A suspended collinear scandium-doped aluminum nitride acousto-optic modulator and a preparation method thereof

Abstract

The application provides a suspended collinear scandium-doped aluminum nitride acousto-optic modulator and a preparation method thereof, and relates to the technical field of piezoelectric acousto-optic devices. The acousto-optic modulator comprises Si layers, SiO2 layers and AlScN layers which are sequentially stacked from bottom to top. The AlScN layers are partially etched to form a waveguide structure. The surface of the AlScN layer on the side of the waveguide structure is provided with a focusing interdigital transducer. The input end and the output end of the waveguide structure are respectively provided with optical coupling structures. Nano holes are formed in the AlScN layer. Part of the SiO2 layer below the waveguide structure is removed to form a suspended structure. In the application, the AlScN simultaneously serves as a piezoelectric material and an optical waveguide material. The focusing interdigital transducer excites acoustic waves propagating along the waveguide direction to co-propagate with light waves. Under the action of the suspended structure for enhancing the constraint of the acoustic field, efficient acousto-optic coupling and optical mode conversion are realized.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric acoustic wave device technology, and in particular to a suspended collinear scandium-doped aluminum nitride acousto-optic modulator and its preparation method. Background Technology

[0002] An acousto-optic modulator is a device that uses an external electrical signal to excite sound waves, and then uses the refractive index perturbation, boundary perturbation, and accompanying electric field perturbation caused by the sound waves to modulate the intensity, phase, frequency, or mode of light waves. Traditional bulk acousto-optic devices mostly use bulk materials such as quartz and tellurium dioxide (TeO2), resulting in large device sizes and separation of the driving structure from the optical path structure. With the development of integrated photonics, on-chip acousto-optic modulation based on thin-film waveguides has become an important research direction, especially with significant application value in scenarios such as optical communication, microwave photonics, on-chip frequency shifting, mode conversion, and mode multiplexing.

[0003] Currently, on-chip acousto-optic modulators mainly fall into the following technical categories: From a materials perspective, existing on-chip acousto-optic modulators mainly include heterogeneous integration schemes combining non-piezoelectric integrated photonic platforms such as silicon (Si) or silicon nitride (SiN) with an external piezoelectric layer, as well as intrinsic piezoelectric photonic platforms such as lithium niobate (LN), aluminum nitride (AlN), gallium nitride (GaN), and scandium-doped aluminum nitride (AlScN). Si and SiN platforms have mature fabrication processes and low optical losses, but the materials themselves do not possess piezoelectric properties, requiring the additional integration of piezoelectric thin films such as AlN, AlScN, zinc oxide (ZnO), or lead zirconate titanate (PZT) to excite acoustic waves. In these schemes, the piezoelectric layer is responsible for electroacoustic conversion, while the optical waveguide is located in another material layer. Compared to optical mode fields confined to the subwavelength range, the acoustic energy distribution space is larger, and the overlap between the acoustic and optical fields is limited. Furthermore, the heterogeneous integration fabrication process is complex, and issues such as interface stress, thermal expansion mismatch, and acoustic scattering losses may arise.

[0004] Thin-film lnular nanotubes (LN) possess low optical loss and significant piezoelectric and electro-optic effects, making them an important material system for on-chip acousto-optic devices. Suspended thin-film LN waveguides have been used to achieve collinear acousto-optic mode conversion, and their high acoustic and optical field confinement significantly improves acousto-optic coupling strength. However, the high cost of LN wafers and low-cost, large-scale fabrication remain factors limiting their further widespread adoption.

[0005] GaN platforms possess high refractive index, piezoelectricity, and strong power handling capabilities. Existing GaN-on-sapphire acousto-optic modulators utilize the differences in optical and acoustic properties between GaN and sapphire to achieve co-constraint of optical and acoustic fields in non-suspended structures, and through TE... 00 With TE 10Intermodulation switching enables efficient acousto-optic modulation. This work demonstrates that the key to improving on-chip acousto-optic modulation efficiency lies not only in the piezoelectricity of the material itself, but also in acousto-optic co-constraint, phase matching, and long-distance collinear interactions. However, the fabrication process of GaN materials is difficult to integrate with silicon-based CMOS platforms.

[0006] AlN platforms offer wide transparency windows, good thermal stability, and CMOS process compatibility, allowing them to be used as both piezoelectric and optical waveguide materials, thus making them widely applicable in on-chip acousto-optic devices. However, pure AlN has limited piezoelectric and electromechanical coupling coefficients, resulting in insufficient electroacoustic conversion efficiency. This often necessitates higher RF drive power, longer interaction lengths, or resonant enhancement structures, which limits device miniaturization, bandwidth, and system integration capabilities.

[0007] Compared to pure AlN, AlScN, by introducing Sc elements into the AlN lattice, significantly improves the piezoelectric response and electromechanical coupling capability of the material. Existing research has shown that at higher Sc doping concentrations, AlScN exhibits significantly better piezoelectric performance than AlN, while retaining the wide transparency window and good CMOS process compatibility of nitride materials. Therefore, AlScN is considered a promising material for constructing efficient on-chip acousto-optic devices. For acousto-optic modulators, AlScN's advantage lies in its ability to function as both a piezoelectric transducer to excite acoustic waves and an optical waveguide to transmit optical fields, thus enabling simultaneous electroacoustic conversion, optical field transmission, and acousto-optic interaction within a single material platform.

[0008] From a device structure perspective, existing on-chip acousto-optic modulators can be divided into non-collinear and collinear types. Non-collinear structures typically place interdigital transducers on one side of the optical waveguide, allowing acoustic waves to pass through the waveguide vertically or at an angle. This design is relatively simple, but the acoustic and optical fields only overlap in localized areas, resulting in a short effective interaction length, limited acousto-optic modulation efficiency, and low mode conversion efficiency. When improving modulation efficiency, it is usually necessary to increase RF power or acousto-optic coupling length, leading to problems such as excessive power consumption and device size.

[0009] In a collinear structure, sound waves and light waves propagate in the same direction. Compared to non-collinear structures, collinear structures allow the sound and light fields to overlap over a longer waveguide range, thus extending the effective interaction length. Optical mode conversion efficiency can accumulate along the propagation direction, making it easier to achieve higher modulation efficiency with the same driving power. For inter-mode acousto-optic modulation, collinear structures also offer a clear momentum matching advantage. The input optical mode can be converted to another order optical mode when the phase-matching condition is met, accompanied by a frequency shift. Therefore, collinear structures can not only achieve ordinary phase modulation but are also more suitable for realizing TE modulation. 00 –TE 10Complete mode conversion between different optical modes, on-chip frequency shifting, and non-reciprocal transfer.

