Micro-ring resonator based on multi-circle square structure

Abstract

The invention relates to a micro-ring resonator based on a multi-circle square structure, the micro-ring resonator comprises a coupling waveguide and a multi-circle square micro-ring resonant cavity, the coupling waveguide comprises an S-bend waveguide, an input waveguide and an output waveguide which are all single-mode waveguides, and the multi-circle square micro-ring resonant cavity comprises a crossed waveguide chain and a multi-mode waveguide section connected with the crossed waveguide chain. The multi-mode waveguide section comprises a multi-mode straight waveguide and a 90-degree multi-mode Euler bending waveguide. By introducing the multi-mode waveguide, the energy distribution of the guided mode on the side wall is reduced, and the transmission loss of the micro-ring resonant cavity is reduced. Through the arrangement of the multi-circle square micro-ring resonant cavity, the length of the micro-ring is increased within a limited size, and the Q value of the multi-circle square micro-ring resonant cavity is improved. By means of the 90-degree multimode Euler bending waveguide, compact 90-degree turning is achieved, generation of a high-order mode is restrained, and meanwhile the micro-ring surrounding area is increased. Therefore, a solution can be provided for the high-performance sensing unit for the integrated micro-ring sensor.

Description

Technical Field

[0001] This invention relates to the field of optical sensing, and more particularly to a microring resonator based on a multi-ring square structure. Background Technology

[0002] Microring sensors are a novel type of sensor that uses a microring resonator as its sensing element. A microring resonator typically consists of a microring cavity and a coupling waveguide. When light propagates within the microring cavity, it resonates at a specific wavelength. The propagation of light within the microring resonator is determined by both the cavity's propagation characteristics and the external environment. This allows for the detection of physical quantities such as angular velocity, temperature, refractive index, and electric field. Microring sensors are characterized by their small size, high sensitivity, integrability, and all-solid-state nature. A higher Q-value in the microring cavity results in a sharper resonance peak, lower energy loss, and better frequency stability. A high Q-value microring cavity is fundamental for realizing high-sensitivity microring sensors.

[0003] The Q-factor of a microring resonator is related to waveguide transmission loss and optical propagation path length. Regarding reducing waveguide transmission loss, the polishing and etching processes involved in ultra-high Q-factor microring resonators are incompatible with standard processes, failing to meet the demands of low-cost mass production. Currently, increasing the waveguide width reduces the energy distribution of the guided mode on the rough sidewalls of the waveguide, thereby improving the Q-factor. Reducing transmission loss alone has limited impact on Q-factor improvement; increasing the optical propagation path length can further enhance the Q-factor. However, the currently commonly used multi-ring cascaded structures suffer from a positive correlation between optical propagation path length and area, making it impossible to simultaneously achieve high Q-factor and finite size. Summary of the Invention

[0004] To address the shortcomings of current technologies, this invention provides a microring resonator based on a multi-ring square structure, which reduces the transmission loss of the microring resonator, increases the optical propagation path length and effective area within a limited size, and further improves the Q value of the microring.

[0005] To achieve the above-mentioned objectives, the present invention provides a microring resonator based on a multi-ring square structure, comprising: a coupled waveguide and a multi-ring square microring resonator cavity; The coupled waveguide and the multi-turn square microring resonant cavity are coupled by evanescent wave; The multi-ring square micro-ring resonant cavity is provided with multiple multimode waveguide segments from the outside to the inside; External light is coupled to the outermost multimode waveguide segment by the coupling waveguide, and then directly transmitted to the innermost multimode waveguide segment based on the connection position of each multimode waveguide segment. It is then transmitted sequentially along the direction from the innermost multimode waveguide segment to the outermost multimode waveguide segment, and finally output by the coupling waveguide.

[0006] According to one aspect of the present invention, in the multi-ring square micro-ring resonant cavity, the outermost multimode waveguide segment is provided with a straight waveguide coupling segment, and the coupling waveguide is coupled to the multi-ring square micro-ring resonant cavity based on the straight waveguide coupling segment.

[0007] According to one aspect of the present invention, the straight waveguide coupling section comprises: a first adiabatic tapered waveguide, an intermediate single-mode straight waveguide, and a second adiabatic tapered waveguide connected in sequence; The width of the intermediate single-mode straight waveguide is the same as the width of the coupled waveguide.

