Continuous domain bound state metasurface microcavity structure based on symmetric protection and design method

Abstract

The invention relates to a continuous domain bound state metasurface microcavity structure based on symmetric protection and a design method. The structure comprises a substrate layer, a low-refractive-index material layer and a metasurface array structure which are sequentially stacked in the z-axis direction. The metasurface array structure is composed of a plurality of square block structures which are periodically arranged in the x-axis direction and the y-axis direction respectively, and the circle centers of round holes formed in the square block structures deviate relative to the centers of the square block structures. The structures of the square blocks and the positions, the sizes and the shapes of the round holes formed in the square blocks are the same; the metasurface array structure provided with the position offset circular holes is used for exciting dipole moment in the z-axis direction when plane waves polarized in the y-axis direction are normally incident, a bound state in a quasi-continuous domain is formed, and the bound state in the quasi-continuous domain is used for forming a resonant cavity with a high Q value. By breaking the internal rotational symmetry of the structure, an ideal BIC is converted into a quasi-BIC state with an extremely high Q value and limited service life, high-performance optical constraint is obtained, the emission performance of various low-dimensional gain material devices is improved, and the development of integrated and miniaturized optical devices is promoted.

Description

Technical Field

[0001] The present invention relates to the fields of micro-nano processing and metamaterial technology, and in particular to a continuous domain bound state metasurface microcavity structure based on symmetry protection and a design method thereof. Background Art

[0002] The development trend of modern silicon-based photonics devices is always miniaturization and integration. As the number of transistors on the same chip increases to a certain extent, Moore's Law in integrated circuits begins to fail, so people turn their attention to photons, which are information carriers with more stable control and reuse dimensions than electrons. Among them, on-chip light sources play an important role in the realization of highly integrated photonic circuits. Therefore, how to achieve high performance of light-emitting devices with small size becomes the key in photonic circuits. Studies have shown that through the theory of continuous domain bound states (BIC), the periodic micro-nano cavity structure designed by constructive and destructive interference of electromagnetic fields can achieve high localization of electromagnetic fields, and because the design is theoretically a perfect bound state that does not radiate outward, it can achieve super high quality factors, and through the design of different resonant bands, the directional concentration of the electric field can be achieved, so that the low-dimensional gain medium and the cavity can be efficiently combined, such as a single layer of two-dimensional materials, van der Waals heterojunctions or zero-dimensional quantum dot light-emitting materials.

[0003] Many studies have shown that using plasma in metal structures to achieve miniaturization of resonant cavities is a feasible approach. However, although the use of plasma structures can effectively reduce the volume, due to the high ohmic loss of metals, there are limitations in practical applications, resulting in unsatisfactory performance of actual light sources. At the same time, it has been found that the use of high-refractive-index all-medium structures can avoid cavity loss problems as much as possible, providing a new way to achieve high-performance, miniaturized and highly integrated photonic circuits. So far, research on resonant cavities has included the use of distributed Bragg reflector (DBR) cavities, photonic crystal defect cavities or optical cavities through continuous domain bound states (BIC), which can control the cavity size of the resonant cavity to the order of several microns. For low-dimensional gain materials, since the luminous intensity of gain materials in the infrared band is slightly lower than that of visible materials, and the infrared band occupies a very important position in communication applications, in order to break through the limitations caused by the insufficient luminous intensity of gain materials in the infrared band, the research on high-performance micro-nano optical resonant cavities is crucial, which can efficiently combine the gain medium with the optical cavity, making it possible to achieve high-performance infrared micro-on-chip light sources. . Summary of the invention

[0004] The purpose of the present invention is to provide a continuous domain bound state metasurface microcavity structure and design method based on symmetry protection, which mainly solves the problems existing in the above-mentioned prior art. It breaks the intrinsic rotational symmetry of the structure, transforms the ideal BIC into a quasi-BIC state with extremely high Q value but limited lifetime, thereby obtaining high-performance optical confinement, greatly improving the emission performance of various low-dimensional gain material devices, and promoting the development of integrated and miniaturized optical devices.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A continuous domain bound state metasurface microcavity structure based on symmetry protection, characterized in that it comprises a substrate layer, a low refractive index material layer, and a metasurface array structure sequentially stacked along the z-axis direction;

