Low-repetition-frequency spiral microcavity structure and design method

Abstract

The invention discloses a low-repetition-frequency spiral microcavity structure and a design method, and belongs to the field of silicon-based integrated photon chips. The low-repetition-frequency spiral microcavity structure comprises a first spiral bent waveguide, a second spiral bent waveguide, an internal connection bent waveguide, an external connection bent waveguide and a bus waveguide. The curvature radius of each point of the internal connection bending waveguide changes along with the length and meets the Euler spiral equation, and the internal connection bending waveguide is used for connecting the starting points of the first spiral bending waveguide and the second spiral bending waveguide. The external connection bending waveguide is used for connecting the end points of the first spiral bending waveguide and the second spiral bending waveguide. The first spiral bent waveguide, the second spiral bent waveguide, the internal connection bent waveguide and the external connection bent waveguide form a closed spiral annular waveguide. A light beam transmitted in the bus waveguide is coupled into the spiral annular waveguide. The invention further discloses a design method of the low-repetition-frequency spiral microcavity structure. According to the invention, loss caused by high-order mode crosstalk and mode mismatch can be reduced, and the area utilization rate of a chip is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon-based integrated photonic chips, and relates to a spiral microcavity structure and a design method with low repetition rate, low loss and high chip area utilization, which are applied to chip-based optical atomic clocks, on-chip narrow linewidth lasers and on-chip optical frequency combs. Background Art

[0002] With the increasing development of integrated photonic technology, high-quality factor on-chip micro-ring resonator photonic chips have become a hot research field. Silicon nitride has become the most widely used material due to its compatibility with CMOS platforms and unparalleled photon absorption in the communication band. The application fields of on-chip micro-ring resonators are very wide, including temperature sensors, magnetic field sensors, gas sensors, angular velocity sensors, distance measurement sensors, atomic clocks, etc. However, the detection range of photodetectors usually does not exceed 30GHz. Therefore, designing low-repetition-rate and low-loss micro-ring resonator photonic chips is crucial to the realization of miniaturized and integrated optical atomic clocks and other sensors.

[0003] The traditional microring resonator consists of a bus waveguide and a circular waveguide ring. The repetition frequency of the microring resonator is one of the important design parameters, and its value is inversely proportional to the effective length of the microcavity. For the traditional microring cavity, the smaller the repetition frequency, the larger the radius of its circular waveguide ring. For example, the radius of a 10GHz traditional microring cavity is about 2.3mm, which greatly reduces the chip area utilization. In addition, the quality factor of the microring resonator is mainly related to the loss of the microcavity. The loss of the microcavity mainly includes absorption loss, scattering loss, bending loss and loss caused by mode mismatch. Reducing the bending loss and mode mismatch loss of the microcavity, especially the loss caused by the sudden change of the microcavity curvature radius and high-order mode crosstalk, is often achieved by optimizing the microcavity structure design.

[0004] In order to reduce the loss, the existing new micro-ring resonant cavity often adopts a racetrack structure composed of straight waveguides and curved waveguides. Among them, the straight waveguide adopts a width gradient treatment to achieve the transition from multi-mode to single-mode, or the straight waveguide adopts a single-mode waveguide; the curved waveguide is formed by symmetrically splicing two 45° arc waveguides, and the waveguide can adopt two schemes of gradual width or constant width; the curved waveguide can also be composed of a curve with a gradual curvature. The above schemes still have the problems of low chip area utilization and a large number of sudden change areas of curvature radius. Therefore, the low repetition rate micro-ring cavity of the existing technology cannot meet the technical requirements of low repetition rate, low loss and high chip area utilization. Summary of the invention

[0005] The purpose of the present invention is to provide a low-repetition-frequency spiral microcavity structure and design method, which adopts an adiabatic curved waveguide with a gradually changing curvature, can reduce the loss caused by high-order mode crosstalk and mode mismatch, and solve the problem of low chip area utilization of traditional low-repetition-frequency microring resonant cavity, and improve the chip area utilization of the low-repetition-frequency spiral microcavity structure. The present invention has the advantages of low loss and high chip area utilization.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The present invention discloses a low repetition rate spiral microcavity structure, comprising a first spiral curved waveguide, a second spiral curved waveguide, an internal connection curved waveguide, an external connection curved waveguide and a bus waveguide. The first spiral curved waveguide is a first spiral curved waveguide with a gradually changing radius of curvature, and the second spiral curved waveguide is a second spiral curved waveguide with a gradually changing radius of curvature. The radius of curvature of each point of the internal connection curved waveguide changes with the length and satisfies the Euler spiral equation, and is used to connect the first spiral curved waveguide and the starting point of the second spiral curved waveguide. The external connection curved waveguide is used to connect the end point of the first spiral curved waveguide and the second spiral curved waveguide. The first spiral curved waveguide, the second spiral curved waveguide, the internal connection curved waveguide, and the external connection curved waveguide constitute a closed spiral ring waveguide. The bus waveguide is used to transmit a pump laser emission beam, and the beam transmitted in the bus waveguide is coupled into the spiral ring waveguide.

