A photonic crystal non-reciprocal imaging device

Abstract

The application discloses a photonic crystal non-reciprocal imaging device, which comprises a first copper plate, a second copper plate, a gyromagnetic material module, a ceramic dielectric column, a first wave-absorbing material module and a second wave-absorbing material module which are installed between the first copper plate and the second copper plate, a first magnet is installed on the side of the first copper plate away from the second copper plate and a second magnet is installed on the side of the second copper plate away from the first copper plate, and the first magnet and the second magnet are located in the z-axis direction. The photonic crystal non-reciprocal imaging device disclosed by the application realizes non-reciprocal DDS in a photonic crystal with an asymmetric hyperbolic band structure and anisotropic dissipation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical technology, and particularly relates to a photonic crystal non-reciprocal imaging device. BACKGROUND

[0002] In traditional optical systems, light propagation follows the principle of reciprocity. However, in some special application scenarios (such as security monitoring, military reconnaissance, telecommunications and privacy protection, etc.), it is necessary to break this symmetry and realize the imaging function under one-way or specific conditions. Non-reciprocal imaging can enable the input object (A) to be successfully converted to the output (B), i.e. the A→B process, while the image formation process of the backward path (B→A) is inhibited. Traditional methods can achieve one-way light transmission from one point to another. The most common approach is to use a quarter-wave plate and a polarization beam splitter; this point-to-point transmission method is sensitive to polarization and results in an output with only circular polarization. Other methods include using asymmetric isotropic dielectric gratings and double-layer metamaterials to create spatial mode transmission characteristics that differ in two directions. However, these methods are designed for relatively simple input modes and face challenges in off-axis directions, making it difficult to form an imaging system even with a relatively low numerical aperture. Training a set of continuous dielectric diffraction layers through deep learning can construct a one-way imaging function, but it faces problems such as device complexity, high cost, and large volume. In recent years, with the in-depth study of photonic crystals, their unique energy band structure provides the possibility for realizing new types of non-reciprocal optical imaging devices. SUMMARY

[0003] The main purpose of the present application is to provide a photonic crystal non-reciprocal imaging device, which realizes non-reciprocal DDS in a photonic crystal with an asymmetric hyperbolic energy band structure and anisotropic dissipation.

[0004] To achieve the above purpose, the present application provides a photonic crystal non-reciprocal imaging device, comprising a first copper plate, a second copper plate, and a gyromagnetic material module, a ceramic dielectric column, a first wave-absorbing material module and a second wave-absorbing material module installed between the first copper plate and the second copper plate, wherein:

[0005] The first copper plate is installed with a first magnet on the side away from the second copper plate, and the second copper plate is installed with a second magnet on the side away from the first copper plate, and the first magnet and the second magnet are located in the z-axis direction, wherein:

[0006] The ceramic dielectric column is used to break the C4z symmetry of the overall structure, and the ceramic dielectric column is offset along the y-axis, thereby destroying the MyT symmetry of the overall structure, (this destruction of mirror symmetry) thereby changing the coupling between the g (guided wave mode nested in parallel metal plates) and p mode (mixed mode of magnetic spin dipole interaction, represented as px±ipy) of the overall structure;

[0007] The first wave-absorbing material module and the second wave-absorbing material module are incorporated as loss, thereby generating a non-Hermitian, forming a non-centrosymmetric and anisotropic distribution in the energy dissipation spectrum, i.e. a non-reciprocal DDS.

[0008] As a further preferred technical solution of the above technical solution, the first magnet and the second magnet are used to apply a preset static magnetic field to break the time reversal symmetry.

[0009] As a further preferred technical solution of the above technical solution, under the influence of the momentum and lifetime asymmetric EFC, for the photonic crystal non-reciprocal imaging device, wherein:

[0010] The g mode propagating to the right produces a focusing effect on the incident electromagnetic wave and has (relatively) low loss, while the p mode propagating to the left produces a diffusing effect on the transmitted electromagnetic wave and has (relatively) high loss, thus supporting the non-reciprocal imaging function.

[0011] As a further preferred technical solution of the above technical solution, the first copper plate and the second copper plate are the same in length and width.

[0012] As a further preferred technical solution of the above technical solution, the gyromagnetic material module is made of yttrium iron garnet (YIG).

