Filter based on optical superlattice electro-optical long period grating and its preparation method

Abstract

The present application provides a filter based on an optical superlattice electro-optical long-period grating and a preparation method. Through the coupling between the fundamental mode and the leakage mode, narrowband filtering of the communication band is realized, which can be applied to the field of optical communication and optical waveguide devices. The filter includes: a substrate, a buried insulating layer, a thin film layer, a periodically polarized superlattice waveguide, and a flat electrode; the substrate, the buried insulating layer and the thin film layer of the photonic chip are bonded in sequence through a wafer bonding process, and a thin film for preparing a waveguide is bonded to the substrate and the buried insulating layer. The waveguide is engraved on the upper surface of the film by photolithography technology, and a periodically polarized superlattice is formed on the waveguide by polarization technology, and metal flat electrodes are covered on the flat plates on both sides of the waveguide to realize the function of an adjustable electro-optical grating. The filter based on the optical superlattice electro-optical long-period grating of the present application does not require strict process equipment and conditions, has a simple structure, reduces the difficulty of device manufacturing, has low equipment requirements, large process tolerance, and easy parameter control.

Description

Technical Field

[0001] The present application belongs to the field of filter technology, and specifically relates to a method for preparing a filter based on an optical superlattice electro-optical long-period grating. Background Art

[0002] Optical communication technology provides strong technical support for the construction of the information society, and optical waveguide devices are essential core components for realizing optical communication technology. Over the years, optical waveguide devices with different functions have played a vital role in the evolution of optical communication towards larger capacity, greater flexibility, and more reliable technology.

[0003] Silicon photonics technology and lithium niobate thin film photonics technology, which have emerged in the past decade, are considered to be the two key technologies to promote the further development of optical communication technology. The filter is a key device on the lithium niobate platform. Currently, filters on the lithium niobate platform have been realized by means of exciting electric fields on proton exchange waveguides through interdigitated electrodes and forming refractive index gratings by covering polymers on lithium niobate waveguides.

[0004] Although the long-period grating based on lithium niobate proton exchange waveguide in the past can also achieve a certain filtering effect, it has problems such as high driving voltage, complex preparation process, and difficulty in compatibility with integrated optical circuits. Summary of the invention

[0005] In order to solve the problems that the above-mentioned long-period grating solution can also achieve a certain filtering effect, but has high driving voltage, complex preparation process, and is difficult to be compatible with integrated optical circuits, the present application provides a filter based on optical superlattice electro-optical long-period grating and its preparation method. The electric field of this solution is excited by a flat electrode, which is conducive to combining with subsequent on-chip circuit design and has good compatibility and scalability. The filter based on optical superlattice electro-optical long-period grating described in this solution includes a substrate, a buried insulating layer, a thin film layer, a periodically polarized superlattice waveguide, and a metal flat electrode.

[0006] The buried insulating layer is arranged between the substrate and the thin film layer, a waveguide is arranged on a side of the thin film layer away from the buried insulating layer, and a periodically polarized superlattice is arranged on the waveguide;

[0007] Two metal plate electrodes are also provided on one side of the thin film layer away from the buried insulating layer, and the two metal plate electrodes are correspondingly provided on two sides of the waveguide;

[0008] There is an electrode spacing between the metal plate electrodes, and the electrode spacing is greater than the top width of the waveguide.

[0009] In a feasible implementation manner, the structure of the waveguide is any one of a ridge waveguide structure and a rectangular waveguide structure.

[0010] In a feasible implementation, the periodically polarized superlattice includes the same number of positive domains and negative domains, the positive domains and the negative domains are arranged crosswise, and one positive domain and one negative domain constitute a period.

[0011] In a feasible implementation, the period is greater than 1 μm, there are several periods, and several periods constitute a long-period grating. The waveguide also includes an input end and an output end, and the long-period grating is arranged between the input end and the output end.

[0012] In a feasible implementation, the substrate, the thin film layer and the waveguide are made of lithium niobate or lithium tantalate.