[0008] Furthermore, the light beam emitted by the pump laser is transmitted through the bus waveguide, and part of the light transmitted by the bus waveguide is coupled into the spiral ring waveguide. Since the closed spiral ring waveguide composed of the first spiral curved waveguide, the second spiral curved waveguide, the internal connection curved waveguide, and the external connection curved waveguide calculates the effective length according to the free spectrum range formula, the first spiral curved waveguide and the second spiral curved waveguide are structurally arranged using the Archimedean spiral formula to increase the effective length of the waveguide while reducing the area, thereby improving the chip area utilization of the low repetition rate spiral microcavity structure. Part of the light coupled into the spiral ring waveguide by the bus waveguide is transmitted between the first spiral curved waveguide, the second spiral curved waveguide, the internal connection curved waveguide, and the external connection curved waveguide, and resonance occurs, generating a resonance peak in the output spectrum. Among them: during the transmission of the resonant light in the first spiral curved waveguide, the crosstalk loss of the high-order mode during the transmission of the resonant light is effectively reduced due to the gradual change of the waveguide curvature radius; during the transmission in the second spiral curved waveguide, the crosstalk loss of the high-order mode during the transmission of the resonant light is reduced due to the gradual change of the waveguide curvature radius; during the transmission in the internal connecting curved waveguide, since there is no step change in the curvature radius inside the waveguide, the optical mode mismatch loss is reduced, thereby reducing the optical transmission loss of the spiral microcavity.

[0009] The free spectral range formula is as follows (1-1):

[0010]

[0011] where Δλ represents the FSR of the optical microcavity, L eff is the length of the optical microcavity, n g (λ) is the group refractive index of the waveguide, λ is the wavelength of light, n eff is the effective refractive index.

[0012] The formula of Archimedean spiral is as follows:

[0013] x=(a+bθ)cosθ (1-2)

[0014] y=(a+bθ)sinθ

[0015] Where a represents the polar diameter when θ is 0, b represents the change in the polar diameter for every 1° rotation, θ represents the total angle rotated, and the pitch of the spiral is 2πb.

[0016] Furthermore, the internally connected curved waveguide is designed according to the Euler spiral formula (1-3), and is formed by splicing multiple sections of Euler spiral waveguides. The splicing points of adjacent Euler spiral waveguides satisfy the same coordinates (x, y) and the same radius of curvature, thereby ensuring that the internally connected curved waveguide satisfies the continuous and slow change in the radius of curvature at all locations, and there is no area with a sudden change in the radius of curvature. The change in the radius of curvature at each point presents a variety of change modes, such as gradually increasing to gradually decreasing and then gradually increasing.

[0017] The formula of Euler spiral is as follows (1-3):

[0018]

[0019] In order to reduce the area of ​​the spiral microcavity structure with low repetition rate and improve the chip area utilization rate of the spiral microcavity with low repetition rate, further, the external connection curved waveguide is composed of three types of waveguides: straight line, Euler spiral and circular arc. The external connection curved waveguide is designed as a "9"-shaped structure, which is composed of three types of waveguides: straight line, Euler spiral and circular arc. The curvature radius of the waveguide connection composed of the Euler spiral and the circular arc has a sudden change, and there is no sudden change in the curvature radius at the connection between the straight line and the Euler bend; the curvature radius at the sudden change varies in the range of about 5 to 8 μm. Further, the core material of the first spiral curved waveguide, the second spiral curved waveguide, the internal connection curved waveguide, the external connection curved waveguide and the bus waveguide is preferably silicon nitride. According to the material properties of silicon nitride: it has a transparent window in the range of 400nm to 3.5μm, which can be used in the visible light to mid-infrared range, meeting the use of most scenarios; it has a higher nonlinear coefficient and a lower threshold for exciting nonlinear effects, making silicon nitride suitable for the preparation of microcavity chips.

[0020] The present invention discloses a method for designing a spiral microcavity structure with a low repetition rate, which is used to design the spiral microcavity structure with a low repetition rate. The method for designing a spiral microcavity structure with a low repetition rate comprises the following steps:

[0021] Step 1: Determine the waveguide parameters and waveguide spacing of the spiral microcavity. The waveguide widths of the first spiral curved waveguide, the second spiral curved waveguide, the internal connecting curved waveguide, and the external connecting curved waveguide are analyzed by the finite element method to analyze the waveguide characteristics. int The principle is used to calculate the dispersion curve of the spiral microcavity, determine the waveguide parameters of the spiral microcavity, and realize the waveguide anomalous dispersion. The time-domain finite difference method is used to perform coupled simulation calculations on the spacing between the first spiral curved waveguide and the second spiral curved waveguide to determine the waveguide spacing.

