A dual-mode multi-channel cross waveguide

Abstract

This invention provides a dual-mode multi-channel cross-waveguide, comprising a substrate, on which a top silicon layer is disposed. The top silicon layer includes an optimization region in the form of a regular 2N polygon and N cross-channels, where N≥3. The centerline of each channel is arranged along the perpendicular bisector of the side of the regular 2N polygon. The optimization region is divided into 4N symmetric regions along the axis of symmetry of the regular 2N polygon. Air holes are formed in each symmetric region. By adjusting the state of the air holes in the symmetric regions, an aperiodic perforation array that meets a predetermined output target is formed. The output target refers to each channel supporting two different modes of optical transmission. The dual-mode multi-channel cross-waveguide provided by this invention has a small size, good performance, and can realize the cross-transmission function of two different modes in any channel, further increasing the transmission capacity of the optical interconnect system.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optoelectronic components technology, specifically relating to a dual-mode multi-channel cross waveguide optimized using a multi-dimensional direct binary search algorithm. Background Technology

[0002] Photonic integrated circuits (PICs) have made tremendous progress over the past decade. Due to their high refractive index difference, state-of-the-art silicon-based photonic PICs can now integrate hundreds or even thousands of optical devices on silicon-on-insulator (SOI) wafers. With the rapid increase in integration density, the number of cross-waveguides will increase significantly. Unlike electronic integrated circuits, which can be flexibly interconnected across multiple layers, photonic PICs are mostly designed on a single layer. Therefore, without low-loss, ultra-compact waveguides and multi-channel cross-waveguides, high-density photonic PICs are difficult to achieve.

[0003] In fact, the study of waveguide intersections has long attracted researchers' interest. Since the lateral constraints of waveguides disappear at the intersection, light diffraction occurs. Therefore, effectively mitigating the strong diffraction effect in the intersection region is crucial for various design schemes. Currently, many methods for designing intersecting waveguides have been reported, such as widening the waveguide, multimode interference, and subwavelength gratings. Although these traditional schemes, which rely on prior physical models, produce devices with excellent performance, the optimization process is heavily reliant on manual control due to the small parameter space and low degrees of freedom. Furthermore, the designed devices are relatively large, making them difficult to apply to future large-scale photonic integrated systems.

[0004] With the advancements in micro-nano fabrication technology and the development of computer technology in recent years, the design of micro-nano photonic devices using intelligent algorithms has been extensively studied. Many algorithm-based devices have overcome the limitations of traditional devices, achieving superior performance. In 2017, Luluzi Lu et al. designed four-channel, five-channel, and six-channel star-shaped cross-waveguides using the Direct Binary Search (DBS) algorithm. In 2018, Hailong Han et al. implemented a silicon-based single-mode two-channel cross-waveguide with a size of only 1μm×1μm using a particle swarm optimization algorithm. Besides the number of channels, multi-mode optical devices can also expand transmission capacity; two-channel dual-mode and three-mode cross-waveguides were reported in 2018 and 2019, respectively. However, breakthroughs in small-size, dual-mode, multi-channel cross-waveguides based on intelligent algorithms have yet to be achieved. Furthermore, the Direct Binary Search algorithm only searches the state of the optimization region's partitioning units, resulting in low freedom of optimization parameters and limiting the possibility and diversity of the refractive index distribution in the searched optimization region. The potential of the Direct Binary Search algorithm remains to be further explored. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of existing cross waveguides, such as complex design process, large size, single mode, and small number of channels. It provides a dual-mode multi-channel cross waveguide based on multi-dimensional direct binary search (MDBS) algorithm, which realizes the cross-channel cross-crossing through the principle of multi-symmetry.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a dual-mode multi-channel cross waveguide, comprising a substrate, on which a top silicon layer is provided, the top silicon layer comprising an optimization region in the form of a regular 2N polygon and N cross channels, where N≥3, the center line of the channel is set along the perpendicular bisector of the side of the regular 2N polygon, the optimization region is divided into 4N symmetric regions along the axis of symmetry of the regular 2N polygon, and air holes are provided on the symmetric regions. By adjusting the state of the air holes on the symmetric regions, a non-periodic perforation array that satisfies a predetermined output target is formed, wherein the output target refers to each channel supporting two different modes of optical transmission.

[0007] Preferably, the air pores are filled with silicon or air.

[0008] Preferably, the air hole is a circular hole or an oblong hole.

