Topology protection electromagnetic energy beam combiner

Abstract

The invention provides a topology protection electromagnetic energy beam combiner which comprises a first copper-clad substrate, a photonic crystal group and a second copper-clad substrate which are sequentially connected from top to bottom, the photonic crystal group is formed by splicing various photonic crystals, the photonic crystals are rectangular arrays of square lattice YIG cylinders, and the first copper-clad substrate, the photonic crystal group and the second copper-clad substrate are sequentially connected from top to bottom. The photonic crystals have different topological indexes; the adjacent photonic crystals generate a non-scattering one-way transmission topological boundary state in the first direction or the second direction at the boundary. On the basis of a mode orthogonal excitation theory of topology protection, a unidirectional transmission scattering-free topology boundary state is introduced into electromagnetic energy beam combination, so that the constraint on phase correlation and polarization degree of freedom of an input electromagnetic energy source in a traditional electromagnetic energy beam combination theory is broken through; and the structural design of the electromagnetic energy beam combiner with any phase, high efficiency, wide bandwidth and expandability is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of photonic crystals and energy transmission, and specifically relates to a novel structure of topologically protected electromagnetic energy beam combining. By regulating the topological indicators of multiple YIG photonic crystals and splicing them, multiple single-boundary state input channels and one multi-boundary state output channel are constructed to achieve arbitrary phase, high efficiency, wide bandwidth, and scalable multi-channel electromagnetic energy beam combining. Background Art

[0002] High-energy-density electromagnetic beams have broad application prospects in many fields, including laser weapons / laser particle accelerators / advanced material manufacturing / surgery. In the microwave frequency band, high-energy electromagnetic beam systems have shown great potential in application scenarios such as directed energy radiation / Earth-Moon energy transfer and high-energy radar. However, there are physical limitations to the power amplification of a single laser, including nonlinear effects, thermal problems, optical damage, and pump power limitations. Therefore, combining the output power of multiple lasers has become an important technical means to obtain high-energy electromagnetic beams.

[0003] There are two ways to combine the electromagnetic energy of continuous waves: coherent combining and incoherent combining. Coherent combining technology controls the frequency, phase difference, amplitude, polarization and other parameters between the electromagnetic waves of the cells, so that multiple electromagnetic waves can constructively interfere with each other to obtain high-energy electromagnetic wave beams. It strongly relies on the precise modulation of the phase and other parameters of the electromagnetic waves in the input channel to maintain their coherence in time and space. The huge potential of coherent combining technology has made many important advances in the past few decades, but it is still limited by complex phase feedback and control systems.

[0004] Incoherent beam combining technology refers to combining multiple electromagnetic waves into a high-energy electromagnetic beam through spectral beam combining, polarization beam combining, and spatial beam combining. Compared with coherent beam combining, incoherent beam combining has no phase, amplitude, and other requirements and is easy to debug, but it is limited by the beam combining mechanism and the required devices. For example, the number of input channels of passive beam combiners such as polarization beam combiners is limited by the number of polarizations under the power orthogonality requirement. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the existing electromagnetic energy beam combining technology, the present invention provides a topologically protected yttrium iron garnet (YIG) photonic crystal electromagnetic energy beam combiner to solve these technical problems. The electromagnetic energy beam combiner of the present invention supports electromagnetic waves to propagate at the photonic crystal boundary in the form of boundary states. Since the boundary state has the characteristics of scattering-free unidirectional transmission and power orthogonality, a high-power broadband electromagnetic energy beam combiner that is independent of the phase of the input electromagnetic wave can be realized.

[0006] In order to achieve the above invention purpose, the concept of the present invention is:

[0007] A topologically protected electromagnetic energy combiner described in the present invention adopts a topological protection mechanism, and mode orthogonal excitation realizes scattering-free unidirectional transmission topological boundary states. The mode orthogonal excitation is that the boundary states in different input channels are mutually orthogonal, and no interference or destructive interference occurs. The performance of the electromagnetic energy combiner is independent of the phase of the electromagnetic wave of the input channel. The method of characterizing the mutual orthogonality of the boundary states is that there is power orthogonality between the two boundary states, that is, their inner product in the energy sense is zero. The structure of the combiner includes: a photonic crystal composed of a YIG column array, and upper and lower copper-clad substrates surrounding the photonic crystal. Preferably, the combiner also includes a neodymium iron boron magnet for regulating the relative magnetic permeability tensor of the YIG material. YIG photonic crystals with different topological indicators are spliced ​​together, and topological boundary states are generated at the boundary between the two, and their number is equal to the difference between the topological indicators of the two. The electromagnetic energy combining function can be achieved by regulating the topological indicator values ​​of multiple photonic crystals and splicing them. In addition, the boundary state has the characteristics of unidirectional transmission without scattering and energy orthogonality, and is insensitive to structural defects and impurities. Therefore, a topologically protected multi-channel electromagnetic energy combiner with arbitrary phase, high efficiency, wide bandwidth and scalable can be realized through structural optimization. The topological boundary state is an important property of topological non-trivial photonic crystals. It propagates along the boundary of the photonic crystal, has unidirectional and scattering-free characteristics, and the number of topological boundary states is equal to the difference in the topological indicators of the photonic crystals on both sides of the boundary.

