Broadband omni-directional fully transparent system realized by twist structure and application thereof

Abstract

The present application relates to a kind of wideband omni-directional completely transparent system and its application of torsion structure implementation, the system includes several first structure and second structure connected alternately, the first structure rotates set angle in Z axis direction towards clockwise direction, the second structure rotates set angle in Z axis direction towards counterclockwise direction;The first structure and the second structure all include several first structure layer and second structure layer, which are arranged in up-down overlap along X axis direction;The omni-directional completely transparent system meets the following zero shift condition.The system of the present application realizes the rotation of IFCs (Iso-frequency curves, equal frequency curve) in k space by twisting by multiple layers of alternatingly arranged dielectric materials, and realizes wideband OPT under zero reflection condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical systems, in particular to a broadband omnidirectional perfect transparency system realized by a twisted structure and application thereof. BACKGROUND

[0002] In optical systems, transparent materials play a crucial role in the manipulation of electromagnetic waves. In this field, omnidirectional perfect transparency (OPT) is particularly important, providing broad prospects for the application of optical and photonic devices. However, achieving OPT is a great challenge because it requires materials to be able to completely transmit light at all incident angles. The emergence of metamaterials and photonic crystals has changed the way electromagnetic waves are controlled, providing new strategies for achieving omnidirectional transparency. For example, combining Brewster's angle and complex electromagnetic coupling response to achieve OPT for transverse magnetic (TM) and transverse electric (TE) waves, using the spatial dispersion parameter of photonic crystals to achieve omnidirectional impedance matching, or designing metasurfaces to achieve angle-insensitive longitudinal impedance matching. Then, existing methods are limited by complex electromagnetic interactions and single frequency, hindering their practical application. Broadband OPT with simple structures, especially in one-dimensional systems, remains a scientific problem that needs to be solved. SUMMARY

[0003] The purpose of the present application is to overcome the defects of the prior art and provide a broadband omnidirectional perfect transparency system realized by a twisted structure and application thereof, solving the problem that existing methods for achieving omnidirectional transparency are limited by complex electromagnetic interactions and single frequency, hindering their practical application, and the problem that broadband OPT with simple structures is difficult to achieve.

[0004] The technical solution to achieve the above-mentioned purpose is:

[0005] The present application provides a broadband omnidirectional perfect transparency system realized by a twisted structure, comprising a plurality of first structures and second structures connected alternately, wherein the first structure is rotated by a set angle in the clockwise direction along the Z-axis direction, and the second structure is rotated by a set angle in the counterclockwise direction along the Z-axis direction.

[0006] The first structure and the second structure each comprise a plurality of first structure layers and second structure layers arranged in an up-down overlapping manner along the X-axis direction.

[0007] The omnidirectional perfect transparency system satisfies the following zero shift condition:

[0008]

[0009] In formula 1, is a differential of the phase difference of two reflected waves, is a differential of the wave vector along the x direction, d A is a thickness of the A layer material, is a differential of the wave vector of the A layer material along the z direction, d B is a thickness of the B layer material, is a differential of the wave vector of the B layer material along the z direction, and ω0 is a frequency satisfying the OPT condition.

[0010] The further improvement of the wideband omnidirectional completely transparent system realized by the twisted structure is that the first structure layer and the second structure layer are both all-dielectric materials.

[0011] The further improvement of the wideband omnidirectional completely transparent system realized by the twisted structure is that the first structure body and the second structure body are adjacent and form a lattice, and the lattice is arranged periodically with a set lattice constant.

[0012] The further improvement of the wideband omnidirectional completely transparent system realized by the twisted structure is that the frequency range of the omnidirectional completely transparent system can be adjusted by changing the size of the lattice constant.

[0013] The further improvement of the wideband omnidirectional completely transparent system realized by the twisted structure is that the number and quality factor of the transmission peaks can be controlled by adjusting the number of arrangement periods of the first structure body and the second structure body in the Z-axis direction.