[0010] Collinear structures have been achieved on sapphire-based GaN platforms and suspended thin-film LN platforms. For the AlScN-SiO2-Si platform, the low-refractive-index SiO2 cladding layer is beneficial for confining the optical field within the AlScN waveguide core. However, due to the low acoustic velocity of SiO2, acoustic waves easily leak into the substrate, resulting in the acoustic energy not being effectively localized within the optical waveguide region, thus limiting the acousto-optic overlap. Considering that there is currently no cladding material that simultaneously satisfies both high acoustic and optical field constraints and is compatible with silicon-based integrated platforms, forming a local suspended structure in the acousto-optic interaction region can effectively reduce acoustic wave leakage into the substrate while maintaining high optical field confinement. This enhances the confinement of acoustic modes within AlScN and effectively improves the acousto-optic overlap.

[0011] The current problems with on-chip acousto-optic modulators are: ① limitations in cost, compatibility, and flexibility in manufacturing processes; ② the performance of acousto-optic coupling strength and optical conversion efficiency needs to be improved. Summary of the Invention

[0012] This invention provides a suspended collinear scandium-doped aluminum nitride acousto-optic modulator and its fabrication method, which meets the following three requirements for integrated acousto-optic modulators: ① Thin-film AlScN simultaneously satisfies excellent piezoelectric and optical properties; ② The suspended collinear structure effectively confines the acoustic and optical fields to the same waveguide structure, which can greatly improve the acousto-optic coupling strength and optical conversion efficiency; ③ The fabrication process has high compatibility and flexibility, and is easy to carry out low-cost, large-scale production and integration.

[0013] The purpose of this invention is to solve the problems of existing on-chip acousto-optic modulators: ① in terms of process, there are limitations in cost, compatibility and flexibility; ② in terms of performance, there is a need to improve the acousto-optic coupling strength and optical conversion efficiency.

[0014] This invention utilizes AlScN thin films as both piezoelectric and optical waveguide materials, and its fabrication process is compatible with silicon-based integrated platforms, offering low processing costs and high flexibility.

[0015] This invention employs a collinear structure, enabling the acoustic and optical fields to highly overlap within the AlScN waveguide, thereby enhancing the acousto-optic coupling strength and achieving high optical mode conversion efficiency within a relatively short acousto-optic coupling length.

[0016] This invention employs a focusing interdigital transducer to excite acoustic waves and focuses the acoustic energy into the AlScN waveguide region, causing the acoustic and optical waves to propagate in the same direction within the waveguide. Compared to ordinary interdigital transducers or non-collinear acousto-optic structures, the focusing interdigital transducer is advantageous in increasing the acoustic energy density entering the acousto-optic interaction region, thereby enhancing the acousto-optic interaction.

[0017] The present invention also reduces the leakage of acoustic waves to the substrate and enhances the confinement of the acoustic field in the optical waveguide region by locally removing the SiO2 layer below the acousto-optic interaction region, thereby further improving the acousto-optic mode overlap and modulation efficiency.

[0018] This invention provides a fabrication process for an on-chip suspended collinear AlScN acousto-optic modulator.

[0019] Therefore, the present invention aims to provide an on-chip AlScN acousto-optic modulator structure that combines the advantages of better fabrication process and stronger acousto-optic coupling strength, and provides a corresponding fabrication method, which is suitable for applications such as on-chip optical communication, microwave photonics, mode conversion, frequency shifting and non-reciprocal optical transmission.

[0020] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a suspended collinear aluminum scandium nitride acousto-optic modulator, comprising a Si layer, a SiO2 layer and an AlScN layer stacked sequentially from bottom to top; A portion of the AlScN layer is partially etched to form a waveguide structure, which extends along a straight line. A focusing interdigital transducer is also provided on the AlScN layer. The focusing interdigital transducer is disposed on the surface of the AlScN layer on the side of the waveguide structure. It is used to excite acoustic waves propagating along the extension direction of the waveguide structure, so that the acoustic waves and the optical waves transmitted in the waveguide structure propagate collinearly and undergo acousto-optic interaction, thereby realizing the conversion between different optical modes. The waveguide structure is provided with optical coupling structures at its input and output ends, and the optical coupling structures are used to realize the coupling input and / or coupling output of optical signals between the waveguide structure and the off-chip optical path. The AlScN layer is also provided with nanopores that penetrate the AlScN layer, and the nanopores are located on the outer periphery of the acousto-optic region of the waveguide structure. A portion of the SiO2 layer beneath the waveguide structure is removed, forming a suspended structure located beneath the waveguide structure.

[0021] Preferably, in the above-mentioned suspended collinear scandium-doped aluminum nitride acousto-optic modulator, the optical coupling structure includes an input directional coupler and an output directional coupler; The input directional coupler is disposed on the side of the input end of the waveguide structure and is used to convert TE 00 The mode light is coupled into the acousto-optic region of the waveguide structure; The output directional coupler is disposed on the side of the output end of the waveguide structure and is used to convert the TE signal after acousto-optic modulation. 10 The mode light is coupled and separated from the waveguide structure and output.

[0022] Preferably, in the above-mentioned suspended collinear aluminum scandium nitride acousto-optic modulator, the width of the input directional coupler is 1.2μm~2μm, the coupling spacing is 200nm~800nm, and the coupling length is 3μm~50μm; the width of the output directional coupler is 0.6μm~1μm, the coupling spacing is 200nm~800nm, and the coupling length is 3μm~50μm.

[0023] Preferably, in the above-mentioned suspended collinear scandium-doped aluminum nitride acousto-optic modulator, the optical coupling structure further includes four grating couplers. All four grating couplers are formed on the surface of the AlScN layer. One is located at the input end of the device and connected to the incident waveguide port of the input directional coupler, serving as the vertical input interface for off-chip optical signals. The other three are located at the output end of the device, arranged sequentially along the waveguide transmission direction, and are respectively connected to the through waveguide output of the input directional coupler, the coupled waveguide output of the output directional coupler, and the end through output of the waveguide structure, serving as vertical output interfaces for optical signals with different transmission paths. The duty cycle of the grating coupler is 0.5, and the period is 600nm~1600nm.