[0008] The photonic crystal is formed by arranging YIG columns in a square lattice. By adjusting the diameter of the YIG columns, the corresponding photonic crystal can have different topological indicators, that is, photonic crystals with different topological properties can be constructed. The topological indicator is the sum of the topological numbers of all energy bands under the band gap of the photonic crystal, and the topological number is the Chern number as one of the topological invariants.

[0009] The upper and lower copper-clad substrates surround the YIG photonic crystal in the middle, so that the electromagnetic energy is localized between the two copper-clad substrates and propagates only in the photonic crystal.

[0010] The YIG material has a magnetic anisotropy response, produces ferromagnetic resonance under an external magnetic field, and has excellent characteristics such as high dielectric constant, low dielectric loss, large saturation magnetization intensity, and narrow ferromagnetic resonance line width. The external magnetic field can be applied to YIG using a neodymium iron boron magnet to optimize the photonic crystal parameters.

[0011] According to the above inventive concept, the present invention adopts the following technical solutions:

[0012] A topological protection electromagnetic energy combiner, comprising a first copper-clad substrate, a photonic crystal group, and a second copper-clad substrate connected in sequence from top to bottom, wherein the photonic crystal group is formed by splicing a plurality of photonic crystals, wherein the photonic crystal is a rectangular array of square lattice YIG columns, wherein the YIG columns of each array have different diameters, so that each photonic crystal has a different topological index, wherein the topological index is the sum of the topological numbers of all energy bands below the band gap of the photonic crystal;

[0013] Adjacent photonic crystals generate unidirectional transmission topological boundary states without scattering in a first direction or a second direction at the boundary, and the number of topological boundary states is equal to the difference in topological indexes of the photonic crystals on both sides of the boundary, and the first direction and the second direction are perpendicular to each other;

[0014] The unidirectional transmission topological boundary state whose number of topological boundary states is equal to 1 constitutes an input channel, the boundary states in different input channels are orthogonal to each other, and no interference or destructive interference occurs, and the performance of the electromagnetic energy combiner is independent of the phase of the electromagnetic wave of the input channel;

[0015] The topological boundary states whose number is greater than 1 constitute the output channels, and all the output channels are on the same straight line.

[0016] Optionally, the photonic crystal group is formed by splicing photonic crystals whose topological indices are 0, 1, and -1 respectively in an adjacent manner.

[0017] According to a specific embodiment of the present invention, the photonic crystals whose topological indices are 0, 1, and -1 are spliced ​​in the following order:

[0018] Place the photonic crystal with topological index 0, and the other two types of photonic crystals are used as a reference and arranged next to it;

[0019] A photonic crystal with a topological index of 1 is placed on the upper right side of a photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state, which serves as electromagnetic energy input channel 1.

[0020] A photonic crystal with a topological index of -1 is placed on the lower right side of the photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state as the electromagnetic energy input channel 2;

[0021] The photonic crystal with a topological index of -1 is also on the lower side of the photonic crystal with a topological index of 1. The boundary between the two can produce two topological boundary states, which serve as output channels after the electromagnetic energy is combined.

[0022] Optionally, three photonic crystals with different topological indices are constructed by adjusting the diameter of the YIG column. Further, the YIG column radii of the photonic crystals with topological indices of -1, 1, and 0 are 0.152*L, 0.202*L, and 0.360*L, respectively, where L refers to the lattice constant, which is equal to 2 cm.

[0023] Optionally, the photonic crystal group is formed by splicing photonic crystals with topological indices of -1, 0, 1, and 2 in a clockwise manner, wherein the photonic crystal with a topological index of 0 is adjacent to the photonic crystals with topological indices of 1 and -1, respectively, and the photonic crystal with a topological index of 2 is adjacent to the photonic crystals with topological indices of 1 and -1, respectively.

