Plasmon waveguide structure and refractive index sensor

Abstract

The embodiment of the invention provides a plasmon waveguide structure and a refractive index sensor, and the plasmon waveguide structure comprises a metal substrate layer; a multi-period composite metal grating layer; the dielectric layer is arranged between the metal substrate layer and the multi-period composite metal grating layer; wherein the multi-period composite metal grating layer is composed of nano-metal supercell structures which are periodically arranged in the direction, and each nano-metal supercell structure is formed by periodically arranging at least two metal structures with different grating periods in the direction according to a preset grating interval; and the structures are alternately arranged in the direction at preset periodic intervals. According to the invention, decoupling and flexible regulation and control of resonance position and intensity can be realized based on a plurality of independent resonant cavities with spatial separation provided by the multi-period composite metal grating layer.

Description

Technical Field

[0001] This application relates to the field of micro-nano photonics, and to, but is not limited to, a plasmonic waveguide structure and a refractive index sensor. Background Technology

[0002] With the rapid development of photonics technology, various application scenarios are placing increasingly stringent demands on the functionality of optical devices. This makes the precise control of resonant characteristics a core technological bottleneck for breaking through the current performance limits of optical devices. Metal-Dielectric-Metal (MDM) structures in the field of micro-nano optics are widely considered as potential structures for achieving efficient light control due to their unique wavelength-localized confinement characteristics. However, existing MDM structures still have significant shortcomings in terms of resonant tuning flexibility and light energy harvesting efficiency: on the one hand, the design of traditional MDM structures has obvious limitations in independently controlling the resonant position and intensity; on the other hand, the overlap of resonant fields significantly reduces the overall utilization rate of light energy. These defects not only hinder the miniaturization and integration of optical devices containing MDM structures but also restrict the overall improvement of the comprehensive performance of optical devices. Summary of the Invention

[0003] To address the above issues, this application provides a plasmonic waveguide structure and a refractive index sensor. The aim is to achieve decoupling and flexible control of the resonant position and intensity based on multiple spatially separated independent resonant cavities provided by a multi-period composite metal grating layer.

[0004] The technical solution of this application embodiment is implemented as follows: In a first aspect, embodiments of this application provide a plasmonic waveguide structure, comprising: a metal substrate layer; a multi-period composite metal grating layer; and a dielectric layer disposed between the metal substrate layer and the multi-period composite metal grating layer; wherein the multi-period composite metal grating layer is formed by... It is composed of periodically arranged nanoscale metal supercell structures, wherein the nanoscale metal supercell structure is composed of at least two metal structures with different grating periods, each in a specific direction. The gratings are arranged periodically in the direction according to a preset grating spacing, and in... A structure formed by alternating arrangements at preset periodic intervals in a certain direction.

[0005] In some embodiments, the metal structure with at least two different grating periods includes: a cuboid metal structure with at least two different grating periods.

[0006] In some embodiments, the cuboid metal structure with at least two different grating periods includes: a first nanometal structure with a first geometric length and a second nanometal structure with a second geometric length; the supercell period of the nanometal supercell structure is the least common multiple of the first sub-period and the second sub-period; wherein, the first sub-period is the sum of the first length and the preset grating spacing, and the second sub-period is the sum of the second length and the preset grating spacing.

[0007] In some embodiments, the geometric widths of the first nanometal structure and the second nanometal structure are both preset grating widths; the width of the nanometal superstructure is twice the spatial width; wherein the spatial width is the sum of the preset grating width and the preset periodic spacing.

[0008] In some embodiments, the cuboid metal structures with at least two different grating periods include: at least two cuboid metal structures with the same geometric thickness and geometric width but different geometric lengths; or, the cuboid metal structures with at least two different grating periods include: at least two cuboid metal structures with the same geometric width but different geometric lengths and geometric thicknesses.

[0009] In some embodiments, both the metal substrate layer and the multi-period composite metal grating layer are made of metallic silver.

[0010] Secondly, embodiments of this application provide a refractive index sensor, comprising: a detection unit; and an optical unit consisting of a plasmonic waveguide structure as described in any of the preceding claims, and a material to be measured layer on a multi-period composite metal grating layer covering the plasmonic waveguide structure; the optical unit is configured to receive and excite multi-band composite incident light, so that the multi-band composite incident light and the material to be measured layer undergo optical interaction based on surface plasmon resonance; the detection unit is configured to detect the optical parameters of different band probes in the multi-band composite incident light after the optical interaction, thereby realizing the refractive index measurement of the material to be measured.

[0011] In some embodiments, the optical unit is specifically used to receive the multi-band composite incident light and, through the diffraction effect of the grating within the multi-period composite metal grating layer, couple the momentum of the multi-band composite incident light to the momentum of the surface plasmons, thereby exciting the surface plasmon resonance at the interface of the multi-period composite metal grating layer, the dielectric layer, and the material to be tested, so that the evanescent field of the surface plasmon resonance interacts with the material to be tested; the detection unit is specifically used to detect the change in the optical parameters corresponding to the resonance of different band probes in the multi-band composite incident light after the optical interaction when the change in the properties of the material to be tested causes a change in the interface refractive index of the material to be tested, thereby obtaining the change in the refractive index of the material to be tested.

[0012] In some embodiments, the optical parameters include: resonant position and coupling strength.

[0013] In some embodiments, the properties of the substance to be tested include: concentration, adsorption amount, impurity content, and composition.

[0014] The beneficial effects of the technical solutions provided in this application include at least the following: The plasmonic waveguide structure provided in this application includes: a metal substrate layer; a multi-period composite metal grating layer; and a dielectric layer disposed between the metal substrate layer and the multi-period composite metal grating layer; wherein the multi-period composite metal grating layer is composed of... It consists of periodically arranged nanoscale metal supercells, each composed of at least two metal structures with different grating periods. The gratings are arranged periodically in the direction according to a preset grating spacing, and in... The structure is formed by alternating elements at preset periodic intervals in the direction of the grating. In this way, by utilizing the multiple independent resonant cavities with spatial separation provided by the multi-period composite metal grating layer, the physical isolation and field localization characteristics of the multi-period units can be achieved, and the resonant position and intensity can be decoupled and flexibly controlled.

