A thin film lithium niobate acousto-optic modulator

Abstract

The present application aims at the low efficiency and insufficient radio frequency bandwidth of the current thin film lithium niobate single sideband acousto-optic modulation device, and proposes a thin film lithium niobate single sideband acousto-optic modulation device based on horizontal shear surface acoustic wave. The device comprises a silicon substrate, a silicon dioxide layer and a thin film lithium niobate layer from bottom to top. The thin film lithium niobate layer comprises an intermodal acousto-optic modulation unit and an asymmetric directional coupler unit. Through calculation and analysis, the efficiency of the thin film lithium niobate acousto-optic modulation device proposed in the present application can be improved by at least one order of magnitude compared with the traditional Rayleigh surface acoustic wave scheme, and the radio frequency bandwidth can be improved by about 5 times. In addition, the present application adopts the scheme of on-chip integration of the intermodal acousto-optic modulation unit and the asymmetric directional coupler, which can further realize high modulation efficiency, high bandwidth and single sideband acousto-optic modulation, and has the advantages of high integration, simple process, high robustness and scalable expansion, thereby laying an important foundation for the practical application of high-performance thin film lithium niobate acousto-optic modulation device.

Description

Technical Field

[0001] This invention belongs to the field of integrated optical chips, and in particular to a thin-film lithium niobate single-sideband acousto-optic modulation device based on horizontal shear surface acoustic waves. Background Technology

[0002] On-chip single-sideband acousto-optic modulators (SSBEMs) are devices that integrate surface acoustic waves (SAWs) and optical waveguides on a multifunctional material platform to achieve single-sideband acousto-optic modulation. They offer advantages such as miniaturization, high efficiency, and non-reciprocity. Therefore, they are often used as acousto-optic frequency shifters, acousto-optic isolators, or acousto-optic switches, and are widely applied in fields such as optical chip interconnects, laser signal processing, and microwave photonics.

[0003] Thin-film lithium niobite (LiNbO3) is considered an ideal platform for realizing high-performance on-chip acousto-optic modulators due to its advantages such as low propagation loss, wide transparency window, strong piezoelectric effect, and photoelastic effect. Currently, on-chip acousto-optic modulators based on thin-film lithium niobite mainly rely on Rayleigh surface acoustic waves to achieve single-sideband acousto-optic modulation. Related technologies have been disclosed in a number of patents and academic studies, including patent documents CN 116300156A, CN 114859579A, L. Shao et al., Integrated microwave acousto-optic frequency shifter on thin-film lithium niobite, Optics Express 28,23728 (2020), and Z. Yu et al., Gigahertz acousto-optic modulation and frequency shifting on etchless lithium niobite integrated platform, ACS Photonics 8,798 (2021). However, acousto-optic modulation schemes based on Rayleigh surface acoustic waves (SAWs) face two major technical bottlenecks: First, the electromechanical coupling coefficient of Rayleigh SAWs is relatively low, and this coefficient is further weakened by the non-piezoelectric silicon dioxide layer, leading to increased RF power consumption and limited modulation bandwidth in the acousto-optic modulation devices. Second, because the propagation speed of Rayleigh SAWs in thin-film lithium niobate is often greater than that in the silicon dioxide layer, the acoustic mode field leaks into the lower silicon dioxide region, reducing the localization of the mode field within the optical waveguide and the acousto-optic modulation efficiency, making it difficult to meet the high-speed, high-efficiency modulation requirements of modern communication systems. Summary of the Invention

[0004] To overcome the problems of insufficient RF bandwidth and low modulation efficiency of traditional Rayleigh SAW modulators in the prior art, the present invention aims to propose a thin-film lithium niobate single-sideband acousto-optic modulation scheme based on horizontal shear surface acoustic waves (SAWs). This scheme addresses the issues of high RF power consumption, insufficient bandwidth, and low modulation efficiency inherent in Rayleigh SAW modulation schemes. By utilizing the high electromechanical coupling coefficient and highly localized sound field distribution of SAWs, combined with the mode demultiplexing function of an on-chip asymmetric directional coupler, a highly integrated, high-bandwidth, and high-modulation-efficiency single-sideband acousto-optic modulation device is achieved.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A thin-film lithium niobate single-sideband acousto-optic modulation device based on horizontal shear surface acoustic waves includes, from bottom to top, a silicon substrate, a silicon dioxide buried oxide layer, and a thin-film lithium niobate layer. The device is characterized in that the thin-film lithium niobate layer integrates an intermodal acousto-optic modulation unit and an asymmetric directional coupler unit. The intermodal acousto-optic modulation unit modulates the optical field using horizontal shear surface acoustic waves, and the asymmetric directional coupler unit separates the modulated optical signal and outputs a single-sideband modulated signal.

