A lithium niobate / lithium tantalate thin film polarization method with precise control of periodic domain reversal duty cycle

Abstract

The application relates to a lithium niobate / lithium tantalate thin film polarization method for accurate control of a period domain reversal duty cycle, which comprises the following steps: S1, providing a lithium niobate / lithium tantalate thin film as a polarization substrate; S2, defining an asymmetric interdigital electrode pattern on the surface of the polarization substrate; S3, forming a metal layer on the polarization substrate after step S2 through metal deposition, and then forming an asymmetric interdigital electrode through a stripping process; and S4, applying a high-voltage pulse sequence on the asymmetric interdigital electrode to drive the ferroelectric domains in the lithium niobate / lithium tantalate thin film to be periodically reversed. According to the method, the electric field distribution is geometrically preset controlled through the asymmetric interdigital electrode structure, the ferroelectric domain reversal region is mainly defined by the electrode structure, and thus the polarization result is less dependent on the accurate adjustment of the voltage amplitude and pulse parameters.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic materials technology, specifically relating to a polarization method for lithium niobate / lithium tantalate thin films with precise control of the duty cycle of periodic domain inversion. Background Technology

[0002] Lithium niobate / lithium tantalate thin films are widely used in nonlinear optical frequency conversion devices and on-chip quantum light sources due to their excellent second-order nonlinear optical coefficients. In such devices, quasi-phase matching is typically achieved through periodic ferroelectric domain reversal to obtain high nonlinear efficiency. In existing technologies, periodic polarization of ferroelectric thin films is usually achieved as follows: a comb-shaped electrode is fabricated on one side of the lithium niobate / lithium tantalate film as the anode, and a continuous planar electrode or a toothed electrode is placed on the other side as the cathode. A high-voltage pulse is applied to drive the ferroelectric domains to reverse along the z-axis. This method has been widely used in the fabrication of ferroelectric thin film devices.

[0003] However, the aforementioned traditional periodic polarization method has significant shortcomings. Because the electrode structure lacks effective constraint on ferroelectric domain expansion in the lateral direction, ferroelectric domains are prone to uncontrolled lateral expansion during inversion. This results in the duty cycle of the final inversion region being heavily dependent on process parameters such as polarization voltage amplitude, pulse width, period size, and electrode spacing. This problem is prevalent in various ferroelectric thin film material systems. Therefore, to obtain an ideal duty cycle close to 50%, repeated experiments involving "polarization-characterization-repolarization" are often necessary to find a suitable parameter window. Furthermore, the process parameters obtained through this empirical adjustment lack repeatability across different wafer locations and batches of samples, severely restricting the consistency, yield, and large-scale manufacturing capabilities of periodically polarized lithium niobate / lithium tantalate thin film devices. Especially in the fields of high-performance quantum light sources and integrated nonlinear photonic devices, these problems have become a major bottleneck restricting industrialization.

[0004] Therefore, a new technical solution is urgently needed that can fundamentally reduce the accuracy requirements of empirical parameters such as polarization voltage, improve the certainty of ferroelectric domain inversion duty cycle, and have good applicability to different ferroelectric thin film materials, thereby achieving stable periodic polarization without the need for pre-calibration voltage. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a polarization method for lithium niobate / lithium tantalate thin films with precise control of the ferroelectric domain inversion duty cycle. During the periodic polarization process of the lithium niobate / lithium tantalate thin film, the deterministic and designable controllable ferroelectric domain inversion duty cycle is achieved, thereby reducing the dependence of the polarization result on precise adjustment of process parameters such as voltage amplitude, pulse parameters, and period size. Furthermore, by suppressing the lateral expansion of ferroelectric domains during the polarization process, an accurate, stable, and repeatable periodic polarization structure with a consistent duty cycle is achieved without prior voltage calibration or repeated parameter trial and error.

[0006] The technical solution of the present invention is as follows: This invention provides a method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain inversion, comprising the following steps: S1. Provide a lithium niobate / lithium tantalate thin film as a polarization substrate; S2. Define an asymmetric interdigitated electrode pattern on the surface of the polarized substrate; S3. A metal layer is formed on the polarized substrate after step S2 by metal deposition, and then an asymmetric interdigitated electrode is formed by a lift-off process. S4. Apply a high-voltage pulse sequence to the asymmetric interdigitated electrode to drive the ferroelectric domains in the lithium niobate / lithium tantalate film to undergo periodic reversal.

