A subwavelength acoustic waveguide-enhanced acousto-optic modulator

Abstract

The present invention discloses an acousto-optic modulator enhanced by a subwavelength acoustic waveguide, which relates to the field of integrated optical technology; the substrate comprises a sapphire substrate and a silicon dioxide layer arranged on the sapphire substrate, a lithium niobate film is arranged on the substrate, the lithium niobate film comprises an etched transduction region, a subwavelength acoustic waveguide, an acousto-photonic crystal cavity and a side-coupled photonic crystal; an interdigital transducer is arranged on the transduction region, the subwavelength acoustic waveguide is coupled to the transduction region through an etched conical transition region, the acousto-photonic crystal cavity is directly coupled to the subwavelength acoustic waveguide, and is coupled to the optical waveguide side. The present invention uses a non-suspended subwavelength acoustic waveguide to drive a suspended acousto-photonic crystal cavity, which can simultaneously excite a Love-like acoustic wave mode and a Rayleigh-like acoustic wave mode of a strongly bound state, significantly improving the modulation efficiency and conversion efficiency of the acousto-optic modulator. At the same time, the device has a simple preparation process and has broad application prospects in the field of signal processing.

Description

Technical Field

[0001] The invention relates to the technical field of integrated optics, and in particular to an acousto-optic modulator enhanced by a sub-wavelength acoustic waveguide. Background Art

[0002] High-performance acousto-optic modulators play an important role in the conversion of microwaves to light waves. They control the light field by changing the refractive index of the medium through phonon-photon interaction. With the explosive growth of information communication, higher requirements are put forward for acousto-optic control devices in terms of the frequency band of light wave use, modulation rate, acousto-optic conversion efficiency and electrical power consumption. However, due to the size and physical properties of the acousto-optic material, the conversion efficiency of traditional acousto-optic control devices is not satisfactory. Integrated acousto-photonic crystal cavity provides a very important structural prototype for efficient microwave to light wave conversion in quantum information processing. Similar to photonic integrated circuits, phononic integrated circuits provide a localized way for phonons and photons to interact. The enhancement of on-chip phonon-photon interaction further promotes the development of microwave to light wave conversion and quantum information processing. As a representative platform, acousto-photonic crystals play an important role in studying photon and phonon resonance. Based on the electrostrictive effect, suspended thin film silicon was first used to make acousto-photonic crystal cavity. Due to its relatively large refractive index, silicon waveguides can well confine photons in acousto-photonic crystal cavity, thereby obtaining a higher optomechanical coupling rate. However, the lack of piezoelectric effect has hindered the development of suspended thin film silicon platforms in microwave to light wave conversion applications. The commonly used method is to design an acoustic suspension cavity under the crystal cavity, and induce acoustic resonance in the cavity by means of optomechanical vibration. However, this method requires a relatively strict optical Q value of transmission, usually above 10^7, and has strict requirements on actual processes, making it extremely difficult to manufacture. How to effectively achieve acoustic wave coupling and acoustic resonance mode excitation in the same material platform has attracted extensive research.

[0003] In recent years, lithium niobate materials have attracted widespread attention in the industry due to their outstanding electro-optical, nonlinear optical, acousto-optic, piezoelectric, photorefractive, pyroelectric and photoconductive properties. It has been reported that the interdigital transducer is designed to excite surface acoustic waves by combining the piezoelectric properties of lithium niobate, and the surface perturbation is used to couple the surface acoustic wave into the acousto-photonic crystal cavity. However, this method requires harsh coupling conditions and the acoustic wave has high loss when it is transmitted on the surface. Another method is to couple the acoustic mode to a mechanical waveguide at a subwavelength scale and couple it to the acousto-photonic crystal cavity. This method greatly improves the coupling efficiency of the acoustic wave, but the device needs to be suspended as a whole to obtain a better acoustic bound state, the working mode is complex, the conversion efficiency of microwaves to light waves is limited, and the device preparation process is harsh. At present, no researchers have used subwavelength acoustic waveguides on non-suspended platforms to couple the acousto-photonic crystal cavity. The differences in the acousto-photonic crystal cavity determine different mechanical coupling conditions, which requires strict design of the interdigital transducer and the acoustic waveguide to match the phonon energy band of the acousto-photonic crystal cavity. Therefore, it is of great practical significance to design an acousto-photonic crystal cavity that is insensitive to mechanical coupling conditions and has a wide range of working conditions. Summary of the invention

