Broadband omni-directional completely transparent system realized by torsion structure and application thereof

Abstract

The invention relates to a broadband omni-directional completely transparent system realized by a torsion structure and application thereof, the system comprises a plurality of first structural bodies and second structural bodies which are alternately connected, and the first structural bodies rotate by a set angle clockwise in the Z-axis direction. The second structural body rotates anticlockwise by a set angle in the Z-axis direction; each of the first structural body and the second structural body comprises a plurality of first structural layers and second structural layers which are arranged in an up-and-down overlapping manner in the X-axis direction; the omni-directional completely transparent system satisfies the following zero shift condition. According to the system provided by the invention, the rotation of IFCs (Iso-frequency curves) in a k space is realized by twisting a plurality of layers of all-dielectric materials which are alternately arranged, and the broadband OPT is realized under the condition of zero reflection.

Description

Technical Field

[0001] The invention relates to the technical field of optical systems, and in particular to a broadband omnidirectional fully transparent system realized by a torsion structure and applications thereof. Background Art

[0002] In optical systems, transparent materials play a vital role in the manipulation of electromagnetic waves. In this field, omnidirectional perfect transparency (OPT) is particularly important and provides broad prospects for the application of optical and photonic devices. However, achieving OPT is a huge challenge because it requires materials to be able to fully transmit light at all incident angles. The emergence of metamaterials and photonic crystals has changed the way electromagnetic waves are controlled and provided new strategies for achieving omnidirectional transparency. For example, OPT of transverse magnetic waves (TM) and transverse electric waves (TE) is achieved by combining the Brewster angle and complex electromagnetic coupling response, omnidirectional impedance matching is achieved by using the spatial dispersion parameters of photonic crystals, or angle-insensitive longitudinal impedance matching is achieved by designing metasurfaces. However, existing methods are limited by complex electromagnetic interactions and single frequency, which hinders their practical application. The realization of broadband OPT with simple structures, especially in one-dimensional systems, is still a scientific problem that needs to be solved urgently. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a broadband omnidirectional fully transparent system and its application realized by a torsional structure, so as to solve the problem that the existing methods for realizing omnidirectional transparency are subject to complex electromagnetic interactions and single-frequency limitations, thus hindering their practical application, and the problem that broadband OPT with a simple structure is difficult to realize.

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

[0005] The present invention provides a broadband omnidirectional fully transparent system realized by a torsion structure, comprising a plurality of first structures and second structures connected alternately, wherein the first structures are rotated in a clockwise direction at a set angle in the Z-axis direction, and the second structures are rotated in a counterclockwise direction at a set angle in the Z-axis direction;

[0006] The first structure body and the second structure body each include a plurality of first structure layers and second structure layers which are overlapped vertically along the X-axis direction;

[0007] The omnidirectional fully transparent system satisfies the following zero-shift condition:

[0008]

[0009] 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 satisfies the OPT condition.

[0010] A further improvement of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention is that both the first structural layer and the second structural layer are made of all-dielectric materials.

[0011] A further improvement of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention is 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.

[0012] A further improvement of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention is that the frequency range of the omnidirectional fully transparent system can be adjusted by changing the size of the lattice constant.

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

[0014] A further improvement of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention is that the range of the set angle is between 40° and 90°.

[0015] A further improvement of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention is that the number of arrangement periods of the first structural layer and the second structural layer is greater than or equal to 4.

[0016] The present invention also provides an application of a broadband omnidirectional fully transparent system realized by a twisted structure in the optical field and photonic devices.

[0017] The present invention further provides an application of a broadband omnidirectional fully transparent system realized by a twisted structure in a building to improve the transmittance of signals.

[0018] The broadband omnidirectional fully transparent system realized by the torsion structure of the present invention and the beneficial effects of its application are:

[0019] The system of the present invention realizes the rotation of IFCs (Iso-frequency curves) in k-space by twisting multiple layers of alternating all-dielectric materials, and realizes broadband OPT under zero reflection conditions. The present invention not only solves the problem of high complexity and limitation of single-frequency transparency in traditional designs, but also explores a new physical method to achieve broadband omnidirectional transparency on a low-loss and feasible platform, providing a new research direction for photonics and materials science, and opening up an important path for achieving high-efficiency, low-complexity, wide-band omnidirectional transparency.

[0020] The system of the present invention can adjust the frequency range and loan of OPT by changing structural parameters, such as the size of the lattice constant.

