High-sensitivity and high-robustness BZF-BIC mode refractive index sensor with perturbation

Abstract

The invention discloses a high-sensitivity and high-robustness BZF-BIC mode refractive index sensor with perturbation, the sensor comprises a silicon dioxide substrate and a silicon nitride film provided with a square hole array, the silicon dioxide substrate is a bottom plate of the refractive index sensor, and the silicon nitride film with high refractive index is deposited on the surface of the silicon dioxide substrate to form an optical functional layer; a square hole array which is regularly arranged is arranged on the silicon nitride thin film, each primitive cell of the square hole array comprises two square holes with size perturbation or position perturbation, and strong localization and high-sensitivity refractive index response of a light field are achieved through perturbation excitation of a BZF-BIC mode. The device has the advantages of high sensitivity, high robustness, simple structure, high stability, low possibility of being interfered and influenced by processing factors, and high measurement result accuracy.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing technology, and in particular to a high-sensitivity and high-robustness BZF-BIC mode refractive index sensor with perturbation. Background Technique

[0002] The refractive index (RI) is an important optical parameter of materials. The change in refractive index can reflect the changes in physical quantities such as concentration, temperature, and pressure. A refractive index sensor is a sensor that uses the principle of light refraction for measurement, mainly used to measure the refractive index of substances such as liquids, gases, and solutions. It is a label-free optical sensor with high sensitivity and fast response speed, so it is widely used in fields such as disease diagnosis, environmental monitoring, food safety, and biochemical sensing. Taking the surface plasmon refractive index sensor as an example, as the concentration of the liquid to be measured changes, its effective refractive index also changes, and the resonance peak of the surface plasmon excited by the liquid to be measured will shift in the spectrum, thereby measuring the concentration of the liquid to be measured. For refractive index sensors with different principles, their manifestations include changes in the intensity of the outgoing light, resonance peak shift, phase change, etc.

[0003] Brillouin Zone Folding Bound States in the Continuum (BZF-BIC) is a non-radiative bound state in the continuum, which allows the construction of a resonant cavity with confined electromagnetic energy and high Q factor. This state is different from the traditional Bound States in the Continuum (BIC) based on symmetry protection. They exhibit a perturbation-dependent and significantly enhanced Q factor in the entire momentum space and have strong resistance to structural disorders. By introducing periodic perturbations, the guided modes originally below the light cone can be folded into the continuum to form BZF-BIC. The main feature of BZF-BIC is that they can exhibit ultra-high Q factors in a large and tunable momentum space. This property makes BZF-BIC have potential applications in fields such as terahertz devices, nonlinear optics, quantum computing, and photonic integrated circuits.

[0004] As a label-free optical sensor, the refractive index sensor has high sensitivity and fast response speed. Therefore, it is widely used in fields such as disease diagnosis, environmental monitoring, food safety, and biochemical sensing. However, generally, refractive index sensors based on bound states in the continuum, such as a terahertz sensor based on symmetry-protected bound states in the continuum disclosed in CN202111269748, are easily interfered by processing factors, affecting the accuracy of their measurement results. Therefore, it is very important to study refractive index sensors that can reduce the interference of processing factors and have more accurate measurement results. Summary of the Invention

[0005] The object of the present invention is to provide a BZF - BIC mode refractive index sensor with high sensitivity, high robustness, not easily interfered by processing factors, and more accurate measurement results.

[0006] The technical solution to achieve the object of the present invention is: a highly sensitive and highly robust BZF - BIC mode refractive index sensor with perturbation, including a silica substrate and a silicon nitride thin film provided with a square hole array;

[0007] The silica substrate is the bottom plate of the refractive index sensor, and an optical functional layer is formed by depositing a silicon nitride thin film on its surface;

[0008] The silicon nitride thin film is provided with a regularly arranged square hole array;

[0009] Each unit cell of the square hole array contains two square holes with size perturbation or position perturbation, and the BZF - BIC mode is excited through the perturbation.

[0010] Further, the cross - section of each unit cell of the square hole array is rectangular, and the long side length is 2 times the short side length.

[0011] Further, the cross - section of each unit cell of the square hole array is evenly divided into two squares along the long side, and the geometric centers of the two square holes corresponding to this unit cell are respectively located at the centers of the two squares.