[0024] Preferably, in the above-mentioned suspended collinear scandium-doped aluminum nitride acousto-optic modulator, the waveguide structure is a multimode waveguide used to transmit TE signals. 00 Model and TE 10 The mode operates in the C-band; the width of the waveguide structure is 1.2μm~2μm, the bending radius is greater than 100μm, the waveguide height is 300nm~500nm, and the length is 0.1mm~3mm.

[0025] Preferably, in the above-mentioned suspended collinear aluminum scandium nitride acousto-optic modulator, the interdigital angle of the focusing interdigital transducer is 15° to 30°, the number of interdigital pairs is 50 to 120, and the electrode period is 1 μm to 4 μm; the electrode material of the focusing interdigital transducer is AuCr / or Au / Ti.

[0026] Preferably, in the above-mentioned suspended collinear scandium-doped aluminum nitride acousto-optic modulator, the pore size of the nanopore is 500 nm to 2 μm, the nanopore penetrates the AlScN layer and extends to the upper surface of the SiO2 layer, and is used to allow the etching solution to pass through to remove the SiO2 layer below the waveguide structure.

[0027] Preferably, in the above-mentioned suspended collinear aluminum scandium nitride acousto-optic modulator, the Sc doping concentration of the AlScN layer is 0 to 50%, the overall thickness of the AlScN layer is 300 nm to 500 nm, the etching depth of the waveguide structure is 200 nm to 400 nm, the thickness of the SiO2 layer is 3 μm to 6 μm, and the thickness of the Si layer is 725 μm.

[0028] Secondly, the present invention also provides a method for preparing the suspended collinear scandium-doped aluminum nitride acousto-optic modulator as described above, comprising the following steps: Step 1: Provide a Si layer as a substrate, and form a SiO2 layer on the surface of the Si layer; Step 2: Deposit an AlScN layer on the SiO2 layer; Step 3: Pattern and partially etch the AlScN layer to form a waveguide structure extending in a straight line, and form optical coupling structures at the input and output ends of the waveguide structure respectively; Step 4: Patterning, depositing a metal layer, and stripping the metal on the AlScN layer to form a focused interdigital transducer on the surface of the AlScN layer on the side of the waveguide structure; Step 5: Form nanopores penetrating the AlScN layer on the outer periphery of the acousto-optic region of the waveguide structure, introduce etching solution through the nanopores, and laterally etch away the SiO2 layer below the waveguide structure to form a suspended region below the waveguide structure.

[0029] Preferably, in the above preparation method, in step 2, the AlScN layer is deposited using magnetron sputtering, and the Sc doping concentration of the AlScN layer is adjusted by controlling the atomic percentage of Sc and Al in the target material, with the Sc doping concentration being 0 to 50%; in step 3, the AlScN layer is patterned using electron beam lithography or ultraviolet lithography, and partially etched using reactive ion etching and / or inductively coupled plasma etching; in step 5, wet etching is performed using a buffer oxide etchant selective for SiO2.

[0030] The suspended collinear scandium-doped aluminum nitride acousto-optic modulator and its preparation method provided by the present invention have at least the following beneficial effects: (1) The present invention uses AlScN as both a piezoelectric material and an optical waveguide material. The same AlScN thin film layer is partially etched to form a waveguide structure, which simultaneously carries the functions of optical signal transmission and acoustic wave excitation. Compared with AlN, it has a higher piezoelectric response and electromechanical coupling coefficient, which can significantly reduce the driving voltage and driving power consumption. Moreover, the single material platform avoids the interface optical loss and additional process complexity introduced by the separation of the piezoelectric layer and the optical waveguide layer in the heterogeneous integration scheme.

[0031] (2) This invention adopts a collinear structure, in which a focusing interdigital transducer is placed on the surface of the AlScN layer on the side of the waveguide structure to excite acoustic waves propagating along the extension direction of the waveguide structure. This allows the acoustic waves and optical waves to propagate in the same direction and collinearly within the same waveguide structure. The optical conversion efficiency changes periodically along the propagation direction, and the acoustic field and optical field maintain a high degree of overlap over a relatively long interaction length, achieving strong acoustic-optical coupling. TE can be achieved within a relatively short coupling length. 00 Model and TE 10 Efficient mode conversion between modules.

[0032] (3) The present invention removes part of the SiO2 layer below the acousto-optic region of the waveguide structure to form a suspended structure below the waveguide structure, which effectively reduces the leakage of acoustic waves to the silicon substrate, enhances the constraint of acoustic modes in the waveguide structure, and further improves the acousto-optic overlap and modulation efficiency.

[0033] (4) This invention uses an input directional coupler to connect TE 00 The mode light is coupled into the acousto-optic region of the waveguide structure, and the converted TE signal is transmitted through the output directional coupler. 10 The mode light is coupled and separated from the waveguide structure and output. With the help of four grating couplers, the vertical input of off-chip optical signals and the vertical output of optical signals with different transmission paths are realized respectively. The input and output coupling method is flexible, which is convenient for on-chip integration and system-level testing.

[0034] (5) This invention is based on the AlScN / SiO2 / Si substrate platform. The fabrication process is compatible with the silicon-based integration platform. It has strong process flexibility and scalability, which is conducive to low-cost, large-scale production and on-chip system integration. It can be widely used in on-chip optical communication, microwave photonics, mode conversion, optical frequency shifting and non-reciprocal optical transmission and other fields. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0036] Figure 1 A three-dimensional structural diagram of a suspended collinear aluminum scandium nitride acousto-optic modulator provided in an embodiment of the present invention; Figure 2 This is a top view of a suspended collinear aluminum scandium nitride acousto-optic modulator provided in an embodiment of the present invention; Figure 3 A cross-sectional view of a suspended collinear aluminum scandium nitride acousto-optic modulator provided in an embodiment of the present invention; Figure 4A schematic diagram illustrating the working principle of a suspended collinear aluminum scandium nitride acousto-optic modulator provided in this embodiment of the invention; wherein, (a) the acoustic wave displacement distribution of the AlScN waveguide, and (b) the TE of the AlScN waveguide. 00 and TE 10 (c) Schematic diagram of the electric field intensity of the optical mode; (d) Schematic diagram of phase matching and mode conversion of the acousto-optic modulator; Figure 5 The flowchart illustrates a method for preparing a suspended collinear aluminum scandium nitride acousto-optic modulator according to an embodiment of the present invention; wherein (a)-(e) represent schematic diagrams of the structures prepared in steps 1-5, respectively.

