Micro-ring filter and design method thereof

Abstract

The invention belongs to the technical field of optical devices, and discloses a micro-ring filter and a design method thereof. The method comprises the following steps: establishing a simulation model of a micro-ring filter by utilizing a three-dimensional time domain finite difference algorithm, wherein the micro-ring filter comprises a micro-ring region and a coupling waveguide region; according to a set free spectral range and a set coupling coefficient, the fundamental mode transmittance is taken as an optimization target, the first curve is taken as a waveguide center curve, the width of the waveguide is adjusted by utilizing a second curve, and a micro-ring region and a coupling waveguide region are reversely designed; and iteratively optimizing to obtain a group of optimal micro-ring structure parameters and a group of optimal coupling waveguide structure parameters, and finishing the design of the micro-ring filter. According to the invention, the free spectral range can be obviously improved, and the loss performance of the micro-ring filter is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical devices, and more specifically, relates to a micro-ring filter and a design method thereof. Background Art

[0002] As a key optical device, microring filters are widely used in optical communications, optical wavelength division multiplexing (WDM) systems, and integrated quantum photonics. With its compact size, high channel isolation, and adjustable bandwidth, they have become an important functional module in silicon photonic integrated circuits.

[0003] However, with the continuous improvement of communication rate and integration, traditional microring filters face many challenges in design and performance. For example, the free spectral range (FSR) is insufficient. Due to the limitation of the free spectral range, the number of channels that can be realized by microring filters is limited, and the bandwidth of each channel is also limited. The size of the free spectral range is negatively correlated with the physical size of the microring, that is, the smaller the microring size, the larger the free spectral range. However, in order to ensure that the microring loss is maintained within a reasonable range, the reduction of the microring size must be carefully controlled. For example, the microring loss is large, that is, the loss increases when the microring size is reduced. When the microring size is reduced to a free spectral range of 37nm, its half-ring loss is 0.018dB / 180°. Under this design, if the microring size is further reduced to a free spectral range of 55nm, its half-ring loss will exceed 0.036dB / 180°, which means that the loss has doubled, limiting the performance of the microring filter. In addition, conventional microring filters may have problems such as excessive coupling loss between the curved directional coupler and the microring (in the prior art, the coupling loss between the curved directional coupler and the microring is usually 0.07 dB. This high coupling loss not only reduces the transmission efficiency of the optical signal, but also affects the isolation between channels and increases crosstalk), insufficient flat-top effect of the output spectrum, increased loss in the long wavelength range, and bandwidth changes, which also significantly affect the performance consistency and applicability of the filter. Therefore, there is an urgent need for an improved design method for microring filters to reduce losses while increasing the free spectral range and improve the performance of microring filters, thereby meeting the needs of the next generation of high-speed optical communications and integrated photonics systems. Summary of the invention

[0004] The present invention provides a micro-ring filter and a design method thereof, thereby solving the problems in the prior art that the free spectral range of the micro-ring filter is insufficient and the loss performance of the micro-ring filter needs to be improved.

[0005] The present invention provides a design method of a micro-ring filter, comprising the following steps:

[0006] A simulation model of a micro-ring filter is established by using a three-dimensional finite-difference time-domain algorithm, wherein the micro-ring filter includes a micro-ring region and a coupled waveguide region;

[0007] According to the set free spectral range and the set coupling coefficient, with the fundamental mode transmittance as the optimization target, the first curve is used as the waveguide center curve, the second curve is used to adjust the width of the waveguide, the microring area and the coupled waveguide area are reversely designed, and an optimal set of microring structure parameters and an optimal set of coupled waveguide structure parameters are obtained through iterative optimization to complete the design of the microring filter.

[0008] Preferably, a plurality of microrings with the same structure are arranged in the microring region, the structure of each microring is divided into four sections of quarter microring curved waveguides, the central curve of the quarter microring curved waveguide is the first curve, and the quarter microring curved waveguide is used as a target of reverse design;

[0009] The coupling waveguide region is provided with a first coupling waveguide and a second coupling waveguide respectively located at the upper and lower sides of the micro-ring region; the first coupling waveguide includes an input port straight waveguide, a first curved coupling waveguide unit and an output port straight waveguide; the second coupling waveguide includes a first transmission unit, a second curved coupling waveguide unit and a second transmission unit; the structure of the second curved coupling waveguide unit is symmetrical with that of the first curved coupling waveguide unit, the first curved coupling waveguide unit is divided into four sections of curved coupling waveguides, which are respectively recorded as a first curved coupling waveguide, a second curved coupling waveguide, a third curved coupling waveguide and a fourth curved coupling waveguide, the central curve of the third curved coupling waveguide is the first curve, the central curve of the fourth curved coupling waveguide is an antisymmetric curve of the central curve of the third curved coupling waveguide, the second curved coupling waveguide is horizontally mirror-symmetrical with the third curved coupling waveguide, and the first curved coupling waveguide is horizontally mirror-symmetrical with the fourth curved coupling waveguide; the third curved coupling waveguide and the fourth curved coupling waveguide are taken as targets of reverse design.

[0010] Preferably, the transmittance of the TE fundamental mode light of the working wavelength through the microring is recorded as the first TE fundamental mode transmittance; the transmittance of the TE fundamental mode light of the working wavelength through the first curved coupling waveguide unit is recorded as the second TE fundamental mode transmittance; the transmittance of the TE fundamental mode light of the working wavelength through the intersection of two adjacent quarter microring curved waveguides in a certain microring structure is recorded as the third TE fundamental mode transmittance;

[0011] The microring region is reversely designed by using one of the particle swarm optimization algorithm, the gradient algorithm, the swarm intelligence algorithm, and the neural network algorithm, with the first TE fundamental mode transmittance as the optimization target; the coupled waveguide region is reversely designed by using the particle swarm optimization algorithm, with the sum of the absolute value of the second TE fundamental mode transmittance and the absolute value of the third TE fundamental mode transmittance as the optimization target.

[0012] Preferably, the first curve is one of an Euler curve, an Archimedean spiral, a logarithmic spiral, and a B-spline curve, and the second curve is one of a Bezier curve, a spline interpolation curve, and a B-spline curve.

[0013] Preferably, when the first curve is an Euler curve and the second curve is a Bezier curve, the starting waveguide width W0 of the microring is set, and according to the set free spectrum range, the circumference L of the central Euler curve of the quarter microring curved waveguide is determined, and the range of the maximum curvature radius Rmax of the central Euler curve of the quarter microring curved waveguide and the range of the arc length proportional coefficient A of the central Euler curve of the quarter microring curved waveguide are determined;

[0014] The maximum value of the abscissa of the central Euler curve of the quarter micro-ring curved waveguide is recorded as Xmax, and the width of the quarter micro-ring curved waveguide is adjusted by a third-order Bezier curve, and each Bezier control point is recorded as P0=[0, W0], P1=[xx1, yy1], P2=[xx2, yy2], P3=[Xmax, yy3]; wherein the value ranges of xx1 and xx2 are both [Xmax / 3, 2Xmax], the value ranges of yy1 and yy2 are both [-W0 / 2, 3W0], and the value range of yy3 is [W0 / 2, 3W0];

[0015] Taking Rmax, A, xx1, yy1, xx2, yy2, and yy3 as variables, the microring region is reversely designed using a particle swarm optimization algorithm, and a set of optimal microring structural parameters are obtained through iterative optimization.