[0009] Preferably, the substrate has a thickness of 3 μm, the top silicon layer has a thickness of 220 nm, the optimization region is a regular hexagon, the channel width W1 is 900 nm, the distance W2 between the two parallel sides of the optimization region is 5640 nm, the center line connecting any three air holes forms an equilateral triangle with a side length d of 150 nm, the arc diameter d1 of the waist-shaped hole is 90 nm, the straight side length W3 of the waist-shaped hole is 30 nm, and the diameter of the circular hole is 90–120 nm.

[0010] Preferably, the waist-shaped hole located on the axis of symmetry of the optimization zone has its axis of symmetry coinciding with the axis of symmetry of the optimization zone.

[0011] Preferably, the two different modes are the TE0 mode in the 1540nm to 1560nm band and the TE1 mode in the 1540nm to 1560nm band.

[0012] A method for manufacturing a dual-mode multi-channel cross waveguide includes the following steps:

[0013] Step S1: Set the initial structure for optimization and set the objective function for reflector performance in the multi-dimensional direct binary algorithm;

[0014] Step S2: Select an air hole in any symmetrical region as the starting point for optimization;

[0015] Step S3: Fill the selected air holes and the corresponding air holes in other symmetrical regions with silicon material, and calculate the objective function value;

[0016] Step S4: Set the shape of the selected air hole and the corresponding air holes in the other symmetrical areas to be waist-shaped holes, and symmetrically change their rotation angle with the center of the waist-shaped hole as the origin until they rotate 180° back to the original position. Calculate the objective function value once for each change in rotation angle.

[0017] Step S5: Set the shape of the selected air hole and the corresponding air holes in other symmetrical areas to circular holes, and synchronously change the diameter of the circular holes. Calculate the objective function value once each time the size is changed.

[0018] Step S6: Compare the objective function values ​​calculated for all state parameters of the selected air vents, select the optimal value, and retain the corresponding dimensional parameters of the optimal value in all symmetric regions;

[0019] Step S7: Select the next air hole and repeat steps S3 to S6. One iteration is defined as traversing all air holes in the symmetric region. After multiple iterations, compare the objective function value after the previous iteration. If the change in the objective function value between the two iterations is less than 0.1%, the objective function converges, the algorithm stops, and the hole array of the symmetric region is determined.

[0020] Preferably, the waist-shaped hole changes its rotation angle in 10° increments, and the diameter of the circular hole is between 90nm and 120nm, changing in 10nm increments.

[0021] Preferably, the objective function value is the sum of the transmittance of the two different modes in channel 4.

[0022] Preferably, the optimized initial structure is such that all air holes on the channel are filled with silicon, and all other air holes in the optimized region are filled with air.

[0023] This invention divides the optimization region of a regular 2N-sided polygon into 4N symmetrical regions based on the perpendicular bisectors of its sides and its diagonals. Several air holes are distributed within each symmetrical region. The multi-dimensional direct binary algorithm optimizes the distribution of air holes in only one symmetrical region. The distribution of air holes in other symmetrical regions is obtained through the symmetry of the optimization region. This not only reduces computation time costs and optimizes device size, but more importantly, it enables cross-transmission of two different modes in any channel, further increasing the transmission capacity of the optical interconnect system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of one embodiment of the present invention;

[0025] Figure 2 for Figure 1 The diagram shows the structure of the top silicon layer.

[0026] Figure 3 This refers to the initial structural design process; among which, Figure 3 (a) Schematic diagram of the arrangement of air holes, where the line connecting the centers of any three air holes forms an equilateral triangle; Figure 3 (b) is a schematic diagram showing the structure of the optimization region divided into twelve symmetrical regions by the perpendicular bisectors and diagonals of a regular hexagon; Figure 3 (c) is a schematic diagram of the structure of air holes distributed in the symmetrical region.

[0027] Figure 4 The schematic diagram is for optimizing the initial structure, in which the air holes on the channels are filled with silicon, and the other air holes in the optimization area are filled with air.

[0028] Figure 5 This is a schematic diagram of the waist-shaped hole.

[0029] Figure 6 This is a schematic diagram of a waist-shaped hole located on the axis of symmetry of a regular hexagon.

[0030] Figure 7 The transmission spectra are for TE0 and TE1 modes.