[0021] The system of the present invention can achieve flexible control of the number of transmission peaks and quality factors by adjusting the number of periods of the structure, thereby improving the applicability of the material in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of the structure of an embodiment of a broadband omnidirectional fully transparent system implemented by the torsional structure of the present invention.

[0023] Figure 2 Corresponding IFCs of positive and negative TAMs in the broadband omnidirectional fully transparent system implemented by the twisted structure of the present invention.

[0024] Figure 3 The magnetic field distribution of uniform materials and equivalent materials in a broadband omnidirectional fully transparent system realized by the twisted structure of the present invention.

[0025] Figure 4 The relationship between the transmittance, incident angle and frequency of a broadband omnidirectional fully transparent system with a period number of 6 realized by the twisted structure of the present invention.

[0026] Figure 5 The transmission spectra corresponding to the incident angles of 0°, 30° and 60° with a period number of 6 for the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention.

[0027] Figure 6 The relationship between the structural reflection phase, the incident angle and the frequency of the broadband omnidirectional fully transparent system with a period number of 6 realized by the twisted structure of the present invention.

[0028] Figure 7 The relationship between the transmittance, incident angle and frequency of a broadband omnidirectional fully transparent system with a period number of 8 realized by the twisted structure of the present invention.

[0029] Figure 8 The transmission spectra corresponding to the incident angles of 0°, 30° and 60° with a period number of 8 for the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention.

[0030] Fig. 9 The relationship between the structural reflection phase, the incident angle and the frequency of the broadband omnidirectional fully transparent system with a period number of 8 realized by the twisted structure of the present invention.

[0031] Fig.10 Schematic diagram of the experimental device of the broadband omnidirectional fully transparent system realized by the torsional structure of the present invention.

[0032] Fig.11 Schematic diagram of an experimental sample of a broadband omnidirectional fully transparent system implemented by the torsional structure of the present invention.

[0033] Fig.12 This is a simulated transmission spectrum diagram at 0°, 30° and 60° in the experiment of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention.

[0034] Fig.13 The experimental transmission spectra at 0°, 30° and 60° in the experiment of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention.

[0035] Fig.14 When the incident angle of the experiment of the broadband omnidirectional fully transparent system realized by the torsion structure of the present invention is 30°, the normalized magnetic field distribution is at 1.23, 1.62, 2.05, 2.48, and 2.84 GHz.

[0036] Fig.15 The projected spectra of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention at different frequencies and with different incident angles. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] See also Figure 1The present invention provides a broadband omnidirectional fully transparent system and its application realized by a torsional structure, proposes a zero shift condition, realizes the rotation of the IFC in the k-space by twisting the all-dielectric material composed of multiple layers arranged alternately, and realizes broadband OPT under zero reflection conditions. Finally, the inventors adjust the frequency range and bandwidth of the OPT by changing the structural and material parameters, further adjust the number of periods of the metamaterial, realize flexible control of the number of transmission peaks and quality factors, and improve the applicability of the material in practical applications. The inventors verified through simulation experiments and microwave experiments that the structure realizes broadband omnidirectional transparency, which not only solves the problem of high complexity and limited single-frequency transparency in traditional designs, but also explores a new physical method to realize broadband omnidirectional transparency on a low-loss and feasible platform, providing a new research direction for photonics and materials science, and opening up an important path for realizing high-efficiency, low-complexity, wide-band omnidirectional transparency. The broadband omnidirectional fully transparent system and its application realized by the torsional structure of the present invention are described below in conjunction with the accompanying drawings.

[0039] See also Figure 1 , showing a schematic diagram of a structure of an embodiment of a broadband omnidirectional fully transparent system implemented by a twisted structure of the present invention. Figure 1 , the broadband omnidirectional fully transparent system realized by the torsional structure of the present invention is described.

[0040] like Figure 1 As shown, the broadband omnidirectional fully transparent system realized by the twisting structure of the present invention comprises a plurality of first structures B and second structures A connected alternately, the first structure B rotates in the clockwise direction of the Z axis by a setting angle α, and the second structure A rotates in the counterclockwise direction of the Z axis by a setting angle α;

[0041] The first structure body B and the second structure body A both include a plurality of first structure layers C and second structure layers D which are overlapped vertically along the X-axis direction;

[0042] The omnidirectional fully transparent system satisfies the following zero-shift conditions:

[0043]

[0044] 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 satisfies the OPT condition.

[0045] Furthermore, the first structure layer C and the second structure layer D are all made of dielectric materials. The dielectric materials have the characteristic of no dispersion, and this OPT can be satisfied at multiple frequencies, thereby realizing broadband OPT.