[0016] Preferably, the width of the quarter micro-ring curved waveguide is adjusted using the Bezier curve as follows: when the horizontal coordinate of a point on the Bezier curve is equal to the horizontal coordinate of a point on the Euler curve, the vertical coordinate value of the Bezier point is used as the waveguide width of the Euler point, and the waveguide width direction of the Euler point is parallel to the direction of the line connecting the Euler point and the center of curvature of the Euler point, and half of the waveguide width is expanded to both sides of the Euler point.

[0017] Preferably, when the first curve is an Euler curve and the second curve is a Bezier curve, a two-step particle swarm optimization algorithm is used to perform reverse design on the coupled waveguide region;

[0018] The first step of reverse design includes: determining the maximum curvature radius Rmax_bend of the central Euler curve of the third curved coupling waveguide, the minimum spacing Wgap between the microring and the coupling waveguide, and the width W_bend of the coupling waveguide according to the set coupling coefficient; determining the range of the circumference L_bend of the central Euler curve of the third curved coupling waveguide according to the value of Rmax_bend, and determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of L_bend; determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of L_bend; determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of the coupling waveguide area ... The range of the actual number of points num of the central Euler curve is determined; the transmittance of the second TE fundamental mode is simulated and calculated, and L_bend, A_bend, and num are used as variables. The coupled waveguide region is reversely designed by a particle swarm optimization algorithm, and the parameters of the central Euler curve are obtained by iterative optimization; wherein the starting point of the central Euler curve of the third curved coupled waveguide is its leftmost end, and this point is recorded as its origin, and the horizontal right is the positive direction of the x-axis; the starting point of the central Euler curve of the fourth curved coupled waveguide is its rightmost end, and this point is recorded as its origin, and the horizontal left is the positive direction of the x-axis;

[0019] The second step of reverse design includes: using a third-order Bessel function to adjust the width of the third curved coupled waveguide, and using a fourth-order Bessel function to adjust the width of the fourth curved coupled waveguide.

[0020] Preferably, the Bessel control points of the third curved coupled waveguide are recorded as P0_bend1=[0, W_bend], P1_bend1=[xx1_bend1, W_bend], P2_bend1=[xx2_bend1, W_bend], and P3_bend1=[Xmax_bend, yy3_bend1]; wherein the value ranges of xx1_bend1 and xx2_bend1 are both [Xmax×2 / 3, Xmax_bend], the range of yy3_bend1 is selected as [W_bend, W1], W1 is the starting waveguide width of the set curved coupled waveguide, Xmax_bend is the maximum value of the abscissa of the central Euler curve of the third curved coupled waveguide, and Xmax is the maximum value of the abscissa of the central Euler curve of the quarter microring curved waveguide;

[0021] The Bessel control points of the fourth curved coupled waveguide are recorded as P0_bend2=[0, W1], P1_bend2=[xx1_bend2, yy1_bend2], P2_bend2=[xx2_bend2, yy2_bend2], P3_bend2=[xx3_bend2, yy3_bend2], P4_bend2=[xx4_bend2, yy4_bend2]; wherein, the ranges of xx1_bend2, xx2_bend2, and xx3_bend2 are all [0, Xmax_bend], the ranges of yy1_bend2, yy2_bend2, and yy3_bend2 are all [0, 4W_bend], and P4_bend2=P3_bend1;

[0022] Taking xx1_bend1, xx2_bend1, yy3_bend1, xx1_bend2, xx2_bend2, xx3_bend2, yy1_bend2, yy2_bend2, yy3_bend2 as variables, the coupled waveguide region is reversely designed by particle swarm optimization algorithm, and a set of optimal coupled waveguide structure parameters are obtained by iterative optimization.

[0023] Preferably, when establishing a simulation model of a microring filter using a three-dimensional finite-difference time-domain algorithm, basic parameters of the microring filter are used as constraints; the basic parameters include the operating wavelength of the microring filter, the waveguide material, and the height of the waveguide.

[0024] On the other hand, the present invention provides a micro-ring filter designed by using the above-mentioned design method of the micro-ring filter.

[0025] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0026] The present invention uses a three-dimensional time-domain finite difference algorithm to establish a simulation model of a microring filter (including a microring region and a coupled waveguide region), according to a set free spectral range and a set coupling coefficient, with fundamental mode transmittance (such as TE fundamental mode transmittance, or TM fundamental mode transmittance) as an optimization target, with a first curve as a waveguide center curve, using a second curve to adjust the width of the waveguide, reverse designing the microring region and the coupled waveguide region (for example, reverse designing the microring region and the coupled waveguide region through a particle swarm optimization algorithm), iteratively optimizing to obtain a set of optimal microring structural parameters and a set of optimal coupled waveguide structural parameters, and completing the design of the microring filter. The present invention uses a first curve (such as an Euler curve) as a waveguide center line, combines a second curve (such as a Bessel curve) to adjust the waveguide width, realizes smooth optical signal transmission through reverse design, reduces bending loss, and significantly improves the free spectral range and spectral response performance of the microring. The present invention adopts a two-step optimization strategy. Through reverse design, the geometric structure of the curved coupled waveguide is first optimized using a first curve (such as an Euler curve), and then the waveguide width is precisely controlled by a second curve (such as two Bessel curves), which can ensure a high coupling coefficient and low coupling loss. That is, in view of the problems in the prior art that the free spectrum range is insufficient and the loss performance of the microring filter needs to be improved (the microring loss is large and the coupling loss between the curved directional coupler and the microring is large), the present invention proposes a reverse design optimization method using multiple curves, which achieves a significant improvement in performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the structure of a micro-ring filter provided by the present invention;

[0028] Figure 2 A schematic diagram of each microring structure in a microring filter provided by the present invention being divided into four sections of quarter microring curved waveguides;

[0029] Figure 3 A schematic diagram of a curved coupled waveguide and a coupling region in a microring filter provided by the present invention;

[0030] Figure 4 It is a schematic diagram of the structure of a third-order ring 16-channel filter;

[0031] Figure 5 It is a schematic diagram of a third-order Bezier curve;

[0032] Figure 6 It is a schematic diagram of a fourth-order Bezier curve;

[0033] Figure 7 It is a schematic diagram of the bending radius and waveguide width curves at various angles of a quarter micro-ring bending waveguide;

[0034] Figure 8This is a spectrum diagram of the FDTD simulation results of the third-order microring filter. DETAILED DESCRIPTION

[0035] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0036] In a first aspect, the present invention provides a method for designing a microring filter, comprising the following steps:

[0037] A simulation model of a micro-ring filter is established by using a three-dimensional finite-difference time-domain algorithm, wherein the micro-ring filter includes a micro-ring region and a coupled waveguide region;

[0038] According to the set free spectral range and the set coupling coefficient, with the fundamental mode transmittance as the optimization target, the first curve is used as the waveguide center curve, the second curve is used to adjust the width of the waveguide, the microring area and the coupled waveguide area are reversely designed, and an optimal set of microring structure parameters and an optimal set of coupled waveguide structure parameters are obtained through iterative optimization to complete the design of the microring filter.