[0008] According to one aspect of the present invention, the coupled waveguide comprises: an input waveguide, an S-bend waveguide, and an output waveguide connected in sequence; The input waveguide, the S-bend waveguide, and the output waveguide are all single-mode waveguides; The widths of the input waveguide, the S-bend waveguide, and the output waveguide are the same.

[0009] According to one aspect of the present invention, the multi-ring square micro-ring resonator further includes: a cross waveguide chain for connecting the plurality of said multimode waveguide segments; The cross waveguide chain includes: multiple cross waveguides connected in series, used to connect the third adiabatic tapered waveguide of the multimode waveguide segment; In the multi-ring square micro-ring resonant cavity, if the number of cross waveguides is M, then the number of multimode waveguide segments is M+1; wherein, the innermost multimode waveguide segment is connected to one cross waveguide at the end of the cross waveguide chain, the outermost multimode waveguide segment is connected to another cross waveguide at the end of the cross waveguide chain, and the remaining multimode waveguide segments are based on two adjacent cross waveguides connected in series on the cross waveguide chain; The multimode waveguide segment is connected to the cross waveguide based on the third adiabatic tapered waveguide.

[0010] According to one aspect of the invention, the cross waveguide comprises: a central square waveguide, and straight waveguide arms perpendicularly distributed along the four sides of the central square waveguide; In the cross waveguide chain, two connected cross waveguides are directly connected based on the straight waveguide arm, and the multimode waveguide segment is connected to the straight waveguide arm based on the third adiabatic tapered waveguide.

[0011] According to one aspect of the present invention, the straight waveguide arm has a four-segment structure, comprising: a first straight waveguide segment, a first tapered waveguide segment, a second tapered waveguide segment, and a second straight waveguide segment connected in sequence; One end of the second straight waveguide segment is connected to the middle square waveguide, and the other end is connected to the wide end of the second tapered waveguide segment. The narrow end of the second tapered waveguide segment is connected to the wide end of the first tapered waveguide segment, and the narrow end of the first tapered waveguide segment is connected to the first straight waveguide segment.

[0012] According to one aspect of the present invention, the first straight waveguide segment is a single-mode waveguide segment; The first tapered waveguide segment is a non-insulated tapered waveguide segment; The second conical waveguide segment is an adiabatic conical waveguide segment; The second straight waveguide segment is a multimode interference segment.

[0013] According to one aspect of the present invention, the multimode waveguide segment includes: a plurality of multimode straight waveguides for connecting a 90° multimode Euler bent waveguide to the multimode straight waveguides; The 90° multimode Euler bent waveguide includes two identical 45° multimode Euler bent waveguides; wherein the beginnings of the two 45° multimode Euler bent waveguides are respectively connected to different multimode straight waveguides, and the ends of the two 45° multimode Euler bent waveguides are connected to each other. Along the direction from the beginning to the end of the 45° multimode Euler bent waveguide, the curvature of the 45° multimode Euler bent waveguide increases linearly from the first curvature ρ1 to the second curvature ρ2. The width of the multimode straight waveguide is the same as the width of the 90° multimode Euler bent waveguide.

[0014] According to one aspect of the present invention, in the 90° multimode Euler bent waveguide, the first curvature ρ1 is obtained with the goal of no other mode excitation when TEO mode light passes through the connection between the multimode straight waveguide and the 90° multimode Euler bent waveguide; the second curvature ρ2 is obtained with the goal of TEO mode light passing through the 90° multimode Euler bent waveguide with a loss of less than 0.15 dB and no other mode excitation. The waveguide structure of the coupling waveguide and the multi-ring square micro-ring resonator is consistent, and it is selected from one of the ridge waveguide and the strip waveguide. The material of the coupling waveguide and the multi-ring square micro-ring resonator is consistent, and it is selected from one of the silicon-on-insulator, silicon nitride, and lithium niobate-on-insulator.

[0015] The technical effects of this invention are as follows: According to one aspect of the present invention, this approach can be implemented based on a standard process platform. The process is simple, requiring only one etching step, and is suitable for mass production.

[0016] According to one aspect of the present invention, the single-mode waveguide coupling based on the coupled waveguide and the intermediate single-mode straight waveguide can effectively prevent the excitation of higher-order modes when light propagates between the multi-ring square micro-ring resonator and the coupled waveguide, ensuring single-mode transmission within the multi-ring square micro-ring resonator, while also improving coupling efficiency.

[0017] According to one aspect of the present invention, by introducing a multimode wide waveguide, the waveguide's ability to confine the guided mode can be increased, the optical field can be moved away from the rough sidewalls, the transmission loss can be reduced, and the Q value can ultimately be improved.