[0007] Furthermore, the intermodal acousto-optic modulation unit includes a horizontal shear wave acoustic resonator, an input single-mode optical waveguide, a first tapered waveguide, and a multimode optical waveguide. The horizontal shear wave acoustic resonator includes an interdigital transducer, electrodes connected to an external radio frequency circuit, and Bragg reflection gratings evenly spaced on both sides. It is used to convert the external microwave electrical signal into a horizontal shear acoustic wave propagating within the thin-film lithium niobate layer, and to achieve modulation of the intermodal optical field based on the photoelastic effect and the second-order electro-optic effect.

[0008] Furthermore, the tangential direction of the thin-film lithium niobate is YX, indicating that the normal direction of the device surface is along the crystal Y-axis, and the direction of horizontal shear acoustic wave propagation is the crystal X-axis.

[0009] Furthermore, the horizontal shear wave acoustic resonator includes an interdigital transducer, electrodes connected to an external radio frequency circuit, and Bragg reflection gratings evenly spaced on both sides; through the interdigital transducer of the acoustic resonator, the external microwave electrical signal is converted into an acoustic vibration wave propagating through the thin-film lithium niobate layer, and the optical field inside the waveguide is modulated based on the photoelastic effect and the second-order electro-optic effect.

[0010] Optionally, the metal electrodes of the acoustic resonator are made of Al, Cu, or Au materials with a thickness of 100 nm to 500 nm.

[0011] Furthermore, the electrode width of the interdigital transducer and the Bragg grating is 372.5nm-497.5nm, and the horizontal shear acoustic wavelength λ is 1.49μm-1.99μm; the number of electrode pairs of the interdigital transducer is 20-100; and the number of periods of the Bragg grating is 20-100.

[0012] Furthermore, the aperture width of the interdigital transducer and the Bragg reflection grating is set to (20~40)λ.

[0013] Furthermore, the distance between the interdigital transducer and the Bragg reflection grating is nλ, where n is an integer, and the set spacing parameter must satisfy the single-mode condition of the surface acoustic wave resonator.

[0014] Furthermore, the waveguide width of the input single-mode optical waveguide is 0.5μm to 1μm, which is the unit that couples the input light into the on-chip optical path; the waveguide width of the multimode optical waveguide is 1.5μm to 2μm, which is the region where the acousto-optic field interacts; and the first tapered waveguide is the part that connects the single-mode optical waveguide and the multimode optical waveguide.

[0015] Furthermore, the etching tilt angle of the input single-mode optical waveguide, the first tapered waveguide, and the multimode optical waveguide ranges from 65° to 90°; the etching depth is half the thickness of the thin film lithium niobate.

[0016] Furthermore, the asymmetric directional coupler unit includes the multimode optical waveguide, the coupling narrow waveguide, the S-shaped curved waveguide, the second tapered waveguide, the third tapered waveguide, the first single-mode optical waveguide at the output end, and the second single-mode optical waveguide at the output end. The asymmetric directional coupler unit is responsible for converting the acousto-optic modulated TE1 signal into a single-mode TE0 output under phase matching conditions, so as to realize the independent output of the single-sideband acousto-optic modulated signal.

[0017] Furthermore, the multimode optical waveguide is connected to the second tapered waveguide, and finally connected to the first single-mode optical waveguide at the output end.

[0018] Furthermore, the coupled narrow waveguide, the S-shaped curved waveguide, the third tapered waveguide, and the second single-mode optical waveguide at the output end are connected in sequence, and finally connected to the external optical path.