[0015] The refractive index sensor provided in this application includes: a detection unit; an optical unit consisting of a plasmonic waveguide structure and a test material layer on a multi-period composite metal grating layer covering the plasmonic waveguide structure; the optical unit is used to receive and excite multi-band composite incident light so that the multi-band composite incident light and the test material layer undergo optical interaction based on surface plasmonic resonance; the detection unit is used to detect the optical parameters of different band probes in the multi-band composite incident light after optical interaction, thereby realizing the refractive index measurement of the test material. Thus, based on the decoupling and flexible control of the resonance position and intensity of the plasmonic waveguide structure with a multi-period composite metal grating layer, an integrated optical unit corresponding to the plasmonic waveguide structure (multi-period composite metal grating layer) and the test material layer is further constructed to realize the refractive index measurement of the test material. That is, by combining the multi-band composite light source detection mechanism and the multi-resonance mode coordinated response excited by the multi-period composite grating, a high-sensitivity and wide dynamic range measurement of the refractive index of the test material is achieved.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the technical solutions provided in the embodiments of this application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 A schematic diagram of a plasmonic waveguide structure provided in an embodiment of this application; Figure 2 A schematic diagram of the grating surface profile and cross-section of a plasmonic waveguide structure provided in an embodiment of this application; Figure 3 A schematic diagram showing the reflectivity, electric field distribution, and magnetic field distribution of a nano-metal supercell structure in a plasmonic waveguide structure provided in this application embodiment when the nano-metal supercell structure is composed of different periodic structures; Figure 4 This is a schematic diagram illustrating the influence of a cuboid metal structure with different thicknesses on the intensity of transversely magnetically polarized plasmon dual resonant modes in a plasmonic waveguide structure provided in this application embodiment. Figure 5 A schematic diagram illustrating the influence of a plasmonic waveguide structure on the resonant position in three-period and two-period scenarios, as provided in an embodiment of this application. Figure 6A schematic diagram illustrating the influence of a plasmonic waveguide structure on the resonant mode characteristics under different incident angles, polarization angles, and thicknesses of the intermediate dielectric layer, as provided in this application embodiment. Figure 7 A schematic diagram illustrating the influence of different horizontal displacements, cell spacings, grating gaps, and grating widths on the resonant mode characteristics of a plasmonic waveguide structure provided in this application embodiment; Figure 8 A schematic diagram illustrating the composition of a refractive index sensor provided in an embodiment of this application; Figure 9 This is a schematic diagram of a refractive index sensor and the corresponding reflectivity of its surface when different refractive indices are introduced into it, as provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The following embodiments are used to illustrate this application, but are not intended to limit the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0020] It should be noted that the terms "first, second, and third" used in the embodiments of this application are merely to distinguish similar objects and do not represent a specific order of objects. It is understood that "first, second, and third" can be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0021] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this application pertain. It should also be understood that terms such as those defined in general dictionaries should be understood to have a meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0022] Example 1: See Figure 1The diagram shown is a schematic of a plasmonic waveguide structure provided in an embodiment of this application, wherein the plasmonic waveguide structure 100 includes: Metal substrate 101; Multi-period composite metal grating layer 103; Dielectric layer 102 is placed between the metal substrate layer and the multi-period composite metal grating layer; The multi-period composite metal grating layer 103 is composed of... The structure is composed of periodically arranged nano-metal supercells 1031, wherein each nano-metal supercell 1031 is composed of at least two metal structures with different grating periods. The gratings are arranged periodically in the direction according to a preset grating spacing, and in... A structure formed by alternating arrangements at preset periodic intervals in a certain direction.

[0023] here, Figure 1 The multi-period composite metal grating layer 103 shown is composed of... The orientation refers to three (for example only) periodically arranged nanoscale metal supercell structures 1031 arranged perpendicular to the grating extension direction. In practical applications, the number of nanoscale metal supercell structures 1031 included in the multi-periodic composite metal grating layer 103 is not limited to... Figure 1 The specific number of the three shown can be determined according to actual needs, and this application does not impose any limit on it.

[0024] Correspondingly, Figure 1 The nanoscale metal supercell structure 1031 shown is composed of two cuboid metal structures with different grating periods. They are arranged in rows periodically according to a preset grating spacing in the direction, and in... The direction, i.e. the structure formed by alternating arrangements at a preset periodic interval perpendicular to the extension direction of the grating, is also just an example; that is to say, the number of types of metal structures included in the nano metal supercell structure 1031, and the corresponding structures of the metal structures, can be determined according to actual needs.

[0025] In other words, the plasmonic waveguide structure 100 is a three-dimensional MDM structure; in this structure, the multi-period composite metal grating layer 103 is specifically formed by the spacing of thin dielectric layers.

[0026] In some embodiments, the thickness of the dielectric layer 102 is on a subwavelength scale.

[0027] In some embodiments, the metal substrate 101 and the multi-period composite metal grating layer 103 are both made of metallic silver.

[0028] In some embodiments, the plasmonic waveguide structure 100 uses silver (Ag) as the metal substrate because Ag has advantages such as high conductivity, excellent optical performance, low resistance loss, cost-effectiveness, and a small imaginary part of its dielectric constant. In terms of manufacturing feasibility, it aligns with mature nanofabrication processes. Specifically, a thin waveguide layer (i.e., dielectric layer 102) is deposited on the Ag substrate. Here, magnetron sputtering can be used to deposit inorganic materials or spin-coating can be used to deposit polymers. The thickness of the dielectric layer 102 can be controlled by the deposition time or solution concentration. After coating with photoresist, a supercell pattern (i.e., the nanometal supercell structure 1031) is defined using electron beam lithography (EBL) or nanoimprint lithography (NIL). The supercell pattern is transferred to the dielectric layer 102 using reactive ion etching (RIE), with Ag serving as an etching stop layer to form a multi-period composite metal grating layer 103. This method has been widely used in the field of metal-waveguide nanostructures. For direct metal patterning or changing the layer thickness, focused ion beam (FIB) milling can be considered as an alternative.

[0029] In other words, the plasmonic waveguide structure 100 comprises three functional layers: a top multi-periodic composite metal grating layer 103, a middle uniform dielectric spacer layer (i.e., dielectric layer 102), and a bottom metal substrate layer 101. This layered architecture provides a solid foundation for efficient optical field modulation and localized field enhancement. Regarding material selection, Ag possesses excellent plasmonic properties—high conductivity, low optical loss, and a small imaginary part of its relative permittivity. These properties facilitate the effective excitation and propagation of surface plasmons and support high-quality resonant modes. Therefore, Ag is used in both the top multi-periodic composite metal grating layer 103 and the bottom metal substrate layer 101 in this application. Furthermore, mature silver micro / nano fabrication technology provides solid technical support for the manufacture of controllable devices (e.g., deposition and patterning processes). From a geometric design perspective, the plasmonic waveguide structure 100 provided in this application achieves independent control of resonant modes through multi-dimensional optimization, thereby enhancing field localization and energy confinement effects.

[0030] In some embodiments, the metal structure with at least two different grating periods includes: a cuboid metal structure with at least two different grating periods.

[0031] In some embodiments, the at least two cuboid metal structures with different grating periods can refer to: at least two cuboid metal structures with the same geometric thickness and geometric width but different geometric lengths; or, at least two cuboid metal structures with the same geometric width but different geometric lengths and geometric thicknesses.

[0032] In some embodiments, at least two cuboid metal structures with different grating periods will have different geometric lengths.

[0033] Based on this, the cuboid metal structure with at least two different grating periods includes: a first nano-metal structure with a first geometric length and a second nano-metal structure with a second geometric length; the supercell period of the nano-metal supercell structure 1031 is the least common multiple of the first sub-period and the second sub-period.

[0034] Wherein, the first sub-period is the sum of the first length and the preset grating spacing, and the second sub-period is the sum of the second length and the preset grating spacing.

[0035] In this application, the first length is assumed to be different from the second length.