[0014] The further improvement of the wideband omnidirectional completely transparent system realized by the twisted structure is that the range of the set angle is between 40° and 90°.

[0015] The further improvement of the wideband omnidirectional completely transparent system realized by the twisted structure is that the number of arrangement periods of the first structure layer and the second structure layer is greater than or equal to 4.

[0016] The application also provides an application of the wideband omnidirectional completely transparent system realized by the twisted structure in the field of optics and photonic devices.

[0017] The application also provides an application of the wideband omnidirectional completely transparent system realized by the twisted structure in a building to improve the transmission rate of signals.

[0018] The wideband omnidirectional completely transparent system realized by the twisted structure and the application thereof have the following beneficial effects:

[0019] The system of the application realizes the rotation of IFCs (Iso-frequency curves) of k space by twisting the full dielectric material arranged in multiple layers alternately, and realizes the broadband OPT under the condition of zero reflection. The application not only solves the problems of high complexity and limitation to single-frequency transparency in traditional design, but also explores a new physical method for realizing broadband omnidirectional transparency on a low-loss and feasible platform, provides a new research direction for photonics and material science, and opens an important path for realizing high-efficiency, low-complexity broadband omnidirectional transparency.

[0020] The system of the application can realize the adjustment of the frequency range and the loan of the OPT by changing the structure parameters, such as the size of the lattice constant.

[0021] The system of the application can realize the flexible control of the number and quality factor of the transmission peaks by adjusting the period number of the structure, and improves the applicability of the material in practical application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A structural schematic diagram of one embodiment of the broadband omnidirectional completely transparent system realized by the twisting structure of the application.

[0023] Figure 2 The corresponding IFCs of the positive and negative TAMs in the broadband omnidirectional completely transparent system realized by the twisting structure of the application.

[0024] Figure 3 The magnetic field distribution of the uniform material and the equivalent material in the broadband omnidirectional completely transparent system realized by the twisting structure of the application.

[0025] Figure 4 The relationship between the transmittance and the incident angle and the frequency of the broadband omnidirectional completely transparent system realized by the twisting structure of the application with the period number of 6.

[0026] Figure 5 The transmission spectrum corresponding to the incident angles of 0°, 30° and 60° of the broadband omnidirectional completely transparent system realized by the twisting structure of the application with the period number of 6.

[0027] Figure 6 The relationship between the structural reflection phase and the incident angle and the frequency of the broadband omnidirectional completely transparent system realized by the twisting structure of the application with the period number of 6.

[0028] Figure 7 The relationship between the transmittance and the incident angle and the frequency of the broadband omnidirectional completely transparent system realized by the twisting structure of the application with the period number of 8.

[0029] Figure 8 The transmission spectrum corresponding to the incident angles of 0°, 30° and 60° of the broadband omnidirectional completely transparent system realized by the twisting structure of the application with the period number of 8.

[0030] Figure 9 The relationship between the reflection phase of the structure with 8 periods of the broadband omni-directional and completely transparent system realized by the twisted structure of the application and the incident angle and frequency.

[0031] Figure 10 The schematic diagram of the experimental device of the broadband omni-directional and completely transparent system realized by the twisted structure of the application.

[0032] Figure 11 The schematic diagram of the experimental sample of the broadband omni-directional and completely transparent system realized by the twisted structure of the application.

[0033] Figure 12 The simulated transmission spectrum diagram of 0°, 30° and 60° in the experiment of the broadband omni-directional and completely transparent system realized by the twisted structure of the application.

[0034] Figure 13 The experimental transmission spectrum diagram of 0°, 30° and 60° in the experiment of the broadband omni-directional and completely transparent system realized by the twisted structure of the application.

[0035] Figure 14 The normalized magnetic field distribution at 1.23, 1.62, 2.05, 2.48, 2.84 GHz when the incident angle is 30° in the experiment of the broadband omni-directional and completely transparent system realized by the twisted structure of the application.