[0024] Preferably, the photonic crystals with topological indices of -1, 0, 1, and 2 are spliced ​​in the following order:

[0025] S1: Place the photonic crystal with topological index 0, and the other three types of photonic crystals are used as a reference and arranged next to it;

[0026] S2: Place a photonic crystal with a topological index of 1 on the right side of a photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state as electromagnetic energy input channel 1;

[0027] S3: Place a photonic crystal with a topological index of 2 on the bottom side of a photonic crystal with a topological index of 1. The boundary between the two can generate a topological boundary state as an electromagnetic energy input channel 2;

[0028] S4: A photonic crystal with a topological index of -1 is placed under the photonic crystal with a topological index of 0. The photonic crystal with a topological index of -1 is also placed on the left side of the photonic crystal with a topological index of 2. The boundaries of the photonic crystals with topological indexes of 0 and 1 can generate one boundary state as an electromagnetic energy input channel 3, and the boundaries of the photonic crystals with topological indexes of -1 and 2 can generate three boundary states as output channels after electromagnetic energy is combined.

[0029] Optionally, four photonic crystals with different topological indices are constructed by adjusting the diameter of the YIG cylinder. Furthermore, the YIG cylinder radii of the photonic crystals with topological indices of -1, 0, 1, and 2 are 1.13, 1.36, 1.54, and 1.66 mm, respectively, and the corresponding lattice constants are 7.14, 6.55, 7.87, and 10.26 mm, respectively.

[0030] Furthermore, the beam combiner also includes a neodymium iron boron magnet located below the second copper-clad substrate, and the neodymium iron boron magnet optimizes the parameters of the YIG photonic crystal with magnetic anisotropy through a magnetic field to put the system in a ferromagnetic resonance state.

[0031] Furthermore, the NdFeB magnets are distributed in an array and correspond one-to-one with the YIG column array of the photonic crystal. That is, each NdFeB magnet in the array is directly below the corresponding YIG column, so as to adjust the photonic crystal parameters and put the system in a ferromagnetic resonance state, in which the YIG column absorbs electromagnetic waves to a maximum value.

[0032] Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

[0033] 1. The present invention is based on the fact that the topological boundary states existing on the boundaries of YIG photonic crystals have the characteristics of scattering-free unidirectional transmission, so the electromagnetic energy beam combining efficiency is high, and the energy between the boundary states is orthogonal, so the performance of the topologically protected electromagnetic energy combiner is independent of the phase of the input electromagnetic wave, which greatly enhances the stability of the combiner;

[0034] 2. The present invention can significantly improve the working bandwidth of the electromagnetic energy combiner by optimizing the topological non-trivial band gap of the YIG photonic crystal;

[0035] 3. The present invention has the advantages of miniaturization, integration, modularization, and scalability, providing a new design platform for electromagnetic energy combiners. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly understand and illustrate the implementation and features of the examples of the present invention, a brief introduction will be given in conjunction with the drawings of the examples of the present invention.

[0037] Figure 1 This is a schematic diagram of the primitive cell structure of a topologically protected electromagnetic energy combiner described in the present invention.

[0038] Figure 2 These are the topological non-trivial photonic crystal energy bands of the three YIG photonic crystals in Example 1.

[0039] Figure 3 It is the projected energy band of the topological boundary states of the three YIG photonic crystals in Example 1.

[0040] Figure 4 It is the mode field distribution of the full-wave simulation of the Y-type electromagnetic energy combiner in Example 1.

[0041] Figure 5 It is a full-wave simulation diagram of the boundary state and electromagnetic energy beam combination in Example 1.

[0042] Figure 6 It is the inner product between the topological boundary states in the two input channels in Example 1.

[0043] Figure 7 This is a full-wave simulation diagram of the topologically protected 3-channel spiral staircase configuration electromagnetic energy combiner in Example 2.

[0044] Figure 8 This is a simulation diagram of the beam combining efficiency of the topologically protected 3-channel spiral staircase configuration electromagnetic energy combiner in Example 2. DETAILED DESCRIPTION

[0045] The above scheme is further described below in conjunction with specific implementation examples, and preferred embodiments of the present invention are as follows:

[0046] Example 1

[0047] See also Figure 1-6 This embodiment conveniently and clearly explains the structural design process of the topological protection electromagnetic energy combiner through the most basic Y-type electromagnetic energy combiner.

[0048] In this embodiment, the Y-type electromagnetic energy combiner includes three types of YIG photonic crystals, and the arrangement structure thereof is shown in Figure 4 The upper and lower channels belong to the input channel, and the right channel belongs to the output channel. The YIG column in the photonic crystal group (1) is surrounded by the first copper-clad substrate (2) and the second copper-clad substrate (3) to form a three-dimensional structure, and the corresponding NdFeB magnet (4) is installed under the second copper-clad substrate (3). Figure 1 The photonic crystal group (1) is composed of three types of photonic crystals. The structural difference between the three types of photonic crystals is only the different radius of the YIG column. Figure 4 shown.