[0039] Among them, multiple microrings with the same structure are arranged in the microring area, and the structure of each microring is divided into four quarter microring curved waveguides. The central curve of the quarter microring curved waveguide is the first curve, and the quarter microring curved waveguide is used as the target of reverse design.

[0040] The coupling waveguide region is provided with a first coupling waveguide and a second coupling waveguide respectively located at the upper and lower sides of the micro-ring region; the first coupling waveguide includes an input port straight waveguide, a first curved coupling waveguide unit and an output port straight waveguide; the second coupling waveguide includes a first transmission unit, a second curved coupling waveguide unit and a second transmission unit; the structure of the second curved coupling waveguide unit is symmetrical with that of the first curved coupling waveguide unit, the first curved coupling waveguide unit is divided into four sections of curved coupling waveguides, which are respectively recorded as a first curved coupling waveguide, a second curved coupling waveguide, a third curved coupling waveguide and a fourth curved coupling waveguide, the central curve of the third curved coupling waveguide is the first curve, the central curve of the fourth curved coupling waveguide is an antisymmetric curve of the central curve of the third curved coupling waveguide, the second curved coupling waveguide is horizontally mirror-symmetrical with the third curved coupling waveguide, and the first curved coupling waveguide is horizontally mirror-symmetrical with the fourth curved coupling waveguide; the third curved coupling waveguide and the fourth curved coupling waveguide are taken as targets of reverse design.

[0041] The present invention can use TE (Transverse Electric) fundamental mode transmittance as the optimization target, or can use TM (Transverse Magneticwave) fundamental mode transmittance as the optimization target, preferably TE fundamental mode transmittance. The following description will take TE fundamental mode transmittance as the optimization target as an example.

[0042] The transmittance of the TE fundamental mode light of the working wavelength through the microring is recorded as the first TE fundamental mode transmittance; the transmittance of the TE fundamental mode light of the working wavelength through the first curved coupled waveguide unit is recorded as the second TE fundamental mode transmittance; the transmittance of the TE fundamental mode light of the working wavelength through the intersection of two adjacent quarter microring curved waveguides in a microring structure is recorded as the third TE fundamental mode transmittance. When the microring area is reversely designed by the particle swarm optimization algorithm, the first TE fundamental mode transmittance is used as the optimization target; the coupled waveguide area is reversely designed by the particle swarm optimization algorithm, the gradient algorithm, the swarm intelligence algorithm, the neural network algorithm and other algorithms, and the absolute value of the second TE fundamental mode transmittance and the absolute value of the third TE fundamental mode transmittance are used as the optimization target.

[0043] That is, the present invention can use a variety of algorithms including but not limited to particle swarm optimization algorithm, gradient algorithm, swarm intelligence algorithm, neural network algorithm for reverse design. In the embodiment, the particle swarm optimization algorithm is used as an example for explanation.

[0044] The first curve is one of an Euler curve, an Archimedean spiral, a logarithmic spiral, and a B-spline curve, and the second curve is one of a Bezier curve, a spline interpolation curve, and a B-spline curve.

[0045] In addition, when the simulation model of the micro-ring filter is established using the three-dimensional finite difference time domain algorithm, the basic parameters of the micro-ring filter are used as constraints; the basic parameters include the working wavelength of the micro-ring filter, the waveguide material and the height of the waveguide.

[0046] In a second aspect, the present invention provides a micro-ring filter designed using the above-mentioned design method for the micro-ring filter.

[0047] Based on the above content, the present invention provides multiple embodiments for further explanation.

[0048] Embodiment 1:

[0049] Embodiment 1 provides a design method for a micro-ring filter, using an Euler curve as the first curve and a Bezier curve as the second curve.

[0050] The starting waveguide width W0 of the microring is set, and the perimeter L of the central Euler curve of the quarter microring curved waveguide is determined according to the set free spectrum range, and the range of the maximum radius of curvature Rmax of the central Euler curve of the quarter microring curved waveguide and the range of the arc length proportional coefficient A of the central Euler curve of the quarter microring curved waveguide are determined; the maximum value of the abscissa of the central Euler curve of the quarter microring curved waveguide is recorded as Xmax, and the width of the quarter microring curved waveguide is adjusted by using a third-order Bezier curve, and each Bezier control point is recorded as P0=[ 0, W0], P1=[xx1,yy1], P2=[xx2,yy2], P3=[Xmax,yy3]; wherein, the value ranges of xx1 and xx2 are both [Xmax / 3, 2Xmax], the value ranges of yy1 and yy2 are both [-W0 / 2, 3W0], and the value range of yy3 is [W0 / 2, 3W0]; with Rmax, A, xx1, yy1, xx2, yy2, yy3 as variables, the microring region is reversely designed by the particle swarm optimization algorithm, and a set of optimal microring structure parameters are obtained by iterative optimization.

[0051] The method of using the Bezier curve to adjust the width of the quarter micro-ring curved waveguide is as follows: when the horizontal coordinate of a point on the Bezier curve is equal to the horizontal coordinate of a point on the Euler curve, the vertical coordinate value of the Bezier point is used as the waveguide width of the Euler point, and the waveguide width direction of the Euler point is parallel to the direction of the line connecting the Euler point and the center of curvature of the Euler point, and half of the waveguide width is expanded to both sides of the Euler point.

[0052] The coupled waveguide region is inversely designed using a two-step particle swarm optimization algorithm.

[0053] The first step of reverse design includes: determining the maximum curvature radius Rmax_bend of the central Euler curve of the third curved coupling waveguide, the minimum spacing Wgap between the microring and the coupling waveguide, and the width W_bend of the coupling waveguide according to the set coupling coefficient; determining the range of the circumference L_bend of the central Euler curve of the third curved coupling waveguide according to the value of Rmax_bend, and determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of L_bend; determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of L_bend; determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of the coupling waveguide area ... The method comprises the following steps: determining the range of the actual number of points num of the central Euler curve; simulating and calculating the transmittance of the second TE fundamental mode, taking L_bend, A_bend, and num as variables, performing reverse design on the coupled waveguide region through a particle swarm optimization algorithm, and iteratively optimizing to obtain the parameters of the central Euler curve; wherein, the starting point of the central Euler curve of the third curved coupled waveguide is its leftmost end, and this point is recorded as its origin, and the horizontal rightward direction is the positive direction of the x-axis; the starting point of the central Euler curve of the fourth curved coupled waveguide is its rightmost end, and this point is recorded as its origin, and the horizontal leftward direction is the positive direction of the x-axis.

[0054] The second step of reverse design includes: using a third-order Bessel function to adjust the width of the third curved coupled waveguide, and using a fourth-order Bessel function to adjust the width of the fourth curved coupled waveguide.

[0055] Specifically, the Bessel control points of the third curved coupled waveguide are recorded as P0_bend1=[0, W_bend], P1_bend1=[xx1_bend1, W_bend], P2_bend1=[xx2_bend1, W_bend], and P3_bend1=[Xmax_bend, yy3_bend1]; wherein the value ranges of xx1_bend1 and xx2_bend1 are both [Xmax×2 / 3, Xmax_bend], the range of yy3_bend1 is selected as [W_bend, W1], W1 is the starting waveguide width of the set curved coupled waveguide, Xmax_bend is the maximum value of the abscissa of the central Euler curve of the third curved coupled waveguide, and Xmax is the maximum value of the abscissa of the central Euler curve of the quarter microring curved waveguide.