[0036] Figure 15 The projection spectrum of the broadband omni-directional and completely transparent system realized by the twisted structure of the application with different frequencies and incident angles. DETAILED DESCRIPTION

[0037] The application will be further described below in combination with the drawings and specific embodiments.

[0038] Reference Figure 1The application provides a twisted structure realized broadband omnidirectional completely transparent system and application thereof, proposes a zero shift condition, realizes rotation of IFC in k space through twisting of a plurality of layers of full dielectric materials arranged alternately, realizes broadband OPT under the condition of zero reflection, finally, the inventor adjusts the frequency range and bandwidth of the OPT by changing the structure and material parameters, further adjusts the period number of the superstructure material, realizes flexible control of the number and quality factor of the transmission peaks, and improves the applicability of the material in practical application, the inventor verifies that the structure realizes broadband omnidirectional transparency through simulation experiment and microwave experiment, which not only solves the problems of high complexity and limitation to single-frequency transparency in traditional design, explores a new physical method for realizing broadband omnidirectional transparency on a low-loss and feasible platform, provides a new research direction for photonics and material science, and opens an important path for realizing high-efficiency, low-complexity broadband omnidirectional transparency.

[0039] Referring to Figure 1 , a structure schematic diagram of one embodiment of the twisted structure realized broadband omnidirectional completely transparent system is shown. Figure 1 The twisted structure realized broadband omnidirectional completely transparent system is described below.

[0040] As shown in Figure 1 , the twisted structure realized broadband omnidirectional completely transparent system of the application comprises a plurality of first structure bodies B and second structure bodies A connected alternately, the first structure body B is rotated by a set angle alpha in the clockwise direction in the Z-axis direction, and the second structure body A is rotated by a set angle alpha in the counterclockwise direction in the Z-axis direction.

[0041] The first structure body B and the second structure body A both comprise a plurality of first structure layers C and second structure layers D arranged up and down in the X-axis direction.

[0042] The omnidirectional completely transparent system satisfies the following zero shift condition:

[0043]

[0044] In formula 1, is the differential of the phase difference of two reflected waves, is the differential of the wave vector in the x direction, d A is the thickness of the A layer material, is the differential of the wave vector in the z direction of the A layer material, d B is the thickness of the B layer material, is the differential of the wave vector in the z direction of the B layer material, and ω0 is the frequency satisfying the OPT condition.

[0045] Further, the first structure layer C and the second structure layer D are both full dielectric materials. The full dielectric material has the characteristic of no dispersion, and the OPT can meet at multiple frequencies, thereby realizing a wideband OPT.

[0046] Still further, as shown in the figure, the adjacent first structure B and the second structure A form a lattice, and the lattice is arranged in a set lattice constant a. The lattice constant is the total width of the adjacent first structure B and the second structure A in the Z-axis direction. Figure 1

[0047] By changing the size of the lattice constant a, the frequency range of the omnidirectional completely transparent system can be adjusted. The smaller the lattice constant a, the greater the frequency range of the OPT.

[0048] Still further, by adjusting the arrangement period number of the first structure B and the second structure A in the Z-axis direction, the number and quality factor of the transmission peaks can be controlled. The more the period number, the more the number of transmission peaks, and the quality factor is also improved.

[0049] Still further, the angle a is set to be between 40° and 90°.

[0050] Still further, the arrangement period number of the first structure layer C and the second structure layer D is greater than or equal to 4. The more the period number of the first structure layer C and the second structure layer D in the X-axis direction, the better.

[0051] The application also provides an application of the wideband omnidirectional completely transparent system realized by the twisted structure in the field of optics and photonic devices.

[0052] The application provides a new research direction for photonics and materials, and opens an important path for realizing a high-efficiency, low-complexity wideband omnidirectional transparent system.

