A MULTI-LAYER SENSOR STRUCTURE FOR WIDE RANGE REFRACTIVE INDEX ANALYTE DETECTION

Abstract

The present invention introduces a hexagonal-shaped hybrid plasmonic waveguide (HPW) sensor designed as a versatile refractive index (RI) sensor, capable of detecting RI values from 1.3 to 1.5. The sensor structure consists of a substrate (101), a metal layer (102), a hexagonal high-index dielectric core (103) with slanted surfaces, and slanted low-index dielectric layers (104), enhancing electric field localization and sensitivity. This sensor is effective for detection of various chemicals and organic solvents, including blood components and glucose, showcasing high linear sensitivity for accurate detection. The HPW structure minimizes losses by confining light predominantly in low-index dielectric layers, expanding the range of detectable RI variations. Furthermore, the sensor allows strong electromagnetic field concentration near the metal-dielectric interfaces, enhancing interaction with analytes. This invention advances the field of refractive index sensing with its improved performance and broad applicability across diverse analytes.

Specification

Description:FIELD OF INVENTION:
[0001] The present invention relates to a sensor technologies, particularly to a refractive index (RI) sensors. More specifically, the present invention pertains to a multi-layer sensor structure designed for enhanced analyte detection, offering improved sensitivity and accuracy in detecting refractive index changes.

BACKGROUND AND PRIOR ART:
[0002] The subject matter discussed in the background section should not be assumed to be prior art merely because of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art.

[0003] Conventionally, a refractive index (RI) sensor, particularly those based on hybrid plasmonic waveguide (HPW) structures, have been developed for various sensing applications, including biosensing and chemical detection. However, many of these sensors are limited in terms of sensitivity and the range of refractive index (RI) they can detect. Additionally, most HPW-based sensors utilize racetrack or ring resonator configurations, which, while effective, tend to have relatively large footprints and are often optimized for narrow RI ranges, making them less versatile for wider applications.

[0004] For example, Vankalkunti et al. (2024) presented a rectangular-shaped hybrid plasmonic waveguide sensor specifically designed for a blood glucose detection. This solution offers a compact design but is restricted to a narrow application in glucose sensing. Similarly, Butt (2024) demonstrated a racetrack ring resonator-based sensor optimized for RI sensing in the range of 1.30 to 1.35, limiting its applicability in broader chemical and biosensing applications. Kumari et al. (2022) also explored hybrid plasmonic ring resonators for RI sensing within the range of 1.33 to 1.38, but the relatively large footprint of such designs poses challenges in compact and integrated sensing applications. Include other prior arts

[0005] Furthermore, the prior art related to "Hybrid Plasmonic Waveguide Based Platform for Refractive Index and Temperature Sensing" (September 2022_DOI:10.1109/LPT.2022.3195666) in nanoscale biochemical sensing involves hybrid plasmonic waveguide (HPWG) structures, combining dielectric and metallic layers to enhance sensitivity for refractive index (RI) and temperature detection. Commonly used materials include silicon dioxide (SiO₂), titanium dioxide (TiO₂), and gold (Au), with TiO₂ improving light confinement and sensitivity. Numerical simulations, such as Finite Element Method (FEM), are applied to optimize performance, predicting key metrics like RI sensitivity and temperature response. These sensors enable precise, low-cost, and compact on-chip solutions, suitable for various applications in biochemical sensing.

[0006] Furthermore, the prior art related to "Highly sensitive refractive index sensor based on hybrid plasmonic waveguide microring resonator" (https://doi.org/10.1080/17455030.2018.1506191) involves a highly sensitive refractive index (RI) sensor using a hybrid plasmonic waveguide microring resonator. The sensor features a Metal-Air-Silicon structure that enhances the electric field in the narrow air gap, improving detection sensitivity. Simulated via Finite Element Method (FEM), the design offers strong optical field overlap with the sensing medium, making it suitable for both gas and bio sensing. The sensor achieves sensitivities of 690 nm/RIU for gas sensing and 401 nm/RIU for bio sensing, surpassing conventional dielectric microring resonators. This technology shows promise for biomedical applications and nanophotonic circuits.

[0007] The limitations of these conventional designs, including their restricted RI detection ranges and relatively larger footprints, and limited capability in detecting a broad range of analytes, make them less suitable for applications that require both high sensitivity and versatility across a wide range of refractive indices. Furthermore, while the sensitivity of these designs is adequate for specific applications, there is a growing need for sensors with enhanced sensitivity and figure of merit (FOM) to improve detection precision, particularly in biosensing and chemical sensing.

