An optical power splitter based on adiabatic coupling structure of thin film lithium niobate and polymer heterogeneous integrated waveguide and a preparation method thereof

Abstract

The application relates to a thin-film lithium niobate and polymer hetero-integrated waveguide optical power divider based on an adiabatic coupling structure and a preparation method thereof, and belongs to the technical field of planar optical waveguide photonic integrated chips and preparation thereof. The waveguide is composed of a silicon substrate, a silicon dioxide oxidation layer, thin-film lithium niobate and a polymer loading strip waveguide from bottom to top; the polymer loading strip waveguide is based on an adiabatic coupling structure and is composed of a first straight waveguide, a second straight waveguide, a third straight waveguide, a fourth straight waveguide, a fifth straight waveguide, a first output curved waveguide, a second output curved waveguide, a first output straight waveguide and a second output straight waveguide; light is input from the third straight waveguide, is adiabatically coupled into the second straight waveguide and the fourth straight waveguide respectively, is then adiabatically coupled into the first straight waveguide and the fifth straight waveguide respectively, and is finally output from the first output straight waveguide and the second output straight waveguide, so that uniform distribution of optical power is realized. The application has the characteristics of low production cost, high efficiency and large-scale batch production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of planar lightwave circuit photonic integrated chip and its preparation technology, and particularly relates to a thin film lithium niobate and polymer heterogeneous integrated waveguide optical power divider based on adiabatic coupling structure and a preparation method thereof. BACKGROUND

[0002] In recent years, with the rapid development of information technology, people have put forward higher requirements on the communication capacity, transmission rate and reliability of optical communication systems. As the core device of optical communication systems and on-chip optical interconnection chips, the optical power divider uniformly distributes the input optical signal power to several output ports, thereby realizing the distribution and synthesis of optical signals, and is a basic element for constructing optical switches, optical modulators, multiplexers and demultiplexers. Among them, the optical power divider based on planar lightwave circuit structure not only has good compatibility with optical fibers, but also has the advantages of compact structure, tunability, small insertion loss and flexible design.

[0003] The materials commonly used in existing optical power dividers mainly include the following three types: thin film lithium niobate (Lithium Niobate, LN), silicon (Silicon, Si) and polymer (Polymer). Among them, thin film lithium niobate has excellent electro-optic properties, a wide optical transparent window and high process compatibility, and is currently an ideal optical material. According to the different types of waveguides, thin film lithium niobate waveguides can be divided into two types: etched (Dry-etched) and loaded (Rib-loaded) waveguides. Due to the chemical inertness of the material, physical dry etching is a common method for preparing etched lithium niobate waveguides, which can accurately control the etching depth and waveguide shape. However, in different etching equipment, the dry etching process shows low selectivity and reproducibility, and the inclined sidewall formed by etching will increase the transmission loss of the waveguide. The loaded waveguide is to directly deposit or spin-coat a second material (SiN, TiO2, Polymer, etc.) on lithium niobate, and then etch the loaded material (i.e. the second material) to form a waveguide structure, which can avoid the dry etching process of lithium niobate and is conducive to realizing low-loss transmission of the waveguide. Among them, by spin-coating or depositing a low refractive index polymer on the thin film lithium niobate to form a continuous bound state waveguide, it can realize low-loss transmission of light at a certain width, which provides a thought for designing low-loss devices.

[0004] The traditional optical power divider structure mainly includes directional coupler (DC), multimode interference (MMI) and Y-branch type. For the directional coupler structure power divider, the phase matching condition needs to be strictly met, so that the power divider can only realize power division in a small operating bandwidth. For the multimode interference structure power divider, the self-imaging principle needs to be met, and the designed device usually has a large size. For the Y-branch type power divider, the branch angle has a great influence on the loss performance, and strict manufacturing process and relatively long device length are required. In order to meet the requirements of optical interconnection chip integration and miniaturization, it is urgent to design an optical power divider with small size, low loss and large operating bandwidth. SUMMARY

[0005] In order to overcome the shortcomings of the traditional optical power divider, the purpose of the present application is to provide a low-loss, large-bandwidth optical power divider based on adiabatic coupling structure of thin film lithium niobate and polymer hetero-integrated waveguide and a preparation method thereof.

