Bandwidth-controllable topological optical filter without external magnetic field

Abstract

The invention discloses a bandwidth-controllable topological optical filter without an external magnetic field. According to the device, air, isotropic media and topological continuous media are in direct contact to form a topological optical filter which does not need an external magnetic field and is controllable in bandwidth. The topological continuous medium has a chiral surface state in the same transmission direction in the air and at the boundary of the isotropic medium. By introducing a plurality of structural defects, the scattering suppression transmission characteristic of the surface wave can be tested. By changing the relative dielectric constant epsilon of isotropic media in the topological optical filter, the topological optical filter with adjustable bandwidth and scattering suppression can be realized. The method is suitable for bandwidth-adjustable topological devices such as topological optical filters, topological optical isolators, topological optical waveguides and topological optical routers, and higher flexibility is provided for designing bandwidth-adjustable multi-channel topological photonic devices without additional magnetic fields.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device manufacturing technology, and relates to a light scattering suppression transmission topology device, and more particularly to a topology optical filter with controllable bandwidth without the need for an external magnetic field. Background Technology

[0002] A classic example in topological physics is the quantum Hall effect, observed in a two-dimensional system under the influence of a magnetic field. Its topological properties are characterized by the defined global invariant—the Chern number. In recent years, topological concepts have been introduced into classical wave systems, including photonics and acoustic systems. Among these, due to the high tunability of photonic systems, photonic crystals and continuous topological media have become new platforms for designing and realizing multifunctional topological photonic devices, providing new ideas for optical field manipulation schemes and thus greatly enhancing the potential for information processing.

[0003] Recently, the scattering suppression transmission properties of bandgap edge states have been confirmed in photonic crystals. For example, in a photonic crystal system, when the system symmetry is broken at the interface, a bandgap is opened in the edge states, resulting in bandgap edge states. Due to the presence of the bandgap, topological filtering devices can be designed in photonic crystals with bandgap edge states. However, photonic crystal platforms typically require strict periodicity conditions and complex unit cell structures. Therefore, using photonic crystal platforms to design and implement topological optical filters results in a loss of the system's relatively flexible tunability and controllability.

[0004] Conversely, the optical response in a photonic topological continuum can be described by a relatively equivalent electromagnetic tensor. Based on effective medium theory and topological band theory, the specific spatial distribution of the topological continuum can be obtained analytically. In recent years, topological continuum has been extensively studied in the design and application of topological devices with different functions, such as topological optical isolators, topological photonic waveguides, and topological optical filters. However, current research methods for topological optical filters designed based on topological continuum are limited. Most filter designs rely on external magnetic fields and topological optical filter systems with single-size structural defects, while designs of photonic devices such as topological optical filters with controllable bandwidth are rarely reported. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a topological optical filter with controllable bandwidth that does not require an external magnetic field. It is a design scheme for a topological functional device with controllable scattering suppression and transmission bandwidth.

[0006] In a first aspect, the present invention provides a topological optical filter with adjustable bandwidth that does not require an external magnetic field. The topological optical filter is composed of air, at least one isotropic medium, and a topologically continuous medium in direct contact. This topological optical filter requires no external magnetic field. Chiral surface states with the same propagation direction exist at the contact boundary between the air, the isotropic medium, and the topologically continuous medium. If multiple isotropic media exist, their relative electromagnetic parameters may be the same or different, and gaps may or may not exist between adjacent isotropic media.

[0007] Preferably, the topological continuous medium is a uniform bulk material described by equivalent relative permittivity tensors and permeability tensors. In other words, the optical response of the topological continuous medium can be described by relatively equivalent electromagnetic tensors, thus freeing it from the limitation of strict periodicity conditions.

[0008] Preferably, multiple structural defects of different sizes exist at the contact boundary between the air and the topologically continuous medium to test the scattering suppression characteristics of the topological filter. The shape of the structural defects is not limited to square, triangular, etc. Gaps exist between adjacent structural defects.

[0009] Preferably, the height of each structural defect gradually decreases along the transmission direction of the chiral surface states.

[0010] Preferably, the components of the electromagnetic tensor in the topological continuous medium are: the dielectric component ε in the xy direction. t =2, dielectric component ε in the z-direction z =1-1 / ω, permeability component μ in the xy direction t =2, z-direction permeability component μ z =1-1 / ω 2 ω represents the operating frequency.