[0008] Therefore, there is a need for a more compact, high-performance refractive index (RI) sensor capable of operating over a wider RI range and detecting a broad spectrum of analytes with enhanced sensitivity and figure of merit (FOM). The proposed hexagonal-shaped hybrid plasmonic waveguide (HPW) sensor addresses these challenges by offering a significantly broader RI detection range and improved sensitivity. This performance can be further enhanced by incorporating graphene layers. Additionally, its compact design, combined with a high figure of merit, makes it well-suited for a wide variety of biosensing and chemical sensing applications, providing considerable advancements over existing solutions.

OBJECTS OF THE INVENTION:
[0009] The primary object of the present invention is to provide an advanced sensor technology specifically for a refractive index (RI) sensor, focusing on a multi-layer sensor structure that is designed for enhanced analyte detection with wide range refractive index (RI), thereby offering improved sensitivity and accuracy in detecting changes in refractive index (RI).

[0010] Another object of the present invention is to develop a compact hexagonal-shaped hybrid plasmonic waveguide (HPW) sensor that significantly reduces the footprint compared to traditional sensing technologies, facilitating integration into space-constrained applications.

[0011] Another object of the present invention is to provide the sensor that operates over a wider refractive index (RI) range, enabling the detection of a broad spectrum of analytes, which enhances its versatility for various biosensing and chemical sensing applications.

[0012] Another object of the present invention is to develop the sensor with improved sensitivity that can be further enhanced by incorporating graphene layers, allowing for more precise measurements and reliable detection capabilities.

[0013] Another object of the present invention is to provide the sensor with a high figure of merit (FOM), ensuring effective performance while enhancing its reliability and accuracy in detecting changes in refractive index, which is critical for sensitive applications.

[0014] Another object of the present invention is to develop an innovative HPW sensor that effectively addresses the limitations of existing technologies, offering a solution that combines enhanced sensitivity, a wide detection range, and a compact footprint, leading to substantial improvements over current refractive index sensing solutions.

[0015] Overall, another object of the present invention is to provide the sensor that not only meets the demands for advanced analytical performance but also opens new opportunities for applications in fields such as environmental monitoring, biomedical diagnostics, and chemical analysis.


SUMMARY OF THE INVENTION:
[0016] The present invention pertains to a novel sensor structure characterized by its multi-layer design, which significantly improves the detection capabilities of refractive index (RI) changes in various analytes.

[0017] The sensor structure comprises a substrate forming the base, upon which a metal layer is deposited. At the core of this structure is a hexagonal-shaped core made of a high-index dielectric material, which is central to the sensor's enhanced performance.

[0018] In an aspect, the sensor includes a slanted surface of the high-index dielectric layer encapsulated by a slanted low-index dielectric layer, optimizing the interaction of light with the analyte for improved sensitivity.

[0019] In another aspect, the low-index dielectric layer is further encapsulated by a slanted metal layer, which helps to enhance the plasmonic effects within the sensor, facilitating greater detection capabilities.

[0020] Additionally, the sensor features two vertical metal bars positioned on opposite sides of the hexagonal structure, which serve to confine the analyte and enhance the sensor's ability to detect changes in refractive index.

[0021] In an aspect, the analyte is positioned above the hexagonal-shaped core and between the vertical metal bars, allowing direct contact with the sensor structure to enable accurate and efficient detection of the refractive index changes.

[0022] In an aspect, the proposed sensor structure provides a compact and efficient solution for high-performance refractive index sensing, making it suitable for a wide range of biosensing and chemical analysis applications.

BRIEF DESCRIPTION OF DRAWINGS:

Fig. 1 illustrates a 2D cross-sectional view of the sensor structure of the present invention which is hexagonal HPW based sensor structure with dimensions of different layers/materials.

Fig. 2(a) illustrates a 3D structure of HPW sensor, without semi-metal (graphene) layers on the slanted metal layers.
Fig. 2(b) illustrates a 3D structure of HPW sensor, with semi-metal (graphene) layers on the slanted metal layers.

Figure 3(a) illustrates a 3D Mode profile of HPW sensor, without semi-metal (graphene) layers over the slanted metal layers.
Figure 3(b) illustrates a 3D Mode profile of HPW sensor, with semi-metal (graphene) layers over the slanted metal layers.

Figure 4 (a) illustrates a 2D cross-sectional electric field profile of the sensor, without semi-metal (graphene) over the slanted metal layers.
Figure 4 (b) illustrates a 2D cross-sectional electric field profile of the sensor, with semi-metal (graphene) layers over the slanted metal layers.