[0013] In a feasible implementation, the buried insulating layer is made of silicon dioxide, and the metal plate electrode is made of any one of gold, aluminum, nickel, and chromium.

[0014] In a feasible implementation, the method is applied to any of the above-mentioned filters based on optical superlattice electro-optical long-period grating, comprising the steps of:

[0015] Bonding the substrate to one side of the buried insulating layer by a wafer bonding process;

[0016] Bonding the other side of the buried insulating layer to the thin film layer through a wafer bonding process;

[0017] Carving out a waveguide on a side of the thin film layer away from the buried insulating layer by an etching process;

[0018] forming a periodically polarized superlattice on the waveguide by using a polarization technique;

[0019] The thin film layer on both sides of the waveguide is covered with metal plate electrodes.

[0020] In a feasible implementation, the etching process is any one of electron beam lithography, reactive ion beam etching and inductively coupled plasma etching.

[0021] In a feasible implementation, the total height of the waveguide and the thin film layer is 600-900 nm; the height of the waveguide is 100-500 μm; the top width of the waveguide is 1-3 μm; and the inclination angle of the waveguide sidewall is 70-90°.

[0022] According to the above content, the present application provides a filter based on an optical superlattice electro-optical long period grating, including a substrate, a buried insulating layer, and a thin film layer; the buried insulating layer is arranged between the substrate and the thin film layer, and a waveguide is arranged on the side of the thin film layer away from the buried insulating layer; two metal plate electrodes are also arranged on the side of the thin film layer away from the buried insulating layer, and the two metal plate electrodes are arranged on both sides of the waveguide respectively; there is an electrode spacing between the metal plate electrodes, and the electrode spacing is greater than the top width of the waveguide. The filter of the present invention realizes the function of an electro-optically adjustable long period grating, and realizes the complete coupling of the fundamental mode in the waveguide and the high-order mode leaking to the thin film near the waveguide through the grating structure, thereby improving the optical coupling efficiency of the device. And compared with the traditional long period grating, the filter based on the optical superlattice electro-optical long period grating of the present application does not require strict process equipment and conditions, has a simple structure, greatly reduces the difficulty of device manufacturing, has low equipment requirements, large process tolerance, and easy to control parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings herein are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the implementation of the present invention, and together with the specification are used to explain the principles of the embodiments of the present invention. Obviously, the accompanying drawings described below are only some embodiments of the implementation of the present invention, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0024] Figure 1 A schematic diagram of a three-dimensional structure of a filter shown as an exemplary embodiment of the present application;

[0025] Figure 2 A right side view of a filter shown as an exemplary embodiment of the present application;

[0026] Figure 3 A schematic diagram of positive domains and negative domains of a periodically poled superlattice shown in an exemplary embodiment of the present application;

[0027] Figure 4 A top view of a filter according to an exemplary embodiment of the present application;

[0028] Figure 5 A front view of a filter shown as an exemplary embodiment of the present application;

[0029] Figure 6 A mode field distribution diagram of a guided mode and a leaky mode supported by a waveguide shown as an exemplary embodiment of the present application;

[0030] Figure 7 A transmission characteristic diagram of a guided mode and a leaky mode under one condition shown in an exemplary embodiment of the present application;

[0031] Figure 8 This is a distribution diagram of transmittance versus transmission distance of a guided mode of a filter shown in an exemplary embodiment of the present application when the working wavelength is 1550nm;

[0032] Fig. 9 This is a graph showing the relationship between the transmittance of a filter's guided mode and the electric field strength when the operating wavelength is 1550 nm according to an exemplary embodiment of the present application.

[0033] Description of reference numerals:

[0034] 100-substrate; 200-buried insulating layer; 300-thin film layer; 400-waveguide; 500-metal plate electrode; 600-periodic polarized superlattice; 700-guided mode; 800-leakage mode; 410-long period grating; 420-input end; 430-output end; 610-positive domain; 620-negative domain. DETAILED DESCRIPTION

[0035] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the embodiments of the present invention will be more comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a full understanding of the implementation of the embodiments of the present invention.