[0036] Correspondingly, you can refer to Figure 2 As shown in A, this represents the first and second sub-periods, i.e. ( A schematic diagram of the surface profile of the multi-period composite metal grating layer 103 of the plasmonic waveguide structure 100 with a wavelength of (400 nm, 500 nm) is shown. Figure 2 Figure B shows a cross-sectional view of the nanometal supercell structure 1031 (which is an example of a cuboid metal structure including two different grating periods, i.e.) Figure 2 Supercell shown in B).

[0037] Continue to refer to this section. Figure 2 As shown, the first length Second length Its corresponding first sub-period Second sub-period Correspondingly, the supercell period of the nanometal supercell structure 1031 (That is, the length of the 1031 nanoscale metal supercell structure), as defined by formula (1): Formula (1); in, For calculation and The greatest common divisor function; For calculation and The least common multiple function.

[0038] Here, if the nanometal supercell structure 1031 is composed of... Metal structures with different grating periods, namely... Metal structures of different geometric lengths, that is, made of ( ) are constructed in sequence; in other words, Metal structures with different grating periods each have their own characteristics. They are arranged in rows periodically according to a preset grating spacing in the direction, and in... A structure formed by alternating arrangements of nanomaterial supercells at predetermined periodic intervals. The supercell period of the 1031 nanomaterial supercell structure is then determined. Defined as the least common multiple of the sub-periods corresponding to all metallic structures, i.e., the smallest spatial length divisible by each sub-period. This definition ensures that the nanometal supercell structure 1031 contains repeating units that are integer multiples of each sub-period, thereby maintaining the periodicity of the nanometal supercell structure 1031. This relationship can be expressed as: Formula (2); Meanwhile, the geometric widths of the first and second nano-metal structures are both preset grating widths; the width of the nano-metal supercell structure 1031 is twice the spatial width.

[0039] Wherein, the spatial width is the sum of the preset grating width and the preset periodic spacing.

[0040] Here, continue to refer to Figure 2 As shown in B, the width of the nanometal supercell structure 1031 is... It can be defined as: Formula (3); in, For the geometric width of the metal structure, The preset periodic interval.

[0041] In this application, it is assumed that the geometric widths of at least two metal structures with different grating periods (e.g., the first nanometal structure and the second nanometal structure) are the same.

[0042] Here, if the nanometal supercell structure 1031 is composed of... Metal structures with different grating periods ( If the nanostructure is constructed in sequence, then the width of the corresponding nanometal supercell structure 1031 is... It can be defined as: Formula (4); at the same time, Figure 2A corresponds to a schematic diagram of the plasmonic waveguide structure 100 provided in a practical application. Here, the surface profile of the multi-period composite metal grating layer 103 can be described by a rectangular function, which represents a three-dimensional periodic array, as shown in formula (5). This rectangular function can be further defined as a height function. Through the nano-metal supercell structure 1031 along Direction and grating area along It is constructed by the periodic superposition and coupling of directions.

[0043] Formula (5); Among them, any point of the multi-period composite metal grating layer 103 Highly ,and , ;at the same time , ; Among them, variables Indicates the index within a single period, taking the integer value; and They represent direction and Periodic indices in the direction (all integers).

[0044] Thus, the multi-period design of the multi-period composite metal grating layer 103 in this application provides a structural basis for realizing multiple independent resonant modes. The thicknesses of the first and second nanometer metal structures in the multi-period composite metal grating layer 103 are denoted as […]. and (Continue to refer to this section) Figure 2 As shown, the geometric thicknesses of two cuboid metal structures are given; the preset periodic spacing is... The geometric widths corresponding to the first and second nanometer metal structures, i.e., the preset grating widths, are both... The preset grating spacing is Meanwhile, the thickness of the intermediate dielectric layer (dielectric layer 102) is... Furthermore, the dielectric layer 102 can be made of a precisely designed dielectric material, which ensures both effective localization of the optical field and provides high flexibility for resonant mode modulation. Based on this, by optimizing these geometric parameters, the plasmonic waveguide structure 100 provided in this application can achieve subwavelength-scale optical field manipulation and support multidimensional design optimization to independently adjust the mode frequency and field distribution, which has significant advantages for high-performance micro / nano photonic devices.

[0045] In some embodiments, the plasmonic waveguide structure 100 provided in this application has three core advantages: First, the dielectric layer 102 between the top multi-periodic composite metal grating layer 103 and the metal substrate layer 101 forms a highly efficient waveguide, which can confine the light field within the subwavelength scale, thereby enhancing the light-matter interaction; second, the periodically arranged nanoscale metal supercell structure 1031 in the top multi-periodic composite metal grating layer 103 can confine different resonance modes within their respective periodic units, achieving independent control of the resonance position and intensity; finally, through precise adjustment... , , , , and The uniform geometric parameters enable the plasmonic waveguide structure 100 to achieve multifunctional integration over a wide spectral range, making it suitable for applications such as photoluminescence enhancement, multi-band optical filtering, and high-sensitivity sensing. Furthermore, the plasmonic waveguide structure 100 provided in this application allows for independent control of resonant modes and precise tuning of multiple wavelengths in different spatial domains, thereby opening up new possibilities for multifunctional photonic devices.

[0046] It should be noted that the current figure of merit (FOM) of the plasmonic waveguide structure 100 is limited by the ohmic loss in the metallic substrate 101, which restricts the quality factor (Q) of the resonant mode to approximately 23 (Q = resonant wavelength / full width at half maximum). To improve the FOM while maintaining mode independence, two strategies can be considered in this application: 1. Replace Ag with low-loss materials, such as gold to enhance oxidation resistance, or dielectrics such as Si or Si3N4 to completely eliminate ohmic losses.

[0047] 2. Further optimize structural parameters (e.g.: and To enhance field constraints.

[0048] Here, implementing the above two strategies can improve Q and FOM without sacrificing mode space isolation, which is crucial for high-sensitivity sensing that requires balancing multimode control and performance.

[0049] For reference here. Figure 3 As shown in A, it demonstrates ( The corresponding nanoscale metal supercell structure 1031 (corresponding to) when ) = (400nm, 500nm) The reflection characteristics of (2000nm) are compared with those of a single-period structure (the nano-metal supercell structure 1031 is a structure formed by arranging only one type of metal structure in a periodic row according to a preset grating spacing): =400nm and =500nm for comparison. Here, the remaining geometric parameters of the plasmonic waveguide structure 100 are the same, that is: = =40nm =50nm =100nm =200nm =80nm. Figure 3 As shown in Figure A, the reflection curves of the multi-period grating of the plasmonic waveguide structure 100 exhibit a significant decreasing trend at both wavelengths. That is, the resonant position is located at: ( , (621.8nm, 735.9nm), the reflectivity value is lower than that of the single-period structure, and the corresponding reflectivity value is: ( , ) = (0.0016, 0.0134), while the single-period structure only exhibits resonance at its characteristic wavelength, that is, the resonance position of the single-period structure is: =632.7nm and =759nm, with corresponding reflectance values ​​of 0.1278 and 0.1066, respectively. This indicates that the multi-period composite structure of the supercell (nanometallic supercell structure 1031) can simultaneously tune two wavelengths of light, exhibiting excellent spectral selectivity and multifunctionality. Furthermore, compared to a conventional single-period grating, the resonance position of the supercell structure shows a blue shift. This may be because the multi-period structure introduces a new interference path, altering the phase relationship of the reflected light, thus leading to the blue shift of the resonance position.

