High-Q flat photonic crystal with resonant frequency insensitive to thickness

Abstract

The invention discloses a high-Q flat photonic crystal with resonant frequency insensitive to thickness. Comprising a dielectric plate and through holes which are arranged on the dielectric plate in a two-dimensional periodic mode, each through hole is composed of two semi-cylindrical holes with different radiuses, the axes of the two semi-cylindrical holes coincide, and the bottom faces of the two semi-cylindrical holes coincide. The plate photonic crystal breaks the symmetry of the C2V structure, and when electromagnetic waves are normally incident to the plate photonic crystal in the thickness direction of the dielectric plate, a symmetric protection continuous domain bound state can be converted into a quasi-continuous domain bound state. By changing structural parameters, the quasi-continuous domain bound state can be subjected to destructive interference with different guided modes, so that a plurality of high-Q continuous domain bound states are formed. In addition, the method has robustness, the resonant frequency of a high-Q continuous domain bound state is insensitive to the thickness of the dielectric plate, and the advantage is beneficial to device processing and engineering application.

Description

Technical Field

[0001] The invention relates to a high-Q planar photonic crystal whose resonance frequency is insensitive to thickness, and belongs to the technical field of photonic crystals. Background Art

[0002] Photonic crystals refer to material structures with periodic dielectric constants, which can regulate the propagation of light. Through the rational design of the structure, the desired resonance characteristics can be effectively achieved, and they are widely used in sensing, filtering, and electromagnetic control.

[0003] Planar photonic crystals are easy to integrate due to their planar structure. In the study of planar photonic crystals, the realization of high resonance quality factor (Q factor) has always been a research hotspot. Q factor is an important parameter that describes the energy loss of an optical resonant cavity. A high Q factor means that the resonant cavity can store energy for a longer period of time, providing a larger local field enhancement, thereby making the interaction between light and matter stronger. Therefore, achieving a high Q factor is crucial.

[0004] Planar photonic crystals can support different types of continuum bound states. Continuum bound states consist of non-radiative localized waves located in the continuous spectrum, and theoretically have infinite quality factors due to zero radiation loss. Utilizing this feature, continuum bound states have a wide range of applications in many fields, including lasers, sensors, filters, nonlinear photonics, and imaging.

[0005] The resonant frequency of the continuous domain bound state reported so far in the planar photonic crystal is sensitive to the structural parameters, especially the thickness change will have a great impact on its frequency, which is not conducive to the processing and practical application of the device. There are still challenges in realizing a continuous domain bound state high Q planar photonic crystal that is insensitive to thickness. Summary of the invention

[0006] In order to overcome the above defects in the prior art, the present invention provides a new technology for generating continuous domain bound states in a planar photonic crystal, thereby realizing a high-Q planar photonic crystal whose resonant frequency is insensitive to thickness.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A high-Q planar photonic crystal whose resonant frequency is insensitive to thickness comprises a dielectric plate and through holes arranged in a two-dimensional periodic manner on the dielectric plate, wherein the lattice constants of the through holes in two directions of the two-dimensional periodic arrangement are equal, and the through holes are composed of two semi-cylindrical holes with different radii, the axes of the two semi-cylindrical holes coincide, and the bottom surfaces of the two semi-cylindrical holes overlap.

[0009] The thickness t of the dielectric plate satisfies 1.06Λ≤t≤1.47Λ, and the radii of the two semi-cylinders respectively satisfy r 1 =0.33Λ, 0≤r 2 <Λ / 2, where Λ represents the lattice constant.

[0010] The planar photonic crystal operates within the electromagnetic wave wavelength range of 2.6Λ-2.7Λ.

[0011] When working, the incident electromagnetic wave is incident parallel to the Z-axis direction, and the electric field polarization direction of the incident electromagnetic wave is along the X-axis direction, wherein the direction of the height of the dielectric plate is the Z-axis direction, the upper surface or the lower surface of the dielectric plate is the XOY plane, the direction of the bottom edges of the two semicircles on the XOY plane is the X-axis direction, and the direction perpendicular to the bottom edges of the two semicircles is the Y-axis direction.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] (1) The planar photonic crystal is composed of a dielectric plate and through holes arranged in a two-dimensional periodic manner on the dielectric plate, which can conveniently select the radius r 2 Thereby achieving different continuous domain bound states.