[0036] The filter is a key device on the lithium niobate platform. Currently, filters on the lithium niobate platform have been realized by means of exciting electric fields on proton exchange waveguides through interdigitated electrodes and forming refractive index gratings by covering polymers on lithium niobate waveguides. However, filters based on thin-film lithium niobate superlattice electro-optical long-period gratings have not yet been reported. Although long-period gratings based on lithium niobate proton exchange waveguides in the past can also achieve certain filtering effects, they have problems such as high driving voltage, complex preparation process, and difficulty in compatibility with integrated optical circuits.

[0037] In order to solve the above problems, the present application provides a filter based on an optical superlattice electro-optical long period grating, referring to Figure 1As shown, it includes a substrate 100, a buried insulating layer 200, and a thin film layer 300; the buried insulating layer 200 is arranged between the substrate 100 and the thin film layer 300, and a waveguide 400 is arranged on the side of the thin film layer 300 away from the buried insulating layer 200, and a periodically polarized superlattice 600 is arranged on the waveguide 400; two metal flat electrodes 500 are also arranged on the side of the thin film layer 300 away from the buried insulating layer 200, and the two metal flat electrodes 500 are correspondingly arranged on both sides of the waveguide 400; there is an electrode spacing between the metal flat electrodes 500, and the electrode spacing is greater than the top width of the waveguide 400.

[0038] In some embodiments of the present application, the material of the substrate 100, the thin film layer 300 and the waveguide 400 may be one of lithium niobate and lithium tantalate.

[0039] Lithium niobate and lithium tantalate are both multifunctional crystal materials. Specifically, lithium niobate crystals have many excellent optical properties, such as piezoelectric effect, electro-optic effect, nonlinear optical effect, photorefractive effect, acousto-optic effect and other photoelectric properties; the lattice structure and rich defect structure of lithium niobate crystals make the performance of lithium niobate crystals highly controllable. Many properties of lithium niobate crystals can be greatly controlled by crystal composition, element doping, valence control, etc. Lithium niobate crystals have stable physical and chemical properties, are easy to process, have a wide light transmission range, have large birefringence, and are easy to prepare high-quality optical waveguides.

[0040] Lithium tantalate crystals also have important properties such as piezoelectricity, dielectricity, pyroelectricity, electro-optical effect, nonlinear optical effect and acousto-optic effect. The main raw materials of lithium tantalate crystals are high-purity tantalum oxide and lithium carbonate. They are good materials for microwave acoustic devices, so they can also be used as the base material of filters.

[0041] In the embodiment of the present application, lithium niobate material is mainly used as an example, wherein the periodic poled superlattice 600 disposed on the waveguide 400 is formed by a poling technology on the waveguide 400. The periodic poled superlattice 600 is a lithium niobate superlattice crystal.

[0042] The theory and technology of optical superlattice are based on the principle of quasi-phase matching. It is a theory and technology that realizes phase matching and improves the conversion efficiency of nonlinear processes by alternating the growth of thin layers of two different components in the range of several nanometers to tens of nanometers and maintaining periodicity (or quasi-periodicity) through multilayer films, that is, a specific form of layered fine composite materials, to compensate for the reciprocal lattice vector, which is usually used to prepare nonlinear frequency conversion crystals. The frequency conversion crystals prepared by superlattice technology have the advantages of high frequency conversion efficiency, design freedom, small size, and low cost, and can achieve laser output of specific wavelengths within the light transmission range of the matrix crystal. The combination of optical superlattice crystals and all-solid-state laser technology can broaden the wavelength range of laser light sources. It can also generate high-brightness entangled photon pairs for optical quantum information technology. Lithium niobate, as a ferroelectric crystal, is widely used in nonlinear optical frequency conversion. By applying high-voltage electric pulses, the electric dipole moment in the crystal can be reversed, thereby changing the sign of the second-order nonlinear coefficient of the crystal. With the assistance of electrodes of various patterns, periodic, quasi-periodic, and non-periodic nonlinear superlattice structure materials can be prepared.

