Independent control method of photonic crystal double-band high-Q resonance mode and resonant cavity

Abstract

The application discloses an independent regulation method of photonic crystal double-band high-Q resonance mode and a resonant cavity, wherein the method comprises the following steps: designing an initial resonant cavity, which is a photonic crystal structure arranged periodically and having high rotational symmetry; respectively calculating quality factors of all modes on two high symmetry points of a first unit cell of a minimum repeatable unit; screening BIC modes with infinite quality factors; optimizing parameters of the first unit cell so that the BIC modes on the two high symmetry points are located at required frequencies; adding a first perturbation change amount to the first unit cell and only reducing the rotational symmetry so as to adjust the BIC mode of the center point of the Brillouin zone to be a quasi-radiation mode; and adding a second perturbation change amount so as to only make the other high symmetry point fold to the center of the Brillouin zone to adjust the BIC mode of the other high symmetry point to be a quasi-radiation mode. The application regulates one variable, which only affects the quality factor of one resonance and does not affect the performance of another resonance.

Description

Technical Field

[0001] The present invention relates to the field of photonic crystals, and in particular to an independent control method for a photonic crystal dual-band high-Q resonance mode and a resonant cavity. Background Art

[0002] High-Q (infinite high quality factor) optical modes in photonic crystals are beneficial for various on-chip applications such as sensing, optical filtering, nonlinear optics, light absorption and emission, etc.

[0003] Bound states in the continuum (BIC) are a unique phenomenon that maintains localization within the continuum, possessing an infinite high quality factor (Q). BICs perfectly localize light fields. When perturbed, BIC states can transform into quasi-BIC states with high quality factors, greatly facilitating light-matter interactions. Symmetry-protected BICs typically exist in micro- and nanostructures with high symmetry, typically corresponding to high symmetry points on band diagrams.

[0004] Bound states in continuum media (BICs) are localized modes in the radiative continuum with infinite Q factors. Due to the symmetry mismatch with the vacuum mode, these states are always found in the center of the Brillouin zone (BZ) of periodic systems and are called symmetry-protected (SP) BICs. However, resonances with infinite Q factors do not couple to the outside world and cannot be detected externally. However, when the symmetry of a highly symmetric structure is broken, it can be transformed into a quasi-BIC state with a high quality factor (Q value), and the Q value can be effectively controlled by the asymmetry parameter. Generally, the larger the asymmetry parameter, the smaller the Q value.

[0005] To maximize light-matter interactions, providing universal control over radiative losses in nanophotonic systems is essential. Incorporating more than one high-Q resonance into a nanophotonic system can help extend the operating bandwidth and potentially improve performance, and this has been investigated in numerous studies. However, independent control of the quality factors of two high-Q modes in two-dimensional photonic crystals has not yet been achieved. Therefore, developing a method to independently control dual-band high-Q resonances is a major challenge that urgently needs to be addressed in this field. Summary of the Invention

[0006] The main purpose of the present invention is to provide a photonic crystal resonant cavity and a control method thereof, which can independently control the quality factors of two high-Q modes in a two-dimensional photonic crystal and regulate the two BIC modes into quasi-radiative modes respectively.

[0007] The technical solution adopted in the present invention is:

[0008] Provided is a method for independently controlling a dual-band high-Q resonant mode of a photonic crystal, comprising the following steps:

[0009] Designing an initial resonant cavity, which is a photonic crystal structure with periodic arrangement and high rotational symmetry, wherein the smallest repeatable unit of the initial photonic crystal structure is the first unit cell;

[0010] Calculate the quality factors of all modes at two high symmetry points of the first unit cell respectively, and screen out BIC modes with infinite quality factors. One of the high symmetry points is the center point of the Brillouin zone of the first unit cell, and the other high symmetry point is the diagonal point or the midpoint of the edge of the Brillouin zone of the first unit cell.