[0022] Step 2: Draw the first spiral waveguide. According to the designed waveguide parameters and waveguide spacing, use the Archimedean spiral formula (1-2) to calculate the a1 value and b1 value of the first spiral waveguide, and give the starting angle θ 01 and the end angle θ E1 , the spiral curved waveguide is drawn according to the Archimedean spiral formula (1-2). Where a1 is the polar diameter of the first spiral curved waveguide when θ is 0, b1 is the change in the polar diameter when the first spiral curved waveguide rotates 1°, θ 01 is the starting angle of rotation, θ E1 The end angle of the rotation.

[0023] Step 3: Draw the second spiral waveguide. According to the designed waveguide parameters and waveguide spacing, use the Archimedean spiral formula (1-2) to calculate the a2 value and b2 value of the second spiral waveguide, and give the starting angle θ 02 and the end angle θ E2 , the spiral curved waveguide is drawn according to the Archimedean spiral formula (1-2). Where a2 is the polar diameter of the second spiral curved waveguide when θ is 0, b2 is the change in the polar diameter when the second spiral curved waveguide rotates 1°, θ 02 is the starting angle of rotation, θ E2 is the end angle of rotation. And b2=b1, θ 02 With θ 01 The difference is an integer multiple of 180°.

[0024] Step 4: Draw the internal connection waveguide. According to the coordinates of the starting points of the first spiral waveguide and the second spiral waveguide, the curvature radius at the point is calculated in combination with the Archimedean spiral curvature radius formula (1-4). The internal connection waveguide is composed of multiple Euler spiral waveguides, and the connection coordinates of each Euler spiral waveguide are the same and the curvature radius is the same.

[0025] Archimedean spiral curvature radius formula (1-4)

[0026]

[0027] Where a represents the polar diameter when θ is 0, b represents the change in the polar diameter for each rotation of 1°, and θ represents the total angle of rotation.

[0028] Step 5: Draw the external connection waveguide. According to the coordinates of the end points of the first spiral waveguide and the second spiral waveguide, the curvature radius at the point is calculated in combination with the Archimedean spiral curvature radius formula (1-4), and the Euler spiral parameters are determined according to the curvature radius. According to the curvature radius at the end point of the Euler spiral, the arc radius and the center angle range are determined, and the characteristic that the Euler spiral has a curvature point of 0 is used to realize the connection between the Euler curved waveguide and the straight waveguide.

[0029] Step 6: Calculate the length of the internal connection waveguide and the external connection waveguide.

[0030] Step 7: Calculate the effective length of the microcavity of the designed repetition frequency according to the free spectrum range formula (1-1). The effective length of the spiral microcavity is: L = L (第一螺旋弯曲波导) +L (第二螺旋弯曲波导) +L (内部连接波导3) +L (外部连接波导4)

[0031] Step 8: Calculate the end angles of the first spiral waveguide and the second spiral waveguide, and redraw the spiral waveguide. Since the starting angles are unchanged, the positions of the internal connecting waveguides are not affected.

[0032] Step 9: According to the redrawn spiral curved waveguide, calculate the curvature radius of the termination point of the first spiral curved waveguide and the second spiral curved waveguide, and adjust the curvature radius and coordinates of the connection point of the external connecting curved waveguide connecting the first spiral curved waveguide and the second spiral curved waveguide. Adjust the position of the external connecting waveguide; make the two ends of the external connecting curved waveguide have the same coordinate position as the termination point of the first spiral curved waveguide and the second spiral curved waveguide, that is, obtain a spiral microcavity with a low repetition frequency.

[0033] Beneficial effects:

[0034] 1. The present invention discloses a low-repetition-rate spiral microcavity structure and design method. The low-repetition-rate spiral microcavity structure is composed of a first spiral curved waveguide, a second spiral curved waveguide, an internally connected curved waveguide, an externally connected curved waveguide, and a bus waveguide. Among them, the first spiral curved waveguide, the second spiral curved waveguide, and the internally connected curved waveguide satisfy the gradual change of the radius of curvature at each point, which can prevent the crosstalk of high-order modes during light transmission and reduce waveguide loss. The externally connected curved waveguide includes three types: straight waveguide, Euler curved waveguide, and circular arc waveguide, which can realize the connection of the termination points of the first spiral curved waveguide and the second spiral curved waveguide to form a microring cavity.

[0035] 2. The present invention discloses a low-repetition-rate spiral microcavity structure and design method. The internally connected curved waveguide is designed according to the Euler spiral formula and is formed by splicing multiple segments of Euler spiral waveguides. The splicing points of adjacent Euler spiral waveguides satisfy the same coordinates (x, y) and the same radius of curvature, thereby ensuring that the internally connected curved waveguides all satisfy the continuous and slow change in radius of curvature, and there is no area with sudden change in radius of curvature, thereby effectively reducing the optical mode mismatch loss and thus reducing the optical transmission loss of the spiral microcavity.

