CN114966969A - Parallel multimode cross structure based on asymmetric directional coupler - Google Patents
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Abstract
The invention relates to a parallel multimode crossing structure based on an Asymmetric Directional Coupler (ADC), which is characterized in that a first multimode waveguide, a second multimode waveguide, a third multimode waveguide, a first single-mode waveguide queue positioned between the first multimode waveguide and the second multimode waveguide and a second single-mode waveguide queue positioned between the second multimode waveguide and the third multimode waveguide are arranged, the multimode waveguide is formed by connecting n-1 straight waveguide sections and a tapered waveguide section end to end, the single-mode waveguide queue comprises n sub single-mode waveguides, each sub single-mode waveguide is formed by sequentially connecting a first waveguide section, a 180-degree bent waveguide section and a second waveguide section end to end, the straight waveguide section in the multimode waveguide and the first waveguide section and the second waveguide section in the single-mode waveguide respectively form an ADC, and the waveguide crossing structure can realize multimode crossing with high integration level, low loss and low crosstalk, and more mode crossing extensions can be easily performed.
Description
Technical Field
The invention relates to the field of optical communication, in particular to a parallel multimode cross structure based on an asymmetric directional coupler.
Background
The development of modern photon technology has higher and higher requirements on the integration of devices, the density, the functions, the performance and the like of devices on a chip, so that the crossing times of optical waveguides on a single chip are greatly increased. In recent years, Mode Division Multiplexing (MDM) technology on silicon-on-insulator (SOI) platforms has provided a more promising and attractive approach to further improve the transmission spectral efficiency and capacity of on-chip optical interconnects. Meanwhile, an SOI (silicon On isolator) material has good light guiding property as a hotspot material of optical integration research, but the spatial divergence angle of a guided mode of the SOI is large due to large core-cladding refractive index difference of the SOI, so that light can generate remarkable scattering at the crossed part of the waveguide. A single direct crossover of the SOI optical waveguide will result in severe crosstalk and multimode excitation, and the loss and crosstalk generated by a large number of crossovers will be unacceptable for a single chip.
For an optical waveguide cross-over cell, the scattered power is proportional to the refractive index difference of the waveguide material. In materials with high refractive index differences, the problems of loss and crosstalk due to optical waveguide crossings are particularly acute. Waveguide crossing as an important component of densely integrated MDM optical networks, multimode waveguide crossing reported in recent years is mainly based on different schemes: MMI coupler, two-dimensional nano structure, Maxwell fish eye lens. However, these structures have problems in that it is difficult to satisfy the intersection of a plurality of modes or processes, manufacturing difficulty is large, and the like.
Disclosure of Invention
The invention aims at providing a parallel multimode cross structure based on an asymmetric directional coupler, which at least comprises the following scheme.
A parallel multi-mode cross structure based on an asymmetric directional coupler comprises a first multi-mode waveguide, a second multi-mode waveguide which is a straight waveguide, a third multi-mode waveguide, a first single-mode waveguide queue positioned between the first multi-mode waveguide and the second multi-mode waveguide, and a second single-mode waveguide queue positioned between the second multi-mode waveguide and the third multi-mode waveguide;
the first multimode waveguide is formed by sequentially connecting a 1 st straight waveguide section and a 1 st conical waveguide section, a 2 nd straight waveguide section and a 2 nd conical waveguide section … …, a t-1 th straight waveguide section and a t-1 th conical waveguide section end to end, wherein t is more than or equal to 2;
the third multimode waveguide is formed by sequentially connecting a 1 st conical waveguide section and a 1 st straight waveguide section, a 2 nd conical waveguide section and a 2 nd straight waveguide section … …, and a t-1 th conical waveguide section and a t-1 th straight waveguide section end to end;
the first single-mode waveguide queue comprises a 1 st sub single-mode waveguide, a 2 nd sub single-mode waveguide … … and a tth sub single-mode waveguide; the 1 st sub single mode waveguide to the t-1 st sub single mode waveguide are formed by sequentially connecting a first waveguide section, a 180-degree bent waveguide section and a second waveguide section end to end; the tth sub single-mode waveguide is formed by sequentially connecting a 180-degree bent waveguide section and a second waveguide section end to end;
