Wide waveguide high coupling efficiency silicon nitride micro-ring resonator cavity structure and design method thereof

Abstract

The application discloses a wide waveguide high-coupling-efficiency silicon nitride micro-ring resonant cavity structure and a design method thereof. The structure comprises a SiO2 substrate, a Si3N4 micro-ring cavity etched above the SiO2 substrate, a Si3N4 Gaussian filter mode pulley coupler and a SiO2 upper cladding layer. The Si3N4 micro-ring cavity is composed of a ring waveguide and an adiabatic shrinkage conical filter mode waveguide narrowed from the ring waveguide, the width of the adiabatic shrinkage conical filter mode waveguide changes with the position and satisfies a Gaussian function; the width of the narrowest part of the adiabatic shrinkage conical filter mode waveguide is such that only a basic mode exists in the ring waveguide and the adiabatic shrinkage conical filter mode waveguide; the Gaussian filter mode pulley coupler is arranged in a coupling area of the micro-ring resonant cavity as a coupling waveguide, and the radius change of the Gaussian filter mode pulley coupler and the width change of the adiabatic shrinkage conical filter mode waveguide satisfy the same Gaussian function. The application can realize a high quality factor, enhance the coupling effect and ensure a single mode condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photonics and nonlinear optics, and particularly relates to a wide-waveguide high-coupling-efficiency silicon nitride micro-ring resonator structure and a design method thereof. BACKGROUND

[0002] With the continuous development of modern photonics and nonlinear optics, optical frequency comb (OFC) has been widely used in metrology, microwave photonics, optical communication and quantum optics due to its small size, wide spectrum, low power consumption and adjustable dispersion. Among them, the abnormal dispersion optical frequency comb generated in a high-quality factor (Q) microcavity based on Kerr nonlinear effect has become an important choice for many application scenarios due to its high frequency, high integration and high stability.

[0003] Silicon nitride (Si3N4) has been an important carrier for optical frequency comb technology in recent years and has shown outstanding performance in the development of chip-level optical frequency comb systems. Si3N4 has a relatively large band gap, a wide transparent wavelength range from visible light to infrared light, and is not affected by two-photon absorption in the wavelength range. In addition, the nonlinear coefficient of Si3N4 is about one order of magnitude larger than that of silicon, and it is compatible with CMOS technology, which is more conducive to the production of high-Q silicon-based micro-ring resonators.

[0004] A key factor affecting the Q value of the silicon nitride microcavity is the sidewall roughness of the waveguide. Limited by the precision of photolithography and etching process, the sidewall of the waveguide will have nanoscale fluctuations, causing Rayleigh scattering loss. In the micro-ring resonator, the light field is repeatedly reflected at the sidewall, and the impact of the sidewall roughness is further amplified. The existing micro-ring resonator commonly uses a waveguide size of 800nm×1650nm. The narrow waveguide extends more in the micro-ring, and is more likely to leak to the cladding or radiate out, causing loss, which is not conducive to the improvement of the Q value. The narrow waveguide mode field is not concentrated enough, and the nonlinear effect is weak under the same input power, which is not conducive to the generation of optical frequency comb. Therefore, a wider waveguide can be used to reduce the loss introduced by the sidewall roughness. The light field of the wide waveguide is more widely distributed transversely, and the electric field strength near the sidewall is significantly reduced. The peak value moves to the center of the waveguide, and the disturbance amplitude of the rough sidewall to the light field is reduced, and the scattering loss is relatively reduced. Therefore, a wider waveguide can be used to reduce the loss introduced by the sidewall roughness.