[0036] 3. The present invention discloses a low-repetition-frequency spiral microcavity structure and design method. The first spiral curved waveguide and the second spiral curved waveguide are structurally laid out using the Archimedean spiral formula to increase the effective length of the waveguide while reducing the area, thereby improving the chip area utilization of the low-repetition-frequency spiral microcavity structure. The design is an adiabatic bending curve that satisfies the gradual change of the curvature radius, which can effectively prevent crosstalk in high-order modes and effectively reduce crosstalk losses in the microcavity waveguide.

[0037] 4. The present invention discloses a low-repetition-rate spiral microcavity structure and design method, which adopts spiral microcavities with different repetition frequencies to share an internal connecting curved waveguide. By only changing the termination angles of the first spiral curved waveguide and the second spiral curved waveguide and adjusting the curvature of the Euler curved waveguides at both ends of the external connecting waveguide, it is possible to efficiently design the structure of spiral microcavities with different repetition frequencies.

[0038] 5. The present invention discloses a low-repetition-rate spiral microcavity structure and design method, wherein the core material of the first spiral curved waveguide, the second spiral curved waveguide, the internal connecting curved waveguide, the external connecting curved waveguide, and the bus waveguide is selected as silicon nitride; according to the material properties of silicon nitride: it has a transparent window in the range of 400nm to 3.5μm, which can be used in the range of visible light to mid-infrared, and is applied to chip-based optical clocks, on-chip narrow-linewidth lasers, on-chip optical frequency combs and other fields.

[0039] 6. The present invention discloses a low-repetition-frequency spiral microcavity structure and design method, in which the external connection curved waveguide is designed as a "9"-shaped structure, which can reduce the area of ​​the low-repetition-frequency spiral microcavity structure and improve the chip area utilization of the low-repetition-frequency spiral microcavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the structure of a traditional annular microcavity, which consists of a circular waveguide ring and a bus straight waveguide.

[0041] Figure 2 It is a schematic diagram of a low repetition rate spiral microcavity structure of the present invention.

[0042] Figure 3 This is a design flow chart of a low repetition rate spiral microcavity structure of the present invention.

[0043] Figure 4 Schematic diagram of a cross section of a spirally bent waveguide according to an example of the present invention.

[0044] Figure 5 is the resonance peak of the silicon nitride spiral microcavity of the example of the present invention.

[0045] Among them: 1 is the first spiral bending waveguide, 2 is the second spiral bending waveguide, 3 is the internal connection bending waveguide, 4 is the external connection bending waveguide, and 5 is the bus waveguide. DETAILED DESCRIPTION

[0046] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0047] Embodiment 1:

[0048] like Figure 1 The figure shows the structure of a conventional annular microcavity, which consists of a circular waveguide and a bus straight waveguide. The relationship between the repetition frequency and radius of the annular microcavity satisfies the free spectrum range formula. When the repetition frequency of the annular microcavity is 10 GHz, the radius of the circular waveguide is about 2.3 mm using the free spectrum range calculation.

[0049] The free spectral range formula is as follows (1-1):

[0050]

[0051] where Δλ represents the FSR of the optical microcavity, L eff is the length of the optical microcavity, n g (λ) is the group refractive index of the waveguide, λ is the wavelength of light, n eff is the effective refractive index.

[0052] like Figure 2As shown, a low repetition rate spiral microcavity structure disclosed in this embodiment includes a first spiral curved waveguide 1, a second spiral curved waveguide 2, an internal connection curved waveguide 3, an external connection curved waveguide 4 and a bus waveguide 5. The first spiral curved waveguide 1 is a spiral curved waveguide 1 with a gradually changing radius of curvature, and the second spiral curved waveguide 2 is a spiral curved waveguide 2 with a gradually changing radius of curvature. Figure 4 It is a schematic cross-sectional view of the first spiral curved waveguide 1 and the second spiral curved waveguide 2, wherein the lower cladding and the upper cladding are made of silicon dioxide material, and the waveguide core layer is made of silicon nitride material. The waveguide width is 1.6 μm, the height is 800 nm, and the distance between adjacent waveguides is 1.6 μm. This example uses a thick film silicon nitride single-mode waveguide, and the design is also applicable to weakly bound silicon nitride waveguides and multi-mode silicon nitride waveguides. Moreover, since the design is based on a spiral line with a gradually changing radius of curvature, it has a better effect of reducing losses and improving the quality factor for the microcavity composed of weakly bound multi-mode silicon nitride waveguides. The waveguide width of the internally connected curved waveguide 3 is 1.6 μm, the waveguide height is 800 nm, the waveguide core layer is made of silicon nitride material, and the radius of curvature of each point changes with the length to satisfy the Euler spiral equation, which is used to connect the starting point of the first spiral curved waveguide 1 and the second spiral curved waveguide 2. The waveguide width of the external connection curved waveguide 4 is 1.6 μm, the waveguide height is 800 nm, the waveguide core layer is made of silicon nitride material, and is used to connect the end points of the first spiral curved waveguide 1 and the second spiral curved waveguide 2. The first spiral curved waveguide 1, the second spiral curved waveguide 2, the internal connection curved waveguide 3, and the external connection curved waveguide 4 constitute a closed spiral ring waveguide. The bus waveguide 5 is used to transmit the pump laser emission beam, and the beam transmitted in the bus waveguide 5 is coupled into the spiral ring waveguide.