[0006] The present application uses silicon with a silica buffer layer as a waveguide substrate, lithium niobate thin film as a flat plate layer of loaded waveguide, and polymer with a smaller refractive index than lithium niobate thin film as a loaded strip waveguide. The selected polymer is various and has a large refractive index difference with the lithium niobate thin film. The preparation process adopted by the present application is simple, can be well compatible with semiconductor process, easy to integrate, meets the requirements of large-scale production, and has important application value in the field of optical communication and planar optical waveguide power divider.

[0007] The technical scheme adopted by the present application to solve its technical problems is as follows:

[0008] As shown in the accompanying Figure 1 The optical power divider based on adiabatic coupling structure of thin film lithium niobate and polymer hetero-integrated waveguide according to the present application is composed of silicon substrate 10, silicon dioxide oxidation layer 11, thin film lithium niobate 12 and polymer loaded strip waveguide 13 from bottom to top. The thickness h1 of the silicon substrate 10 is 480-520 μm, the thickness h2 of the silicon dioxide oxidation layer 11 is 1-5 μm, the thickness h3 of the thin film lithium niobate 12 is 100-800 nm, and the thickness h4 of the polymer loaded strip waveguide 13 is 200-900 nm.

[0009] As shown in the accompanying Figure 2As shown, the polymer-loaded strip waveguide 13 is based on an adiabatic coupling structure, which is composed of a first straight waveguide 1, a second straight waveguide 2, a third straight waveguide 3, a fourth straight waveguide 4, a fifth straight waveguide 5, a first output curved waveguide 6, a second output curved waveguide 7, a first output straight waveguide 8, and a second output straight waveguide 9; wherein the first straight waveguide 1, the third straight waveguide 3, and the fifth straight waveguide 5 are parallel to each other, and the first straight waveguide 1 and the fifth straight waveguide 5 are symmetrically arranged about the third straight waveguide 3; the second straight waveguide 2 and the fourth straight waveguide 4 are symmetrically arranged about the third straight waveguide 3 and are obliquely arranged; the first output straight waveguide 8, the second output straight waveguide 9, and the third straight waveguide 3 are parallel to each other, and the first output straight waveguide 8 and the second output straight waveguide 9 are symmetrically arranged about the third straight waveguide 3; the first straight waveguide 1, the first output curved waveguide 6, and the first output straight waveguide 8 are sequentially connected; and the fifth straight waveguide 5, the second output curved waveguide 7, and the second output straight waveguide 9 are sequentially connected; the lengths a1, a2, a3, a4, and a5 of the first straight waveguide 1, the second straight waveguide 2, the third straight waveguide 3, the fourth straight waveguide 4, and the fifth straight waveguide 5 are equal to 2000-3000 μm, and the widths w1, w2, w3, w4, and w5 are equal to 1-5 μm. Figure 2 In the embodiment, the starting end and the terminal end of the second straight waveguide 2 and the fourth straight waveguide 4 are recessed by a distance compared to the starting end and the terminal end of the third straight waveguide 3.

[0010] The projection lengths a6 and a7 of the first output curved waveguide 6 and the second output curved waveguide 7 in the direction of the third straight waveguide 3 (i.e. the input light direction) are equal to 1000-3000 μm, and the widths w6 and w7 are equal to 1-5 μm; the lengths a8 and a9 of the first output straight waveguide 8 and the second output straight waveguide 9 are equal to 500-1000 μm, and the widths w8 and w9 are equal to 1-5 μm; the spacings S1 and S2 between the third straight waveguide 3 and the first straight waveguide 1 and the fifth straight waveguide 5 are equal to 4-10 μm; the spacings d1 and d2 between the third straight waveguide 3 and the second straight waveguide 2 and the fourth straight waveguide 4 at the input end are equal to 0.8-2.5 μm, and the spacings d3 and d4 at the output end are equal to 0.5-2 μm, and d3 < d1 and d4 < d2; the spacing d5 between the second straight waveguide 2 and the first straight waveguide 1 at the input end is 1.2-5.5 μm, and the spacing d6 at the output end is 1.5-6 μm, and d5 < d6, d1 + d5 = d3 + d6; the spacing d7 between the fourth straight waveguide 4 and the fifth straight waveguide 5 at the input end is 1.2-5.5 μm, and the spacing d8 at the output end is 1.5-6 μm, and d7 < d8, d2 + d7 = d4 + d8; d5 = d7, and d6 = d8. And w8 = w6 = w1.

