Dielectric compact structure for realizing continuous spectrum bound state

Abstract

The invention relates to the field of photonics. Existing various structures for realizing a continuous spectrum bound state still have the limitations that an infinite periodic structure cannot be realized in practice, the dielectric constant is nearly zero or the metal material loss is relatively large and the like. The invention discloses a dielectric compact structure for realizing a continuous spectrum bound state, which comprises a dielectric layer and a double-ring grating, the double-ring grating and the dielectric layer are concentric circles, the double-ring grating is of a sub-wavelength structure, and all grating units are uniformly distributed in a circumferential array manner and have the same radian. When vortex light or cylindrical wave serving as an incident source enters the continuous spectrum bound state laser, a real continuous spectrum bound state can be achieved, an infinite periodic structure is not needed, a high-loss material is not needed, the continuous spectrum bound state laser has the advantages of being compact in structure and easy to integrate, a full-dielectric scheme is adopted, and cost is reduced. The problem of large material loss caused by materials with near-zero or infinite dielectric constants is reduced, and the material can be applied to photonic devices such as lasers and sensors.

Description

Technical Field

[0001] This invention relates to the field of photonics, and more specifically, to a compact dielectric structure for realizing continuous spectrum bound states. Background Technology

[0002] Continuum-bound states (CBSs) are nonradiative eigenmodes in the radiation continuum. Theoretically, they possess an infinite radiation quality factor and zero resonant linewidth, enabling extremely strong energy localization and field enhancement, making them valuable for applications in lasers and sensors. Existing technologies have proposed various structural schemes to realize CBSs, such as photonic crystals, grating arrays, and metasurfaces. These structures typically rely on periodic extensions in one or more directions. However, in practical device fabrication, infinitely periodic structures are difficult to achieve, and finite-size structures cause CBSs to degenerate into quasi-continuum-bound states with finite quality factors. Furthermore, some existing technologies rely on materials with near-zero or infinite dielectric constants to realize CBSs, but these materials typically exhibit significant material losses, leading to a substantial decrease in the quality factor and limiting the practical application of CBSs in high-quality factor devices and low-loss applications. Currently, a compact dielectric structure for realizing CBSs remains lacking. Summary of the Invention

[0003] To address the shortcomings of the prior art, this invention proposes a compact dielectric structure for realizing a continuous spectrum bound state. When vortex light or cylindrical wave as the incident source is incident on the compact dielectric structure of this invention, a true continuous spectrum bound state can be realized.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A compact dielectric structure for realizing continuous-spectrum bound states includes a ring-shaped dielectric layer. A double-ring grating is disposed between the outer and inner circular boundaries of the dielectric layer. The double-ring grating is concentric with the outer and inner circular boundaries of the dielectric layer. The double-ring grating is a subwavelength structure, comprising an inner ring grating and an outer ring grating. Both the inner and outer ring gratings include several grating units with a period number of s. All grating units are uniformly distributed in a circular array with the same radian. The thickness of the inner ring grating is smaller than that of the outer ring grating. The structure also includes an incident source, propagating from the inner circular boundary to the outer circular boundary. The incident source has a topological charge of... l Vortex light or cylindrical waves.

[0005] Furthermore, the outer circular boundary radius of the dielectric layer is 1 / a The radius of the inner circle boundary is 1 / ( ae aL ),in a =2π / ( sD), D and L These are preset adjustable parameters.

[0006] Furthermore, the refractive index of the dielectric layer is 1 / ( ar A refractive index-gradient medium, where r represents the radius from the center of the circle to any position within the medium layer.

[0007] Furthermore, the angular period of the double-ring grating is 2π / s The thickness of the outer annular grating is e ad / 2 ( e aD / 5 -1) / ( ae aL / 2 The thickness of the inner annular grating is (1- e -aD / 5 ) / ( ae ad / 2+aL / 2 ), d This is an adjustable parameter.

[0008] Furthermore, the spacing between the outer annular grating and the inner annular grating is ( e ad / 2 - e -ad / 2 ) / ( ae aL / 2 The distance between the outer annular grating and the outer circular boundary is (1- e ad / 2+aD / 5-aL / 2 ) / a The distance between the inner annular grating and the inner circular boundary is ( e -ad / 2-aD / 5-aL / 2 - e -aL ) / a .

[0009] Furthermore, the grating units in the double-ring grating include those with a filling refractive index of [missing information]. n / ( ar The high-refractive-index medium portion and the low-refractive-index medium portion that is the same as the filling medium in the medium layer. n It is a constant.

[0010] Furthermore, the proportion of the high-refractive-index medium portion of all grating units in the double-ring grating over the entire circumference is... p ,in p It is a constant and satisfies 0 < p <1.