[0004] The purpose of the present invention is to provide a subwavelength acoustic waveguide enhanced acousto-optic modulator, which gives full play to the excellent piezoelectric effect and elasto-optic effect of lithium niobate, combines the contribution of sapphire substrate to surface acoustic wave-like bound states, utilizes local acoustic resonance and optical resonance to enhance the intensity of acousto-optic interaction, and improves the conversion efficiency of microwaves to light waves.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A sapphire-silicon dioxide substrate is used, the substrate includes a sapphire substrate and a silicon dioxide layer arranged on the sapphire substrate, a lithium niobate film is arranged on the substrate, the lithium niobate film includes an etched transduction area, a tapered transition area, a subwavelength acoustic waveguide, an acousto-photonic crystal cavity and a side-coupled photonic crystal, an interdigital transducer is arranged on the transduction area, the subwavelength acoustic waveguide is connected to the transduction area through the etched tapered lithium niobate, the acousto-photonic crystal cavity is connected to a non-suspended subwavelength acoustic waveguide, and is parallel to the suspended side-coupled photonic crystal.

[0007] Furthermore, the interdigital transducer, the tapered transition zone and the subwavelength acoustic waveguide are in a non-suspended state relative to the substrate, and the acousto-photonic crystal cavity and the side-coupled photonic crystal are in a suspended state relative to the substrate.

[0008] Furthermore, the subwavelength acoustic waveguide guides a basic surface acoustic wave-like mode, the contrast between the sound velocity of the waveguide material and the sapphire substrate is large, the surface acoustic wave-like mode volume is smaller, and the surface acoustic wave-like is mainly confined in the lithium niobate waveguide.

[0009] Furthermore, the size of the subwavelength acoustic waveguide is smaller than the wavelength of the sound wave propagating therein, and the width of the acousto-photonic crystal cavity is consistent with the width of the subwavelength acoustic waveguide, which is 800nm ​​to 2500nm. The overall device uses the bent subwavelength acoustic waveguide to match the optimization results of the piezoelectric effect and the elasto-optic effect in their respective directions, with a bending angle of 0° to 90° and a bending radius generally greater than 20 sound wave wavelengths.

[0010] Furthermore, the thickness of the acousto-photonic crystal cavity and the side-coupled photonic crystal is consistent with that of the subwavelength acoustic waveguide, and better optomechanical properties are shown in that the lattice constant of the acousto-photonic crystal is 300nm-600nm, the major axis is 400nm-1000nm, and the minor axis is 100nm-500nm. The acousto-photonic crystal cavity is formed by an air hole with a regular etching change of a suspended straight waveguide with the same height and width as the subwavelength acoustic waveguide; the air hole is divided into a defect area in the middle and mirror areas on both sides; the defect area is used to limit resonance, and the mirror area is used for reflection and enhanced resonance; the number of defect area units is 15-60, and the number of mirror area units is 15-60, and the better light wave coupling effect is shown in that the lattice constant of the side-coupled photonic crystal is 150nm-400nm, the major axis is 200nm-600nm, and the minor axis is 80nm-400nm.

[0011] Furthermore, the tangent direction of the lithium niobate film is XY for the IDT, the width of the transducer region is 2 μm to 20 μm, the finger width of the IDT is 0.2 μm to 5 μm, the number of finger pairs is 20 to 100 pairs, and the IDT can achieve 300 MHz to 8 GHz Rayleigh-like modes and Love-like modes excitation.

[0012] Furthermore, the thickness of the lithium niobate film is 200nm to 500nm, the thickness of the silicon dioxide layer in the sapphire silicon dioxide substrate is 500nm to 2000nm, and at a certain microwave operating frequency, the mirror area of ​​the subwavelength acoustic waveguide and the acousto-photonic crystal cavity always has mode band lines that can characterize stable forward transmission of Love-like waves and shear-like waves.