[0011] Optimize the parameters of the first unit cell so that the BIC modes of the two highly symmetric points are located at the desired frequencies;

[0012] Adding the first perturbation variation to the first unit cell only reduces the rotational symmetry of the first unit cell, so as to adjust the BIC mode at the center point of the Brillouin zone to a quasi-radiation mode;

[0013] A second perturbation variation is added to a plurality of adjacent first unit cells, so that only the other high symmetry point is folded to the center of the Brillouin zone, so as to adjust the BIC mode of the other high symmetry point to a quasi-radiation mode.

[0014] Following the above technical solution, the photonic crystal structure is nano-cylinders periodically arranged on a substrate, and each nano-cylinder has a penetrating pore.

[0015] Following the above technical solution, the addition of the first disturbance variation is specifically to shift the pore from the center of the nano-cylinder.

[0016] Following the above technical solution, the displacement is a vector, which is determined by the moving distance and direction.

[0017] Following the above technical solution, the addition of the second disturbance variation is specifically to enlarge the radius of a pair of nano-cylinders located on a diagonal line, and to correspondingly reduce the radius of another pair of nano-cylinders located on another diagonal line.

[0018] Following the above technical solution, the substrate is a silicon substrate, and the material of the nano-columns is SiO2, SiN, PDMS or BCB.

[0019] Following the above technical solution, the photonic crystal structure is a periodically arranged nanocolumn connected by connecting bridges, the substrate is air, and each nanocolumn is provided with an air hole.

[0020] Following the above technical solution, the addition of the first disturbance variation is specifically to shift the air holes of the nanocolumns; the addition of the second disturbance variation is specifically to expand the radius of a pair of air holes located on the diagonal line and to reduce the radius of another pair of air holes located on the other diagonal line accordingly.

[0021] The present invention also provides a photonic crystal resonant cavity, which is prepared by the photonic crystal resonant cavity control method described in the above technical solution.

[0022] The present invention also provides a multi-band device having the photonic crystal resonant cavity described in the above technical solution.

[0023] Following the above technical solution, the multi-band device is a refractive index sensor, a saturated absorber, a filter, a resonance absorption enhanced laser, a nonlinear light radiator, etc.

[0024] The beneficial effects of the present invention are as follows: the present invention reduces only the rotational symmetry of the first unit cell by adding a first perturbation variation to the first unit cell, so as to adjust the BIC mode at the center point of the Brillouin zone to a quasi-radiation mode; the first perturbation variation keeps the minimum repeatable unit of the periodic array unchanged, but significantly reduces the rotational symmetry; a second perturbation variation is added to a plurality of adjacent first unit cells, the second perturbation variation does not change the rotational symmetry, but only causes the other high symmetry point to fold to the center of the Brillouin zone, so as to adjust the BIC mode of the other high symmetry point to a quasi-radiation mode; therefore, the present invention uses different geometric parameters to respectively break the rotational symmetry and the minimum unit cell, and the superposition of these two variations can be achieved by breaking the symmetry of the BIC or by expanding the lattice and folding the originally non-radiating mode into the light cone, thereby realizing independent regulation of dual-band high-Q resonance.

[0025] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1A This is a flow chart of a method for independently controlling a dual-band high-Q resonant mode of a photonic crystal according to an embodiment of the present invention;

[0028] Figure 1B This is a flow chart of a method for independently controlling a dual-band high-Q resonant mode of a photonic crystal according to another embodiment of the present invention;

[0029] Figure 2A Schematic diagram of the two-dimensional photonic crystal structure;

[0030] Figure 2B Schematic diagram of different possible perturbations of a two-dimensional photonic crystal structure;

[0031] Figure 3 is the spectral response band diagram of the two-dimensional photonic crystal structure;

[0032] Figure 4 The electromagnetic field distributions of two resonances are shown respectively: the SP quasi-BIC in the upper part and the BZF-GMR in the lower part;

[0033] Figure 5 It shows that two BICs are controlled independently, the upper part is SP-BIC and the lower part is BZF-GMR. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic illustrations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0036] In the present invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like are used to indicate positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present application and to simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present application. Furthermore, the terms "first" and "second" are used solely for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0037] In addition, it should be noted that the features of the various embodiments of the present invention may be combined or coupled in part or in whole, and, as will be appreciated by those skilled in the art, may interact and operate in different ways. Each embodiment may be implemented independently of one another or in an associated relationship.