[0018] According to one aspect of the present invention, the cross-waveguide chain configured in this scheme optimizes mode matching and reduces reflection and scattering during optical signal transmission by optimizing the waveguide structure in the intersecting region, thereby achieving low-loss and low-crosstalk transmission of optical signals between the cross-waveguide paths. Furthermore, by introducing cross-waveguides to realize a multi-loop micro-ring structure, the optical propagation distance can be further increased.

[0019] According to one aspect of the present invention, this approach effectively ensures the adiabatic transmission of the fundamental mode in a multi-ring square micro-ring resonator by connecting the cross waveguide and the multimode waveguide segment using a third adiabatic conical waveguide.

[0020] According to one aspect of the present invention, by introducing a 90° multimode Euler bent waveguide, not only can a compact 90° turn be achieved to realize a square microring, but it can also ensure low-loss transmission of the TEO mode without exciting other modes. Compared with a circular microring, the square microring structure can achieve a larger effective area and optical propagation distance within the same size.

[0021] The improvements in the above five aspects further enhance the Q value of the microring resonator in this scheme, thereby providing a reliable guarantee for realizing high-sensitivity resonant integrated optical gyroscopes and other high-performance integrated microring sensors. Attached Figure Description

[0022] Figure 1 This is a structural diagram of a microring resonator based on a multi-ring square structure according to one embodiment of the present invention; Figure 2 This is a structural diagram of a straight waveguide coupling section according to one embodiment of the present invention; Figure 3 This is a structural diagram of a cross waveguide chain according to one embodiment of the present invention; Figure 4 This is a structural diagram of a cross waveguide according to one embodiment of the present invention; Figure 5 An electric field diagram of a cross waveguide according to one embodiment of the present invention; Figure 6 This is a structural diagram of a 90° multimode Euler bent waveguide according to one embodiment of the present invention; Figure 7 The electric field diagram of a 90° multimode Euler bent waveguide according to one embodiment of the present invention is shown. Detailed Implementation

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0024] In describing embodiments of the present invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" express orientations or positional relationships based on the orientations or positional relationships shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on the present invention.

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the embodiments of the present invention are not limited to the following embodiments.

[0026] like Figure 1 As shown, according to one embodiment of the present invention, a microring resonator based on a multi-ring square structure includes: a coupling waveguide 1 and a multi-ring square microring resonator 2. In this embodiment, the coupling waveguide 1 and the multi-ring square microring resonator 2 are coupled by evanescent wave coupling. Light that satisfies the resonance condition after external light is input into the coupling waveguide 1 can be input into the multi-ring square microring resonator 2, while light that does not satisfy the resonance condition is directly output from the coupling waveguide 1. Specifically, the multi-ring square microring resonator 2 is provided with multiple multimode waveguide segments 21 arranged in a ring shape from the outside to the inside. The dimensions of each multimode waveguide segment 21 are different, thus achieving an interval distribution from the outside to the inside or from the inside to the outside in the planar direction, thereby realizing the basic structure of the multi-ring square microring resonator 2. In this embodiment, external light is coupled from the coupling waveguide 1 to the outermost multimode waveguide segment 21, and then directly transmitted to the innermost multimode waveguide segment 21 based on the connection position of each multimode waveguide segment 21. The light is then transmitted sequentially along the direction from the innermost multimode waveguide segment 21 to the outermost multimode waveguide segment 21, and finally output by the coupling waveguide 1.

[0027] Combination Figure 1 and Figure 2As shown, according to one embodiment of the present invention, in the multi-ring square micro-ring resonant cavity 2, the outermost multimode waveguide segment 21 is provided with a straight waveguide coupling segment 2a. In this embodiment, the straight waveguide coupling segment 2a includes: a first adiabatic tapered waveguide 2a1, an intermediate single-mode straight waveguide 2a2, and a second adiabatic tapered waveguide 2a3 connected in sequence; wherein, the width of the intermediate single-mode straight waveguide 2a2 is consistent with the width of the coupling waveguide 1.

[0028] In this embodiment, the first adiabatic tapered waveguide 2a1 and the second adiabatic tapered waveguide 2a3 have identical structures. The width of the narrow end of both the first adiabatic tapered waveguide 2a1 and the second adiabatic tapered waveguide 2a3 is the same as the width of the intermediate single-mode straight waveguide 2a2, and the width of their wide end is the same as the width of the multimode waveguide segment 21. In this embodiment, the widths of both the first adiabatic tapered waveguide 2a1 and the second adiabatic tapered waveguide 2a3 change linearly.

