A nano-optical structure for implementing the phenomenon of electromagnetic induced transparency

Abstract

The application relates to a nano-optical structure for realizing an electromagnetic induction transparency phenomenon, comprising a surface plasmon effect layer and a guided mode resonance layer, wherein the surface plasmon effect layer is located above the guided mode resonance layer. The application can realize the electromagnetic induction transparency phenomenon on the premise that a unit cell structure is symmetrical.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-nano photonics, and in particular to a nano-optical structure for realizing electromagnetically induced transparency. BACKGROUND

[0002] Electromagnetically induced transparency (EIT) is a kind of electromagnetic phenomenon in a three-level atomic system due to the interference between excitation paths and energy levels on the atom. The EIT image has a clear narrow window, which has great application value in nonlinear optical processing, ultrafast switching and slow light devices, etc. In recent years, researchers have found EIT-like phenomenon in some classic structures similar to atomic systems, which is called EIT-like. Common systems for realizing EIT-like include metal-dielectric-metal waveguide, metal polymer, photonic crystal and metamaterial, etc. Among them, artificial electromagnetic metamaterial based on subwavelength unit structure has excellent electromagnetic properties, such as negative refractive index, super-resolution and polarization conversion, etc., which makes the study of metamaterials become the forefront of research in the field of quantum communication, nano-optics, etc. in recent years.

[0003] In recent years, researchers have used metamaterials to realize EIT phenomenon in order to study its slow light effect and other characteristics. Generally speaking, due to the symmetry breaking of the structure, the mutual coupling effect between different modes of light waves will produce EIT phenomenon. However, in many previous studies based on metamaterials, EIT phenomenon needs to break the symmetry of the structure, which undoubtedly brings difficulties to etching processing. How to realize EIT phenomenon under the premise of maintaining the symmetry of the unit cell structure (i.e. symmetry about x and y axes) is a technical problem to be solved. SUMMARY

[0004] The purpose of the present application is to provide a nano-optical structure for realizing electromagnetically induced transparency phenomenon, which can realize electromagnetically induced transparency phenomenon under the premise of maintaining the symmetry of the unit cell structure.

[0005] The technical solution for realizing the purpose of the present application is as follows:

[0006] A nano-optical structure for realizing electromagnetically induced transparency phenomenon, comprising a surface plasmon effect layer and a guided mode resonance layer, wherein the surface plasmon effect layer is located above the guided mode resonance layer.

[0007] Further, a dielectric substrate layer is provided between the surface plasmon effect layer and the guided mode resonance layer.

[0008] Further, the surface plasmon effect layer is made of a metal material, and the guided mode resonance layer is made of a high refractive index material.

[0009] Further, the surface plasmon effect layer is provided with a cross-shaped hollow resonant cavity, a circular hollow resonant cavity or a square hollow resonant cavity.

[0010] Further, the surface plasmon effect layer is made of silver or gold, the guided mode resonance layer is made of silicon, and the dielectric substrate layer is made of silicon dioxide.

[0011] Further, the dielectric substrate layer has a refractive index n = 1.45.

[0012] Further, the silicon has a value of [wavelength, refractive index real part, refractive index imaginary part] = [688 708 729 751 774 799 826, 3.788 3.764 4 3.741 9 3.720 4 3.699 9 3.680 1 3.661 1, 0.011 2 0.009 92 0.008 65 0.007 45 0.006 3 0.005 22 0.004 21], wherein the unit of wavelength is nm.

[0013] Further, the nano-optical structure is a periodic structure composed of a plurality of unit cell structures, the X direction and the Y direction are periodic, and the Z direction is single, and each unit cell structure is composed of the surface plasmon effect layer, the dielectric substrate layer and the guided mode resonance layer from top to bottom.

[0014] Further, the unit cell structure is symmetrically arranged about the X axis and the Y axis.