[0005] But the increase of waveguide width also brings new problems, first, the too wide waveguide will lead to the effect of reducing the coupling between the straight waveguide and the ring cavity, which requires higher power to excite the light frequency comb. Simulation proves that when the waveguide width is set to 2.6μm, and the micro ring waveguide and the coupling waveguide are not processed, the transmittance between them is far less than 1%. The mainstream method to improve the coupling efficiency is to use a gradual transition structure in the coupling area, which slowly transitions the width of the straight waveguide to the width close to the micro ring. The gradual coupling transition structure generally needs a long transition section, which is not conducive to compact layout. Secondly, when the waveguide width is too large, there will be more modes, leading to mode competition, nonlinear effect dispersion and unstable light frequency comb. High-order modes can be attenuated by designing the shape of the micro ring, such as replacing the circular ring with Euler curve, secant function, etc. But this method requires accurate design of the shape of the micro ring, and the design process is complex. How to improve the microcavity Q value by using wide waveguide, enhance the coupling effect and ensure the single mode condition has become an important problem to be solved in current design. SUMMARY

[0006] The purpose of the present application is to solve the problems of low coupling efficiency and mode competition existing in the existing wide waveguide silicon nitride micro ring resonant cavity, and to provide a wide waveguide high coupling efficiency silicon nitride micro ring resonant cavity structure and a design method thereof, which can realize high quality factor, enhance coupling effect and ensure single mode condition.

[0007] In order to achieve the above purpose, one aspect of the present application provides a wide waveguide high coupling efficiency silicon nitride micro ring resonant cavity structure, comprising a SiO2 substrate, a Si3N4 micro ring cavity and a Si3N4 Gaussian filter mode pulley coupler etched above the SiO2 substrate, and a SiO2 upper cladding layer superimposed on the Si3N4 micro ring cavity and the Si3N4 Gaussian filter mode pulley coupler.

[0008] The Si3N4 micro ring cavity is composed of a ring waveguide and an adiabatic contraction tapered filter mode waveguide connected from the ring waveguide, and the adiabatic contraction tapered filter mode waveguide is arranged in the coupling area of the micro ring resonant cavity, and the width of the adiabatic contraction tapered filter mode waveguide changes with the position and satisfies the following Gaussian function:

[0009]

[0010] Wherein, is the width of the adiabatic contraction tapered filter mode waveguide at the position, is the width of the ring waveguide, is the width of the ring waveguide, is the parameter for controlling the change of the width of the adiabatic contraction tapered filter mode waveguide;

[0011] The width of the narrowest part of the adiabatic shrinkage conical filter mode waveguide is such that the annular waveguide and the adiabatic shrinkage conical filter mode waveguide only have a fundamental mode, so that single-mode transmission is achieved; the Gaussian filter mode pulley coupler is arranged in the coupling area of the micro-ring resonant cavity as a coupling waveguide, the radius of the Gaussian filter mode pulley coupler changes with the width of the adiabatic shrinkage conical filter mode waveguide, the change of the radius of the Gaussian filter mode pulley coupler and the change of the width of the adiabatic shrinkage conical filter mode waveguide satisfy the same Gaussian function, so that the adiabatic shrinkage conical filter mode waveguide is always kept at an equal interval.

[0012] Another aspect of the present application provides a design method of the above structure, comprising:

[0013] Step S1: setting the refractive index of the SiO2 substrate and the refractive index of the Si3N4 micro-ring cavity;

[0014] Step S2: calculating the dispersion of the Si3N4 annular waveguide with different widths, and selecting the width with slow dispersion as the width of the annular waveguide under the condition that the annular waveguide is guaranteed to be abnormal dispersion;

[0015] Step S3: calculating the mode distribution in the Si3N4 annular waveguide with different widths, and selecting the width with only the fundamental mode in the annular waveguide as the width of the narrowest part of the adiabatic shrinkage conical filter mode waveguide;

[0016] Step S4: calculating the width of each position of the adiabatic shrinkage conical filter mode waveguide according to the Gaussian function, and selecting the length of the adiabatic shrinkage conical filter mode waveguide;

[0017] Step S5: determining the position of the adiabatic shrinkage conical filter mode waveguide in the coupling area of the micro-ring resonant cavity obtained in step S4;

[0018] Step S6: setting the Gaussian filter mode pulley coupler according to the Gaussian function, setting the coupling interval between the adiabatic shrinkage conical filter mode waveguide and the Gaussian filter mode pulley coupler, and obtaining the Si3N4 micro-ring resonant cavity structure.