[0056] The Bessel control points of the fourth curved coupled waveguide are recorded as P0_bend2=[0, W1], P1_bend2=[xx1_bend2, yy1_bend2], P2_bend2=[xx2_bend2, yy2_bend2], P3_bend2=[xx3_bend2, yy3_bend2], P4_bend2=[xx4_bend2, yy4_bend2]; wherein, the ranges of xx1_bend2, xx2_bend2, and xx3_bend2 are all [0, Xmax_bend], the ranges of yy1_bend2, yy2_bend2, and yy3_bend2 are all [0, 4W_bend], and P4_bend2=P3_bend1.

[0057] Taking xx1_bend1, xx2_bend1, yy3_bend1, xx1_bend2, xx2_bend2, xx3_bend2, yy1_bend2, yy2_bend2, yy3_bend2 as variables, the coupled waveguide region is reversely designed by particle swarm optimization algorithm, and a set of optimal coupled waveguide structure parameters are obtained by iterative optimization.

[0058] The following further describes Example 1 in conjunction with parameters.

[0059] The Euler curve is a curve with a smooth transition in curvature. It is used to reduce bending loss in microring filter design. The curve equation is as follows:

[0060]

[0061] Where A is the arc length ratio of the curve, R max is the maximum radius of curvature, L is the total curve length, that is, the circumference of the curve, and t is a parameter indicating the position in the curve.

[0062] The Bezier curve is used to control the change of the waveguide width. The shape of the curve is regulated by controlling the position of the control point. The ordinate of the Bezier curve is the waveguide width at the Euler curve where the abscissa is located. The Bezier curve supports ascending order definition. The present invention mainly uses third-order and fourth-order Bezier curves, and their equations are as follows:

[0063] Figure 5 It is a schematic diagram of a third-order Bezier curve. The equation of the third-order Bezier curve is as follows:

[0064] W(t)=P0(1-t) 3 +3P1(1-t) 2 ·t+3P2(1-t)·t 2 +P3t 3t∈[0,1] (3)

[0065] Among them, P0, P1, P2, and P3 are the control point positions, and t is a parameter, which indicates the position in the curve. Figure 5 As shown, P0 is the starting point of the curve, P3 is the ending point of the curve, P1 and P2 regulate the shape of the curve, and P0 = [xx0, yy0], P1 = [xx1, yyl], P2 = [xx2, yy2], and P3 = [xx3, yy3].

[0066] Figure 6 It is a schematic diagram of the fourth-order Bezier curve, and the fourth-order Bezier curve equation is:

[0067] W(t)=P0(1-t) 4 +4P1(1-t) 3 ·t+6P2(1-t) 2 ·t 2 +4P3(1-t)·t 3 +P4t 4 t∈[0,1] (4)

[0068] Among them, P0, P1, P2, P3, and P4 are the control point positions, and t is a parameter, which indicates the position in the curve. Figure 6 As shown, P0 is the starting point of the curve, P4 is the ending point of the curve, P1, P2, and P3 regulate the shape of the curve. Note that P0 = [xx0, yy0], P1 = [xx1, yy1], P2 = [xx2, yy2], P3 = [xx3, yy3], and P4 = [xx3, yy3].

[0069] A silicon nanowire optical waveguide based on silicon-on-insulator SOI material is selected: its core layer is silicon material with a thickness of 220nm, that is, the waveguide height is 220nm, and the refractive index is 3.47; its lower / upper cladding materials are both SiO2, the lower cladding SiO2 thickness is 2μm, the upper cladding SiO2 thickness is 1μm, the refractive index is 1.44, the operating wavelength range is around 1550nm, and the operating polarization state is TE (Transverse Electric) polarization.

[0070] The micro-ring region is provided with a plurality of micro-rings with the same structure, and the coupling waveguide region is provided with a first coupling waveguide and a second coupling waveguide respectively located at the upper and lower sides of the micro-ring region. Figures 1 to 3 A first microring 110, a second microring 120 and a third microring 130 are arranged in the microring region, and a first coupling waveguide 200 and a second coupling waveguide 300 are arranged in the coupling waveguide region.

[0071] The structure of the first microring 110 is divided into four sections of quarter microring curved waveguides, namely a first curved waveguide 111 of the first microring, a second curved waveguide 112 of the first microring, a third curved waveguide 113 of the first microring, and a fourth curved waveguide 114 of the first microring. The center of the first microring 110 is the origin. The second curved waveguide 112 of the first microring is a vertical mirror-symmetric change of the first curved waveguide 111 of the first microring. The fourth curved waveguide 114 of the first microring is a horizontal mirror-symmetric change of the first curved waveguide 111 of the first microring. The third curved waveguide 113 of the first microring is a centrally symmetric change of the first curved waveguide 111 of the first microring with the origin as the center.

[0072] The second microring 120 and the third microring 130 are replicas of the first microring 110. The structure of the second microring 120 is divided into four sections of quarter microring curved waveguides, namely, a first curved waveguide 121 of the second microring, a second curved waveguide 122 of the second microring, a third curved waveguide 123 of the second microring, and a fourth curved waveguide 124 of the second microring. The structure of the third microring 130 is divided into four sections of quarter microring curved waveguides, namely, a first curved waveguide 131 of the third microring, a second curved waveguide 132 of the third microring, a third curved waveguide 133 of the third microring, and a fourth curved waveguide 134 of the third microring.

[0073] The first microring 110 and the second microring 120 are directional coupled to each other, and the second microring 120 and the third microring 130 are directional coupled to each other. The entire filtering working area is recorded as a resonance area 60.

[0074] The first curved waveguide 121 of the second microring and the first curved waveguide 131 of the third microring are both replicas of the first curved waveguide 111 of the first microring. Therefore, once the first curved waveguide 111 of the first microring is determined, the structure of the entire microring is also determined.

[0075] In the first curved waveguide 111 of the first microring, its waveguide center curve is an Euler curve, and its waveguide width is controlled by a Bezier curve. The length (i.e., circumference) of the center Euler curve of the first curved waveguide 111 of the first microring is controlled to be L, which is a constant value, so that the total length of the center curve of the microring is 4L, thus determining the basic size of the microring. The Bezier curve controls the waveguide width of the first curved waveguide 111 of the first microring in such a way that when the horizontal coordinate of a point on the Bezier curve is equal to the horizontal coordinate of a point on the Euler curve, the waveguide width of the Euler point is the value of the vertical coordinate of the Bezier point, and the waveguide width direction of the point is parallel to the direction of the line connecting the Euler point and the center of curvature of the Euler point, and half of the waveguide width is respectively expanded to both sides of the Euler point.