[0037] Figure label: 1. Waveguide structure; 2. Input directional coupler; 3. Focusing interdigital transducer; 4. Grating coupler; 5. Output directional coupler; 6. Nanopore; 7. AlScN layer; 8. SiO2 layer; 9. Si layer; 10. Suspension structure.

[0038] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0039] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0040] Example 1: Currently, on-chip acousto-optic modulators ① suffer from limitations in terms of cost, compatibility, and flexibility in manufacturing processes; ② their performance needs improvement in terms of acousto-optic coupling strength and optical conversion efficiency. To address these issues, this invention provides a suspended collinear scandium-doped aluminum nitride acousto-optic modulator, such as... Figures 1 to 3As shown, the suspended collinear scandium-doped aluminum nitride acousto-optic modulator includes a Si layer 9, a SiO2 layer 8, and an AlScN layer 7 stacked sequentially from bottom to top. A portion of the AlScN layer 7 is partially etched to form a waveguide structure 1, which extends in a straight line. A focusing interdigital transducer 3 is also disposed on the AlScN layer 7, located on the surface of the AlScN layer 7 to the side of the waveguide structure 1. The focusing interdigital transducer 3 is used to excite acoustic waves propagating along the extension direction of the waveguide structure 1, so that the acoustic waves and the optical waves transmitted within the waveguide structure 1 resonate with each other. The optical signal propagates along a line and undergoes acousto-optic interaction, enabling the conversion between different optical modes. Optical coupling structures are respectively provided at the input and output ends of the waveguide structure 1. The optical coupling structures are used to realize the coupling input and / or coupling output of optical signals between the waveguide structure 1 and the off-chip optical path. A nanopore 6 penetrating the AlScN layer 7 is also formed on the AlScN layer 7. The nanopore 6 is located on the outer periphery of the acousto-optic interaction region of the waveguide structure 1. Part of the SiO2 layer 8 below the waveguide structure 1 is removed to form a suspended structure 10 located below the waveguide structure 1.

[0041] In this embodiment, the AlScN layer 7 serves as both a piezoelectric material and an optical waveguide material. When a radio frequency signal is applied to the focusing interdigital transducer 3, the electrical signal is converted into an acoustic wave propagating along the waveguide structure 1 through the inverse piezoelectric effect of AlScN. This acoustic wave generates a periodic strain field within the waveguide structure 1, changing the refractive index of the waveguide structure 1 material through photoelasticity, moving boundary effect, and cascaded piezoelectric-electro-optic effect, thereby modulating the light wave transmitted within the waveguide structure 1. The optical mode conversion rate increases along the propagation direction until it reaches a maximum, then decreases to a minimum, and then increases again, exhibiting a periodic change. The greater the coupling strength, the smaller the period. The collinear structure ensures that the acoustic field and the optical field maintain a high degree of overlap within the waveguide structure 1, resulting in a stronger acousto-optic coupling strength than the non-collinear structure, thereby achieving efficient optical mode conversion within a shorter acousto-optic coupling length. The suspended structure 10 is formed by locally removing the SiO2 layer 8 beneath the waveguide structure 1, effectively reducing acoustic wave leakage to the Si layer 9 substrate, enhancing the confinement of acoustic modes within the waveguide structure 1, and further improving acousto-optic overlap. The nanopore 6 penetrates the AlScN layer 7 and extends to the upper surface of the SiO2 layer 8, providing an entry channel for the etching solution to achieve selective removal of the SiO2 layer 8 beneath the waveguide structure 1.

[0042] In some embodiments, waveguide structure 1 is a multimode waveguide partially etched from an AlScN thin film, used to transmit TE signals. 00 Model and TE 10 The operating band is C-band, but not limited to this band. The waveguide width is between 1.2 μm and 2 μm. The waveguide height is between 300 nm and 500 nm, and the length is between 0.1 mm and 3 mm, but not limited to these dimensions.

[0043] Waveguide structure 1 employs a multimode waveguide design, capable of simultaneously supporting TE. 00 Base model and TE 10 Higher-order mode optical transmission provides the necessary optical mode channels for inter-mode acousto-optic conversion. The operating wavelength is C-band (1530nm~1565nm), compatible with existing fiber optic communication systems, facilitating direct application in optical communication networks. The waveguide width is set to 1.2μm~2μm to ensure TE within the C-band. 00 Model and TE 10 All modes can transmit stably and meet TE requirements. 00 Pattern and TE 10 Mode conversion conditions between modes. A waveguide bending radius greater than 100 μm effectively reduces the impact of bending loss on optical signal transmission, ensuring low-loss transmission of the optical signal during coupling at the input and output ends. A waveguide height of 300 nm to 500 nm provides strong constraint on the optical field and facilitates energy concentration of acoustic modes within the waveguide cross-section, enhancing the intensity of acousto-optic interaction. A waveguide length of 0.1 mm to 3 mm provides sufficient interaction distance for acousto-optic coupling, optimizing optical conversion efficiency within a reasonable device size.

[0044] In some embodiments, such as Figure 1 and Figure 2 As shown, the optical coupling structure includes an input directional coupler 2 and an output directional coupler 5; the input directional coupler 2 is disposed on the side of the input end of the waveguide structure 1, and is used to connect the TE... 00 The mode light is coupled into the acousto-optic region of waveguide structure 1; the output directional coupler 5 is located on the side of the output end of waveguide structure 1 to convert the TE signal after acousto-optic modulation. 10 The mode light is coupled and separated from waveguide structure 1 and output.

[0045] Both the input directional coupler 2 and the output directional coupler 5 employ the principle of directional coupling. By bringing two waveguides close together to a sub-micron spacing, evanescent wave coupling occurs between the two waveguides, achieving directional transmission and mode selection of optical power. The input directional coupler 2 connects the input TE... 00 The mode light is gradually coupled from the input waveguide into waveguide structure 1, allowing the optical signal to enter the acousto-optic interaction region and participate in mode conversion; the output directional coupler 5 then converts the TE signal generated after acousto-optic modulation... 10 The mode light is coupled and separated from waveguide structure 1 to the output waveguide, achieving independent output of the signal light after mode conversion. By setting directional couplers at both the input and output ends, path control of the optical signal can be achieved, allowing only the desired TE signal to be modulated. 00 The mode light enters the acousto-optic region, simultaneously converting the TE... 10 The mode light is extracted efficiently, reducing unnecessary optical crosstalk and loss.