[0013] The beneficial effects of the invention are:

[0014] Non-reciprocal DDS is realized in photonic crystals with asymmetric hyperbolic band structures and anisotropic dissipation. The destruction of time reversal symmetry, geometric symmetry and non-Hermitian symmetry is highlighted to endow these photonic crystals with new propagation forms and loss distributions, so that electromagnetic waves can propagate efficiently along certain directions, while being hindered along other directions. In addition, the application of non-reciprocal DDS is also demonstrated to realize abnormal electromagnetic wave propagation phenomena, such as body state reflection-free transmission and imaging in photonic crystal plates without three-dimensional or multi-layer structures. Its non-reciprocal characteristics can be controlled by the symmetry of the photonic crystal, providing a reference for the construction of miniaturized non-reciprocal devices. The research work can be further expanded to multi-band or multi-layer twisted structures with different non-reciprocal behaviors, providing unprecedented flexibility for adjusting complex band structures. Although this work focuses on dissipative systems, it can be used in the future to explore lattices with active gain modulation, selective amplification and focusing to achieve highly directional and reconfigurable electromagnetic wave control in artificial media. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a comparison of the same frequency reciprocity and non-reciprocal DDS in the embodiments of the present application, wherein different color depths represent the lifetime of the mode on the EFC.

[0016] Figure 2 The figure is a schematic diagram of the non-reciprocal imaging principle realized by the non-reciprocal DDS in the embodiment of the present application.

[0017] Figure 3 The figure is a schematic diagram of the photonic crystal structure unit and parameter setting in the embodiment of the present application.

[0018] Figure 4 The figure is an electric field distribution of the imaging numerical simulation based on the non-reciprocal DDS in the embodiment of the present application.

[0019] Figure 5 The figure is an electric field distribution of the imaging experiment based on the non-reciprocal DDS in the embodiment of the present application.

[0020] The reference signs include: 1, a first copper plate; 2, a second copper plate; 3, a gyromagnetic material module; 4, a ceramic dielectric column; 5, a first wave-absorbing material module; 6, a second wave-absorbing material module; 7, a first magnet; 8, a second magnet. DETAILED DESCRIPTION

[0021] The following description is used to disclose the present application so that those skilled in the art can implement the present application. The preferred embodiments in the following description are only used as examples, and other obvious modifications can be thought of by those skilled in the art. The basic principles of the present application defined in the following description can be applied to other embodiments, modifications, improvements, equivalents and other technical solutions without departing from the spirit and scope of the present application.

[0022] In the preferred embodiments of the present application, those skilled in the art should note that the magnets and the like involved in the present application can be regarded as prior art.

[0023] The present patent relies on the national key research and development plan, the project name is: microwave cavity and superconducting artificial atom and solid meta-excitation strong coupling system of material state regulation; the project number is: 2022YFA1405200.

[0024] Preferred embodiments.

[0025] As Figures 1-5 shown, the present application proposes a non-reciprocal dynamic degeneracy splitting (DDS) phenomenon based on the symmetry breaking of photonic crystals, which realizes non-reciprocal imaging in a two-dimensional flat structure through reflection-free negative refraction.

[0026] The concept of non-reciprocal DDS can be illustrated by comparison with reciprocal DDS. Physically, each eigenvalue on the inverse space equi-frequency contour (EFC) represents an excited mode. In the Hermitian case, all excited modes are degenerate on the EFC because their imaginary parts are always zero. However, once the non-Hermitian term is introduced, the non-zero imaginary part broadens the EFC and breaks the degeneracy of the modes, as shown in Figure 1 (a). The degeneracy splitting caused by the excited mode lifetime difference at the same frequency has a dynamic result and is called dynamic degeneracy splitting (DDS). The reciprocal DDS shows a central symmetric mode lifetime distribution, as shown in Figure 1 (a), which limits its application to certain geometric conditions. By breaking the degeneracy of the excited mode lifetime in the momentum and making it have a non-central symmetric anisotropic lifetime distribution, it can be called non-reciprocal DDS, as shown in Figure 1 (b).

