Multi-channel topological photonic waveguide without coating layer and method thereof

Abstract

The invention discloses a multi-channel topological photonic waveguide without a coating layer and a method thereof. The waveguide is composed of at least two gyromagnetic blocks with different topological properties. The adjacent gyromagnetic blocks do not need to be spliced into a heterogeneous photon structure, and a topological surface state is formed between the gyromagnetic blocks and air. According to the invention, dependence on a topological domain wall structure can be eliminated, namely topological photon routing without a coating layer structure is realized at an interface in direct contact with air. While topological beam splitting of the surface wave is realized, the surface wave transmitted by the gyromagnetic medium and the air interface and the polarization state of the surface wave are locked. The waveguide is placed in the air, so that the gyromagnetic block body is in direct contact with the air; and the directions of the magnetic fields of the gyromagnetic blocks and the relative arrangement positions of the gyromagnetic blocks in the air are adjusted, so that the beam splitting of topological photons emitted by different surface waves is realized, and the multi-channel topological guided wave device with reconfigurable emitting ports and controllable port number can be realized.

Description

Technical Field

[0001] The present invention relates to a photonic topological multi-channel device, in particular to a multi-channel topological photonic waveguide based on gyromagnetic media. Background Art

[0002] In recent years, topological photonics has developed rapidly and has become a vibrant and highly-watched research field. The concept of "non-trivial topological phases" in photonics originated from the study of condensed matter systems. This concept provides a new solution for high-precision and high-robust electromagnetic wave propagation manipulation. With its ease of operation and direct connection with quantum states, topological photonics has opened up new possibilities for basic scientific research and practical applications, thus providing a highly promising platform for the design and realization of new topological devices.

[0003] One of the most notable features of topological photonic systems is the existence of unidirectional topological surface states at the boundaries. It is a direct corollary of the body-edge correspondence principle. Such unidirectional surface states are robust, allowing them to persist stably in structures with structural defects and effectively suppress backscattering, even in disordered or defect-filled environments. So far, researchers have designed and realized different types of topological devices such as topological photonic waveguides, topological beam splitters, topological directional couplers, and topological photonic switches using the photonic crystal platform.

[0004] Nevertheless, because photonic crystals usually rely on strict periodic conditions and complex unit cell structures, topological devices based on photonic crystal platforms lack flexible adjustability. The existing gyromagnetic topological photonic crystal waveguide design relies on strict periodic conditions because photonic crystals cannot be described using equivalent medium theory. Due to the limitations of such periodic structures, an additional cladding structure (heterogeneous photonic structure) is usually required in the photonic crystal system so that the mode on the surface of the photonic crystal is located 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, making it impossible to effectively guide the mode. 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 object of the present invention is to overcome the above-mentioned deficiencies of the prior art and to provide a cladding-free multi-channel topological photonic waveguide and a method thereof, so as to provide a design of a multi-channel cladding-free topological photonic device.

[0006] Different from 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 by 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, which is specifically used to verify the topological protection characteristics of the surface wave 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 beam 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 position 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 the existing topological devices that rely on strict periodic structure design, the present invention has the following advantages:

[0018] This multi-channel topological device can get rid of the dependence on the topological domain wall structure, that is, to achieve topological photon routing without a cladding structure at the interface in direct contact with the air. While realizing the topological beam 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 changing the magnetic field direction of the gyromagnetic medium in the device and the relative spatial position of the material block, a multi-channel topological waveguide device with reconfigurable output ports and controllable port number can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

[0020] Figure 1 This is one of the embodiments of the 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] Fig. 9 Middle (a)- Fig. 9 (b) is the energy band diagram of a single gyromagnetic block under different electromagnetic parameters. Fig. 9 Middle (c)- Fig. 9 (d) is the Berry curvature distribution diagram induced by the gyromagnetic parameter g with different sign directions.

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

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

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

[0032] Fig.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] Fig.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 in conjunction with the accompanying drawings in the embodiments of the present invention.

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

[0036] One embodiment provides a multi-channel topological photonic waveguide structure, see 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 shown is the same. 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, which is composed of an integrally formed sub-gyromagnetic block A2031 and a sub-gyromagnetic block B2032 stacked up and down, and this type of T-shaped structure is an integral block material, which is essentially different from the 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 is in contact with 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 Attached Figure 3 , which is composed of a sixth gyromagnetic block 301, a seventh gyromagnetic block 302, an eighth gyromagnetic block 303, and a ninth gyromagnetic block 304, and is exposed to the air. The sixth gyromagnetic block 301, the seventh gyromagnetic block 302, and the eighth gyromagnetic block 303 are structured and attached. Figure 2 The waveguide structure shown is the same. Figure 2 The ninth gyromagnetic block 304 is added to the waveguide structure shown. The eighth gyromagnetic block 303 is also an inverted T-shaped structure composed of an integrally formed sub-gyromagnetic block C3031 and a sub-gyromagnetic block D3032. The ninth gyromagnetic block 304 is a rectangular block, which is above the other side end of the eighth gyromagnetic block 303. There is an air cavity with the same height as the sub-gyromagnetic block C3031 between the ninth gyromagnetic block 304 and the sub-gyromagnetic block D3032, and the lower end corner of the ninth gyromagnetic block 304 contacts the upper end corner of the sub-gyromagnetic block C3031.