[0011] Preferably, the chiral surface states at the contact boundary between the isotropic medium and the topologically continuous medium have a filtering bandgap at the operating frequency.

[0012] Preferably, the relative electromagnetic parameters of the air, the isotropic medium, and the topologically continuous medium are different.

[0013] Preferably, the chiral surface state is excited by an excitation source and has scattering suppression transmission characteristics.

[0014] Preferably, the length of the isotropic medium affects the waveguide performance of the topology filter.

[0015] Isotropic media may or may not come into contact with the outer casing.

[0016] Preferably, the excitation source is located at the port of the topologically continuous medium that is far from the isotropic medium, i.e., the side where the structural defect is located.

[0017] Secondly, the present invention provides a topological optical filter control method for the above-mentioned topological optical filter. The method involves, without an external magnetic field, emitting an excitation source from the outermost structural defect end of the topological continuous medium to the other end of the topological continuous medium, thereby generating chiral surface states at the contact boundary between air, isotropic medium, and the topological continuous medium. The chiral surface states enter the contact boundary between the isotropic medium and the topological continuous medium along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic medium, the operating frequency range of the topological filter is further adjusted, thereby achieving controllable light output.

[0018] Compared to existing topological photonic devices that typically rely on strictly periodic conditions and complex unit cell structures, this invention offers the following advantages: This bandwidth-controllable topological optical filter eliminates dependence on an external magnetic field; that is, it utilizes direct contact between air, an isotropic medium, and a topologically continuous medium to design a topological optical filter that suppresses scattering propagation. While achieving the topological filtering effect, the specific operating frequency range corresponding to the filtering is correlated with the relative permittivity ε in the isotropic medium. Furthermore, by changing the length of the isotropic medium, the topological optical filter can achieve both complete and partial filtering functions. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 1 of the present invention.

[0020] Figure 2 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 2 of the present invention.

[0021] Figure 3 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 3 of the present invention.

[0022] Figure 4 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 4 of the present invention.

[0023] Figure 5 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 5 of the present invention.

[0024] Figure 6 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 6 of the present invention.

[0025] Figure 7 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 7 of the present invention.

[0026] Figure 8 This is a schematic diagram of the xy-section structure of the topological optical filter with adjustable bandwidth that does not require an external magnetic field, as provided in Embodiment 8 of the present invention.

[0027] Figure 9 The analysis results of the bandgap range and bandwidth of the topology filter of the present invention with the relative permittivity ε in isotropic media are shown in (a)-(b), which are the evolution topological phase diagrams of the bandgap range and bandwidth of the topology filter of the present invention with the relative permittivity ε in isotropic media, and (c) are the band structure and surface state distribution diagrams under different relative permittivity ε conditions.

[0028] Figure 10 To modify the operating frequency ω and the thickness d of the isotropic medium, this invention designs and implements a topological optical filter with controllable bandwidth, where (a) is d=d1, (b) is d=d2, (c) is d=d3, and (d) is d=0, d1>d2>d3>0;

[0029] Figure 11 The normalized electric field intensity corresponds to different spatial positions in the bandwidth-controllable topological optical filter device in air, isotropic media and topological continuous media of the present invention.

[0030] Reference numerals in the figures: 1. Topologically continuous medium; 1-1. Structural defect; 2. Isotropic medium; 3. Air; 4. Insulating shield; 5. Excitation source. Detailed Implementation

[0031] The technical solution of the present invention will be further explained below with reference to the figures.

[0032] Example 1:

[0033] See appendix Figure 1 The topological optical filter provided in this embodiment includes an insulating shield, air disposed inside the insulating shield, an isotropic medium and a topologically continuous medium, and an excitation source. The relative electromagnetic parameters of the air, the isotropic medium, and the topologically continuous medium are different.

[0034] A topologically continuous medium is disposed at the bottom of an insulating shield. Three spaced structural defects are arranged on the left end of its upper surface, with the height of the three defects gradually decreasing from left to right. An isotropic medium is placed directly on the right end. There is also a gap between the isotropic medium and the rightmost structural defect. An excitation source is disposed at the left end of the topologically continuous medium. Chiral surface states with the same direction of propagation (from left to right) exist at the contact boundaries between the air, the isotropic medium, and the topologically continuous medium.