[0012] Further, the two square holes included in each unit cell have rectangular cross - sections with different sizes. The long sides of the two rectangles are parallel to the long side of the unit cell, and the long side lengths of the two rectangles are both 2 times the short side lengths.

[0013] Further, for the rectangle corresponding to the cross - section of each unit cell, the short side length is 100 nm - 150 nm.

[0014] Further, for the rectangle corresponding to the cross - section of each square hole, the short side length is 15 nm - 60 nm.

[0015] Further, the thickness of the silicon nitride thin film is 75 nm - 250 nm, and the depth of each square hole is the same as the film thickness.

[0016] Further, the short side lengths of the two square holes in the unit cell of the square hole array are set with a perturbation not exceeding 8 nm, and the two square hole centers are longitudinally set with a perturbation not exceeding 16 nm from the initial center position.

[0017] Compared with the prior art, the significant advantages of the present invention are as follows: (1) By introducing perturbations between the unit silicon nitride square hole arrays, the refractive index sensor based on symmetry-protected BIC composed of periodic arrangements of unit structures can achieve the quasi-BZF-BIC mode, and resonance peaks with a quality factor of more than 4.75×10 8 can be obtained in the transmission spectrum, improving the sensitivity of the BZF-BIC mode refractive index sensor; (2) polarization-insensitive, the BIC mode can be achieved when TE waves or TM waves are incident, with high robustness; (3) simple structure, easy to process, strong stability, not easily oxidized or corroded, not easily interfered by processing factors, and the measurement results are more accurate. Description of the Drawings

[0018] Figure 1 It is a structural diagram of the high-sensitivity and high-robustness BZF-BIC mode refractive index sensor with perturbations of the present invention.

[0019] Figure 2 It is a schematic diagram of energy band folding when the perturbation is not 0 in the embodiment of the present invention.

[0020] Figure 3 It is a schematic diagram of the x and y components of the electric field of BZF-TE, BZF-TM and symmetry-protected BIC when size perturbation and position perturbation are added in the embodiment of the present invention.

[0021] Figure 4 It is a schematic diagram of the quality factors of BZF-BIC and symmetry-protected BIC when changing the size perturbation and the transverse wave vector at a refractive index of 1.44 in the embodiment of the present invention.

[0022] Figure 5 It is a schematic diagram of the quality factors of BZF-BIC and symmetry-protected BIC when changing the position perturbation and the transverse wave vector at a refractive index of 1.44 in the embodiment of the present invention.

[0023] Figure 6 It is a schematic diagram of the transmittance when the positioning perturbation is 2 nm at a refractive index of 1.44 in the embodiment of the present invention.

[0024] Figure 7 It is a schematic diagram of the change of the quality factor of BZF-TE with the short side length of the square hole and the depth of the hole when the positioning perturbation is 2 nm in the embodiment of the present invention.

[0025] Figure 8 It is a schematic diagram of the change of the sensitivity of BZF-TE with the short side length of the square hole and the depth of the hole when the positioning perturbation is 2 nm in the embodiment of the present invention.

[0026] Figure 9Schematic diagram of the quality factor of BZF-TE varying with the short side length and depth of the square hole when the positioning perturbation is 2 nm in the embodiments of the present invention.

[0027] Figure 10 Schematic diagram of the quality factor of BZF-TM varying with the short side length and depth of the square hole when the size perturbation is 2 nm in the embodiments of the present invention.

[0028] Figure 11 Schematic diagram of the sensitivity of BZF-TM varying with the short side length and depth of the square hole when the size perturbation is 2 nm in the embodiments of the present invention.

[0029] Figure 12 Schematic diagram of the quality factor of BZF-TM varying with the short side length and depth of the square hole when the size perturbation is 2 nm in the embodiments of the present invention.

[0030] Figure 13 Schematic diagram of the resonant peak frequency shift of BZF-TE at different refractive indices when the positioning perturbation is 2 nm and the incident angle is 0.5° in the embodiments of the present invention.