[0043] The waveguide 400 in this application is a channel for light propagation in the filter, similar to a wire in electronics. Similar to an optical fiber, the waveguide 400 confines light in the channel through total internal reflection, and is a structure used to directional guide electromagnetic waves. Due to the occurrence of total internal reflection, light is confined inside the ridge waveguide for propagation, thereby directional guiding the optical signal that needs to be filtered. In this application, a thin film system is used, and a ridge waveguide is etched on the thin film, so that the waveguide 400 has a stronger light field confinement ability, and the superlattice 600 can be periodically polarized directly on the waveguide 400 through polarization technology. Therefore, strict process equipment and conditions are not required, the structure is simple, and the difficulty of device manufacturing is greatly reduced.

[0044] In some embodiments of the present application, the structure of the waveguide 400 is any one of a ridge waveguide structure and a rectangular waveguide structure. Figure 1 As shown, in this application, a ridge waveguide structure is taken as an example. Specifically, compared with a non-ridge waveguide of similar size, the ridge waveguide structure has a lower cutoff frequency and can extend the high-order mode frequency, which is beneficial to the design of waveguide filters.

[0045] In some embodiments of the present application, reference Figure 3 As shown, the periodic poled superlattice 600 includes the same number of positive domains 610 and negative domains 620 , the positive domains 610 and the negative domains 620 are arranged crosswise, and one positive domain 610 and one negative domain 620 constitute one period.

[0046] The positive domain 610 and the negative domain 620 are ferroelectric domains in opposite regions. Ferroelectric domains refer to regions in the ferroelectric body with the same spontaneous polarization direction. The appearance of ferroelectric domains is caused by the different structures of the material at high and low temperatures. When the high-temperature paraelectric phase undergoes a structural phase transition at the Curie temperature Tc, in order to release the internal stress caused by the different high and low temperature phase structures and avoid the huge depolarization electric field, some small regional structures called electric domains are formed in the ferroelectric body.

[0047] In the same electric domain, all electric dipole moments are arranged in the same direction, while the directions of the electric polarization vectors in different regions may be different. For details, please refer to Figure 3 As shown, in lithium niobate and lithium tantalate ferroelectric crystals, the spontaneous polarization vector of the ferroelectric domain is either parallel to the z-axis, i.e., the positive domain 610, or antiparallel to the z-axis, i.e., the negative domain 620. A pair of positive domain 610 and negative domain 620 is taken as a structural unit, and the structural units of positive domain 610 and negative domain 620 are repeatedly arranged to form a periodically polarized superlattice 600.

[0048] In some embodiments of the present application, reference Figure 2 As shown, the length of one period is greater than 1 μm, there are several periods, and several periods constitute a long-period grating 410. The waveguide 400 also includes an input end 420 and an output end 430. The long-period grating 410 is arranged between the input end 420 and the output end 430.

[0049] In the present application, a period length formed by a pair of positive domains 610 and negative domains 620 is greater than 1 μm. Compared with traditional long-period gratings, it does not require strict process equipment and conditions, has a simple structure, and the key structures prepared by polarization methods are simple to prepare. The sizes of key waveguide structures that need to be prepared by photolithography are all greater than 1 μm and can be produced by ordinary photolithography machines, which greatly reduces the difficulty of device production, has low equipment requirements, large process tolerances, and easy parameter control.

[0050] In some embodiments of the present application, the material of the buried insulating layer 200 is silicon dioxide, and the material of the metal plate electrode 500 is any one of gold, aluminum, nickel, and chromium.

[0051] The lithium niobate and lithium tantalate used in this application are both ferroelectric materials. At higher temperatures, the conductivity will increase, the resistance will decrease, and the leakage current will increase. Therefore, silicon dioxide is used as the buried insulating layer 200. Silicon dioxide is an excellent insulating material and has very stable chemical properties. It can be used as an insulating medium between the upper and lower layers of ferroelectric materials to prevent leakage.