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

[0047] The frequency range of the omnidirectional fully transparent system can be adjusted by changing the size of the lattice constant a. The smaller the lattice constant a is, the larger the frequency range of the OPT is.

[0048] Furthermore, by adjusting the number of periods of the first structure B and the second structure A in the Z-axis direction, the number of transmission peaks and the quality factor can be controlled. The more the number of periods, the more transmission peaks and the higher the quality factor.

[0049] Furthermore, the angle α is set in a range between 40° and 90°.

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

[0051] The present invention also provides an application of a broadband omnidirectional fully transparent system realized by a twisted structure in the optical field and photonic devices.

[0052] The present invention provides a new research direction for photonics and materials science, and opens up an important path for achieving high-efficiency, low-complexity, wide-band omnidirectional transparency.

[0053] The present invention further provides an application of a broadband omnidirectional fully transparent system implemented by a torsion structure in a building to achieve complete transmission of signals. Specifically, the broadband omnidirectional fully transparent system implemented by the torsion structure of the present invention is arranged in the wall of the building, or can be directly used to design a broadband microwave transparent wall to improve the transmittance of WI-FI and 5G signals.

[0054] The principle of the broadband omnidirectional fully transparent system realized by the twisted structure of the present invention is described below.

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

[0056]

[0057] Among them, k Az(d A ) and k Bz (d B ) represent the wave vectors of the A layer material and the B layer material along the Z direction (thickness), and N represents the number of periods of the structure. At oblique incident angles, since the IFCs of the A and B materials are circular or elliptical, k Az and k Bz will decrease with the increase of the incident angle. In order to satisfy the above equation, the frequency can only increase, so the transmission peak moves to high frequency (blue shift). In order to overcome the physical limitation of the incident angle causing blue shift in the traditional structure, by studying the zero shift conditions for all incident angles, it is found that the following conditions need to be satisfied:

[0058]

[0059] For conventional materials, Leading to the blue shift property, in order to satisfy equation 1, it is necessary to satisfy and Physically, Equation 1 is the condition for compensating the propagation phase change between materials A and B.

[0060] Consider a simple case d A =d B , based on formula 1, when TAMs (Tilted Anisotropic Metamaterials) When , OPT is realized. Considering the TM wave incident on the xoy plane at an incident angle θ, the effective relative dielectric constant tensor of the anisotropic metamaterial can be expressed as:

[0061]

[0062] In formula 3, ε x represents the relative dielectric constant of the material in the x direction, ε z It represents the relative dielectric constant of the material in the z direction, and reflects the response characteristics of the material to the electric field in this direction.

[0063] It is worth noting that the present invention does not directly use anisotropic materials, but uses two isotropic media (C and D) arranged alternately according to the effective medium theory. At this time, ε x and ε z It is expressed as:

[0064] ε x =ρε C +(1-ρ)ε D Formula 4,

[0065]

[0066] In Equation 4 and Equation 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 equation, the isofrequency line 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 two alternating deep subwavelength isotropic dielectric layers. It is worth mentioning that the IFC of this effective anisotropic metamaterial can be flexibly adjusted by changing the material and structural parameters of the dielectric layer. It is also noted that since all-dielectric materials without dispersion are used, this OPT can be satisfied at multiple frequencies, thus achieving broadband OPT.

[0070] like Figure 1 As shown, C and D, which are composed of all dielectric components, are rotated clockwise and counterclockwise by α, respectively. In this case, it can be achieved 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). In addition, there is no loss and dispersion in the structure of the present invention. 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 illustrated. In order to illustrate the unique properties of these two IFCs, k x = 0.5k0 (corresponding to θ = 30°). The conservation of the tangential wave vector ensures that the electromagnetic wave with wave vector k1 (and the associated energy flow S1) incident from the negative TAM (α < 0) to the positive TAM (α > 0) will propagate along the k2 direction. Due to the law of causality, the energy flow in the positive TAM (α < 0) is along the S2 direction, resulting in negative refraction at its interface. Figure 3The lower part uses the equivalent TAMs of alternating multilayer films, and the results are consistent with those of homogeneous materials, indicating that this structure is applicable to the effective medium theory. Figure 2 In the figure, the red (lavender) and green (pink) arrows indicate the wave vector and group velocity in the negative and positive TAM, respectively. Figure 3 The upper part shows the magnetic field patching in the uniform TAM, and the lower part shows 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 arrows indicate the group velocity of the two.

[0072] The following is an explanation of the experimental process of the broadband omnidirectional fully transparent system implemented by the torsion structure of the present invention.