[0011] Light is input from the third straight waveguide 3, and the light input from the third straight waveguide 3 is adiabatically coupled into the second straight waveguide 2 and the fourth straight waveguide 4 respectively, and then is adiabatically coupled into the first straight waveguide 1 from the second straight waveguide 2 and is adiabatically coupled into the fifth straight waveguide 5 from the fourth straight waveguide 4, and finally is output from the first output straight waveguide 8 and the second output straight waveguide 9, so as to realize uniform distribution of optical power. The mode of the output light is the same as that of the input light, and the input TM0 mode is output as the TM0 mode.

[0012] The preparation method of the thin-film lithium niobate and polymer heterogeneous integrated power divider based on the adiabatic coupling structure is shown in the following process flow chart: Figure 3 , and the specific steps are as follows:

[0013] A: cleaning of a lithium niobate wafer composed of a silicon substrate 10, a silicon dioxide oxidation layer 11 and a thin-film lithium niobate 12 from bottom to top (the lithium niobate wafer is purchased from Shanghai Xin Silicon Polymer Semiconductor Co., Ltd.)

[0014] First, the surface of the thin-film lithium niobate 12 is cleaned 2-3 times with acetone, methanol and isopropyl alcohol solvents in sequence to ensure the cleanliness of the lithium niobate surface.

[0015] B: preparation of a polymer loaded strip waveguide

[0016] A polymer (the polymer is a series of organic polymer materials with good transparency, including polyEpoCore, methyl methacrylate (PMMA), SU-8 2002 and SU-8 2005, and the refractive index of the polymer as the loaded strip waveguide is lower than that of the thin-film lithium niobate 12) used as the loaded strip waveguide is spin-coated on the surface of the cleaned thin-film lithium niobate 12 at a speed of 5000-8000 rpm to obtain a polymer thin film 13' with a thickness of 200-900 nm; the device is first baked at 20-60°C for 2-10 minutes, and then baked at 70-120°C for 2-20 minutes for curing, and then cooled to room temperature; the polymer thin film 13' is subjected to photolithography, the wavelength of the ultraviolet light emitted by the photolithography machine is 350-400 nm, and the waveguide mask 14 is complementary to the structure of the polymer loaded strip waveguide 13 of the power divider to be prepared (for example Figure 2The polymer thin film 13' in the structure of the first straight waveguide 1, the second straight waveguide 2, the third straight waveguide 3, the fourth straight waveguide 4, the fifth straight waveguide 5, the first output curved waveguide 6, the second output curved waveguide 7, the first output straight waveguide 8 and the second output straight waveguide 9 is exposed to ultraviolet light for 2-40 seconds when the photoetching plate is tightly attached to the wafer; the device after photoetching is taken out of the photoetching machine and is subjected to intermediate baking, that is, baking at 20-90 DEG C for 2-10 minutes and then baking at 70-120 DEG C for 2-10 minutes, and then natural cooling to room temperature; the polymer thin film 13' is developed, that is, wet etching in a developing solution corresponding to the material of the polymer thin film 13' for 2-15 seconds to remove the unexposed polymer thin film 13' and leave the polymer loaded strip waveguide 13 structure corresponding to the waveguide mask 14, then isopropanol solution is used to wash away the developing solution and the residual polymer thin film 13' material on the surface of the device, deionized water is used to rinse the isopropanol on the surface of the device clean and nitrogen is used to dry; finally, post-baking is performed at a temperature of 120-150 DEG C for 30-60 minutes to harden the film, thereby completing the preparation of the thin film lithium niobate and polymer hetero-integrated power divider based on the adiabatic coupling structure.