the second single-mode waveguide queue comprises a 1 st sub single-mode waveguide, a 2 nd sub single-mode waveguide … … and a tth sub single-mode waveguide; the 1 st sub single-mode waveguide is formed by sequentially connecting a second waveguide section and a 180-degree bent waveguide section end to end, and the 2 nd sub single-mode waveguide to the t th sub single-mode waveguide are formed by sequentially connecting a second waveguide section, a 180-degree bent waveguide section and a first waveguide section end to end; the 180 DEG curved waveguide segment of the 1 st sub-single mode waveguide is connected to the 1 st tapered waveguide segment of the third multimode waveguide;
the straight waveguide of the multi-mode waveguide and the first waveguide section and the second waveguide section of the sub single-mode waveguide respectively form an ADC;
the optical signal with t modes is transmitted into a first multimode waveguide, is converted into a fundamental mode through ADC demultiplexing, the fundamental mode is transmitted to a second multimode waveguide through a first single-mode waveguide queue, is simultaneously converted into a reverse transmission optical signal of a t +1 mode in the second multimode waveguide through ADC multiplexing, the optical signal of the t +1 mode is converted into the fundamental mode through ADC demultiplexing, the fundamental mode is transmitted to a third multimode waveguide through a second single-mode waveguide queue, and is simultaneously converted into optical signals of t modes in the third multimode waveguide through ADC multiplexing.
The width of the multimode waveguide supports transmission of at least the first t +1 TEi modes, where i ═ 0,1, … …, t.
The first waveguide section and the second waveguide section are respectively formed by connecting n right-angle trapezoidal waveguide sections, the right-angle side of the right-angle trapezoidal waveguide is close to and parallel to the straight waveguide in the ADC, and n is more than or equal to 2; and the parameters of the right-angle trapezoidal waveguide section are obtained by optimization of a particle swarm algorithm.
The ADCs are used for both multiplexing and demultiplexing.
And the mode conversion among the second straight waveguide section in the first single-mode waveguide queue, the second multimode waveguide and the second straight waveguide section in the second single-mode waveguide queue adopts a three-waveguide directional coupler structure.
The first multi-mode waveguide and the first array of single-mode waveguides and the third multi-mode waveguide and the second array of single-mode waveguides are axisymmetric about the second multi-mode waveguide.
In the first single-mode waveguide queue, a first S-type waveguide segment and a third straight waveguide segment are further arranged between a first straight waveguide segment from the 1 st sub single-mode waveguide to the t-1 st sub single-mode waveguide and the 180-degree curved waveguide segment, and a second S-type waveguide segment is further arranged between the 180-degree curved waveguide segment and the second straight waveguide segment.
And a first S-type waveguide section is also arranged between the t-1 conical waveguide section of the first multimode waveguide and the t-sub single mode waveguide.
In the second single-mode waveguide queue, a second S-type waveguide segment is further disposed between a second straight waveguide segment from the 2 nd sub single-mode waveguide to the t-th sub single-mode waveguide and the 180-degree curved waveguide segment, and a third straight waveguide segment and a first S-type waveguide segment are further disposed between the 180-degree curved waveguide segment and the first straight waveguide segment.
And a first S-shaped waveguide section is also arranged between the 1 st sub single-mode waveguide in the second single-mode waveguide queue and the 1 st tapered waveguide section of the third multi-mode waveguide.
Compared with the prior art, the invention has at least the following beneficial effects:
the multimode cross structure provided by the invention aims at the requirement of high integration level of modern photon technology, avoids the generation of larger transmission loss and crosstalk caused by the crossing of a large number of single-mode optical waveguides, and adopts the tapered ADC cascade to construct the multimode cross unit, so that the cross functions of low loss and low crosstalk are simultaneously realized on one cross structure by a plurality of transverse propagation modes, and the device structure is very compact. The invention realizes the high-efficiency crossing of a plurality of transverse modes and solves the problem that the traditional waveguide crossing scheme can not realize the crossing of the transverse mode and the longitudinal mode at the same time.