[0007] According to a preferred embodiment of the present invention, the asymmetric interdigitated electrode includes an array of anode fingers and an array of cathode fingers arranged opposite to each other; the array of anode fingers includes an anode busbar and a plurality of anode fingers connected thereto and arranged periodically; the array of cathode fingers includes a cathode busbar and a plurality of cathode fingers connected thereto and arranged periodically; the anode fingers and cathode fingers are arranged alternately to form a periodic interdigitated structure.

[0008] Preferably, the width W_a of the anode finger is not equal to the width W_c of the cathode finger; more preferably, the width W_a of the anode finger is greater than the width W_c of the cathode finger, and the target polarization period is Λ, with W_a = 0.30Λ~0.40Λ and W_c = 0.15Λ~0.25Λ; most preferably, W_a = 0.35Λ and W_c = 0.20Λ.

[0009] In this invention, because the widths W_a and W_c of the anode and cathode fingers are not equal, a spatially uneven electric field is formed between the electrodes when a polarization voltage is applied. The anode finger width W_a is greater than the cathode finger width W_c. Between the wider anode finger and the opposite wider cathode region, the electric field component is dominant and strong, effectively driving the longitudinal reversal of domains. The narrower cathode finger, resulting in an uneven electric field distribution, acts as an electric field shield, thereby suppressing the lateral expansion of ferroelectric domains during polarization. This constrains the reversed domain region by the electrode geometry, enabling the designable and stable control of the duty cycle.

[0010] According to a preferred embodiment of the present invention, in step S1, the thickness of the lithium niobate / lithium tantalate film is 300 nm to 5000 nm, and more preferably, the thickness is 300 nm to 1000 nm.

[0011] According to a preferred embodiment of the present invention, in step S1, the lithium niobate / lithium tantalate film is bonded to an insulating substrate, wherein the insulating substrate is silicon dioxide (SiO2) or sapphire (Al2O3); in the present invention, the insulating substrate is used to provide mechanical support and electrical isolation for the lithium niobate film.

[0012] According to a preferred embodiment of the present invention, in step S2, the formation of an asymmetric interdigitated electrode pattern on the surface of a polarized substrate includes: spin-coating photoresist on the surface of a lithium niobate / lithium tantalate thin film, transferring the asymmetric interdigitated electrode pattern to the photoresist layer using micro-nano pattern transfer technology, and forming a corresponding electrode pattern photoresist mold after development. Preferably, the micro-nano pattern transfer technology is laser direct writing lithography, mask lithography, or electron beam lithography.

[0013] According to a preferred embodiment of the present invention, in step S3, the metal deposition method is physical vapor deposition or chemical vapor deposition; Preferably, the physical vapor deposition is magnetron sputtering, electron beam evaporation, or thermal evaporation.

[0014] According to a preferred embodiment of the present invention, in step S3, the thickness of the metal layer is 20 nm to 300 nm, and more preferably, the thickness is 30 nm to 100 nm.

[0015] According to a preferred embodiment of the present invention, in step S3, the material of the metal layer is a single metal or an alloy of any combination of chromium (Cr), aluminum (Al), nickel (Ni), silver (Ag) or gold (Au).

[0016] According to a preferred embodiment of the present invention, in step S4, applying a high-voltage pulse sequence to the asymmetric interdigitated electrodes to drive the ferroelectric domains to reverse includes: connecting the positive and negative output terminals of the high-voltage pulse generator to the anode and cathode finger arrays of the asymmetric interdigitated electrodes, respectively, and applying one or more polarization pulses at room temperature or a controlled temperature to generate a strong electric field between the asymmetric interdigitated electrodes that can drive the ferroelectric domains to reverse.

[0017] The technical features and beneficial effects of this invention are as follows: 1. Single-step periodic polarization capability: The method of this invention uses an asymmetric interdigitated electrode structure to geometrically pre-control the electric field distribution, so that the ferroelectric domain inversion region is mainly defined by the electrode structure. This reduces the dependence of the polarization result on the precise adjustment of voltage amplitude and pulse parameters. The target periodic structure can be formed without repeated voltage calibration or parameter trial and error, thus achieving single-step periodic polarization.

[0018] 2. Precise confinement control of reversed domains: In the method of the present invention, the electric field distribution strictly confines the domain reversal to a strip-shaped region extending from the anode finger to the cathode. This region is predefined by the geometric edge of the electrode. The lateral expansion of the reversed domains is strongly suppressed on the narrow cathode finger side, thus achieving precise spatial control of the reversed domains.