[0017] Compared with the existing device structure and preparation technology, the present application has the following beneficial effects:

[0018] The present application selects a polymer with a refractive index less than the thin film lithium niobate as the loaded strip waveguide, forms a continuous domain bound state of the waveguide on the platform of the thin film lithium niobate and polymer hetero-integration, and the TM0 mode has small transmission loss at a specific width; and a straight waveguide with a specific width is used as a basic structure, a waveguide type power divider with small size, low loss and large working bandwidth is designed based on the adiabatic coupling principle. In addition, the process for preparing the device by using the polymer material is relatively simple, only conventional processes such as spin coating and photoetching are needed, and the process is not difficult, and the production cost is low, the efficiency is high, and the device can be mass-produced, which is a mode power divider that can be applied to actual use. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The cross section (corresponding to the a-a' position) structure schematic diagram of the optical power divider of the thin film lithium niobate and polymer hetero-integrated waveguide based on the adiabatic coupling structure according to the present application is shown in FIG. 1; Figure 2

[0020] Figure 2 The structure schematic diagram of the polymer loaded strip waveguide of the optical power divider according to the present application is shown in FIG. 2;

[0021] Figure 3 The process flow chart of the preparation of the optical power divider of the thin film lithium niobate and polymer hetero-integrated waveguide based on the adiabatic coupling structure according to the present application is shown in FIG. 3; ​

[0022] Figure 4 The curve showing the transmission loss as a function of width for the straight waveguide based on the heterogeneous integration of thin-film lithium niobate and polymer, as described in this invention;

[0023] Figure 5(a): Simulation of the optical field distribution of the TMO mode of the thin-film lithium niobate and polymer heterogeneous integrated waveguide based on the thermally adiabatic coupling structure described in this invention;

[0024] Figure 5(b): Simulation diagram of optical field transmission in the input TM0 mode of the optical power divider based on the thermally coupled thin film lithium niobate and polymer heterogeneous integrated waveguide of the present invention;

[0025] Figure 5(c): The curve showing the relationship between the input TM0 mode normalized output power and wavelength of the optical power divider based on the thermally coupled thin film lithium niobate and polymer heterogeneous integrated waveguide of the present invention.

[0026] like Figure 1 The diagram shows a schematic of an optical power divider based on a thermally coupled thin-film lithium niobate and polymer heterogeneous integrated waveguide. The components are named as follows: silicon substrate 10, silicon dioxide oxide layer 11, thin-film lithium niobate 12, and polymer loading strip waveguide 13.

[0027] like Figure 2 The diagram shows the structure of the polymer-loaded waveguide. The names of the components are: first straight waveguide 1, second straight waveguide 2, third straight waveguide 3, fourth straight waveguide 4, fifth straight waveguide 5, first output curved waveguide 6, second output curved waveguide 7, first output straight waveguide 8, and second output straight waveguide 9.

[0028] like Figure 3 The diagram shows the process flow of an optical power divider based on a thermally coupled thin-film lithium niobate and polymer heterogeneous integrated waveguide. In the diagram, 10 is a silicon substrate, 11 is a silicon dioxide oxide layer, 12 is a thin-film lithium niobate, 13' is a spin-coated polymer film serving as a loading strip waveguide, 13 is the polymer loading strip waveguide, and 14 is... Figure 2 Waveguide mask with complementary loading strip waveguide structure.

[0029] like Figure 4 As shown, the transmission loss curve of a straight waveguide based on thin-film lithium niobate and polymer heterogeneous integration (the loss is only related to the waveguide width, and the width of the five straight waveguides is the same, which represents the loss of all straight waveguides) varies with the width. In the simulation process, the material used in Example 1 shows that when the waveguide width is 2.1 μm, the transmission loss is 0.048 dB / cm.

[0030] Figure 5(a) is a simulation diagram of the optical field distribution of the TMO mode input in the first direct waveguide 1 of the optical power divider based on the thermally coupled thin film lithium niobate and polymer heterogeneous integrated waveguide. In the simulation process, we selected the materials and waveguide dimensions used in Example 1. It can be clearly seen from the simulation diagram that the optical field is mainly concentrated in the polymer loading strip waveguide, thus ensuring that the TMO mode optical signal can be effectively transmitted in the optical waveguide.

[0031] Figure 5(b) is a simulation diagram of the optical field transmission of the input TM0 mode in the first straight waveguide 1 of the optical power divider based on the thermally coupled thin film lithium niobate and polymer heterogeneous integrated waveguide. In the simulation process, we selected the materials and waveguide dimensions used in Example 1. It can be clearly seen from the simulation diagram that when the input TM0 mode is used, the output is the same TM0 mode with the same power.