[0007] The metasurface array structure comprises a plurality of square block structures periodically arranged along the x-axis direction and the y-axis direction, wherein the square block structure has a circular hole, and the center of the circular hole is offset by a certain distance along the x-axis direction relative to the geometric center of the square block structure; the x-axis direction is perpendicular to the y-axis direction;

[0008] The positions, sizes and shapes of the square block structures and the circular holes arranged thereon are exactly the same;

[0009] The metasurface array structure with circular holes with offset positions is used to excite the dipole moment along the z-axis direction when a plane wave polarized along the y-axis direction is normally incident, forming a bound state in the quasi-continuous domain, and using the bound state in the quasi-continuous domain to form a high-Q resonant cavity.

[0010] The continuous domain bound state metasurface microcavity structure based on symmetry protection is characterized in that the number of periods of the multiple square block structures periodically arranged along the x-axis and y-axis directions is greater than or equal to 100, the length of each period is P, P is 600-1500nm, the side length L of the square block structure is 200-1000nm, the diameter d of the circular hole is 100-450nm, the offset distance dr between the center of the circular hole and the geometric center of the circular hole where it is located along the x-axis direction is 20-50nm, and the height of the metasurface array structure along the z-axis direction is 220-740nm.

[0011] The continuous domain bound state metasurface microcavity structure based on symmetry protection is characterized in that: the diameter d of the circular hole does not exceed the side length L of the square block structure; and the offset distance dr does not exceed half of the side length L of the square block structure.

[0012] The continuous domain bound state metasurface microcavity structure based on symmetry protection is characterized by:

[0013] The base layer is used for physical support of the ultrasonic sensor chip and is made of high-strength silicon-based material;

[0014] The refractive index of the material of the low-refractive-index material layer is lower than the refractive index of the material of the metasurface array structure, so as to facilitate the confinement of the light field and achieve efficient field enhancement;

[0015] The metasurface of the metasurface array structure can sense external incident light.

[0016] The continuous domain bound state metasurface microcavity structure based on symmetry protection is characterized by:

[0017] The material of the base layer is quartz or silicon;

[0018] The material of the low refractive index material layer is silicon dioxide or calcium fluoride;

[0019] The material of the metasurface array structure is silicon or germanium or titanium dioxide high-refractive dielectric material.

[0020] The continuous domain bound state metasurface microcavity structure based on symmetry protection is characterized in that the corresponding emission wavelength in the operating frequency of the structure is between 0.4μm and 10μm, and when the emission wavelength of the gain medium is within the operating wavelength range of the microcavity, a significant near-field enhancement can be formed on the microcavity surface.

[0021] A design method of the above-mentioned continuous domain bound state metasurface microcavity structure based on symmetry protection is characterized in that it comprises the following steps:

[0022] Step A: Selecting a gain medium of a corresponding band according to the required photoluminescence band;

[0023] Step B: According to the wavelength position of photoluminescence, the parameters of the eccentric circular hole and the square block structure are changed to achieve strong near-field enhancement of the metasurface structure;

[0024] Step C: Optimizing the Q value and electromagnetic field local effect of the symmetrical protection BIC through simulation calculation;

[0025] Step D: Processing the bound state metasurface structure in the symmetric protection continuous domain by electron beam exposure, dry etching, wet etching and other steps;

[0026] Step E: Perform experimental effect test on the designed symmetrical protection BIC. If the implemented result does not meet the requirements, return to step B, adjust and optimize the symmetrical protection BIC, and repeat steps C and D until the experimental results meet the requirements.