[0019] 3. High geometric certainty of duty cycle: The domain inversion width (corresponding to the duty cycle) ultimately formed in the method of this invention is directly determined by the anode finger width W_a and the relative position of the electrodes. By pre-designing the electrode geometry, the target duty cycle can be designed and repeatedly controlled. For example, when W_a = 0.35Λ is designed, an approximately 50% duty cycle can be directly obtained, realizing the pre-design and precise realization of the duty cycle.

[0020] 4. Excellent process robustness: The method of this invention eliminates the batch-to-batch and batch-to-batch differences caused by parameter sensitivity in traditional methods because the duty cycle is determined by a more easily defined and stable geometry rather than by difficult-to-control electric field parameters. This significantly improves the consistency of device performance and the repeatability of the manufacturing process. At the same time, it is not sensitive to changes in key process parameters such as polarization voltage, allowing operation in a wider range of imprecise voltages, reducing process difficulty and equipment accuracy requirements.

[0021] 5. Wide applicability and scalability: The method of this invention is highly versatile and applicable to lithium niobate / lithium tantalate thin film devices with different periods (Λ) and different target reversal lengths. It provides a universal and reliable polarization solution for nonlinear photonic devices with multiple wavelengths and functions (such as frequency doublers and quantum light sources). The method of this invention is highly scalable and fully compatible with high-precision photolithography technology (such as electron beam lithography). It can be easily extended to smaller feature sizes such as submicron periods, laying the foundation for the development of future high-performance and highly integrated photonic devices. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the asymmetric interdigitated electrode structure of the present invention; Figure 2 This is a schematic diagram of the fabrication process of the asymmetric interdigitated electrode in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the expected periodic polarization effect of the asymmetric interdigitated electrode of the present invention under ideal conditions; Figure 4 This is a schematic diagram illustrating the expected polarization effect of a conventional periodic electrode under ideal conditions. Figure 5 These are piezoelectric microscopy (PFM) characterization images of the actual polarization effect of lithium niobate thin films under different polarization voltage conditions in Example 1 of the present invention; wherein, Figure 5 (a) shows the PFM characterization of the actual polarization effect of the lithium niobate thin film under a polarization voltage of 200V. Figure 5 (b) shows the PFM characterization of the actual polarization effect of the lithium niobate film under a polarization voltage of 250V. Figure 5 (c) is a PFM characterization diagram of the actual polarization effect of the lithium niobate film under a polarization voltage of 300V; Figure 6 These are piezoelectric microscopy (PFM) characterization images of the actual polarization effect of the lithium tantalate film under different polarization voltage conditions in Example 2 of the present invention; wherein, Figure 6 (a) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under a polarization voltage of 300V. Figure 6 (b) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under a polarization voltage of 350V. Figure 6 (c) is a PFM characterization diagram of the actual polarization effect of the lithium tantalate film under a polarization voltage of 400V; Figure 7 These are piezoelectric microscopy (PFM) characterization images of the actual polarization effect of lithium tantalate films under different polarization periods Λ in Example 3 of the present invention; wherein, Figure 7 (a) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under a polarization period Λ of 6 μm. Figure 7 (b) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under the condition of 8 μm polarization period Λ. Figure 7 (c) is a PFM characterization diagram of the actual polarization effect of lithium tantalate film under a polarization period Λ of 12 μm; Figure 8 These are piezoelectric microscopy (PFM) characterization images of the actual polarization effect of lithium tantalate films under different electrode spacings D in Example 4 of the present invention; wherein, Figure 8 (a) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under a 6 μm electrode spacing D. Figure 8 (b) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under an 8 μm electrode spacing D. Figure 8 (c) is a PFM characterization diagram of the actual polarization effect of the lithium tantalate film under a 10 μm electrode spacing D. Figure 9 The images shown are piezoelectric microscopy (PFM) characterizations of the actual polarization effect of the lithium niobate thin film using a conventional periodic electrode structure under different polarization voltage conditions in Comparative Example 1 of this invention; wherein, Figure 9 (a) shows the PFM characterization of the actual polarization effect of the lithium niobate thin film under a polarization voltage of 200V using a conventional periodic electrode structure. Figure 9 (b) shows the PFM characterization of the actual polarization effect of the lithium niobate thin film under a polarization voltage of 250V using a conventional periodic electrode structure. Figure 9 (c) is a PFM characterization diagram of the actual polarization effect of lithium niobate thin film under a polarization voltage of 300V using a conventional periodic electrode structure. Figure 10 The images shown are piezoelectric microscopy (PFM) characterizations of the actual polarization effect of the lithium tantalate thin film using a conventional periodic electrode structure under different polarization voltage conditions in Comparative Example 2 of this invention; wherein, Figure 10 (a) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under a polarization voltage of 300V using a conventional periodic electrode structure. Figure 10 (b) shows the PFM characterization of the actual polarization effect of the lithium tantalate film under a polarization voltage of 350V using a conventional periodic electrode structure. Figure 10 (c) is a PFM characterization diagram of the actual polarization effect of lithium tantalate film under a polarization voltage of 400V using a conventional periodic electrode structure. Wherein: the red area is the domain inversion region, and the blue area is the non-inverted region. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments, but is not limited thereto. The embodiments described are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified in the embodiments of the present invention, all techniques existing in the art can be used.