[0019] The wide waveguide high-coupling-efficiency silicon nitride micro-ring resonant cavity structure and the design method thereof according to the above aspect of the present application can achieve high quality factors, enhance the coupling effect and guarantee single-mode conditions. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor:

[0021] Figure 1A schematic diagram of a tangential combination structure of a Si3N4 micro-ring cavity with an adiabatic shrinkage conical filter mode waveguide according to an embodiment of the present application;

[0022] Figure 2 A schematic diagram of a tangential combination structure of a Gaussian filter mode pulley coupler according to an embodiment of the present application;

[0023] Figure 3 Dispersion of Si3N4 waveguides with different widths at a wavelength of 1550 nm according to an embodiment of the present application;

[0024] Figure 4 A simulation result diagram of a transmittance of a coupling region of a conventional Si3N4 micro-ring resonant cavity at a wavelength of 1550 nm;

[0025] Figure 5 A simulation result diagram of a transmittance of an adiabatic shrinkage conical filter mode waveguide at different positions according to an embodiment of the present application;

[0026] Figure 6 A simulation result diagram of a coupling efficiency of a Gaussian filter mode pulley coupler with different widths according to an embodiment of the present application;

[0027] Figure 7 A simulation result diagram of a transmittance of a Si3N4 micro-ring resonant cavity after optimization of a coupling region at a wavelength of 1550 nm according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort fall within the protection scope of the present application.

[0029] An embodiment of the present application provides a wide waveguide high-coupling-efficiency silicon nitride micro-ring resonant cavity structure, as shown in Figure 1 and Figure 2 The wide waveguide high-coupling-efficiency silicon nitride micro-ring resonant cavity structure according to the embodiment of the present application includes a SiO2 substrate, a Si3N4 micro-ring cavity 1 etched above the SiO2 substrate, a Si3N4 Gaussian filter mode pulley coupler 3, and a SiO2 upper cladding layer, wherein the SiO2 upper cladding layer is superimposed above the etched Si3N4 micro-ring cavity 1 and the etched Si3N4 Gaussian filter mode pulley coupler 3.

[0030] Figure 1 The dashed part in FIG. 1 is a cross section of an adiabatic shrinkage conical filter mode waveguide 2, as shown in Figure 1As shown, Si3N4 micro-ring cavity 1 is composed of a ring waveguide and an adiabatic shrinkage conical filter mode waveguide 2 connected from the ring waveguide, and the adiabatic shrinkage conical filter mode waveguide 2 is located in the coupling region of the micro-ring resonant cavity.

[0031] Gaussian filter mode pulley coupler 3 is used to improve the coupling effect of Si3N4 micro-ring cavity 1, Figure 2 The dashed part in the figure is the cross section of the adiabatic shrinkage conical filter mode waveguide 3 and the Gaussian filter mode pulley coupler 2, as shown in the figure, this part is a curved waveguide with a radius that satisfies the Gaussian function and maintains an equal interval with the adiabatic shrinkage conical filter mode waveguide. Figure 2

[0032] The effective refractive index of SiO2 substrate is given by the geometric dispersion and Sellmeier material dispersion formula 1; the effective refractive index of Si3N4 micro-ring cavity is given by the geometric dispersion and Sellmeier material dispersion formula 2:

[0033] (1)

[0034] (2)

[0035] wherein, represents the wavelength in unit, represents the Sellmeier coefficient.

[0036] The relationship between the effective refractive index n eff and the dispersion is expressed as:

[0037] (3)

[0038] (4)

[0039] (5)

[0040] (6)

[0041] wherein is the first-order and second-order dispersion coefficient, is the group refractive index, is the group velocity dispersion. When , the high-frequency component in the optical pulse is transmitted faster than the low-frequency component, which is called abnormal dispersion; ​When the high-frequency component in the light pulse is transmitted slower than the low-frequency component, it is called normal dispersion. In normal dispersion, the actual resonant frequency of the high-order mode deviates from the ideal linear distribution, which is not conducive to the generation of dissipative Kerr soliton (DKS), but is more likely to enter a chaotic state or a Turing state; in abnormal dispersion, the actual resonant frequency of the high-order mode is closer to the ideal linear distribution, which is conducive to the generation of DKS, and is more likely to enter a soliton state with high coherence and high stability.