[0014] (2) The planar photonic crystal has a radius r 2 Under certain conditions, the conditions for the formation of continuous domain bound states are met within a large thickness range, and the influence of structural thickness is relatively small. This advantage is conducive to reducing the processing accuracy requirements of the device.

[0015] (3) The frequency of the continuous domain bound state supported by the planar photonic crystal is insensitive to the thickness of the dielectric plate and has robustness to the frequency of the continuous domain bound state. This advantage greatly improves the stability and reliability of the device operation and has important application value in the fields of high-power lasers, nonlinear optics, and high-sensitivity sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a planar photonic crystal structure is provided for a specific embodiment of the present invention;

[0017] Figure 2 A top view of the unit structure of the present invention;

[0018] Figure 3 for Figure 1 The structure shown in r 2 =r 1 =Dispersion curves of three TE modes at 50 μm;

[0019] Figure 4 for Figure 1 The structure shown is at the through hole radius r 2Quality factor curve graph under changing conditions;

[0020] Figure 5 for Figure 1 The thickness t and radius r required for the structure shown in the continuous domain bound state BIC 3 to form 2 The value of

[0021] Figure 6 for Figure 1 The frequency variation diagram of BIC 3 is shown in the range of structure thickness 160 μm ≤ t ≤ 220 μm. DETAILED DESCRIPTION

[0022] In order to better understand the present invention, it is further described in detail below with reference to the accompanying drawings.

[0023] Figure 1 and Figure 2 A schematic diagram of a high-Q planar photonic crystal of the present invention whose resonant frequency is insensitive to thickness is shown, comprising a dielectric plate and through holes arranged in a two-dimensional periodic manner on the dielectric plate, wherein the lattice constants of the through holes in two directions of the two-dimensional periodic arrangement are equal, and the through holes are composed of two semi-cylindrical holes with different radii, the axes of the two semi-cylindrical holes coincide, and the bottom surfaces of the two semi-cylindrical holes overlap.

[0024] The incident electromagnetic wave is incident parallel to the Z-axis direction, and the electric field polarization direction of the incident electromagnetic wave is along the X-axis direction, wherein the direction of the height of the dielectric plate is the Z-axis direction, the upper surface or the lower surface of the dielectric plate is the XOY plane, the direction of the bottom edges of the two semicircles on the XOY plane is the X-axis direction, the direction perpendicular to the bottom edges of the two semicircles is the Y-axis direction, and t is the thickness of the dielectric plate.

[0025] In the implementation process of the present invention, when r 2 =r 1 When the propagation mode of the normally incident electromagnetic wave does not match the symmetry between the internal mode of the structure, the bound state cannot couple with the electromagnetic wave, so that the energy is confined inside and cannot radiate outward, forming a continuous domain bound state 1 (BIC 1).

[0026] When 2 ≠r 1 When the radius r is changed, the symmetry of the structure is broken, the radiation channel is opened, and energy leaks, causing the ideal continuous domain bound state to be transformed into the quasi-continuous domain bound state. 2 , causing the quasi-continuum bound state to destructively interfere with two different guided modes, forming continuum bound state 2 (BIC 2) and continuum bound state 3 (BIC 3).

[0027] The frequencies of BIC 1 and BIC 2 are sensitive to the thickness of the slab photonic crystal, and the resonant frequency can be adjusted by changing the thickness. The frequency of BIC 3 is not sensitive to the thickness of the slab photonic crystal and is robust.

[0028] The technical effects of the present invention are described below with reference to specific embodiments.

[0029] The planar photonic crystal of the present invention is simulated in the terahertz band, the electromagnetic wave is normally incident, and the electric field polarization direction of the incident electromagnetic wave is in the X direction. The material of the substrate 1 is silicon, the dielectric constant is 11.67, the thickness t is 200 microns, the period Λ along the X direction and along the Y direction is equal and equal to 150 microns, wherein the radius r of the through hole 4 is 1 To 50 microns, change the radius r 2 .