[0029] like Figure 1 As shown, according to one embodiment of the present invention, the coupling waveguide 1 includes an input waveguide 11, an S-bend waveguide 12, and an output waveguide 13 connected in sequence; wherein the input waveguide 11 is used to receive external light, and the output waveguide 13 is used to output light. In this embodiment, the input waveguide 11, the S-bend waveguide 12, and the output waveguide 13 are all single-mode waveguides; wherein the widths of the input waveguide 11, the S-bend waveguide 12, and the output waveguide 13 are consistent. When light enters from the input waveguide 11, only light that satisfies the resonance condition after passing through the S-bend waveguide 12 enters the multi-turn square micro-ring resonant cavity 2, and light that does not satisfy the resonance condition is output from the output waveguide 13. In this embodiment, the width of the coupling waveguide 1 is designed to support only the fundamental mode transmission and is obtained through simulation; wherein the simulation method used is finite element simulation, such as using COMSOL simulation software or Lumerical FDTD simulation software.

[0030] With the above configuration, the single-mode waveguide coupling composed of the coupled waveguide 1 and the intermediate single-mode straight waveguide 2a2 can effectively prevent the excitation of higher-order modes when light propagates between the multi-ring square micro-ring resonator 2 and the coupled waveguide 1, ensuring single-mode transmission within the multi-ring square micro-ring resonator 2, and improving coupling efficiency.

[0031] like Figure 1As shown, according to one embodiment of the present invention, the width of each multimode waveguide segment 21 in the multi-ring square micro-ring resonator 2 is the same. The width of the multimode waveguide segment 21 is obtained through simulation with the goal of reducing the proportion of TEO mode sidewall energy, and the width of the coupling waveguide 1 is smaller than the width of the multimode waveguide segment 21. The simulation method used is finite element simulation, such as using COMSOL simulation software or Lumerical FDTD simulation software. For example, for a lithium niobate ridge waveguide on an insulator, the top thin film lithium niobate has a thickness of 360 nm, an etching depth of 180 nm, an etching tilt angle of 65°, an upper silicon dioxide layer thickness of 2 μm, and a lower silicon dioxide layer thickness of 4.7 μm. At 1550 nm, the width of the multimode waveguide segment 21 can be set to 2 μm.

[0032] Combination Figure 1 and Figure 3 As shown, according to one embodiment of the present invention, the multi-ring square micro-ring resonator 2 further includes: a cross waveguide chain 22 for connecting multiple multimode waveguide segments 21; wherein, the cross waveguide chain 22 includes: multiple cross waveguides 221 connected in series, and a third adiabatic tapered waveguide 222 for connecting the multimode waveguide segments 21. The width of the third adiabatic tapered waveguide 222 varies linearly.

[0033] In this embodiment, the cross waveguide 221 has a cross-shaped central symmetric structure. Thus, the cross waveguide 221 can extend four arms spaced 90° apart, thereby enabling docking with adjacent cross waveguides 221 or connecting with the connection end of the corresponding multimode waveguide segment 21 so that the multimode waveguide segment 21 forms a corresponding closed loop.

[0034] In this embodiment, in the multi-ring square micro-ring resonant cavity 2, the number of cross waveguides 221 is M, and the number of multimode waveguide segments 21 is M+1. For ease of description, the corresponding cross waveguides 221 and multimode waveguide segments 21 can be numbered respectively. Specifically, from the inside out, the M cross waveguides 221 are the first cross waveguide, the second cross waveguide, ..., the Mth cross waveguide; and from the inside out, the M+1 multimode waveguide segments 21 are the first multimode waveguide segment, the second multimode waveguide segment, ..., the M+1th multimode waveguide segment. Furthermore, in this embodiment, the innermost multimode waveguide segment 21 (i.e., the first multimode waveguide segment) is connected to a cross waveguide 221 (i.e., the first cross waveguide) at the end of the cross waveguide chain 22, and the outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment) is connected to another cross waveguide 221 (i.e., the Mth cross waveguide) at the end of the cross waveguide chain 22. The remaining multimode waveguide segments 21 are connected in series based on two adjacent cross waveguides 221 on the cross waveguide chain 22. For example, the two connecting ends of the second multimode waveguide segment are connected to the first cross waveguide and the second cross waveguide, respectively, and the two connecting ends of the third multimode waveguide segment are connected to the second cross waveguide and the third cross waveguide, respectively. In this way, the connection between M+1 multimode waveguide segments 21 and M cross waveguides can be realized, and the construction of the entire multi-ring square micro-ring resonant cavity 2 is realized based on the series connection of M cross waveguides.

