Intermediate infrared refractive index sensor based on PIT effect

Abstract

The utility model relates to a mid-infrared refractive index sensor based on a PIT effect. The mid-infrared refractive index sensor comprises a silicon substrate, a sapphire layer, a graphene nano-strip waveguide, a first graphene rectangular resonant cavity and a second graphene rectangular resonant cavity, the sapphire layer is arranged above the silicon substrate; a graphene nano-strip waveguide, a first graphene rectangular resonant cavity and a second graphene rectangular resonant cavity are arranged on the upper surface of the sapphire layer; the first graphene rectangular resonant cavity is directly coupled with the graphene nano-strip waveguide; the second graphene rectangular resonant cavity and the first graphene rectangular resonant cavity are arranged in parallel; and the second graphene rectangular resonant cavity is indirectly coupled with the graphene nano-strip waveguide through the first graphene rectangular resonant cavity. According to the utility model, the problem of low sensing sensitivity of a refractive index sensor is solved; the problem that a sensing device is not easy to integrate in an on-chip plasmon light path is solved; the graphene refractive index sensor is high in sensitivity, small in size, wide in sensing bandwidth and easy to integrate.

Description

Technical Field

[0001] The utility model relates to the field of sensing technology, in particular to a mid-infrared refractive index sensor based on the PIT effect. Background Art

[0002] Refractive index sensors, with their advantages of label-free, real-time detection, and high sensitivity, are widely used in fields such as biosensing, chemical detection, food safety, and environmental monitoring, and are important components in sensing technology. With the development of large-scale integrated photonic devices, the demand for refractive index sensors in the mid-infrared band with small size, high sensitivity, and wide sensing bandwidth is becoming increasingly apparent. Therefore, it is extremely important to develop refractive index sensors with new working mechanisms that combine small device size, high sensitivity, wide sensing bandwidth, and ease of integration.

[0003] Surface plasmon polaritons (SPPs) are surface electromagnetic evanescent waves that propagate along metal-dielectric interfaces and decay exponentially perpendicular to the metal surface. SPPs have the potential to break through the diffraction limit of conventional optics and exhibit strong localized optical field enhancement, enabling the guidance and manipulation of light at the subwavelength scale. SPPs can serve as both energy and information carriers, and their applications are significant in high-density integrated photonic circuits.

[0004] Currently, SPPs-based sensors have been widely studied, such as refractive index sensors, temperature sensors, and biosensors. Due to the strong localized light field enhancement properties of SPPs and their ability to overcome the traditional diffraction limit, SPPs-based sensors have small structural dimensions and high sensing sensitivity. The propagation direction of SPPs is parallel to the device surface, facilitating chip integration and design. Therefore, the surface plasmon waveguide coupled with resonator (PWCR) structure is widely used in refractive index sensors.

[0005] SPPs (Spherical Polymer Precipitated Polymers) (SPPs) refractive index sensors based on the plasmon-induced transparency (PIT) effect are attracting increasing attention. The PIT phenomenon is similar to the electromagnetically induced transparency (EIT) effect in atomic gases. However, compared to EIT in atomic gases, which is determined by the absorption properties of the material, the EIT-like phenomenon generated by the geometry of a resonant cavity-coupled plasmonic waveguide system offers greater application prospects due to its room-temperature operation, compatibility with chip integration, tunability of the transmission band, and controllable bandwidth. The PIT effect can be tuned in a static state by adjusting the geometry of the nanocavity (e.g., cavity diameter and spacing between the two cavities) and intrinsic Drude losses. The PIT effect is well-suited for sensing applications due to its large quality factor and steep transmission spectrum. Furthermore, the PIT effect can induce the generation of slow light, which enhances the contact between SPPs and the probe material, thereby improving the sensitivity of refractive index sensors.

[0006] In recent years, graphene, a single-atomic-layer two-dimensional material, has provided a novel, low-loss method for confining and controlling SPPs, leading to its application in the design of SPP devices. Leveraging the spatial contact between SPPs on the graphene surface and the sensing material, the present invention proposes a graphene refractive index sensor with advantages such as small device size, high sensitivity, and a wide sensing bandwidth. Because the mid-infrared band contains the vibrational characteristics of biological nanoparticles, mid-infrared graphene refractive index sensors are particularly suitable for the detection of proteins and chemicals.

[0007] The defects of the prior art are as follows:

[0008] 1. Because traditional refractive index sensors do not enhance the contact between light waves and the detected material, the sensitivity of the sensor is low, which limits the application and development of the sensor in sensing technology.