[0046] In some embodiments, the input directional coupler 2 will TE 00 The mode light is coupled into the upper waveguide with a width of 1.2 μm to 2 μm, a coupling spacing of 200 nm to 800 nm, and a coupling length of 3 μm to 50 μm, but is not limited to these dimensions.

[0047] The width of the input directional coupler 2 is 1.2μm~2μm, matching the width of waveguide structure 1, ensuring that the directional coupler 2 and waveguide structure 1 have similar propagation constants and satisfy the phase matching condition for directional coupling. The coupling spacing is 200nm~800nm. Within this spacing range, the evanescent tail fields of the two waveguides can generate sufficient overlap to achieve efficient optical power coupling. The coupling length is 3μm~50μm. The coupling length of the directional coupler determines the proportion of optical power exchange between the two waveguides. By reasonably designing the coupling length, the input directional coupler 2 can be adjusted to transfer TE... 00 The coupling ratio of the mode light coupled into waveguide structure 1 is adjusted to meet the coupling efficiency requirements of different application scenarios.

[0048] In some embodiments, the output directional coupler 5 will TE 10 The mode light is coupled out to the upper waveguide, with a width of 0.6 μm to 1 μm, a coupling spacing of 200 nm to 800 nm, and a coupling length of 3 μm to 50 μm, but not limited to these dimensions.

[0049] The waveguide width of the coupling section of the output directional coupler 5 is 0.6μm~1μm, and its waveguide width range is used to improve TE. 10 The coupling extraction efficiency of the mode light and the suppression of unconverted TE 00 The coupling spacing is 200nm~800nm, consistent with the input directional coupler 2, ensuring sufficient evanescent wave overlap between the two coupled waveguides. The coupling length is 3μm~50μm; by adjusting the coupling length, the pairing of the output directional coupler 5 with the TE waveguide can be optimized. 10 The extraction efficiency of the mode light is improved to achieve efficient output of the converted signal light, while suppressing the unconverted TE. 00 The mode light enters the output port, improving the mode purity of the output signal.

[0050] In some embodiments, such as Figure 1As shown, the optical coupling structure also includes four grating couplers 4, all of which are formed on the surface of the AlScN layer 7. One of them is located at the input end of the device and is connected to the incident waveguide port of the input directional coupler 2, serving as the vertical input interface for off-chip optical signals. The other three are located at the output end of the device and are arranged sequentially along the waveguide transmission direction. They are respectively connected to the through waveguide output end of the input directional coupler 2, the coupled waveguide output end of the output directional coupler 5, and the end through output end of the waveguide structure 1, serving as the vertical output interface for optical signals with different transmission paths.

[0051] Four grating couplers 4 are fabricated using periodic grating structures on the surface of the AlScN layer 7. The periodic refractive index distribution of the gratings can diffract horizontally propagating optical signals within the waveguide to a vertical output, or couple vertically incident off-chip optical signals into the waveguide for horizontal propagation. The grating coupler 4 at the input end is connected to the incident waveguide port of the input directional coupler 2, allowing off-chip light sources to transmit TE signals via near-vertical incident mode. 00 The mode optical coupling enters the device, and the coupler is not limited to a grating coupler; alternatives include, but are not limited to, end-face couplers. Three grating couplers 4 at the output end are arranged sequentially along the waveguide transmission direction: the first is connected to the through-waveguide output of the input directional coupler 2, used to monitor the unmodulated through-wavelight signal; the second is connected to the coupling waveguide output of the output directional coupler 5, used to output the TE signal after acousto-optic modulation. 10 The third signal is connected to the direct-through output of waveguide structure 1 and is used to monitor the residual TE signal that has not undergone mode conversion after acousto-optic interaction. 00 Mode optical signals. This structural design enables multi-port output of different optical signals, facilitating independent monitoring and analysis of signals at different locations on the device, and is beneficial for on-chip integration testing and system-level optical path layout.

[0052] In some embodiments, the grating coupler 4 has a duty cycle of 0.5 and a period of 1014 nm, but is not limited to this size.

[0053] The duty cycle of grating coupler 4 is 0.5, meaning the ridge width of the grating occupies 50% of the period. At this duty cycle, the grating exhibits high diffraction efficiency, which is beneficial for improving the vertical coupling efficiency of the optical signal. The period is 10¹⁴ nm. By adjusting the grating period, the diffraction angle of grating coupler 4 can be matched with the near-vertical emission direction of the C-band optical signal, satisfying the phase-matching condition for grating-assisted coupling and achieving efficient near-vertical input and output of optical signals. The adjustable range of the grating period covers the coupling requirements of different wavelengths in the C-band, enabling the device to maintain good coupling performance over a wide spectral range.

[0054] It should be noted that the grating coupler 4 is used to couple optical input and output. Other devices with optical input and output coupling functions can also be used as alternatives to the grating coupler 4, such as end face couplers.

[0055] In some embodiments, the material of the focusing interdigital transducer 3 is Au / Cr, Au / T, or other electrode materials, which generates acoustic waves and focuses them onto the AlScN waveguide, but is not limited to a focusing interdigital transducer. The angle is 15° to 30°, the number of interdigital pairs is 50 to 120, and the electrode period is 1 μm to 4 μm, but is not limited to these dimensions.

[0056] The focusing interdigital transducer 3 employs an arc-shaped interdigital design with an interdigital angle of 15° to 30°. This arc-shaped structure allows the acoustic waves excited by the transducer to propagate along the direction pointing to the focal point and gradually converge in the region where the waveguide structure 1 is located, concentrating acoustic energy in the optical waveguide region, increasing the acoustic energy density in the acousto-optic interaction region, and thus enhancing the intensity of acousto-optic interaction. The number of interdigital pairs ranges from 50 to 120. Increasing the number of interdigital pairs is beneficial to the electroacoustic conversion efficiency of the transducer, allowing more radio frequency electrical signal energy to be converted into acoustic energy. However, it also increases the impedance of the transducer and the device size. This range strikes a balance between energy efficiency and device compactness. The electrode period ranges from 1 μm to 4 μm. The electrode period determines the frequency of the acoustic waves excited by the focusing interdigital transducer 3. By selecting different electrode periods, the frequency of the acoustic waves can be adjusted to match the acousto-optic phase matching conditions between different optical modes. The electrode material adopts Au / Cr or Au / Ti combination, in which the Cr or Ti layer acts as an adhesion layer to enhance the adhesion between the Au layer and the AlScN layer 7, and the Au layer acts as a conductive layer to provide good radio frequency signal transmission performance.