[0050] To fully elucidate the physical mechanism of the resonance mode, this application presents detailed calculations of the electric field amplitude (|E|) distribution within the 1031 nanoscale metal supercell structure. For direct comparison, Figure 3 B and C respectively demonstrate single-period structures: =400nm and The distribution of electric field amplitude at 500nm. In a dual-period composite grating: ( , In the region (400nm, 500nm), the resonance location is: , ) = (621.8nm, 735.9nm); correspondingly, such as Figure 3 As shown in D1 and D2, and E1 and E2, the single-cycle structure is illustrated respectively: =400nm and =500nm at The distribution of electric field amplitudes across the cross-section and within the plane indicates that the electric field is completely confined within the waveguide layers and gaps corresponding to their respective periods. Meanwhile, The electric field in In a grating structure with a diameter of 400 nm, the electric field distribution exhibits a highly concentrated state, which can be obtained from... Figure 3 The D1 showcase It is clearly visible in the cross-sectional view.

[0051] At the same time Figure 3 The grating-waveguide interface presented by D3 This is also confirmed in the floor plan. The region remains inactive. Conversely, in Figure 3 The grating-waveguide interface presented by D3 This is also confirmed in the floor plan. Conversely, in The electric field is only =500nm grating structure localization. Figure 3 In E2 Electric field amplitude distribution in a plane and Figure 3 In E3 The electric field amplitude distribution in the plane confirms this selective excitation. This spatial exclusivity is further verified when the wavelength does not match the grating period, such as... Figure 3 As shown in D2 and E1, no resonance enhancement occurs at this point. (This refers to the area at the grating-waveguide interface.) The planar distribution provides direct evidence of spatial decoupling, showing that the field maximum aligns with the active grating gap and that penetration into adjacent periods is minimal. This explicit wavelength selectivity and spatial independence stems from a modified Bragg phase-matching condition, which ensures that each sub-period interacts selectively only with its corresponding resonant wavelength. While this condition reveals the dominant relationship between the grating period and the resonant wavelength, the effective refractive index is not constant but dynamically tuned by structural parameters (grating thickness, waveguide thickness, gap width) and incident light conditions, resulting in a secondary tuning effect that complements the period dependence.

[0052] In the study of optically coupled systems, the distribution of the magnetic field (Hy) is an important diagnostic tool for understanding the characteristics of coupling modes. By analyzing the magnetic field modes, the formation mechanism and physical significance of the resonance modes in the nanoscale metallic supercell structure 1031 of this application can be elucidated. In the cross-sectional view, the magnetic field distribution at the resonant wavelength exhibits significant coupling behavior, i.e., in =621.8nm ( Figure 3 (D4), it can be seen =5 pairs of field nodes, while =735.9nm ( Figure 3 (E5), then output =4 pairs of field nodes. These field nodes correspond to the minimum magnetic field strength accompanied by antinodes of opposite polarity during adjacent cycles. This alternating mode reflects the interaction between waveguide modes and confirms the standing wave characteristics of the resonance. To supplement the cross-sectional analysis, this application also investigated the in-plane magnetic field distribution at the grating-waveguide interface ( Figure 3 (D6 and E6), these The plan view provides direct evidence of spatial pattern isolation.

[0053] in, Figure 3 The D6 shows The Hy distribution, where the maximum magnetic field value is related to The grating gap of 400 nm was precisely aligned and exhibited the expected pattern in the supercell. =5 node period, while The region shows the minimum field penetration; Figure 3 The E6 in The magnetic field is shown to be confined only to Within a grating of 500 nm, and exhibiting the expected results in the supercell. The node period is 4. There is no field crosstalk between different periodic regions within these nanoscale metal supercells (1031), further confirming the spatial independence of the resonance modes.

[0054] Based on these magnetic field analysis results, this application reveals a coupling configuration characterized by: =2 and =1, the former corresponding to the near-field coupling of positive and negative magnetic field components within each grating gap, and the latter reflecting the coupling occurring directly beneath the grating ridge. This coupling configuration originates from the near-field interaction between adjacent waveguide segments, where mode overlap leads to energy transfer. Each node location marks the region where waveguide modes undergo destructive interference, while the inter-node region exhibits enhanced magnetic intensity. This behavior is consistent with established results from coupled resonance systems, where the number of nodes is related to the coupling strength and mode order. The presence of 5 or 4 pairs of nodes in this application clearly demonstrates the coupling complexity characteristics associated with the multimode nature of the supercell design.

[0055] Correspondingly, this application also relates to the derivation of the Bragg phase matching condition, that is, when light propagates in the plasmonic waveguide structure 100 provided in this application, if the optical path difference (OPD) between the scattered light of adjacent grating units is equal to the wavelength... When the period is an integer multiple of the period, constructive interference (resonance) will occur. For a grating, under conditions of perpendicular light incidence, the round-trip optical path difference of the scattered light between adjacent units is... According to the condition for constructive interference: =M (M is the diffraction order, an integer). In the plasmonic waveguide structure 100, light travels at an effective refractive index... Therefore, the wavelength within the plasmonic waveguide structure 100 is: Substituting the interference conditions, we get: p Formula (6); This application shows ( In the nanoscale metal supercell structure 1031 corresponding to (400nm, 500nm), for In terms of resonant wavelength =621.8nm and satisfies = ;for In other words, =735.9nm and satisfies = At the same time, the period difference =100nm causes spectral separation, i.e., the formation of: and For example, a bimodal reflection curve. Figure 3 As shown in A, in At 621.8nm, Figure 3 The electric field distribution shown in D is confined to =400nm grating region ( Figure 3 (as shown in D1 and D3), while =500nm grating region ( Figure 3 The electric field shown in D2 and D3 is negligible, i.e., it is only related to... = Resonance is generated. At 735.9nm, Figure 3 The electric field distribution shown by E is confined to =500nm grating region ( Figure 3 Within (as shown in E2 and E3), while =400nm grating region ( Figure 3 The electric field shown in E1 and E3 is negligible, i.e., it only interacts with... = Resonance is produced. Here, regarding detuning (e.g.: , ),Right now Figure 3 D2 and E1 show that no resonance was observed in either grating because None of the following conditions are met: or .