[0053] Furthermore, the light beam emitted by the pump laser is transmitted through the bus waveguide 5, and part of the light transmitted by the bus waveguide 5 is coupled into the spiral ring waveguide. Since the effective length of the closed spiral ring waveguide composed of the first spiral curved waveguide 1, the second spiral curved waveguide 2, the internal connection curved waveguide 3, and the external connection curved waveguide 4 is calculated according to the free spectrum range formula, when the repetition frequency is 10 GHz, the effective length of the closed spiral ring waveguide is 1430.06 μm. The first spiral curved waveguide 1 and the second spiral curved waveguide 2 are structurally arranged using the Archimedean spiral formula, and the starting angle θ of the first spiral curved waveguide 1 is 01 is 9000rad, the end angle θ E1 The starting angle θ of the second spiral waveguide 2 is 11111 rad, the curvature radius of the starting point is about 157 μm, and the curvature radius of the ending point is about 193.9 μm. 01 is 8820rad, the end angle θ E1The curvature radius of the starting point is about 163μm, and the curvature radius of the ending point is about 197.8μm. The effective length of the waveguide is increased while the area is reduced, thereby improving the chip area utilization rate of the low-repetition-rate spiral microcavity structure. Part of the light coupled into the spiral ring waveguide by the bus waveguide 5 is transmitted between the first spiral bending waveguide 1, the second spiral bending waveguide 2, the internal connection bending waveguide 3, and the external connection bending waveguide 4, and resonance occurs, generating a resonance peak in the output spectrum. Figure 5 It is the resonance peak of the silicon nitride spiral microcavity of the example of the present invention. Wherein: during the transmission of the resonant light in the first spiral curved waveguide 1, due to the gradual change of the waveguide curvature radius, the crosstalk loss of the high-order mode during the resonant light transmission process is effectively reduced; during the transmission in the second spiral curved waveguide 2, due to the gradual change of the waveguide curvature radius, the crosstalk loss of the high-order mode during the resonant light transmission process is reduced; during the transmission in the internal connecting curved waveguide 3, due to the absence of a step change in the curvature radius inside the waveguide, the optical mode mismatch loss is reduced, thereby reducing the optical transmission loss of the spiral microcavity.

[0054] The free spectral range formula is as follows (1-1):

[0055]

[0056] where Δλ represents the FSR of the optical microcavity, L eff is the length of the optical microcavity, n g (λ) is the group refractive index of the waveguide, λ is the wavelength of light, n eff is the effective refractive index.

[0057] The formula of Archimedean spiral is as follows:

[0058] x=(a+bθ)cosθ (1-2)

[0059] y=(a+bθ)·sinθ

[0060] Where a represents the polar diameter when θ is 0, b represents the change in the polar diameter for every 1° rotation, θ represents the total angle rotated, and the pitch of the spiral is 2πb.

[0061] Furthermore, the internally connected curved waveguide 3 is designed according to the Euler spiral formula (1-3), with a total length of about 543.3 μm, and is formed by splicing multiple sections of Euler spiral waveguides. The splicing points of adjacent Euler spiral waveguides satisfy the same coordinates (x, y) and the same radius of curvature, thereby ensuring that the internally connected curved waveguide 3 satisfies the continuous and slow change in the radius of curvature at all locations, and there is no area with a sudden change in the radius of curvature, and the change in the radius of curvature at each point presents a variety of change modes such as gradually increasing to gradually decreasing and then gradually increasing.

[0062] The formula of Euler spiral is as follows (1-3):

[0063]

[0064] Furthermore, the external connection curved waveguide 4 is composed of three types of waveguides: straight line, Euler bend, and circular arc, with a total length of about 753.1 μm, and there are a few sudden changes in the radius of curvature at the connection between the waveguides composed of the Euler bend and the circular arc, and there is no sudden change in the radius of curvature at the connection between the straight line and the Euler bend. The curvature radius at the sudden change varies in the range of about (5 to 8) μm. In order to reduce the area of ​​the low-repetition-frequency spiral microcavity structure and improve the chip area utilization of the low-repetition-frequency spiral microcavity, the external connection curved waveguide 4 is designed as a "9"-shaped structure.

[0065] Furthermore, the core material of the first spiral curved waveguide 1, the second spiral curved waveguide 2, the internal connection curved waveguide 3, the external connection curved waveguide 4, and the bus waveguide 5 is preferably silicon nitride. According to the material properties of silicon nitride: it has a transparent window in the range of 400nm to 3.5μm, which can be used in the range of visible light to mid-infrared, meeting the use of most scenes; it has a higher nonlinear coefficient and a lower threshold for exciting nonlinear effects, making silicon nitride suitable for the preparation of microcavity chips.