[0052] There are two metal plate electrodes 500, which are arranged on both sides of the waveguide 400, forming a parallel plate capacitor. When there is a certain potential difference between the metal plate electrodes 500, there will be an electrostatic field distribution between the metal plate electrodes 500. The parallel plate capacitor is the simplest capacitor. Using materials with high conductivity such as gold, aluminum, nickel, chromium, etc. as the metal plate electrodes 500 can meet the performance requirements of the filter, further reducing the difficulty of making the filter.

[0053] It can be seen from the above embodiments that the present application provides a filter based on an optical superlattice electro-optical long period grating, including a substrate, a buried insulating layer, and a thin film layer; the buried insulating layer is arranged between the substrate and the thin film layer, and a waveguide is arranged on the side of the thin film layer away from the buried insulating layer; two metal plate electrodes are also arranged on the side of the thin film layer away from the buried insulating layer, and the two metal plate electrodes are correspondingly arranged on both sides of the waveguide; there is an electrode spacing between the metal plate electrodes, and the electrode spacing is greater than the top width of the waveguide. The filter of the present invention realizes the function of an electro-optically adjustable long period grating, and realizes the complete coupling of the fundamental mode in the waveguide and the high-order mode leaking to the thin film near the waveguide through the grating structure, thereby improving the optical coupling efficiency of the device. And compared with the traditional long period grating, the filter based on the optical superlattice electro-optical long period grating of the present application does not require strict process equipment and conditions, has a simple structure, greatly reduces the difficulty of device manufacturing, has low equipment requirements, large process tolerance, and easy to control parameters.

[0054] On the other hand, the present application provides a method for preparing a filter based on an optical superlattice electro-optical long period grating, which is applied to any of the above-mentioned filters based on an optical superlattice electro-optical long period grating, comprising the steps of:

[0055] S100: bonding the substrate to one side of the buried insulating layer by a wafer bonding process; S200: bonding the other side of the buried insulating layer to the thin film layer by a wafer bonding process.

[0056] Specifically, still taking lithium niobate as an example, the thin film layer 300 can be obtained by ion slicing technology. Specifically, a lithium niobate wafer is first mounted on a substrate, and then helium ions are vertically injected into the lithium niobate wafer. The crystal after ion injection is then placed in diluted hydrofluoric acid for corrosion, and the surface layer of the lithium niobate crystal will be peeled off, thereby obtaining a single crystal thin film. That is, the thin film lithium niobate is obtained by ion slicing to peel off the lithium niobate thin film from the block lithium niobate crystal, and bonded to the buried insulating layer 200 made of silicon dioxide to form a thin film layer 300. Compared with the traditional bulk material structure, the thin film layer of lithium niobate material can achieve higher integration and better performance.

[0057] S300: a waveguide is etched on a side of the thin film layer away from the buried insulating layer by an etching process; S400: a periodically polarized superlattice is formed on the waveguide by a polarization technique; S500: metal plate electrodes are covered on the thin film layers on both sides of the waveguide.

[0058] Among them, the etching process is any one of electron beam lithography, reactive ion beam etching and inductively coupled plasma etching. Specifically, electron beam lithography is a kind of maskless lithography, and the electron beam lithography system has the advantages of ultra-high resolution and flexible mapping. Reactive ion beam etching is based on ion beam etching, and corrosive gas is added. For materials suitable for chemical assistance, the etching rate can be greatly increased and the etching quality can be improved. Inductively coupled plasma etching is a technology that uses a high-energy ion beam of inductively coupled plasma to etch the surface of a material. In the present application, the etching process can be arbitrarily selected according to actual conditions to form a waveguide 400 on the thin film layer 300.

[0059] In some embodiments of the present application, reference Figure 4 and Figure 5 As shown, the total height H of the waveguide and the thin film layer is 600-900 nm; the height h of the waveguide is 100-500 μm; the top width w of the waveguide is 1-3 μm; and the inclination angle of the waveguide side wall is 70-90°.