[0038] One embodiment provides a multi-channel topological photonic waveguide structure, see Attached Figure 4 , which is composed 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, and 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 and the attached Figure 3 The waveguide structure shown is the same. Figure 3The waveguide structure shown is added with a fourteenth gyromagnetic block 405. The air cavity between the twelfth gyromagnetic block 403 and the thirteenth gyromagnetic block 404 is provided with a rectangular structure of the fourteenth gyromagnetic block 405, and 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 Attached Figure 5 , which is composed of a fifteenth gyromagnetic block 501 and a sixteenth gyromagnetic block 502, which is exposed to the air, and its structure is similar to that of 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 Attached Figure 6 , which is composed of a seventeenth gyromagnetic block 601 and an eighteenth gyromagnetic block 602, which is exposed to the air and has a similar structure to the attached Figure 1 The waveguide structures shown are 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 Attached Figure 7 , which is composed of a nineteenth gyromagnetic block 701, a twentieth gyromagnetic block 702, a twenty-first gyromagnetic block 703, and a twenty-second gyromagnetic block 704, which is exposed to the air, and the first part structure composed of the nineteenth gyromagnetic block 701 and the twentieth gyromagnetic block 702 is attached Figure 1 The second part structure composed of the twenty-first gyromagnetic block 703 and the twenty-second gyromagnetic block 704 is attached Figure 1 The waveguide structure shown. 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 Attached Figure 8 , which is composed of a twenty-third gyromagnetic block 801, a twenty-fourth gyromagnetic block 802, and a twenty-fifth gyromagnetic block 803, which is exposed to the air, and the structure composed of the twenty-third gyromagnetic block 801 and the twenty-fourth gyromagnetic block 802 is attached Figure 1 There is an air cavity between the structure formed by the twenty-fifth gyromagnetic block 803 and the twenty-third gyromagnetic block 801 and the twenty-fourth gyromagnetic block 802. And 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 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. 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 position 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] Fig. 9 The energy band diagram and Berry curvature distribution diagram of a single gyromagnetic block (hereinafter referred to as the gyromagnetic medium) under different electromagnetic parameters of the present invention are shown in Figure 2. 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 Fig. 9 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 energy band distribution is shown as follows: Fig. 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 topological properties of the energy band. The corresponding Berry curvature specific distribution is calculated based on the intrinsic electromagnetic field of the gyromagnetic medium at each momentum. The Berry curvature distribution that diverges outward is defined as a positive value, and the one that converges inward is defined as a negative value, as shown in FIG. Fig. 9 Middle (c)- Fig. 9 By integrating the Berry curvature at each point in the three-dimensional space, the specific value of the topological invariant of the gyromagnetic medium can be obtained as follows: Fig. 9 In the present invention, the magnetic permeability parameter μ of the gyromagnetic medium in the xy plane is t = 1, the magnetic permeability parameter μ in the out-of-plane 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 Fig.10As shown in (a), a single gyromagnetic block forms a topological photonic waveguide without a cladding layer in the air. Fig.10 As shown in (c), Fig.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 orientation configurations, such as Fig.10 (b) and Fig.10 As shown in (d), the topological surface waves under 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, and LEP and REP are defined as left-handed polarization state and right-handed polarization state, respectively; in addition, the topological surface states in both cases run through the entire common band gap region and connect band structures with different topological properties. Fig.10 (e)-(f) are the electric field intensity distribution diagrams of topological surface states with different group velocities within the band gap. In both cases, the field intensity is mainly concentrated at the interface between the gyromagnetic medium and the air, and as it moves away from the interface, the field distribution on both sides shows an exponential decay, which proves the high localization characteristics of the topological surface state. This kind of topological surface state with high localization characteristics gets rid of the dependence of the topological waveguide on the domain wall structure, and can provide a basis for the design and realization of topological devices in the system where the gyromagnetic medium without the coating structure is in direct contact with the air.

[0051] Fig.11 It is the simulation result of topological surface wave scattering immune transmission of the coating-free structure of the present invention.

