excluding electrodes. Figure 4 This is a cross-sectional view of the waveguide in the modulation region, including the electrodes. Figure 4 In this process, the ferroelectric plate layer below the electrode is completely etched away, eliminating the microwave loss introduced by the high dielectric constant. However, this also causes the electric field to accumulate at the edge of the optical waveguide core composed of the ferroelectric plate layer and the ferroelectric waveguide layer, thereby reducing the modulation efficiency. When the distance between the electrode edge and the ferroelectric plate layer is reduced to ~100nm, the modulation efficiency can decrease rapidly. In this embodiment, the distance between the electrode (51, 52 or 53) edge and the ferroelectric plate layer (32 or 33) is 150nm.

[0028] Example 2

[0029] Figure 5 This is a fabrication process flow diagram for a waveguide in the non-modulation region that does not contain electrodes. Figure 6 This is a flowchart illustrating the fabrication process of the modulation region waveguide, which includes electrodes. Figure 5 and Figure 6As shown, the substrate (1) is silicon with a thickness of 550 μm; its surface has a 3 μm thick silicon dioxide undercoat (2). First, a lanthanum-modified lead zirconate titanate (PLZT) solution was spin-coated onto the silicon dioxide undercoat (2). The solution was then annealed at 600°C using rapid thermal annealing (RTA) technology to form a thick ferroelectric planar layer (3). The surface of this layer was then chemically and mechanically polished to a thickness of 300 nm. A photolithography mask was formed, and ICP etching was performed to obtain a ferroelectric waveguide layer comprising a ferroelectric waveguide layer (41), a first ferroelectric waveguide layer (42), and a second ferroelectric waveguide layer (43), and a thin ferroelectric planar layer (30) located below the ferroelectric waveguide layer. The thickness of the ferroelectric waveguide layer was 100 nm. A photolithography mask was then formed on the thin ferroelectric planar layer (30) below the ferroelectric waveguide layer (41), and ICP etching was performed to obtain a ferroelectric planar layer (31) with a width smaller than the silicon dioxide undercoat (2) and a thickness of 200 nm. The thin ferroelectric planar layer below the first ferroelectric waveguide layer (42) and the second ferroelectric waveguide layer (43) were then etched. (30) A photolithography mask is formed and ICP etching is performed to obtain a discrete first ferroelectric plate layer (32) and second ferroelectric plate layer (33) with a thickness of 200 nm. Then, the first ground electrode (51), signal electrode (52) and second ground electrode (53) are prepared on the surface of the silicon dioxide lower cladding (2) in the outer and middle regions of the first ferroelectric waveguide layer (42) and the second ferroelectric waveguide layer (43) by a lift-off process. Finally, a silicon dioxide upper cladding (6) is deposited on the surface of the obtained device by PECVD. The silicon dioxide upper cladding (6) above the first ground electrode (51), signal electrode (52) and second ground electrode (53) is etched by ICP to form contact holes for connecting an external power supply to apply a modulation voltage to the electrodes. The thickness of the first ground electrode (51), signal electrode (52) and second ground electrode (53) is 400 nm, and the thickness of the silicon dioxide upper cladding (6) is 1 μm.

[0030] After polarization, the modulation efficiency of the electrode was measured as follows: Figure 7 As shown, a triangular wave signal is applied to the signal electrode (52), and the voltage changes from reverse modulation to forward modulation. Finally, when the modulation voltage is 3.10V (1.1V-(-2V)), the maximum extinction ratio of 17.66dB can be measured, that is, the voltage that satisfies the π phase shift is 3.10V. At this time, since the lengths of the first modulation straight waveguide (300) and the second modulation straight waveguide (301) are 0.5cm, it means that the modulation efficiency and the π phase shift voltage-length product is 1.55Vcm. The microwave probe contains three probes. The three probes of the 67GHz high-speed microwave probe are pressed on the first ground electrode (51), the signal electrode (52), and the second ground electrode (53) respectively. The bandwidth of the modulator is measured accordingly, and the following can be obtained: Figure 8The curves shown indicate that within the 70GHz range, the E21 parameter characterizes the degree of microwave signal attenuation. Starting from 0GHz, a drop of 6.41dB is used to characterize the bandwidth attenuation during this period, referred to as the EE21 parameter. The EE11 parameter characterizes the reflected signal strength. It can be seen that within the device's detection range (0~67GHz), the microwave loss of EE21 is less than 6.4dB. Through polynomial fitting, it can be seen that the 6.4dB loss bandwidth reaches 167GHz, indicating that the modulator has the ability to modulate 334Gbit / s OOK signals, far exceeding the current research bottlenecks. Finally, experiments were conducted on high-speed signal transmission, such as... Figure 9 As shown, a 200Gbaud OOK eye diagram can be successfully detected with a signal-to-noise ratio of 6.89, indicating that the modulator can load a 200Gbit / s OOK signal.