[0056] Furthermore, for periodic structures, Bloch's theorem states that their electric / magnetic fields have the following form: , Formula (7); in, It is periodic data (which matches the grating period), and It is the Bloch wave vector. Substituting it into Maxwell's equations, we get: and .for and Based on formula (6), it is confirmed that the Bragg condition is a necessary condition for achieving resonance and mode confinement. (See the electric field distribution diagram.) Figure 3 As shown in D), whether it is a short period ( ) or long cycle ( In the waveguide layer (dielectric layer 102) corresponding to the grating, the electric field energy is highly concentrated, indicating that each period of the grating unit can be regarded as an independent resonant cavity. This finding is consistent with the multi-cavity synergistic effect disclosed in the prior art. Specifically, gratings of different periods form independent resonant cavities through physical isolation, and their mode distribution is affected by their respective geometric dimensions ( and This limitation allows for independent control of the resonance. When When it increases, the corresponding and The resonant wavelength spacing will also expand accordingly, which is consistent with the theoretical model of the linear relationship between period and wavelength in long-period fiber gratings. However, if Too small ( When the wavelength is <50nm, mode overlap may occur, thus affecting mode independence. This directly affects the localization strength of the electric field. When Approaching subwavelength scale (e.g.) At wavelengths <100 nm, strong localized surface plasmon resonances or Fabry-Perot resonances can be excited within the gap, significantly improving the efficiency of light-matter interactions. This characteristic plays a crucial role in the design of solar cells or sensors. The dielectric constant of the waveguide layer material changes. Therefore, adjusting the resonant wavelength is crucial. By selecting a high-refractive-index material (such as TiO or Si), a longer resonant wavelength can be obtained within the same period, providing flexibility for the design of multi-band devices. Figure 3 Analysis of the electric field distribution in D and E shows that the total area of ​​the energy localization region (waveguide layer and gap) in the supercell composite structure provided in this application is larger than that of the single-period structure. The superposition effect of the two resonance peaks significantly improves the overall absorption rate or scattering efficiency.

[0057] In some embodiments, taking the nanoscale metal supercell structure 1031 comprising two cuboid metal structures with different geometric lengths as an example, the following cases are studied: Scenario 1: The two cuboid metal structures have the same thickness. = The influence of the transverse magnetic polarization plasmon dual resonance mode on the intensity of the transverse magnetic polarization plasmon dual resonance mode (with corresponding values ​​of 10nm, 20nm, 40nm, and 70nm). Scenario 2: In With a fixed 40nm, The effects on the intensity of transverse magnetic polarization plasmon dual resonant modes at wavelengths of 10nm, 15nm, 20nm, 40nm, and 80nm, respectively. Scenario 3: In With a fixed 40nm, The effects on the intensity of transverse magnetic polarization plasmon dual resonant modes at wavelengths of 10nm, 15nm, 20nm, 40nm, and 80nm, respectively.

[0058] The corresponding view can be referenced. Figure 4 As shown in A, in case one, when = Furthermore, as the thickness increases from 10 nm to 40 nm, a blue shift occurs in the resonant wavelength; however, a further increase in thickness to 70 nm results in a red shift, indicating that excessive thickness reverses the tuning direction. This blue shift phenomenon... Figure 3 In A, it was also observed that the wavelength of the composite structure was shorter than that of the single-period grating, which is due to the increased overlap of metallic modes at medium thickness. This overlap reduces the effective refractive index. The modified Bragg condition in Equation (6) leads to a blue shift. Similar thickness-dependent blue shift phenomena have been reported in coupled waveguide and plasmonic systems, where mode confinement and effective refractive index variations dominate the spectral response. When the thickness is too large, the accumulated ohmic loss and mode confinement deterioration cause the geometric path length effect to dominate, resulting in a red shift. Correspondingly, this application analyzes the phenomenon when the thickness is equal ( = ) grating structure, such as Figure 4 As shown in A, the thickness of the double-period grating is... = As the thickness increases from 10 nm to 40 nm, the intensity of the double resonance peaks gradually increases. When the thickness reaches 40 nm, the resonance intensity reaches its maximum value, and the resonance position undergoes a blue shift. When the thickness increases to 70 nm, the resonance intensity weakens due to excessive metal loss, and the resonance wavelength begins to red shift relative to the 40 nm case. Correspondingly, for thicknesses of unequal ( In cases such as (cases two and three), Figure 4As shown in Figures B and C, when the thickness on one side is fixed at 40 nm and the thickness on the other side varies from 10 to 80 nm, the fixed resonance positions (FRPs) remain stable at 621.8 nm and 735.9 nm. In both cases, the variable resonance peak first undergoes a blue shift and then a red shift at the extreme thickness (80 nm). It is noteworthy that the fixed resonance peak position... Figure 4 Even in C, , Even at (80nm, 40nm), only a slight change is observed. This indicates its excellent stability, and its actual impact on device performance is negligible. The reduction in light intensity at extreme thicknesses confirms that both insufficient and excessive thickness reduce coupling efficiency. This independent adjustment capability opens up broad application prospects for photoluminescent optical devices. By rationally designing structural parameters, precise wavelength control can be achieved while maintaining the flexibility of tunable other resonant characteristics.

[0059] This application further analyzes the mechanism by which other periodic metallic nanostructures within the 1031 nanomesh supercell modulate the resonance characteristics, thus laying a crucial foundation for achieving precise control of the resonance position. For example... Figure 5 As shown, this application focuses on dual-period (two different nanoscale metal structures) and triple-period (three different nanoscale metal structures) composite gratings to explore the influence of different period combinations on the resonant position. Figure 5 In A, the periods of the two double-period structures are respectively ( ) = (500nm, 600nm) and ( ) = (600nm, 700nm), corresponding to =3000nm and =4200nm. From Figure 5 From the reflection spectrum shown in Figure A, we can see that the resonant positions corresponding to these two sets of periodic combinations are (736.5nm, 855.4nm) and (853.9nm, 978.8nm), respectively. It is worth noting that when the same period of 600nm is used, i.e.: ( , When ) = (600nm, 600nm), the corresponding resonant wavelengths are 855.4nm and 853.9nm, respectively, which are almost completely overlapping. This indicates that the resonant modes of different period combinations are independent of each other, and the period difference of the supercell structure does not produce significant coupling interference. For a double-period composite grating with a smaller period interval, i.e.: ( , ) = (400nm, 420nm), that is =20nm, such as Figure 5As shown in Figure B, the two resonance peaks exhibit a merging trend, with wavelength positions of 626.8 nm and 658.9 nm respectively (wavelength deviation). =32.1nm). It should be noted that, Increasing the wavelength by 8400 nm leads to a decrease in resonance intensity. A similar pattern has been observed in three-period composite gratings, i.e., as... Figure 5 As shown in C, ( , , ) = (400nm, 500nm, 600nm), corresponding =12000nm, its reflection spectrum clearly shows three independent resonance peaks, corresponding to wavelengths of 622.5nm, 739.5nm, and 857.3nm, respectively. This research demonstrates that, regardless of whether it is a dual-period or triple-period composite grating, its resonance position and intensity can be precisely controlled through careful design of the period combination. This characteristic is of significant value in optical device design: given a fixed wavelength position and intensity, other resonance parameters can be independently and flexibly adjusted, thus providing crucial design freedom for integrating multi-band functions.