[0027] In view of the above technical features, the present invention has the following advantages:

[0028] The metasurface in the present invention is an artificially designed nano-sized structure that can adjust the propagation characteristics of electromagnetic waves. The metasurface array designed based on the BIC principle has a significantly improved structural Q value and a significant strong field enhancement effect, thereby improving the emission intensity of the light source and having accurate wavelength selection characteristics; the BIC optical microcavity can still produce considerable emission intensity when combined with a poor quality gain material, thereby improving the quantitative intensity of the light source and the accuracy of the emission wavelength. In an embodiment of the present invention, through the microcavity structure, the BIC metasurface layer can modulate the light field in the visible and infrared bands, and by detecting the light field changes of the BIC metasurface, such as spectral changes, high-performance luminescence of the low-dimensional gain medium can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention.

[0030] Figure 2 It is a schematic structural diagram of the super surface array structure in the present invention.

[0031] Figure 3 It is a transmission spectrum comparison diagram of a square silicon block array with no circular hole position shift and a square silicon block array with circular hole position shift in the present invention under the same conditions of other structural parameters.

[0032] Figure 4 It is a schematic diagram of the electromagnetic field distribution in the xy cross section when the thickness at the resonant wavelength is the height of the metasurface structure.

[0033] Figure 5 It is a schematic diagram of the distribution of electromagnetic field enhancement factors in the xz cross section of the metasurface unit structure at the resonant wavelength.

[0034] Figure 6 It is a schematic diagram of the distribution of the electromagnetic field enhancement multiples in the xy cross section when the thickness at the resonant wavelength is the height of the metasurface structure. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0036] See also Figure 1 , 2 The present invention discloses a continuous domain bound state metasurface microcavity structure based on symmetry protection. As shown in the figure: it includes a substrate layer 1, a low refractive index material layer 2, and a metasurface array structure which are sequentially stacked along the z-axis direction.

[0037] The metasurface array structure comprises a plurality of square block structures 3 periodically arranged along the x-axis direction and the y-axis direction, wherein the square block structure 3 has a circular hole 4, and the center of the circular hole 4 is offset by a certain distance along the x-axis direction relative to the geometric center of the square block structure 3; the x-axis direction is perpendicular to the y-axis direction;

[0038] The positions, sizes and shapes of the square block structures 3 and the circular holes 4 arranged thereon are exactly the same;

[0039] The metasurface array structure has a metasurface facing the positive direction of the z-axis, which can sense incident light with a propagation direction opposite to the z-axis. The BIC metasurface array forms a micro-nano optical resonant cavity with a high Q value.

[0040] The metasurface array structure with position-offset circular holes 4 is used to excite the dipole moment along the z-axis direction when a plane wave polarized along the y-axis direction is normally incident, forming a bound state in the quasi-continuous domain, and using the bound state in the quasi-continuous domain to form a high-Q resonant cavity.

[0041] In the present invention, the number of periods of the multiple square block structures 3 periodically arranged along the x-axis and y-axis directions is greater than or equal to 100, the length of each period is P, P is 600-1500nm, the side length L of the square block structure 3 is 200-1000nm, the diameter d of the circular hole 4 is 100-450nm, the offset distance dr between the center of the circular hole 4 and the geometric center of the circular hole 4 where it is located along the x-axis direction is 20-50nm, and the height of the super surface array structure along the z-axis direction is 220-740nm.

[0042] In the present invention, the diameter d of the circular hole 4 does not exceed the side length L of the square block structure 3 ; and the offset distance dr does not exceed half of the side length L of the square block structure 3 .

[0043] The metasurface in the present invention is an artificially designed nano-sized structure that can adjust the propagation characteristics of electromagnetic waves. The metasurface array designed based on the BIC principle has a significantly improved structural Q value and a significant strong field enhancement effect, thereby improving the emission intensity of the light source and having accurate wavelength selection characteristics; the BIC optical microcavity can still produce considerable emission intensity when combined with a poor quality gain material, thereby improving the quantitative intensity of the light source and the accuracy of the emission wavelength. In an embodiment of the present invention, through the microcavity structure, the BIC metasurface layer can modulate the light field in the visible and infrared bands, and by detecting the light field changes of the BIC metasurface, such as spectral changes, high-performance luminescence of the low-dimensional gain medium can be achieved.