Drawings
Fig. 1 is a schematic view of a multimode crossover structure according to an embodiment of the invention.
Fig. 2 is a schematic diagram of an ADC structure obtained by particle swarm optimization according to an embodiment of the present invention.
FIG. 3 is an optical microscope photograph of a multimode cross-over structure in accordance with an embodiment of the invention.
FIG. 4 is a diagram of the transverse fundamental mode, first order, second order and third order optical field distribution of the multimode cross-over structure according to an embodiment of the invention.
FIG. 5 is a diagram of a four-mode cross-simulated light field distribution of a multimode cross-structure according to an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by persons of ordinary skill in the art without any creative effort belong to the protection scope of the present invention.
Spatially relative terms, such as "below," "lower," "above," "over," "upper," and the like, may be used in this specification to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures.
In addition, terms such as "first", "second", and the like, are used to describe various elements, layers, regions, sections, and the like and are not intended to be limiting. The use of "having," "containing," "including," "comprising," and the like, are open-ended terms that specify the presence of stated elements or features, but do not exclude additional elements or features. Unless the context clearly dictates otherwise.
Asymmetric directional couplers are generally classified into conventional ADCs and tapered ADCs. Both waveguides of the conventional ADC are rectangular, while the tapered ADC has a linear variation of W compared to the width W of the rectangular waveguide in the conventional ADC, i.e. the inner side of the input tapered waveguide is parallel to the wide waveguide, i.e. the gap between the two waveguides of the tapered ADC is constant, and only the outer side of the tapered waveguide is inclined by a similar linearity. In the structure, the outer side of the tapered waveguide is subjected to simulation value taking by a particle swarm algorithm, so that the optimal width value is obtained. Then the S-shaped curved waveguide, the taper and the 180-degree curved waveguide are connected and assembled to form the multimode cross structure. The structure is not only suitable for transmission of more transverse modes, but also suitable for cross transmission of longitudinal modes. Because of the maturity of multiplexing (demultiplexing) mux (demux) devices today, we can easily extend to more lateral modes. Even thanks to the maturity of Polarizing Beam Splitters (PBS), our crossover can be easily extended to more polarization states.
Optionally, an S-waveguide segment (i.e., S-bend waveguide) in the optical crossbar structure is present in each ADC, which serves to pull the two coupled waveguides apart. The tapered structure of the optical waveguide is used for cascade connection of the ADCs, and can be divided into a forward tapered (taper) structure and an inverted tapered (reverse taper) structure according to different orders of the light inlet and outlet ports. In the inverted cone structure, light is input from a port with a larger width and output from a port with a smaller width, and the width of the optical waveguide is gradually reduced in the light transmission direction; in contrast, in the forward tapered structure, light is input from a port with a small width and output from a port with a large width, and the optical waveguide width gradually increases in the light transmission direction. And the 180-degree bent waveguide is used for realizing crossed connection of a bus waveguide (namely a multi-mode waveguide) through mode conversion of a basic mode → an N +1 mode → the basic mode, so that an optical crossed structure tends to be complete.
An embodiment of the present invention provides an ADC-based multimode parallel multimode intersection structure, which includes a first multimode waveguide 10, a second multimode waveguide 20, a third multimode waveguide 30, a first single-mode waveguide queue 45 and a second single-mode waveguide queue 50, where the first single-mode waveguide queue 40 is disposed between the first multimode waveguide 10 and the second multimode waveguide 20, and the second single-mode waveguide queue 50 is disposed between the second multimode waveguide 20 and the third multimode waveguide 30.