[0025] Example 1 A method for precisely controlling the duty cycle of lithium niobate thin films by periodic domain reversal includes the following steps: S1. Provide an X-cut lithium niobate on insulator wafer with a thickness of 600 nm as a polarization substrate; S2. Spin-coat photoresist on the surface of the polarized substrate, and then use laser direct writing lithography to transfer the asymmetric interdigitated electrode pattern onto the photoresist. Then develop the photoresist to form a photoresist mold of the asymmetric interdigitated electrode pattern on the surface of the polarized substrate. S3. On the polarized substrate after step S2, a 50nm chromium layer is deposited over the entire surface by magnetron sputtering. A stripping process is then performed to remove the chromium layer above the photoresist area, leaving only the formed asymmetric interdigitated electrodes on the polarized substrate. The asymmetric interdigitated electrodes include an anode finger array and a cathode finger array. The anode finger array includes an anode busbar and multiple anode fingers connected to it and arranged periodically. The cathode finger array includes a cathode busbar and multiple cathode fingers connected to it and arranged periodically. The anode and cathode fingers are arranged alternately to form a periodic interdigitated structure. The anode finger width W_a is greater than the cathode finger width W_c. The target polarization period Λ = 7.5 μm, W_a = 0.35Λ = 2.6 μm, and W_c = 0.20Λ = 1.5 μm. The longitudinal distance between the anode finger and the cathode busbar, and between the cathode finger and the anode busbar, is D. D is designed based on the target domain reversal length. In this embodiment, D=6μm. The longitudinal length of the anode finger and the cathode finger is L=20μm.

[0026] S4. Connect the positive and negative output terminals of the high voltage pulse generator to the anode and cathode arrays of the asymmetric interdigitated electrodes, respectively. Apply a series of high voltage pulses of 200V, 250V, and 300V at room temperature. A strong electric field is generated between the asymmetric interdigitated electrodes, which drives the ferroelectric domains to reverse.

[0027] In this embodiment, the X-cut lithium niobate wafer on the insulator is made by bonding a single-crystal lithium niobate thin film onto an insulating substrate. The lithium niobate thin film has a thickness of 600 nm, and the insulating substrate is SiO2.

[0028] The piezoelectric power microscopy (PFM) characterization images of the actual polarization effect of the lithium niobate thin film under different polarization voltage conditions in this example are shown below. Figure 5 As shown.

[0029] Depend on Figure 5 It can be seen that the formation of periodic ferroelectric domain structures can be completed by applying a polarization electric pulse once under different voltage conditions. The resulting inverted domains are distributed in a regular strip shape, and the duty cycle is stable and close to the design value (about 50%). This shows that the method of the present invention has good stability to polarization voltage changes and can realize single-step periodic polarization.

[0030] Example 2 A method for precisely controlling the duty cycle of lithium tantalate thin films by periodic domain reversal, as described in Example 1, differs in that: In step S1, the polarization substrate is replaced by a lithium niobate film with a lithium tantalate film.

[0031] In step S4, polarization pulses with peak voltages of 300V, 350V and 400V are applied at room temperature to drive the ferroelectric domains in the lithium tantalate film to undergo periodic reversal.

[0032] The other steps and conditions are the same as in Example 1.

[0033] The piezoelectric power microscopy (PFM) characterization of the actual polarization effect of the lithium tantalate film under different polarization voltage conditions in this example is shown below. Figure 6 As shown.

[0034] Depend on Figure 6 It can be seen that under different voltage conditions, the formation of periodic ferroelectric domain structures can be completed by applying a polarization electric pulse once. The resulting reverse domains are distributed in a regular strip shape, and their width is determined by the width of the anode fingers. The duty cycle is stable and close to the preset target value, indicating that the method of the present invention also has good process stability in the lithium tantalate thin film system and can achieve single-step periodic polarization without pre-calibration voltage.