[0035] The upper surface, structural defects, and isotropic media of the topologically continuous medium are all in direct contact with the air inside the insulating shield.

[0036] In this embodiment, the length of each isotropic medium is 1-15 times the wavelength of the chiral surface state corresponding to the operating frequency, and its height is less than the distance between the upper surface of the topological continuous medium and the top of the insulating shield.

[0037] The cross-sectional shape of the structural defect is not limited to square, triangular, etc.; in this embodiment, it is square.

[0038] In one embodiment, the insulating shield is made of an insulating material, such as plastic or glass.

[0039] In one embodiment, the isotropic medium is a material whose surface can transmit electromagnetic waves, such as polytetrafluoroethylene or polypropylene.

[0040] In one embodiment, the topological continuous medium is a uniform bulk material described by equivalent relative permittivity tensors and permeability tensors, such as hyperbolic electromagnetic media.

[0041] This embodiment provides a topology optical filter control method for the above-mentioned topology optical filter, the method specifically being:

[0042] Without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic medium, and topological continuous medium. These chiral surface states enter the contact boundary between isotropic medium and topological continuous medium along the contact boundary between structural defects and air. By changing the relative permittivity ε of the isotropic medium, the operating frequency range of the topological filter can be further adjusted, thereby achieving controllable light output.

[0043] Example 2:

[0044] See appendix Figure 2 Based on Example 1, only the length of the isotropic medium is changed to more than 5 times the wavelength of the chiral surface state corresponding to the operating frequency.

[0045] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in Embodiment 1.

[0046] Example 3:

[0047] See appendix Figure 3 Based on Example 1, only the length of the isotropic medium is changed to less than 5 times the wavelength of the chiral surface state corresponding to the operating frequency.

[0048] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in Embodiment 1.

[0049] Example 4:

[0050] See appendix Figure 4 Based on Example 1, the only change is the use of two isotropic media with a gap between them. Both of these isotropic media are located on the right side, and they are made of the same material (e.g., polytetrafluoroethylene, polypropylene, etc.). Their lengths are both less than 5 times the wavelength of the chiral surface state corresponding to the operating frequency.

[0051] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in Embodiment 1.

[0052] Example 5:

[0053] See appendix Figure 5 Based on Example 4, only the length of the isotropic medium used on the left is changed to more than 5 times the wavelength of the chiral surface state corresponding to the operating frequency.

[0054] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in embodiment 4.

[0055] Example 6:

[0056] See appendix Figure 6 Based on Example 4, the only difference is that the distance between the two isotropic media is changed to 0, and different materials are used (for example, one is polytetrafluoroethylene and the other is polypropylene).

[0057] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in embodiment 4.

[0058] Example 7:

[0059] See appendix Figure 7 Based on Example 2, only the number of structural defects was changed to 2.

[0060] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in Embodiment 2.

[0061] Example 8:

[0062] See appendix Figure 8 Based on Example 2, only the cross-sectional shape of the structural defect is changed to a triangle.

[0063] During operation, without an external magnetic field, an excitation source is used to generate chiral surface states at the contact boundary between air, isotropic media, and topological continuous media. These chiral surface states enter the contact boundary between the isotropic media and the topological continuous media along the contact boundary between the structural defect and air. By changing the relative permittivity ε of the isotropic media, the operating frequency range of the topology filter is further adjusted, thereby achieving controllable light output. The operating frequency range of the topology filter in this embodiment is different from that in Embodiment 2.

[0064] Figure 9 Figure (a) shows the two-dimensional evolution phase diagram of the topological filtering bandgap range as a function of the angular frequency electromagnetic constant ε / μ under different relative permittivity ε in isotropic media according to the present invention. The purple shaded area represents the topological filtering bandgap range. From the specific spatial locations of the upper and lower boundaries of the surface states in the figure, it can be seen that the range of the topological filtering bandgap disappears when ε / μ=1. Figure 9 (b) Figure 9(c) is a phase diagram showing the change of the topology filter bandwidth and surface states with the electromagnetic constant ε / μ in this invention. The topology filter bandwidth is turned off under the condition that ε / μ=1. Furthermore, the results in the figure show that the topology filter bandwidth can exist stably under different ε / μ parameters, and the topology bandwidth changes. This is a prerequisite for realizing a topology optical filter with controllable bandwidth.

