A cladding-free multi-channel topological photonic waveguide and photon beam splitting method thereof

Abstract

The present invention discloses a multi-channel topological photon waveguide without a cladding layer and a photon splitting method thereof. The waveguide of the present invention is composed of at least two gyromagnetic blocks with different topological properties; there is no need to piece together adjacent gyromagnetic blocks into a heterogeneous photon structure, and a topological surface state is formed between the gyromagnetic blocks and the air. The present invention can get rid of the dependence on the topological domain wall structure, that is, to realize topological photon routing without a cladding layer structure at the interface in direct contact with the air. While realizing the topological splitting of the surface wave, the surface wave transmitted at the interface between the gyromagnetic medium and the air is locked with its own polarization state. By placing the waveguide under the air, the gyromagnetic blocks are in direct contact with the air; adjusting the magnetic field direction of the gyromagnetic blocks and the relative arrangement position of the gyromagnetic blocks in the air, topological photon splitting with different surface waves output can be realized, and a multi-channel topological waveguide device with reconfigurable output ports and controllable port numbers can be realized.

Description

Technical Field

[0001] The present invention relates to a photonic topological multi-channel device, in particular to a cladding-free multi-channel topological photonic waveguide and a photon beam splitting method thereof. Background Art

[0002] In recent years, topological photonics has rapidly developed into a vibrant and highly sought-after research field. The concept of "nontrivial topological phases" in photonics, originating from the study of condensed matter systems, offers a novel solution for high-precision and robust manipulation of electromagnetic wave propagation. With its operational ease and direct connection to quantum states, topological photonics opens up new possibilities for fundamental scientific research and practical applications, providing a highly promising platform for the design and implementation of novel topological devices.

[0003] One of the most striking features of topological photonic systems is the existence of unidirectional topological surface states at their boundaries. This is a direct consequence of the bulk-edge correspondence principle. These unidirectional surface states are robust, allowing them to persist stably in structures with structural defects and effectively suppress backscattering, even in disordered or defect-ridden environments. To date, researchers have designed and realized various topological devices using photonic crystal platforms, including topological photonic waveguides, topological beam splitters, topological directional couplers, and topological photonic switches.

[0004] Nevertheless, because photonic crystals usually rely on strict periodic conditions and complex unit cell structures, the realization of topological devices based on the photonic crystal platform lacks flexible adjustability. The existing gyromagnetic topological photonic crystal waveguide design relies on strict periodic conditions. The reason is that photonic crystals cannot be described using equivalent medium theory. Due to the limitations of such periodic structures, an additional cladding layer structure (heterogeneous photonic structure) is usually required in the photonic crystal system to place the mode on the surface of the photonic crystal above the light cone, thereby limiting the energy leakage to the air side. Otherwise, when the photonic crystal is in direct contact with the air, the energy on the surface of the photonic crystal will leak to the air side, and effective mode guidance will not be possible. In addition, the current research methods for topological waveguides based on gyromagnetic media are single, and most of them focus on single-channel topological waveguide systems, while there is little research on devices such as multi-channel topological photonic waveguides. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a cladding-free multi-channel topological photonic waveguide and a photon splitting method thereof, so as to provide a design of a multi-channel cladding-free topological photonic device.

[0006] Unlike photonic crystals that rely on strict periodic conditions and complex unit cell structures, the gyromagnetic medium in the present invention is a uniform and continuous bulk material, and its optical response and band structure are calculated and analyzed using equivalent electromagnetic parameters.

[0007] The present invention is implemented as follows: in a first aspect, the present invention provides a multi-channel topological photonic waveguide without a cladding layer, which is composed of at least two gyromagnetic blocks with different topological properties; the gyromagnetic blocks are in direct contact with the air; wherein, adjacent gyromagnetic blocks do not need to be assembled into a heterogeneous photonic structure, and topological surface states are formed between the gyromagnetic blocks and the air.

[0008] Preferably, adjacent gyromagnetic blocks have different topological properties.

[0009] Preferably, adjacent gyromagnetic blocks may be in direct contact or have an air gap therebetween.

[0010] Preferably, the gyromagnetic block is made of a gyromagnetic medium material with continuous optical response characteristics, and its optical behavior can be described by equivalent electromagnetic parameters; when the direction of the external magnetic field changes, the Berry curvature distribution of the gyromagnetic medium also presents different directional characteristics.