[0060] Furthermore, this application also investigated the effects of the incident angle, polarization angle, and thickness of the dielectric layer 102. Here, to gain a deeper understanding of the key factors influencing the characteristics of the resonant mode, the effects of the incident angle, polarization angle, and the thickness of the intermediate dielectric layer 102 on device performance were studied. These parameters have a significant impact on the design and application of optical devices. Figure 6 As shown in Figure A, when the incident angle changes from 0° to 10°, the intensity and peak position of the reflection spectrum remain stable, indicating that the plasmonic waveguide structure 100 provided in this application has low sensitivity to changes in the incident angle within this small angular range. This characteristic has significant advantages in practical applications because the incident angle usually does not exceed 10° in most scenarios. However, as the incident angle further increases, additional resonance valleys begin to appear in the reflection spectrum. This phenomenon may be due to the change in the coupling condition between the grating and the incident light caused by the increase in the incident angle, thereby exciting new resonance modes. Although the Bragg condition nominally depends on the incident angle... That is, the incident light wave vector at Components of direction for (in, (where the wave vector is the light wave vector in a vacuum), but the MDM waveguide mode of this application exhibits low angular dispersion within a ±10° range. This is due to strong vertical confinement, where the resonance condition is primarily determined by the thickness and effective refractive index of the dielectric layer 102. The determination is based on the wave vector within the plane, not the in-plane wave vector. Therefore, in While remaining stable, the coupling efficiency (resonance intensity) exhibits a stronger angle dependence. Furthermore, this application investigated the effect of polarization angle on the resonance characteristics, with results as follows: Figure 6 As shown in Figure B, when the polarization angle increases from 0° to 50°, the resonance position and intensity remain essentially unchanged, but some additional resonance valleys are observed. This polarization insensitivity is a key characteristic in optical device design because it ensures the stability of performance under different polarization states. The appearance of additional resonance valleys may be due to small fluctuations in the coupling efficiency between the grating and the waveguide layer caused by the change in polarization angle, thereby exciting new resonance modes. Furthermore, this application also analyzes the influence of the thickness of the intermediate dielectric waveguide layer on the resonance characteristics. This parameter plays a crucial role in determining the coupling efficiency between the incident light, the grating, and the waveguide layer (dielectric layer 102). Figure 6 As shown in Figure C, when the waveguide layer thickness is 20 nm, the coupling between the grating and the waveguide layer is weak, leading to a decrease in resonance intensity. As the thickness gradually increases... At a thickness of 20 nm, the resonance intensity increases accordingly, indicating that increasing the waveguide layer thickness can improve coupling efficiency. When the thickness reaches 80 nm, the optimal coupling conditions are broken, leading to a decrease in resonance intensity and the emergence of other resonance modes. This phenomenon may be due to the fact that an excessively thick waveguide layer alters the coupling conditions between the grating and the incident light, suppressing the original resonance modes while exciting new ones.

[0061] It should be noted that, Figure 6 Other parameters of the plasmonic waveguide structure 100 involved in the reflection spectrum diagram are: ( , ) = (400nm, 500nm); =80nm; =200nm; =100nm, and Figure 6 All three cases shown use the top air interface as the incident surface.

[0062] In some embodiments, this application also studies the effects of horizontal displacement, unit cell spacing, grating gap, and grating width, that is, the effects on the resonant characteristics of the plasmonic waveguide structure 100 (multi-period composite grating structure) provided in this application, which is to say, the study of horizontal displacement ( ), , and The impact on the resonant mode. First, this application studies the horizontal displacement ( The effect of ) on resonance characteristics. For example Figure 7 As shown in A, with From 0 to 60 nm, the intensity and peak position of the reflection spectrum remain essentially unchanged, indicating that the plasmonic waveguide structure 100 provided in this application has a certain degree of immunity to horizontal displacement, which is of great significance for controlling process errors in actual manufacturing. Secondly, this application also analyzes the multi-period grating spacing ( The influence of ) on the resonant mode, such as Figure 7 As shown in B, the results indicate that when At 50nm or 300nm, the interaction between gratings is weak, leading to a decrease in resonance intensity. Conversely, when... At a spacing of 200 nm, the interaction becomes relatively strong, indicating that as the spacing changes... At a wavelength of 100 nm, the resonance characteristics of the two-period gratings exhibit independence; therefore, variations in the spacing between multi-period gratings have a negligible impact on the resonance characteristics. Furthermore, this application also investigated... and The effect on the resonant mode, such as Figure 7 As shown in C and D, and It has a significant impact on resonance characteristics, among which, as As the refractive index increases, the effective refractive index decreases, causing a blue shift at the resonance position and a gradual increase in coupling strength. As the grating size increases, the resonant position exhibits a redshift. These results demonstrate that the resonant position and coupling strength can be precisely controlled by adjusting the grating gap and width. It is particularly important to note that... The definition of is the distance between the centers of the ridge lines, therefore increasing is... It will only reduce the duty cycle. This will weaken the near-field coupling between adjacent ridges and reduce the effective refractive index of the modes. According to the modified Bragg condition, this ultimately leads to the observed blueshift. Conversely, increasing... Can enhance This can trigger redshift, such as Figure 7 As shown in D.

[0063] It should be noted that, Figure 7 Other parameters of the plasmonic waveguide structure 100 involved in the reflection spectrum diagram are: ( , ) = (400nm, 500nm); and Figure 7 The incident light for the subgraphs corresponding to A, B, C, and D all enters from the top (air medium).

[0064] Based on the above description, this application proposes a three-dimensional multi-periodic supercell structure, namely a plasmonic waveguide structure 100, to address the problems of coupling interference between resonant modes and limited control degrees of freedom. Through field design, independent and arbitrary control of the resonant position and intensity can be achieved, while simultaneously realizing efficient light trapping. This plasmonic waveguide structure 100 is based on subwavelength waveguide units formed by dual-periodic composite gratings on a metal substrate layer 101, namely a multi-periodic composite metal grating layer 103. Simultaneously, by utilizing the difference in Bragg phase-matching conditions, the electric field energy is confined within the gaps between the waveguide layers and the corresponding periodic units (…). Within <100nm), mode overlap can be avoided. And according to... Figure 3 The electric field distribution shown indicates that there is no significant coupling within the localized regions of field strength corresponding to the resonant wavelengths of the short-period and long-period units. The magnetic field nodes exhibit a periodic inversion distribution (five pairs of short-period nodes and four pairs of long-period nodes), confirming the independent resonant cavity characteristics of the plasmonic waveguide structure 100. The strong localized surface plasmonic resonance or Fabry-Perot resonance excited by the subwavelength gap significantly enhances the local field energy density, which manifests as a significant improvement in the light-matter interaction efficiency. By adjusting the grating thickness, period, and dielectric layer parameters, the plasmonic waveguide structure 100 achieves independent and arbitrary control over its resonant characteristics. Under TM polarization, the refractive index sensitivity of the plasmonic waveguide structure 100 in the corresponding spectral channels reaches 149 nm / RIU and 204 nm / RIU, respectively. Despite the presence of metallic ohmic losses, its multi-band independent tunability (dual-period dual-resonance peak, three-period three-band) compensates for the limitations of single-mode devices, making it suitable for the parallel detection of various analytes.