[0066] like Figure 3 As shown, the present embodiment discloses a method for designing a spiral microcavity structure with a low repetition rate, which is used to design the spiral microcavity structure with a low repetition rate. The specific implementation steps of the method for designing a spiral microcavity structure with a low repetition rate are as follows:

[0067] Step 1: Determine the waveguide parameters and waveguide spacing of the spiral microcavity. The waveguide widths of the first spiral curved waveguide 1, the second spiral curved waveguide 2, the internal connecting curved waveguide 3, and the external connecting curved waveguide 4 are analyzed by the finite element method to analyze the waveguide characteristics. int The principle is used to calculate the dispersion curve of the spiral microcavity, and the waveguide parameters of the spiral microcavity are determined to be 1.6μm in width and 800nm ​​in height to achieve waveguide anomalous dispersion. The time-domain finite difference method is used to perform coupled simulation calculations on the spacing between the first spiral curved waveguide 1 and the second spiral curved waveguide 2, and the waveguide spacing is determined to be 1.6μm.

[0068] Step 2: Draw the first spiral curved waveguide 1. According to the designed waveguide parameters and waveguide spacing, use the Archimedean spiral formula (1-2) to calculate the a1 value and b1 value of the first spiral curved waveguide 1, and give the starting angle θ 01 is 9000rad and the end angle θ E1 =12600 rad, and the spiral waveguide is drawn according to the Archimedean spiral formula (1-2). Where a1 is the polar diameter of the first spiral waveguide 1 when θ is 0, b1 is the change in the polar diameter when the first spiral waveguide 1 rotates 1°, θ01 is the starting angle of rotation, θ E1 The end angle of the rotation.

[0069] Step 3: Draw the second spiral waveguide 2. According to the designed waveguide parameters and waveguide spacing, use the Archimedean spiral formula (1-2) to calculate the a2 value and b2 value of the second spiral waveguide 2, and give the starting angle θ 02 is 8820rad and the end angle θ E2 =12554 rad, and the spiral waveguide is drawn according to the Archimedean spiral formula (1-2). Where a2 is the polar diameter of the second spiral waveguide 2 when θ is 0, b2 is the change in the polar diameter when the second spiral waveguide 2 rotates 1°, θ 02 is the starting angle of rotation, θ E2 is the end angle of rotation. And b2=b1, θ 02 With θ 01 The difference is an integer multiple of 180°.

[0070] Step 4: Draw the internal connection waveguide. According to the coordinates of the starting points of the first spiral waveguide 1 and the second spiral waveguide 2, the curvature radius at the point is calculated by combining the Archimedean spiral curvature radius formula (1-4) to be 157μm and 163μm respectively. The internal connection waveguide is composed of multiple Euler spiral waveguides, and the connection coordinates of each Euler spiral waveguide are the same and the curvature radius is the same.

[0071] Archimedean spiral curvature radius formula (1-4)

[0072]

[0073] Where a represents the polar diameter when θ is 0, b represents the change in the polar diameter for each rotation of 1°, and θ represents the total angle of rotation.

[0074] Step 5: Draw the external connection waveguide. According to the coordinates of the end points of the first spiral waveguide 1 and the second spiral waveguide 2, the curvature radius at the point is calculated in combination with the Archimedean spiral curvature radius formula (1-4), and the Euler spiral parameters are determined based on the curvature radius. According to the curvature radius at the end point of the Euler spiral, the arc radius is determined to be 75.6 μm and the center angle range, and the characteristic that the Euler spiral has a curvature point of 0 is used to realize the connection between the Euler curved waveguide and the straight waveguide.

[0075] Step 6: Calculate the lengths of the internal connection waveguide and the external connection waveguide, which are 543.3 μm and 753.1 μm respectively.

[0076] Step 7: Calculate the effective length of the microcavity of the designed repetition frequency according to the free spectrum range formula (1-1). The effective length of the spiral microcavity is: L = L(第一螺旋弯曲波导1) +L (第二螺旋弯曲波导2) +L (内部连接波导3) +L (外部连接波导4) When the repetition frequency is 10 GHz, according to the free spectrum range formula, the effective length of the spiral microcavity is calculated to be 1430.06 μm, and the required spiral waveguide length is about 1300.4 μm.

[0077] Step 8: Calculate the end angles of the first spiral waveguide 1 and the second spiral waveguide 2 to be 11111 rad and 10800 rad respectively, and redraw the spiral waveguides. Since the starting angles are unchanged, the positions of the internal connecting waveguides are not affected.