[0011] Preferably, at least one structural defect is provided inside the gyromagnetic block, specifically for verifying the topological protection characteristics of surface waves during transmission. More preferably, the structural defect is square, triangular or elliptical.

[0012] Preferably, a point source for exciting topological surface waves is provided at a boundary position of one of the gyromagnetic blocks exposed to the air side.

[0013] The second aspect provides a multi-channel topological photon splitting method based on the above waveguide, specifically:

[0014] The waveguide is placed in an air environment so that the gyromagnetic block of the waveguide is in direct contact with the air;

[0015] By adjusting the magnetic field direction of the gyromagnetic blocks and the relative arrangement of the gyromagnetic blocks in the air, topological photon splitting with different surface wave outputs can be achieved.

[0016] Preferably, the different surface waves are excited by setting a point source at a boundary position of the gyromagnetic block.

[0017] Compared with existing topological devices that rely on strict periodic structure design, the present invention has the following advantages:

[0018] This multi-channel topological device eliminates the need for topological domain walls, enabling topological photon routing without a cladding layer at the interface with air. While achieving surface wave topological beam splitting, the surface waves propagating at the interface between the gyromagnetic medium and air are locked to their own polarization state. By varying the magnetic field direction of the gyromagnetic medium and the relative spatial position of the material blocks within the device, a multi-channel topological waveguide device with reconfigurable output ports and a controllable number of ports can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is one embodiment of a schematic diagram of a multi-channel topological photonic waveguide structure.

[0021] Figure 2 This is the second embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0022] Figure 3 This is the third embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0023] Figure 4 This is the fourth embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0024] Figure 5 This is the fifth embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0025] Figure 6 This is the sixth embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0026] Figure 7 This is the seventh embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0027] Figure 8 This is the eighth embodiment of the schematic diagram of the multi-channel topological photonic waveguide structure.

[0028] Figure 9 Middle (a)- Figure 9 (b) is the energy band diagram of a single gyromagnetic block under different electromagnetic parameters. Figure 9 (c)- Figure 9 (d) is the Berry curvature distribution diagram induced by the gyromagnetic parameter g with different sign directions.

[0029] Figure 10 (a) and Figure 10(c) is a schematic diagram of the cladding-free waveguide structure under different gyromagnetic sign directions of the present invention. Figure 10 (b) and Figure 10 (d) is the topological surface state distribution of the present invention under different magnetic field directions. Figure 10 (e) and Figure 10 Middle (f) is the high local electric field distribution of the topological surface state of the present invention.

[0030] Figure 11 (a) is a test of the robust transmission properties of the topological surface wave of the present invention and the traditional surface wave to defects. Figure 11 Middle (b)- Figure 11 (d) is a robustness test of the topological surface wave of the present invention against defects of different structural types. Figure 11 (e) is the surface wave located at Figure 10 The simulation results of the electric field intensity in mode A3 in (b) are as follows: Figure 11 (f) is the surface wave located at Figure 10 Simulation results of the electric field intensity in the B1 point mode in (d).

[0031] Figure 12 (a) is the transmission spectrum of surface wave topology protection transmission within the specific wave vector range of the present invention, Figure 12 Middle (b)- Figure 12 Middle (d) is the normalized electric field intensity distribution diagram before and after the defect under different wave vector conditions of the present invention.

[0032] Figure 13 The present invention realizes topological photon routing with six different surface wave ports by changing the magnetic field direction of the gyromagnetic medium in the multi-channel topological photon waveguide and the relative position of the gyromagnetic medium block in space.

[0033] Figure 14 The electric field intensity distribution at different port positions of the multi-channel topological photon beam splitter based on gyromagnetic media of the present invention is normalized. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0035] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 1 The first gyromagnetic block 101 and the second gyromagnetic block 102 are stacked on top of each other and are exposed to the air. The first gyromagnetic block 101 and the second gyromagnetic block 102 can be of equal size and are rectangular in shape.