[0019] Furthermore, the waveguide width of the coupled narrow waveguide and the S-bend waveguide is 0.5μm to 0.8μm; the waveguide width of the first single-mode optical waveguide and the second single-mode optical waveguide at the output end is 0.5μm to 1μm, which are units for coupling the modulated light (unmodulated light) out of the on-chip optical path;

[0020] Furthermore, the etching tilt angle of the coupled narrow waveguide, S-shaped curved waveguide, second tapered waveguide, third tapered waveguide, first single-mode optical waveguide at the output end, and second single-mode optical waveguide at the output end ranges from 65° to 90°; the etching depth is 1 / 2 of the thickness of the thin film lithium niobate.

[0021] Furthermore, the silicon substrate is monocrystalline silicon with a thickness of 300μm to 700μm; the silicon dioxide buried oxide layer has a thickness of 2μm to 4.7μm, and its main function is to prevent the optical field mode in the thin-film lithium niobate waveguide from leaking to the underlying monocrystalline silicon substrate; the thin-film lithium niobate has a thickness of 300nm to 900nm; and the optical operating wavelength range is 400nm to 5000nm.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) By optimizing parameters such as the wavelength of horizontal shear surface acoustic waves, the thickness of thin-film lithium niobate, and the thickness of interdigital transducer electrodes, it is expected that the efficiency of current single-sideband acousto-optic modulators based on Rayleigh surface acoustic waves will be improved by at least one order of magnitude, while the RF bandwidth will be increased by about 5 times.

[0024] 2) Horizontal shear surface acoustic waves (SAWs) have a higher electromechanical coupling coefficient, resulting in significantly improved RF bandwidth and modulation efficiency compared to traditional Rayleigh SAWs. The horizontal shear wave forms a localized sound field within the geometric space confined by the Bragg grating, enhancing acousto-optic interaction and improving modulation efficiency. Independent channel outputs of modulated and unmodulated light are achieved through an asymmetric directional coupler, realizing a single-sideband modulation effect.

[0025] 3) This invention employs an on-chip integrated inter-modal acousto-optic modulation unit and an asymmetric directional coupler unit, enabling on-chip single-sideband modulation functionality. The entire device is integrated on a thin-film lithium niobate platform, offering advantages such as high integration density, good process compatibility, strong stability, and ease of scalability. It also incorporates features like simple fabrication, high robustness, and large-scale integration, providing new ideas and solutions for the practical application of thin-film acousto-optic modulators. Attached Figure Description

[0026] Figure 1 This is a top view of the thin-film lithium niobate single-sideband acousto-optic modulation device based on horizontal shear surface acoustic waves according to the present invention.

[0027] Figure 2 This is a cross-sectional schematic diagram of the intermodal acousto-optic modulation unit in this invention;

[0028] Figure 3 This is a schematic diagram of the surface acoustic wave resonator based on horizontal shear waves in this invention.

[0029] Figure 4This is a schematic diagram of the cross-sectional structure of the asymmetric directional coupler in this invention.