[0076] Since the size of the micro-ring is small enough, the present invention only uses the third-order Bezier curve to adjust the waveguide width. Each Bezier control point is recorded as P0 = [xx0, yy0], P1 = [xx1, yy1], P2 = [xx2, yy2], P3 = [xx3, yy3], and the starting waveguide width is determined to be W0 = 0.4um, then the P0 control point is determined to be [0, W0]. In order to ensure that the FSR is not less than 55nm, the circumference L of the center Euler curve of the first curved waveguide 111 of the first micro-ring is determined to be 2.6585um. At this time, the maximum curvature radius Rmax of the Euler curve is selected to be 2.2um to 2.5um, and the corresponding A value range is 2.55um to 3.45um. In addition, the horizontal coordinate xx3 of the P3 control point is the maximum value of the horizontal coordinate of the Euler center curve of the first curved waveguide 111 of the first micro-ring, recorded as Xmax. In this way, there are a total of seven variables, A, Rmax, xx1, yy1, xx2, yy2, and yy3. Once their values ​​are determined, the structure of the microring is also determined. In order to ensure that the initial waveguide width does not change drastically, the values ​​of xx1 and xx2 are set to be greater than Xmax / 3. And in order to break through the limitations of the Bezier curve change, the maximum values ​​of xx1 and xx2 are set to 2Xmax. Then the ranges of xx1 and xx2 are [Xmax / 3, 2Xmax] and [Xmax / 3, 2Xmax], respectively. At the same time, in order to ensure that the waveguide width has a sufficient range of change, the ranges of yy1, yy2, and yy3 are set to [-W0 / 2, 3W0], [-W0 / 2, 3W0], and [W0 / 2, 3W0], respectively.

[0077] The simulation algorithm uses a high-precision three-dimensional finite-difference time-domain algorithm (Finite-Difference Time-Domain, FDTD), and places the light source at the center of the top waveguide of the microring. The input light is the TE fundamental mode with a wavelength of 1550nm. The monitor is placed at the center of the bottom waveguide of the microring to calculate the transmittance of the TE fundamental mode. The bending radius and bending direction of the light source and the monitor are set to the bending radius and bending direction of the waveguide respectively. The particle swarm reverse design optimization algorithm (PSO) is introduced, and the independent variables are A, Rmax, xx1, yy1, xx2, yy2, yy3, a total of seven variables. The number of iterations is set to 200, and the size of each round is 32. The size of each round is determined by the number of parameters and the number of GPUs. The optimization target value (FOM) is the transmittance of the TE fundamental mode at the half ring. The present invention uses GPU to accelerate the simulation calculation, which speeds up the calculation time of the reverse design by more than 32 times compared with the time of using only CPU calculation. At around 120 rounds, the reverse design is completely converged. The calculated optimal value is 0.008dB / 180°, the FSR of the ring is 55.5nm, and the curves of its bending radius and waveguide width changing with angle are as follows: Figure 7As shown, the Euler curve has Rmax=2.2um, A=3.05042um, which meets the expected design requirements.

[0078] Bend-coupled waveguide design method: see Figure 1 , Figure 3 The first coupling waveguide 200 includes an input port straight waveguide (referred to as the first straight waveguide 201, with a width of 500 nm), a first curved coupling waveguide unit (including a first curved coupling waveguide 202, a second curved coupling waveguide 203, a third curved coupling waveguide 204 and a fourth curved coupling waveguide 205, which are used for directional coupling with the third microring 130, and the coupling region is recorded as the second coupling region 50) and an output port straight waveguide (referred to as the second straight waveguide 206); the second coupling waveguide 300 includes a first transmission unit (including a first transmission waveguide 301 and a first curved waveguide 302), a second curved coupling waveguide unit (including a fifth curved coupling waveguide 303, a sixth curved coupling waveguide 304, a seventh curved coupling waveguide 305 and an eighth curved coupling waveguide 306, which are used for directional coupling with the first microring 110, and the coupling region is recorded as the first coupling region 40) and a second transmission unit (including a second curved waveguide 307 and a second transmission waveguide 308). The second curved waveguide 307 and the first curved waveguide 302 are mutually symmetrical 90° curved waveguides, with a radius of 3um, a circular curve at the center of the curve, and a Bessel function to control the change of the waveguide width, in order to reduce the size of the entire structure and reduce bending loss. The first transmission waveguide 301 is a download port for outputting filtered light. The second transmission waveguide 308 is an upload port.

[0079] TE polarized light is input from the first straight waveguide 201 as the input port, and enters the first curved coupling waveguide 202, the second curved coupling waveguide 203, the third curved coupling waveguide 204, and the fourth curved coupling waveguide 205, wherein a part of the light is output to the next microring filter input end or directly output via the second straight waveguide 206, and the other part of the light is directionally coupled into the third microring 130. Of the part of the light that enters the third microring 130, a part is coupled into the next microring, i.e., the second microring 120, a part circulates in the ring, and a part is coupled back to the first curved coupling waveguide 202, the second curved coupling waveguide 203, the third curved coupling waveguide 204, and the fourth curved coupling waveguide 205, and is output via the second straight waveguide 206.

[0080] Similarly, the second microring 120 is coupled with the first microring 110 and the third microring 130 respectively, and the first microring 110 is coupled with the second microring 120, the eighth curved coupling waveguide 306, the seventh curved coupling waveguide 305, the sixth curved coupling waveguide 304, and the fifth curved coupling waveguide 303 respectively. A resonance region 60 is formed between the microrings and between the microrings and the curved coupling waveguides. The light input from the first straight waveguide 201 is filtered by the resonance region 60, and then output by the first transmission waveguide 301 after passing through the first curved waveguide 302 bent at 90°, completing the function of the filter.

[0081] The first curved coupled waveguide 202, the second curved coupled waveguide 203, the third curved coupled waveguide 204, and the fourth curved coupled waveguide 205 are all curved coupled waveguides, and the fifth curved coupled waveguide 303, the sixth curved coupled waveguide 304, the seventh curved coupled waveguide 305, and the eighth curved coupled waveguide 306 are symmetrical curved coupled waveguides. The center curve of the seventh curved coupled waveguide 305 is an Euler curve, and the starting point of the Euler curve is the leftmost end of the seventh curved coupled waveguide 305. The center curve of the eighth curved coupled waveguide 306 is its antisymmetric curve. The sixth curved coupled waveguide 304 and the fifth curved coupled waveguide 303 are horizontal mirror-symmetric changes of the seventh curved coupled waveguide 305 and the eighth curved coupled waveguide 306, respectively.

[0082] In order to ensure that the coupling coefficients of the eighth curved coupling waveguide 306, the seventh curved coupling waveguide 305, the sixth curved coupling waveguide 304, the fifth curved coupling waveguide 303 and the first microring 110 remain substantially unchanged during the reverse design, the present invention adopts two restriction conditions. Restriction condition 1 is: the maximum curvature radius Rmax_bend of the central Euler curve of the seventh curved coupling waveguide 305 is determined (i.e., the value of the maximum curvature radius Rmax_bend is determined according to the coupling coefficient); Restriction condition 2 is: the width of the waveguide of the portion of the seventh curved coupling waveguide 305 that is relatively close to the first microring 110 remains substantially unchanged, i.e., the width of the seventh curved coupling waveguide 305 changes slowly. At the same time, the waveguide width of the eighth curved coupling waveguide 306 can change more dramatically on the premise that the waveguide at the junction with the seventh curved coupling waveguide 305 is smoothly connected.

[0083] In order to shorten the calculation time of the reverse design, a particle swarm reverse design optimization algorithm is used in two steps. The purpose of the first step is to determine the central Euler curves of the eighth curved coupled waveguide 306, the seventh curved coupled waveguide 305, the sixth curved coupled waveguide 304, and the fifth curved coupled waveguide 303. At this time, as long as the central Euler curve of the eighth curved coupled waveguide 306 is determined, the central curves of other waveguides are also determined.