[0030] When the size parameters of the structure of the present invention are under the above parameters, when r 2 =r 1 =50 microns, the dispersion curves of the three TE modes of the planar photonic crystal are obtained by eigenmode calculation, such as Figure 3 As shown in the figure, they are named TE 1, TE 2 and TE 3, and their frequencies at Γ point are 0.842THz, 0.826THz and 0.805THz respectively. Among them, TE 1 is a four-electric symmetric protection BIC, and TE 2 and TE 3 are guided modes.

[0031] The TE 1 at 20 μm ≤ r was calculated by eigenmode. 2 Quality factor at ≤55 microns, such as Figure 4 As shown. It can be found that there are three continuous domain bound states. 2 = 50 μm for the continuous domain bound state 1 (BIC 1), r 2 = 44.5 μm for the continuous domain bound state 2 (BIC 2) and r 2 =31.5 microns is the continuous domain bound state 3 (BIC 3). Among them, BIC 1 is the four-electrolyte symmetry protection BIC mentioned above.

[0032] BIC 2 is formed by the interaction between TE 1 (quasi-BIC 1) and TE 2. These two modes are coupled into the same radiation channel and interfere with each other, resulting in the phenomenon of avoiding crossing. 2 The Q factor of TE 1 reaches 10 at 44.5 μm 8 (theoretically infinite), forming the Friedrich-Wintgen (FW) BIC.

[0033] BIC 3 is formed by the interaction between TE 1 (quasi-BIC 1) and TE 3. These two modes are coupled into the same radiation channel and interfere with each other, resulting in the phenomenon of avoiding crossing. 2 The Q factor of TE 1 reaches 10 at 31.5 μm 8 Above (theoretically infinite), the FW BIC is formed.

[0034] The calculated BIC 3 formation time r for slab photonic crystals with thickness ranging from 160 μm to 220 μm 2 The value of Figure 5 As shown. When the radius r 2 =31.5 (±0.3) microns, the planar photonic crystal can achieve high Q TE1 resonant output under large thickness changes.

[0035] The calculated BIC 3 frequency variation when the thickness of the slab photonic crystal ranges from 160 μm to 220 μm is as follows: Figure 6 The frequency of BIC 3 is 0.75 (±0.016) THz at different thicknesses. The frequency of BIC 3 is insensitive to changes in thickness and is robust. This advantage is conducive to reducing the processing accuracy requirements of the device and helps to improve the working stability of the device.

Claims

1. A high-Q planar photonic crystal whose resonant frequency is insensitive to thickness, characterized in that: It includes a dielectric plate and through holes arranged in a two-dimensional periodic manner on the dielectric plate, and the lattice constants of the through holes in two directions of the two-dimensional periodic arrangement are equal. The through holes are composed of two semi-cylindrical holes with different radii, the axes of the two semi-cylindrical holes coincide, and the bottom surfaces of the two semi-cylindrical holes overlap.

2. A high-Q planar photonic crystal whose resonance frequency is insensitive to thickness according to claim 1, characterized in that: The thickness t of the dielectric plate satisfies 1.06Λ≤t≤1.47Λ, and the radii of the two semi-cylinders respectively satisfy r1=0.33Λ, 0≤r2<Λ / 2, where Λ represents the lattice constant.

3. A high-Q planar photonic crystal whose resonance frequency is insensitive to thickness according to claim 1, characterized in that: The planar photonic crystal operates within the electromagnetic wave wavelength range of 2.6Λ-2.7Λ.

4. A high-Q planar photonic crystal whose resonance frequency is insensitive to thickness according to claim 1, characterized in that: When working, the incident electromagnetic wave is incident parallel to the Z-axis direction, and the electric field polarization direction of the incident electromagnetic wave is along the X-axis direction, wherein the direction of the height of the dielectric plate is the Z-axis direction, the upper surface or the lower surface of the dielectric plate is the XOY plane, the direction of the bottom edges of the two semicircles on the XOY plane is the X-axis direction, and the direction perpendicular to the bottom edges of the two semicircles is the Y-axis direction.

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