[0065] The core advantage of the plasmonic waveguide structure 100 provided in this application lies in the physical isolation and field localization characteristics of its multi-period units. These characteristics not only provide efficient local field enhancement for photoluminescent devices but also enable the construction of multi-band filters and sensors with independently controllable characteristics, covering a wide spectral range. Furthermore, in the field of biosensing, by customizing different periodic units, it can respond to the absorption wavelengths of specific molecules, thereby effectively avoiding signal crosstalk. Further improvements in the quality factor are expected by replacing traditional materials with low-loss dielectric materials (such as Si or Si3N4) based on the plasmonic waveguide structure 100 provided in this application, promoting the development of applications in high-resolution spectral analysis, integrated optical chips, and related fields. In other words, this application represents a breakthrough from "single-mode control" to "multi-mode independent manipulation," opening a new paradigm for the design of high-performance micro / nano photonic devices through field localization and mode separation technologies.

[0066] This application proposes a 3D-MPSC structure composed of a metal-dielectric-metal matrix. This structure features multiple spatially separated independent resonant cavities, effectively preventing the overlap of resonant fields and enabling independent and flexible adjustment of resonant position and intensity (resonance decoupling and arbitrary adjustment), thus allowing efficient and independent control of the optical properties of multiple resonant wavelengths. Furthermore, the optimized geometric layout and material selection significantly enhance light-matter interaction, improving overall light energy utilization. Through waveguide resonant mode-based design optimization, the enhanced localized field can be confined within a single periodic unit, achieving independent control of multiple resonant wavelengths. This approach provides new insights for the development of multi-band optical devices. The proposed structure also exhibits superior refractive index sensing performance under TM polarization, with sensitivities as high as 149 nm / RIU and 204 nm / RIU. Overall, this 3D-MPSC structure provides a solution to the major limitations of traditional MDM configurations in terms of resonant tuning and light-harvesting efficiency. It offers innovative guidance for the design of photonic materials and drives the development of micro- and nano-photonic devices toward higher performance, multifunctionality, and miniaturization, thus injecting new momentum into the field of micro- and nano-photonics.

[0067] Based on the foregoing embodiments, this application further provides a refractive index sensor, see [link to previous embodiment]. Figure 8 As shown, the refractive index sensor 800 includes: Detection unit 801; An optical unit 802 is composed of the plasmonic waveguide structure 100 described above and the material under test layer 8021 covering the multi-period composite metal grating layer 103 within the plasmonic waveguide structure 100. The optical unit 802 is used to receive and excite multi-band composite incident light so that the multi-band composite incident light and the test material of the test material layer 8021 can undergo optical interaction based on surface plasmon resonance. The detection unit 801 is used to detect the optical parameters of the probe light of different bands in the multi-band composite incident light after passing through the optical interaction, so as to realize the refractive index measurement of the substance to be tested.

[0068] In some embodiments, the optical unit 802 is specifically used to receive the multi-band composite incident light and, through the diffraction effect of the grating within the multi-period composite metal grating layer 103, couple the momentum of the multi-band composite incident light to the momentum of surface plasmons, thereby exciting the surface plasmon resonance at the interface of the multi-period composite metal grating layer 103, the dielectric layer 102, and the test material layer 8021, so that the evanescent field of the surface plasmon resonance interacts with the test material.

[0069] The detection unit 801 is specifically used to detect the change in the optical parameters corresponding to the resonance of different band probes in the multi-band composite incident light after the optical interaction when the change in the properties of the substance to be tested causes a change in the interface refractive index of the substance to be tested, thereby obtaining the change in the refractive index of the substance to be tested.

[0070] Here, the evanescent field is an electromagnetic field generated on the side of an optically less dense medium during total internal reflection. It is confined to the interface, decays exponentially, and propagates along the interface.

[0071] In some embodiments, when the refractive index of the substance to be tested changes, the spectrum corresponding to the resonance of different bands of probe light in the multi-band composite light source after optical interaction will produce a red shift or blue shift. Based on this red shift or blue shift phenomenon, the rate of change of the refractive index of the substance to be tested can be detected.

[0072] In some embodiments, the optical parameters include: resonant position and coupling strength.

[0073] In some embodiments, the properties of the substance to be tested include: concentration, adsorption amount, impurity content, and composition.

[0074] In some embodiments, the multi-period composite metal grating layer 103 is used to receive incident light from multi-band composite incident light (multi-band composite light source) and achieve momentum coupling to excite the multi-band composite light source to interact with the test material in the test material layer 8021; by detecting the changes in optical parameters (specifically manifested as the shift of optical peaks, such as the shift of the center wavelength or angle of the resonance peak in the reflection or transmission spectrum) after the interaction of different band probe light in the multi-band composite incident light (which leads to a change in the resonance conditions of surface plasmon resonance), the sensing measurement of the test material can be realized, that is, by detecting the shift of optical peaks, the high-sensitivity refractive index sensing detection of the test material can be realized.

[0075] It should be noted that when the properties of the substance being tested, such as concentration, adsorption amount, impurity content, and composition, change, the refractive index of the interface will change, which will lead to a change in the resonance conditions (momentum matching conditions) of surface plasmon resonance.

[0076] Based on the above description, the plasmonic waveguide structure 100 proposed in this application exhibits a relatively narrow resonance peak in the TM polarized near-infrared region, making it particularly suitable for multi-band refractive index sensing applications. Furthermore, the sensitivity of the refractive index sensor primarily depends on the change in the amplitude of the detectable optical signal induced by the refractive index change. The plasmonic waveguide structure 100 proposed in this application allows for flexible tuning of multiple resonant modes, providing significant potential for sensitivity adjustment. To evaluate the performance of the multi-band refractive index sensor corresponding to the plasmonic waveguide structure 100 proposed in this application, this application introduces a refractive index (RI) on the surface of the multi-period composite metal grating layer 103 of the plasmonic waveguide structure 100. Different materials. Specific configurations are as follows: Figure 9 As shown in A. (As indicated by...) Figure 9 As clearly shown in B, when the refractive index As the refractive index increases from 1.05 to 1.3, the position of the resonance peak in the reflection spectrum shifts significantly. This shift generates a unique optical response signal, and by monitoring the change in the wavelength of the resonance peak, the refractive index change can be accurately measured. Each refractive index corresponds to a unique resonance peak position, thus providing a clear identification feature for multi-band refractive index sensors, thereby improving their measurement accuracy and sensitivity. In analyzing the optical response of the refractive index sensor, this study found that as the ambient refractive index increases, the reflection intensity at short wavelengths gradually weakens. This phenomenon occurs at periods of (…). , This is particularly evident in grating structures with a period of (400nm, 500nm). However, this is especially true for grating structures with larger periods, such as (…). , ) = (500nm, 600nm) or ( , When the wavelength range is (600nm, 700nm), no similar phenomenon was observed, indicating that the variation in reflection intensity at short wavelengths is closely related to the period and geometry of the grating structure. In the short wavelength region, the interaction between light and the grating structure may be more restricted due to the shorter wavelength, leading to a decrease in reflectivity. Furthermore, the geometry of the grating may not effectively couple and guide the propagation of short-wavelength light, further affecting reflectivity. Specifically, when the refractive index... When the value increases from 1.05 to 1.3, the redshift at the resonance position increases from 630.9 nm to 668.3 nm. ≈37.4nm), and increased from 743.8nm to 794.8nm ( ≈51.0 nm). Meanwhile, the resonance intensity changed from 0.0016 to 0.27 (≈51.0 nm). ≈0.13), and changed from 0.0134 to 0.05 ( ≈0.03). For the rate of change of refractive index... When the value is 0.05, the corresponding step interval is... They are approximately 7.4nm and 10.2nm, respectively.