[0011] In summary, the invention has the following beneficial effects: In use, when vortex light or cylindrical waves, acting as the incident source, are incident from the inner circular boundary onto the compact dielectric structure of this invention, a true continuous-spectrum bound state is achieved. Achieving a true continuous-spectrum bound state within a compact structure of finite size overcomes the problems of strong dependence on infinite-periodic structures and difficulty in practical fabrication in existing technologies. The all-dielectric approach reduces the significant material loss associated with materials with near-zero or infinite dielectric constants. This invention requires neither an infinite-periodic structure nor high-loss materials, offering advantages such as compact structure and ease of integration, making it applicable to photonic devices such as lasers and sensors. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the compact dielectric structure designed in this invention.

[0013] Figure 2 This is a refractive index distribution diagram of the compact dielectric structure designed in this invention.

[0014] Figure 3 The dielectric compact structure designed in this invention is different in parameters d Transmission spectrum under the given conditions.

[0015] (1) is the center, (2) is the dielectric layer, (3) is the double ring grating, (4) is the outer circular boundary, (5) is the inner circular boundary, and (6) is the incident source. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and examples.

[0017] like Figures 1-3 As shown, this invention discloses a compact dielectric structure for realizing continuous spectrum bound states, comprising an annular dielectric layer 2, with a double-ring grating 3 disposed between the outer circular boundary 4 and the inner circular boundary 5 of the dielectric layer 2. The double-ring grating 3 is embedded in the dielectric layer 2, and the two circular boundaries and the double-ring grating 3 share the same center 1. The double-ring grating 3 is a subwavelength structure, where subwavelength is a comparison between the structure size and the incident source wavelength, and the size is smaller than the incident source wavelength. It includes an inner ring grating and an outer ring grating, both of which include several grating units with a period number of s. All grating units are uniformly distributed in a circular array with the same curvature, and the thickness of the inner ring grating is smaller than that of the outer ring grating. Figure 1 As shown, the double-ring grating 3 is composed of multiple grating units arranged periodically along the angular direction. Each grating unit is the smallest repeatable structure in the grating that forms the entire grating. The high-refractive-index medium filling portion within the grating unit is... Figure 1 The orange arc-shaped structure in the image refers to the low-refractive-index medium filling portion of the grating unit. Figure 1 The dashed lines represent the arc-shaped sections between adjacent orange arc-shaped structures, with a period number of [number missing]. s, s It is a positive integer, and its angular period is 2π / s The entire structure satisfies rotational symmetry; the radius of the outer circular boundary 4 in dielectric layer 2 is 1 / a The radius of the inner circular boundary is 1 / ( ae aL ),in a =2π / ( sD ), D and L The preset adjustable parameters; the spacing between the outer and inner annular gratings in the double annular grating 3 is ( e ad / 2 - e -ad / 2 ) / ( ae aL / 2 The thickness of the outer annular grating is... e ad / 2 ( e aD / 5 -1) / ( ae aL / 2 The thickness of the inner annular grating is (1- e -aD / 5 ) / ( ae ad / 2+aL / 2 The distance between the outer annular grating and the outer circular boundary 4 is (1- e ad / 2+aD / 5-aL / 2 ) / a The distance between the inner annular grating and the inner circular boundary 5 is ( e -ad / 2-aD / 5-aL / 2 - e -aL ) / a ,in d It is an adjustable parameter, and d >0; the refractive index of the medium filling layer 2 is 1 / ( ar A refractive index graded medium, wherein r Let r represent the radius from the center 1 to any position within the dielectric layer 2. Different radii have different refractive indices, and the value of r lies between the radii of the outer circular boundary 4 and the inner circular boundary 5. This radius is the radius with the center 1 as the origin of the coordinate system. Several grating units in the double-ring grating 3 are arranged periodically along the circumference. Each grating unit contains a filling element with a refractive index of... n / ( ar The high-refractive-index medium portion and the low-refractive-index medium portion, which are the same as those in medium layer 2, are filled with a medium. n The value is a constant. The proportion of the high-refractive-index medium portion of all grating units in the double-ring grating 3 within the entire circumference is... p ,in p It is a constant and satisfies 0 < p<1, the number of periods s and the proportion p of the grating units are both adjustable parameters; length D , L The number of periods of the grating units within the double-ring grating 3 s Adjustments can be made as needed; the invention also includes an incident source 6, the propagation direction of which is from the inner circular boundary 5 to the outer circular boundary 4, and the incident source 6 has a topological charge of l The vortex light or cylindrical wave incident on source 6 has an exit angle based on the topological charge of source 6. l It is determined that when the topological load number is l When vortex light or cylindrical waves are incident on a compact dielectric structure, a truly continuous spectrum bound state is achieved. l When the topological charge is 0, the vortex light is a cylindrical wave. At this time, the direction of the source is tangent to the inner circular boundary everywhere, and the topological charge is zero. l Adjustments can be made based on actual usage needs.