[0009] 2. Due to the small size of SPPs waveguides and resonant cavities, it is difficult to fill substances such as proteins, oils, and DNA into the structure, which is not conducive to the application of sensors in biosensing and chemical detection, thereby limiting the integration of sensor devices in on-chip plasmon optical paths.

[0010] 3. Since the actual sensor should be three-dimensional and fabricated on a substrate, many of the proposed PWCR structures only study two-dimensional planar structures without taking the gold film thickness and out-of-plane losses into account, which is not conducive to the structural design and performance analysis of the sensor.

[0011] 4. Because the mid-infrared band contains the vibration characteristics of biological nanoparticles, it has been proven to be particularly suitable for application in the detection of proteins and chemicals, but refractive index sensors in the mid-infrared band have rarely been studied.

[0012] 5. Once the structural dimensions of the sensor are determined, traditional sensors are unable to achieve dynamic control of the sensing range, and the sensor's sensing bandwidth is very narrow, thus failing to meet the application requirements of wide sensing bandwidth sensors. Summary of the Invention

[0013] In response to the above problems, the present utility model provides a mid-infrared refractive index sensor based on the PIT effect, which aims to solve the problem of low sensing sensitivity of the refractive index sensor; solve the problem that the sensor device is difficult to integrate in the on-chip plasmon optical path; and realize a graphene refractive index sensor with high sensitivity, small size, wide sensing bandwidth and easy integration.

[0014] In order to solve the above problems, the technical solution provided by the present invention is as follows:

[0015] A mid-infrared refractive index sensor based on the PIT effect includes a silicon substrate, a sapphire layer, a graphene nanostrip waveguide, a first graphene rectangular resonant cavity, and a second graphene rectangular resonant cavity, wherein:

[0016] The sapphire layer is provided above the silicon substrate; the graphene nanostrip waveguide, the first graphene rectangular resonant cavity, and the second graphene rectangular resonant cavity are provided on the upper surface of the sapphire layer;

[0017] The first graphene rectangular resonant cavity is directly coupled to the graphene nanostrip waveguide;

[0018] The second graphene rectangular resonant cavity is arranged in parallel with the first graphene rectangular resonant cavity;

[0019] The second graphene rectangular resonant cavity is indirectly coupled to the graphene nanostrip waveguide through the first graphene rectangular resonant cavity.

[0020] Preferably, the thickness of the silicon substrate is 300 nm; the thickness of the sapphire layer is 300 nm.

[0021] Preferably, the width of the graphene nanostrip waveguide is 10 nm.

[0022] Preferably, the chemical potential of the graphene nanostrip waveguide is fixed at 0.40 eV.

[0023] Preferably, the width of the first graphene rectangular resonant cavity is 10 nm and the length is 140 nm; the width of the second graphene rectangular resonant cavity is 10 nm and the length is 140 nm.

[0024] Preferably, the coupling distance between the graphene nanostrip waveguide and the first graphene rectangular resonant cavity is 10 nm.

[0025] Preferably, a coupling distance between the first graphene rectangular resonant cavity and the second graphene rectangular resonant cavity is 20 nm.

[0026] Preferably, a position deviation between the first graphene rectangular resonant cavity and the second graphene rectangular resonant cavity is 0.

[0027] Preferably, the thickness of the single-layer graphene used in the sensor of the present invention is 0.2 nm.

[0028] Preferably, the size of the sensor of the present invention is less than 0.05 μm. 2 .

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. Since the utility model adopts a graphene nanostrip waveguide structure, the PIT effect generated by the graphene nanostrip waveguide coupled with a rectangular resonant cavity structure is applied to the integrated refractive index sensor. When the refractive index change of the detected material is very small, it will cause a large resonant wavelength offset, thereby solving the problem of low sensing sensitivity of the refractive index sensor.

[0031] 2. Since the refractive index sensor based on the graphene nanostrip waveguide coupled rectangular resonant cavity structure of the present invention has a size of less than 0.05μm2, it can achieve an ultra-compact structure, thereby solving the problem of the difficulty of integrating sensor devices in the on-chip plasmon optical path. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic structural diagram of a mid-infrared refractive index sensor based on the PIT effect according to a specific embodiment of the present invention;

[0033] Figure 2a Schematic diagram of the transmission spectrum of the double rectangular resonant cavity coupled graphene nanostrip waveguide structure under different refractive indices of the present invention;

[0034] Figure 2b This is a schematic diagram of the transmission spectrum of the sensor structure obtained when the surface of the refractive index sensor of the present invention is covered with different substances.