[0013] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0014] The sub-wavelength acoustic waveguide enhanced acousto-optic modulator provided by the present invention is arranged on a sapphire-silicon dioxide substrate and consists of an interdigital transducer, a tapered transition zone, a sub-wavelength acoustic waveguide and an acousto-photonic crystal cavity;

[0015] First, sapphire is used as the substrate material and XY lithium niobate film is used as the piezoelectric material. The large contrast in sound velocity between sapphire, lithium niobate and silicon dioxide is utilized. While obtaining the effective surface acoustic wave mode volume, the interdigital transducer can excite Love-like waves or pure Rayleigh-like waves as working modes. Both have high microwave-to-acoustic wave conversion efficiency. The acoustic waveguide designed based on this substrate has a stronger ability to bind acoustic waves.

[0016] Second, a curved non-suspended subwavelength acoustic waveguide is used to adjust the lithium niobate tangent to X-(θ)Y, and a suspended acousto-photonic crystal cavity is connected at its end to make full use of the excellent elasto-optic effect of lithium niobate in this tangent direction.

[0017] Third, the optimized acousto-photonic crystal cavity is insensitive to the coupling conditions of acoustic waves, has a wide range of working conditions, and can be driven to resonate by various types of IDTs, including but not limited to focusing IDT, unidirectional IDT, unidirectional focusing IDT and the general IDT introduced in the present invention.

[0018] Fourth, the basic surface acoustic wave-like method is used to stimulate the acoustic resonance of the acousto-photonic crystal cavity. Compared with the method of using suspended high-order acoustic wave modes, this method has higher conversion efficiency and working stability. At the same time, the designed side-coupled photonic crystal is used to stimulate the optical resonance of the acousto-photonic crystal cavity. The working mode of simultaneous resonance of photons and phonons is much better than the form of traveling wave interaction in terms of the intensity of acousto-optic interaction. In addition, the proposal of this scheme will provide new ideas for the development of ultra-efficient acousto-optic modulators.

[0019] The above-mentioned acousto-optic modulator has high modulation efficiency, strong acousto-optic interaction, and broad application prospects. In addition, topological acousto-photonic crystals can be used to further limit the mode volume, strengthen the local effect, and obtain good anti-defect capability. The acousto-photonic crystal modulator designed based on topological ideas is expected to have new breakthroughs in conversion efficiency and acousto-optic interaction strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 It is a cross-sectional view of the sub-wavelength acoustic waveguide in Embodiments 1 and 2 of the present invention;

[0022] Figure 2 Schematic diagram of the top view of the acousto-photonic crystal cavity in Embodiments 1 and 2 of the present invention;

[0023] Figure 3 Schematic diagram of the top view of the structure of the sub-wavelength acoustic waveguide enhanced acousto-optic modulator in embodiments 1 and 2 of the present invention.

[0024] Explanation of the reference numerals: 1. sapphire substrate; 2. silicon dioxide layer; 3. lithium niobate film; 4. defect region; 5. mirror region; 6. interdigital transducer; 7. tapered transition region; 8. subwavelength acoustic waveguide; 9. acousto-photonic crystal cavity; 10. side-coupled photonic crystal. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The purpose of the present invention is to provide an acousto-optic modulator enhanced by a subwavelength acoustic waveguide, which comprehensively utilizes the smaller volume of the surface acoustic wave mode on the sapphire substrate, maintains the higher electromechanical coupling coefficient and the easier excitation of the Love wave-like characteristics of the XY lithium niobate, and can also select the Rayleigh wave as the working mode, and couples the acoustic wave excited by the interdigital transducer 6 into the subwavelength acoustic waveguide 8 through the conical region, and uses the curved waveguide to deflect the acoustic wave to X-(θ)Y, and the acoustic wave confined by the subwavelength acoustic waveguide 8 further excites the acoustic resonance of the acousto-photonic crystal cavity 9, and the side-coupled photonic crystal 10 uses the light wave incident on the end face to excite the optical resonance of the acousto-photonic crystal. Finally, the acoustic resonance and the optical resonance interact with each other, combined with the characteristics of the high elastic-optic effect of the X-(θ)Y tangential lithium niobate, the invention first solves the problem of the coupling of the surface acoustic wave-like subwavelength acoustic waveguide 8, and secondly solves the problem of the weak acoustic wave excited by the interdigital transducer 6 and the low coupling efficiency, and finally solves the problem of the weak interaction intensity between the acoustic wave and the light wave of the traditional acousto-optic modulator.