[0035] In this embodiment, each arm of the cross waveguide 221 needs to be connected to the multimode waveguide segment 21 via a third adiabatic tapered waveguide 222. Therefore, the number of third adiabatic tapered waveguides 222 is consistent with the number of ports in the multimode waveguide segment 21. indivual.

[0036] With the above configuration, the connection between the cross waveguide 221 and the multimode waveguide segment 21 based on the third adiabatic conical waveguide 222 effectively ensures the adiabatic transmission of the fundamental mode in the multi-ring square micro-ring resonator 2.

[0037] With the above settings, the configured cross waveguide chain 22 optimizes mode matching and reduces reflection and scattering during optical signal transmission by optimizing the waveguide structure in the intersecting region, thereby enabling low-loss and low-crosstalk transmission of optical signals between cross waveguide paths.

[0038] like Figure 1As shown, according to one embodiment of the present invention, when external light is coupled into the outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment) of the multi-ring square micro-ring resonant cavity 2 via the coupling waveguide 1, it first propagates counterclockwise along the transmission path of the outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment). After reaching the outermost cross waveguide 221 (i.e., the Mth cross waveguide), the light propagation direction remains vertical as it passes through the cross waveguide chain 22 and directly enters the innermost multimode waveguide segment 21 (i.e., the first multimode waveguide segment). After circling the innermost multimode waveguide segment 21 (i.e., the first multimode waveguide segment) once, it reaches the innermost cross waveguide 221 (i.e., the first cross waveguide). The light propagation direction remains horizontal as it passes through the cross waveguide 221 (i.e., the first cross waveguide) and enters the second multimode waveguide segment. After circling the second multimode waveguide segment, the light reaches the second cross waveguide. Maintaining the horizontal direction of light transmission, it passes through the second cross waveguide and enters the third multimode waveguide segment... and so on. When the light passes through the Mth cross waveguide in a horizontal direction, it enters the outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment) again, and enters the coupling waveguide 1 from the multi-ring square micro-ring resonator 2 through the straight waveguide coupling segment 2a, and finally exits from the output waveguide 13.

[0039] Combination Figure 3 and Figure 4 As shown, according to one embodiment of the present invention, the cross waveguide 221 includes: a central square waveguide 221a, and four straight waveguide arms 221b perpendicularly distributed along the four sides of the central square waveguide 221a; wherein, in the cross waveguide chain 22, two connected cross waveguides 221 are directly connected based on the straight waveguide arms 221b, and the multimode waveguide segment 21 is connected to the straight waveguide arms 221b based on the third adiabatic tapered waveguide 222.

[0040] Combination Figure 3 and Figure 4 As shown, according to one embodiment of the present invention, the straight waveguide arm 221b has a four-segment structure, comprising: a first straight waveguide segment 221b1, a first tapered waveguide segment 221b2, a second tapered waveguide segment 221b3, and a second straight waveguide segment 221b4 connected sequentially; wherein, one end of the second straight waveguide segment 221b4 is connected to the intermediate square waveguide 221a, and the other end is connected to the wide end of the second tapered waveguide segment 221b3; the narrow end of the second tapered waveguide segment 221b3 is connected to the wide end of the first tapered waveguide segment 221b2; and the narrow end of the first tapered waveguide segment 221b2 is connected to the first straight waveguide segment 221b1. In this embodiment, the widths of the first tapered waveguide segment 221b2 and the second tapered waveguide segment 221b3 are linearly varied.

[0041] In this embodiment, the first straight waveguide segment 221b1 is a single-mode waveguide segment, and its width is consistent with the narrow end width of the third adiabatic tapered waveguide 222. Based on the first straight waveguide segment 221b1, which is set up as an input / output waveguide, it ensures that the optical signal maintains stable single-mode transmission before entering the cross region and after leaving it.

[0042] In this embodiment, the first tapered waveguide segment 221b2 is a non-insulated tapered waveguide segment. The width of its narrow end is consistent with the width of the first straight waveguide segment 221b1. As the length of the first tapered waveguide segment 221b2 extends, the width increases, thereby achieving the requirement that the width of the wide end meets the requirements for exciting higher-order modes.