Figure 5(a) illustrates a graphical representation of the normalized electric field for refractive index of 1.33, at the SPR wavelength of 1178 nm, without application of semi-metal (graphene) layer.
Figure 5(b) illustrates a graphical representation of the normalized electric field for refractive index of 1.33, at the SPR wavelength of 1181 nm, with application of three semi-metal (graphene) layers over the slanted metal layers.

Figure 6(a) illustrates a graphical representation of a variations in transmittance curves, for RI varying from 1.3 to 1.4, without semi-metal (graphene) layer over the slanted metals layers.
Figure 6(b) illustrates a graphical representation of a linear variations in resonance wavelength with respect to varying RI, without semi-metal (graphene) layer over the slanted metals layers.

Figure 7(a) illustrates a graphical representation of a variations in transmittance curves, for RI varying from 1.3 to 1.5, with semi-metal (graphene) layers over the slanted metals layers.
Figure 7(b) illustrates a graphical representation of a linear variations in resonance wavelength with respect to varying RI, with semi-metal (graphene) layers over the slanted metals layers.

DETAILED DESCRIPTION OF THE INVENTION:
[0023] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0024] The invention is described herein in detail with the help of figures appended at the end of the specification. The figures illustrate the preferred embodiment as well as other embodiments that define the scope of the present invention. However, it may be understood that the figures presented herein are intended to exemplify the scope of the invention only. The person skilled in art may note that by no means the figures limit the scope of the invention. Any variation in the drawings by any other person will be falling in the scope of the present invention.

[0025] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0026] The terminology "sensor", "sensor structure", "hexagonal HPW based sensor structure", "HPW sensor" have the same meaning and are used alternatively throughout the specification.

[0027] The terminology "refractive index", "RI" have the same meaning and are used alternatively throughout the specification.

[0028] The terminology "semi-metal layer", "graphene layer" have the same meaning and are used alternatively throughout the specification.

[0029] The terminology "two vertical metal bars", "metal bars", "vertical bars" "copper bars", "Cu bars" have the same meaning and are used alternatively throughout the specification.

[0030] The present invention introduces a nano-photonic device designed as a refractive index (RI) sensor, capable of detecting a wide range of refractive indices, from 1.3 to 1.5. This makes it suitable for sensing various chemicals, liquids, and organic solvents, including blood components, glucose, methanol, ethanol, sulfuric acid, olive oil, silicone oil, benzene, chloroform, and ethylene glycol, all of which fall within this refractive index (RI) range. The proposed sensor demonstrates a high degree of linear performance in terms of sensitivity, ensuring accurate detection for a wide range of analytes.

[0031] The present invention is based on a hybrid plasmonic waveguide (HPW) structure, incorporating a hexagonal shape for the refractive index (RI) sensor. This sensor offers a significant advantage, particularly in electric field localization at the sharp edges, leading to higher sensitivity and improved coupling efficiency when compared to conventional smooth nanostructures. These enhancements make the sensor of the present invention particularly effective for applications requiring precise refractive index detection.

[0032] The primary objective of the present invention is to provide a versatile refractive index sensor capable of detecting the large variety of analytes, including, but not limited to, chemicals, biological elements, and aqueous solutions, within the RI range of 1.3 to 1.5, it is not limited to this range. The sensor structure and analysis of efficient refractive index sensing applications is a critical research focus globally, and this invention contributes to advancing this domain with improved performance and broader applicability.

[0033] Fig. 1 illustrates a 2D cross-sectional view of a sensor (100) of the present invention which is a HPW sensor (100) with dimensions of different layers/materials.

[0034] The sensor (100) illustrated in the figure 1 consists of several key components. At the foundation of the sensor is a substrate (101), which forms the base. On the top of this substrate (101), a metal layer (102) is deposited, serving as the bottom layer. Centrally positioned above the metal layer (102) is a hexagonal-shaped core (103) made from a high-index dielectric material. This core (103) is crucial for enhancing the sensor's refractive index detection capabilities.

[0035] The high-index dielectric layer of the hexagonal-shaped core (103) features slanted surfaces, which are encapsulated by a slanted low-index dielectric layer (104). These slanted low-index layers (104) are then further encapsulated by a slanted metal layers (105), providing structural stability and enabling effective electric field localization. Additionally, the sensor includes the two vertical metal bars (106), positioned on opposite sides of the hexagonal core (103), which enhance the sensor's detection capabilities by improving field confinement.

[0036] Finally, an analyte (107) to be detected is placed above the hexagonal-shaped core (103), positioned between the vertical metal bars (106), ensuring direct interaction with the sensor for accurate and sensitive detection. This innovative structure allows for effective refractive index sensing across the wide range of analytes (107).