[0084] Keep the waveguide widths of the eighth curved coupling waveguide 306, the seventh curved coupling waveguide 305, the sixth curved coupling waveguide 304, and the fifth curved coupling waveguide 303 unchanged, determine the Rmax_bend value of the Euler curve, and the minimum spacing Wgap=150nm between the microring and the curved coupling waveguide that meets the processing technology. At this time, the coupling coefficient of the coupling region of the first microring 110 and the eighth curved coupling waveguide 306, the seventh curved coupling waveguide 305, the sixth curved coupling waveguide 304, and the fifth curved coupling waveguide 303, that is, the first coupling region 40, is basically determined. In order to ensure the coupling coefficient K=0.25, Rmax_bend=12um and the curved coupling waveguide width W_bend=0.31um are selected by simulation. Then, the Euler curve length L_bend and the control coefficient (arc length proportional coefficient) A_bend, as well as the interception coefficient of the Euler curve (that is, the actual number of points of the central Euler curve) num are still to be determined. The definition of num is: there are 600 points in the Euler curve, and the value of num is the first num points of the Euler curve. According to the value of Rmax_bend, the range of L_bend is selected as [6um, 20um], and then the range of A_bend is selected as [10um, 120um] according to the range of L_bend. In order to ensure that the first coupling region 40 has enough curved coupling parts, the range of num is selected as [180, 600]. The simulation algorithm uses a high-precision three-dimensional finite difference time domain algorithm (FDTD), shields other simulation structures, and only calculates the TE fundamental mode transmittance of the TE fundamental mode light through the eighth curved coupling waveguide 306, the seventh curved coupling waveguide 305, the sixth curved coupling waveguide 304, and the fifth curved coupling waveguide 303. The particle swarm inverse design optimization algorithm (PSO) is introduced, and the number of iterations is set to 40, the size of each round is 16, the independent variables are A_bend, L_bend, num, a total of 3 variables, and the optimization target value (FOM) is the TE fundamental mode transmittance. In this way, the parameters of the central Euler curve are determined (the parameters of the central Euler curve include Rmax_bend, A_bend, L_bend, num).

[0085] In the second step, the third-order Bessel function and the fourth-order Bessel function are used to control the waveguide width changes of the seventh curved coupled waveguide 305 and the eighth curved coupled waveguide 306. The Bessel control point of the seventh curved coupled waveguide 305 is recorded as:

[0086] P0_bend1=[xx0_bend1,yy0_bend1],

[0087] P1_bend1=[xx1_bend1,yy1_bend1],

[0088] P2_bend1=[xx2_bend1,yy2_bend1],

[0089] P3_bend1=[xx3_bend1,yy3_bend1].

[0090] The maximum value of the horizontal coordinate of the central Euler curve of the seventh curved coupling waveguide 305 is Xmax_bend, P0_bend1 = [0, W_bend], yy1_bend1 = yy2_bend1 = W_bend, xx3_bend1 = Xmax_bend. The value ranges of xx1_bend1 and xx2_bend1 are both [Xmax×2 / 3, Xmax_bend]. The reason for limiting their minimum values ​​to be greater than Xmax×2 / 3 is to ensure that the width of the curved coupling waveguide close to the micro-ring is basically unchanged relative to W_bend, so as to ensure a sufficient coupling coefficient. The range of yy3_bend1 is selected as [W_bend, W1], W1 is the starting waveguide width of the set curved coupling waveguide, and according to the result of the first step, the range of yy3_bend1 is selected as [W_bend, 0.5um].

[0091] The width variation control of the eighth curved coupled waveguide 306 is controlled by a fourth-order Bezier curve. The Bezier control points of the eighth curved coupled waveguide 306 are recorded as:

[0092] P0_bend2=[xx0_bend2,yy0_bend2],

[0093] P1_bend2=[xx1_bend2,yy1_bend2],

[0094] P2_bend2=[xx2_bend2,yy2_bend2],

[0095] P3_bend2=[xx3_bend2,yy3_bend2],

[0096] P4_bend2=[xx4_bend2,yy4_bend2].

[0097] The starting point of the central Euler curve of the eighth curved coupling waveguide 306 is the rightmost end, which is recorded as the origin. The horizontal left is the positive direction of the x-axis, and the y-axis direction remains unchanged. The starting waveguide width of the eighth curved coupling waveguide 306 is set to 0.5um, and the control point P0_bend2 = [0, 0.5um]. In order to smoothly connect with the seventh curved coupling waveguide 305, the termination control point P4_bend2 = P3_bend1. The ranges of xx1_bend2, xx2_bend2, and xx3_bend2 are all set to [0, Xmax_bend], and the ranges of yy1_bend2, yy2_bend2, and yy3_bend2 are all set to [0, 4×W_bend]. The simulation algorithm uses a high-precision three-dimensional finite-difference time-domain algorithm (FDTD), shields other simulation structures, and only retains the eighth curved coupled waveguide 306, the seventh curved coupled waveguide 305, the sixth curved coupled waveguide 304, the fifth curved coupled waveguide 303, the eighth curved coupled waveguide 306, the straight waveguides connected to the left and right of the fifth curved coupled waveguide 303, and the first microring 110. The TE fundamental mode light enters from the straight waveguide connected to the left of the fifth curved coupled waveguide 303, and the TE fundamental mode transmittance T_bend of the TE fundamental mode light passing through the fifth curved coupled waveguide 303, the sixth curved coupled waveguide 304, the seventh curved coupled waveguide 305, and the eighth curved coupled waveguide 306, as well as the TE fundamental mode transmittance T_ring at the junction of the first curved waveguide 111 of the first microring and the second curved waveguide 112 of the first microring are calculated. The particle swarm reverse design optimization algorithm (PSO) was introduced, with 9 variables including xx1_bend1, xx2_bend1, yy3_bend1, xx1_bend2, xx2_bend2, xx3_bend2, yy1_bend2, yy2_bend2, and yy3_bend2. The number of iterations was set to 250, the size of each round was 32, and the optimization objective value (FOM) was the sum of the absolute value of the TE fundamental mode transmittance T_bend and the absolute value of T_ring. After the reverse design was fully converged, the coupling coefficient K>0.25 was obtained, and the coupling loss was less than <0.019dB.

[0098] Figure 4This is a schematic diagram of the structure of a 16-channel third-order microring filter. Channel 1 is the input port, channels 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17 are download ports, and channel 18 is a pass-through port. Channels 2 to 17 are from long wavelength channels to short wavelength channels. Because the input light intensity of the later channels is smaller, the loss difference between the long wavelength and short wavelength channels can be balanced. The spacing between each adjacent channel is 3.2nm, and the bandwidth of each passband is 2.6nm. A 16-channel filter is formed.

[0099] The three-dimensional finite-difference time-domain algorithm was used to simulate and verify the third-order micro-ring filter, whose size is 13.4um×12um. Figure 8 As shown, it is the simulation result of simulation verification, where the horizontal axis is the wavelength and the vertical axis is the transmittance of the TE (Transverse Electric) fundamental mode. As can be seen from the figure, the device of the present invention realizes the filtering function of a high-order micro-ring filter, the central wavelengths of the two bands are 1533nm and 1588.5nm respectively, the 3dB bandwidths are 2.6nm and 3.5nm respectively, the channel loss is less than 0.6dB, the extinction ratio is greater than 60dB, it has a flattened channel and a high steepness, has a relatively idealized square spectral response, and the free spectral range (FSR) = 55.5nm. It can be seen that the device of the present invention can obtain an on-chip optical multi-channel filter with low loss, large free spectral range, high extinction ratio and small size.