[0027] Non-reciprocal imaging can be performed in a two-dimensional photonic crystal slab by non-reciprocal DDS. The conventional negative refractive medium usually allows the occurrence of reflection behavior, but by the non-reciprocal DDS of the present work, the negative refraction phenomenon without reflection can be performed in the bulk state of the photonic crystal slab, which can be used for non-reciprocal imaging function. As shown in Figure 2 (a), when the incident wave enters the photonic crystal from the left through negative refraction and is focused back into the air through negative refraction again, this process is supported by the hyperbolic-like EFC induced by the non-reciprocal DDS, which suppresses the reflection inside the photonic crystal by dissipation. The required modes can propagate with low loss, and the interference between the incident signal and the reflected signal is suppressed, which reduces the mode crosstalk of the imaging process. In addition, as shown in Figure 2 (b) on the right, when the wave is incident into the photonic crystal in the opposite direction, there are basically no modes that can exist. Therefore, the non-reciprocal DDS characteristics in the present work can be used for non-reciprocal imaging, so that forward propagation can be successfully focused, while backward propagation cannot be imaged due to the energy dissipation in a wide range of momentum space.

[0028] As shown in Figure 3 , non-reciprocal dynamic degeneracy splitting (DDS) can be realized by breaking the symmetry of the photonic crystal, including time reversal, geometric structure and Hermitian. The present application discloses a photonic crystal non-reciprocal imaging device, the unit cell of the photonic crystal has a square lattice with C4z rotational symmetry, mainly studies the transverse magnetic (TM) mode in the photonic crystal, including a first copper plate 1, a second copper plate 2, and a gyromagnetic material module 3, a ceramic dielectric column 4, a first wave-absorbing material module 5 and a second wave-absorbing material module 6 installed between the first copper plate 1 and the second copper plate 2, wherein:

[0029] The first copper plate 1 is installed with a first magnet 7 on the side away from the second copper plate 2, and the second copper plate 2 is installed with a second magnet 8 on the side away from the first copper plate 1, and the first magnet 7 and the second magnet 8 are located in the z-axis direction, wherein:

[0030] The ceramic dielectric column 4 is used to break the C4z symmetry of the whole structure, and offset the ceramic dielectric column 4 along the y-axis (as shown in Figure 3 The offset center of the first / second copper plate), thereby destroying the MyT symmetry of the whole structure, (the destruction of this mirror symmetry) thereby changing the coupling between the g (the guided wave mode nested in the parallel metal plate) and the p mode (the mixed mode of the magnetic spin dipole interaction, represented as px±ipy) of the whole structure;

[0031] The first microwave absorbing material module 5 and the second microwave absorbing material module 6 are included as losses, thereby generating a non-Hermite, forming a non-central symmetric and anisotropic distribution in the energy dissipation spectrum, that is, a non-reciprocal DDS, as shown in Figure 1 (b). The EFC of momentum and lifetime asymmetry can realize the control of the dynamic behavior of the mode.

[0032] Specifically, the first magnet 7 and the second magnet 8 are used to apply a preset static magnetic field to break the time reversal symmetry.

[0033] More specifically, under the influence of the EFC of momentum and lifetime asymmetry, for the photonic crystal non-reciprocal imaging device, wherein:

[0034] The g mode propagating to the right produces a focusing effect on the incident electromagnetic wave and has a (relatively) low loss, while the p mode propagating to the left produces a diffusion effect on the transmitted electromagnetic wave and has a (relatively) high loss, thereby supporting the non-reciprocal imaging function.

[0035] Further, the length and width of the first copper plate 1 and the second copper plate 2 are the same, as shown in Figure 3 The working process of the present application is illustrated by an example of a gyromagnetic photonic crystal non-reciprocal imaging device working near a frequency of 7.6 GHz:

[0036] Including a gyromagnetic material yttrium iron garnet (YIG), a ceramic dielectric column (dielectric constant ε=6.15), parallel metal copper plates (i.e. first copper plate and second copper plate), microwave absorbing material (ε=1.8-1.2i, i.e. first microwave absorbing material module and second microwave absorbing material module), as shown in Figure 3 The specific parameters are: p x =p y =17.4mm, d=6mm, h=5mm, h1=5.6mm, h2=6mm, w=2mm. The thickness of the copper plate is 4mm, the radius of the magnet is 6mm, and the thickness is 3mm: p xand p y represents the length and width of the first / second copper plate, d represents the diameter of the gyromagnetic material module (also represents the diameter of the first / second magnet), h represents the distance between the first copper plate and the second copper plate, h1 represents the width of the ceramic dielectric column, h2 represents the length and width of the first / second wave-absorbing material module.

[0037] Further, the material of the gyromagnetic material module is yttrium iron garnet (YIG).