[0030] Figure reference numerals: 1. Thin-film lithium niobate (LiNbO3); 2. Silicon dioxide (SiO2); 3. Silicon substrate (Si); 4. Left Bragg reflection grating of the horizontal shear wave acoustic resonator; 5. Interdigital transducer of the horizontal shear wave acoustic resonator; 6. Right Bragg reflection grating of the horizontal shear wave acoustic resonator; 7. Multimode optical waveguide; 8. Etched groove of thin-film lithium niobate; 9. Metal electrode at the ground end of the interdigital transducer; 10. Metal electrode at the signal end of the interdigital transducer; 11. Metal electrode of the Bragg reflection grating; 12. Ground end electrode of the interdigital transducer; 13. Signal end electrode of the interdigital transducer; 14. Input single-mode optical waveguide; 15. First tapered waveguide; 16. Second tapered waveguide; 17. First single-mode optical waveguide at the output end; 18. Coupled narrow waveguide; 19. S-shaped curved waveguide; 20. Third tapered waveguide; 21. Second single-mode optical waveguide at the output end. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0032] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0033] Please see Figure 1 , Figure 1 This is a top view of the thin-film lithium niobate single-sideband acousto-optic modulation device based on horizontal shear surface acoustic waves, as shown in the figure. The thin-film lithium niobate single-sideband acousto-optic modulation device proposed in this invention is constructed based on a thin-film LiNbO3 / SiO2 / Si platform. From bottom to top, it consists of a silicon substrate 3, a silicon dioxide layer 2, and a thin-film LiNbO3 layer 1, with the corresponding thickness defined as h. Si h SiO2 and h LN The thickness of silicon substrate 3 is 300μm to 700μm, h SiO2 The value range is 2μm to 4.7μm, h LNThe wavelength range is set to 300nm–900nm. This device includes an intermodal acousto-optic modulation unit based on a thin-film lithium niobate / SiO2 / Si platform and an asymmetric directional coupler unit. Employing a horizontal shear wave acoustic mode with a high electromechanical coupling coefficient and localized acoustic field, intermodal acousto-optic modulation is constructed in a thin-film lithium niobate multimode optical waveguide, and a highly efficient single-sideband acousto-optic modulation is achieved by integrating an asymmetric directional coupler on the back-end chip.

[0034] Figure 2 This is a cross-sectional schematic diagram of the intermodal acousto-optic modulation unit in this invention. As shown in the figure, the intermodal acousto-optic modulation unit includes a horizontal shear wave acoustic resonator, an input single-mode optical waveguide, a first tapered waveguide, and a multimode optical waveguide. The horizontal shear wave acoustic resonator is fabricated on a thin-film LiNbO3 layer 1, and the metal electrode material used is aluminum, copper, or gold, etc. The thickness h of the metal electrode... e The wavelength range is 100nm to 500nm. The horizontal shear wave acoustic resonator includes Bragg reflection gratings 4 and 6 evenly spaced on both sides and interdigital transducers 5. By applying a microwave driving signal to the interdigital transducers, the electrical signal is converted into an acoustic signal under the action of the inverse piezoelectric effect, forming a localized horizontal shear wave acoustic field within the geometric space confined by the Bragg reflection gratings 4 and 6. This propagating acoustic field crosses the grooves 8 etched on the thin-film lithium niobate and interacts acousto-optically with the localized optical field in the multimode optical waveguide 7, thereby achieving intermode acousto-optic modulation. To prevent the optical field in the multimode optical waveguide 7 from leaking laterally into the slab region on the side, the width of the grooves 8 must be greater than 2μm.

[0035] Figure 3 This is a schematic diagram of a horizontal shear wave acoustic resonator. The interdigital transducer 5 includes several sets of periodic electrodes with opposite polarities, wherein the negative electrode 9 is connected to the ground signal terminal 12, and the positive electrode 10 is connected to the input signal terminal 13.

[0036] Number of electrode cycles N of interdigital transducers T The wavelength ranges from 20 to 100, and its period length is equal to the surface acoustic wave wavelength λ. The transverse wavelength of the acoustic resonator is equal to the waveguide width W of the multimode optical waveguide 7. b To ensure impedance matching between the interdigital transducer and the external microwave signal, and simultaneously enhance the coupling strength between the surface acoustic wave and the optical field within the multimode waveguide 7, W b The value range is 1.5μm to 2μm, which satisfies the following formula:

[0037] λ=W b cosθ (1)

[0038] Wherein, θ is the angle between the propagation direction of the surface acoustic wave and the normal direction of the optical axis. To satisfy the wave vector matching condition for intermodal acousto-optic scattering, the angle θ is taken as 1° to 20°, and the wavelength λ of the surface acoustic wave is taken as 1.49 μm to 1.99 μm.