[0052] for Fig.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 Fig.11 That is, Fig.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 Fig.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 Fig.10 The A2 point mode in (b) shows that the surface wave can bypass any sharp defect and transmit stably and robustly. Fig.11 Middle (b) - Fig.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 there is only a single topological surface mode. Fig.10 In mode A3 in (b), since this mode intersects with the body state of the gyromagnetic medium, the surface wave will leak into the gyromagnetic medium. The simulation results of its electric field strength are as follows: Fig.11 On the other hand, for Fig.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 in Fig.11 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 the defects can be bypassed for topological protection transmission. If the magnetic field direction is in the positive Z direction (i.e., clockwise direction), the transmission property test diagram is shown in Fig.11 Middle (b) - Fig.11 As shown in (d). If the magnetic field direction is in the negative Z direction (i.e. counterclockwise direction), the transmission property test diagram is shown in Fig.11 Middle (f). Fig.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 Fig.10 At mode A3 in (b), due to the presence of a square defect in the gyromagnetic block, energy leaks to the gyromagnetic block side, making it impossible to bypass the defect for topological protection transmission.

[0054] Fig.12 (a) shows the reflection-free transmission test spectrum of a single gyromagnetic block in a specific wave vector range for a topological photonic waveguide mode to a sharp defect, with the definition coefficient R = |S B2 -S A2 | / |S B2 +S A2 |, where S B2 With S A2 Respectively represent Fig.11 The energy of the surface wave after bypassing the defect and before the defect in (b). From the distribution of the coefficient R in the figure, it can be seen that in the wave vector kz∈[1.1,2.0] region, the value of the coefficient R approaches 0, which means that the difference in the energy of the surface wave after bypassing the defect and before the defect can be ignored, which directly proves the robust transmission of the photonic waveguide mode; outside the common band gap region, the value of R is between 0 and 1, which means that the energy of the surface wave will be scattered more strongly when passing through a sharp defect. Fig.12 Middle (b) - Fig.12(d) is the quantitative distribution result of the normalized electric field intensity distribution of the surface wave 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 Fig.11 Middle (a), Fig.11 (b) and Fig.11 (e) Energy distribution of the surface wave before and after passing through the defect. From the simulation results in the figure, it can be seen that only in the mode in the common band gap region, the electric field mode of the surface wave has the boundary high localization characteristics 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 Fig.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 Fig.12 (b) and Fig.12 As shown in (d).

[0055] Fig.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 with 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 in FIG. 1 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 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), then only the right ports P4 and P6 output the split beam; 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), then only the left ports P1 and P3 output the split beam, and no reflection or scattering occurs in the process of mode splitting of the surface wave, thereby realizing a multi-channel topological beam splitting device with an adjustable number of output ports, see FIG. Fig.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 gyromagnetic block 304 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 ninth gyromagnetic block 304 (i.e., the positive transmission direction of the y-axis), the split beam is output only at the right ports P5 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 split beam is output only at the left ports P2 and P3, see Fig.13 As shown in (b).

[0057] by Figure 4 Taking the waveguide shown in the figure 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 1, and they are made of yttrium iron garnet (YIG) and 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 only the beam is output at the right port P4, as shown in FIG. Fig.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 is 1, and the material is yttrium iron garnet (YIG), and the gyromagnetic block 203 is placed in the 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. Fig.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), 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. Fig.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), the beam splitting 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, see Fig.13 As shown in (f).

[0060] Such direction-controllable multi-channel topological photonic waveguide modes 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 practical topological photonics.

[0061] Fig.14 The normalized electric field intensity quantitative distribution result of the multi-channel topological photonic waveguide based on gyromagnetic medium in the present invention, where the one-dimensional cross-sections of AA-DD correspond to Fig.13 Middle (a)- Fig.13 (c) and Fig.13 The results in (f) are shown in the figure. Fig.14 The electric field strength in (a) only exists at ports P4 and P6, while P5 has no energy output. The calculation result is the same as Fig.13 The simulation results of (a) are consistent. Fig.14 Middle (b) - Fig.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 with reconfigurable output port without a cladding layer structure.

[0062] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle 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 It 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 a topological surface state is formed between the gyromagnetic blocks and the air.

2. The waveguide according to claim 1, characterized in that: The topological properties of adjacent gyromagnetic blocks are different.

3. The waveguide according to claim 1, characterized in that: Adjacent gyromagnetic blocks may be in direct contact or have an air gap.

4. The 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.

5. The waveguide according to claim 1, characterized in that: At least one structural defect is also provided inside the gyromagnetic block.

6. The waveguide according to claim 1, characterized in that: The structural defect is square, triangle or ellipse.

7. The waveguide according to claim 1, characterized in that: A point source for exciting topological surface waves is arranged at a boundary position where one of the gyromagnetic blocks is exposed to the air side.

8. A multi-channel topological photon beam splitting method, characterized in that: The method is specifically: Placing the waveguide according to any one of claims 1 to 7 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 position of the gyromagnetic blocks in the air, topological photon splitting with different surface wave outputs can be achieved.

9. The method according to claim 1, characterized in that: The different surface waves are excited by setting a point source at a boundary position of the gyromagnetic block.

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