[0037] In one embodiment, to further enhance the sensing performance, a semi-metal layer (108), wherein the semi-metal known for its exceptional electrical and optical properties, have been deposited over the slanted metal layers (105) of the sensor (100). This additional semi-metal layer improves light-matter interaction, increasing sensitivity. However, this embodiment is described in detail with reference to Figure 2(b) and is not depicted in figures 1 or 2(a).

[0038] The present invention, based on a Hybrid Plasmonic Waveguide (HPW) structure, offers significant advantages over conventional Plasmonic Waveguide (PW) structures. Unlike PW, which confines light at the metal-dielectric interface and suffers from higher losses, the HPW structure confines light predominantly in the low-index dielectric layer (104), leading to enhanced light confinement and reduced propagation losses. Therefore, the sensor of the present invention enables better performance, particularly in sensing applications, by improving sensitivity and expanding the range of detectable refractive index variations, making it more effective and versatile than traditional PW-based sensors.

[0039] Furthermore, at a certain wavelength, called the surface plasmon resonance (SPR) wavelength, the electromagnetic fields become very strong and focused near the points where the metal and dielectric materials meet. In the hexagonal HPW structure, these fields are especially intense around the sharp edges. This strong concentration of energy helps the HPW sensor interact more effectively with the analyte (107) (substance being tested), making it more sensitive and efficient for detecting changes.

[0040] The sensor (100) comprises the following dimensions, providing flexibility in its design: the substrate (101) thickness is 200 nm, while the metal layer (102) thickness is 80 nm. The width of the hexagonal core (103) (one side) is specified to range from 120 nm to 140 nm. The thickness of the slanted low-index dielectric layers (104) are set between 5 nm and 20 nm, and the width of the slanted metal layers (105) ranges from 140 nm to 160 nm. The vertical bars (106), which support the analyte detection, has width and height of respectively of 80 nm, and ~375 nm. Additionally, the thickness of three layers of graphene is 1.02 nm. These specified ranges ensure that the sensor (100) can accommodate various applications while maintaining optimal performance.

[0041] In one embodiment, the sensor (100) comprises the substrate (101) as the base, with the metal layer (102) forming the bottom, which has a thickness of 80 nm. The hexagonal-shaped core (103) serves as the high-index dielectric layer, with a one-side width of 130 nm. This core (103) is encapsulated by the slanted low-index dielectric layers (104), each having a thickness of 15 nm, which are further encapsulated by the slanted metal layers (105) with a width of 150 nm. The two vertical bars (106), each with a width of 80 nm and a height of approximately 375 nm, flank the hexagonal core (103), supporting the analyte detection within the sensor. In one embodiment, three layers of graphene, each with a thickness of 0.34 nm, are deposited over the four slanted metal layers (105), contributing to a total graphene thickness of 1.02 nm. The sensor has been designed with a length of 500 nm and Width of 950 nm, optimizing its compactness for practical applications.
[0042] More particularly, as illustrated in Fig. 1, the key dimensions of the sensor (100) are as follows:
• Width of the sensor (W): 950 nm
• Thickness of copper layers (t_Cu): 80 nm
• Width of the silicon layer (W_Si): 130 nm
• Width of the silicon dioxide layer (W_(SiO2)): 15 nm
• Width of the copper layer (W_Cu): 150 nm
These dimensions are critical for ensuring the sensor's effectiveness and functionality in refractive index sensing applications.
[0043] In terms of structure, the substrate (101) and the metal layer (102) forming the bottom layer are both rectangular in shape, with the metal layer (102) having the same width as the substrate (101) but differing in thickness. The hexagonal-shaped core (103) of the high-index dielectric layer is encapsulated by multiple layers, and both the high-index dielectric layer and the low-index dielectric layers (104) feature four slanted surfaces. This geometric configuration supports the efficient operation of the sensor.

[0044] The sensor is capable of measuring a wide range of refractive indices, specifically ranging from but not limited to 1.3 to 1.5, making it suitable for detecting the various analytes (107), including chemicals, bio-elements, aqueous solutions, and organic solvents. In one embodiment, the wide range of analytes (107) that can be detected includes blood components, glucose, methanol, ethanol, sulfuric acid, olive oil, silicone oil, benzene, chloroform, and ethylene glycol, among others. Furthermore, in another embodiment, the sensor is designed to implement both as a biosensor and a chemical sensor.

[0045] Now in one embodiment, the aforementioned sensor (100) is composed of specific materials to enhance its performance and detection capabilities. These materials are detailed below, outlining the composition of each layer.
[0046] In one embodiment, the sensor comprises a hexagonal-shaped hybrid plasmonic waveguide structure. This structure includes the substrate (101) forming the base, made of silica (SiO₂), which provides a stable foundation for the entire sensor assembly. Above the substrate (101), the metal layer (102) is deposited, made of copper (Cu), which forms the bottom layer of the sensor and plays a crucial role in the sensor's overall conductivity and performance.