[0035] Wherein: 1. Silicon substrate, 2. Sapphire layer, 3. Graphene nanostrip waveguide, 4. First graphene rectangular resonant cavity, 5. Second graphene rectangular resonant cavity, 6. Front direction, 7. Back direction DETAILED DESCRIPTION

[0036] The present invention is further illustrated below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, modifications of various equivalent forms of the present invention made by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0037] Mid-infrared refractive index sensors based on the PIT effect, such as Figure 1 As shown, it includes a silicon substrate 1, a sapphire layer 2, a graphene nanostrip waveguide 3, a first graphene rectangular resonant cavity 4, and a second graphene rectangular resonant cavity 5, wherein:

[0038] The sapphire layer 2 is provided on the silicon substrate 1 ; the upper surface of the sapphire layer 2 is provided with a graphene nanostrip waveguide 3 , a first graphene rectangular resonant cavity 4 , and a second graphene rectangular resonant cavity 5 .

[0039] The first graphene rectangular resonant cavity 4 is directly coupled to the graphene nanostrip waveguide 3 .

[0040] The second graphene rectangular resonant cavity 5 is arranged in parallel with the first graphene rectangular resonant cavity 4 .

[0041] The second graphene rectangular resonant cavity 5 is indirectly coupled to the graphene nanostrip waveguide 3 through the first graphene rectangular resonant cavity 4 .

[0042] It should be noted that the present invention combines the PIT effect and the SPPs propagation-type boundary mode to design a dynamically adjustable graphene refractive index sensor.

[0043] It should be further explained that the analyte can be detected by covering the surface of the graphene nanostrip waveguide 3, the first graphene rectangular resonant cavity 4, and the second graphene rectangular resonant cavity 5. In practical applications, the SPPs on the graphene nanostrip waveguide 3 can be excited using a grating or prism; the present invention uses a dipole to excite boundary-mode surface plasmons at the front end of the graphene nanostrip waveguide 3.

[0044] It should be noted that the present invention adopts the FDTD-solution software simulation method to determine the structural parameters of the refractive index sensor based on the graphene nanostrip waveguide coupled rectangular resonant cavity structure.

[0045] In this specific embodiment, the thickness of the silicon substrate 1 is 300 nm; the thickness of the sapphire layer 2 is 300 nm.

[0046] In this specific embodiment, the width of the graphene nanostrip waveguide 3 is 10 nm.

[0047] In this specific embodiment, the chemical potential of the graphene nanostrip waveguide 3 is fixed at 0.40 eV.

[0048] In this specific embodiment, the width of the first graphene rectangular resonant cavity 4 is 10 nm and the length is 140 nm; the width of the second graphene rectangular resonant cavity 5 is 10 nm and the length is 140 nm.

[0049] In this specific embodiment, the coupling distance between the graphene nanostrip waveguide 3 and the first graphene rectangular resonant cavity 4 is 10 nm.

[0050] In this specific embodiment, the coupling distance between the first graphene rectangular resonant cavity 4 and the second graphene rectangular resonant cavity 5 is 20 nm.

[0051] In this specific embodiment, the position deviation between the first graphene rectangular resonant cavity 4 and the second graphene rectangular resonant cavity 5 is 0.

[0052] In this specific embodiment, the thickness of the single-layer graphene used in the sensor of the present invention is 0.2 nm.

[0053] In this specific embodiment, the size of the sensor of the utility model is less than 0.05 μm 2 .

[0054] It should be noted that the long sides of the graphene nanostrip waveguide 3 , the long sides of the first graphene rectangular resonant cavity 4 , and the long sides of the second graphene rectangular resonant cavity 5 are respectively parallel to the axes of the front end direction 6 and the rear end direction 7 .

[0055] It should be noted that the rectangular resonant cavity structure coupled with the graphene nanostrip waveguide 3 of the present invention can reduce the size of the refractive index sensor.

[0056] like Figure 1 As shown, it should be noted that since the first graphene rectangular resonant cavity 4 is directly connected to the graphene nanostrip waveguide 3, the SPPs wave transmitted in the graphene nanostrip waveguide 3 can be directly coupled into the first graphene rectangular resonant cavity 4, so that the first graphene rectangular resonant cavity 4 can act as a bright mode. The second graphene rectangular resonant cavity 5 can indirectly couple with the graphene nanostrip waveguide 3 through the first graphene rectangular resonant cavity 4, and the second graphene rectangular resonant cavity 5 acts as a dark mode in the entire system. The coherent destructive interaction between the bright mode and the dark mode induces the PIT effect.

[0057] like Figure 2aAs shown, in this specific embodiment, when the refractive index of the detection material increases from 1.00 to 1.01, the resonant wavelength shifts of the resonant modes at 6.39 μm and 7.55 μm are 16.50 nm and 20.00 nm, respectively, which means that the structure has a high quality factor and sensing sensitivity, and is very suitable for designing a refractive index sensor.