[0039] The electrode width 'a' of the interdigital transducer 4 and the Bragg reflection gratings 5 ​​and 6 is equal to λ / 4, i.e., 372.5 nm - 497.5 nm. To reduce the transmission loss of horizontal shear surface acoustic waves, the number of periods N of the Bragg reflection gratings 5 ​​and 6 is... g The value is 20-100, ensuring that the surface acoustic wave is completely emitted by the Bragg grating. The intermodal acousto-optic modulation efficiency of the device is related to the acousto-optic interaction length, i.e., the aperture width W of the acoustic resonator. a It is proportional to the square of the value. To balance the modulation efficiency and acoustic diffraction loss of the device, this invention sets the aperture width W of the acoustic resonator. a The effective electromechanical coupling coefficient of the thin-film lithium niobate horizontal shear surface acoustic wave based on the YX tangential direction can be calculated by formula (2).

[0040]

[0041] Among them, f s f p These are the resonant and anti-resonant frequencies of the horizontal shear wave acoustic resonator, respectively. The thickness h of the thin-film lithium niobate is used as the reference. LN Taking 400nm as an example, when the surface acoustic wave wavelength is set to 1.7μm, the simulated extracted f s and f p The frequencies are 2.142 GHz and 2.313 GHz, respectively, and the calculated effective electromechanical coupling coefficient is 20.5%. For Rayleigh surface acoustic waves with the same design parameters, the simulation-extracted f... s and f p The frequencies are 1.851 GHz and 1.884 GHz, respectively, and their corresponding effective electromechanical coupling coefficients are 4.4%.

[0042] Compared to Rayleigh surface acoustic waves, the effective electromechanical coupling coefficient of the horizontal shear wave-based acoustic resonator proposed in this invention can be improved by nearly 5 times, and the corresponding RF bandwidth is also improved by 5 times. Devices based on other parameter ranges also exhibit the same performance improvement in effective electromechanical coupling coefficient.

[0043] A transverse electric field fundamental mode TE0 light with frequency ω0 and propagation wave vector k0 is input from the single-mode optical waveguide 14, passes through the first tapered waveguide 15, and enters the multimode optical waveguide 7, where it interacts with the horizontal shear wave acoustic field. When a microwave signal with frequency Ω is applied to the signal terminal 13 of the horizontal shear wave acoustic resonator, its excited acoustic strain field undergoes anti-Stokes scattering with the TE0 light in the multimode optical waveguide 7. Under the condition of wave vector matching as per formula (3), the incident light TE0 will be scattered and converted into modulated light TE1 with frequency (ω0+Ω).

[0044]

[0045] In formula (3), k1 is the propagation wave vector of the TE1 mode. The acousto-optic modulation efficiency is positively correlated with the acousto-optic field overlap integral factor Γ. Therefore, this invention will evaluate the acousto-optic modulation efficiency through the calculation results of the acousto-optic field overlap integral factor Γ. In this invention, the acousto-optic field overlap integral factor mainly comes from two contributions: the photoelastic effect term Γ. AO and the second electro-optic effect term Γ EO The photoelastic effect refers to the interaction between the acoustic strain field and the optical field within the waveguide, while the second electro-optic effect refers to the interaction between the electric field generated by the surface acoustic wave through the piezoelectric effect and the optical field within the waveguide. The total acousto-optic field overlap integral factor Γ is the sum of two terms.

[0046] Γ=Γ AO +Γ EO (4)

[0047] Formula (5) below represents the photoelastic interaction term, and formula (6) represents the secondary electro-optic interaction term. The specific calculation formulas are as follows:

[0048]

[0049] , where p 11 p 12 p 13 p 14 p 15 p 16 The term refers to the photoelastic coefficient of the YX tangential lithium niobate material. E0(x,z) and E1(x,z) represent the electric field distributions in the TE0 and TE1 modes, respectively. S1, S2, and S3 represent the principal strain components in the x, y, and z directions, respectively. S4, S5, and S6 represent the shear strain components in the yz, xz, and xy directions, respectively. x, y, and z are spatial geometric coordinates. The second-order electro-optic effect term Γ... EO The calculation formula is as follows:

[0050]

[0051] , where r 11 r 12 r13 These refer to the electro-optic coefficients of YX tangential lithium niobate materials, ε x , ε y , ε z Let h represent the acoustic-electric field in the x, y, and z directions. The thickness h of the thin lithium niobate film is used as the reference value. LN Taking 400nm as an example, when the surface acoustic wave wavelength is set to 1.7μm, the normalized acousto-optic overlap integral factor Γ based on horizontal shear surface acoustic waves, calculated by formulas 5 and 6, is equal to 0.034. Under the same parameter conditions, the normalized acousto-optic overlap integral factor Γ based on Rayleigh surface acoustic waves is equal to 4e-4. Based on the above results, it can be seen that compared with the acousto-optic modulation efficiency of the traditional Rayleigh surface acoustic wave scheme, the acousto-optic modulation efficiency of the present invention can achieve an improvement of more than one order of magnitude.