[0038] The present invention enables the Q factor of one resonant mode to be continuously tuned without affecting the optical properties of another resonant mode. Independent Q factor control greatly enriches the design freedom and facilitates the development of dual-band, powerful, and multifunctional nanophotonic devices.

[0039] Example 1

[0040] like Figure 1A As shown, the independent control method of the photonic crystal dual-band high-Q resonance mode according to the embodiment of the present invention includes the following steps:

[0041] S101, designing an initial resonant cavity, which is a photonic crystal structure with a periodic arrangement and high rotational symmetry, wherein the smallest repeatable unit of the initial photonic crystal structure is a first unit cell;

[0042] S102, respectively calculating the quality factors of all modes at two high symmetry points of the first unit cell, and screening out BIC modes with infinite quality factors, where one high symmetry point is the center point of the Brillouin zone of the first unit cell, and the other high symmetry point is the diagonal point or the midpoint of an edge of the Brillouin zone of the first unit cell;

[0043] S103, optimizing the parameters of the first unit cell so that the BIC modes of the two high symmetry points are located at the desired frequency;

[0044] S104, adding a first perturbation variation to the first unit cell, reducing only the rotational symmetry of the first unit cell, so as to adjust the BIC mode at the center point of the Brillouin zone to a quasi-radiation mode;

[0045] S105 , adding a second perturbation variation to a plurality of adjacent first unit cells, so as to fold only the other high symmetry point to the center of the Brillouin zone, so as to adjust the BIC mode of the other high symmetry point to a quasi-radiation mode.

[0046] The photonic crystal structure can take various forms, such as a periodically arranged array of nanocylinders on a substrate, each with a penetrating air hole. The substrate can be a silicon substrate, with the nanocylinders made of SiO2, SiN, PDMS, or BCB. Alternatively, the photonic crystal structure can be a gain material substrate with periodically arranged air holes. The gain material can be a high-refractive-index multi-quantum-well material. These photonic crystal structures can be arranged in either a regular tetragonal or hexagonal configuration, both exhibiting high rotational symmetry.

[0047] like Figure 2A As shown in the figure, when the photonic crystal structure is a periodic arrangement of nanocylinders on a substrate, the first perturbation variation is applied by shifting the pores away from the center of the nanocylinders. This displacement is a vector, determined by both the distance and direction of the movement. In this case, the second perturbation variation is applied by increasing the radius of a pair of nanocylinders on a diagonal line and decreasing the radius of another pair of nanocylinders on the other diagonal line.

[0048] like Figure 2BAs shown, when the photonic crystal structure is a periodically arranged nanopillar (when the substrate is air, the nanopillars can be connected by connecting bridges), the addition of the first perturbation variation is specifically to reduce the symmetry of the unit cell (such as shifting the air holes); the addition of the second perturbation variation is specifically to fold the mode at point X or point M to point Γ (such as the X-point perturbation includes expanding the radius of a pair of air holes located on the diagonal (or moving them closer to the center), and correspondingly reducing the radius of another pair of air holes located on the other diagonal (or moving them away from the center); the M-point perturbation is to replace the diagonal with a pair of left and right (or top and bottom) air holes to expand or reduce the radius). The second perturbation variation is also applicable to Figure 2A structure.

[0049] The present invention adds a first perturbation variation to a first unit cell, thereby only reducing the rotational symmetry of the first unit cell, so as to adjust the BIC mode at the center point of the Brillouin zone to a quasi-radiative mode; the first perturbation variation keeps the minimum repeatable unit of the periodic array unchanged, but significantly reduces the rotational symmetry; a second perturbation variation is added to a plurality of adjacent first unit cells, wherein the second perturbation variation does not change the rotational symmetry, but only causes the other high symmetry point to fold to the center of the Brillouin zone, so as to adjust the BIC mode at the other high symmetry point to a quasi-radiative mode; therefore, the present invention utilizes different geometric parameters to respectively break the rotational symmetry and the minimum unit cell, and the superposition of these two variations can be achieved by either breaking the symmetry of the BIC or by expanding the lattice and folding the originally non-radiative mode into the light cone, thereby realizing independent regulation of dual-band high-Q resonance.