[0031] In the figure, 1 is the substrate; 2 is the top silicon layer; 3 is the optimization region; 31 is the symmetry region; 32 is the air hole; 321 is the first waist-shaped hole; 322 is the second waist-shaped hole; 323 is the third waist-shaped hole; 324 is the circular hole; and 4 is the channel. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0033] Please refer to the following: Figure 1-6 The dual-mode multi-channel cross waveguide provided in this embodiment includes a substrate 1, on which a top silicon layer 2 is provided. The top silicon layer 2 includes an optimization region 3 in the shape of a regular 2N polygon and N intersecting channels 4, where N≥3. The center line of each channel 4 is set along the perpendicular bisector of the side of the regular 2N polygon, and the intersection point of the center lines of all channels 4 coincides with the center of the optimization region 3. The optimization region 3 is divided into 4N symmetric regions 31 along the axis of symmetry of the regular 2N polygon. Air holes 32 are provided on each symmetric region 31. By adjusting the state of the air holes 32 on the symmetric region 31, a non-periodic perforation array that meets a predetermined output target is formed. The output target refers to each channel supporting two different modes of optical transmission.

[0034] This invention divides the optimization region 3 of a regular 2N-sided polygon into 4N symmetrical regions 31 by the perpendicular bisectors of its sides and its diagonals. Several air holes are distributed within each symmetrical region 31. The multi-dimensional direct binary search algorithm optimizes the distribution of air holes 32 within only one symmetrical region 31. The distribution of air holes 32 in other symmetrical regions 31 is obtained through the symmetry of the optimization region 3. This not only reduces computation time costs, but more importantly, it can reduce device size and enable the cross-connection function of two different modes of light sources passing through any channel 4, further increasing the transmission capacity of the optical interconnect system.

[0035] More specifically, the air hole 32 is in a state of being filled with silicon or air.

[0036] More specifically, the air hole 32 is a circular hole or an oblong hole.

[0037] More specifically, in this embodiment, the dual-mode multi-channel cross waveguide is designed on an insulator substrate silicon platform with a substrate thickness of 3 μm and a top silicon thickness of 220 nm. The optimization region 3 is a regular hexagon with a spacing W2 of 5640 nm between its two parallel sides. The perpendicular bisectors and diagonals of the regular hexagon divide the optimization region 3 into twelve symmetrical regions 31. The width W1 of the channel 4 is 900 nm, which can support the transmission of TE0 and TE1 modes.

[0038] The center line connecting any three air holes forms an equilateral triangle with a side length d of 150 nm. The diameter d1 of the arc of the waist-shaped hole is 90 nm, the side length W3 of the straight side of the waist-shaped hole is 30 nm, and the depth of the waist-shaped hole is 0–220 nm. The diameter of the circular hole is 90–120 nm, and the depth of the circular hole is 0–220 nm.

[0039] In this embodiment, the depth of the waist-shaped aperture is 220nm, and the depth of the circular aperture is 220nm. It can be understood that the optimization region 3 can also be a regular polygon such as a regular octagon or a regular decagon, and can realize any number of cross waveguides as needed.

[0040] More specifically, the waist-shaped holes located on the axis of symmetry of the optimization region 3 have their axes of symmetry coincident with the axis of symmetry of the optimization region 3. The waist-shaped holes include a first waist-shaped hole 321 located in the symmetry region 31, a second waist-shaped hole 322 located on the diagonal of the regular hexagon, and a third waist-shaped hole 323 located on the perpendicular bisector of the side of the regular hexagon. The second waist-shaped hole 322 is symmetrically arranged about the diagonal of the regular hexagon, and the third waist-shaped hole 323 is symmetrically arranged about the perpendicular bisector of the side of the regular hexagon. This ensures that when the perforation array on the symmetry region 31 is symmetrically arranged on the optimization region 3, the waist-shaped holes on the axis of symmetry can completely coincide. On the one hand, this reduces the computation time cost, and on the other hand, it ensures that the perforation array can achieve the desired function.

[0041] More specifically, the two different modes are the TE0 mode in the 1540nm to 1560nm band and the TE1 mode in the 1540nm to 1560nm band.

[0042] This invention also provides a method for manufacturing a dual-mode multi-channel cross waveguide, comprising the following steps:

[0043] Step S1: Set the initial structure for optimization and set the objective function for reflector performance in the multi-dimensional direct binary algorithm;

[0044] Step S2: Select an air hole in any symmetrical region as the starting point for optimization;

[0045] Step S3: Fill the selected air holes and the corresponding air holes in other symmetrical regions with silicon material, and calculate the objective function value;

[0046] Step S4: Set the shape of the selected air hole and the corresponding air holes in the other symmetrical areas to be waist-shaped holes, and symmetrically change their rotation angle with the center of the waist-shaped hole as the origin until they rotate 180° back to the original position. Calculate the objective function value once for each change in rotation angle.