[0038] A non-reciprocal imaging mechanism based on photonic crystal slabs is revealed by the anisotropic loss distribution of quasi-hyperbolic bands caused by non-reciprocal DDS. Non-reciprocal imaging means that the imaging process is allowed only along a certain direction, while it is suppressed when the wave propagates along the opposite path. To verify the proposed properties, two comparative experiments are carried out: one is forward propagation of the wave from air through the sample, and the other is backward propagation. The setup for forward propagation is shown in Figure 4 (a), which corresponds to the case described in Figure 2 (a). For backward propagation, the position of the source and other auxiliary media (such as wave-absorbing material) are slightly adjusted.

[0039] Figure 4 The E z field distribution obtained by numerical simulation demonstrates the unidirectional focusing achieved by the photonic crystal slab structure. In the simulation setup, the dipole source is located near the photonic crystal, as shown in Figure 4 (a). As expected in Figure 2 (a), the wave radiated by the point source is negatively refracted when it crosses the interface of the photonic crystal. At the same time, there is no reflected wave inside the photonic crystal due to the unequal efficiency of the two quasi-hyperbolic band branches on the equal-energy surface, which indicates the realization of reflection-free negative refraction. Generally, EFCs with symmetric loss inevitably produce unwanted interface reflections. However, through the asymmetric dissipation distribution inside the photonic crystal in this work, the interface reflection is suppressed, which can be seen from the fast Fourier transform (FFT) results of the photonic crystal in Figure 4 (a), where there is no obvious reflected momentum. The measured near-field intensity distribution is highly consistent with the predicted EFC analysis at this frequency, as shown in Figure 5 (a), which proves the successful imaging in the expected direction. In contrast, in Figure 4 (b) and 5(b), due to the large corresponding mode loss, the reverse direction imaging cannot be supported. Therefore, non-reciprocal imaging can be achieved by the photonic crystal slab, which proves the effectiveness of the invention in terms of non-reciprocal imaging and focusing ability.

[0040] It is worth mentioning that the technical features such as the magnet involved in the present patent application should be regarded as the prior art, the specific structure, working principle and possible control mode and spatial arrangement mode of these technical features can be selected by using the conventional selection in the field, and should not be regarded as the invention point of the present patent, and the present patent will not be further expanded and described in detail.

[0041] For those skilled in the art, the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalents, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A photonic-crystal non-reciprocal imaging device, characterized by, The application relates to a photonic crystal nonreciprocal imaging device, which comprises a first copper plate, a second copper plate, a gyromagnetic material module, a ceramic dielectric column, a first wave-absorbing material module and a second wave-absorbing material module which are installed between the first copper plate and the second copper plate, wherein: The first copper plate is provided with a first magnet on the side far from the second copper plate, and the second copper plate is provided with a second magnet on the side far from the first copper plate, and the first magnet and the second magnet are located in the z-axis direction. The ceramic dielectric column is used for breaking the C4z symmetry of the whole structure and offsetting the ceramic dielectric column along the y-axis, so as to destroy the MyT symmetry of the whole structure and change the coupling between the g mode and the p mode of the whole structure. The first wave-absorbing material module and the second wave-absorbing material module are taken as loss, so as to generate a non-Hermite, form a non-central symmetry and anisotropic distribution in an energy dissipation spectrum, namely a nonreciprocal DDS.

2. The photonic-crystal non-reciprocal imaging device according to claim 1, wherein, The first magnet and the second magnet are used for exerting a preset static magnetic field to break the time reversal symmetry.

3. The photonic-crystal non-reciprocal imaging device according to claim 1, characterized in that, Under the influence of the momentum and lifetime asymmetry EFC, for the photonic crystal nonreciprocal imaging device, wherein: The g mode propagating to the right produces a focusing effect on the incident electromagnetic wave and has low loss, and the p mode propagating to the left produces a diffusion effect on the transmitted electromagnetic wave and has high loss, so as to support the nonreciprocal imaging function.

4. The photonic-crystal non-reciprocal imaging device according to claim 1, characterized in that, The length and width of the first copper plate and the second copper plate are the same.

5. The photonic-crystal non-reciprocal imaging device according to claim 1, wherein The material of the gyromagnetic material module is yttrium iron garnet. The application also relates to a preparation method of the photonic crystal nonreciprocal imaging device.

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