[0050] Example 2

[0051] The principle of this embodiment 2 is the same as that of embodiment 1. To make the structure more specific, this embodiment 2 uses a two-dimensional photonic crystal structure composed of hollow nanocylinder dimers as an example.

[0052] The design method of the nanoresonator of this embodiment can independently control two high-Q resonances. The photonic crystal supports SP (symmetry-protected, SP) quasi-BIC and BZ folding induced resonance (Brillouin zone folding introduced-guided mode resonance, BZF-GMR) with different mode symmetries and field distributions. By using different geometric parameters to break the rotational symmetry and the minimum unit cell respectively, the Q factor of one resonance mode can be continuously tuned without affecting the optical properties of another resonance mode. Independent Q factor control greatly enriches the design freedom and contributes to the development of dual-band, powerful and multifunctional nanophotonic devices.

[0053] The independent control method of the photonic crystal dual-band high-Q resonance mode of embodiment 2 is as follows: Figure 1B As shown, it mainly includes the following steps:

[0054] S1. Design a photonic crystal resonator consisting of a periodic array, distributed in a regular quadrilateral or hexagonal pattern, and having high rotational symmetry;

[0055] S2. Calculate the quality factors of all modes in the unit cell at the center of the Brillouin zone and another high-symmetry point (either a diagonal point or a midpoint on an edge), and select the mode with infinite quality factor;

[0056] S3. The radius of the air hole, the column spacing, the thickness of the resonant cavity, etc. can be designed through simulation software so that the center of the Brillouin zone and another high symmetry point mode are located at the required frequency (such as 200 Thz and 215 Thz);

[0057] S4. Add variation 1, which leaves the smallest unit cell of the periodic array unchanged but significantly reduces the rotational symmetry. Observe the effect on the mode field distribution at the center of the Brillouin zone and another highly symmetric point.

[0058] S5. Add variation 2, which causes another high-symmetry point to fold to the center of the Brillouin zone, but partially preserves the rotational symmetry. Observe the effect on the mode field distribution in the center of the Brillouin zone (both the original mode and the folded mode).

[0059] S6, mixed variable 1 and variable 2;

[0060] S7. Calculate the spectral response of the structure under the action of different variables, extract the resonance peaks, and observe the resonance changes;

[0061] S8. Verify the independence of variables 1 and 2 on the extracted quality factors.

[0062] Optionally, step S1 includes: 1) providing a mechanically supportive substrate, such as low-refractive-index silicon oxide, or other materials such as silicon nitride, polydimethylsiloxane (PDMS), benzocyclobutene (BCB), or air (when the substrate is air, bridges can be used to connect the nanopillars). 2) growing hollow nanopillars in a square arrangement on the substrate. 3) each nanopillar has an air hole penetrating therethrough.

[0063] Optionally, in step S2, the infinite modes include the Γ-point mode at the center point of the Brillouin zone and the X-point mode at the edge corner points.

[0064] Optionally, in step S3 , the designed photonic crystal structure has a period P=Px=Py=605 nm, a thickness t=224 nm, a nanocolumn radius R=243 nm, and a circular hole radius r=44 nm.

[0065] Optionally, in step S4, the air hole can be designed to be displaced from the center of the nano-cylinder. It should be noted that displacement is a vector quantity, which is determined by the moving distance (m) and direction (θ).

[0066] Alternatively, step S5 can be designed such that the radius of the hollow nanocylinders on a diagonal of the square lattice is enlarged by 1+Δr, while the radius of the hollow nanocylinders on the other diagonal is reduced by 1-Δr, thereby forming a supercell consisting of two hollow nanocylinders. The perturbation intensity can be quantified by Δr.