[0100] In summary, Example 1 achieves a smooth curvature transition by introducing the Euler ring curve and combining the Bessel function to control the waveguide width, so that the size of the microring can be further reduced, while effectively controlling the loss caused by the curvature change. The design achieves an ultra-large free spectral range of 55.5nm, supports 16 channels, and each channel is spaced 3.2nm apart, significantly expanding the number of channels and bandwidth range of the filter.

[0101] Example 1 uses a reverse design method to optimize the geometric parameters and waveguide width of the microring, making the transmission of optical signals in the microring smoother and significantly reducing the loss. When the microring size is reduced to a free spectrum range of 55.5nm, a half-ring loss of less than 0.008dB / 180° is achieved, which is significantly lower than the existing technology, providing a more reliable low-loss solution for high-performance optical communication applications.

[0102] Example 1 uses the Euler ring curve and Bessel to control the waveguide width to optimize the design of the directional coupler. Under the premise of ensuring a sufficiently large coupling coefficient, a smoother curvature transition is achieved, the excitation of high-order modes is reduced, and a coupling loss of less than 0.019 dB is achieved (that is, the coupling loss between the curved directional coupler and the microring in Example 1 is significantly reduced), and a coupling coefficient of 0.25 is guaranteed, which significantly improves the transmission efficiency of the optical signal and effectively suppresses crosstalk between channels.

[0103] The present invention also supports the design of filters with different numbers of channels, different passband widths, and different channel intervals, and supports filters with different orders of micro-rings, and can realize high-order micro-ring filters.

[0104] In the present invention, the design schemes of the Euler curve and the Bezier curve can be replaced by other curves with control points to achieve similar optical signal transmission and performance optimization effects. The following are several alternative schemes, which are respectively described in Examples 2 to 5.

[0105] Embodiment 2:

[0106] Embodiment 2 provides a design method for a micro-ring filter, which is different from Embodiment 1 in that Embodiment 2 uses an Archimedean spiral instead of an Euler curve to design the center line of the micro-ring waveguide.

[0107] The Archimedean spiral has a fixed angle increment, and its regular geometric shape helps to reduce transmission loss and maintain good spectral response characteristics. It is suitable for applications that require high stability of the waveguide structure.

[0108] The polar coordinate equation of the Archimedean spiral is:

[0109] r(θ)=a+bθ

[0110] Where r is the radial distance, θ is the angle, and a and b are constants.

[0111] In Example 2, the shape of the curve is controlled by controlling the constants a and b, and a portion of the curve is intercepted as the central curve of the curved waveguide.

[0112] Embodiment 3:

[0113] Embodiment 3 provides a design method for a micro-ring filter. The difference from Embodiment 1 is that Embodiment 3 uses a logarithmic spiral instead of an Euler curve to design the center line of the micro-ring waveguide.

[0114] The logarithmic spiral has an exponentially growing curvature characteristic, and its smooth curvature change can effectively reduce the bending loss and improve the free spectral range of the microring.

[0115] In the polar coordinate system (r,θ), the logarithmic spiral curve can be written as:

[0116] r(θ)=r0e kθ

[0117] Where: r is the radial distance, θ is the angle, r0 is the initial radial distance, and k is a constant.

[0118] In Embodiment 3, the shape of the curve is controlled by controlling r0 and k, and a section of the curve within a specified range of θ can be taken as the central curve of the curved waveguide.

[0119] Embodiment 4:

[0120] Embodiment 4 provides a design method for a micro-ring filter, which is different from Embodiment 1 in that Embodiment 4 uses a spline interpolation curve instead of a Bezier curve to adjust the waveguide width.

[0121] The spline interpolation curve generates a smooth interpolation curve through control points, which is suitable for dynamically adjusting the waveguide width, optimizing the spectral response characteristics and reducing the optical signal loss.

[0122] The spline interpolation curve is expressed as:

[0123]

[0124] Where C(t) is a point on the curve, a n is the coordinate of the nth control point, n is the order of the curve, and t is the parameter, indicating the position in the curve.

[0125] Embodiment 4 can control the shape of the spline curve by controlling each control point.

[0126] Embodiment 5:

[0127] Embodiment 5 provides a design method for a micro-ring filter. The difference from Embodiment 1 is that Embodiment 5 replaces the Euler curve and the Bezier curve with a B-spline curve.

[0128] The B-spline curve is defined by multiple control points and can achieve smooth curve transition. Its curvature change can be effectively controlled, which is suitable for the smooth design of the waveguide center curve and the gradual regulation of the waveguide width, thereby reducing bending loss and optimizing spectral response performance.

[0129] The B-spline curve is expressed as:

[0130]

[0131] Where C(t) is a point on the curve, P i is the control point. i,kis the B-spline basis function, k is the order of the curve, and n is the number of control points minus 1.

[0132] Similar to the Bezier curve, the order k of the curve and the position of the control point are defined to define the shape of the curve, thereby controlling the width change of the curved waveguide.

[0133] In summary, the present invention can realize an on-chip multi-channel optical filter by introducing a design method combining the first curve with the second curve and adopting a particle swarm inverse design optimization algorithm. The filter has an ultra-large free spectral range, low loss and high extinction ratio, and exhibits an excellent spectral flat-top response. The design of the present invention is not only highly flexible and can support a variety of channel numbers and bandwidth configurations, but also has spectral characteristics of low crosstalk and high steepness. The on-chip microring filter has a compact structure, excellent performance, and a simple manufacturing process, and is suitable for large-scale integrated photonic applications.

[0134] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A design method for a microring filter, characterized in that: The following steps are involved: A simulation model of a micro-ring filter is established by using a three-dimensional finite-difference time-domain algorithm, wherein the micro-ring filter includes a micro-ring region and a coupled waveguide region; According to the set free spectral range and the set coupling coefficient, with the fundamental mode transmittance as the optimization target, the first curve is used as the waveguide center curve, the second curve is used to adjust the width of the waveguide, the microring area and the coupled waveguide area are reversely designed, and an optimal set of microring structure parameters and an optimal set of coupled waveguide structure parameters are obtained through iterative optimization to complete the design of the microring filter.

2. The design method of the microring filter according to claim 1, characterized in that: A plurality of microrings with the same structure are arranged in the microring region, the structure of each microring is divided into four sections of quarter microring curved waveguides, the central curve of the quarter microring curved waveguide is the first curve, and the quarter microring curved waveguide is used as a target of reverse design; The coupling waveguide region is provided with a first coupling waveguide and a second coupling waveguide respectively located at the upper and lower sides of the micro-ring region; the first coupling waveguide includes an input port straight waveguide, a first curved coupling waveguide unit and an output port straight waveguide; the second coupling waveguide includes a first transmission unit, a second curved coupling waveguide unit and a second transmission unit; the structure of the second curved coupling waveguide unit is symmetrical with that of the first curved coupling waveguide unit, the first curved coupling waveguide unit is divided into four sections of curved coupling waveguides, which are respectively recorded as a first curved coupling waveguide, a second curved coupling waveguide, a third curved coupling waveguide and a fourth curved coupling waveguide, the central curve of the third curved coupling waveguide is the first curve, the central curve of the fourth curved coupling waveguide is an antisymmetric curve of the central curve of the third curved coupling waveguide, the second curved coupling waveguide is horizontally mirror-symmetrical with the third curved coupling waveguide, and the first curved coupling waveguide is horizontally mirror-symmetrical with the fourth curved coupling waveguide; the third curved coupling waveguide and the fourth curved coupling waveguide are taken as targets of reverse design.