[0042] After determining the structural dispersion of the waveguide, i.e., determining the waveguide size used by the micro-ring cavity, for a circular micro-ring resonant cavity, the main geometric parameters are the micro-ring radius R and the coupling distance gap.

[0043] Considering designing a micro-ring resonant cavity with a working wavelength in the 1550 nm band, after determining the required FSR = 100 GHz, the radius R of the micro-ring can be determined according to formula 7, wherein is the working wavelength of the device, is the waveguide group refractive index calculated by formula 4.

[0044] (7)

[0045] For the high-order mode existing in the wide waveguide, by adding an adiabatic shrinkage tapered filter mode waveguide in the micro-ring cavity, the originally wide waveguide is smoothly shrunk to a narrower width, and in this process, the high-order mode will be gradually attenuated due to its large bending loss, so that only the fundamental mode is left, realizing the existence of only a single mode. This local size change will not affect the overall dispersion and Q value of the micro-cavity, and at the same time, only the fundamental modes of TE and TM exist in the micro-cavity.

[0046] The adiabatic shrinkage needs to ensure that the mode transformation rate is much lower than the difference in propagation constants between modes, which is usually realized by optimizing the geometric function of the shrinkage path. The Gaussian function has an infinite-order continuous derivative, which can ensure the smoothness of the change in waveguide width, significantly reduce the end reflection, and the gradual change rate of the Gaussian type shrinkage naturally fits the fiber-waveguide mode field diffusion characteristics, which can improve the coupling efficiency. The width of the adiabatic shrinkage tapered filter mode waveguide changes with its position using the following Gaussian function expression:

[0047] (8)

[0048] wherein, is the width of the adiabatic shrinkage tapered filter mode waveguide at the position x, is the width of the adiabatic shrinkage tapered filter mode waveguide at the position x, is the width of the waveguide before narrowing, is the independent variable, is a parameter that controls the speed of the change in the width of the adiabatic shrinkage tapered filter mode waveguide, and a smaller which will cause the waveguide to shrink rapidly from a wider width to a narrower width, and the larger The waveguide width changes slowly, but it can cause the adiabatic shrinking conical filter mode waveguide to be too long, thereby affecting the quality factor.

[0049] The effective range of a typical Gaussian function is (covering 99.7% of the energy change), so the width of the waveguide is generally selected to be , The maximum allowed taper length is determined by the process. By adiabatically shrinking the width of a small section of the annular waveguide at the coupling region in the Si3N4 microcavity from 2.6 μm to 0.68 μm according to formula 8, an adiabatic shrinking conical filter mode waveguide with a length of μm is formed. At this time, the waveguide can effectively filter the high-order modes in the micro-ring resonant cavity and only retain the fundamental mode, resulting in a more stable optical frequency comb.

[0050] In addition to the problem of high-order modes in traditional wide waveguides, the coupling efficiency is also greatly reduced. The micro-ring resonant cavity is composed of an annular waveguide and a straight waveguide, and the two are coupled by evanescent waves. A waveguide that is too wide restricts the light field more strictly within the core, resulting in a decrease in the penetration depth of the evanescent field in the coupling gap gap.

[0051] The method for solving the low coupling efficiency is to introduce a local taper structure (adiabatic shrinking conical filter mode waveguide) in the coupling region to restore the strength of the evanescent field. The adiabatic shrinking conical filter mode waveguide is placed in the coupling region, and the position of the thinnest point (narrowest point) is designed to simultaneously perform the functions of filtering and restoring the strength of the evanescent field, thereby avoiding the introduction of too many structures in the annular waveguide, and avoiding both increasing the complexity of the design and being detrimental to improving the quality factor of the microcavity.