[0053] The application also provides an application of the wideband omnidirectional completely transparent system realized by the twisted structure in a building to realize complete transmission of signals. Specifically, the wideband omnidirectional completely transparent system realized by the twisted structure of the application is arranged in a wall of a building, or can be directly used for designing a wideband microwave transparent wall to improve the transmission rate of WI-FI and 5G signals.

[0054] The principle of the wideband omnidirectional completely transparent system realized by the twisted structure of the application will be described below.

[0055] In a multilayer structure composed of conventional isotropic or anisotropic materials, the interference cancellation condition for realizing complete transparency under normal incidence is:

[0056]

[0057] where k Az ​(d A ) and k Bz (d B ) represent the wave vector of the A and B layer materials along the Z direction (thickness) respectively, and N represents the number of periods of the structure. At the oblique incidence angle, since the IFC of the A and B materials is circular or elliptical, both k Az and k Bz will decrease as the incidence angle increases. In order to satisfy the above equation, only the frequency can increase, so the transmission peak moves to high frequency (blue shift). In order to overcome the physical limitation of the blue shift caused by the incidence angle in the conventional structure, by studying the zero shift condition of all incidence angles, it is obtained that the following needs to be satisfied:

[0058]

[0059] For conventional materials, resulting in a blue shift property, in order to satisfy equation 1, the following needs to be satisfied: and and vice versa. Physically, equation 1 is the condition for the compensation of the change in the propagation phase between the A and B materials.

[0060] Consider a simple case d A =d B , based on equation 1, when the OPT is achieved when TAMs (Tilted Anisotropic Metamaterials) in . When TM waves are incident on the xoy plane at an incidence angle θ, the effective relative permittivity tensor of the anisotropic metamaterial can be represented as:

[0061]

[0062] In equation 3, ε x represents the relative permittivity of the material in the x direction, and ε z represents the relative permittivity of the material in the z direction, which respectively reflects the response characteristics of the material to the electric field in the direction.

[0063] It is worth noting that the present application does not directly use anisotropic materials, but according to the effective medium theory, it is composed of two kinds of isotropic (C and D) media arranged alternately, at this time, ε x and ε z are represented as:

[0064] ε x =ρε C +(1-ρ)ε D Equation 4,

[0065]

[0066] In Equations 4 and 5, ε C and ε D are the dielectric constants of C and D respectively. d C and d D are the thicknesses of C and D respectively.

[0067] By introducing the effective relative permittivity tensor of anisotropic metamaterials into Maxwell's curl equations, the isofrequency equations of TM waves in anisotropic metamaterials are derived:

[0068]

[0069] Among them, k x represents the x-component of the wave vector in the anisotropic metamaterial, k z represents the z component of the wave vector in the anisotropic metamaterial. From Equation 6, we can see that in anisotropic metamaterials with positive relative permittivity tensor, the IFC of TM waves is elliptical. This is achieved by twisting a multilayer structure consisting of alternating two deep-subwavelength isotropic dielectric layers. It is worth noting that the IFC of this effective anisotropic metamaterial can be flexibly tuned by varying the material and structural parameters of the dielectric layers. It is also noted that because all dispersion-free all-dielectric materials are used, this OPT can be achieved at multiple frequencies, thus achieving broadband OPT.

[0070] like Figure 1 As shown, C and D, which are composed of alternating all-medium components, are rotated clockwise and counterclockwise by α, respectively. In this case, The anisotropic metamaterial with rotation +α is called positive TAM, and the anisotropic metamaterial with rotation -α is called negative TAM. The lattice constant is represented by a, where the thickness of positive and negative TAM is a / 2. Assume that OPT satisfies at frequency ω0, except that φ(ω0) = π, (or ) is satisfied for all incident angles (θ). Furthermore, the structure of the present invention is free of loss and dispersion. Therefore, multi-frequency OPT can be achieved.