3. The design method of the micro-ring filter according to claim 2, characterized in that: The transmittance of the TE fundamental mode light of the working wavelength through the microring is recorded as the first TE fundamental mode transmittance; the transmittance of the TE fundamental mode light of the working wavelength through the first curved coupling waveguide unit is recorded as the second TE fundamental mode transmittance; the transmittance of the TE fundamental mode light of the working wavelength through the intersection of two adjacent quarter microring curved waveguides in a microring structure is recorded as the third TE fundamental mode transmittance; The microring region is reversely designed by using one of the particle swarm optimization algorithm, the gradient algorithm, the swarm intelligence algorithm, and the neural network algorithm, with the first TE fundamental mode transmittance as the optimization target; the coupled waveguide region is reversely designed by using the particle swarm optimization algorithm, with the sum of the absolute value of the second TE fundamental mode transmittance and the absolute value of the third TE fundamental mode transmittance as the optimization target.

4. The design method of the microring filter according to claim 1, characterized in that: The first curve is one of an Euler curve, an Archimedean spiral, a logarithmic spiral, and a B-spline curve, and the second curve is one of a Bezier curve, a spline interpolation curve, and a B-spline curve.

5. The design method of the micro-ring filter according to claim 3, characterized in that: When the first curve is an Euler curve and the second curve is a Bezier curve, the starting waveguide width W0 of the microring is set, and according to the set free spectrum range, the circumference L of the central Euler curve of the quarter microring curved waveguide is determined, and the range of the maximum curvature radius Rmax of the central Euler curve of the quarter microring curved waveguide and the range of the arc length proportional coefficient A of the central Euler curve of the quarter microring curved waveguide are determined; The maximum value of the abscissa of the central Euler curve of the quarter micro-ring curved waveguide is recorded as Xmax, and the width of the quarter micro-ring curved waveguide is adjusted by a third-order Bezier curve, and each Bezier control point is recorded as P0=[0, W0], P1=[xx1, yy1], P2=[xx2, yy2], P3=[Xmax, yy3]; wherein the value ranges of xx1 and xx2 are both [Xmax / 3, 2Xmax], the value ranges of yy1 and yy2 are both [-W0 / 2, 3W0], and the value range of yy3 is [W0 / 2, 3W0]; Taking Rmax, A, xx1, yy1, xx2, yy2, and yy3 as variables, the microring region is reversely designed using a particle swarm optimization algorithm, and a set of optimal microring structural parameters are obtained through iterative optimization.

6. The design method of the microring filter according to claim 5, characterized in that: The method of using the Bezier curve to adjust the width of the quarter micro-ring curved waveguide is as follows: when the horizontal coordinate of a point on the Bezier curve is equal to the horizontal coordinate of a point on the Euler curve, the vertical coordinate value of the Bezier point is used as the waveguide width of the Euler point, and the waveguide width direction of the Euler point is parallel to the direction of the line connecting the Euler point and the center of curvature of the Euler point, and half of the waveguide width is expanded to both sides of the Euler point.

7. The design method of the micro-ring filter according to claim 3, characterized in that: When the first curve is an Euler curve and the second curve is a Bezier curve, a two-step particle swarm optimization algorithm is used to perform reverse design on the coupled waveguide region; The first step of reverse design includes: determining the maximum curvature radius Rmax_bend of the central Euler curve of the third curved coupling waveguide, the minimum spacing Wgap between the microring and the coupling waveguide, and the width W_bend of the coupling waveguide according to the set coupling coefficient; determining the range of the circumference L_bend of the central Euler curve of the third curved coupling waveguide according to the value of Rmax_bend, and determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of L_bend; determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of L_bend; determining the range of the arc length proportional coefficient A_bend of the central Euler curve of the third curved coupling waveguide according to the range of the coupling waveguide area ... The range of the actual number of points num of the central Euler curve is determined; the transmittance of the second TE fundamental mode is simulated and calculated, and L_bend, A_bend, and num are used as variables. The coupled waveguide region is reversely designed by a particle swarm optimization algorithm, and the parameters of the central Euler curve are obtained by iterative optimization; wherein the starting point of the central Euler curve of the third curved coupled waveguide is its leftmost end, and this point is recorded as its origin, and the horizontal right is the positive direction of the x-axis; the starting point of the central Euler curve of the fourth curved coupled waveguide is its rightmost end, and this point is recorded as its origin, and the horizontal left is the positive direction of the x-axis; The second step of reverse design includes: using a third-order Bessel function to adjust the width of the third curved coupled waveguide, and using a fourth-order Bessel function to adjust the width of the fourth curved coupled waveguide.

8. The design method of the micro-ring filter according to claim 7, characterized in that: The Bessel control points of the third curved coupled waveguide are recorded as P0_bend1=[0, W_bend], P1_bend1=[xx1_bend1, W_bend], P2_bend1=[xx2_bend1, W_bend], and P3_bend1=[Xmax_bend, yy3_bend1]; wherein the value ranges of xx1_bend1 and xx2_bend1 are both [Xmax×2 / 3, Xmax_bend], the range of yy3_bend1 is selected as [W_bend, W1], W1 is the starting waveguide width of the set curved coupled waveguide, Xmax_bend is the maximum value of the abscissa of the central Euler curve of the third curved coupled waveguide, and Xmax is the maximum value of the abscissa of the central Euler curve of the quarter microring curved waveguide; The Bessel control points of the fourth curved coupled waveguide are recorded as P0_bend2=[0, W1], P1_bend2=[xx1_bend2, yy1_bend2], P2_bend2=[xx2_bend2, yy2_bend2], P3_bend2=[xx3_bend2, yy3_bend2], P4_bend2=[xx4_bend2, yy4_bend2]; wherein, the ranges of xx1_bend2, xx2_bend2, and xx3_bend2 are all [0, Xmax_bend], the ranges of yy1_bend2, yy2_bend2, and yy3_bend2 are all [0, 4W_bend], and P4_bend2=P3_bend1; Taking xx1_bend1, xx2_bend1, yy3_bend1, xx1_bend2, xx2_bend2, xx3_bend2, yy1_bend2, yy2_bend2, yy3_bend2 as variables, the coupled waveguide region is reversely designed by particle swarm optimization algorithm, and a set of optimal coupled waveguide structure parameters are obtained by iterative optimization.

9. The design method of a microring filter according to claim 1, characterized in that: When a simulation model of a micro-ring filter is established using a three-dimensional finite-difference time-domain algorithm, basic parameters of the micro-ring filter are used as constraints; the basic parameters include the operating wavelength of the micro-ring filter, the waveguide material and the height of the waveguide.

10. A microring filter, characterized in that: The micro-ring filter is designed by using the design method of the micro-ring filter as described in any one of claims 1 to 9.

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