[0052] The traditional micro-ring resonant cavity is point-coupled, i.e., the design principle of the coupling region is to take the distance from the lowest point of the annular waveguide to the straight waveguide as the gap. If a nonlinear taper structure is introduced in the coupling region, the lowest point in the annular waveguide will be offset from the original center position to a certain extent, and there will be a certain coupling at the lowest point in addition to the thinnest position of the nonlinear taper waveguide.

[0053] In order to solve the problem, the present application designs a Gaussian filter mode pulley coupler, the basic principle of which is to use pulley coupling to ensure equal coupling intervals in a certain area, so as to couple two curved waveguides. Unlike the general pulley coupler which adopts a fixed radius circular arc waveguide, in order to ensure that the coupling waveguide and the nonlinear tapered part (adiabatic shrinkage tapered filter mode waveguide) in the ring waveguide are equally spaced, the bending radius of the coupling waveguide (Gaussian filter mode pulley coupler) is set to be the same as the Gaussian function of the width change of the nonlinear tapered waveguide, that is, the radius of the Gaussian filter mode pulley coupler changes nonlinearly with the width of the adiabatic shrinkage tapered filter mode waveguide, and the change of the radius of the Gaussian filter mode pulley coupler is subject to formula 8, which can ensure that the coupling waveguide and the adiabatic shrinkage tapered filter mode waveguide are always equally spaced. At the same time, in order to make the light more easily coupled into the micro-ring resonant cavity, the width of the Gaussian filter mode pulley coupler is designed to improve the coupling efficiency, when the width is 1.3 μm, the coupling efficiency can reach about 13% when the interval between the adiabatic shrinkage tapered filter mode waveguide and the Gaussian filter mode pulley coupler is 0.4 μm. By adding a small section of adiabatic shrinkage tapered filter mode waveguide in the ring waveguide of the micro-ring resonant cavity and using the Gaussian filter mode pulley coupler, the coupling efficiency of the micro-ring resonant cavity can be effectively improved, and the optical frequency comb is more easily generated.

[0054] The embodiment of the present application also provides a design method of a wide waveguide high-coupling-efficiency silicon nitride micro-ring resonant cavity structure, which comprises the following steps S1-S6.

[0055] Step S1: set the refractive index of the SiO2 substrate according to formula 1, set the refractive index of the Si3N4 micro-ring cavity according to formula 2, and set the Sellmeier coefficient according to table 1 .

[0056] Table 1: Refractive index coefficients of SiO2 and Si3N4 materials

[0057]

[0058] Step S2: create a silicon nitride waveguide structure (including a SiO2 substrate, a Si3N4 waveguide and a SiO2 upper cladding layer). Set the thickness of the SiO2 substrate to be 730 μm, the thickness of the silicon nitride film to be 730 nm, and the thickness of the SiO2 upper cladding layer to be 730 μm. Calculate the effective refractive index of the Si3N4 waveguide with a thickness of 730 nm at different widths under a wavelength range of 1550 nm, and calculate the dispersion D of the Si3N4 waveguide with different widths under the corresponding wavelength according to formula 6, such as Figure 3 .

[0059] Under the condition of ensuring that the waveguide is anomalous dispersion, select a width W=2.6 μm with the flattest dispersion. ​​

[0060] Step S3: Create a conventional silicon nitride micro-ring resonator cavity, set its radius to be 227 μm, the width of the ring waveguide to be 2.6 μm, and the width of the coupling waveguide to be 2.6 μm. Calculate the electric field distribution of the silicon nitride micro-ring resonator cavity at a center wavelength of 1550 nm and the transmittance T of the through and drop ends, as shown in FIG. 3. Figure 4 It can be seen that the transmittance of the drop end of the micro-ring resonator cavity is very small even at the minimum coupling interval gap = 0.1 μm, only 0.65%, and at gap = 0.4 μm (critical coupling distance), there is almost no coupling light in the micro-ring resonator cavity.