[0071] like Figure 2 and Figure 3 As shown in the figure, the IFCs corresponding to the two TAMs are described. In order to illustrate the unique properties of these two IFCs, k x = 0.5k0 (corresponding to θ = 30°). Tangential wave vector conservation ensures that an electromagnetic wave with wave vector k1 (and the associated energy flow S1) incident from a negative TAM (α < 0) into a positive TAM (α > 0) will propagate along k2. Due to the law of causality, the energy flow in the positive TAM (α < 0) is along S2, resulting in negative refraction at the interface. Figure 3The lower half uses the equivalent TAMs of the alternating multi-layer films, and the results are consistent with the uniform material, which shows that this structure is suitable for the effective medium theory. Figure 2 In the middle, the red (purple) and green (pink) arrows represent the wave vector and group velocity in the negative and positive TAMs, respectively. Figure 3 The upper part is the magnetic field stitching in the uniform TAM, and the lower part is the magnetic field distribution in the multi-layer equivalent TAM. The electromagnetic wave is incident from the negative TAM to the positive TAM, and the yellow arrow represents the group velocity of both.

[0072] The experimental process of the wideband omnidirectional completely transparent system realized by the twist structure of the present application will be described below.

[0073] In order to verify the wideband OPT, the dielectric constant of medium C is selected as 2.2 and the dielectric constant of medium D is selected as 10.2. Their thicknesses are d C = 0.6a and d D = 0.2a, and the period number N is set as 6. As shown in Figure 4 , the transmission spectrum of TM wave is simulated with the finite element method. It is found that the five omnidirectional perfect transmission frequencies are located at 6.28c / a, 7.09c / a, 8.01c / a, 9.00c / a, and 9.76c / a. The transmission spectrum under the incident angles of 0°, 30° and 60° is shown in Figure 5 . It can be seen that all the transmission peaks (the peak value is very close to 1) almost overlap, indicating that the twist structure is completely transparent and insensitive to the incident angle. Figure 5 The points P1, P2, P3, P4 and P5 in Figures 7 to 9 are represented by each line. When the incident angle changes from 0° to nearly 90°, the frequency shift of the transmission peak is less than 1%. In practical applications, it is necessary to adjust the number and quality factor of the transmission peak by tuning the period number of the structure. When the period number is N = 8, as shown in Figures 7 to 9 , there are now six omnidirectional perfect transmissions instead of five. The corresponding frequencies are 6.24c / a, 6.79c / a, 7.51 / a, 8.41c / a, 9.21c / a, and 9.87c / a. When the period number increases, a sharper transmission peak is also generated by increasing the quality factor of the transmission peak. Through the transmission spectrum, it is proved that this twist structure can realize the wideband OPT. In order to clarify the physical mechanism of the OPT, the reflection phase of the twist structure with the period N = 6 and N = 8 is calculated, as shown in Figure 6 and 9 . On the one hand, within the transparent waveband, the reflection phase remains unchanged as the incident angle increases. On the other hand, it can be seen that the reflection phase corresponding to the omnidirectional complete transmission is 0.5π, indicating that the two reflected waves satisfy the condition of destructive interference. Figure 5 and Figure 8The transmission spectrum at a medium incidence angle of 0° is shown as a blue line, the transmission spectrum at an incidence angle of 30° is shown as a red line, and the transmission spectrum at an incidence angle of 60° is shown as a green line.

[0074] The present application also verifies the broadband OPT through microwave experiments. In order to meet the requirements of high and low dielectric constant, F4BM220 is selected as the dielectric material C and TP1020 is selected as the dielectric material D. According to the data table of the manufacturer, the relative dielectric constants of F4BM220 and TP1020 are 10.2 and 2.2 respectively in the frequency range of 0.5-10 GHz. The lattice constants of the sample are set as a = 30 mm, d C = 18 mm and d D = 6 mm. By using 6 periods in the z direction and 12 periods in the x direction, a sample size of 23 cm x 36 cm is obtained.