[0036] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 2The third gyromagnetic block 201, the fourth gyromagnetic block 202, and the fifth gyromagnetic block 203 are formed and exposed to the air. The third gyromagnetic block 201 and the fourth gyromagnetic block 202 are rectangular blocks of equal size and are stacked up and down. Figure 1 The waveguide structure is the same as shown. Figure 1 A fifth gyromagnetic block 203 is added to the waveguide structure shown. The fifth gyromagnetic block 203 is an inverted T-shaped structure, consisting of an integrally formed sub-gyromagnetic block A2031 and a sub-gyromagnetic block B2032 stacked on top of each other. This type of T-shaped structure is a whole block material, which is essentially different from a photonic crystal that relies on a strict and complex unit cell structure. The length of the sub-gyromagnetic block A2031 is smaller than that of the sub-gyromagnetic block B2032. The fourth gyromagnetic block 202 is located above one side of the sub-gyromagnetic block B2032, and one side end of the fourth gyromagnetic block 202 contacts one side end of the sub-gyromagnetic block A2031. The thickness of the fourth gyromagnetic block 202 and the sub-gyromagnetic block A2031 can be the same.

[0037] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 3 , consisting of the sixth gyromagnetic block 301, the seventh gyromagnetic block 302, the eighth gyromagnetic block 303, and the ninth gyromagnetic block 304, which are exposed to the air. Figure 2 The waveguide structure is the same as shown. Figure 2 A ninth gyromagnetic block 304 is added to the illustrated waveguide structure. The eighth gyromagnetic block 303 also features an inverted T-shaped structure, consisting of an integrally formed sub-gyromagnetic block C3031 and a sub-gyromagnetic block D3032. Ninth gyromagnetic block 304 is a rectangular block, located above the other end of the eighth gyromagnetic block 303. An air cavity, at the same height as sub-gyromagnetic block C3031, exists between ninth gyromagnetic block 304 and sub-gyromagnetic block D3032. The lower corner of ninth gyromagnetic block 304 contacts the upper corner of sub-gyromagnetic block C3031.

[0038] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 4 , consisting of the tenth gyromagnetic block 401, the eleventh gyromagnetic block 402, the twelfth gyromagnetic block 403, the thirteenth gyromagnetic block 404, and the fourteenth gyromagnetic block 405, which is exposed to the air. The structure of the tenth gyromagnetic block 401, the eleventh gyromagnetic block 402, the twelfth gyromagnetic block 403, and the thirteenth gyromagnetic block 404 is similar to the attached Figure 3 The waveguide structure is the same as shown. Figure 3The waveguide structure shown is added with a fourteenth gyromagnetic block 405. The fourteenth gyromagnetic block 405 is arranged in a rectangular shape in the air cavity between the twelfth gyromagnetic block 403 and the thirteenth gyromagnetic block 404. The upper and lower ends of the fourteenth gyromagnetic block 405 are in contact with the thirteenth gyromagnetic block 404 and the twelfth gyromagnetic block 403, respectively.

[0039] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 5 , which is composed of the fifteenth gyromagnetic block 501 and the sixteenth gyromagnetic block 502, which is exposed to the air and has the same structure as the one without the fourth gyromagnetic block 202. Figure 2 The waveguide structures shown are identical.

[0040] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 6 , consisting of the seventeenth gyromagnetic block 601 and the eighteenth gyromagnetic block 602, which is exposed to the air and has the same structure as the attached Figure 1 The waveguide structure shown is similar, but the seventeenth gyromagnetic block 601 located above the eighteenth gyromagnetic block 602 is shorter than the eighteenth gyromagnetic block 602 .

[0041] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 7 , which is composed of the nineteenth gyromagnetic block 701, the twentieth gyromagnetic block 702, the twenty-first gyromagnetic block 703, and the twenty-second gyromagnetic block 704, and is exposed to the air. The first part of the structure composed of the nineteenth gyromagnetic block 701 and the twentieth gyromagnetic block 702 is attached. Figure 1 The second part of the structure composed of the twenty-first gyromagnetic block 703 and the twenty-second gyromagnetic block 704 is attached. Figure 1 The waveguide structure shown in FIG. The first part structure and the second part structure can be the same, and there is an air cavity between the two.

[0042] One embodiment provides a multi-channel topological photonic waveguide structure, see the attached Figure 8 , which is composed of the twenty-third gyromagnetic block 801, the twenty-fourth gyromagnetic block 802, and the twenty-fifth gyromagnetic block 803, which is exposed to the air. The structure composed of the twenty-third gyromagnetic block 801 and the twenty-fourth gyromagnetic block 802 is attached. Figure 1 The waveguide structure shown in FIG. An air cavity exists between the twenty-fifth gyromagnetic block 803 and the structure formed by the twenty-third gyromagnetic block 801 and the twenty-fourth gyromagnetic block 802. Furthermore, the height of the twenty-fifth gyromagnetic block 803 is equal to the height of the structure formed by the twenty-third gyromagnetic block 801 and the twenty-fourth gyromagnetic block 802.