In this embodiment, the cross structure selects four transverse electric polarization modes, and the first multimode waveguide 10 is formed by sequentially connecting the 1 st straight waveguide segment, the 1 st tapered waveguide segment, the 2 nd straight waveguide segment, the 2 nd tapered waveguide segment, the 3 rd straight waveguide segment, and the 3 rd tapered waveguide segment end to end. The first single-mode waveguide array 40 includes a 1 st sub single-mode waveguide, a 2 nd sub single-mode waveguide, a 3 rd sub single-mode waveguide, and a 4 th sub single-mode waveguide arranged in sequence from left to right.
In this embodiment, the 1 st sub-single mode waveguide is formed by sequentially connecting a first waveguide segment, a first S-shaped waveguide segment, a first straight waveguide segment, a 180 ° curved waveguide segment, a second S-shaped waveguide segment, and a second waveguide segment end to end. The 2 nd sub-single mode waveguide is formed by sequentially connecting a first waveguide section, a first S-shaped waveguide section, a first straight waveguide section, a 180-degree bent waveguide section, a second S-shaped waveguide section and a second waveguide section end to end. The 3 rd sub single mode waveguide is formed by sequentially connecting a first waveguide section, a first S-shaped waveguide section, a 180-degree bent waveguide section, a second S-shaped waveguide section and a second waveguide section end to end. The 4 th sub-single mode waveguide is formed by sequentially connecting a first S-shaped waveguide section, a 180-degree bent waveguide section and a second waveguide section end to end.
The second multimode waveguide is a straight waveguide. The third multimode waveguide is formed by connecting the 1 st conical waveguide section, the 1 st straight waveguide section, the 2 nd conical waveguide section, the 2 nd straight waveguide section, the 3 rd conical waveguide section and the 3 rd straight waveguide section end to end.
The second single-mode waveguide queue 50 includes a 1 st sub single-mode waveguide, a 2 nd sub single-mode waveguide, a 3 rd sub single-mode waveguide, and a 4 th sub single-mode waveguide, which are sequentially arranged from left to right. The 1 st sub single mode waveguide is formed by connecting a second waveguide section, a 180-degree bent waveguide section and a first S-shaped bent waveguide end to end, and the 2 nd sub single mode waveguide is formed by sequentially connecting the second waveguide section, the second S-shaped bent waveguide section, the 180-degree bent waveguide section, the first S-shaped bent waveguide section and the first waveguide section end to end. The 3 rd sub single mode waveguide is formed by sequentially connecting a second waveguide section, a second S-shaped bent waveguide section, a 180-degree bent waveguide section, a first straight waveguide section, a first S-shaped bent waveguide section and a first waveguide section end to end. The 4 th sub-single mode waveguide is formed by sequentially connecting a second straight waveguide section, a second S-shaped bent waveguide section, a 180-degree bent waveguide section, a first straight waveguide section, a first S-shaped bent waveguide section and a first waveguide section end to end. In this embodiment, the first and second single- mode waveguide arrays 40 and 50 are axisymmetric about the second multimode waveguide 20. In other embodiments, an S-bend waveguide may be selectively disposed between the straight waveguide segment and the 180 ° bend waveguide segment, and a straight waveguide may be selectively disposed between the S-bend waveguide segment and the 180 ° bend waveguide segment. The S-bend waveguide is used to pull the two coupled waveguides apart.
The straight waveguide section of the first multimode waveguide and the first waveguide section and the second waveguide section of the sub-single mode waveguide in the first single mode waveguide queue respectively form an ADC, and are used for fundamental mode multiplexing and multimode demultiplexing. In a preferred embodiment, the first waveguide section and the second waveguide section are respectively formed by connecting n waveguide sections of a right trapezoid (one of cones), the right-angle side of the right trapezoid waveguide is close to and parallel to the straight waveguide in the ADC, wherein n is greater than or equal to 2. The mode conversion efficiency can be improved, the bandwidth can be increased, and the process tolerance can be improved by adopting the tapered design of the right-angled trapezoidal waveguide. In other embodiments, the first waveguide and the second waveguide may also be straight waveguide segments. The width of the multimode waveguide supports transmission of at least the first t +1 TEi or TMi modes, where i ═ 0,1, … …, t. And the parameters of the ADC are obtained by optimization of a particle swarm algorithm. One multimode waveguide is converted into a fundamental mode through the ADC and crosses the other multimode waveguide to realize crossing, and the crossing part of the fundamental mode and the multimode waveguide realizes the crossing function by the fundamental mode → N +1 mode (N mode crossing structure) → fundamental mode. In another embodiment, the first and third arrays of multi-mode waveguides and the second array of single-mode waveguides are axisymmetric about the second multi-mode waveguide.