[0047] Furthermore, in one embodiment, the core (103) of the sensor is a hexagonal-shaped high-index dielectric layer, composed of silicon (Si), positioned centrally above the metal layer (102). Yet in another embodiment, this core (103) is encapsulated by the slanted low-index dielectric layers (104) made of silicon dioxide (SiO₂), providing a contrast in refractive indices that enhances the sensor's sensitivity. Additionally, in another embodiment, the slanted low-index dielectric layers (104) are further encapsulated by the slanted metal layers (105) made of copper (Cu), which contribute to the sensor's ability to localize the electric field at the sharp edges, improving the coupling efficiency.

[0048] Furthermore, in one embodiment, on either side of the hexagonal structure, the two vertical metal bars (106) made of copper (Cu) are positioned. These bars (106) support the containment of the analyte (107) within the sensor (100), allowing for accurate detection. The analyte layer (107) is positioned above the core (103) of the high-index dielectric layer and the slanted low-index dielectric layers (104) enabling interaction with the external analytes (107) for sensing purposes.

[0049] The sensor (100) comprises the silica (SiO₂) substrate (101) as the base, with a copper (Cu) metal layer (102) forming the bottom, which has a thickness of 80 nm. The hexagonal-shaped silicon (Si) core (103) serves as the high-index dielectric layer, with a one-side width of 130 nm. This core (103) is encapsulated by slanted low-index silicon dioxide (SiO₂) layers, each having a thickness of 15 nm, which are further encapsulated by slanted copper (Cu) metal layers with a width of 150 nm. The two vertical copper (Cu) bars (106), each with a width of 80 nm and a height of approximately 375 nm, flank the hexagonal core (103), supporting the analyte detection within the sensor.
[0050] Fig. 2(a) illustrates a 3D structure of the HPW sensor (100), which is consistent with the two-dimensional drawing described earlier. This 3D visualization provides a comprehensive view of the sensor's layered structure and spatial arrangement, enhancing the understanding of its structure and the relationships between its various components. The sensor (100) comprises the silica (SiO₂) substrate (101) as the base, with the copper (Cu) metal layer (102) forming the bottom. The hexagonal-shaped silicon (Si) core (103) serves as the high-index dielectric layer, encapsulated by slanted low-index silicon dioxide (SiO₂) layers, which are further encapsulated by slanted copper (Cu) metal layers. The two vertical copper (Cu) bars (106) flank the hexagonal core (103), supporting the analyte detection within the sensor.

[0051] Fig. 2(b) illustrates a similar sensor (100) of HPW sensor (100) as depicted in Fig. 2(a), with the key distinction being the addition of the semi-metal layer (108). This semi-metal layer (108) is deposited on the slanted metal layer (105), enhancing the functionality of the sensor. The incorporation of this layer aims to improve the sensor's performance by facilitating better interactions with the external analytes and optimizing its detection capabilities.
[0052] In one embodiment, the slanted metal layers (105) are encapsulated by the semi- metal layers, specifically graphene, which enhances the sensor's capability to detect and analyze variations in refractive index in real-time. This innovative sensor allows for high precision in refractive index measurements, making the sensor versatile for multiple applications.

[0053] Figure 3(a) illustrates a 3D mode profile of the HPW sensor (100) without semi-metal (graphene) layers (108) on the slanted metal layers (105). The red glow represents the electromagnetic field intensity around the hexagonal core (103), with stronger fields on the slanted surfaces. In this embodiment, the metal surfaces directly interact with the propagating light, effectively guiding the electromagnetic waves.
[0054] Figure 3(b) illustrates a 3D mode profile of the HPW sensor (100) with the semi-metal (graphene) layers (108) on the slanted metal layers (105). The red glow represents the electromagnetic field intensity, which is more concentrated around the hexagonal core (103). The addition of graphene results in stronger field confinement, with the red regions more focused along the hexagonal core (103). The electromagnetic field is more concentrated, especially near the surfaces covered by the graphene.
[0055] This results in stronger light-matter interaction, improving the sensitivity of the sensor for detecting changes in the refractive index of the analytes (107). The graphene layer further refines the sensor's ability to capture subtle variations with higher precision.