[0057] It should be noted that the focused interdigital transducer 3 is merely an example of an interdigital transducer and does not imply that the present invention must rely on this focused interdigital transducer 3 to be realized. Other interdigital transducers capable of exciting surface acoustic waves can be used as conventional replacements for the focused interdigital transducer 3. The focused interdigital transducer 3 is only a preferred option.

[0058] In some embodiments, the pore size of the nanopore 6 is 500 nm to 2 μm. The nanopore 6 penetrates the AlScN layer 7 and extends to the upper surface of the SiO2 layer 8, and is used to allow the etching solution to pass through in order to remove the SiO2 layer 8 below the waveguide structure 1.

[0059] Nanopores 6 form through-holes in the AlScN layer 7, with a pore size ranging from 500 nm to 2 μm. The pore size of the nanopores 6 is minimized while ensuring the smooth passage of the etching solution. This is designed in conjunction with the electrode period of the focusing interdigital transducer 3 and the wavelength of the excited acoustic wave to minimize the impact on the optical and acoustic properties of the AlScN layer 7. Multiple nanopores 6 are distributed around the outer periphery of the acousto-optic interaction region of the waveguide structure 1. After the etching solution enters through the nanopores 6, it laterally contacts and dissolves the SiO2 layer 8 beneath the waveguide structure 1. Due to the good tolerance of the AlScN layer 7 to the buffered oxide etching solution, the etching solution can selectively remove the SiO2 layer 8 without damaging the AlScN layer 7, thereby achieving selective local removal of the SiO2 layer 8 beneath the waveguide structure 1, forming a suspended structure 10. The position of the suspended structure 10 is determined by the distribution of the nanopores 6. By controlling the arrangement area of ​​the nanopores 6, the suspended structure 10 can be confined below the acousto-optic interaction region, while maintaining the integrity of the SiO2 layer 8 beneath other areas of the device to provide sufficient mechanical support.

[0060] In some embodiments, the Sc doping concentration of AlScN layer 7 is 0 to 50%, and the overall thickness of AlScN layer 7 is 300 nm to 600 nm.

[0061] The Sc doping concentration of AlScN layer 7 ranges from 0% to 50%. With increasing Sc doping concentration, the piezoelectric coefficient and electromechanical coupling coefficient of the AlScN material increase significantly, leading to improved electroacoustic conversion efficiency and the generation of stronger acoustic waves at the same driving power. However, excessively high Sc doping concentrations may result in decreased thin film crystal quality and increased optical loss. The 0-50% range is beneficial for balancing thin film quality and optical transmission performance while improving piezoelectric performance. The overall thickness of AlScN layer 7 is 300 nm to 600 nm. This thickness range ensures effective confinement of the optical field by waveguide structure 1, concentrating the optical mode field within the waveguide core layer. This facilitates the adjustment of acoustic and optical mode distributions, maintaining a high degree of overlap between the two within the waveguide cross-section.

[0062] In some embodiments, the thickness of the SiO2 layer 8 is 3 μm to 6 μm, but is not limited to this size.

[0063] The SiO2 layer 8 has a thickness of 3μm to 6μm. This thickness serves two purposes: firstly, it acts as an optical cladding layer, utilizing the significant refractive index difference between SiO2 (refractive index approximately 1.44) and AlScN (refractive index approximately 2.0 to 2.1) to effectively confine the light field within the waveguide structure in the non-levitated region, preventing optical signals from leaking into the Si layer 9 substrate; secondly, it acts as a sacrificial layer, providing sufficient vertical space for the etching of the levitated structure 10, ensuring a sufficient gap between the waveguide structure 1 and the Si layer 9 below the levitated region, thus reducing the substrate's influence on the acoustic mode. Simultaneously, the thickness of the SiO2 layer 8 also contributes to the mechanical stability of the non-levitated region of the device, preventing deformation or breakage of the waveguide structure 1 due to excessively large suspension spans.

[0064] In some embodiments, the thickness of the Si layer 9 is 725 μm, but it is not limited to this size.

[0065] Si layer 9 serves as the substrate layer for the device, providing overall mechanical support and structural strength. With a thickness of 725 μm, consistent with standard silicon wafers, Si layer 9 facilitates device fabrication using commercial silicon wafers, offering good process compatibility and low material costs. During fabrication, Si layer 9 acts as the substrate layer, sequentially supporting the deposition and processing of SiO2 layer 8 and AlScN layer 7. Its excellent surface smoothness and thermal stability provide favorable conditions for the deposition of high-quality AlScN thin films.

[0066] The working principle of the suspended collinear scandium-doped aluminum nitride acousto-optic modulator provided in this embodiment of the invention is as follows: This suspended collinear scandium-doped aluminum nitride acousto-optic modulator applies a radio frequency signal to a focusing interdigital transducer. The transducer converts the electrical signal into an acoustic wave propagating along the waveguide direction through the inverse piezoelectric effect of AlScN. Because AlScN possesses both piezoelectric and optical properties, the acoustic wave can generate a periodic strain field in the region near the optical waveguide. This strain field alters the refractive index of the waveguide material through photoelasticity, moving boundary effects, and cascaded piezoelectric-electro-optic effects, thereby modulating the effective refractive index of the optical mode and achieving modulation of the optical field by the acoustic field.

[0067] Specifically, the off-chip signal light enters the device through the grating coupler 4 on the input side, TE 00 The mode signal light is coupled into waveguide structure 1 via input directional coupler 2 and propagates linearly towards the output end within waveguide structure 1. Simultaneously, the focusing interdigital transducer 3, excited by the radio frequency signal, excites acoustic waves through the inverse piezoelectric effect of AlScN layer 7. The arc-shaped interdigital structure converges the acoustic waves to the region of waveguide structure 1, causing them to propagate along the extension direction of waveguide structure 1. The acoustic wave and light wave propagate collinearly in the same direction within waveguide structure 1. Since the acoustic wave wave vector satisfies TE... 00 Model and TE 10 When the phase matching condition between modes is met, the optical signal from TE00 Mode conversion to TE 10 The pattern, accompanied by a frequency shift. The converted TE... 10 The mode light is coupled and separated from the waveguide structure 1 through the output directional coupler 5, and is vertically output to the off-chip via the grating coupler 4 on the output side; the unconverted TE 00 The mode light is output through the direct-through output terminal of waveguide structure 1 via grating coupler 4, or through the direct-through waveguide output terminal of input directional coupler 2 via grating coupler 4, for external equipment monitoring and analysis. Since sound waves are directional along the propagation direction of light waves, when the optical signal is input in the opposite direction, the propagation directions of the sound wave and the light wave are opposite, failing to meet the phase matching condition. Therefore, mode conversion only occurs when the propagation directions of the sound wave and the light wave are the same, thus achieving non-reciprocal optical transmission characteristics.