[0032] Figure 5(c) shows the relationship between the normalized output power of the TM0 mode and the wavelength in the two output ports (curve O1 represents the first output straight waveguide 8, and curve O2 represents the second output straight waveguide 9) of the optical power divider based on the thermally coupled thin film lithium niobate and polymer heterogeneous integrated waveguide. We used the materials and waveguide dimensions selected in Example 1. It can be seen that in the 1500-1650nm band, the output power of the two ports of the device is the same (curves O1 and O2 coincide), and the output power fluctuates little with the wavelength. The device is not sensitive to wavelength. Detailed Implementation

[0033] Example 1

[0034] As attached Figure 1 As shown, the thickness h1 of the silicon substrate 10 is 500 μm, the thickness h2 of the silicon dioxide oxide layer 11 is 2 μm, the thickness h3 of the thin film lithium niobate 12 is 300 nm, and the thickness h4 of the polymer loading strip waveguide 13 is 400 nm.

[0035] like Figure 2As shown, the lengths a1, a2, a3, a4, a5 of the first straight waveguide 1, the second straight waveguide 2, the third straight waveguide 3, the fourth straight waveguide 4, and the fifth straight waveguide 5 are equal to 2700 μm, and the widths w1, w2, w3, w4, w5 are equal to 2.1 μm; the projection lengths a6, a7 of the first output curved waveguide 6 and the second output curved waveguide 7 in the input light direction are equal to 1000 μm, and the widths w6, w7 are equal to 2.1 μm; the lengths a8, a9 of the first output straight waveguide 8 and the second output straight waveguide 9 are equal to 600 μm, and the widths w8, w9 are equal to 2.1 μm. The distances S1, S2 between the third straight waveguide 3 and the first straight waveguide 1 and the fifth straight waveguide 5 are equal to 4.8 μm; the distances d1, d2 between the third straight waveguide 3 and the second straight waveguide 2 and the fourth straight waveguide 4 at the input end are equal to 1.8 μm, and the distances d3, d4 at the output end are equal to 1 μm; the distance d5 between the second straight waveguide 2 and the first straight waveguide 1 at the input end is 1.1 μm, and the distance d6 at the output end is 1.7 μm; the distance d7 between the fourth straight waveguide 4 and the fifth straight waveguide 5 at the input end is 1.1 μm, and the distance d8 at the output end is 1.7 μm.

[0036] The preparation method of the low-loss power divider based on the thin film lithium niobate and polymer hetero-integrated by the adiabatic coupling structure according to the present application comprises the following steps:

[0037] (1) cleaning of the lithium niobate wafer (the lithium niobate wafer is purchased from Shanghai Xin Silicon Polymer Semiconductor Co., Ltd., and is composed of a silicon substrate 10, a silicon dioxide oxidation layer 11, and a thin film lithium niobate 12):

[0038] The surface of the thin film lithium niobate 12 is cleaned by using acetone, methanol, and isopropanol solvents in sequence for 2 times.

[0039] (2) preparation of the polymer-loaded strip waveguide 13: an EpoCore polymer is coated on the surface of the cleaned thin film lithium niobate 12 by using a spin coating process, and the rotation speed is 6500 revolutions per minute, so that a polymer thin film 13' with a thickness of 400 nm is prepared; the device is first baked at 40℃ for 5 minutes, and then baked at 80℃ for 5 minutes for solidification, and then cooled to room temperature; the polymer thin film 13' is subjected to photolithography, the wavelength of the ultraviolet light emitted by the photolithography machine is 365 nm, and the waveguide mask plate 14 is complementary to the structure of the polymer-loaded strip waveguide 13 of the power divider to be prepared (for example Figure 2The first straight waveguide 1, the second straight waveguide 2, the third straight waveguide 3, the fourth straight waveguide 4, the fifth straight waveguide 5, the first output curved waveguide 6, the second output curved waveguide 7, the first output straight waveguide 8, the second output straight waveguide 9 and the polymer thin film 13' in the structures are exposed to ultraviolet light when the photolithography plate is tightly attached to the wafer, and the exposure time is 12 seconds; the device after photolithography is taken out of the photolithography machine for intermediate baking, first baked at 50°C for 2 minutes, then baked at 90°C for 5 minutes, and naturally cooled to room temperature after baking; the polymer thin film 13' is developed, that is, the polymer thin film 13' material is wet etched in EpoCore developer for 10 seconds to remove the unexposed polymer thin film 13', leaving the polymer loaded waveguide 13 structure corresponding to the waveguide mask 14, then isopropanol solution is used to wash away the developer and the residual polymer thin film 13' material on the surface of the device, then deionized water is used to rinse the residual isopropanol on the surface clean and dry with nitrogen; finally, post-baking is performed at 120°C for 30 minutes to harden the film, thus completing the preparation of the power divider based on the adiabatic coupling structure of the thin film lithium niobate and polymer hetero-integration.