[0043] In the above embodiment, at least adjacent gyromagnetic blocks have different topological properties, and the adjacent gyromagnetic blocks do not need to be assembled into a heterogeneous photonic structure. The topological surface states are formed between the gyromagnetic blocks and the air. The gyromagnetic blocks can be made of yttrium iron garnet (YIG).

[0044] This embodiment also provides a multi-channel topological photon beam splitting method based on the above waveguide structure, specifically:

[0045] placing the waveguide in an air environment so that the gyromagnetic block of the waveguide is in direct contact with the air;

[0046] By adjusting the magnetic field direction of the gyromagnetic blocks and the relative arrangement of the gyromagnetic blocks in the air, topological photon splitting with different surface wave outputs can be achieved.

[0047] The waveguide system of the present invention can realize multi-channel topological splitting of surface waves within a specific wave vector range; in simulation, the waveguide system is composed of multiple block materials with different topological properties, fully demonstrating its excellent splitting performance.

[0048] Figure 9 The energy band diagram and Berry curvature distribution diagram of a single gyromagnetic block (hereinafter referred to as gyromagnetic medium) under different electromagnetic parameters of the present invention are shown below. When the gyromagnetic parameter g is 0, there are two secondary degenerate points in the different polarization energy bands of the gyromagnetic medium, such as Figure 9 As shown in (a). When the gyromagnetic medium introduces a non-zero gyromagnetic parameter g, that is, gyromagnetic parameters of different sign directions g = 1 and g = -1, the energy bands of different polarization states will degenerate due to the magneto-optical response, thus forming a complete topological band gap, and its band distribution is shown as follows Figure 9 The present invention uses Berry curvatures distributed in different directions to specifically demonstrate the influence of the direction of the gyromagnetic parameter on the band topological properties. Based on the calculation of the intrinsic electromagnetic field of the gyromagnetic medium at each momentum, the corresponding Berry curvature distribution is obtained. The Berry curvature distribution that diverges outward is defined as positive, and the one that converges inward is defined as negative, as shown in FIG. Figure 9 (c)- Figure 9 As shown in (d). By integrating the Berry curvature at each point in three-dimensional space, the specific value of the topological invariant of the gyromagnetic medium can be obtained as follows: Figure 9 In the present invention, the magnetic permeability parameter μ in the xy plane of the gyromagnetic medium is t =1, out-of-plane magnetic permeability parameter μ in the z direction z =1; dielectric parameter ε in the xy plane t =2, out-of-plane dielectric parameter ε z = -1, defining the gyromagnetic parameter g along the positive direction of the z-axis as a positive value.

[0049] like Figure 10As shown in (a), a single gyromagnetic block forms a topological photonic waveguide with no cladding layer in the air. Figure 10 As shown in (c), Figure 10 (a) A single gyromagnetic block with different topological properties forms a topological photonic waveguide with no cladding layer in air.

[0050] The distribution of topological surface states was calculated under different gyromagnetic parameter configurations, such as Figure 10 (b) and Figure 10 As shown in (d), the topological surface waves in different gyromagnetic parameter directions have opposite polarization states and group velocities, and the number of surface states in the common band gap region corresponds to the band gap Chern value, defined as LEP and REP, respectively, for the left-handed and right-handed polarization states. Furthermore, in both cases, the topological surface states run through the entire common band gap region and connect band structures with different topological properties. Figure 10 Figures (e)-(f) show the electric field intensity distribution of topological surface states at different group velocities within the band gap. In both cases, the field intensity is primarily concentrated at the interface between the gyromagnetic medium and air, and the field distribution on both sides exhibits an exponential decay as the distance from the interface increases, demonstrating the highly localized nature of the topological surface states. These highly localized topological surface states free topological waveguides from their reliance on domain wall structures and provide a basis for the design and implementation of topological devices in systems where gyromagnetic media without a cladding structure are in direct contact with air.

[0051] Figure 11 These are the simulation results of the topological surface wave scattering immune transmission of the cladding-free structure of the present invention.