[0035] Example 3 A method for precisely controlling the duty cycle of lithium tantalate thin films under different periods, as described in Example 1, differs in that: In step S1, the polarization substrate is replaced by a 600 nm thick lithium tantalate film instead of a lithium niobate film.

[0036] In step S3, the target polarization period Λ is 6 μm, 8 μm, and 12 μm. For different target periods, the geometric parameters of the asymmetric interdigitated electrode are set proportionally as follows: The width of the anode finger bar is W_a = 0.35Λ; the width of the cathode finger bar is W_c = 0.20Λ; the longitudinal distance between the anode finger bar and the cathode busbar, and between the cathode finger bar and the anode busbar, is D = 6 μm; the longitudinal length of the anode finger bar and the cathode finger bar is L = 20 μm.

[0037] In step S4, a polarization pulse with a peak voltage of 400 V is uniformly applied at room temperature to drive the ferroelectric domains in the lithium tantalate film to undergo periodic reversal.

[0038] The other steps and conditions are the same as in Example 1.

[0039] The piezoelectric power microscopy (PFM) characterization of the actual polarization effect of lithium tantalate films under different polarization periods Λ in this example is shown below. Figure 7 As shown.

[0040] Depend on Figure 7 It can be seen that, under different period size conditions, the formation of periodic ferroelectric domain structures is completed by applying a polarization electric pulse once. The resulting inverted domains are distributed in a regular strip shape, and their width is determined by the width of the anode fingers. The duty cycle matches the preset target value, indicating that the method of the present invention can still achieve stable polarization of different periodic structures under fixed polarization voltage conditions. This further proves the advantages of the method of the present invention in terms of insensitivity to polarization voltage parameters and the geometric determinism of its duty cycle.

[0041] Example 4 A method for precisely controlling the duty cycle of periodic domain inversion under different spacings for lithium tantalate thin films, as described in Example 1, differs in that: In step S1, the polarization substrate is replaced by a lithium niobate film with a lithium tantalate film.

[0042] In step S3, the target polarization period Λ is set to 7.5 μm, the anode finger width W_a = 0.35Λ, the cathode finger width W_c = 0.20Λ, and the longitudinal length L of the anode and cathode fingers is 20 μm. The longitudinal distance D of the electrodes is designed to be 6 μm, 8 μm, and 10 μm, respectively.

[0043] In step S4, a polarization pulse with a peak voltage of 400 V is uniformly applied at room temperature to drive the ferroelectric domains in the lithium tantalate film to undergo periodic reversal.

[0044] The other steps and conditions are the same as in Example 1.

[0045] The piezoelectric power microscopy (PFM) characterization of the actual polarization effect of the lithium tantalate film under different electrode spacings D in this example is shown below. Figure 8 As shown.

[0046] Depend on Figure 8 It can be seen that under different electrode spacing D, the formation of periodic ferroelectric domain structures can be completed by applying a polarization electric pulse once. The resulting reverse domains are distributed in a regular strip shape, with a stable lateral width that corresponds to the width of the anode fingers. The duty cycle is close to the preset target value, indicating that the method of the present invention still has good process stability and duty cycle controllability under different polarization length design conditions.

[0047] Comparative Example 1 A lithium niobate thin film polarization method, as described in Example 1, except that: In step S3, the asymmetric interdigitated electrode is replaced with a conventional periodic electrode structure, which includes an anode finger electrode disposed on the upper surface of the lithium niobate film and a cathode plate electrode disposed opposite to it. The anode finger electrode is connected to the anode busbar, and the cathode plate electrode is a continuous metal electrode.

[0048] The target polarization period Λ = 7.5 μm, the anode finger width W_a = 0.35Λ = 2.6 μm, and the cathode is a continuous plate electrode. The distance between the anode finger and the cathode plate electrode is D, which is designed according to the target domain inversion length. In this embodiment, D = 6 μm, and the longitudinal length of the anode finger is L = 20 μm.

[0049] The other steps and conditions are the same as in Example 1.

[0050] Polarization experiments conducted under the same polarization voltage conditions revealed significant non-uniform domain expansion in the obtained ferroelectric domain structures, making precise control of the polarization region width difficult. Insufficient domain inversion occurred under low voltage, while excessive domain expansion occurred under high voltage, leading to deviations in the duty cycle of the obtained periodic domain structures from the target value and poor uniformity of the periodic structures. Figure 9 As shown.