[0049] based on Figure 4 In the three photonic crystal arrangement structures, in order to satisfy the corresponding input / output channel functions, this embodiment sets the topological index of the lower right photonic crystal to -1, the topological index of the upper right photonic crystal to 1, and the topological index of the left photonic crystal to 0.

[0050] In this embodiment, the YIG column radii of the three photonic crystals with topological indices of -1, 1, and 0 are 0.152*L, 0.202*L, and 0.360*L, respectively, where L refers to the lattice constant, which is equal to 2 cm. The topological non-trivial photonic crystal energy bands of these three YIG photonic crystals are as follows: Figure 2 As shown, the horizontal solid line represents the energy band, the shaded area represents the topological non-trivial band gap, the Chern number corresponding to the energy band is represented by the black number, and the topological index of the band gap is the sum of the Chern numbers of all energy bands below the band gap. Figure 2 It can be seen that the band gaps represented by the shaded areas in the three sub-figures have frequency overlaps and can therefore be used in the same photonic system, and their topological indices are -1, 1, and 0, respectively, meeting the above requirements.

[0051] In this embodiment, the projected energy bands of the unidirectional transmission topological boundary states generated by splicing two by two of the three photonic crystals are as follows: Figure 3As shown. The vertical thick lines indicate the existence of topological boundary states and their unidirectional transmission properties: the number of vertical thick lines is equal to the number of topological boundary states existing on the interfaces of the two corresponding photonic crystals, and the positive and negative slopes of the thick lines indicate the transmission direction of the boundary states. Therefore, the propagation direction of the topological boundary states in the second and third sub-graphs is the same, but opposite to that in the first sub-graph; secondly, there are two topological boundary states in the second sub-graph, while there is only one topological boundary state in the other two sub-graphs.

[0052] In this embodiment, the full-wave simulation of the Y-type electromagnetic energy combiner is as follows Figure 4 As shown in Figure 1, two electromagnetic energies are input from the upper and lower boundaries, and then combined and output at the right boundary. Figure 5 The three sub-figures show the two input boundary states of the Y-type electromagnetic energy combiner and the simulation of its combining.

[0053] In this embodiment, Figure 6 The inner product of the two input boundary states is shown, and its value basically remains at 0, indicating that the two input boundary states have energy orthogonality, that is, the performance of the combiner is independent of the phase.

[0054] Example 2

[0055] See also Figure 7-8 The structural design process of this embodiment is basically the same as that of embodiment 1, except that:

[0056] This embodiment uses four YIG photonic crystals with different topological indices to form a topologically protected three-channel electromagnetic energy combiner. Their topological indices are -1, 0, 1 and 2, respectively, and are arranged in a clockwise manner in a spiral staircase configuration, such as Figure 7 The specific splicing order is as follows:

[0057] S1: Place the photonic crystal with topological index 0, and the other three types of photonic crystals are used as a reference and arranged next to it;

[0058] S2: Place a photonic crystal with a topological index of 1 on the right side of a photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state as electromagnetic energy input channel 1;

[0059] S3: Place a photonic crystal with a topological index of 2 on the bottom side of a photonic crystal with a topological index of 1. The boundary between the two can generate a topological boundary state as an electromagnetic energy input channel 2;

[0060] S4: A photonic crystal with a topological index of -1 is placed under the photonic crystal with a topological index of 0, and the photonic crystal with a topological index of -1 is also placed on the left side of the photonic crystal with a topological index of 2, wherein the boundaries of the photonic crystals with topological indexes of 0 and 1 can generate 1 boundary state as an electromagnetic energy input channel 3, and the boundaries of the photonic crystals with topological indexes of -1 and 2 can generate 3 boundary states as output channels after electromagnetic energy beam combination. In this embodiment, the YIG column radii of the four types of photonic crystals are 1.13, 1.36, 1.54 and 1.66 mm, respectively, and the corresponding lattice constants are 7.14, 6.55, 7.87 and 10.26 mm, respectively.

[0061] In this embodiment, the full-wave simulation of the topologically protected three-channel electromagnetic energy combiner is as follows: Figure 7 As shown in Figure 1, three electromagnetic energies are input from the left, top, and right boundaries, and then combined and output at the bottom boundary.

[0062] In this embodiment, Figure 8 The simulation of the beam combining efficiency of a topologically protected 3-channel electromagnetic energy combiner is demonstrated, with a beam combining efficiency of up to 96.2% and a corresponding bandwidth of 1.47 GHz.