[0052] for Figure 10 In the A1 point mode in (b), since there is an intersection between the surface state and the air state at this time, that is, this mode is not located in the common band gap region of the gyromagnetic medium and the air system, this mode will leak energy to the air side when passing through the square sharp defect, and thus cannot bypass the defect for topological protection transmission, such as Figure 11 As shown in (a). That is, Figure 11 As shown in (a), the surface wave vector kz supported by the gyromagnetic block is not located in the common band gap region, but the surface wave is located in Figure 10 In mode A1 in (b), due to the presence of a square defect in the gyromagnetic block, energy leaks to the air side, making it impossible to bypass the defect for topologically protected transmission.

[0053] for Figure 10 In the A2 point mode in (b), the surface wave can bypass any sharp defect and transmit stably and robustly, as shown in Figure 2. Figure 11 Middle (b)- Figure 11As shown in (d) in the figure, the surface wave in the waveguide is always transmitted along the positive y-axis direction, and no back reflection and scattering will occur. The reason is that the A2 point mode is located in the common band gap region of the material system, and only a single topological surface mode exists. Figure 10 In mode A3 in (b), since this mode intersects with the bulk of the gyromagnetic medium, the surface wave leaks into the gyromagnetic medium. The simulation results of its electric field strength are shown as follows: Figure 11 On the other hand, for Figure 10 The B1 point mode in (d) is different from the A2 mode in that they have opposite polarization states and group velocities. Therefore, the energy carried by the B1 mode is only stably transmitted along the negative y-axis direction. The simulation results are shown as follows: Figure 11 As shown in (f). That is to say, when the surface wave vector kz supported by the gyromagnetic block is in the band gap region, even if there are different types of defects in the gyromagnetic block, it will not cause energy leakage, and topological protection transmission can be carried out by bypassing the defects. If the magnetic field direction is in the positive Z direction (i.e., clockwise direction), the transmission property test diagram is shown in Figure 11 Middle (b)- Figure 11 As shown in (d). If the magnetic field direction is the negative Z direction (i.e. counterclockwise direction), the transmission property test diagram is shown in Figure 11 Middle (f). Figure 11 As shown in (e), the surface wave vector kz supported by the gyromagnetic block is not located in the common band gap region, but the surface wave is located in Figure 10 At mode A3 in (b), due to the presence of a square defect in the gyromagnetic block, energy leaks to the side of the gyromagnetic block, making it impossible to bypass the defect for topologically protected transmission.

[0054] Figure 12 (a) shows the reflection-free transmission test spectrum of the topological photonic waveguide mode to a sharp defect in a single gyromagnetic block within a specific wave vector range, with the definition coefficient R = |S B2 -S A2 | / |S B2 +S A2 |, where S B2 With S A2 Respectively represent Figure 11 Figure (b) shows the energy of the surface wave before and after bypassing the defect. The distribution of the coefficient R in the figure shows that within the wave vector kz∈[1.1,2.0] region, the value of the coefficient R approaches 0, indicating that the difference in the energy of the surface wave before and after bypassing the defect is negligible, directly demonstrating the robust transmission of the photonic waveguide mode. Outside the common bandgap region, the value of R is between 0 and 1, indicating that the energy of the surface wave is strongly scattered when passing through a sharp defect. Figure 12 Middle (b)- Figure 12(d) is the quantitative distribution result of the surface wave normalized electric field intensity distribution before and after the topological waveguide mode of the present invention and the traditional waveguide mode pass through the defect. Here A1-A3 and B1-B3 represent Figure 11 (a) Figure 11 (b) and Figure 11 (e) The energy distribution of the surface wave before and after passing through the defect. From the simulation results in the figure, we can see that only in the mode of the common band gap region, the electric field mode of the surface wave has the boundary high localization characteristic before and after passing through the defect, and at this time the distribution of the two modes along the x-axis in space is almost completely overlapped, as shown in the figure. Figure 12 In addition, for the two modes outside the band gap, there is a huge difference in the mode distribution before and after the defect, and the surface wave loses its high localization characteristics due to mode leakage, as shown in (c). Figure 12 (b) and Figure 12 As shown in (d).

[0055] Figure 13 The simulation results of the multi-channel topological photonic waveguide in the gyromagnetic medium of the present invention are shown. Six ports P1-P6 at different spatial positions are defined to qualitatively analyze the beam splitting effect of the topological waveguide mode. The out-of-plane is the positive direction of the z-axis, and the in-plane is the negative direction of the z-axis. The point source is the excitation source. The topological surface waves are excited by the point source, and the magnetic field directions of the first to fourth gyromagnetic blocks are all in the positive direction of the z-axis. From the simulation results in the figure, it can be seen that by changing the magnetic field direction of the gyromagnetic medium in the multi-channel topological photonic waveguide and the relative position of the gyromagnetic medium block in space, a topological photonic beam splitter with six different surface wave ports is obtained.