[0068] In this embodiment of the invention, a levitation structure 10 is formed below the acousto-optic interaction region of the waveguide structure 1. This allows the acoustic mode to be unconstrained by the SiO2 layer 8 and the Si layer 9 in the levitation region, while confining the acoustic energy within the waveguide structure 1. This significantly improves the acousto-optic overlap and enhances the acousto-optic coupling strength. The synergistic effect of the levitation structure 10 and the collinear propagation structure enables this embodiment of the invention to achieve high optical mode conversion efficiency with lower RF drive power and shorter device length.

[0069] Please combine further Figure 4 As shown, Figure 4 (a) shows the Rayleigh wave mode shape diagram of the suspended waveguide, where the suspended structure confines the acoustic energy to the suspended waveguide. Figure 4 Figure (b) shows the TE of the AlScN suspended waveguide. 00 and TE 10 The light mode. Figure 4 (c) shows ω - k Intermodal acousto-optic modulation in space. This is achieved through the input TE... 00 The light has an angular frequency of ω a The transducer excites sound waves with an angular frequency of Ω. When phase matching is satisfied, the sound field and the light field are strongly coupled. TE 00 Convert to TE 10 mode, angular frequency is ω b = ω a -Ω. It can be observed that as the waveguide length increases, i.e. the coupling length increases, there is a reciprocating energy exchange between the two modes.

[0070] Figure 4 Image (d) shows a top view of the device. In the input section, the input mode is TE. 00The signal light is transmitted through a directional coupler to a waveguide that overlaps with the sound field. Sound waves, excited by a focusing interdigital transducer, interact with the light and propagate in the same direction within the waveguide. The signal light's TE... 00 The mode has been changed to TE 10 And output through a directional coupler. If from the inverted input TE 00 If light and sound waves propagate in opposite directions and there is a phase mismatch, then mode switching will not occur.

[0071] Example 2: This invention provides a method for preparing a suspended collinear aluminum scandium nitride acousto-optic modulator as described in any of the embodiments in Example 1. Figure 5 As shown, it includes the following steps: Step 1: Provide Si layer 9 as a substrate, and form SiO2 layer 8 on the surface of Si layer 9.

[0072] In this embodiment, a 725μm thick silicon wafer is used as a substrate. The wafer is ultrasonically cleaned sequentially using acetone, isopropanol and deionized water, and then dried with nitrogen gas. After obtaining a clean wafer, a 3μm SiO2 layer is grown on the surface of the silicon wafer through a thermal oxidation process to form SiO2 layer 8.

[0073] Step 2: Deposit AlScN layer 7 on SiO2 layer 8.

[0074] In this embodiment, a magnetron sputtering process is used to first deposit a 30 nm AlN seed layer, followed by a 400 nm AlScN thin film. The required Sc ratio is controlled by using single AlSc alloy targets with different Al:Sc atomic percentages. By controlling process parameters such as seed layer thickness, RF power, gas flow rate, temperature, and time, the quality and thickness of the c-axis preferred oriented film are controlled to deposit the AlScN thin film to form the AlScN layer 7.

[0075] In one embodiment, an AlSc target with a 20% Sc concentration is used, with Ar as the sputtering gas and N2 as the reactive gas, and reactive magnetron sputtering deposition is performed in an Ar / N2 mixed atmosphere. The base vacuum level of magnetron sputtering can be lower than 10. -4 The working pressure can be 3.5 Pa, the Ar flow rate can be 20 sccm, the N2 flow rate can be 12 sccm, and the substrate temperature can be 350℃. To improve the crystal quality of the thin film, an AlN seed layer can be deposited before depositing the AlScN layer 7, and substrate rotation can be used during the deposition process to improve the film thickness uniformity, composition uniformity, and c-axis preferred orientation. The above parameters can be adjusted according to the target Sc doping concentration, film quality, thickness, and stress requirements, and are not limited to the above ranges.

[0076] Step 3: Pattern and partially etch the AlScN layer 7 to form waveguide structure 1, input directional coupler 2, grating coupler 4, and output directional coupler 5.

[0077] In this embodiment, a 500nm SiO2 hard mask layer is deposited on the surface of the AlScN thin film, preferably using PECVD. The SiH4 gas flow rate is 5 sccm, the N2O gas flow rate is 50 sccm, the power is 200W, the pressure is 5Pa, and the temperature is 400℃. After patterning using electron beam lithography or ultraviolet lithography, the SiO2 hard mask layer is first etched using reactive ion etching (RIE). CHF3 / Ar gas is used for etching, with flow rates of 10 sccm and 15 sccm respectively, an RF bias power of 20W, and an ICP power of 600W. Then, inductively coupled plasma etching (ICP) is used to partially etch away 200nm of the AlScN film. The AlScN thin film ICP etching uses a BCl3 / Cl2 / Ar mixed gas with flow rates of 32 / 8 / 4 sccm respectively. The RF power and ICP power are 100W and 400W respectively.

[0078] Step 4: Patterning, depositing a metal layer and stripping the metal on AlScN layer 7 to form a focused interdigital transducer 3 on the surface of AlScN layer 7 on the side of waveguide structure 1.

[0079] In this embodiment, the electrode pattern is formed by electron beam lithography or ultraviolet lithography, and then 10Cr and 60nm Au metal are deposited by electron beam evaporation at a vacuum degree of 10. -3 Below Pa, the focused interdigital transducer is then immersed in acetone solution and sonicated for 1 to 10 minutes to complete the peeling process.

[0080] Step 5: A nanopore 6 penetrating the AlScN layer 7 is formed on the outer periphery of the acousto-optic region of the waveguide structure 1. An etching solution is introduced through the nanopore 6 to laterally etch and remove the SiO2 layer 8 below the waveguide structure 1, so that a suspended structure 10 is formed below the waveguide structure 1.