[0015] Further, the incident light is linearly polarized +z direction normal incidence, and the linearly polarized wavelength range is 700 nm ~ 800 nm.

[0016] The present application has the beneficial effects:

[0017] The present application includes a surface plasmon effect layer and a guided mode resonance layer, and the surface plasmon effect layer is located above the guided mode resonance layer. Compared with the prior art, the present application combines the surface plasmon effect and the guided mode resonance characteristics of high refractive index materials to realize the EIT-like phenomenon, and proposes a new structure to realize the electromagnetic induced transparency phenomenon, while maintaining the symmetry of the x and y directions of the unit cell structure.

[0018] The application is characterized in that a dielectric substrate layer is arranged between the surface plasmon effect layer and the guided mode resonance layer; the surface plasmon effect layer is made of metal material, and the guided mode resonance layer is made of high refractive index material; the surface plasmon effect layer is provided with a cross-shaped hollow resonant cavity, a circular hollow resonant cavity or a square hollow resonant cavity. The application further guarantees the significant effect of the electromagnetic induced transparency phenomenon through the above specific structure. The structural system of the application is relatively simple, and the system reflection spectrum can produce a clear EIT window through structural parameter optimization. When only the metal cross-shaped slit resonant cavity is used, the reflection spectrum of the system shows a typical Lorentz line type; when the dielectric substrate and the high refractive index material are added, a clear transparent window appears near the position of the original Lorentz valley, that is, a typical EIT spectrum line. In addition, changing the refractive index of the dielectric substrate can linearly change the transparent window. The application realizes the EIT-like under the premise of maintaining the symmetry of the microstructure, and has the advantages of simple technical scheme and strong operability, and greatly expands the application range of the surface plasmon metamaterial.

[0019] The refractive index of the dielectric substrate layer is n=1.45; the value of silicon is [wavelength, refractive index real part, refractive index imaginary part]=[688 708 729 751 774 799 826, 3.788 3.7644 3.7419 3.7204 3.6999 3.6801 3.6611, 0.0112 0.00992 0.00865 0.00745 0.0063 0.00522 0.00421], wherein the unit of wavelength is nm; the incident light is linearly polarized+z direction normal incidence, and the wavelength range of the linearly polarized light is 700 nm-800 nm. The application further guarantees the significant effect of the electromagnetic induced transparency phenomenon through the selection of the above parameters. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the unit cell structure of the application;

[0021] Figure 2 It is the reflection spectrum of the substrate and silicon after structural parameter optimization in the application;

[0022] Figure 3 It is a normalized electric field and magnetic field modulus distribution diagram when the wavelength of light is λ=754 nm;

[0023] Figure 4 It is the reflection spectrum corresponding to the substrates with different refractive indexes. DETAILED DESCRIPTION

[0024] The application will be described in detail below with reference to the embodiments shown in the drawings, but it should be noted that these embodiments are not a limitation on the application, and equivalent transformations or substitutions of function, method, or structure made by those of ordinary skill in the art based on these embodiments are within the protection scope of the application.

[0025] The nano-optical structure of the application is a periodic structure composed of a plurality of unit cell structures, the X direction and the Y direction are periodic, and the Z direction is single.

[0026] As shown in Figure 1 , the Z direction of the unit cell structure is composed of a surface plasmon effect layer 1 (thickness t1), a dielectric substrate layer 2 (thickness t2), and a guided mode resonance layer 3 (thickness t3) from top to bottom. The surface plasmon effect layer 1 is provided with a cross-shaped hollow resonant cavity, a circular hollow resonant cavity, or a square hollow resonant cavity. In this embodiment, a cross-shaped hollow resonant cavity 4 is adopted. The unit cell structure is symmetrically arranged about the X and Y axes, and the cross-shaped hollow resonant cavity 4 is symmetric about the x and y axes, with a length L and a width w.