[0067] Optionally, in step S8, by adjusting the perturbation parameters of the photonic crystal structure, the quality factors of the two modes can be independently controlled. The first high-Q resonant mode is the BZF-GMR mode; the second high-Q resonant mode is the symmetry-protected (SP) BIC mode; specifically, the quality factor of the BZF-GMR mode is regulated by Δr and can be arbitrarily configured from infinite to extremely low. Correspondingly, the quality factor of the SP-BIC mode is regulated by m and can be arbitrarily configured from infinite to extremely low. And the change of m does not affect the quality factor of the BZF-GMR mode; the change of Δr does not affect the quality factor of the SP-BIC mode.

[0068] in, Figure 2A In Figure 1, a is a schematic diagram of a two-dimensional photonic crystal. Unless otherwise specified, the structure used in this embodiment has the following geometric parameters: P = Px = Py = 605 nm, t = 224 nm, R = 243 nm, and R = 44 nm. The specific parameters can be adjusted according to the desired wavelength, and the period can be preset to half the wavelength. b shows different types of perturbations: Type 1: Initial structure, Type 2: Pore displacement, Type 3: Scaling of (two) nanopillar clusters, and Type 4: Both displacement and scaling. c is a schematic diagram of the first Brillouin band corresponding to different lattices.

[0069] Figure 2B The scheme without substrate connected by bridge and different perturbation types of perturbation 2 are shown.

[0070] Figure 3 for Figure 2A Band diagram of the spectral response of the structure under different parameters. (a) The band structure without the applied variation, obtained by calculating the characteristic frequency and (b) the angle-resolved transmission spectrum. (c) The spectral response of the structure with both variations. (d) Transmission spectra of the original structure and the structure with both variations at normal incidence (θ = 0, Δr = 0.015, m = 40 nm).

[0071] Figure 4The electromagnetic field distributions of two resonances are shown separately: the SP quasi-BIC (θ = 0, m = 50nm) in the upper part; the BZF-GMR (Δr = 0.035) in the lower part. a is the electric field distribution in the xy plane: the color represents the electric field intensity, and the arrows represent the electric field components. The symbols "+" and "-" represent the direction of the electric field, and the size of the symbol represents the electric field amplitude. b is the electric field distribution in the xz plane. The dots of different colors represent the real-space high symmetry points of the original structure to illustrate the influence of geometric variables on the optical mode. c is the z-direction magnetic field distribution in the xy plane.

[0072] Figure 5 This image shows two BICs controlled independently: the SP-BIC on top and the BZF-gmr on the bottom. (a) Q factor versus m and Δr; (b) transmission spectrum response as m(Δr) varies; (c) Q factor versus m and Δr.

[0073] Figure 2 is used to illustrate steps S1 and S2. Figure 3 For explaining step S3, Figure 4 For explaining steps S4 and S5, Figure 5 Used to explain steps S6, S7, and S8.

[0074] To demonstrate the independent control of high-Q modes, a two-dimensional photonic crystal (PhC) structure is considered, which consists of silicon (n = 3.45) nanocylinders arranged periodically on a silicon dioxide substrate (n = 1.44). Each nanocylinder has a penetrating air hole, such as Figure 2A The symmetry of the structure can be disturbed in three ways, such as Figure 2A As shown in b in . First, the pores are displaced from the center of the nanocylinder. It should be noted that the perturbation intensity is determined by the moving distance (m) and direction (θ). Secondly, the hollow nanocylinders on the diagonal of the square lattice can be expanded by 1+Δr, while those on the other diagonal can be reduced by 1-Δr, thus forming a supercell consisting of four hollow nanocylinders. The perturbation intensity can be quantified by Δr. Finally, the structure can also be perturbed in a combined manner, that is, first moving the pores and then adjusting the size of the hollow nanocylinders. The lattices of these periodic structures are represented by different square grids. The corresponding first Brillouin zone is Figure 2A The c is represented in the same square style. Figure 2B Shows more possible structures and perturbations 2 different perturbation types.