[0056] Furthermore, figure 4(a) illustrates a 2D cross-sectional electric field profile of the sensor (100) without the semi-metal (graphene) layers (108) on the slanted metal surfaces (105). In this profile, the electric field distribution indicates that the field is primarily localized at the metal-dielectric interfaces, with some strength radiating outwards. The absence of semi-metal (graphene) layer (108) results in a more dispersed field pattern, suggesting that the interaction with the light may not be as strong or focused. The increased exposure suggests that the field is not tightly confined, which may lead to a weaker interaction with the analyte (107) and potentially lower sensitivity to refractive index changes. This configuration allows for a clearer visualization of how the light interacts with the underlying slanted metal layers (105), which guide the electromagnetic wave but may limit overall sensitivity to changes in the refractive index of the surrounding analytes (107).

[0057] Similarly, figure 4(b) illustrates a 2D cross-sectional electric field profile of the sensor (100), now incorporating the semi-metal (graphene) layers (108) over the slanted metal layers (105). This profile reveals a more concentrated electric field, particularly at the interfaces between the graphene and the metal layers. The inclusion of graphene enhances the electric field's localization and intensity, indicating stronger light-matter interactions. This improved field confinement suggests that the sensor (100) is better equipped to detect variations in the refractive index of the nearby analytes, thereby enhancing overall sensing performance compared to the configuration shown in Figure 4(a). Therefore, figure 4(b) illustrates a more confined electric field with graphene, enhancing sensitivity and the analyte interaction.

[0058] Figure 5(a) illustrates a graphical representation of the normalized electric field for refractive index of 1.33, at the SPR wavelength of 1178 nm, without application of semi-metal (graphene) layer (108). Furthermore, this graph shows the normalized electric field profile of the sensor without graphene layer.

[0059] As illustrated in the graph, X-axis represents the position along the sensor (100) in nanometers (nm), ranging from 0 to 950 nm. Y-axis shows the normalized electric field strength in V/m (×10^8), with values ranging from 0 to 5.8.

[0060] The peaks in the graph, represented by the green and blue lines, provide insights into the distribution and intensity of the electric field at specific positions along the sensor (100). The peaks in both the green and blue lines represent regions of higher electric field intensity, meaning these are areas where the sensor is most sensitive to external changes, such as refractive index variations of the analyte (107).
[0061] The difference in the peak heights and positions between the blue and green lines may indicate how the field distribution varies between the center and top of the hexagonal structure, suggesting that different parts of the sensor interact with the electric field differently.

[0062] The blue line corresponds to the electric field intensity measured at the center of the hexagonal structure. The peaks in this line indicate regions where the electric field is stronger at the center of the hexagon. The recurring peaks along the X-axis suggest areas of enhanced electric field strength, likely at intervals where the geometry of the sensor concentrates the electromagnetic energy, such as at sharp edges or interfaces within the sensor. The valleys, or lower points between peaks, show regions where the electric field is weaker.

[0063] The green line represents the electric field measured at the top of the hexagonal structure. The peaks in this line show areas of higher electric field intensity near the top surfaces of the sensor. Similar to the blue line, the peaks shown by the green line represent strong electric field concentrations, possibly due to the interaction between the slanted metal layers (105) and the surrounding medium. The shape and number of these peaks can indicate how the geometry and material properties affect field distribution near the top of the structure.

[0064] Figure 5(b) illustrates a graphical representation of the normalized electric field for a refractive index of 1.33, at the SPR wavelength of 1181 nm, with the application of three semi-metal (graphene) layers (108) over the slanted metal layers (105). This graph represents the normalized electric field profile of the sensor after the graphene layers have been applied.

[0065] As shown in the graph, the X-axis represents the position along the sensor (100) in nanometers (nm), ranging from 0 to 950 nm. The Y-axis shows the normalized electric field strength in V/m (×10^9), with values ranging from 0 to 1.2.

[0066] The peaks in the graph, represented by the green and blue lines, highlight the areas where the electric field is most intense along specific positions of the sensor (100). These peaks indicate regions where the sensor's sensitivity is maximized, with stronger fields responding more acutely to external changes, such as variations in the refractive index of the surrounding analyte.

[0067] The blue line corresponds to the electric field intensity measured at the center of the hexagonal structure. The peaks in this line show where the electric field is stronger at the center. These recurring peaks suggest locations along the X-axis where the sensor's geometry concentrates electromagnetic energy. The differences in the peak heights compared to Figure 5(a) reflect how the addition of graphene layers enhances the electric field strength, making the sensor more sensitive and efficient.

[0068] The green line represents the electric field intensity measured at the top of the hexagonal structure. The peaks along this line indicate stronger electric field intensities near the top surfaces of the sensor. The shape and magnitude of these peaks suggest how the presence of graphene layers enhances the field distribution, particularly at the top, likely due to the interaction between the graphene, the slanted metal layers (105), and the surrounding medium. The additional peaks and higher values, compared to Figure 5(a), indicate improved sensitivity and field enhancement after the application of graphene layers.