[0078] Step 9: According to the curvature radius of the redrawn spiral waveguide at the end point of 193.9μm and 197.8μm, adjust the curvature radius and coordinates of the Euler curved waveguides at both ends of the external connection curved waveguide. Make the coordinates of the end points of the external connection curved waveguide, the first spiral curved waveguide and the second spiral curved waveguide the same, and complete the drawing of the spiral microcavity with a repetition frequency of 10GHz. The area of ​​the spiral microcavity of this structure is about 0.544mm×0.402mm.

[0079] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low repetition rate spiral microcavity structure, characterized in that: The invention comprises a first spiral curved waveguide (1), a second spiral curved waveguide (2), an internal connecting curved waveguide (3), an external connecting curved waveguide (4) and a bus waveguide (5); the first spiral curved waveguide (1) is a first spiral curved waveguide (1) with a gradually changing radius of curvature, and the second spiral curved waveguide (2) is a second spiral curved waveguide (2) with a gradually changing radius of curvature; the radius of curvature of each point of the internal connecting curved waveguide (3) changes with the length and satisfies the Euler spiral equation, and the internal connecting curved waveguide (3) is used to connect the starting point of the first spiral curved waveguide (1) and the second spiral curved waveguide (2); the external connecting curved waveguide (4) is used to connect the end point of the first spiral curved waveguide (1) and the second spiral curved waveguide (2); the first spiral curved waveguide (1), the second spiral curved waveguide (2), the internal connecting curved waveguide (3) and the external connecting curved waveguide (4) constitute a closed spiral ring waveguide; the bus waveguide (5) is used to transmit a pump laser emission light beam, and the light beam transmitted in the bus waveguide (5) is coupled into the spiral ring waveguide.

2. A low repetition rate spiral microcavity structure as claimed in claim 1, characterized in that: The light beam emitted by the pump laser is transmitted through the bus waveguide (5), and part of the light transmitted by the bus waveguide (5) is coupled into the spiral ring waveguide; since the closed spiral ring waveguide composed of the first spiral bending waveguide (1), the second spiral bending waveguide (2), the internal connection bending waveguide (3), and the external connection bending waveguide (4) has an effective length calculated according to the free spectrum range formula, the first spiral bending waveguide (1) and the second spiral bending waveguide (2) are structurally arranged using the Archimedean spiral formula, thereby increasing the effective length of the waveguide while reducing the area, thereby improving the chip area utilization rate of the low repetition rate spiral microcavity structure; part of the light coupled into the spiral ring waveguide by the bus waveguide (5) is transmitted to the first spiral bending waveguide ( 1), the second spiral curved waveguide (2), the internal connection curved waveguide (3), and the external connection curved waveguide (4), resonance occurs, and a resonance peak is generated in the output spectrum; wherein: during the transmission of the resonant light in the first spiral curved waveguide (1), due to the gradual change of the waveguide curvature radius, the crosstalk loss of the high-order mode in the resonant light transmission process is effectively reduced; during the transmission in the second spiral curved waveguide (2), due to the gradual change of the waveguide curvature radius, the crosstalk loss of the high-order mode in the resonant light transmission process is reduced; during the transmission in the internal connection curved waveguide (3), due to the absence of a step change in the curvature radius inside the waveguide, the optical mode mismatch loss is reduced, thereby reducing the optical transmission loss of the spiral microcavity; The free spectral range formula is as follows (1-1): where Δλ represents the FSR of the optical microcavity, L eff is the length of the optical microcavity, n g (λ) is the group refractive index of the waveguide, λ is the wavelength of light, n eff is the effective refractive index; The formula of Archimedean spiral is as follows: x=(a+b·θ)·cosθ (1-2) y=(a+b·θ)·sinθ Where a represents the polar diameter when θ is 0, b represents the change in the polar diameter for every 1° rotation, θ represents the total angle rotated, and the pitch of the spiral is 2πb.

3. A low repetition rate spiral microcavity structure as claimed in claim 2, characterized in that: The internal connection curved waveguide (3) is designed according to the Euler spiral formula (1-3), and is formed by splicing multiple sections of Euler spiral waveguides. The splicing points of adjacent Euler spiral waveguides satisfy the same coordinates (x, y) and the same radius of curvature, thereby ensuring that the internal connection curved waveguide (3) satisfies the continuous and slow change of the radius of curvature at all locations, and there is no region where the radius of curvature suddenly changes, and the change of the radius of curvature at each point presents the characteristics of gradually increasing, gradually decreasing, and then gradually increasing. The formula of Euler spiral is as follows (1-3):

4. A low repetition rate spiral microcavity structure as claimed in claim 2, characterized in that: The external connection curved waveguide (4) is designed as a "9"-shaped structure, which is composed of three types of waveguides: a straight line, an Euler spiral, and an arc. The curvature radius at the connection of the waveguide formed by the Euler spiral and the arc changes suddenly, while there is no curvature radius mutation at the connection of the straight line and the Euler spiral. The curvature radius at the mutation point varies in the range of about 5 to 8 μm.