[0031] Figure 14 Schematic diagram of the corresponding relationship between the resonant peak wavelength and the refractive index of BZF-TE when the positioning perturbation is 2 nm and the incident angle is 0.5° in the embodiments of the present invention. Detailed implementation manners

[0032] As Figure 1 shown, a highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation of the present invention includes a silica substrate and a silicon nitride thin film provided with a square hole array;

[0033] The silica substrate is the bottom plate of the refractive index sensor, and an optical functional layer is formed by depositing a silicon nitride thin film on its surface;

[0034] A regularly arranged square hole array is provided on the silicon nitride thin film;

[0035] Each unit cell of the square hole array contains two square holes with size perturbation or position perturbation, and the BZF-BIC mode is excited through the perturbation to realize strong localization of the optical field and high-sensitivity refractive index response.

[0036] As a specific example, the cross-section of each unit cell of the square hole array is rectangular, and the long side length is twice the short side length.

[0037] As a specific example, the cross-section of each unit cell in the square hole array is evenly divided into two squares along the long side, and the geometric centers of the two square holes corresponding to the unit cell are respectively located at the centers of the two squares.

[0038] As a specific example, each unit cell contains two square holes with cross-sections being rectangles of different sizes. The long sides of the two rectangles are parallel to the long side of the unit cell, and the long side lengths of both rectangles are twice the short side lengths.

[0039] As a specific example, for the rectangle corresponding to the cross-section of each unit cell, the short side length is 100 nm to 150 nm.

[0040] As a specific example, for the rectangle corresponding to the cross-section of each square hole, the short side length is 15 nm to 60 nm.

[0041] As a specific example, the thickness of the silicon nitride thin film is 75 nm to 250 nm, and the depth of each square hole is the same as the film thickness. By combining perturbation to regulate the light field coupling efficiency, the sensor sensitivity can reach more than 110 nm / RIU.

[0042] As a specific example, the short side lengths of the two square holes in the unit cell of the square hole array are set with a perturbation not exceeding 8 nm, and the two square hole centers are longitudinally perturbed by a distance not exceeding 16 nm from the initial center position. Through the design of the geometric center positions of the symmetrically distributed holes and the manufacturing error of ±8 nm, the BZF-BIC mode can be ensured to work stably under process errors.

[0043] As a specific example, the square holes are precisely prepared by electron beam lithography and plasma etching processes.

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Embodiment

[0046] This embodiment provides a high-sensitivity and high-robustness BZF-BIC mode refractive index sensor with perturbation, including a silica substrate and a silicon nitride thin film provided with a square hole array.

[0047] The silica substrate is composed of fused quartz with a dielectric constant of 2.076. The cross-section of the silica substrate is a rectangle, with the long side length of the unit being 260 nm and the short side length being 130 nm. A layer of silicon nitride thin film is closely attached to the upper surface of the silica substrate, and there are multiple square hole arrays arranged periodically on the film. Each unit has two square holes. The geometric center of one square hole is located at 65 nm from the center of the long side and 65 nm from the center of the short side of the unit, and the geometric center of the other square hole is located at 195 nm from the center of the long side and 65 nm from the center of the short side of the dielectric layer. The depth of the square hole is 75 nm, and the short side length is 30 nm. When the sizes of the two square holes are the same, the metasurface obtained by periodically arranging the unit structure at this time is a common optical waveguide without longitudinal resonance.

[0048] By introducing a size perturbation of 2 nm between two square holes in the silicon nitride unit, in this embodiment, by changing the short side length of the square hole so that it varies within the range of ±2 of the initial value, the silicon nitride square hole array with a periodic arrangement of the unit structure realizes the BZF-BIC mode and has a resonant peak with a high quality factor.

[0049] Figure 2 When the perturbation is not 0, the unit structure is periodically arranged, and its energy band analysis is carried out. The perturbation leads to the doubling of the primitive cell period, which in turn causes the folding of the energy bands in the reciprocal lattice space and excites the BZF-BIC mode.

[0050] Figure 3 Schematic diagrams of the x and y components of the electric fields of BZF-TE and BZF-TM when the positioning perturbation and size perturbation are added, as well as the x and y components of the electric field of the symmetry-protected BIC after considering the perturbation. All modes are first-order modes.

[0051] Figure 4 Trend diagram of the quality factor of the BZF-TE mode with the change of the transverse wave vector when the positioning perturbation is 1 nm, 2 nm, 4 nm, 8 nm, and 12 nm and the refractive index of the analyte is 1.44. At this time, the initial value of the short side length of the square hole is 40 nm. When only the positioning perturbation exists, the quality factor of BZF-TE is always higher than that of the symmetry-protected BIC in a wide range of transverse wave vectors.