In this embodiment, silicon is used as the waveguide layer, the waveguide layer is wrapped by silicon dioxide, the thickness of the silicon used as the waveguide layer is 220nm, the refractive index of silicon is 3.42, and the refractive index of silicon dioxide is 1.46. The number of transmission modes supported in a silicon waveguide is positively correlated to the width of the silicon waveguide, and thus for a multi-mode waveguide, the width should be chosen to be sufficient to support all of the modes required. By using a common full vector finite difference method (FVFD) or Finite Element Method (FEM), the modes of the three-dimensional rectangular waveguide can be numerically calculated to obtain the effective refractive indices of all modes and the spatial distribution of the optical fields (electric and magnetic fields) in the silicon waveguide of a specific thickness and width. For example, in this embodiment, it is necessary to design a waveguide crossing device with 4 modes in Transverse Electric (TE) polarization, and according to the design principle of the present invention, it is necessary to use the fifth mode for mode switching during crossing, so the width of the bus multimode waveguide needs to support at least the first 5 TEs i The mode (i ═ 0,1,2,3,4), so the width can be set to be more than 1.8-1.9 microns to ensure the transmission of 5 TE modes, and the transmission loss of the high-order mode is smaller as the width is larger. Meanwhile, the smaller the waveguide width is, the weaker the waveguide is in the optical field constraint of each mode, and the easier the waveguides serving as two arms of the ADC are to be subjected to mode coupling, so that the coupling efficiency is improved, the coupling length is reduced, the length of the whole ADC device is shortened, and the integration level is improved. Therefore, the width of the multimode waveguide as one arm of the ADC should be reduced as much as possible, so that the ADC for conversion between TE0 and TE4 in this embodiment 4 The width of the multimode waveguide in (2) may preferably be 1.9 um. Similarly, the multi-mode waveguide widths in ADCi (i ═ 1,2,3) for transitions from TE0 to TE1, TE2, and TE3 are preferably 0.75um, 1.15um, and 1.55um, respectively, to ensure that the corresponding modes propagate with low loss and to minimize the coupling length of the ADC. The smaller the gap between the two waveguides in the ADC is, the better the coupling efficiency is improved, and the length is reduced, but the process precision limit is usually not less than 0.1um, so the process precision limit is usually set to be between 0.1um and 0.2 um. ADC in this embodiment 1-4 The gaps of the two waveguides in (1) are respectively 0.15um, 0.15um and 0.1 um. The other arm of the ADC adopts an irregular single-mode waveguide formed by n (in the example, n is 9) sections of right-angle trapezoidal waveguides to replace the conventional single-mode straight waveguide, so that the effects of improving the coupling efficiency, increasing the tolerance, improving the bandwidth and the like are achieved. The n sections of tapered waveguides are all formed by right-angled trapezoids, the right-angled edges of the n sections of tapered waveguides are all the edges close to the multimode waveguide,see fig. 2. After the multi-mode waveguide width and the waveguide gap in the ADC are determined, the structural parameters of the single-mode waveguide can be calculated using a conventional optimization algorithm, which is a Particle Swarm Optimization (PSO) method used in the present invention. The particle swarm optimization is adopted to optimize the ADC structure, and the main purpose is to solve the following two technical problems. For one, tapered ADCs optimized by particle swarm have better coupling efficiency, bandwidth, and greater manufacturing tolerances than conventional ADCs. Compared with the traditional ADC, the tapered ADC optimized by the particle swarm has shorter coupling length, and the occupied area of a cross structure can be greatly reduced in the cascading process. Specifically, it is required to obtain the end width W of the n-segment tapered waveguide by the PSO method i0-n . As an initial condition for the optimization algorithm, set W i0 0.35um, and then sets the boundary condition of the algorithm, i.e. defines the width W i1-n The variation range of (2) is 0.2-0.6 um. The n sections of tapered waveguides are set to be equal in length, and the total length change range is 7-10 um. Then, the target evaluation function FOM of the algorithm is set to be the slave TE 0 To a to-be-switched mode TE i The larger the FOM is, the higher the mode conversion efficiency of the ADC device is, and the better the performance is. After initial and boundary conditions are set, the FOM value can be gradually increased through iterative calculation of a PSO algorithm. The number of iterations or FOM values can typically be set to end the algorithm. In the embodiment, the optimization algorithm is terminated when the iteration times reach 400 times, and at the moment, the FOM can be as high as 98-99% generally, so that the very high mode conversion efficiency can be achieved. The dimensional parameters of the four ADCs are shown in table 1 below.