[0061] For this, in this step, a Si3N4 adiabatic tapered filter waveguide with a thickness of 730 nm is created, and the width of the adiabatic tapered filter waveguide at the thinnest part is calculated. Calculate the mode distribution in the Si3N4 waveguide at a center wavelength of 1550 nm, and when the width is 0.68 μm, only the fundamental mode (including TE00 and TM00) exists in the waveguide, and the rest of the high-order modes are all cut off, that is, the width of the adiabatic tapered filter waveguide at the thinnest part is 0.68 μm.

[0062] Step S4: Calculate the width of the adiabatic tapered filter waveguide at each position according to formula 8, set the number of sampling points to be 2000, and obtain the coordinates of each point. The length of the adiabatic tapered filter waveguide is scanned at a center wavelength of 1550 nm, and the length range is from 50 μm to 150 μm with an interval of 10 μm.

[0063] Select a suitable length of the adiabatic tapered filter waveguide, that is, neither introduce additional bending loss, nor ensure smaller transmission loss, at this time the length is L = 110 μm.

[0064] Step S5: Determine the specific position of the adiabatic tapered filter waveguide obtained in step S4 in the coupling region of the micro-ring resonator cavity. Take the thinnest part of the adiabatic tapered filter waveguide as the starting point, at this time the angle between the position and the vertical direction is 13°, and the angle θ of the adiabatic tapered filter waveguide is scanned from 13° to 0° with an interval of 1°, and the transmittance T of the adiabatic tapered filter waveguide after passing through the coupling waveguide is obtained, as shown in FIG. 6. Figure 5 The coupling effect is best when the adiabatic tapered waveguide is at an angle of 0° with the vertical direction, at this time the transmittance is the highest, about 70%.

[0065] Step S6: Set the Gaussian filter pulley coupler according to formula 8, and set the coupling interval between the adiabatic tapered filter waveguide and the Gaussian filter pulley coupler to be 0.4 μm according to the empirical value. The width of the Gaussian filter pulley coupler is scanned from 0.4 μm to 2.6 μm with an interval of 0.2 μm, and the transmittance T of the Gaussian filter pulley coupler is obtained, as shown in FIG. 7. The transmission effect of the Gaussian filter pulley coupler on the light source was obtained by scanning from 1.0μm to 2.5μm at 0.1μm intervals, as shown below. Figure 6 .

[0066] The width of the Gaussian filter pulley coupler should have the highest possible coupling efficiency, and there should be no overcoupling even with the smallest coupling interval (e.g., ...). When the gap is 1.0 μm, the gap at 0.2 μm is higher than that at 0.1 μm. Therefore, a suitable width for the Gaussian filter mode pulley coupler should be selected. =1.3μm.

[0067] The Si3N4 microring resonator assembly structure is obtained through the above steps (see...). Figure 2 This includes a SiO2 substrate, an etched Si3N4 microring cavity, an etched Si3N4 Gaussian filter pulley coupler, and a SiO2 cladding. The parameters of each part of the microring are set according to the optimal results of steps S1-S6. The transmittance T at the through and drop ends of the coupling region of the silicon nitride microring resonator at a center wavelength of 1550 nm is calculated, see [reference needed]. Figure 7 .

[0068] After adopting a structure combining an adiabatic shrinkable tapered filter waveguide and a Gaussian filter pulley coupler in the coupling region of the microring resonator, the transmittance of the adiabatic shrinkable tapered filter waveguide section, i.e., the coupling efficiency of the microring resonator, can be observed to be approximately 27%.

[0069] In summary, the wide-waveguide, high-coupling-efficiency silicon nitride microring resonator structure and its design method of this invention transform the coupling region of the silicon nitride microring resonator from traditional point coupling to a combination of an adiabatic shrinking tapered mode-filtering waveguide and a Gaussian mode-filtering pulley coupler, increasing its coupling efficiency from 0.65% to approximately 27%. While achieving a high quality factor, it improves the coupling effect between the straight waveguide and the ring cavity, ensuring single-mode conditions and reducing intracavity mode competition, thereby obtaining a more easily generated and more stable optical frequency comb, significantly improving the output performance of the optical frequency comb. This invention is applicable to the design of integrated optical frequency comb chips and has broad application prospects in metrology, microwave photonics, optical communication, and quantum optics.