[0063] In summary, the above embodiments demonstrate the structural design process of the electromagnetic energy combiner, and design a topologically protected three-channel electromagnetic energy combiner with arbitrary phase, high efficiency and wide bandwidth.

[0064] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A topological protection electromagnetic energy combiner, characterized in that: The components include a first copper-clad substrate, a photonic crystal group, and a second copper-clad substrate connected in sequence from top to bottom. The photonic crystal group is formed by splicing a plurality of photonic crystals. The photonic crystal is a rectangular array of square lattice YIG columns. The YIG columns of each array have different diameters, so that each photonic crystal has a different topological index. The topological index is the sum of the topological numbers of all energy bands below the band gap of the photonic crystal. Adjacent photonic crystals generate unidirectional transmission topological boundary states without scattering in a first direction or a second direction at the boundary, and the number of topological boundary states is equal to the difference in topological indexes of the photonic crystals on both sides of the boundary, and the first direction and the second direction are perpendicular to each other; The unidirectional transmission topological boundary state whose number of topological boundary states is equal to 1 constitutes an input channel, the boundary states in different input channels are orthogonal to each other, and no interference or destructive interference occurs, and the performance of the electromagnetic energy combiner is independent of the phase of the electromagnetic wave of the input channel; The topological boundary states whose number is greater than 1 constitute the output channels, and all the output channels are on the same straight line.

2. The beam combiner according to claim 1, characterized in that: The photonic crystal group is formed by splicing photonic crystals whose topological indices are 0, 1, and -1 respectively in a mutually adjacent manner.

3. The beam combiner according to claim 2, characterized in that: The photonic crystals with topological indices of 0, 1, and -1 are spliced ​​in the following order: Place the photonic crystal with topological index 0, and the other two types of photonic crystals are used as a reference and arranged next to it; A photonic crystal with a topological index of 1 is placed on the upper right side of a photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state, which serves as electromagnetic energy input channel 1. A photonic crystal with a topological index of -1 is placed on the lower right side of the photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state as the electromagnetic energy input channel 2; The photonic crystal with a topological index of -1 is also on the lower side of the photonic crystal with a topological index of 1. The boundary between the two can produce two topological boundary states, which serve as output channels after the electromagnetic energy is combined.

4. The beam combiner according to claim 3, characterized in that: The YIG column radii of the photonic crystals with topological indices of -1, 1, and 0 are 0.152*L, 0.202*L, and 0.360*L, respectively, where L refers to the lattice constant, which is equal to 2 cm.

5. The beam combiner according to claim 1, characterized in that: The photonic crystal group is composed of photonic crystals with topological indices of -1, 0, 1, and 2 spliced ​​in a clockwise manner, wherein the photonic crystal with topological index 0 is adjacent to the photonic crystals with topological indices of 1 and -1, and the photonic crystal with topological index 2 is adjacent to the photonic crystals with topological indices of 1 and -1.

6. The beam combiner according to claim 5, characterized in that: The photonic crystals with topological indices of -1, 0, 1, and 2 are spliced ​​in the following order: S1: Place the photonic crystal with topological index 0, and the other three types of photonic crystals are used as a reference and arranged next to it; S2: Place a photonic crystal with a topological index of 1 on the right side of a photonic crystal with a topological index of 0. The boundary between the two can generate a topological boundary state as electromagnetic energy input channel 1; S3: Place a photonic crystal with a topological index of 2 on the bottom side of a photonic crystal with a topological index of 1. The boundary between the two can generate a topological boundary state as an electromagnetic energy input channel 2; S4: A photonic crystal with a topological index of -1 is placed under the photonic crystal with a topological index of 0. The photonic crystal with a topological index of -1 is also placed on the left side of the photonic crystal with a topological index of 2. The boundary of the photonic crystals with topological indexes of 0 and 1 can generate one topological boundary state as an electromagnetic energy input channel 3. The boundary of the photonic crystals with topological indexes of -1 and 2 can generate three topological boundary states as output channels after electromagnetic energy is combined.

7. The beam combiner according to claim 6, characterized in that: The YIG column radii of the photonic crystals with topological indices of -1, 0, 1, and 2 are 1.13, 1.36, 1.54, and 1.66 mm, respectively, and the corresponding lattice constants are 7.14, 6.55, 7.87, and 10.26 mm, respectively.

8. The beam combiner according to any one of claims 1 to 7, characterized in that: The beam combiner also includes a neodymium iron boron magnet located below the second copper-clad substrate. The neodymium iron boron magnet optimizes the parameters of the YIG photonic crystal with magnetic anisotropy through a magnetic field to put the system in a ferromagnetic resonance state.

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