SiN-based photonic crystal nano-beam cavity and manufacturing method thereof

Abstract

The invention provides a SiN-based photonic crystal nano-beam cavity and a manufacturing method, the SiN-based photonic crystal nano-beam cavity comprises a substrate, a lower cladding and a one-dimensional SiN waveguide layer, the lower cladding is located above the substrate, the one-dimensional SiN waveguide layer is located above the lower cladding, the one-dimensional SiN waveguide layer comprises a first gradual change region and a second gradual change region, and the first gradual change region is located above the substrate. A plurality of gradually-changing holes which are distributed at intervals are formed in the first gradually-changing area and the second gradually-changing area, and the first gradually-changing area and the second gradually-changing area are symmetrically arranged relative to the center of the gradually-changing area; in the first gradual change area and in the direction from the second gradual change area to the first gradual change area, the vertical axis lengths of the multiple gradual change holes are gradually reduced, and the horizontal axis lengths of the multiple gradual change holes are equal. According to the invention, the length of the horizontal axis of the gradual change hole is kept unchanged, so that the optical phase matching between adjacent unit cells is ensured, and only the length of the vertical axis of the gradual change hole is modulated, so that the limitation on an optical mode field is realized, the Q value is increased, and higher optical storage is realized.

Description

Technical Field

[0001] This invention belongs to the field of optical microcavities and relates to a SiN-based photonic crystal nanobeam cavity and its fabrication method. Background Technology

[0002] Photonic crystals are artificial structures with periodically varying dielectric constants. Through their bandgap effect on photons, they allow for the manipulation of both bandgap and in-band propagation of light. These structures hold significant promise for applications in optical communication, photonic integrated circuits, sensors, and quantum computing. Photonic crystal nanobeamcavities are miniature resonant cavities that integrate photonic crystal structures into nanoscale optical waveguides. Due to their compact structure and high optical efficiency, they are attracting increasing attention from researchers.

[0003] Traditional photonic crystal materials such as silicon (Si) and gallium arsenide (GaAs) have been widely used in manufacturing processes and optical performance. However, these materials have limitations in certain applications, such as high manufacturing costs, susceptibility to oxidation, and insufficient mechanical strength. Silicon nitride (SiN), as a novel photonic material, has become an ideal alternative due to its excellent optical properties, low cost, and good mechanical strength.

[0004] SiN materials possess a wide optical transparency window (0.4-7 μm) and low optical loss, making them suitable for various optical applications. Compared to traditional materials, SiN nanobeam cavities exhibit superior optical stability, mechanical strength, and thermal stability, thus demonstrating higher reliability in complex optical environments. In practical applications, SiN-based photonic crystal nanobeam cavities can be used not only for optical filtering and switching but also as highly sensitive biosensors and chemical sensors. Furthermore, SiN nanobeam cavities show potential in quantum computing, particularly in the optical cavity design of quantum dots and qubits, providing excellent photon manipulation capabilities.

[0005] Although SiN materials have broad application prospects in photonic crystal nanobeam cavities, there are still some technical challenges, such as how to control the geometry and size of the nanobeam cavity and optimize the fabrication process to improve the quality factor (Q value) of the photonic crystal nanobeam cavity. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a SiN-based photonic crystal nanobeam cavity and its fabrication method, so as to solve the problem of low performance of existing photonic crystal nanobeam cavities.

[0007] To achieve the above and other related objectives, the present invention provides a SiN-based photonic crystal nanobeam cavity, comprising:

[0008] A substrate, on which a lower cladding layer is disposed;

[0009] A one-dimensional SiN waveguide layer is located above the lower cladding layer. The one-dimensional SiN waveguide layer includes a gradient region. Along the extension direction of the one-dimensional SiN waveguide layer, the gradient region includes a first gradient region and a second gradient region that are symmetrically arranged about the center of the gradient region. Both the first gradient region and the second gradient region are provided with a plurality of gradient holes arranged at intervals. The gradient holes in the first gradient region and the second gradient region are symmetrically arranged about the center of the gradient region.

[0010] The horizontal axis of the gradient aperture is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the gradient aperture is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. In the first gradient region and along the direction from the second gradient region to the first gradient region, the vertical axis length of the plurality of gradient apertures gradually decreases, and the horizontal axis length of the plurality of gradient apertures is equal.