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] like Figures 1 to 3 As shown, the present invention provides a subwavelength acoustic waveguide enhanced acousto-optic modulator, comprising: a substrate, the substrate comprising a sapphire substrate 1, and a silicon dioxide layer 2 arranged on the sapphire substrate 1, and a lithium niobate film 3 is arranged on the substrate, such as Figure 1; A transducing region is etched on the lithium niobate film 3, and an interdigital transducer 6 is arranged on the transducing region; it also includes a subwavelength acoustic waveguide 8, an acousto-photonic crystal cavity 9 and a side-coupled photonic crystal 10; the subwavelength acoustic waveguide 8 is connected to the transducing region through a conical transition region 7, and the conical transition region 7 is formed by etched conical lithium niobate; the acousto-photonic crystal cavity 9 is connected to the subwavelength acoustic waveguide 8, and the acousto-photonic crystal cavity 9 is parallel to the side-coupled photonic crystal 10, such as Figure 3 .

[0029] The transducer region, the tapered transition region 7, the subwavelength acoustic waveguide 8, and the acousto-photonic crystal cavity 9 are all etched from the same lithium niobate film 3. The sapphire substrate 1 is made of sapphire, and the silicon dioxide layer 2 disposed on the sapphire substrate 1 is made of silicon dioxide.

[0030] Specifically, the interdigital transducer 6, the subwavelength acoustic waveguide 8 and the tapered transition zone 7 are all in a non-suspended state relative to the substrate, and the acousto-photonic crystal cavity 9 and the side-coupled photonic crystal 10 are in a suspended state relative to the substrate.

[0031] For example, Figure 2 The acousto-photonic crystal cavity 9 is formed by an air hole with a suspended straight waveguide of equal height and width to the subwavelength acoustic waveguide 8 and with a regular etching pattern. The air hole is divided into a defect region 4 (in the middle) and a mirror region 5 (on both sides). The defect region 4 is used to limit the resonance, and the mirror region 5 is used for reflection and enhanced resonance. Generally, the number of holes in the defect region 4 is 15 to 60, and the number of holes in the mirror region 5 is 15 to 60. By designing the lattice constant, major axis and minor axis of the hole, the optical resonance wavelength can be adjusted to 1450nm to 1600nm, and the acoustic resonance frequency can be adjusted to 0.5GHz to 5GHz. In addition, the lattice constant, major axis and minor axis of the air hole are distributed in the defect region 4 according to a quadratic law. The suspended acousto-photonic crystal cavity 9 needs to etch the silicon dioxide layer 2 in contact with the lithium niobate film 3, exposing the sapphire substrate 1 to the air. The acoustic resonance mode here is more specifically called the breathing mode, and its vibration type is alternating between contraction and relaxation. Thanks to the suspension structure, this vibration can occur very strongly.

[0032] The side-coupled photonic crystal 10 is etched with air holes to form a mirror reflection area, and the acousto-photonic crystal cavity 9 can obtain the opportunity of coupling the incident wave and the reflected wave twice, and the air holes can increase the scattering and enhance the evanescent field, thereby improving the coupling efficiency.

[0033] The width of the transducer zone should not be set too wide, because the Rayleigh-like waves and Love-like waves excited by such a wide transducer zone are not easy to couple with the subwavelength acoustic waveguide 8; similarly, the width of the transducer zone should not be too narrow, because such a narrow transducer zone is not easy to achieve impedance matching of microwaves, resulting in low conversion efficiency of microwaves to sound waves.

[0034] In particular, the quasi-surface acoustic wave excited by the interdigital transducer 6 here is similar to the surface acoustic wave, both of which propagate on the surface of the medium. The difference is that since the subwavelength acoustic waveguide 8 can achieve a strong bound state for the sound wave, the quasi-surface acoustic wave is used to distinguish the guided propagating sound wave in the bound state from the diffusive surface acoustic wave that propagates in a single direction.

[0035] It cannot be ignored that the complete mediated surface acoustic wave is used to excite acoustic resonance, which requires the matching of dispersion curves (band lines) in the entire propagation path of the acoustic wave. The acoustic resonance frequency of the acousto-photonic crystal cavity 9 can also be inferred through the band lines.