[0073] In order to verify the broadband OPT, the dielectric constant of medium C is selected to be 2.2 and the dielectric constant of medium D is selected to be 10.2. Their thicknesses are d C = 0.6a and d D = 0.2a, and set the number of cycles N = 6. Figure 4 As shown in the figure, the finite element method is used to simulate the relationship between the transmission spectrum of TM waves and the frequency and incident angle. It is found that the frequencies of the five omnidirectional perfect transmittances are located at 6.28c / a, 7.09c / a, 8.01c / a, 9.00c / a, and 9.76c / a. The transmission spectra at 0°, 30°, and 60° incident angles are shown in Figure 5 As shown, all transmittance peaks (the peak values ​​are very close to 1) almost overlap, indicating that the twisted structure is completely transparent and insensitive to the incident angle. Figure 5 Points P1, P2, P3, P4 and P5 in are represented by each line. When the incident angle varies from 0° to nearly 90°, the frequency shift of the transmission peak is less than 1%. In practical applications, it is very necessary to be able to adjust the number and quality factor of transmission peaks by tuning the number of periods of the structure. When the number of periods is N = 8, as shown in Figures 7 to 9 As shown, there are now 6 omnidirectional perfect transmittances instead of 5. 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 number of periods increases, a sharper transmission peak is also produced by improving the quality factor of the transmission peak. The transmission spectrum proves that this twist structure can achieve broadband OPT. In order to clarify the physical mechanism of OPT, the reflection phases of the twist structures with periods N=6 and N=8 are calculated, as shown in Figure 6 and 9 As shown. On the one hand, within the transparent band, as the incident angle increases, the reflection phase remains unchanged. On the other hand, it can be seen that the reflection phase corresponding to the omnidirectional complete transmittance is 0.5π, indicating that the two reflected waves meet the destructive interference condition. Figure 5 and Figure 8The transmission spectrum at an incident angle of 0° is the blue line, the transmission spectrum at an incident angle of 30° is the red line, and the transmission spectrum at an incident angle of 60° is the green line.

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

[0075] In the experiment, the sample was placed in a waveguide between two conical horns, each representing a transmitter and a receiver with an antenna. Rotating the sample allowed for flexible adjustment of the incident angle. The two antennas were connected to an Agilent N5222A vector network analyzer via coaxial cables. To enhance transmission and reduce boundary reflections, the gaps in the sample were filled with absorbing materials. Fig.10 The experimental setup is shown, including example images and a schematic view. Fig.11 An image of an experimental sample is shown, which was produced using a conventional cutting method with an accuracy tolerance of ±0.15 mm. In this experiment, the cone angle was chosen over a conventional corner antenna because it can emit a Gaussian-like beam with a larger waist radius, smaller scattering angle, and better angular resolution.

[0076] like Fig.12 As shown in FIG. 1 , the transmission spectra of the structure at 0°, 30° and 60° are first simulated. The data show that the transmission peak remains basically unchanged and the transmittance is close to 1. The inventors experimentally measured the transmission spectrum of the sample, as shown in FIG. Fig.13 As shown. In the 1.23 and 2.62 GHz frequency bands, the measured results are in good agreement with the simulation results. However, at 2.05, 2.48, and 2.84 GHz, the measured data show a slight red shift and the transmittance does not reach 1, which may be due to processing errors and material losses. The broadband OPT is further illustrated by giving the magnetic field distribution at θ = 30° at 1.23, 1.62, 2.05, 2.48, and 2.84 GHz. Fig.14 "We show essentially no electromagnetic wave scattering. As an immediate application, this could be used to design broadband microwave-transparent walls to improve the transmittance of Wi-Fi and 5G signals."

[0077] like Fig.15 As shown, the present invention also quantitatively compares the light transmittance of the twisted structures, further confirming their unique behavior. Fig.15 As shown in the shaded area of ​​, the results show that the transmittance exceeds 95% at ultra-wide incident angles (θ < 83°) at frequencies of 1.23, 1.62, 2.05, 2.48, and 2.84 GHz. These findings indicate that the twisted structure achieves nearly broadband OPT.

[0078] The present invention is described in detail above in conjunction with the embodiments of the drawings, and those skilled in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not constitute limitations of the present invention, and the scope of protection of the present invention shall be defined by the scope of the attached claims.

Claims

1. A broadband omnidirectional fully transparent system realized by 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 second structure layers which are overlapped vertically along the X-axis direction; The omnidirectional fully transparent system satisfies the following zero-shift condition: 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 satisfies 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 realized by the twisted structure as claimed in claim 1 in the optical field and photonic devices.

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

Images