[0052] The modulated TE1 signal then passes through the asymmetric directional coupler unit to separate the modulated light TE1 from the input TE0 light, achieving single-sideband modulation. The asymmetric directional coupler includes a multimode waveguide 7, a second tapered waveguide 16, a coupling narrow waveguide 18, an S-shaped bend waveguide 19, a third tapered waveguide 20, an output first single-mode waveguide 17, and an output second single-mode waveguide 21. By setting the width of the coupling narrow waveguide 18, the effective refractive index of the TE1 mode propagating in the multimode waveguide 7 can be made equal to the effective refractive index of the TE0 mode in the coupling narrow waveguide 18, thus satisfying the phase-matching condition for waveguide coupling. At this point, the modulated light TE1 mode is completely converted into the fundamental mode TE0 light in the coupling narrow waveguide 18, then passes through the S-shaped bend waveguide 19 and the third tapered waveguide 20, and finally enters the output second single-mode waveguide 21, realizing the output of the modulated light. On the other hand, the unmodulated TE0 light cannot be converted to the narrow waveguide 18 because it does not meet the phase matching condition for waveguide coupling. Therefore, it continues to propagate in the multimode waveguide 7, passes through the second tapered waveguide 16 and the first single-mode waveguide 17 at the output end, and is finally output from the chip. The asymmetric directional coupler unit completes the independent channel output of modulated and unmodulated light, realizing the function of single-sideband acousto-optic modulation on the thin-film lithium niobate chip.

[0053] like Figure 4 As shown, the spacing between the multimode waveguide 7 and the output narrow waveguide 18 is d, set to 400nm~700nm, and the coupler length L c The width range is 20μm to 40μm. Based on the width range of the multimode waveguide 7, the waveguide width range of the coupled narrow waveguide 18 is 0.5μm to 0.8μm. Through the parameter optimization design of the above asymmetric directional coupler unit, a high extinction ratio output of the modulated light can be achieved.

[0054] In summary, this invention proposes a single-sideband acousto-optic modulator driven by a horizontal shear surface acoustic wave (SAW) based on a thin-film lithium niobate / SiO2 / Si platform. This device includes an intermodal acousto-optic modulation unit and an asymmetric directional coupler unit. The intermodal AAW modulation unit primarily performs high-efficiency acousto-optic modulation, while the asymmetric directional coupler unit functions as a single-sideband signal separation and output unit with a high extinction ratio. The main advantages of this invention are: (1) Based on the high electromechanical coupling coefficient of the horizontal shear SAW, high-bandwidth acousto-optic modulation can be achieved, with its RF bandwidth increasing by 5 times compared to the traditional Rayleigh SAW scheme; (2) Based on the highly localized sound field distribution of the horizontal shear SAW, high-modulation-efficiency on-chip acousto-optic modulation can be achieved, with its modulation efficiency increasing by at least one order of magnitude compared to the traditional Rayleigh SAW; (3) By using an on-chip integrated intermodal AAW modulation unit and a high-extinction-ratio asymmetric directional coupler, the modulated light can be output independently, achieving the effect of single-sideband modulation and exhibiting higher integration. The on-chip acousto-optic modulation device proposed in this invention has the advantages of high integration, high bandwidth, and high modulation efficiency. At the same time, it has unique advantages in terms of process compatibility, stability, and scalability, and is expected to lay the foundation for the practical application of thin-film lithium niobate acousto-optic modulators.