[0036] The tangent direction of the lithium niobate film 3 is XY or X-(θ)Y, and the high electromechanical coupling coefficient of lithium niobate in the XY tangent direction is used to improve the conversion efficiency of microwaves to sound waves, and at the same time, relatively pure Love-like waves and pure Rayleigh-like waves are obtained. Among them, X-(θ)Y means that the sound wave propagates along the X-axis of the lithium niobate crystal in a direction rotated by θ degrees in the counterclockwise direction along the Y-axis of the crystal; conversely, the clockwise direction is negative θ degrees, which is expressed as X-(-θ)Y, and θ is generally 30° to 90°.

[0037] The thickness of the lithium niobate film 3 is 200nm-500nm, the width of the transducer zone is 2μm-20μm, the finger width of the interdigital transducer 6 is 0.2μm-5μm, the number of interdigital pairs is 20-100 pairs, and the interdigital transducer 6 can achieve the excitation of 300MHz-8GHz Rayleigh-like waves and Love-like waves; the size of the subwavelength acoustic waveguide 8 is smaller than the wavelength of the working acoustic wave, its thickness is consistent with the transducer zone, and its width is 800nm-2500nm; the acousto-photonic crystal cavity 9 and the side-coupled photonic crystal 10 The thickness is consistent with the subwavelength acoustic waveguide 8. The better optomechanical properties are shown in that the lattice constant of the acousto-photonic crystal is 300nm~600nm, the major axis is 400nm~1000nm, the minor axis is 100nm~500nm, the number of units in the defect area 4 is 15~60, and the number of units in the mirror area 5 is 15~60. The better light wave coupling effect is shown in that the lattice constant of the side-coupled photonic crystal 10 is 150nm~400nm, the major axis is 200nm~600nm, and the minor axis is 80nm~400nm.

[0038] The working principle of the sub-wavelength acoustic waveguide enhanced acousto-optic modulator is:

[0039] Based on the inverse piezoelectric coupling effect of the lithium niobate film 3, the input microwave modulation signal is converted into a surface acoustic wave signal of the lithium niobate film 3 through the interdigital transducer 6, so that the lithium niobate film 3 has a mechanical strain field distribution, and the mechanical acoustic wave generated on the surface of the lithium niobate film 3 is further coupled with the subwavelength acoustic waveguide 8 through the conical transition zone 7. The acoustic wave type here is specifically the basic Rayleigh wave and Love wave, which is a transverse wave type of acoustic wave, and the vibration direction is perpendicular to the propagation direction of the acoustic wave. Further, the acoustic wave coupled into the subwavelength acoustic waveguide 8 can be well guided, and then coupled into the acousto-photonic crystal cavity 9, thereby causing the acoustic resonance of the acousto-photonic crystal cavity 9. For the optical mode, the incident light wave is coupled into the defect area 4 of the acousto-photonic crystal cavity 9 through the side-coupled photonic crystal 10 to generate optical resonance. Due to the photoelastic effect, the deformation of the acoustic resonance greatly changes the refractive index of the acousto-photonic crystal cavity 9. At this time, the sound and light interact with each other, and the optical resonance carries the acoustic wave signal, that is, carries the modulation signal, thereby completing the acousto-optic modulation.

[0040] Embodiment 1:

[0041] like Figure 3 As shown, in the first embodiment, a non-suspended sub-wavelength acoustic waveguide 8 enhanced acousto-optic modulator working at a microwave frequency of 1.5 GHz is provided, which mainly includes an interdigital transducer 6, a tapered transition zone formed by etching a lithium niobate film 3, a sub-wavelength acoustic waveguide 8 and an acousto-photonic crystal cavity 9. The width of the transducer region where the interdigital transducer 6 is located is about 4.5 μm, and the transducer period is about 2.7 μm, which can excite Rayleigh-like waves near 1.5 GHz. Furthermore, the sub-wavelength acoustic waveguide 8 is about 1.4 μm wide, the bending angle θ is 45°, the lattice constant of the acousto-photonic crystal cavity 9 is 520 nm, the major axis is 700 nm, and the minor axis is 300 nm. The lattice constant of the side-coupled photonic crystal 10 is 450 nm, the major axis is 500 nm, and the minor axis is 200 nm. Finally, optical resonance will be generated at a wavelength of 1562 nm, and acoustic resonance will occur at 1.5 GHz.