[0069] Figure 6(a) illustrates how the transmittance of the sensor changes across different wavelengths for refractive indices (RIs) varying from 1.3 to 1.4, without the semi-metal (graphene) layer (108) over the slanted metal layers (105). As the RI increases, the curves shift towards longer wavelengths, indicating that the resonance dip (where transmittance is lowest) moves based on the RI. This demonstrates the sensor's ability to detect different RIs by tracking shifts in resonance wavelength, highlighting its sensitivity to environmental changes.

[0070] Figure 6(b) shows the linear relationship between the resonance wavelength (λ_r) and the refractive index (RI), without the semi-metal (graphene) layer (108) over the slanted metal layers (105). As the RI increases, the resonance wavelength shifts to higher values, indicating that the sensor's response is directly dependent on the RI. This linearity allows for accurate and predictable measurements of RI changes.

[0071] Figure 7(a) demonstrates how the transmittance of the sensor changes across different wavelengths for varying refractive indices (RIs) from 1.3 to 1.5, with the application of the semi-metal (graphene) layers (108) over the slanted metal layers (105). The transmittance curves shift towards longer wavelengths as the RI increases, with the resonance dip (where transmittance is lowest) moving accordingly. The addition of graphene layers enhances the sensitivity of the sensor by amplifying the resonance shifts, making the sensor more responsive to changes in the refractive index of the surrounding medium.

[0072] Figure 7(b) shows a linear relationship between the resonance wavelength (λ_r) and the refractive index (RI) with graphene layers applied. As the RI increases, the resonance wavelength shifts to higher values, similar to what was observed without graphene (in Figure 6b), but with improved sensitivity due to the presence of graphene. This linear variation allows for precise detection of RI changes, demonstrating the enhanced performance of the sensor with the graphene layers in terms of accuracy and range of detection.

[0073] Therefore, the aforementioned analysis of transmittance at the output port for the proposed HPW sensor has been conducted over a wavelength range of 1120 nm to 1260 nm (without graphene layers) and up to 1350 nm (with three layers of graphene). The observed transmittance dip corresponds to the surface plasmon resonance (SPR) wavelength, which exhibits a linear red-shift as the refractive index (RI) of the analyte increases. The optical properties of the propagating mode are highly sensitive to changes in the RI of the surrounding environment or analyte (107), showcasing the effectiveness of the proposed sensor (100) in detecting such variations.

[0074] In one embodiment, the hexagonal-shaped hybrid plasmonic sensor has a compact footprint and can sense a wide refractive index range (1.3 to 1.5) with high sensitivity (~700 nm/RIU), further improved to ~750 nm/RIU by adding graphene layers. In one embodiment, the sensor achieves a FOM between 21-34 per RIU, demonstrating efficient performance.

[0075] More particularly, the major performance parameters for this proposed invention are sensitivity and FOM, which have been achieved as 750.89 nm/RIU and 22.02/RIU, respectively, when three graphene layers have been deposited on the slanted metal surfaces. Without the graphene layers, these values were 702.72 nm/RIU and 21.31/RIU, respectively. Thus, the application of graphene layers enhances the surface electric fields, leading to improved performance parameters. Furthermore, the sensor delivers consistent linear sensitivity and SPR wavelength response for accurate measurements.

[0076] The sensor is developed using the finite element method (FEM) within the COMSOL Multiphysics platform, a powerful tool for simulating complex physical phenomena. This approach enables precise modeling of the sensor's performance under various conditions, including the interaction of light with the sensor (100) and its sensitivity to changes in the refractive index. The use of COMSOL Multiphysics ensures that the sensor can be optimized for future applications, such as in biomedical diagnostics, environmental monitoring, and chemical sensing, where high sensitivity and accuracy are critical.

[0077] In one embodiment, the sensor (100) of the present invention covers a broader refractive index range from 1.3 to 1.5, making it suitable for detecting various chemicals and organic solvents like blood components such as glucose. Furthermore, in one embodiment, is also suitable to detect methanol, ethanol, sulfuric acid, olive oil, silicone oil, benzene, chloroform, ethylene glycol, etc. Additionally, it offers label-free sensing for real-time refractive index variations.

[0078] In one embodiment, the proposed nano sensor (100) can be implemented for on chip sensing applications, which can be utilized to do the fast and real time sensing data analysis.