[0011] Optionally, within the first gradient region and along the direction from the second gradient region to the first gradient region, the gradient hole includes a first gradient hole, a second gradient hole, ..., an Nth gradient hole, where N is an integer greater than 2, and the vertical axis radius R of the Kth gradient hole is... y (K) satisfies:

[0012]

[0013] Among them, R y (1) is the vertical axis radius of the first gradient hole, R y (N) is the vertical axis radius of the Nth gradient hole, and K is an integer and 1≤K≤N.

[0014] Optionally, the one-dimensional SiN waveguide layer further includes a reflection region. Along the extension direction of the one-dimensional SiN waveguide layer, the reflection region is located on both sides of the gradient region. The reflection region is provided with a plurality of spaced constant holes. The horizontal axis of the constant holes is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the constant holes is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. The vertical axis lengths of the plurality of constant holes are equal, and the horizontal axis lengths of the plurality of constant holes are equal.

[0015] Optionally, the lower cladding layer is provided with a groove that extends from the upper surface of the lower cladding layer to the interior of the lower cladding layer, wherein the projection of the groove on the substrate covers the projection of the gradient area and the reflection area on the substrate.

[0016] Optionally, the substrate is made of silicon, and the lower cladding is made of silicon dioxide.

[0017] This invention also provides a method for fabricating a SiN-based photonic crystal nanobeam cavity, comprising the following steps:

[0018] Provide a substrate, and form a lower cladding layer on the substrate;

[0019] A one-dimensional SiN waveguide layer is formed on the lower cladding layer. The one-dimensional SiN waveguide layer includes a gradient region. Along the extension direction of the one-dimensional SiN waveguide layer, the gradient region includes a first gradient region and a second gradient region that are symmetrically arranged about the center of the gradient region.

[0020] The one-dimensional SiN waveguide layer is etched to form a plurality of spaced gradient holes in both the first gradient region and the second gradient region, and the gradient holes in the first gradient region and the second gradient region are symmetrically arranged about the center of the gradient region.

[0021] Wherein, the horizontal axis of the gradient aperture is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the gradient aperture is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. In the first gradient region and along the direction from the second gradient region to the first gradient region, the vertical axis length of the plurality of gradient apertures gradually decreases, and the horizontal axis length of the plurality of gradient apertures is equal.

[0022] Optionally, the method for forming the lower cladding includes plasma-enhanced chemical vapor deposition, the method for forming the one-dimensional SiN waveguide layer includes low-pressure vapor deposition, and the method for forming the gradient via includes dry etching.

[0023] Optionally, the one-dimensional SiN waveguide layer further includes a reflection region. Along the extension direction of the one-dimensional SiN waveguide layer, the reflection region is located on both sides of the gradient region. During the process of forming the gradient aperture in the gradient region, a plurality of spaced constant apertures are also formed in the reflection region. The horizontal axis of the constant aperture is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the constant aperture is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. The vertical axis lengths of the plurality of constant apertures are equal, and the horizontal axis lengths of the plurality of constant apertures are equal.

[0024] Optionally, after forming the gradient hole and the constant hole, the method further includes etching the lower cladding to form a groove, wherein the groove extends from the upper surface of the lower cladding to the interior of the lower cladding, and the projection of the groove on the substrate covers the projection of the gradient area and the reflection area on the substrate.

[0025] Optionally, after forming the one-dimensional SiN waveguide layer and before etching the one-dimensional SiN waveguide layer, the step of annealing the one-dimensional SiN waveguide layer is further included.

[0026] As described above, in the SiN-based photonic crystal nanobeam cavity and fabrication method of the present invention, the horizontal axis length of the gradient aperture remains unchanged to ensure optical phase matching between adjacent unit cells, and only the vertical axis length of the gradient aperture is modulated to achieve the confinement effect of the optical mode field, significantly improve the Q value, and achieve higher optical storage; in addition, SiN has low optical loss characteristics, which can reduce the energy loss of light during propagation and improve the overall performance of the nanobeam cavity. Attached Figure Description

[0027] Figure 1 The image shown is a three-dimensional schematic diagram of the SiN-based photonic crystal nanobeam cavity in Embodiment 1 of the present invention.

[0028] Figure 2 The image shown is a top view of the SiN-based photonic crystal nanobeam cavity in Embodiment 1 of the present invention.

[0029] Figure 3 Displayed as Figure 2 Enlarged view of the area within the dashed box.