Claims

1. A ferroelectric domain electro-optic modulator with ultra-high bandwidth, characterized in that: From bottom to top, it consists of a substrate (1), a silicon dioxide lower cladding (2), a ferroelectric planar layer, a ferroelectric waveguide layer, and a silicon dioxide upper cladding (6); the ferroelectric waveguide layer is an MZI type structure, consisting of a 1×2 input multimode interference coupler (100), a first input S-bend waveguide (200), a second input S-bend waveguide (201), a first modulation straight waveguide (300), a second modulation straight waveguide (301), a first output S-bend waveguide (202), a second output S-bend waveguide (203), and a 2×1 output multimode interference coupler (6). The system consists of a multimode interference coupler (400); a first input S-bend waveguide (200), a first modulation straight waveguide (300), and a first output S-bend waveguide (202) are connected in sequence, and a second input S-bend waveguide (201), a second modulation straight waveguide (301), and a second output S-bend waveguide (203) are connected in sequence, forming the two output terminals of a 1×2 input multimode interference coupler (100) and the two input terminals of a 2×1 output multimode interference coupler (400), respectively; the ferroelectric flat plate layer has a hollow structure in the middle. A signal electrode (52) is fabricated on the surface of the exposed silicon dioxide cladding (2) within the hollow structure. A first ground electrode (51) and a second ground electrode (53) are fabricated on the silicon dioxide cladding (2) outside the ferroelectric plate layer, respectively. The first ground electrode (51), the signal electrode (52), and the second ground electrode (53) together constitute a metal electrode layer. The first ground electrode (51) is located outside the first modulation straight waveguide (300), and the signal electrode (52) is located between the first modulation straight waveguide (300) and the second modulation straight waveguide (300). Between the first ground electrode (301), the second ground electrode (53) is located outside the second modulation straight waveguide (301); the first ground electrode (51), the signal electrode (52), the second ground electrode (53), the first modulation straight waveguide (300) and the second modulation straight waveguide (301) form the modulation area of ​​the electro-optic modulator; the first ground electrode (51), the signal electrode (52) and the second ground electrode (53) are rectangular structures with their long sides parallel to each other and parallel to the first modulation straight waveguide (300) and the second modulation straight waveguide (301).

2. The ferroelectric domain electro-optic modulator with ultra-high bandwidth as described in claim 1, characterized in that: The 1×2 input multimode interference coupler (100) and the 2×1 output multimode interference coupler (400) are devices with the same structure and size but opposite usage. The 1×2 input multimode interference coupler (100) is composed of a first wedge waveguide (101), a multimode interference waveguide (104), a second wedge waveguide (102), and a third wedge waveguide (103). The first wedge waveguide (101) serves as the input end of the 1×2 input multimode interference coupler (100), and the second wedge waveguide (102) and the third wedge waveguide (103) serve as the output ends of the 1×2 input multimode interference coupler (100). The first wedge waveguide (101), the second wedge waveguide (102), and the third wedge waveguide (103) have the same structure and size.

3. The ferroelectric domain electro-optic modulator with ultra-high bandwidth as described in claim 1, characterized in that: The ferroelectric planar layer and ferroelectric waveguide layer in the regions of the first modulation straight waveguide (300) and the second modulation straight waveguide (301) are discrete structures. The ferroelectric planar layer includes two parts: a second ferroelectric planar layer (32) and a third ferroelectric planar layer (33). The ferroelectric waveguide layer includes two parts: a second ferroelectric waveguide layer (42) and a third ferroelectric waveguide layer (43). The second ferroelectric waveguide layer (42) is located above the second ferroelectric planar layer (32), and the third ferroelectric waveguide layer (43) is located above the third ferroelectric planar layer (33). The first ground electrode (51) and the second ground electrode (53) are located outside the second ferroelectric planar layer (32) and the third ferroelectric planar layer (33), respectively. The signal electrode (52) is located on the second ferroelectric planar layer (32). Between the second ferroelectric waveguide layer (42) and the third ferroelectric flat plate layer (33); the second ferroelectric waveguide layer (42) corresponds to the first modulation straight waveguide (300), and the third ferroelectric waveguide layer (43) corresponds to the second modulation straight waveguide (301). The second ferroelectric waveguide layer (42), the second ferroelectric flat plate layer (32), the third ferroelectric waveguide layer (43) and the third ferroelectric flat plate layer (33) constitute the optical waveguide core layer; the silicon dioxide cladding layer (6) has a hollow structure, and the first ground electrode (51), the signal electrode (52) and the second ground electrode (53) are exposed to form contact holes, and the second ferroelectric flat plate layer (32), the second ferroelectric waveguide layer (42), the third ferroelectric flat plate layer (33) and the third ferroelectric waveguide layer (43) are completely covered therein.

4. The ferroelectric domain electro-optic modulator with ultra-large bandwidth as described in claim 1, characterized in that: The substrate (1) is one of quartz, silicon, or high-resistivity silicon, and the thickness of the substrate (1) is 500~625μm; the thickness of the silicon dioxide cladding layer (2) is 2~15μm; in the same device, the ferroelectric planar layer and the ferroelectric waveguide layer are the same ferroelectric material, one of lead zirconate titanate, lanthanum-modified lead zirconate titanate, or barium titanate, and the thickness of the ferroelectric planar layer is 100~300nm, and the thickness of the ferroelectric waveguide layer is 50~150nm; in the same device, the first ground electrode (51), the signal electrode (52), and the second ground electrode (53) are the same metal material, one of aluminum, gold, silver, tungsten, or titanium, and the thickness is 300~500nm. The thickness of the electrode is greater than the sum of the thicknesses of the ferroelectric planar layer and the ferroelectric waveguide layer. The width of the signal electrode (52) is 20~50μm. The distance between the first ground electrode (51) and the signal electrode (52) is the same as the distance between the second ground electrode (53) and the signal electrode (52), which is 4.5~6μm. The distance between the first modulation straight waveguide (300) and the second modulation straight waveguide (301) is the sum of the width of the signal electrode (52), the distance between the first ground electrode (51) and the signal electrode (52), and the distance between the second ground electrode (53) and the signal electrode (52). The thickness of the silicon dioxide cladding (6) is 1~5μm.

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