[0047] Step S5: Set the shape of the selected air hole and the corresponding air holes in other symmetrical areas to circular holes, and synchronously change the diameter of the circular holes. Calculate the objective function value once each time the size is changed.

[0048] Step S6: Compare the objective function values ​​calculated for all state parameters of the selected air vents, select the optimal value, and retain the corresponding dimensional parameters of the optimal value in all symmetric regions;

[0049] Step S7: Select the next air hole and repeat steps S3 to S6. One iteration is defined as traversing all air holes in the symmetric region. After multiple iterations, compare the objective function value after the previous iteration. If the change in the objective function value between the two iterations is less than 0.1%, the objective function converges, the algorithm stops, and the hole array of the symmetric region is determined.

[0050] Each time an air hole is selected, its filling state, shape, size, and rotation angle are changed. The air holes in other symmetrical areas corresponding to the selected air holes are treated symmetrically. The device parameters are designed based on the principle of symmetry, which is convenient and can significantly reduce the time cost of computation. The device is small in size and has good performance. It can realize the cross function of two different modes of transmission in any channel, further increasing the transmission capacity of the optical interconnect system.

[0051] More specifically, the waist-shaped hole changes its rotation angle in 10° increments until it rotates 180° back to its original position, and the diameter of the circular hole is between 90nm and 120nm, changing its diameter in 10nm increments.

[0052] A multi-dimensional direct binary algorithm optimizes the parameters of the air holes in the initial structure in multiple dimensions, including state, shape, size, and rotation angle. The state refers to the filling state, i.e., silicon or air; the shape refers to circular or oblong holes; the size refers to the diameter of the circular air hole; and the rotation angle refers to the rotation angle of the oblong hole around its center. An oblong hole consists of two semicircles and a rectangle, each semicircle with a diameter d1 of 90 nm, and the rectangle is 30 nm × 90 nm in size. The oblong hole can rotate 180°. The diameter of the circular air hole varies from 90 nm to 120 nm. The rotation angle step size and diameter step size can be flexibly set to balance time cost and device performance. Here, the rotation angle step size is set to 10°, and the diameter step size is set to 10 nm. These step sizes can be increased or decreased according to design requirements.

[0053] Since the twelve symmetrical regions divided in optimization region 3 are symmetrical, the multi-dimensional direct binary algorithm only optimizes the air hole distribution in one symmetrical region. The air hole distribution in the symmetrical region is obtained through the symmetry of optimization region 3. This satisfies the device crossover function and saves a lot of optimization time.

[0054] More specifically, the objective function value is the sum of the transmittance of the two different modes in channel 4; the objective function reflecting device performance is set in the multi-dimensional direct binary algorithm:

[0055]

[0056] In the formula, Transmittance of TE0 mode in the 1540nm to 1560nm band; Transmittance of TE1 mode in the 1540nm to 1560nm band.

[0057] More specifically, the optimized initial structure is that the air holes on channel 4 are all filled with silicon, and the other air holes in the optimization region 3 are all filled with air. Light propagates in the silicon waveguide, and the refractive index distribution is adjusted through the air holes, thereby constraining and changing the behavior of the light. Therefore, the area through which the light passes can be filled with silicon, while the other parts are filled with air holes to optimize the preset initial structure.

[0058] Before optimizing with a multi-dimensional direct binary algorithm, an initial optimization structure needs to be provided. A reasonable initial optimization structure makes it easier to converge to excellent performance. For example... Figure 3 (a) shows the arrangement of the air holes, where the upper row of air holes is placed in the gaps between the lower row of air holes. This arrangement is beneficial for symmetrical structures and allows for a denser arrangement of air holes while maintaining manufacturability. The center-to-center distance d between each air hole is 150 nm. Optimization region 3 is divided into twelve symmetrical regions, as shown below. Figure 3 As shown in (b). Then, this arrangement of air holes is filled into one of the symmetrical regions, as follows. Figure 3 As shown in (c), the air hole distribution in other symmetrical regions can be obtained using symmetry. For example... Figure 4 The image shows the optimized initial structure.