[0043] In this embodiment, the second tapered waveguide segment 221b3 is an adiabatic tapered waveguide segment. The width of its narrow end is consistent with the width of the wide end of the first tapered waveguide segment 221b. As the length of the second tapered waveguide segment 221b3 extends, the width increases, thereby amplifying the mode and preventing the excitation of other modes due to abrupt changes.

[0044] In this embodiment, the second straight waveguide segment 221b4 is a multimode interference segment, and its width is consistent with the width of the wide end of the second tapered waveguide segment 221b3. Therefore, based on the characteristics of the second straight waveguide segment 221b4, the input optical field is decomposed into multiple higher-order modes. These modes interfere with each other due to phase difference during propagation, and the input field can be reconstructed at the center of the middle square waveguide 221a, thereby realizing accurate reconstruction of the optical signal and low-loss transmission.

[0045] In this embodiment, in the cross waveguide 221, the direction of light transmission between the straight waveguide arms 221b on opposite sides of the middle square waveguide 221a is variable. That is, for the same cross waveguide 221, if the first straight waveguide arm 221b is opposite to the third straight waveguide arm 221b, then light input from the first straight waveguide arm 221b will be output from the third straight waveguide arm 221b, and vice versa; if the second straight waveguide arm 221b is opposite to the fourth straight waveguide arm 221b, then light input from the second straight waveguide arm 221b will be output from the fourth straight waveguide arm 221b, and vice versa. To further illustrate the effect of the cross waveguide 221, an example is provided.

[0046] For a lithium niobate ridge waveguide on an insulator, the top thin film lithium niobate has a thickness of 360 nm, an etching depth of 180 nm, an etching tilt angle of 65°, an upper silicon dioxide layer thickness of 2 μm, and a lower silicon dioxide layer thickness of 4.7 μm. The lengths of the first straight waveguide segment 221b1, the first tapered waveguide segment 221b2, the second tapered waveguide segment 221b3, and the second straight waveguide segment 221b4 are 10 μm, 3 μm, 5 μm, and 8.5 μm, respectively; the widths of the first straight waveguide segment 221b1, the wide-end width of the first tapered waveguide segment 221b2, and the second straight waveguide segment 221b4 are 1 μm, 2.5 μm, and 3.48 μm, respectively. Figure 5 As shown, when the TE0 mode is incident at 1550nm, a single self-imaging of the input coupling mode is generated at the center of the middle square waveguide 221a, realizing low-loss and low-crosstalk cross-transmission of the input light.

[0047] Combination Figure 1 and Figure 6 As shown, according to one embodiment of the present invention, the multimode waveguide segment 21 includes: a plurality of multimode straight waveguides 21a, and a 90° multimode Euler bent waveguide 21b for connecting the multimode straight waveguides 21a; in this embodiment, the 90° multimode Euler bent waveguide 21b includes: two identical 45° multimode Euler bent waveguides 21b1; wherein the starting ends of the two 45° multimode Euler bent waveguides 21b1 are respectively connected to different multimode straight waveguides 21a, and the two 45° multimode Euler bent waveguides 21b1 are connected to different multimode straight waveguides 21a. The terminals of the bent waveguide 21b1 are connected to each other; along the direction from the beginning to the end of the 45° multimode Euler bent waveguide 21b1, the curvature of the 45° multimode Euler bent waveguide 21b1 increases linearly from the first curvature ρ1 to the second curvature ρ2; thus, for the 90° multimode Euler bent waveguide 21b, the change in its curvature can be simply described as follows: the curvature increases linearly from the first curvature ρ1, reaches the maximum value of the second curvature ρ2 after 45°, and then decreases back to the first curvature ρ1 at the same rate.

[0048] In this embodiment, the width of the multimode straight waveguide 21a is the same as the width of the 90° multimode Euler bent waveguide 21b.

[0049] In this embodiment, for the outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment), since it also serves as the input of external light, a straight waveguide coupling segment 2a is provided on the outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment). Furthermore, the straight waveguide coupling segment 2a can be placed between two multimode straight waveguides 21a to achieve the integrity of the entire outermost multimode waveguide segment 21 (i.e., the M+1th multimode waveguide segment). In order to ensure the reliable stability of the connection position, the width of the wide end of the first adiabatic tapered waveguide 2a1 and the second adiabatic tapered waveguide 2a3 is consistent with the width of the multimode straight waveguide 21a.