[0058] It should be noted that the structure of the present invention achieves the above-mentioned high sensing sensitivity because:

[0059] 1. Since graphene nanorods have strong binding properties on surface plasmons, they will enhance the contact between SPPs and the detection material.

[0060] 2. The PIT effect induces the generation of slow light, which also enhances the spatial contact between SPPs and the detection material.

[0061] It should be further explained that the structure proposed in the present invention can be used to distinguish different chemical substances.

[0062] In this specific embodiment, when ovalbumin n=1.15, water n=1.332 and glucose n=1.375 are covered on the surface of the graphene nanostrip waveguide 3, the first graphene rectangular resonant cavity 4 and the second graphene rectangular resonant cavity 5, the simulated system transmission spectrum is as follows: Figure 2b As shown in the figure, the refractive index difference between air and ovalbumin is 0.15, which causes the resonant wavelength to shift by 305nm, while the slight refractive index difference between water and glucose is 0.043, which causes the resonant wavelength to shift by 88nm. The above simulation results show that the present invention can realize a refractive index sensor with high sensing sensitivity.

[0063] It should be noted that this utility model utilizes a rectangular resonant cavity structure coupled with a graphene nanostrip waveguide to realize a compact, dynamically adjustable graphene refractive index sensor in the mid-infrared band. The graphene nanostrips' strong binding properties on SPPs enhance the contact between the SPPs and the probe material. The PIT effect induces the generation of slow light, which similarly enhances the spatial contact between the SPPs and the probe material. This reduces the sensor size while increasing its sensitivity. This novel working mechanism of the graphene refractive index sensor has great scientific research value and potential for future application in the field of photonic device integration, supporting the development of high-sensitivity sensing technologies.

[0064] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0065] The above description of the disclosed embodiments is intended to enable any person skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments presented herein but is intended to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0066] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purposes of describing the above embodiments, but one of ordinary skill in the art will recognize that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to encompass all such changes, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or."

[0067] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mid-infrared refractive index sensor based on the PIT effect, characterized in that: The invention comprises a silicon substrate (1), a sapphire layer (2), a graphene nanostrip waveguide (3), a first graphene rectangular resonant cavity (4), and a second graphene rectangular resonant cavity (5), wherein: The sapphire layer (2) is provided above the silicon substrate (1); the graphene nanostrip waveguide (3), the first graphene rectangular resonant cavity (4), and the second graphene rectangular resonant cavity (5) are provided on the upper surface of the sapphire layer (2); The first graphene rectangular resonant cavity (4) is directly coupled to the graphene nanostrip waveguide (3); The second graphene rectangular resonant cavity (5) is arranged in parallel with the first graphene rectangular resonant cavity (4); The second graphene rectangular resonant cavity (5) is indirectly coupled to the graphene nanostrip waveguide (3) via the first graphene rectangular resonant cavity (4); the positional deviation between the first graphene rectangular resonant cavity (4) and the second graphene rectangular resonant cavity (5) is 0; and the size of the sensor is less than 0.05 μm. 2 .

2. The mid-infrared refractive index sensor based on the PIT effect according to claim 1, characterized in that: The thickness of the silicon substrate (1) is 300 nm; the thickness of the sapphire layer (2) is 300 nm.

3. The mid-infrared refractive index sensor based on the PIT effect according to claim 2, characterized in that: The width of the graphene nanostrip waveguide (3) is 10 nm.

4. The mid-infrared refractive index sensor based on the PIT effect according to claim 3, characterized in that: The chemical potential of the graphene nanostrip waveguide (3) is fixed at 0.40 eV.

5. The mid-infrared refractive index sensor based on the PIT effect according to claim 4, characterized in that: The width of the first graphene rectangular resonant cavity (4) is 10 nm and the length is 140 nm; the width of the second graphene rectangular resonant cavity (5) is 10 nm and the length is 140 nm.

6. The mid-infrared refractive index sensor based on the PIT effect according to claim 5, characterized in that: The coupling distance between the graphene nanostrip waveguide (3) and the first graphene rectangular resonant cavity (4) is 10 nm.

7. The mid-infrared refractive index sensor based on the PIT effect according to claim 6, characterized in that: The coupling distance between the first graphene rectangular resonant cavity (4) and the second graphene rectangular resonant cavity (5) is 20 nm.

8. The mid-infrared refractive index sensor based on the PIT effect according to claim 7, characterized in that: The thickness of the single-layer graphene used in the sensor is 0.2nm.

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