Claims

1. A thin-film lithium niobate acousto-optic modulator, comprising, from bottom to top, a silicon substrate, a silicon dioxide buried oxide layer, and a thin-film lithium niobate layer, characterized in that, The tangential orientation of the thin-film lithium niobate layer is YX, meaning the normal direction of the device surface is along the crystal's Y-axis, and the propagation direction of the horizontal shear surface acoustic wave is along the crystal's X-axis. The thin-film lithium niobate layer integrates an intermodal acousto-optic modulation unit and an asymmetric directional coupler unit. The intermodal acousto-optic modulation unit modulates the optical field using horizontal shear surface acoustic waves. The intermodal acousto-optic modulation unit includes a horizontal shear wave acoustic resonator, an input single-mode optical waveguide, a first tapered waveguide, and a multimode optical waveguide. The horizontal shear wave acoustic resonator incorporates interdigital transduction. The device, electrodes connected to an external radio frequency circuit, and Bragg reflection gratings evenly spaced on both sides are used to convert the external microwave electrical signal into a horizontal shear acoustic wave propagating within a thin-film lithium niobate layer, and to achieve intermodal optical field modulation based on the photoelastic effect and second-order electro-optic effect; the asymmetric directional coupler unit includes a multimode optical waveguide, a coupling narrow waveguide, an S-shaped curved waveguide, a second tapered waveguide, a third tapered waveguide, a first single-mode optical waveguide at the output end, and a second single-mode optical waveguide at the output end, used to separate the modulated optical signal and output a single-sideband modulated signal.

2. The thin-film lithium niobate single-sideband acousto-optic modulation device according to claim 1, characterized in that, The interdigital transducer and the Bragg grating have electrodes made of Al, Cu, or Au, with an electrode thickness of 100 nm to 500 nm; an electrode width of 372.5 nm to 497.5 nm; and a horizontal shear acoustic wavelength λ of 1.49 µm to 1.99 µm. The number of electrode pairs in the interdigital transducer is 20 to 100; and the number of periods N in the Bragg grating is... g The aperture width of the interdigital transducer and the Bragg grating is set to (20~40)λ; the distance between the interdigital transducer and the Bragg grating is nλ, where n is an integer, to satisfy the single-mode condition of the surface acoustic wave resonator.

3. The thin-film lithium niobate single-sideband acousto-optic modulation device according to claim 2, characterized in that, The waveguide width of the input single-mode waveguide is 0.5µm to 1µm; the waveguide width of the multimode waveguide is 1.5µm to 2µm; the first tapered waveguide connects the single-mode waveguide and the multimode waveguide, and the etching tilt angle of the three waveguides ranges from 65° to 90°, with an etching depth of 1 / 2 the thickness of the thin film lithium niobate.

4. The thin-film lithium niobate single-sideband acousto-optic modulation device according to claim 1, characterized in that, The multimode optical waveguide is connected to the first single-mode optical waveguide at the output end through the second tapered waveguide. The coupling narrow waveguide, S-shaped curved waveguide, third tapered waveguide and the second single-mode optical waveguide at the output end are connected in sequence to realize the separate output of modulated light and unmodulated light.

5. The thin-film lithium niobate single-sideband acousto-optic modulation device according to claim 4, characterized in that, The waveguide width of the coupled narrow waveguide and the S-shaped curved waveguide is 0.5µm to 0.8µm; the waveguide width of the first single-mode optical waveguide and the second single-mode optical waveguide at the output end is 0.5µm to 1µm; the etching tilt angle of the coupled narrow waveguide, the S-shaped curved waveguide, the second tapered waveguide, the third tapered waveguide, the first single-mode optical waveguide at the output end, and the second single-mode optical waveguide at the output end ranges from 65° to 90°, and the etching depth is 1 / 2 of the thickness of the thin film lithium niobate.

6. The thin-film lithium niobate single-sideband acousto-optic modulation device according to claim 1, characterized in that, The silicon substrate is single-crystal silicon with a thickness of 300µm to 700µm; the silicon dioxide buried oxide layer has a thickness of 2µm to 4.7µm; the thin film lithium niobate has a thickness of 300nm to 900nm, and its surface normal is along the crystal Y-axis, while the horizontal shear acoustic wave propagation direction is along the crystal X-axis.

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