[0027] The surface plasmon effect layer 1 is made of silver or gold. In this embodiment, it is made of silver. Its dispersion relationship is represented by the drude model: (ε ∞ , ω p , γ)=(3.7, 9.1 eV, 0.018 eV), where ε ∞ is the infinite dielectric constant, ω p is the plasma oscillation frequency, and γ is the collision frequency.

[0028] The guided mode resonance layer 2 is made of a high refractive index material. In this embodiment, the guided mode resonance layer is made of silicon. The value of silicon is [wavelength, refractive index real part, refractive index imaginary part]=[688 708 729 751 774 799 826, 3.788 3.7644 3.7419 3.7204 3.6999 3.6801 3.6611, 0.0112 0.00992 0.00865 0.00745 0.0063 0.00522 0.00421], where the unit of wavelength is nm. The dielectric substrate layer 3 is made of silicon dioxide, and the dielectric substrate layer has a refractive index n=1.45.

[0029] The incident light is linearly polarized +z direction normal incidence, and the linearly polarized wavelength range is 700nm-800nm. The initial state of the light wave is |0> state, and after the cross-shaped hollow resonant cavity 4, the surface plasmon effect is excited to be |1> state; then to the guided mode resonant layer 2, the guided mode resonance is excited to be |2> state. The light wave experiences the following two processes, that is, |0>→|1> and |0>→|1>→|2>→|1>. The mutual coupling of the two light waves will produce the EIT phenomenon in the reflection spectrum of the system.

[0030] The reflection spectra with and without substrates and silicon obtained by simulation are shown in Figure 2 The gray solid line represents the reflection spectrum without substrates and silicon, that is, only the cross-shaped hollow resonant cavity, which is a typical Lorentz line type; the black solid line represents the reflection spectrum after adding the substrates and silicon, which is a typical EIT line type. It can be seen from the figure that at λ=754nm, a transparent window appears in the vicinity of the original reflection valley. At this time, the structure parameters are: period Px=Py=680nm, w=50nm, L=460nm, t1=t2=t3=215nm. Figure 3 The normalized electric field and magnetic field mode value distribution diagrams when the wavelength of the incident light is λ=754nm are given. It can be seen from the figure that the electric field energy is mainly concentrated in the metal slit resonant cavity, and the magnetic field energy is mainly concentrated in the guided mode resonant layer (silicon layer). Figure 4 The variation law of the reflection spectrum with different refractive index substrates is given. It can be seen from the figure that the electromagnetic induced transparent window is linearly red-shifted with the increase of the refractive index, which provides a reference for realizing electromagnetic induced transparency of a specific waveband.

[0031] The above series of detailed descriptions are only specific descriptions of the feasible embodiments of the present application, and are not used to limit the protection scope of the present application. Equivalent embodiments or changes made without departing from the spirit of the present application should be included in the protection scope of the present application.

[0032] It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

Claims

1. A nano-optical structure implementing the phenomenon of electromagnetically induced transparency, characterized in that: The periodic structure is composed of a plurality of unit cell structures, the X direction and the Y direction are periodic, the Z direction is single, the unit cell structures are symmetrically arranged about the X axis and the Y axis, and each unit cell structure is composed of a surface plasmon effect layer, a dielectric substrate layer and a guided mode resonance layer from top to bottom in the Z direction; The surface plasmon effect layer is made of silver or gold, the guided mode resonance layer is made of silicon, and the dielectric substrate layer is made of silicon dioxide; The surface plasmon effect layer is provided with a cross-shaped hollow resonant cavity, a circular hollow resonant cavity or a square hollow resonant cavity; The refractive index of the dielectric substrate layer is n=1.45; The value of the silicon is [wavelength, refractive index real part, refractive index imaginary part]=[688 708 729 751 774 799 826, 3.788 3.7644 3.7419 3.7204 3.6999 3.6801 3.6611, 0.0112 0.00992 0.00865 0.00745 0.0063 0.00522 0.00421], wherein the unit of wavelength is nm.

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