[0030] Figure 4 The image shown is a cross-sectional view of the SiN-based photonic crystal nanobeam cavity in Embodiment 1 of the present invention.

[0031] Figure 5 The diagram shown is a simulation of the SiN-based photonic crystal nanobeam cavity in Embodiment 1 of the present invention, representing the mode field distribution obtained from the simulation.

[0032] Component designation explanation

[0033] 1. Base

[0034] 2. Lower cladding layer

[0035] 20 grooves

[0036] 3 One-dimensional SiN waveguide layer

[0037] 30 Gradient Zone

[0038] 300 First Gradient Zone

[0039] 301 Second Gradient Zone

[0040] 302 gradient hole

[0041] 310 First Reflection Zone

[0042] 311 Second Reflection Zone

[0043] 312 Constant Hole Detailed Implementation

[0044] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0045] Please see Figures 1 to 5 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0046] Example 1

[0047] This embodiment provides a SiN-based photonic crystal nanobeam cavity. Please refer to [link / reference]. Figures 1 to 4 The SiN-based photonic crystal nanobeam cavity includes a substrate 1, a lower cladding layer 2, and a one-dimensional SiN waveguide layer 3. The lower cladding layer 2 is located above the substrate 1, and the one-dimensional SiN waveguide layer 3 is located above the lower cladding layer 2. The one-dimensional SiN waveguide layer 3 includes a gradient region 30. Along the extension direction of the one-dimensional SiN waveguide layer 3, the gradient region 30 includes a first gradient region 300 and a second gradient region 301. Both the first gradient region 300 and the second gradient region 301 are provided with a plurality of gradient holes 302 arranged at intervals. A gradient region 300 and a second gradient region 301 are arranged symmetrically about the center of the gradient region 300; the horizontal axis of the gradient aperture 302 is parallel to the extension direction of the one-dimensional SiN waveguide layer 3, and the vertical axis of the gradient aperture 302 is perpendicular to the extension direction of the one-dimensional SiN waveguide layer 3. In the first gradient region 300 and along the direction from the second gradient region 301 to the first gradient region 300, the vertical axis length of the plurality of gradient apertures 302 gradually decreases, and the horizontal axis length of the plurality of gradient apertures 302 is equal.

[0048] As an example, the shape of the gradient hole 302 includes ellipse, rectangle or rhombus, etc., preferably ellipse.

[0049] As an example, in the gradient zone 30, the horizontal axis lengths of the plurality of gradient holes 302 are equal, that is, the horizontal axis radius R of the gradient holes 302 is... xEqually, the distance a (distance between the centers of the holes) between adjacent gradient holes 302 remains constant to ensure optical phase matching between adjacent unit cells, thereby minimizing the scattering loss of the optical signal in the propagation direction (along the X-axis).

[0050] As an example, since the first gradient region 300 and the second gradient region 301 are symmetrically arranged about the center of the gradient region 30, that is, in the direction from the center of the gradient region 30 to the edge of the gradient region 30, the vertical axis length of the plurality of gradient holes 302 located in the first gradient region 300 gradually decreases, and the vertical axis length of the plurality of gradient holes 302 located in the second gradient region 301 gradually decreases.

[0051] Specifically, in the first gradient region 300 and along the direction from the second gradient region 301 to the first gradient region 300, the number of gradient holes 302 is N, including a first gradient hole, a second gradient hole, ..., an Nth gradient hole, where N is an integer greater than 2, and the vertical axis radius R of the Kth gradient hole is... y (K) satisfies:

[0052]

[0053] Among them, R y (1) is the vertical axis radius of the first gradient hole, R y (N) represents the vertical axis radius of the Nth gradient aperture, and K is an integer where 1 ≤ K ≤ N. By parabolically modulating the vertical axis radius Ry of the gradient aperture 302, a Gaussian reflector is formed, and the resonant optical field of the device is modulated based on the Gaussian attenuation distribution. An electromagnetic field with linearly increasing attenuation is introduced from the center to the edge of the gradient region 30 to achieve a good confinement effect on the optical mode field, reduce scattering and loss, reduce optical signal leakage, and improve the Q value.

[0054] As an example, the gradient aperture 302 gradually decreases in the vertical axis radius Ry from the center to the edge in the gradient region 30, which helps to distribute the light field more evenly, enhances the coupling with the outside world, is suitable for application scenarios that require high coupling efficiency, and is suitable for use as a sensor design.