[0079] The wide range of refractive index (RI) is achieved through this proposed HPW sensor by using several key design features and material choices:

• Material Selection: The use of high-index dielectric layer encapsulated by low-index materials allows for a significant difference in refractive indices, which enhances sensitivity and performance across a broader RI range.
• Layer Structure: The sensor incorporates a hexagonal-shaped core of high-index layer encapsulated by slanted low-index dielectric layers and slanted metal layers. This multi-layer configuration facilitates effective light confinement and enhances the interaction between the light and the analyte, allowing for precise measurement of refractive index ranging from 1.3 to 1.5.
• Design Flexibility: The dimensions of various layers, including the thickness and width of each layer, can be adjusted within specified ranges. This adaptability enables the HPW sensor to effectively respond to different analytes, whether they are chemicals, biological elements, or organic solvents.
• Electric Field Localization: The HPW sensor enhances the localization of the electric field at the sharp edges of the hexagonal structure, improving coupling efficiency and allowing for sensitive detection of refractive index across a wide range.
[0080] Therefore, the aforementioned features enable the HPW sensor to effectively measure a wide range of refractive indices, enhancing its applicability for various analytes, including blood components, organic solvents, and other chemical substances.

[0081] The advantages of the present invention include:
• The HPW sensor offers superior electric field localization and higher coupling efficiency compared to smooth nanostructures, making it ideal for refractive index sensing.
• The invention effectively senses over a broad refractive index range, making it versatile for various applications.
• The proposed sensor (100) delivers a linear response in sensitivity and SPR wavelength, ensuring precise measurements.
• Its versatility makes it suitable for sectors such as chemical, oil/gas, mining, food, and medical industries.
• The use of the copper as a plasmonic material is a significant advantage. Copper (Cu) is a more affordable option compared to commonly used materials like gold (Au) and silver (Ag), making the technology more cost-effective.
, Claims:1. A sensor (100) for detection of range of analytes, the sensor comprises:
a substrate (101) forming the base of the structure;
a metal layer (102) forming the bottom layer deposited on the substrate (101);
a hexagonal-shaped core (103) of a high-index dielectric layer positioned centrally above and directly in contact with the metal layer (102); the hexagonal shaped core (103) being encapsulated by a slanted low-index dielectric layer (104);
the slanted low-index dielectric layer (104) encapsulated by a slanted metal layer (105);
a vertical metal bars (106) positioned on opposite sides of the hexagonal structure;
wherein an analyte (107) is filled above the hexagonal-shaped core (103) and between the vertical metal bars (106) to enable refractive index (RI) detection of the filled analyte (107).

2. The sensor (100) as claimed in claim 1, wherein the multi-layered sensor (100) is hexagonal-shaped hybrid plasmonic waveguide structure and is enabled to detect and analyse variations in refractive index in real-time.

3. The sensor (100) as claimed in claim 1, wherein the substrate (101) forming the base of the structure is made of a silica (SiO2).

4. The sensor (100) as claimed in claim 1, wherein the metal layer (102) is made of copper (Cu).

5. The sensor (100) as claimed in claim 1, wherein the hexagonal shaped core (103) of high-index dielectric layer is made up of silicon (Si).


6. The sensor (100) as claimed in claim 1, wherein the slanted low-index dielectric layers (104) are made up of silicon dioxide (SiO2).

7. The sensor (100) as claimed in claim 1, wherein the slanted metal layer (105) is made up of copper (Cu).

8. The sensor (100) as claimed in claim 1, wherein the two vertical metal bars (106) are made up of copper (Cu).

9. The sensor (100) as claimed in claim 1, wherein the metal layer (102) is enabled to have the same width as the substrate (101).

10. The sensor (100) as claimed in claim 1, wherein the metal layer (102) forming the bottom layer is provided with a different thickness from the substrate (101).

11. The sensor (100) as claimed in claim 1, wherein the metal layer (102) having the thickness of 80 nm.

12. The sensor (100) as claimed in claim 1, wherein both the hexagonal shaped core (103) of the high-index dielectric layer (103) and the low-index dielectric layers (104) have at least four slanted surfaces, enabling the localization of the electric field at the sharp edges along with the higher coupling efficiency.

13. The sensor (100) as claimed in claim 1, wherein the sensor (100) is configured to measure refractive indices ranging from 1.3 to 1.5.


14. The sensor (100) as claimed in claim 1, wherein the analytes (107) are selected from chemical, bio elements, aqueous solutions, liquids, organic solvents, etc, including blood components, glucose, sulfuric acid, olive oil, silicone oil, and such.

15. The sensor (100) as claimed in claim 1, wherein the slanted metal layers (105) are encapsulated by a slanted semi-metal layers (108), wherein the slanted semi-metal layers (108) are made up of graphene layer enabled to improve sensitivity of the sensor (100).

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