[0060] Specifically, the working principle of the filter of the present invention is as follows: at the input end, the input optical fiber is aligned with the end face of the waveguide, the optical signal is efficiently coupled from the optical fiber into the periodic polarization superlattice, and the fundamental mode optical signal is excited therein, the fundamental mode of the fundamental mode optical signal in a specific band and the high-order mode leaking into the thin film near the waveguide are both phase-matched with the long-period grating, and coupling occurs, so that most of the fundamental mode signal at the output end of the filter is filtered out. The device can be used as part of an integrated photonic chip to achieve filtering of optical signals from optical fibers to photonic chips. The filter in the embodiment of the present application is made of lithium niobate, and the size of the sample obtained is as follows: the total height of the waveguide and the thin film layer H = 600nm, the height of the waveguide h = 100μm, the top width of the waveguide w = 1.6μm, and the inclination angle of the waveguide side wall is 75°. When the wavelength of the input optical signal of the sample is 1550nm, the effective refractive index of the lithium niobate waveguide mode is 1.9417, and the effective refractive index of the leakage mode is 1.4468. The fundamental mode of the optical signal input into the periodically polarized superlattice waveguide at the input end of the filter of the present application can be coupled with the high-order mode leaked into the thin film layer near the waveguide through the long-period grating, thereby realizing the conversion of the fundamental mode in a specific band to the high-order mode.

[0061] In the embodiment of the present invention, continue to refer to Figure 4 and Figure 5As shown, the dimensions of the sample are further specified as follows: the total height of the waveguide and the thin film layer is H = 600nm, the height of the waveguide is h = 100μm, the width of the waveguide top is w = 1.6μm, the inclination angle of the waveguide side wall is 75°, and the waveguide length is 1.2cm; the flat electrodes on both sides of the waveguide are 3μm away from the waveguide, the electrode width is 100μm, the electrode length is 1.1cm, and the electrode spacing d = 7.6μm; the period number of the long period grating is 3000, its grating length is L = 0.954cm, the superlattice period Λ = 3.18μm, and the duty cycle is 0.5.

[0062] Taking the above sample size values ​​as an example, refer to Figures 6 to 9 As shown, Figure 6 : is a mode field distribution diagram of the guided mode and leakage supported by the waveguide in the present invention, in which the guided mode is marked as 700 and the leakage mode is marked as 800; Figure 7 This is a transmission characteristic diagram of the guided mode and the leakage mode in the working wavelength range of 1.5μm to 1.6μm in the sample experiment of the embodiment of the present invention when the length of the long period grating is exactly equal to the coupling length required for the 1550nm wavelength; Figure 8 The transmittance distribution diagram of the filter's guided mode at an operating wavelength of 1550nm varies with the transmission distance when the wavelength of the input optical signal is 1550nm; Fig. 9 The figure is a graph showing the relationship between the transmittance of the filter's guided mode and the electric field strength when the working wavelength is 1550nm. It can be seen from the figure that when the dimensions of the sample are the above values, the filter of this embodiment has relatively excellent performance.

[0063] According to the contents of the above embodiments, the present application provides a filter and preparation method for an optical superlattice electro-optical long-period grating. The filter of the present invention realizes the function of an electro-optically adjustable long-period grating, and realizes the complete coupling of the fundamental mode in the waveguide and the high-order mode leaked to the thin film near the waveguide through the grating structure, thereby improving the optical coupling efficiency of the device. And compared with the traditional long-period grating, the filter based on the optical superlattice electro-optical long-period grating of the present application does not require strict process equipment and conditions, has a simple structure, greatly reduces the difficulty of device manufacturing, has low equipment requirements, large process tolerance, and easy to control parameters.

[0064] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a structure, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such structure, article or device. In the absence of further restrictions, an element defined by the phrase "includes..." does not exclude the existence of other identical elements in the structure, article or device including the element.