[0050] In this embodiment, the first curvature ρ1 of the 90° multimode Euler bent waveguide 21b is obtained through simulation with the goal of ensuring no other modes are excited when TE0 mode light passes through the junction of the multimode straight waveguide 21a and the 90° multimode Euler bent waveguide 21b; the second curvature ρ2 is obtained through simulation with the goal of ensuring no other modes are excited when TE0 mode light passes through the 90° multimode Euler bent waveguide 21b with a loss of less than 0.15dB. The simulation method used is finite element simulation, such as using COMSOL simulation software or Lumerical FDTD simulation software.

[0051] By introducing a 90° multimode Euler bend waveguide, not only can a compact 90° bend be achieved, thereby increasing the area of ​​the square microring, but also the low-loss transmission of the TE0 mode can be guaranteed without exciting other modes.

[0052] To further illustrate the effect of the 90° multimode Euler bent waveguide 21b, an example is provided.

[0053] Specifically, for the lithium niobate-on-insulator ridge waveguide, the top thin film lithium niobate has a thickness of 360 nm, an etching depth of 180 nm, and an etching tilt angle of 65°. The upper cladding silicon dioxide layer is 2 μm thick, and the lower cladding silicon dioxide layer is 4.7 μm thick. The 90° multimode Euler bend waveguide 21b has a width of 2 μm and a maximum radius of 3 mm, meaning the first curvature ρ1 is 333.3 m. -1 The minimum radius is 70 μm, meaning the second curvature ρ2 is 14285.71 m. -1 See also Figure 7 As shown, when the TE0 mode is incident at 1550 nm, the light propagates uniformly in the 90° multimode Euler bent waveguide 21b without multimode interference.

[0054] like Figure 1 As shown, according to one embodiment of the present invention, the first straight waveguide segment 221b1 and the intermediate single-mode straight waveguide 2a2 are both single-mode waveguides. The widths of the first straight waveguide segment 221b1 and the intermediate single-mode straight waveguide 2a2 can be different or the same.

[0055] like Figure 1 As shown, according to one embodiment of the present invention, the waveguide structures of the coupling waveguide 1 and the multi-ring square micro-ring resonant cavity 2 are consistent, and are selected from one of the ridge waveguide and the strip waveguide.

[0056] like Figure 1 As shown, according to one embodiment of the present invention, the materials of the coupling waveguide 1 and the multi-ring square micro-ring resonator 2 are the same, and are selected from silicon on insulator, silicon nitride, and lithium niobate on insulator.

[0057] The above description is merely an example of a specific solution of the present invention. For any devices and structures not described in detail herein, it should be understood that they are implemented using common devices and methods already available in the art.

[0058] The above description is merely one embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A microring resonator based on a multi-turn square structure, characterized by, include: Coupled waveguide (1) and multi-ring square micro-ring resonator (2); The coupling waveguide (1) and the multi-ring square micro-ring resonator (2) are coupled by evanescent wave; The multi-ring square micro-ring resonant cavity (2) is provided with multiple multimode waveguide segments (21) from the outside to the inside. External light is coupled from the coupling waveguide (1) to the outermost multimode waveguide segment (21), and is directly transmitted to the innermost multimode waveguide segment (21) based on the connection position of each multimode waveguide segment (21). It is then transmitted sequentially along the direction from the innermost multimode waveguide segment (21) to the outermost multimode waveguide segment (21), and finally output by the coupling waveguide (1).

2. The multi-turn square structure based microring resonator of claim 1, wherein, In the multi-ring square micro-ring resonator (2), the outermost multimode waveguide segment (21) is provided with a straight waveguide coupling segment (2a), and the coupling waveguide (1) is coupled to the multi-ring square micro-ring resonator (2) based on the straight waveguide coupling segment (2a).

3. The microring resonator based on a multi-ring square structure according to claim 2, characterized in that, The straight waveguide coupling section (2a) includes: a first adiabatic conical waveguide (2a1), an intermediate single-mode straight waveguide (2a2), and a second adiabatic conical waveguide (2a3) connected in sequence. The width of the intermediate single-mode straight waveguide (2a2) is consistent with the width of the coupled waveguide (1).

4. The multi-turn square structure based microring resonator of claim 3, wherein, The coupled waveguide (1) includes an input waveguide (11), an S-bend waveguide (12), and an output waveguide (13) connected in sequence. The input waveguide (11), the S-bend waveguide (12), and the output waveguide (13) are all single-mode waveguides; The widths of the input waveguide (11), the S-bend waveguide (12), and the output waveguide (13) are the same.