[0075] Figure 3 Figure a shows the band structure of two modes. Both modes belong to TE-like polarization. To further understand the two bands, the transmission spectrum of the unperturbed structure is calculated as a function of wavelength and incident angle, as shown in Figure 3As shown in b. The results show that when the incidence is close to vertical, a resonance band (manifested as a dip in the transmission spectrum) narrows and then disappears. This behavior is caused by the unique characteristics of BIC, which is an infinitely high Q factor discrete in momentum space. Compared with the eigenfrequency results, the TE_Γ band matches well, but the TE_X band cannot be found in the transmission spectrum. This is due to the fact that the bound state persists at an infinitely high Q factor. Therefore, it cannot be excited in the nearby momentum space. But if the appropriate variation is introduced, both bands can be found, as shown in Figure 3 The detailed spectrum at normal incidence is plotted in Figure 2(c). When there is no perturbation, there is only a background spectrum. However, when two perturbations are applied simultaneously, two narrow transmission dips with Fano lineshapes appear, indicating that the resonance is affected by the perturbation.

[0076] Figure 4 Figures ac show the electromagnetic field distributions of two resonances obtained from COMSOL spectral response simulations. The structure with varying quantities resonates with the incident light. Figure 3 Figure a shows the electric field distribution of two quasi-BICs in the xy plane at half the height of the silicon hollow nanocylinder. For the SP quasi-BIC (top panel), the electric field exhibits a clockwise vortex within each silicon hollow nanocylinder. Clearly, the off-center air hole disrupts the circular current. In this case, each cylinder behaves as an independent resonator, so perturbations exceeding one unit cell have little effect on the eddy currents. Figure 4 The electric field (Ey) profile corresponding to the xz plane in the upper part of b shows that the displacement of the pore (m) destroys the odd symmetry of the SP-BIC with respect to the center of the nanorod (marked by the black dot). However, it is immune to the type 2 variation (Δr). In contrast, Figure 4 The electric field of the BZF-GMR in the lower part of a shows the obvious mutual coupling between the electric dipole and the nanorod. Figure 4 The lower part of b shows the Ey cross-section on the xz plane, which has odd symmetry between two adjacent nanorods and even symmetry at the center of the nanorod. Therefore, the effect of hole displacement is negligible, but the perturbation of the nanorod size will lead to partial cancellation of the two pairs of electric dipoles in the far field and create a radiation channel for the guided mode. In addition, the electric field of SP quasi-BIC is mainly confined to the hollow nanorods, while the electric field of BZF-GMR mainly overlaps with the air, especially the nanopores. Different mode distributions may lead to different applications. SP quasi-BIC is conducive to laser emission because if semiconductor materials are used instead of Si, the large mode overlap with the gain medium can greatly improve stimulated amplification. BZF-GMR is very sensitive to changes in the refractive index nearby, so it can be used for optical sensing. Finally, the two modes are identified by the in-plane symmetry. By Figure 4 From the X-plane cross-section magnetic field profile shown in c, we can see that the SP quasi-BIC originates from the Γ point C 4vA1 irreducible representation of the point group, and BZF-GMR comes from X point C 4v The different symmetries of the two modes offer the possibility of independently tuning the optical resonances.

[0077] To verify the independent control of SP quasi-BIC and BZF-GMR, detailed parameter sweeps of m and Δr were performed to investigate the Q factors of the two modes. Figure 4 As shown in the upper part of a, the Q factor of the SP quasi-BIC gradually decreases when the pore position deviates from the center of the nanorod. However, the effect of the hollow nanorod size perturbation (Δr) on the Q factor can be ignored because it does not affect the electrical distribution of the individual hollow nanorods (see Figure 3 b). Therefore, the Q factor contour is almost parallel to the Δr axis. In contrast, Figure 5 The Q factor of the BZF-GMR shown in the lower part of a is significantly affected by the size perturbation of the hollow nanorods (Δr), but is almost unaffected by the position of the pores. This is mainly because the pores exert similar perturbation strengths on adjacent nanorods and therefore have little effect on the net "electric dipole" charge. The transmittance is also studied as a function of m and Δr. Figure 5 As can be seen from b, if only one disturbance is applied, the transmittance will only drop once, and as the disturbance intensity m (or Δr) changes, the transmittance will become brighter and wider. To further understand the properties of these two resonances, we extracted the Q factors and two variations of the SP quasi-BIC and BZF-GMR respectively. Figure 5 As shown in the upper part of Figure 3, the Q factor of the SP quasi-BIC is unaffected by the perturbation Δr of the nanorod size, but decreases rapidly and continuously with increasing perturbation strength of the pore position. A similar phenomenon applies to the Q factor of the BZF-GMR, which is significantly affected by the perturbation of the hollow nanorod size (Δr) rather than the pore position. Here, we point out that the dependence of the two Q factors on the perturbation strength α (representing Δr or m) follows the general law of quasi-BIC:

[0078] Q=Q0 / α 2

[0079] where Q0 is a constant. These results indicate that the Q factors of SP-quasi-BIC and BZF-GMR can be precisely controlled independently.

[0080] The present invention also provides a photonic crystal resonant cavity, which is prepared by the photonic crystal resonant cavity control method described in the above technical solution.

[0081] The present invention also provides a multi-band device comprising the photonic crystal resonant cavity described in the above technical solution. This multi-band device includes a refractive index sensor, a saturated absorber, a filter, a resonant absorption-enhanced laser, a nonlinear optical radiator, and other components. This device provides an improved solution for applications requiring multiple resonances and can be widely used in various fields of photonic devices.

[0082] In summary, the nanoresonator design method of the present invention can independently control two high-Q resonances, which relates to the field of photonic crystal nanoresonators. This method allows controlling one variable to affect the quality factor of only one resonance without affecting the performance of the other.

[0083] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0084] The size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0085] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for independently controlling a dual-band high-Q resonance mode of a photonic crystal, characterized in that: The following steps are involved: Designing an initial resonant cavity, which is a photonic crystal structure with periodic arrangement and high rotational symmetry, wherein the smallest repeatable unit of the initial photonic crystal structure is the first unit cell; Calculate the quality factors of all modes at two high symmetry points of the first unit cell respectively, and screen out BIC modes with infinite quality factors. One of the high symmetry points is the center point of the Brillouin zone of the first unit cell, and the other high symmetry point is the diagonal point or the midpoint of the edge of the Brillouin zone of the first unit cell. Optimize the parameters of the first unit cell so that the BIC modes of the two highly symmetric points are located at the desired frequencies; Adding the first perturbation variation to the first unit cell only reduces the rotational symmetry of the first unit cell, so as to adjust the BIC mode at the center point of the Brillouin zone to a quasi-radiation mode; A second perturbation variation is added to a plurality of adjacent first unit cells, so that only the other high symmetry point is folded to the center of the Brillouin zone, so as to adjust the BIC mode of the other high symmetry point to a quasi-radiation mode.

2. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 1, characterized in that: The photonic crystal structure is nano-cylinders periodically arranged on a substrate, and each nano-cylinder has a penetrating air hole.

3. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 2, characterized in that: The addition of the first disturbance variation specifically shifts the pore from the center of the nano-cylinder.

4. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 3, characterized in that: The displacement is a vector, determined by both the distance and direction of movement.

5. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 2, characterized in that: The addition of the second disturbance variation specifically increases the radius of a pair of nano-cylinders located on a diagonal line, and correspondingly reduces the radius of another pair of nano-cylinders located on another diagonal line.

6. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 2, characterized in that: The substrate is a silicon substrate, and the material of the nano-cylinder is SiO2, SiN, PDMS or BCB.

7. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 1, characterized in that: The photonic crystal structure is a periodically arranged nanocolumn connected by connecting bridges, the substrate is air, and each nanocolumn is provided with an air hole.

8. The independent control method of the photonic crystal dual-band high-Q resonance mode according to claim 7, characterized in that: The addition of the first perturbation variation is specifically to shift the air holes of the nanocolumns; the addition of the second perturbation variation is specifically to expand the radius of a pair of air holes located on a diagonal line and to correspondingly reduce the radius of another pair of air holes located on the other diagonal line.

9. A photonic crystal resonant cavity, characterized in that: The photonic crystal is prepared by the independent control method of the double-band high-Q resonance mode of the photonic crystal according to any one of claims 1 to 7.

10. A multi-band device, characterized in that: The photonic crystal resonant cavity comprises the photonic crystal resonant cavity according to claim 9.

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