[0042] Embodiment 2:

[0043] like Figure 3As shown, in the first embodiment, a non-suspended sub-wavelength acoustic waveguide 8 enhanced acousto-optic modulator working at a microwave frequency of 1.55 GHz is provided, which mainly includes an interdigital transducer 6, a conical transition zone 7 etched from a lithium niobate film 3, a sub-wavelength acoustic waveguide 8 and an acousto-photonic crystal cavity 9. The width of the transducer region where the interdigital transducer 6 is located is about 8.3 μm, and the transducer period is about 2.05 μm, which can excite Love-like waves near 1.5 GHz. Furthermore, the width of the sub-wavelength acoustic waveguide 8 is about 1.5 μm, the bending angle θ is 40°, the lattice constant of the acousto-photonic crystal cavity 9 is 500 nm, the major axis is 800 nm, and the minor axis is 400 nm, the lattice constant of the side-coupled photonic crystal 10 is 450 nm, the major axis is 600 nm, and the minor axis is 300 nm, which will eventually produce optical resonance at a wavelength of 1543 nm and acoustic resonance at 1.55 GHz.

[0044] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A subwavelength acoustic waveguide enhanced acousto-optic modulator, characterized in that: The invention comprises a substrate, wherein the substrate comprises a sapphire substrate (1) and a silicon dioxide layer (2) arranged on the sapphire substrate (1); a lithium niobate film (3) is arranged on the substrate; the lithium niobate film (3) comprises an etched transduction region, a conical transition region (7), a subwavelength acoustic waveguide (8), an acousto-photonic crystal cavity (9), and a side-coupled photonic crystal (10); an interdigital transducer (6) is arranged on the transduction region; the subwavelength acoustic waveguide (8) is connected to the transduction region via the etched conical transition region (7); the acousto-photonic crystal cavity (8) is connected to a non-suspended subwavelength acoustic waveguide (8) and is parallel to the suspended side-coupled photonic crystal (10); The interdigital transducer (6), the tapered transition zone (7) and the subwavelength acoustic waveguide (8) are in a non-suspended state relative to the substrate; the acousto-photonic crystal cavity (9) and the side-coupled photonic crystal (10) are in a suspended state relative to the substrate; The acousto-photonic crystal cavity (9) is formed by an air hole with a suspended straight waveguide having the same height and width as a subwavelength acoustic waveguide (8) and having an etching pattern that varies; the air hole is divided into a defect region (4) in the middle and mirror regions (5) on both sides; the defect region (4) is used to limit resonance, and the mirror region (5) is used to enhance resonance through reflection.

2. The subwavelength acoustic waveguide enhanced acousto-optic modulator according to claim 1, characterized in that: The acoustic mode in the subwavelength acoustic waveguide (8) is a bound-state surface acoustic wave-like mode.

3. The subwavelength acoustic waveguide enhanced acousto-optic modulator according to claim 1, characterized in that: The widths of the subwavelength acoustic waveguide (8) and the acousto-photonic crystal cavity (9) are 300 nm to 3000 nm; the angle of the subwavelength acoustic waveguide (8) is 0° to 90°, and the bending radius is greater than 20 acoustic wavelengths.

4. The subwavelength acoustic waveguide enhanced acousto-optic modulator according to claim 1, characterized in that: The lattice constant of the acousto-photonic crystal cavity (9) is 200nm-600nm, the long axis is 400nm-1000nm, the short axis is 100nm-500nm, the number of units in the defect region (4) is 15-60, and the number of units in the mirror region (5) is 15-60; a photonic crystal structure exists in the side-coupled photonic crystal (10), wherein the lattice constant of the photonic crystal is 150nm-400nm, the long axis is 200nm-600nm, and the short axis is 80nm-400nm.

5. The subwavelength acoustic waveguide enhanced acousto-optic modulator according to claim 1, characterized in that: The tangent direction of the lithium niobate film (3) with respect to the interdigital transducer (6) is XY, the width of the transducer region is 2 μm to 20 μm, the finger width of the interdigital transducer (6) is 0.2 μm to 5 μm, the number of interdigital pairs is 20 to 300 pairs, and the interdigital transducer (6) is used to achieve the excitation of 300 MHz to 8 GHz Rayleigh-like waves and Love-like waves.

6. A sub-wavelength acoustic waveguide enhanced acousto-optic modulator according to any one of claims 1 to 5, characterized in that: The thickness of the lithium niobate film (3) is 200 nm to 600 nm, and the thickness of the silicon dioxide layer (2) in the substrate is 500 nm to 2000 nm.

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