[0056] by Figure 3 Taking the waveguide shown as an example, the gyromagnetic parameter g of the sixth gyromagnetic block 301, the seventh gyromagnetic block 302, the eighth gyromagnetic block 303, and the ninth gyromagnetic block 304 is 1, and they are made of yttrium iron garnet (YIG) material and are placed in the air. When the topological surface wave is excited at the interface, if the mode of the topological surface wave is toward the ninth gyromagnetic block 304 (i.e., the positive transmission direction of the y-axis), the beam is output only at the right ports P4 and P6; if the mode of the topological surface wave is toward the sixth gyromagnetic block 301 and the seventh gyromagnetic block 302 (i.e., the negative transmission direction of the y-axis), the beam is output only at the left ports P1 and P3, and no reflection or scattering occurs in the process of mode beam splitting of the surface wave, thereby realizing a multi-channel topological beam splitting device with an adjustable number of output ports, see Figure 13 As shown in (a). However Figure 3In the waveguide shown, the gyromagnetic parameter g of the sixth gyromagnetic block 301, the seventh gyromagnetic block 302, and the eighth gyromagnetic block 303 is 1, but the gyromagnetic parameter g of the ninth gyromagnetic block 304 is -1, and the waveguide is placed in air. When a topological surface wave is excited at the interface, if the topological surface wave mode is oriented toward the ninth gyromagnetic block 304 (i.e., in the positive y-axis transmission direction), the split beam is output only at the right ports P5 and P6. If the topological surface wave mode is oriented toward the sixth gyromagnetic block 301 and the seventh gyromagnetic block 302 (i.e., in the negative y-axis transmission direction), the split beam is output only at the left ports P2 and P3, as shown in FIG. Figure 13 As shown in (b).

[0057] by Figure 4 Taking the waveguide shown in FIG. 1 as an example, the gyromagnetic parameter g of the tenth gyromagnetic block 401, the eleventh gyromagnetic block 402, the twelfth gyromagnetic block 403, the thirteenth gyromagnetic block 404, and the fourteenth gyromagnetic block 405 is g=1, and the material is yttrium iron garnet (YIG), and the gyromagnetic block 405 is placed in the air. When the topological surface wave is excited at the interface, if the mode of the topological surface wave is toward the thirteenth gyromagnetic block 404 and the fourteenth gyromagnetic block 405 (i.e., the positive transmission direction of the y-axis), then the beam is output only at the right port P4, as shown in FIG. Figure 13 As shown in (c); if the mode of the topological surface wave is in the direction of the tenth gyromagnetic block 401 and the eleventh gyromagnetic block 402 (i.e., the negative transmission direction of the y-axis), the beam splitting is output only at the left port P1, and no reflection or scattering of the surface wave occurs during the mode beam splitting process, thereby realizing a multi-channel topological beam splitting device with an adjustable number of output ports.

[0058] by Figure 2 Taking the waveguide shown in FIG. 1 as an example, the gyromagnetic parameter g of the third gyromagnetic block 201, the fourth gyromagnetic block 202, and the fifth gyromagnetic block 203 are 1, and they are made of yttrium iron garnet (YIG) and placed in air. When the topological surface wave is excited at the interface, if the mode of the topological surface wave is away from the third gyromagnetic block 201 and the fourth gyromagnetic block 202 (i.e., the positive transmission direction of the y-axis), then only the right port P6 outputs the split beam, as shown in FIG. Figure 13 As shown in (d); if the mode of the topological surface wave is in the direction of the third gyromagnetic block 201 and the fourth gyromagnetic block 202 (i.e., the negative transmission direction of the y-axis), the beam splitting is output only at the left port P3, and no reflection or scattering of the surface wave occurs during the mode beam splitting process, thereby realizing a multi-channel topological beam splitting device with an adjustable number of output ports.