[0040] It should be noted that the specific embodiments are only representative examples of the present application, and it is obvious that the technical solutions of the present application include but are not limited to the above-mentioned embodiments, and there can be more forms, such as each power divider can be cascaded as a unit structure for further expansion and application, and the materials of the design are not limited to this, but also can use silicon, silicon nitride and other waveguide materials. Those skilled in the art, based on the explicit disclosure of the present application or the description of the document without any objection, all belong to the scope of protection of the present patent.

Claims

1. An optical power splitter based on adiabatic coupling structure of thin film lithium niobate and polymer heterogeneous integrated waveguide, characterized by: From bottom to top, it is composed of silicon substrate (10), silicon dioxide oxide layer (11), thin film lithium niobate (12) and polymer loaded strip waveguide (13); the polymer loaded strip waveguide (13) is based on adiabatic coupling structure, which is composed of first straight waveguide (1), second straight waveguide (2), third straight waveguide (3), fourth straight waveguide (4), fifth straight waveguide (5), first output curved waveguide (6), second output curved waveguide (7), first output straight waveguide (8) and second output straight waveguide (9); wherein the first straight waveguide (1), the third straight waveguide (3) and the fifth straight waveguide (5) are parallel to each other, and the first straight waveguide (1) and the fifth straight waveguide (5) are symmetrically arranged about the third straight waveguide (3), the second straight waveguide (2) and the fourth straight waveguide (4) are symmetrically arranged about the third straight waveguide (3) and are obliquely arranged, the first output straight waveguide (8), the second output straight waveguide (9) and the third straight waveguide (3) are parallel to each other, and the first output straight waveguide (8) and the second output straight waveguide (9) are symmetrically arranged about the third straight waveguide (3), the first straight waveguide (1), the first output curved waveguide (6) and the first output straight waveguide (8) are sequentially connected, the fifth straight waveguide (5), the second output curved waveguide (7) and the second output straight waveguide (9) are sequentially connected; the lengths a1, a2, a3, a4 and a5 of the first straight waveguide (1), the second straight waveguide (2), the third straight waveguide (3), the fourth straight waveguide (4) and the fifth straight waveguide (5) are equal, and the widths w1, w2, w3, w4 and w5 are equal; the projection lengths a6 and a7 of the first output curved waveguide (6) and the second output curved waveguide (7) in the direction of the third straight waveguide (3) are equal, and the widths w6 and w7 are equal; the lengths a8 and a9 of the first output straight waveguide (8) and the second output straight waveguide (9) are equal, and the widths w8 and w9 are equal; the distances S1 and S2 between the third straight waveguide (3) and the first straight waveguide (1) and the fifth straight waveguide (5) are equal; the distances d1 and d2 between the third straight waveguide (3) and the second straight waveguide (2) and the fourth straight waveguide (4) at the input end are equal, the distances d3 and d4 at the output end are equal, and d3 < d1 and d4 < d2; the distance between the second straight waveguide (2) and the first straight waveguide (1) at the input end is d5, and the distance at the output end is d6, and d5 < d6, d1 + d5 = d3 + d6; the distance between the fourth straight waveguide (4) and the fifth straight waveguide (5) at the input end is d7, and the distance at the output end is d8, and d7 < d8, d2 + d7 = d4 + d8; d5 = d7, d6 = d8; w8 = w6 = w1; the refractive index of the polymer as the loaded strip waveguide is lower than the refractive index of the thin film lithium niobate (12).