[0065] Those skilled in the art will easily think of other embodiments of the present disclosure after considering the specification and practicing the disclosure disclosed herein. The present application is intended to cover any modification, use or adaptive change of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the technical field that are not disclosed in the present disclosure. The specification and the examples are only to be regarded as exemplary, and the true scope and spirit of the present disclosure are indicated by the following claims. The above specific implementation methods further describe the purpose, technical scheme and beneficial effects of the embodiments of the present application in detail. It should be understood that the above are only specific implementation methods of the embodiments of the present application, and are not used to limit the protection scope of the embodiments of the present application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical schemes of the embodiments of the present application should be included in the protection scope of the embodiments of the present application.

Claims

1. A filter based on an optical superlattice electro-optical long period grating, characterized in that: It comprises a substrate (100), a buried insulating layer (200), and a thin film layer (300); The buried insulating layer (200) is provided between the substrate (100) and the thin film layer (300); a waveguide (400) is provided on a side of the thin film layer (300) away from the buried insulating layer (200); and a periodically polarized superlattice (600) is directly formed on the waveguide (400) by a polarization technology; The periodic polarized superlattice (600) comprises the same number of positive domains (610) and negative domains (620), the positive domains (610) and the negative domains (620) are arranged crosswise, one positive domain (610) and one negative domain (620) constitute a period, and the period is greater than 1 μm; Two metal flat-plate electrodes (500) are also provided on a surface of the thin-film layer (300) away from the buried insulating layer (200), and the two metal flat-plate electrodes (500) are correspondingly provided on two sides of the waveguide (400); There is an electrode spacing between the metal plate electrodes (500), and the electrode spacing is greater than the top width of the waveguide (400).

2. The filter based on optical superlattice electro-optical long period grating according to claim 1, characterized in that: The structure of the waveguide (400) is any one of a ridge waveguide structure and a rectangular waveguide structure.

3. The filter based on optical superlattice electro-optical long period grating according to claim 1, characterized in that: There are a plurality of periods, and a plurality of the periods form a long-period grating (410). The waveguide (400) further comprises an input end (420) and an output end (430), and the long-period grating (410) is arranged between the input end (420) and the output end (430).

4. The filter based on optical superlattice electro-optical long period grating according to claim 1, characterized in that: The substrate (100), the thin film layer (300) and the waveguide (400) are made of lithium niobate or lithium tantalate.

5. The filter based on optical superlattice electro-optical long period grating according to claim 1, characterized in that: The material of the buried insulating layer (200) is silicon dioxide, and the material of the metal flat plate electrode (500) is any one of gold, aluminum, nickel, and chromium.

6. A method for preparing a filter based on an optical superlattice electro-optical long period grating, characterized in that: The method is applied to any one of the filters based on optical superlattice electro-optical long period gratings in claims 1 to 5, comprising the steps of: Bonding the substrate to one side of the buried insulating layer by a wafer bonding process; Bonding the other side of the buried insulating layer to the thin film layer through a wafer bonding process; Carving out a waveguide on a side of the thin film layer away from the buried insulating layer by an etching process; directly forming the periodically polarized superlattice on the waveguide by a polarization technique; The periodic polarized superlattice includes the same number of positive domains and negative domains, the positive domains and the negative domains are arranged crosswise, and one positive domain and one negative domain constitute a period, and the period is greater than 1 μm; The thin film layer on both sides of the waveguide is covered with metal plate electrodes.

7. The method for preparing a filter based on an optical superlattice electro-optical long period grating according to claim 6, characterized in that: The etching process is any one of electron beam lithography, reactive ion beam etching and inductively coupled plasma etching.

8. The method for preparing a filter based on an optical superlattice electro-optical long period grating according to claim 6, characterized in that: The total height of the waveguide and the thin film layer is 600-900nm; the height of the waveguide is 100-500μm; the top width of the waveguide is 1-3μm; and the inclination angle of the waveguide side wall is 70-90°.

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