5. The multi-turn square structure based microring resonator of claim 3, wherein, The multi-ring square micro-ring resonator (2) further includes a cross waveguide chain (22) for connecting multiple multimode waveguide segments (21). The cross waveguide chain (22) includes: a plurality of cross waveguides (221) connected in series, for connecting the third adiabatic conical waveguide (222) of the multimode waveguide segment (21). In the multi-ring square micro-ring resonant cavity (2), the number of cross waveguides (221) is M, and the number of multimode waveguide segments (21) is M+1; wherein, the innermost multimode waveguide segment (21) is connected to one cross waveguide (221) at the end of the cross waveguide chain (22), the outermost multimode waveguide segment (21) is connected to another cross waveguide (221) at the end of the cross waveguide chain (22), and the remaining multimode waveguide segments (21) are connected in series based on two adjacent cross waveguides (221) on the cross waveguide chain (22); The multimode waveguide segment (21) is connected to the cross waveguide (221) based on the third adiabatic conical waveguide (222).

6. The multi-turn square structure based microring resonator of claim 5, wherein, The cross waveguide (221) includes: a central square waveguide (221a) and straight waveguide arms (221b) perpendicularly distributed along the four sides of the central square waveguide (221a). In the cross waveguide chain (22), the two cross waveguides (221) connected to each other are directly connected based on the straight waveguide arm (221b), and the multimode waveguide segment (21) is connected to the straight waveguide arm (221b) based on the third adiabatic tapered waveguide (222).

7. The multi-turn square structure based microring resonator of claim 6, wherein, The straight waveguide arm (221b) has a four-segment structure, which includes: a first straight waveguide segment (221b1), a first tapered waveguide segment (221b2), a second tapered waveguide segment (221b3), and a second straight waveguide segment (221b4) connected in sequence. One end of the second straight waveguide segment (221b4) is connected to the middle square waveguide (221a), and the other end is connected to the wide end of the second tapered waveguide segment (221b3). The narrow end of the second tapered waveguide segment (221b3) is connected to the wide end of the first tapered waveguide segment (221b2), and the narrow end of the first tapered waveguide segment (221b2) is connected to the first straight waveguide segment (221b1).

8. The multi-turn square structure based microring resonator of claim 7, wherein, The first straight waveguide segment (221b1) is a single-mode waveguide segment; The first tapered waveguide segment (221b2) is a non-insulated tapered waveguide segment; The second conical waveguide segment (221b3) is an adiabatic conical waveguide segment; The second straight waveguide segment (221b4) is a multimode interference segment.

9. The multi-turn square structure based microring resonator according to any one of claims 1 to 8, wherein, The multimode waveguide segment (21) includes: multiple multimode straight waveguides (21a) and a 90° multimode Euler bent waveguide (21b) for connecting the multimode straight waveguides (21a). The 90° multimode Euler curved waveguide (21b) includes two identical 45° multimode Euler curved waveguides (21b1); wherein the beginnings of the two 45° multimode Euler curved waveguides (21b1) are respectively connected to different multimode straight waveguides (21a), and the ends of the two 45° multimode Euler curved waveguides (21b1) are connected to each other. Along the direction from the beginning to the end of the 45° multimode Euler bent waveguide (21b1), the curvature of the 45° multimode Euler bent waveguide (21b1) increases linearly from a first curvature ρ1 to a second curvature ρ2. The width of the multimode straight waveguide (21a) is the same as the width of the 90° multimode Euler bent waveguide (21b).

10. The microring resonator based on a multi-ring square structure according to claim 9, characterized in that, In the 90° multimode Euler bent waveguide (21b), the first curvature ρ1 is obtained with the goal of no other mode excitation when TEO mode light passes through the connection between the multimode straight waveguide (21a) and the 90° multimode Euler bent waveguide (21b); the second curvature ρ2 is obtained with the goal of TEO mode light passing through the 90° multimode Euler bent waveguide (21b) with a loss of less than 0.15dB and no other mode excitation. The waveguide structures of the coupling waveguide (1) and the multi-ring square micro-ring resonator (2) are consistent and are selected from one of the ridge waveguide and the strip waveguide. The materials of the coupling waveguide (1) and the multi-ring square micro-ring resonator (2) are consistent and are selected from one of the silicon on insulator, silicon nitride, and lithium niobate on insulator.

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