2. The adiabatic coupling structure based thin film lithium niobate and polymer heterogeneous integrated waveguide optical power splitter of claim 1, wherein: The polymer as the loaded strip waveguide is EpoCore, methyl methacrylate, SU-82002 or SU-8 2005.

3. The adiabatic coupling structure based thin film lithium niobate and polymer heterogeneous integrated waveguide optical power splitter of claim 1, wherein: The thickness h1 of the silicon substrate (10) is 480-520 μm, the thickness h2 of the silicon dioxide oxidation layer (11) is 1-5 μm, the thickness h3 of the thin film lithium niobate (12) is 100-800 nm, and the thickness h4 of the polymer loaded strip waveguide (13) is 200-900 nm.

4. The adiabatic coupling structure based thin film lithium niobate and polymer heterogeneous integrated waveguide optical power splitter of claim 1, wherein: a1, a2, a3, a4, a5 are equal to 2000-3000 μm, w1, w2, w3, w4, w5 are equal to 1-5 μm; a6, a7 are equal to 1000-3000 μm, w6, w7 are equal to 1-5 μm; a8, a9 are equal to 500-1000 μm, w8, w9 are equal to 1-5 μm; S1, S2 are equal to 4-10 μm; d1, d2 are equal to 0.8-2.5 μm, d3, d4 are equal to 0.5-2 μm; d5 is 1.2-5.5 μm, d6 is 1.5-6 μm; d7 is 1.2-5.5 μm, d8 is 1.5-6 μm.

5. A preparation method of the optical power divider based on the thin film lithium niobate and polymer hetero-integrated waveguide of the adiabatic coupling structure according to any one of claims 1-4, comprising the following steps: A: cleaning of the lithium niobate wafer composed of the silicon substrate (10), the silicon dioxide oxidation layer (11) and the thin film lithium niobate (12) from bottom to top First, the surface of the thin film lithium niobate (12) is cleaned 2-3 times in sequence using acetone, methanol and isopropyl alcohol solvents, and the surface of the lithium niobate is determined to be clean; B: preparation of the polymer loaded strip waveguide The polymer serving as the loaded strip waveguide is spin-coated on the cleaned surface of the thin film lithium niobate (12) at a rotation speed of 5000-8000 rpm to obtain a polymer thin film (13'); then the polymer thin film (13') is baked at 20-60°C for 2-10 minutes, and then baked at 70-120°C for 2-20 minutes for solidification, and then cooled to room temperature; the polymer thin film (13') is subjected to plate lithography, the wavelength of the ultraviolet light emitted by the photolithography machine is 350-400 nm, the waveguide mask (14) is complementary to the structure of the polymer loaded strip waveguide (13) of the power divider to be prepared, and the polymer thin film (13') in the structures of the first straight waveguide (1), the second straight waveguide (2), the third straight waveguide (3), the fourth straight waveguide (4), the fifth straight waveguide (5), the first output curved waveguide (6), the second output curved waveguide (7), the first output straight waveguide (8), and the second output straight waveguide (9) is exposed to ultraviolet light when the waveguide mask (14) is tightly attached to the wafer for 2-40 seconds, to obtain a lithography-finished device; the lithography-finished device is taken out of the photolithography machine and subjected to intermediate baking, i.e., first baked at 20-90°C for 2-10 minutes, and then baked at 70-120°C for 2-10 minutes, and then naturally cooled to room temperature after baking; the polymer thin film (13') is developed, i.e., wet etched in a developing solution corresponding to the material of the polymer thin film (13') for 2-15 seconds to remove the unexposed polymer thin film (13') and leave the structure of the polymer loaded strip waveguide (13) corresponding to the waveguide mask (14), then the developing solution and the residual polymer thin film (13') material on the surface of the device are washed away with an isopropyl alcohol solution, and the residual isopropyl alcohol on the surface of the device is washed clean with deionized water and dried with nitrogen; finally, the device is baked at a temperature of 120-150°C for 30-60 minutes for post-baking and hardening, thereby completing the preparation of the thin film lithium niobate and polymer heterojunction power divider based on the adiabatic coupling structure.

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