[0077] The results of this application demonstrate that the plasmonic waveguide structure 100 proposed in this application shows broad application prospects in the field of multi-band refractive index sensing, and can accurately capture subtle changes in the refractive index of materials. Its unique spectral tuning reflection characteristics make it an ideal biosensor for monitoring environmental changes.

[0078] Furthermore, refractive index (RI) sensitivity and FOM (form-of-memory) are key parameters for evaluating the performance of refractive index sensors. Specifically, RI sensitivity is defined as the resonant wavelength shift caused by a change in refractive index (RI). / The FOM (Front-of-Hand Dimension) is quantified as the ratio of sensitivity to the full width at half maximum (FWHM) of the resonance peak (S / FWHM). An ideal RI sensor should possess both high sensitivity and high FOM across a wide spectral range. However, most reported composite structures exhibit single-band sensing capabilities only in the visible to near-infrared or infrared regions, and some studies have not explicitly addressed this limitation. Furthermore, these structures are often polarization-limited.

[0079] In comparison, although the plasmonic waveguide structure 100 proposed in this application does not currently surpass existing designs in terms of reflection index sensitivity and frequency response coefficient, its performance can still be further improved through material optimization. More importantly, this plasmonic waveguide structure 100 achieves independently controllable characteristics of multi-band sensing performance (such as three-band, four-band, etc.) over a wide spectral range, a breakthrough that has not yet been achieved in other studies. By designing a structure with multiple independently tunable resonant modes, not only is multi-band sensing realized, but polarization limitations are also overcome, thereby significantly improving the performance and versatility of the refractive index sensor. This independently controllable characteristic facilitates flexible integration into various optical devices, such as multi-band sensors and filters, thus further expanding its application potential in the field of optical sensing. Especially in photoluminescent devices, the independent control of multiple resonant modes achieves unprecedented functionality—one mode can serve as an excitation channel, and another as an emission enhancer, thereby enabling simultaneous or arbitrary enhancement of the excitation and emission processes.

[0080] It should be noted that the description of the above refractive index sensor embodiments is similar to the description of the above plasmonic waveguide structure embodiments, and has similar beneficial effects. For technical details not disclosed in the refractive index sensor embodiments of this application, please refer to the description of the plasmonic waveguide structure embodiments of this application for understanding.

[0081] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above-described processes do not imply a sequential 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 this application. The sequence numbers of the above-described embodiments are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0082] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0083] In the several embodiments provided in this application, it should be understood that the disclosed device can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components may be combined, or integrated into another system, or some features may be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the various components shown or discussed may be through some interfaces, and the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0084] The units described above as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units; some or all of the units may be selected to achieve the purpose of the embodiments of this application according to actual needs.

[0085] In addition, each functional unit in the various embodiments of this application can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0086] Alternatively, if the integrated units described above are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this application, or the parts that contribute to related technologies, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a device (such as an automatic test line) to execute all or part of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, ROMs, magnetic disks, or optical disks.

[0087] The features disclosed in the several device embodiments provided in this application can be arbitrarily combined without conflict to obtain new device embodiments.

[0088] The above description is merely an exemplary embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A plasmonic waveguide structure, characterized in that, include: Metal substrate; Multi-period composite metal grating layer; A dielectric layer disposed between the metal substrate layer and the multi-period composite metal grating layer; The multi-period composite metal grating layer is composed of... It is composed of periodically arranged nanoscale metal supercell structures, wherein the nanoscale metal supercell structure is composed of at least two metal structures with different grating periods, each in a specific direction. The gratings are arranged periodically in the direction according to a preset grating spacing, and in... A structure formed by alternating arrangements at preset periodic intervals in a certain direction.

2. The plasmonic waveguide structure according to claim 1, characterized in that, The metal structure with at least two different grating periods includes: a cuboid metal structure with at least two different grating periods.

3. The plasmonic waveguide structure according to claim 2, characterized in that, The cuboid metal structure with at least two different grating periods includes: a first nano-metal structure with a first geometric length and a second nano-metal structure with a second geometric length. The supercell period of the nanometal supercell structure is the least common multiple of the first sub-period and the second sub-period; Wherein, the first sub-period is the sum of the first length and the preset grating spacing, and the second sub-period is the sum of the second length and the preset grating spacing.

4. The plasmonic waveguide structure according to claim 3, characterized in that, The geometric widths of the first and second nano-metal structures are both preset grating widths; The width of the nano-metal supercell structure is twice the spatial width; Wherein, the spatial width is the sum of the preset grating width and the preset periodic spacing.

5. The plasmonic waveguide structure according to claim 2, characterized in that, The cuboid metal structure with at least two different grating periods includes: At least two rectangular metal structures with the same geometric thickness and width, but different geometric lengths; or, At least two rectangular metal structures with the same geometric width but different geometric lengths and thicknesses.

6. The plasmonic waveguide structure according to claim 1, characterized in that, Both the metal substrate layer and the multi-period composite metal grating layer are made of metallic silver.

7. A refractive index sensor, characterized in that, include: Detection unit; An optical unit comprising the plasmonic waveguide structure according to any one of claims 1 to 6, and a layer of material under test covering a multi-period composite metal grating layer within the plasmonic waveguide structure. The optical unit is used to receive and excite multi-band composite incident light so that the multi-band composite incident light and the test material in the test material layer undergo optical interaction based on surface plasmon resonance. The detection unit is used to detect the optical parameters of the probe light of different bands in the multi-band composite incident light after passing through the optical interaction, so as to realize the refractive index measurement of the substance to be tested.

8. The refractive index sensor according to claim 7, characterized in that, The optical unit is specifically used to receive the multi-band composite incident light and, through the diffraction effect of the grating in the multi-period composite metal grating layer, couple the momentum of the multi-band composite incident light to the momentum of the surface plasmons, so as to excite the surface plasmon resonance at the interface of the multi-period composite metal grating layer, the dielectric layer and the material to be tested layer, thereby causing the evanescent field of the surface plasmon resonance to interact with the material to be tested in the optical way. The detection unit is specifically used to detect the change in the optical parameters corresponding to the resonance of different band probes in the multi-band composite incident light after the optical interaction when the change in the properties of the substance to be tested causes a change in the interface refractive index of the substance to be tested, thereby obtaining the change in the refractive index of the substance to be tested.

9. The refractive index sensor according to claim 7 or 8, characterized in that, The optical parameters include: resonance position and coupling strength.

10. The refractive index sensor according to claim 7 or 8, characterized in that, The properties of the substance to be tested include: concentration, adsorption capacity, impurity content, and composition.

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