[0051] Comparative Example 2 A lithium tantalate thin film polarization method, as described in Example 2, except that: In step S3, the asymmetric interdigitated electrode is replaced with a conventional periodic electrode structure, which includes an anode finger electrode disposed on the upper surface of the lithium tantalate film and a cathode plate electrode disposed opposite to it. The anode finger electrode is connected to the anode busbar, and the cathode plate electrode is a continuous metal electrode.

[0052] The target polarization period Λ = 7.5 μm, the anode finger width W_a = 0.35Λ = 2.6 μm, and the cathode is a continuous plate electrode. The distance between the anode finger and the cathode plate electrode is D, which is 6 μm in this embodiment, and the longitudinal length of the anode finger is L = 20 μm.

[0053] The other steps and conditions are the same as in Example 2.

[0054] Polarization experiments conducted under the same polarization voltage conditions revealed significant non-uniform domain expansion in the obtained ferroelectric domain structures, making it difficult to form regular and stable periodic domain structures. Figure 10 As shown.

Claims

1. A method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain inversion, characterized in that, Includes the following steps: S1. Provide a lithium niobate / lithium tantalate thin film as a polarization substrate; S2. Define an asymmetric interdigitated electrode pattern on the surface of the polarized substrate; S3. A metal layer is formed on the polarized substrate after step S2 by metal deposition, and then an asymmetric interdigitated electrode is formed by a lift-off process. S4. Apply a high-voltage pulse sequence to the asymmetric interdigitated electrode to drive the ferroelectric domains in the lithium niobate / lithium tantalate film to undergo periodic reversal.

2. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain inversion according to claim 1, characterized in that, The asymmetric interdigitated electrode includes an array of anode fingers and an array of cathode fingers arranged opposite to each other; the anode finger array includes an anode busbar and a plurality of anode fingers connected thereto and arranged periodically; the cathode finger array includes a cathode busbar and a plurality of cathode fingers connected thereto and arranged periodically; the anode fingers and cathode fingers are arranged alternately to form a periodic interdigitated structure.

3. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain inversion according to claim 2, characterized in that, The width W_a of the anode finger is not equal to the width W_c of the cathode finger.

4. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films according to claim 3, characterized in that, The width of the anode finger, W_a, is greater than the width of the cathode finger, W_c, and the target polarization period is Λ, where W_a = 0.30Λ~0.40Λ and W_c = 0.15Λ~0.25Λ; preferably, W_a = 0.35Λ and W_c = 0.20Λ.

5. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain inversion according to claim 1, characterized in that, Step S1 includes one or more of the following conditions: i. The thickness of the lithium niobate / lithium tantalate film is 300 nm to 5000 nm, preferably 300 nm to 1000 nm; ii. The lithium niobate / lithium tantalate film is bonded to an insulating substrate, which is silicon dioxide (SiO2) or sapphire (Al2O3); in this invention, the insulating substrate is used to provide mechanical support and electrical isolation for the lithium niobate film.

6. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films according to claim 1, characterized in that, In step S2, forming an asymmetric interdigitated electrode pattern on the polarized substrate surface includes: spin-coating photoresist onto the surface of a lithium niobate / lithium tantalate thin film, transferring the asymmetric interdigitated electrode pattern to the photoresist layer by laser direct writing lithography, mask lithography or electron beam lithography, and forming a corresponding electrode pattern photoresist mold after development.

7. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films according to claim 1, characterized in that, In step S3, the metal deposition method is physical vapor deposition or chemical vapor deposition; the physical vapor deposition is magnetron sputtering, electron beam evaporation or thermal evaporation.

8. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films according to claim 1, characterized in that, In step S3, the thickness of the metal layer is 20 nm to 300 nm, preferably 30 nm to 100 nm.

9. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain reversal according to claim 1, characterized in that, In step S3, the material of the metal layer is a single metal or an alloy of any combination of Cr, Al, Ni, Ag or Au.

10. The method for precisely controlling the duty cycle of lithium niobate / lithium tantalate thin films by periodic domain inversion according to claim 1, characterized in that, In step S4, applying a high-voltage pulse sequence to the asymmetric interdigitated electrodes to drive the ferroelectric domains to reverse includes: connecting the positive and negative output terminals of the high-voltage pulse generator to the anode and cathode finger arrays of the asymmetric interdigitated electrodes, respectively, and applying one or more polarization pulses at room temperature or a controlled temperature to generate a non-uniform strong electric field between the asymmetric interdigitated electrodes, thereby driving the ferroelectric domains to reverse in a controllable manner.

Images