[0055] As an example, along the extension direction of the one-dimensional SiN waveguide layer 3, the one-dimensional SiN waveguide layer 3 further includes a reflection region, which includes a first reflection region 310 and a second reflection region 311. The first reflection region 310 and the second reflection region 311 are separately disposed on both sides of the gradient region 30 and are symmetrically arranged about the center of the gradient region 30. Multiple constant apertures 312 are provided in both the first reflection region 310 and the second reflection region 311 at intervals. The horizontal axis of the constant apertures 312 is parallel to the extension direction of the one-dimensional SiN waveguide layer 3, and the vertical axis of the constant apertures 312 is perpendicular to the extension direction of the one-dimensional SiN waveguide layer 3. The vertical axis lengths of the multiple constant apertures 312 are equal, and the horizontal axis lengths of the multiple constant apertures 312 are equal.

[0056] As an example, the shape of the constant hole 312 includes ellipse, rectangle or rhombus, etc., preferably ellipse.

[0057] As an example, by setting the reflection areas on both sides of the gradient region 30, and setting the constant aperture 312 with a constant size in the reflection area, a Bragg reflector is formed, which reduces the coupling of the resonant mode to the waveguides on both sides and further improves the Q value. The size of the constant aperture 312 is the same as the size of the outermost gradient aperture 302, and the distance between adjacent constant apertures 312 is a (the distance between the aperture centers).

[0058] As an example, the substrate 1 is made of Si, the lower cladding 2 is made of SiO2, and the one-dimensional SiN waveguide layer 3 is made of SiN. The refractive index of SiO2 is approximately 1.45–1.5, and the refractive index of SiN is approximately 1.92–2.33. SiN has a relatively low refractive index contrast. In this embodiment, a groove 20 is provided in the lower cladding 2, extending from the upper surface of the lower cladding 2 to its interior. The projection of the groove 20 onto the substrate 1 covers the projections of the gradient region 30 and the reflection region onto the substrate 1. This is equivalent to both the upper and lower cladding layers of the one-dimensional SiN waveguide layer 3 in this application using air, increasing the refractive index contrast of SiN and allowing light to be better confined within the nanobeam cavity. Furthermore, it reduces the device size; compared to a design where both the upper and lower cladding layers use SiO2, the device size in this application is reduced by three to four times, significantly reducing the number of holes.

[0059] Specifically, in this embodiment, the thickness of the lower cladding layer 2 is set to 3.18 μm, the thickness of the one-dimensional SiN waveguide layer 3 is 400 nm, and the width W of the one-dimensional SiN waveguide layer 3 is 1 μm. The number of gradient holes 302 in the first gradient region 300 is 30, and the vertical axis radius R of the gradient hole 302 closest to the center of the gradient region 30 is...y (1) The vertical axis radius R of the gradient hole 302 furthest from the center of the gradient region 30 is 300 nm. y (30) is 100nm, and the horizontal axis radius R of the gradient hole 302 is 100nm. x The radius of the gradient aperture 302 is 145 nm, and the distance 'a' between adjacent gradient apertures 302 is 444 nm. The first reflection region 310 contains 15 constant apertures 312, each with a horizontal axis radius of 145 nm and a vertical axis radius of 100 nm. Similarly, the second gradient region 301 contains 30 gradient apertures 302, and the second reflection region 311 contains 15 constant apertures 312. Please refer to [link / reference]. Figure 5 The image shows the mode field distribution obtained from the simulation of a SiN-based photonic crystal nanobeam cavity in this embodiment of the invention. With a TEO mode light source as input, the simulation calculation yielded a resonant wavelength λ = 1293.8 nm, corresponding to a Q value > 5 × 10⁻⁶. 6 .

[0060] As an example, the resonant wavelength of the SiN-based photonic crystal nanobeam cavity in this embodiment is maintained at around 1310nm. The 1310nm band has received widespread attention and application in optical communication systems. It has excellent characteristics in short- to medium-distance optical transmission, such as low dispersion, moderate attenuation, no water peak absorption loss, mature technology and equipment, suitability for various application scenarios, and small nonlinear effects. These advantages make the 1310nm band an ideal choice for scenarios such as local area networks, metropolitan area networks, and data center interconnection.