[0044] In the present invention,

[0045] The base layer 1 is used for physical support of the ultrasonic sensor chip and is made of high-strength silicon-based material; the material of the base layer 1 is quartz or silicon.

[0046] The refractive index of the material of the low-refractive-index material layer 2 is lower than the refractive index of the material of the metasurface array structure, so as to facilitate the confinement of the light field and achieve efficient field enhancement; the material of the low-refractive-index material layer 2 is silicon dioxide or calcium fluoride.

[0047] The metasurface of the metasurface array structure can sense external incident light. In some embodiments, the material refractive index of the BIC metasurface layer 3 should be higher than that of the low-refractive-index medium layer 2, so as to improve the stability of the use and processing tolerance of the metasurface device. The BIC metasurface can sense external incident light. For example, the material of the BIC metasurface layer can be a high-refractive medium material such as silicon, germanium and titanium dioxide.

[0048] In the present invention, the corresponding emission wavelength in the working frequency of the structure is between 0.4 μm and 10 μm. When the emission wavelength of the gain medium is within the working wavelength range of the microcavity, a significant near-field enhancement can be formed on the surface of the microcavity.

[0049] Example

[0050] In this embodiment, P is 1300 nm, L is 720 nm, the diameter of the circular hole d is 400 nm, and the distance dr from the center of the circular hole is 50 nm. Figure 3-6 As shown, in the experiment of this embodiment, when the emission wavelength of the gain medium is within the operating wavelength range of the microcavity, a significant near-field enhancement can be formed on the surface of the microcavity.

[0051] A design method for a continuous domain bound state metasurface microcavity structure based on symmetry protection as described above can be regarded as a high-Q microcavity structure, which can improve the emission intensity and of a gain medium with weak self-radiation, and can achieve a wider range of wavelength selection characteristics under parameter adjustment, and artificially design the emission spectrum peak width; the BIC metasurface structure is simple in design and can be realized through standard micro-nano manufacturing processes, and has the characteristics of miniaturization and no absorption loss.

[0052] It includes the following steps:

[0053] Step A: Selecting a gain medium of a corresponding band according to the required photoluminescence band;

[0054] Step B: according to the wavelength position of photoluminescence, the parameters of the eccentric circular hole 4 and the square block structure 3 are changed to achieve strong near-field enhancement of the metasurface structure;

[0055] Step C: Optimizing the Q value and electromagnetic field local effect of the symmetrical protection BIC through simulation calculation;

[0056] The simulation calculation optimization adopts the FDTD module of Ansys' Lumerical software.

[0057] Step D: Processing the bound state metasurface structure in the symmetric protection continuous domain by electron beam exposure, dry etching, wet etching and other steps;

[0058] Step E: Perform experimental effect test on the designed symmetrical protection BIC. If the implemented result does not meet the requirements, return to step B, adjust and optimize the symmetrical protection BIC, and repeat steps C and D until the experimental results meet the requirements.

[0059] The present invention also discloses a method for manufacturing a material gain high-enhanced metasurface based on a symmetry-protected continuous domain bound state metasurface microcavity structure, comprising the following steps:

[0060] ① In some embodiments, on a silicon-on-insulator (SOI) substrate, a positive photoresist or a negative photoresist is first spin-coated onto the top silicon surface.

[0061] ② Subsequently, the photonic crystal (PhC) pattern on the photoresist layer was defined using an electron beam lithography (EBL) system by JEOL 6300FS.

[0062] ③ Reactive ion etching (RIE) is then used to transfer the BIC pattern from the resist to silicon.

[0063] ④ Then, the remaining photoresist is removed by inductively coupled plasma (ICP) etching.