[0075] In the experiment, the sample is placed in the waveguide between two conical horns, each of which represents a transmitter and a receiver with an antenna. Rotating the sample allows flexible adjustment of the incidence angle. The two antennas are connected to an Agilent N5222A vector network analyzer through coaxial cables. In order to enhance transmission and reduce boundary reflection, the voids of the sample are filled with an absorbing material. Figure 10 The experimental setup is shown, including example images and schematic views. Figure 11 Images of the experimental sample are shown, which is produced using a conventional cutting method with a precision tolerance of ±0.15 mm. In this experiment, the conical angle is selected on the conventional angle antenna because it can emit a Gaussian beam with a larger waist radius, a smaller scattering angle and better angular resolution.

[0076] As Figure 12 shown, the transmission spectrum of the structure at 0°, 30° and 60° is first simulated. The data show that the transmission peaks remain basically unchanged and the transmission rate approaches 1. The inventors experimentally measured the transmission spectrum of the sample, as Figure 13 shown. In the frequency bands of 1.23 and 2.62 GHz, the measured results agree well with the simulation results. However, at 2.05, 2.48 and 2.84 GHz, the measured data shows a slight red shift and the transmission rate does not reach 1, which may be due to processing errors and material loss. By giving the magnetic field distribution at θ = 30° at 1.23, 1.62, 2.05, 2.48 and 2.84 GHz, the broadband OPT is further demonstrated. Figure 14 It is shown that there is basically no scattering of electromagnetic waves. As a direct application, this can be used to design a broadband microwave transparent wall to improve the transmission rate of Wi-Fi and 5G signals.

[0077] As Figure 15 shown, the present application also quantitatively compares the light transmission of the twisted structure, further confirming their unique behavior. AsFigure 15 The results show that the transmittance exceeds 95% for a super-wide incident angle (Θ < 83°) at 1.23, 1.62, 2.05, 2.48 and 2.84 GHz frequencies, as indicated by the shaded regions. These findings show that the twisted structure achieves almost broadband OPT.

[0078] The above embodiments of the present application have been described in detail with reference to the accompanying drawings. Those skilled in the art can make various modifications to the present application based on the above description. Thus, some of the details in the embodiments should not be construed as limiting the present application, and the scope of the present application will be defined by the appended claims.

Claims

1. A broadband omnidirectional fully transparent system implemented with a torsion structure, characterized in that: It comprises a plurality of first structures and second structures connected alternately, wherein the first structures are rotated in a clockwise direction along the Z axis by a set angle, and the second structures are rotated in a counterclockwise direction along the Z axis by a set angle; The first structure body and the second structure body each include a plurality of first structure layers and a second structure layer arranged in an upper and lower overlapping manner along the X-axis direction; The omnidirectional fully transparent system satisfies the following zero-shift conditions: In formula 1, is the differential of the phase difference between the two reflected waves, is the differential of the wave vector along the x direction, d A is the thickness of layer A material, is the differential of the wave vector of layer A along the z direction, d B is the thickness of layer B material, is the differential of the wave vector of the B layer material along the z direction, and ω0 is the frequency that meets the OPT condition.

2. The broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 1, characterized in that: The first structural layer and the second structural layer are both made of all-dielectric materials.

3. The broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 1, characterized in that: The adjacent first structures and the second structures form a lattice, and the lattice is arranged with a set lattice constant as a period.

4. The broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 3, characterized in that: The frequency range of the omnidirectional fully transparent system can be adjusted by changing the size of the lattice constant.

5. The broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 1, characterized in that: By adjusting the number of periods of the first structure and the second structure in the Z-axis direction, the number of transmission peaks and the quality factor can be controlled.

6. The broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 1, characterized in that: The setting angle ranges from 40° to 90°.

7. The broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 1, characterized in that: The number of arrangement periods of the first structural layer and the second structural layer is greater than or equal to 4.

8. Application of a broadband omnidirectional fully transparent system implemented by the torsional structure according to claim 1 in the field of optics and photonic devices.

9. Application of a broadband omnidirectional fully transparent system implemented by the torsion structure according to claim 1 in a building to improve signal transmittance.

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