5. A low repetition rate spiral microcavity structure as claimed in claim 2, characterized in that: The core material of the first spiral curved waveguide (1), the second spiral curved waveguide (2), the internal connecting curved waveguide (3), the external connecting curved waveguide (4), and the bus waveguide (5) is selected to be silicon nitride; according to the material properties of silicon nitride: it has a transparent window in the range of 400nm to 3.5μm, and can be used in the range of visible light to mid-infrared.

6. A method for designing a low-repetition-rate spiral microcavity structure, used for designing a low-repetition-rate spiral microcavity structure as claimed in claim 1, 2, 3, 4 or 5, characterized in that: The following steps are included: Step 1: Determine the waveguide parameters and waveguide spacing of the spiral microcavity; the waveguide widths of the first spiral curved waveguide (1), the second spiral curved waveguide (2), the internal connecting curved waveguide (3), and the external connecting curved waveguide (4) are analyzed according to the finite element method to analyze the waveguide characteristics, and the integrated dispersion D int The invention relates to a method for calculating the dispersion curve of a spiral microcavity, determining the waveguide parameters of the spiral microcavity, and realizing anomalous dispersion of the waveguide; using a time-domain finite difference method to perform coupled simulation calculation on the spacing between a first spiral curved waveguide (1) and a second spiral curved waveguide (2), and determining the waveguide spacing; Step 2: Draw the first spiral curved waveguide (1); according to the designed waveguide parameters and waveguide spacing, use the Archimedean spiral formula (1-2) to calculate the a1 value and b1 value of the first spiral curved waveguide (1), and give the starting angle θ 01 and the end angle θ E1 , the spiral curved waveguide is drawn according to the Archimedean spiral formula (1-2); wherein a1 is the polar diameter of the first spiral curved waveguide (1) when θ is 0, b1 is the change in the polar diameter when the first spiral curved waveguide (1) rotates 1°, θ 01 is the starting angle of rotation, θ E1 is the end angle of rotation; Step 3: Draw the second spiral waveguide (2); according to the designed waveguide parameters and waveguide spacing, use the Archimedean spiral formula (1-2) to calculate the a2 value and b2 value of the second spiral waveguide (2), and give the starting angle θ 02 and the end angle θ E2 , the spiral curved waveguide is drawn according to the Archimedean spiral formula (1-2); wherein a2 is the polar diameter of the second spiral curved waveguide (2) when θ is 0, b2 is the change in the polar diameter when the second spiral curved waveguide (2) rotates 1°, θ 02 is the starting angle of rotation, θ E2 is the end angle of rotation; and b2=b1, θ 02 With θ 01 The difference is an integer multiple of 180°; Step 4: draw an internal connection curved waveguide (3); calculate the curvature radius at the point according to the coordinates of the starting points of the first spiral curved waveguide (1) and the second spiral curved waveguide (2) in combination with the Archimedean spiral curvature radius formula (1-4); the internal connection waveguide is composed of a plurality of Euler spiral waveguides, and the connection coordinates of the Euler spiral waveguides are the same and the curvature radius is the same; Archimedean spiral curvature radius formula (1-4) Where a represents the polar diameter when θ is 0, b represents the change in the polar diameter for every 1° rotation, and θ represents the total angle rotated; Step 5: draw an external connection curved waveguide (4); calculate the curvature radius at the end point coordinates of the first spiral curved waveguide (1) and the second spiral curved waveguide (2) in combination with the Archimedean spiral curvature radius formula (1-4), and determine the Euler spiral parameters according to the curvature radius; determine the arc radius and the center angle range according to the curvature radius at the end point of the Euler spiral, and use the characteristic that the Euler spiral has a curvature zero point to achieve the connection between the Euler spiral waveguide and the straight waveguide; Step 6: Calculate the length of the internal connection waveguide and the external connection waveguide; Step 7: Calculate the effective length of the microcavity of the designed repetition frequency according to the free spectrum range formula (1-1); the effective length of the spiral microcavity is: L = L (第一螺旋弯曲波导(1)) +L (第二螺旋弯曲波导(2)) +L (内部连接波导3) +L (外部连接波导4) Step 8: Calculate the end angles of the first spirally curved waveguide (1) and the second spirally curved waveguide (2), and redraw the spirally curved waveguide; since the start angles are unchanged, the positions of the internally connected waveguides are not affected; Step nine: according to the redrawn spiral curved waveguide, the curvature radius of the end point of the first spiral curved waveguide (1) and the second spiral curved waveguide (2) is calculated, and the curvature radius and coordinates of the connection point of the external connecting curved waveguide (4) connecting the first spiral curved waveguide (1) and the second spiral curved waveguide (2) are adjusted; the two ends of the external connecting curved waveguide (4) are respectively at the same coordinate position as the end point of the first spiral curved waveguide (1) and the second spiral curved waveguide (2), so as to obtain a spiral microcavity with a low repetition frequency.

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