TABLE 1
The length and height of the S-shaped curved waveguide are 5um and 1um respectively; the tapered waveguide is connected with the straight waveguide in each ADC, and the length of the tapered waveguide is not less than 3 um; the radius of the 180 DEG curved waveguide is not less than 3.5 um. The total occupied area of the four-mode waveguide intersection is 25um multiplied by 25um 2 . The two bus waveguides of the structure have different cross paths, and one bus waveguide passes throughThe through fundamental mode → N +1 mode → fundamental mode conversion realizes the intersection, and the other bus waveguide outputs directly.
According to the above design structure, three-dimensional simulation is performed using FDTD Solutions to obtain accurate transmission results of the structure. As shown in fig. 4 (a) to (d), the guided mode electric field distributions of TE0, TE1, TE2, and TE3 in the transverse electric polarization mode are shown. As shown in fig. 5, the simulated light field distribution of each mode is shown. Then, the transmitted light spectrogram of the above 4 cases is obtained by simulation and experimental verification. Only a data plot of the insertion loss for each mode is provided herein.
The simulation result shows that the insertion loss of all modes of the cross device in the whole wave band range (1530-1580nm) is lower than 1.2dB, and the crosstalk is smaller than-20 dB. At the wavelength of 1550nm, the transmission efficiency of all modes reaches more than 90%. Experimental results also demonstrate that cross-devices have less than-20 dB crosstalk and possess unusual insertion loss.
The above example is only the result of the intersection of four transverse electric polarization modes, and the number of modes, transverse magnetic polarization modes, can be further increased to continue to improve the device based on the above analysis. By the design, multi-mode crossing with high integration level, low loss and low crosstalk can be realized, and more modes can be easily expanded.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A parallel multimode cross structure based on an asymmetric directional coupler is characterized by comprising a first multimode waveguide, a second multimode waveguide which is a straight waveguide, a third multimode waveguide, a first single-mode waveguide queue positioned between the first multimode waveguide and the second multimode waveguide and a second single-mode waveguide queue positioned between the second multimode waveguide and the third multimode waveguide;
the first multimode waveguide is formed by sequentially connecting a 1 st straight waveguide section and a 1 st conical waveguide section, a 2 nd straight waveguide section and a 2 nd conical waveguide section … …, a t-1 th straight waveguide section and a t-1 th conical waveguide section end to end, wherein t is more than or equal to 2;
the third multimode waveguide is formed by sequentially connecting a 1 st conical waveguide section and a 1 st straight waveguide section, a 2 nd conical waveguide section and a 2 nd straight waveguide section … …, and a t-1 th conical waveguide section and a t-1 th straight waveguide section end to end;
the first single-mode waveguide queue comprises a 1 st sub single-mode waveguide, a 2 nd sub single-mode waveguide … … and a t th sub single-mode waveguide; the 1 st sub single mode waveguide to the t-1 st sub single mode waveguide are formed by sequentially connecting a first waveguide section, a 180-degree bent waveguide section and a second waveguide section end to end; the tth sub single-mode waveguide is formed by sequentially connecting a 180-degree bent waveguide section and a second waveguide section end to end;
the second single-mode waveguide queue comprises a 1 st sub single-mode waveguide, a 2 nd sub single-mode waveguide … … and a t th sub single-mode waveguide; the 1 st sub single-mode waveguide is formed by sequentially connecting a second waveguide section and a 180-degree bent waveguide section end to end, and the 2 nd sub single-mode waveguide to the t th sub single-mode waveguide are formed by sequentially connecting a second waveguide section, a 180-degree bent waveguide section and a first waveguide section end to end; the 180 DEG curved waveguide segment of the 1 st sub-single mode waveguide is connected to the 1 st tapered waveguide segment of the third multimode waveguide;