[0065] Figure 10 This paper presents simulation results of bandwidth-controllable topological optical filters in air, isotropic media, and topologically continuous media, defining four different structural thicknesses d1-d4 to qualitatively analyze the controllable energy filtering characteristics of the topological optical filters. Figure 10 Numerical simulation results show that by changing the operating frequency ω, a topological filtering effect within a specific operating frequency range can be achieved. Specifically, when the operating frequencies ω=0.5 and ω=0.8, air, co-directional media, and topologically continuous media systems can support surface waves with scattering suppression transmission; when the operating frequency ω=0.65, the operating frequency is located at... Figure 1 Within the bandgap of the topological filter, a topological optical filtering effect is achieved, such as... Figure 10 (a)- Figure 10 As shown in (c). On the other hand, by changing the thickness value in isotropic media, a topology filter for controllable energy transmission can be further designed, such as... Figure 10 As shown in (b)-(d). Figure 10 As shown in (d), when there is no isotropic medium, the chiral surface states can be completely transmitted throughout the entire device, thus rendering the topology filtering function impossible.

[0066] Figure 11 The electric field intensity of the bandwidth-controllable topological optical filter in air, isotropic media, and topologically continuous media in this invention is the one-dimensional normalized electric field intensity, where lines 1-2 correspond to... Figure 10 The result in (a). Figure 11 The normalized electric field intensity distributions corresponding to centerline 1 and centerline 2 can completely overlap, and their one-dimensional distribution results are consistent with... Figure 10 The numerical simulation results in (a) are self-consistent. Further analysis... Figure 11 The one-dimensional electric field intensity distribution proves that the topological optical filter in this invention can be designed with controllable bandwidth and scattering suppression transmission by changing the operating frequency ω, and it eliminates the need to design a topological optical filter with controllable bandwidth by relying on an external magnetic field.

[0067] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A topology optical filter with bandwidth tunable without external magnetic field, characterized in that, The topological optical filter is composed of air, at least one isotropic medium and topological continuous medium in direct contact, and the topological optical filter does not need an external magnetic field; wherein, there is a chiral surface state with a same transmission direction at the contact boundary of the air, the isotropic medium and the topological continuous medium.

2. The topology optical filter with tunable bandwidth without external magnetic field according to claim 1, characterized in that, The topological continuous medium is a uniform bulk material described by equivalent relative dielectric tensor and magnetic permeability tensor.

3. The topology optical filter with tunable bandwidth without external magnetic field according to claim 2, characterized in that, There are a plurality of structural defects with different sizes at the contact boundary of the air and the topological continuous medium.

4. The topology optical filter with tunable bandwidth without external magnetic field according to claim 5, characterized in that, The height of each structural defect gradually decreases along the transmission direction of the chiral surface state.

5. The topology optical filter with tunable bandwidth without external magnetic field according to claim 2, characterized in that, The chiral surface state at the contact boundary of the isotropic medium and the topological continuous medium has a filter band gap at the operating frequency.

6. The topology optical filter with tunable bandwidth without external magnetic field according to claim 1, characterized in that, The relative electromagnetic parameters of the air, the isotropic medium and the topological continuous medium are different.

7. The topology optical filter with tunable bandwidth without external magnetic field according to claim 1, characterized in that, The chiral surface state is excited by an excitation source and has a scattering-repressed transmission characteristic.

8. The topology optical filter with tunable bandwidth without external magnetic field according to claim 1, characterized in that, The length of the isotropic medium affects the guided wave performance of the topological filter.

9. The topology optical filter with tunable bandwidth without external magnetic field according to claim 1, characterized in that, The excitation source is arranged at the end of the topological continuous medium away from the isotropic medium port.

10. A method for controlling the topology of the optical filter according to any one of claims 1-9, without the need for an external magnetic field, characterized in that, The method is to excite the topological continuous medium from one end to the other end by an excitation source arranged at the outermost structural defect of the topological continuous medium without an external magnetic field, so as to generate a chiral surface state at the contact boundary of the air, the isotropic medium and the topological continuous medium; the chiral surface state enters the contact boundary of the isotropic medium and the topological continuous medium along the contact boundary between the structural defect and the air, the relative permittivity ε of the isotropic medium is changed to further adjust the operating frequency range of the topological filter, and then the light output is controlled.

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