[0059] by Figure 5Taking the waveguide shown in FIG. 1 as an example, the gyromagnetic parameter g of the fifteenth gyromagnetic block 501 and the sixteenth gyromagnetic block 502 is 1, and the material is yttrium iron garnet (YIG), and the topological surface wave is excited at the interface. If the mode of the topological surface wave is in the direction of the fifteenth gyromagnetic block 501 and the sixteenth gyromagnetic block 502 (i.e., the negative transmission direction of the y-axis), then the beam splitting is output only at the left ports P2 and P3, and no reflection or scattering occurs in the process of mode beam splitting of the surface wave, as shown in FIG. Figure 13 As shown in (e). However Figure 5 The gyromagnetic parameter g of the fifteenth gyromagnetic block 501 and the sixteenth gyromagnetic block 502 in the waveguide shown is -1, and they are placed in the air. When the topological surface wave is excited at the interface, if the mode of the topological surface wave is in the direction of the fifteenth gyromagnetic block 501 and the sixteenth gyromagnetic block 502 (i.e., the negative transmission direction of the y-axis), then the beam is output only at the left ports P1 and P3, and no reflection or scattering of the surface wave occurs during the mode beam splitting process. Under the condition of reversing the gyromagnetic parameters, the transmission direction of the multi-channel topological photonic waveguide mode can realize the direction of the topological beam splitting mode reconfigurable, thereby realizing a multi-channel topological beam splitting device with an adjustable number of output ports, as shown in FIG. Figure 13 As shown in (f).

[0060] This type of direction-controllable multi-channel topological photonic waveguide mode in the present invention can be applied to multi-channel multiplexing scenarios such as topological beam splitters, topological directional couplers, topological resonant cavities, and topological photonic switches, providing greater flexibility for the design and implementation of cladding-free multi-channel topological devices in actual topological photonics.

[0061] Figure 14 The normalized electric field intensity quantitative distribution results of the multi-channel topological photonic waveguide based on gyromagnetic media of the present invention are shown in FIG. 1 , where the one-dimensional cross-sections AA-DD correspond to Figure 13 Middle (a)- Figure 13 (c) and Figure 13 The results in (f) are shown in the figure. Figure 14 The electric field strength in (a) only exists at ports P4 and P6, while P5 has no energy output. The calculated result is the same as Figure 13 The simulation results of (a) are consistent. Figure 14 Middle (b)- Figure 14 From the one-dimensional electric field intensity distribution in (d), it can be seen that the topological device in the present invention obtains a topological photonic beam splitter with six different surface wave port outputs by changing the magnetic field direction of the gyromagnetic medium in the multi-channel topological photonic waveguide and the relative position of the gyromagnetic medium block in space. Moreover, this type of multi-channel topological photonic waveguide device is free from the limitations of the domain wall structure and can realize a topological beam splitter device with reconfigurable output ports without a cladding layer structure.

[0062] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A cladding-free multi-channel topological photonic waveguide, characterized in that The invention is composed of at least two gyromagnetic blocks with different topological properties, and the topological properties of adjacent gyromagnetic blocks are different. A point source for exciting topological surface waves is provided at the boundary position of one of the gyromagnetic blocks exposed to the air side; the gyromagnetic blocks are in direct contact with the air; wherein, adjacent gyromagnetic blocks do not need to be assembled into a heterogeneous photonic structure, and topological surface states are formed between the gyromagnetic blocks and the air.

2. The cladding-free multi-channel topological photonic waveguide according to claim 1, characterized in that: Adjacent gyromagnetic blocks can be in direct contact or have an air gap.

3. The cladding-free multi-channel topological photonic waveguide according to claim 1, characterized in that: The gyromagnetic block is made of a gyromagnetic medium material with continuous optical response characteristics, and its optical behavior can be described by equivalent electromagnetic parameters. When the direction of the external magnetic field changes, the Berry curvature distribution of the gyromagnetic medium also presents different directional characteristics.

4. The cladding-free multi-channel topological photonic waveguide according to claim 1, characterized in that: At least one structural defect is also provided inside the gyromagnetic block.

5. The cladding-free multi-channel topological photonic waveguide according to claim 4, characterized in that: The structural defect is square, triangle or oval.

6. A multi-channel topological photon beam splitting method, characterized in that: The method is specifically: Placing the cladding-free multi-channel topological photonic waveguide according to any one of claims 1 to 5 in an air environment so that the gyromagnetic block of the waveguide is in direct contact with the air; By adjusting the magnetic field direction of the gyromagnetic blocks and the relative arrangement of the gyromagnetic blocks in the air, topological photon splitting with different surface wave outputs can be achieved.

7. A multi-channel topological photon splitting method according to claim 6, characterized in that: The different surface waves are excited by arranging a point source at a boundary position of the gyromagnetic block.

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