[0018] Example: In this example, the operating wavelength of the vortex light is λ , λ The preset operating wavelength parameters and topology charge number l =2. Figure 1 The dimensional parameters of the compact dielectric structure described in the text are selected as follows: the number of periods of the double-ring grating 3. s =10, angular period is 0.2π rad, set D =2πm, L =8πm, n =2, a =1 / 10m -1 The refractive index of the medium filling the double-ring grating 3 is 20 / r The thickness of the outer annular grating is 10. e d / 20 ( e π / 25 -1) / e 2π / 5 m, the thickness of the inner annular grating is 10(1- m). e -π / 25 ) / e d / 20+2π / 5 m, the distance between the outer annular grating and the outer circular boundary 4 is 10(1- e d / 20-9π / 25 The distance between the inner annular grating and the inner circular boundary 5 is 10 (m). e -d / 20-11π / 25 - e -4π / 5 )m, d The length parameter is adjustable; the radius of the outer circular boundary 4 of the dielectric layer 2 is set to 10m, and the radius of the inner circular boundary 5 is set to 10 / m. e 4π / 5m, the refractive index of the medium filling the dielectric layer 2 is 10 / r ,set up p =0.8, in the double ring grating 3, the high refractive index medium accounts for 80% in a single grating unit, and the remaining 20% ​​of the low refractive index medium region is composed of the medium in the medium layer 2; Figure 2 yes Figure 1 The corresponding refractive index distribution diagram shows that the area outside the outer circular boundary 4 of the dielectric layer 2 is composed of air. Figure 3 yes Figure 1 The corresponding compact dielectric structure of the invention is designed with different parameters. d Transmission spectrum under given conditions, where wave vector k =2π / λ rad / m, G =2π / D =1rad / m. Under specific incident vortex light, structural and material parameters, a resonance vanishing point appeared in the transmission spectrum (marked with a circle in the figure), proving that the structure of the present invention supports a continuous spectrum bound state.

[0019] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A compact dielectric structure for realizing continuous spectrum bound states, characterized in that, The structure includes a circular dielectric layer (2), and a double-ring grating (3) is provided between the outer circular boundary (4) and the inner circular boundary (5) of the dielectric layer (2). The double-ring grating (3) is concentric with the outer circular boundary (4) and the inner circular boundary (5) of the dielectric layer (2). The double-ring grating (3) is a subwavelength structure, including an inner ring grating and an outer ring grating. Both the inner ring grating and the outer ring grating include several grating units with a period number of s. All grating units are evenly distributed in a circular array and have the same curvature. The thickness of the inner ring grating is smaller than that of the outer ring grating. It also includes an incident source (6), whose propagation direction is from the inner circular boundary (5) to the outer circular boundary (4), and the incident source (6) has a topological charge of l Vortex light or cylindrical waves.

2. The compact dielectric structure for realizing continuous spectrum bound states according to claim 1, characterized in that, The radius of the outer circular boundary (4) of the dielectric layer (2) is 1 / a The radius of the inner circular boundary (5) is 1 / ( ae aL ),in a =2π / ( sD ), D and L These are preset adjustable parameters.

3. The compact dielectric structure for realizing continuous spectrum bound states according to claim 2, characterized in that, The dielectric layer (2) is filled with a refractive index of 1 / ( ar The refractive index of the medium is gradually changed, where r represents the radius from the center (1) to any position within the medium layer (2).

4. The compact dielectric structure for realizing continuous spectrum bound states according to claim 1, characterized in that, The angular period of the double-ring grating (3) is 2π / s The thickness of the outer annular grating is e ad / 2 ( e aD / 5 -1) / ( ae aL / 2 The thickness of the inner annular grating is (1- e -aD / 5 ) / ( ae ad / 2+aL / 2 ), d This is an adjustable parameter.

5. The compact dielectric structure for realizing continuous spectrum bound states according to claim 4, characterized in that, The distance between the outer annular grating and the inner annular grating is ( e ad / 2 - e -ad / 2 ) / ( ae aL / 2 The distance between the outer annular grating and the outer circular boundary (4) is (1- e ad / 2+aD / 5-aL / 2 ) / a The distance between the inner annular grating and the inner circular boundary (5) is ( e -ad / 2-aD / 5-aL / 2 - e -aL ) / a .

6. The compact dielectric structure for realizing continuous spectrum bound states according to claim 5, characterized in that, The grating unit in the double-ring grating (3) includes a filling refractive index of n / ( ar The high-refractive-index medium portion and the low-refractive-index medium portion that are the same as those in the medium layer (2) are filled with the same medium. n It is a constant.

7. The compact dielectric structure for realizing continuous spectrum bound states according to claim 4, characterized in that: The proportion of the high-refractive-index medium portion of all grating units in the double-ring grating (3) within the entire circumference is: p ,in p It is a constant and satisfies 0 < p <1.

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