[0059] After algorithm optimization, the device exhibits better performance. Figure 7 (a) is the transmission spectrum of the insertion loss (IL) of the device of the present invention. In the bandwidth range of 1540nm to 1560nm, the insertion loss of TE0 mode and TE1 mode is less than 0.45dB and 0.56dB, respectively. Figure 7 (b) is the crosstalk (CT) transmitted light spectrum of the device of the present invention. In the bandwidth range of 1540nm to 1560nm, the crosstalk of TE0 and TE1 modes is less than -62dB.

[0060] The specific working principle is as follows: Due to the use of multi-symmetry optimization in the design process, this invention can achieve the same function in each transmission waveguide, that is, TE0 and TE1 modes can propagate efficiently in any of the three transmission waveguides. Compared with optical cross waveguides designed by other methods, it has advantages such as better performance, smaller size, dual modes, and multiple channels.

[0061] Compared with existing technologies, this invention not only innovates the direct binary search algorithm and further expands the search freedom of the direct binary search algorithm, but also designs a cross waveguide with dual modes and multiple channels using an innovative multi-dimensional direct binary search algorithm, which can further increase the transmission capacity of optical interconnect systems.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-mode multi-channel cross waveguide, characterized by: The application relates to a substrate provided with a top layer of silicon, the top layer of silicon comprising an optimized region in the shape of a regular 2N-polygon and N intersecting channels, N>=3, the center line of the channels being arranged along the perpendicular bisector of the edges of the regular 2N-polygon, the optimized region being divided into 4N symmetrical regions along the symmetry axes of the regular 2N-polygon, and air holes being arranged in the symmetrical regions, a non-periodic air hole array satisfying a predetermined output target being formed by adjusting the state of the air holes in the symmetrical regions, the output target being that each channel supports two different modes of light transmission. The state of the air holes is filled with silicon or air. The air holes are circular holes and waist-shaped holes. The thickness of the substrate is 3 microns, the thickness of the top layer of silicon is 220 nm, the optimized region is a regular hexagon, the width of the channels is 900 nm, the distance between two parallel edges of the optimized region is 5640 nm, the line connecting the centers of any three air holes is a regular triangle, the side length of the regular triangle is 150 nm, the diameter of the circular arc of the waist-shaped hole is 90 nm, the straight line length of the waist-shaped hole is 30 nm, and the diameter of the circular hole is 90-120 nm. The waist-shaped hole arranged on the symmetry axis of the optimized region has a symmetry axis coinciding with the symmetry axis of the optimized region. The two different modes are a TE0 mode from 1540 nm to 1560 nm and a TE1 mode from 1540 nm to 1560 nm.

2. The method of fabricating a dual-mode multi-channel cross waveguide of claim 1, wherein, The application further relates to a method for designing the optimized region, the method comprising the following steps: S1, setting an optimized initial structure and setting a target function reflecting the performance of the reflector in a multi-dimensional direct binary algorithm; S2, selecting an air hole in any symmetrical region as a starting point for optimization; S3, filling the selected air hole and the corresponding air holes in other symmetrical regions with silicon material and calculating the target function value; S4, setting the shape of the selected air hole and the corresponding air holes in other symmetrical regions into a waist-shaped hole, symmetrically changing the rotation angle of the waist-shaped hole with the center of the waist-shaped hole as the origin until the rotation angle is changed by 180 degrees to return to the original position, and calculating the target function value each time the rotation angle is changed; S5, setting the shape of the selected air hole and the corresponding air holes in other symmetrical regions into a circular hole and synchronously changing the diameter of the circular hole, and calculating the target function value each time the diameter is changed; S6, comparing the target function values calculated by all state parameters of the selected air hole, selecting the optimal value, and retaining the dimensional parameters corresponding to the optimal value in all symmetrical regions; S7, selecting the next air hole and repeating steps S3-S6, one iteration being that all air holes in the symmetrical region are traversed once, and the algorithm being stopped after multiple iterations, the target function value after the last iteration being compared, the change value of the two target function values being lower than 0.1%, the target function converging, and the algorithm being stopped to determine the air hole array of the symmetrical region.

3. The dual mode multi-channel crossed waveguide of claim 2, wherein: The rotation angle of the waist-shaped hole is changed by 10 degrees, and the diameter of the circular hole is changed by 10 nm between 90 nm and 120 nm.

4. The dual mode multi-channel crossed waveguide of claim 3, wherein: The target function value is the sum of the transmittances of the two different modes in the channel.

5. The dual mode multi-channel crossed waveguide of claim 2, wherein: The optimized initial structure is that all the air holes on the channel are filled with silicon, and other air holes in the optimization region are filled with air.

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