[0070] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A silicon nitride microring resonator structure with wide waveguide and high coupling efficiency, characterized in that, It includes a SiO2 substrate, a Si3N4 micro-ring cavity and a Si3N4 Gaussian filter pulley coupler etched on the SiO2 substrate, and a SiO2 cladding layer superimposed on the Si3N4 micro-ring cavity and the Si3N4 Gaussian filter pulley coupler. The Si3N4 microring cavity is composed of a ring waveguide connected to an adiabatic shrinking tapered filter mode waveguide that narrows from the ring waveguide. The adiabatic shrinking tapered filter mode waveguide is located in the coupling region of the microring resonator, and the width of the adiabatic shrinking tapered filter mode waveguide varies with its position according to the following Gaussian function: , Where w(z) is the width of the adiabatic shrinking tapered filter mode waveguide at position z, w start σ is the width of the ring waveguide, and σ is a parameter that controls the rate of change of the width of the adiabatic shrinking tapered filter mode waveguide; The narrowest point of the adiabatic shrinkable tapered filter waveguide ensures that only the fundamental mode exists within both the ring waveguide and the adiabatic shrinkable tapered filter waveguide, thus achieving single-mode transmission. A Gaussian filter pulley coupler is placed as a coupling waveguide in the coupling region of the micro-ring resonator. The radius of the Gaussian filter pulley coupler varies with the width of the adiabatic shrinkable tapered filter waveguide, and the radius variation of the Gaussian filter pulley coupler satisfies the same Gaussian function as the width variation of the adiabatic shrinkable tapered filter waveguide, thus maintaining an equal interval with the adiabatic shrinkable tapered filter waveguide at all times. The parameter σ is set to σ=6L, where L is the maximum allowable cone length determined by the process of the adiabatic shrinkable tapered filter waveguide.

2. The structure as described in claim 1, characterized in that, The width of the ring waveguide in the Si3N4 microring cavity is the width that makes the ring waveguide anomalous dispersion.

3. A design method for the structure as described in claim 1 or 2, characterized in that, include: Step S1: Set the refractive index of the SiO2 substrate and the refractive index of the Si3N4 micro-ring cavity; Step S2: Calculate the dispersion of Si3N4 ring waveguides with different widths. Under the condition that the ring waveguide has anomalous dispersion, select the width with gentle dispersion as the width of the ring waveguide. Step S3: Calculate the mode distribution in Si3N4 ring waveguides of different widths, and take the width of the ring waveguide with only the fundamental mode as the width of the narrowest part of the adiabatic shrinking tapered filter waveguide. Step S4: Calculate the width of the adiabatic shrinkable tapered filter waveguide at each position based on the Gaussian function, and select the length of the adiabatic shrinkable tapered filter waveguide; Step S5: Determine the position of the adiabatic shrinkable tapered filter waveguide obtained in step S4 in the coupling region of the micro-ring resonator; Step S6: Set the Gaussian filter mode pulley coupler according to the Gaussian function, set the coupling interval between the adiabatic shrinkable tapered filter mode waveguide and the Gaussian filter mode pulley coupler, and obtain the Si3N4 micro-ring resonant cavity structure.

4. The method as described in claim 3, characterized in that, In step S5, starting from the narrowest point of the adiabatic shrinkable tapered filter waveguide, the angle of the adiabatic shrinkable tapered filter waveguide is scanned to obtain the position of the adiabatic shrinkable tapered filter waveguide with the highest transmittance after passing through the coupled waveguide, which is taken as the position of the adiabatic shrinkable tapered filter waveguide in the coupling region of the micro-ring resonator.

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