the straight waveguide of the multi-mode waveguide and the first waveguide section and the second waveguide section of the sub single-mode waveguide respectively form an ADC;
the optical signal with t modes is transmitted into a first multimode waveguide, is converted into a fundamental mode through ADC demultiplexing, the fundamental mode is transmitted to a second multimode waveguide through a first single-mode waveguide queue, is simultaneously converted into a reverse transmission optical signal of a t +1 mode in the second multimode waveguide through ADC multiplexing, the optical signal of the t +1 mode is converted into the fundamental mode through ADC demultiplexing, the fundamental mode is transmitted to a third multimode waveguide through a second single-mode waveguide queue, and is simultaneously converted into optical signals of t modes in the third multimode waveguide through ADC multiplexing.
2. The crossbar structure of claim 1 wherein the width of the multimode waveguide supports transmission of at least the first t +1 TEi or TMi modes, where i ═ 0,1, … …, t.
3. The cross-over structure of claim 2, wherein the first waveguide segment and the second waveguide segment are respectively formed by connecting n right-angle trapezoidal waveguide segments, the right-angle sides of the right-angle trapezoidal waveguides are close to and parallel to the straight waveguides in the ADC, and n is greater than or equal to 2.
4. The crossbar structure of any one of claims 1 to 3 wherein the ADCs are used for both multiplexing and demultiplexing.
5. The crossbar structure of claim 4 wherein the mode transition between the second straight waveguide segment in the first alignment of single-mode waveguides, the second multi-mode waveguide, and the second straight waveguide segment in the second alignment of single-mode waveguides is a three-waveguide directional coupler structure.
6. The crossover structure according to any one of claims 1 to 3, wherein the first multimode waveguide and the first alignment of single-mode waveguides are axisymmetric to the third multimode waveguide and the second alignment of single-mode waveguides with respect to the second multimode waveguide.
7. The crossover structure according to any one of claims 1 to 3, wherein in the first alignment of single-mode waveguides, a first S-type waveguide segment and a third straight waveguide segment are further disposed between the first straight waveguide segment and the 180 ° curved waveguide segment of the 1 st sub-single-mode waveguide to the t-1 st sub-single-mode waveguide, and a second S-type waveguide segment is further disposed between the 180 ° curved waveguide segment and the second straight waveguide segment.
8. The crossover structure according to any one of claims 1 to 3, wherein a first S-type waveguide segment is further disposed between the t-1 st tapered waveguide segment and the t-th sub-single mode waveguide of the first multimode waveguide.
9. The crossbar structure according to any one of claims 1 to 3, wherein in the second alignment of single-mode waveguides, a second S-type waveguide segment is further disposed between the second straight waveguide segment and the 180 ° curved waveguide segment of the 2 nd sub-single-mode waveguide to the t-sub-single-mode waveguide, and a third straight waveguide segment and a first S-type waveguide segment are further disposed between the 180 ° curved waveguide segment and the first straight waveguide segment.
10. The crossbar structure according to any one of claims 1 to 3 wherein a first S-type waveguide segment is further disposed between the 1 st sub-single mode waveguide in the second queue of single mode waveguides and the 1 st tapered waveguide segment of the third multimode waveguide.
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