[0061] As described above, in the SiN-based photonic crystal nanobeam cavity of this application, the horizontal axis length of the gradient aperture remains unchanged to ensure optical phase matching between adjacent unit cells. Only the vertical axis length of the gradient aperture is modulated to confine the optical mode field, significantly improving the Q value and achieving higher optical storage. Furthermore, SiN has low optical loss characteristics, which can reduce energy loss during light propagation and improve the overall performance of the nanobeam cavity. In addition, compared with traditional semiconductor materials, SiN materials and their manufacturing processes are less expensive, and the related processes are compatible with existing CMOS manufacturing technologies, facilitating integration into existing electronic and photonic devices, further reducing production costs and improving device performance. In short, the SiN-based photonic crystal nanobeam cavity of this application has advantages such as high Q value, low loss, excellent optical and mechanical properties, multifunctionality, low cost, and compatibility, and has broad application prospects in optical communication, sensing, and quantum computing.

[0062] Example 2

[0063] This embodiment provides a method for fabricating a SiN-based photonic crystal nanobeam cavity, which includes the following steps:

[0064] S1: Provide a substrate 1, and form a lower cladding layer 2 on the substrate 1;

[0065] S2: A one-dimensional SiN waveguide layer 3 is formed on the lower cladding layer 2. The one-dimensional SiN waveguide layer 3 includes a gradient region 30. In the extension direction of the one-dimensional SiN waveguide layer 3, the gradient region 30 includes a first gradient region 300 and a second gradient region 301.

[0066] S3: Etch the one-dimensional SiN waveguide layer 3 to form a plurality of spaced gradient holes 302 in both the first gradient region 300 and the second gradient region 301, and the first gradient region 300 and the second gradient region 301 are symmetrically arranged about the center of the gradient region 30.

[0067] As an example, in step S1, the substrate 1 is made of Si, and the lower cladding layer 2 is made of SiO2. The lower cladding layer 2 is formed using plasma-enhanced chemical vapor deposition (PECVD). The precursors include SiH4, CO2, and Ar. The addition of Ar gas promotes the dissociation of SiH4 and CO2, thereby increasing the deposition rate and reducing the refractive index of SiO2. In other examples, any other suitable method can be used to form the lower cladding layer 2, without being limited to this embodiment.

[0068] As an example, in step S2, the one-dimensional SiN waveguide layer 3 is formed using low-pressure chemical vapor deposition (LPCVD). The SiN film formed by LPCVD has a low hydrogen content, which helps to reduce optical loss.

[0069] As an example, after forming the one-dimensional SiN waveguide layer 3, a high-temperature annealing step is also included to reduce the stress and loss of SiN. The annealing temperature range is 800 to 1200°C.

[0070] As an example, in step S3, the one-dimensional SiN waveguide layer 3 is etched using a dry etching process to form the gradient hole 302; specifically, the gradient hole 302 is formed based on processes such as deep ultraviolet lithography and ICP etching. The geometric dimensions and shape of the gradient hole 302 are described in Example 1, and will not be elaborated here.

[0071] As an example, the one-dimensional SiN waveguide layer 3 also includes the reflection region. During the process of forming the gradient aperture 302, the constant aperture 312 is also formed in the reflection region. The geometric dimensions and shape of the constant aperture 312 are described in Embodiment 1, and will not be elaborated here.

[0072] As an example, after forming the gradient hole 302 and the constant hole 312, the lower cladding 2 is etched using a hydrofluoric acid wet etching process to form the groove 20.

[0073] In summary, in the SiN-based photonic crystal nanobeam cavity and its fabrication method of the present invention, the horizontal axis length of the graded aperture remains unchanged to ensure optical phase matching between adjacent unit cells. Only the vertical axis length of the graded aperture is modulated to confine the optical mode field, significantly improving the Q value and achieving higher optical storage. Furthermore, SiN has low optical loss characteristics, which can reduce energy loss during light propagation and improve the overall performance of the nanobeam cavity. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0074] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A SiN-based photonic crystal nanobeam cavity, characterized in that, include: A substrate, on which a lower cladding layer is disposed; A one-dimensional SiN waveguide layer is located above the lower cladding layer. The one-dimensional SiN waveguide layer includes a gradient region. Along the extension direction of the one-dimensional SiN waveguide layer, the gradient region includes a first gradient region and a second gradient region that are symmetrically arranged about the center of the gradient region. Both the first gradient region and the second gradient region are provided with a plurality of gradient holes arranged at intervals. The gradient holes in the first gradient region and the second gradient region are symmetrically arranged about the center of the gradient region. The horizontal axis of the gradient aperture is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the gradient aperture is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. In the first gradient region and along the direction from the second gradient region to the first gradient region, the vertical axis length of the plurality of gradient apertures gradually decreases, and the horizontal axis length of the plurality of gradient apertures is equal.