[0081] In this embodiment, a 500nm SiO2 hard mask is deposited using PECVD, employing the process formulation from step 3. Nanopore patterns are formed using electron beam lithography or UV lithography, and the SiO2 hard mask layer is first etched using RIE, again employing the process formulation from step 3. Then, the AlScN is fully etched using ICP, again employing the process formulation from step 3. Finally, a buffered oxide etchant (BOE) wet etching process, selectively etching SiO2, is used to laterally remove the SiO2 layer beneath the waveguide, thus suspending the AlScN waveguide region.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A suspended collinear scandium-doped aluminum nitride acousto-optic modulator, characterized in that, It includes a Si layer (9), a SiO2 layer (8) and an AlScN layer (7) stacked sequentially from bottom to top; A portion of the AlScN layer (7) is partially etched to form a waveguide structure (1), which extends along a straight line. A focusing interdigital transducer (3) is also provided on the AlScN layer (7). The focusing interdigital transducer (3) is disposed on the surface of the AlScN layer (7) on the side of the waveguide structure (1) and is used to excite the sound wave propagating along the extension direction of the waveguide structure (1), so that the sound wave and the light wave transmitted in the waveguide structure (1) propagate collinearly and undergo acousto-optic interaction, thereby realizing the conversion between different optical modes. The waveguide structure (1) is provided with optical coupling structures at its input and output ends, respectively. The optical coupling structures are used to realize the coupling input and / or coupling output of optical signals between the waveguide structure (1) and the off-chip optical path. The AlScN layer (7) is also provided with a nanopore (6) penetrating the AlScN layer (7), and the nanopore (6) is located on the outer periphery of the acousto-optic region of the waveguide structure (1). A portion of the SiO2 layer (8) below the waveguide structure (1) is removed to form a suspended structure (10) located below the waveguide structure (1).

2. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 1, characterized in that, The optical coupling structure includes an input directional coupler (2) and an output directional coupler (5); The input directional coupler (2) is disposed on the side of the input end of the waveguide structure (1) and is used to transmit the TE signal. 00 The mode light is coupled into the acousto-optic region of the waveguide structure (1); The output directional coupler (5) is disposed on the side of the output end of the waveguide structure (1) and is used to convert the TE signal after acousto-optic modulation. 10 The mode light is coupled and separated from the waveguide structure (1) and output.

3. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 2, characterized in that, The input directional coupler (2) has a width of 1.2μm to 2μm, a coupling spacing of 200nm to 800nm, and a coupling length of 3μm to 50μm; the output directional coupler (5) has a width of 0.6μm to 1μm, a coupling spacing of 200nm to 800nm, and a coupling length of 3μm to 50μm.

4. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 2, characterized in that, The optical coupling structure also includes four grating couplers (4). All four grating couplers (4) are formed on the surface of the AlScN layer (7). One of them is arranged at the input end of the device and connected to the incident waveguide port of the input directional coupler (2) as a vertical input interface for off-chip optical signals. The other three are arranged at the output end of the device and are arranged sequentially along the waveguide transmission direction. They are respectively connected to the through waveguide output end of the input directional coupler (2), the coupled waveguide output end of the output directional coupler (5), and the end through output end of the waveguide structure (1) as vertical output interfaces for optical signals with different transmission paths. The duty cycle of the grating coupler (4) is 0.4~0.6 and the period is 600nm~1600nm.

5. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 1, characterized in that, The waveguide structure (1) is a multimode waveguide used for transmitting TE signals. 00 Model and TE 10 The mode is C-band; the width of the waveguide structure (1) is 1.2μm~2μm, the bending radius is greater than 100μm, the waveguide height is 300nm~500nm, and the length is 0.1mm~3mm.

6. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 1, characterized in that, The interdigitated angle of the focused interdigitated transducer (3) is 15° to 30°, the number of interdigitated pairs is 50 to 120, and the electrode period is 1μm to 4μm; the electrode material of the focused interdigitated transducer (3) is Au / Cr, Au / Ti, or Al.

7. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 1, characterized in that, The pore size of the nanopore (6) is 500 nm to 2 μm. The nanopore (6) penetrates the AlScN layer (7) and extends to the upper surface of the SiO2 layer (8) for the passage of etching solution to remove the SiO2 layer (8) under the waveguide structure (1).

8. The suspended collinear scandium-doped aluminum nitride acousto-optic modulator according to claim 1, characterized in that, The AlScN layer (7) has a Sc doping concentration of 0 to 50%, the overall thickness of the AlScN layer (7) is 300 nm to 500 nm, the etching depth of the waveguide structure (1) is 200 nm to 400 nm, the thickness of the SiO2 layer (8) is 3 μm to 6 μm, and the thickness of the Si layer (9) is 725 μm.

9. A method for preparing a suspended collinear aluminum scandium nitride acousto-optic modulator as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Provide a Si layer (9) as a substrate, and form a SiO2 layer (8) on the surface of the Si layer (9); Step 2: Deposit an AlScN layer (7) on the SiO2 layer (8); Step 3: Pattern and partially etch the AlScN layer (7) to form a waveguide structure (1) extending in a straight line direction, and form optical coupling structures at the input and output ends of the waveguide structure (1); Step 4: Patterning, depositing a metal layer and stripping the metal on the AlScN layer (7) to form a focused interdigital transducer (3) on the surface of the AlScN layer (7) on the side of the waveguide structure (1). Step 5: A nanopore (6) penetrating the AlScN layer (7) is formed on the outer periphery of the acousto-optic region of the waveguide structure (1). An etching solution is introduced through the nanopore (6) to laterally etch and remove the SiO2 layer (8) below the waveguide structure (1), so that a suspended region (10) is formed below the waveguide structure (1).

10. The preparation method according to claim 9, characterized in that, In step 2, the AlScN layer (7) is deposited using magnetron sputtering. The Sc doping concentration of the AlScN layer (7) is adjusted by controlling the atomic percentage of Sc and Al in the target material, and the Sc doping concentration is 0 to 50%. In step 3, the AlScN layer (7) is patterned using electron beam lithography or ultraviolet lithography, and partially etched using reactive ion etching and / or inductively coupled plasma etching. In step 5, wet etching is performed using a buffer oxide etchant that is selective for SiO2.

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