[0064] ⑤ Combine low-dimensional gain medium with PhC metasurface.

[0065] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A continuous domain bound state metasurface microcavity structure based on symmetry protection, characterized by: It comprises a substrate layer (1), a low refractive index material layer (2), and a super-surface array structure which are sequentially stacked along the z-axis direction; The metasurface array structure comprises a plurality of square block structures (3) periodically arranged along the x-axis direction and the y-axis direction, wherein the square block structure (3) has a circular hole (4), and the center of the circular hole (4) is offset by a certain distance along the x-axis direction relative to the geometric center of the square block structure (3); the x-axis direction is perpendicular to the y-axis direction; The positions, sizes and shapes of the square block structures (3) and the circular holes (4) arranged thereon are completely the same; A metasurface array structure provided with position-shifted circular holes (4) is used to excite a dipole moment along the z-axis direction when a plane wave polarized along the y-axis direction is normally incident, thereby forming a bound state in a quasi-continuous domain, and forming a resonant cavity with a high Q value by utilizing the bound state in the quasi-continuous domain.

2. The continuous domain bound state metasurface microcavity structure based on symmetry protection according to claim 1, characterized in that: The number of periods of the plurality of square block structures (3) periodically arranged along the x-axis direction and the y-axis direction is greater than or equal to 100, the length of each period is P, P is 600-1500nm, the side length L of the square block structure (3) is 200-1000nm, the diameter d of the circular hole (4) is 100-450nm, the offset distance dr between the center of the circular hole (4) and the geometric center of the circular hole (4) where it is located along the x-axis direction is 20-50nm, and the height of the super surface array structure along the z-axis direction is 220-740nm.

3. The continuous domain bound state metasurface microcavity structure based on symmetry protection according to claim 2, characterized in that: The diameter d of the circular hole (4) does not exceed the side length L of the square block structure (3); and the offset distance dr does not exceed half of the side length L of the square block structure (3).

4. The continuous domain bound state metasurface microcavity structure based on symmetry protection according to claim 1, characterized in that: The base layer (1) is used for physical support of the ultrasonic sensor chip and is made of high-strength silicon-based material; The refractive index of the material of the low-refractive-index material layer (2) is lower than the refractive index of the material of the metasurface array structure, so as to facilitate the confinement of the light field and achieve efficient field enhancement; The metasurface of the metasurface array structure can sense external incident light.

5. The continuous domain bound state metasurface microcavity structure based on symmetry protection according to claim 4, characterized in that: The material of the substrate layer (1) is quartz or silicon; The material of the low refractive index material layer (2) is silicon dioxide or calcium fluoride; The material of the metasurface array structure is silicon or germanium or titanium dioxide high-refractive dielectric material.

6. The continuous domain bound state metasurface microcavity structure based on symmetry protection according to claim 1, characterized in that: The corresponding emission wavelength in the operating frequency of this structure is between 0.4μm and 10μm. When the emission wavelength of the gain medium is within the operating wavelength range of the microcavity, a significant near-field enhancement can be formed on the surface of the microcavity.

7. A design method for a continuous domain bound state metasurface microcavity structure based on symmetry protection as claimed in claim 1 or 2 or 3 or 4 or 5 or 6, characterized in that: It includes the following steps: Step A: Selecting a gain medium of a corresponding band according to the required photoluminescence band; Step B: according to the wavelength position of the photoluminescence, the parameters of the eccentric circular hole (4) and the square block structure (3) are changed to achieve strong near-field enhancement of the metasurface structure; Step C: Optimizing the Q value and electromagnetic field local effect of the symmetrical protection BIC through simulation calculation; Step D: Processing the bound state metasurface structure in the symmetric protection continuous domain by electron beam exposure, dry etching, wet etching and other steps; Step E: Perform experimental effect test on the designed symmetrical protection BIC. If the implemented result does not meet the requirements, return to step B, adjust and optimize the symmetrical protection BIC, and repeat steps C and D until the experimental results meet the requirements.

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