2. The SiN-based photonic crystal nanobeam cavity according to claim 1, characterized in that, Within the first gradient zone and along the direction from the second gradient zone to the first gradient zone, the gradient holes include a first gradient hole, a second gradient hole, ..., an Nth gradient hole, where N is an integer greater than 2, and the vertical axis radius R of the Kth gradient hole is... y (K) satisfies: Among them, R y (1) is the vertical axis radius of the first gradient hole, R y (N) is the vertical axis radius of the Nth gradient hole, and K is an integer and 1≤K≤N.

3. The SiN-based photonic crystal nanobeam cavity according to claim 1, characterized in that, The one-dimensional SiN waveguide layer also includes a reflection region. Along the extension direction of the one-dimensional SiN waveguide layer, the reflection region is located on both sides of the gradient region. The reflection region is provided with a plurality of spaced constant holes. The horizontal axis of the constant holes is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the constant holes is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. The vertical axis lengths of the plurality of constant holes are equal, and the horizontal axis lengths of the plurality of constant holes are equal.

4. The SiN-based photonic crystal nanobeam cavity according to claim 3, characterized in that: The lower cladding layer is provided with a groove that extends from the upper surface of the lower cladding layer to the interior of the lower cladding layer, wherein the projection of the groove on the substrate covers the projection of the gradient area and the reflection area on the substrate.

5. The SiN-based photonic crystal nanobeam cavity according to claim 1, characterized in that: The substrate is made of silicon, and the lower cladding is made of silicon dioxide.

6. A method for fabricating a SiN-based photonic crystal nanobeam cavity, characterized in that, Includes the following steps: Provide a substrate, and form a lower cladding layer on the substrate; A one-dimensional SiN waveguide layer is formed on the lower cladding layer. The one-dimensional SiN waveguide layer includes a gradient region. Along the extension direction of the one-dimensional SiN waveguide layer, the gradient region includes a first gradient region and a second gradient region that are symmetrically arranged about the center of the gradient region. The one-dimensional SiN waveguide layer is etched to form a plurality of spaced gradient holes in both the first gradient region and the second gradient region, and the gradient holes in the first gradient region and the second gradient region are symmetrically arranged about the center of the gradient region. Wherein, the horizontal axis of the gradient aperture is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the gradient aperture is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. In the first gradient region and along the direction from the second gradient region to the first gradient region, the vertical axis length of the plurality of gradient apertures gradually decreases, and the horizontal axis length of the plurality of gradient apertures is equal.

7. The method for fabricating a SiN-based photonic crystal nanobeam cavity according to claim 6, characterized in that: The method for forming the lower cladding includes plasma-enhanced chemical vapor deposition, the method for forming the one-dimensional SiN waveguide layer includes low-pressure vapor deposition, and the method for forming the gradient via includes dry etching.

8. The method for fabricating a SiN-based photonic crystal nanobeam cavity according to claim 6, characterized in that: The one-dimensional SiN waveguide layer also includes a reflection region. Along the extension direction of the one-dimensional SiN waveguide layer, the reflection region is located on both sides of the gradient region. During the process of forming the gradient aperture in the gradient region, a plurality of spaced constant apertures are also formed in the reflection region. The horizontal axis of the constant aperture is parallel to the extension direction of the one-dimensional SiN waveguide layer, and the vertical axis of the constant aperture is perpendicular to the extension direction of the one-dimensional SiN waveguide layer. The vertical axis lengths of the plurality of constant apertures are equal, and the horizontal axis lengths of the plurality of constant apertures are equal.

9. The method for fabricating a SiN-based photonic crystal nanobeam cavity according to claim 8, characterized in that: After forming the gradient hole and the constant hole, the method further includes etching the lower cladding to form a groove, wherein the groove extends from the upper surface of the lower cladding to the interior of the lower cladding, and the projection of the groove on the substrate covers the projection of the gradient area and the reflection area on the substrate.

10. The method for fabricating a SiN-based photonic crystal nanobeam cavity according to claim 6, characterized in that: After the one-dimensional SiN waveguide layer is formed, and before etching the one-dimensional SiN waveguide layer, the process further includes an annealing step for the one-dimensional SiN waveguide layer.

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