[0052] Figure 5 Trend diagram of the quality factor of the BZF-TM mode with the change of the transverse wave vector when the size perturbation is 1 nm, 2 nm, 3 nm, 6 nm, and 12 nm and the refractive index of the analyte is 1.44. At this time, the initial value of the short side length of the square hole is 50 nm; when the size perturbation is less than 6 nm, the quality factor of BZF-TE is always higher than that of the symmetry-protected BIC in a wide range of transverse wave vectors.

[0053] Figure 6 Transmission spectrum obtained by simulating the present invention when the silicon nitride unit structure is periodically arranged under the condition of a size perturbation of 2 nm and the refractive index of the analyte is 1.44. When there is a 2 nm perturbation in the short side lengths of the two square holes of the silicon nitride unit, the BZF-BIC mode can be realized near 540 nm, that is, there is a resonant peak with an ultra-high quality factor. By Figure 6 It can be seen that the refractive index sensor based on the BZF-BIC mode still has a high quality factor when the size perturbation is 2 nm. This refractive index sensor has high sensitivity and high robustness to avoid the sensitivity loss caused by perturbation.

[0054] Figure 7The distribution diagram of the quality factor of BZF-TE obtained by changing the short side length and depth of the silicon nitride square hole when the perturbation is 2 nm. As the short side length of the square hole decreases, the quality factor of BZF-TE gradually increases; as the depth of the square hole increases, the quality factor of the resonance peak gradually increases.

[0055] Figure 8 The distribution diagram of the sensitivity of BZF-TE obtained by changing the short side length and depth of the silicon nitride square hole when the perturbation is 2 nm. As the short side length of the square hole changes, the sensitivity of BZF-TE does not change significantly; as the depth of the square hole decreases, the quality factor of the resonance peak gradually increases.

[0056] Figure 9 The distribution diagram of the quality factor of BZF-TE obtained by changing the short side length and depth of the silicon nitride square hole when the perturbation is 2 nm. The quality factor comprehensively considers the optimal situation of the quality factor and sensitivity of BZF-TE as the size changes. When the short side length is 40 - 55 nm and the height is 100 - 120 nm, the quality factor and sensitivity of BZF-TE achieve the optimal solution.

[0057] Figure 10 The distribution diagram of the quality factor of BZF-TM obtained by changing the short side length and depth of the silicon nitride square hole when the size perturbation is 2 nm. As the short side length of the square hole decreases, the quality factor of BZF-TM gradually increases; as the depth increases, the quality factor of the resonance peak gradually increases. There is a high-quality factor band when the size changes, which corresponds to BZF-BIC generated by strong coupling at this time, and the performance is better.

[0058] Figure 11 The distribution diagram of the sensitivity of BZF-TM obtained by changing the short side length and depth of the silicon nitride square hole when the size perturbation is 2 nm. As the short side length of the square hole changes, the sensitivity of BZF-TM does not change significantly; as the depth decreases, the quality factor of the resonance peak gradually increases.

[0059] Figure 12 The distribution diagram of the quality factor of BZF-TM obtained by changing the short side length and depth of the silicon nitride square hole when the size perturbation is 2 nm. The quality factor comprehensively considers the optimal situation of the quality factor and sensitivity of BZF-TM as the size changes. When the short side length is 45 - 55 nm and the height is 140 - 200 nm, the quality factor and sensitivity of BZF-TM achieve the optimal solution, and at this time, the sensitivity of BZF-TM is significantly higher than that of BZF-TE.

[0060] Based on the unchanged parameters of the silicon nitride square hole array, when the period is 117 nm, the short side length is 40 nm, the depth is 179 nm, and the longitudinal relative positioning perturbation is 2 nm, arranging the unit structures in a periodic manner can obtain a high-sensitivity and high-robustness BZF-BIC mode refractive index sensor. When this refractive index sensor is placed in an object with a refractive index to be measured, the position of the resonant peak will change with the refractive index of the object to be measured, and the obtained sensing characteristic curve is as shown in Figure 13 . It can be seen that a high-sensitivity and high-robustness sensor obtained by using this method of breaking symmetry can have excellent performance in refractive index sensing.

[0061] Figure 14 is Figure 13 the curve fitting diagram of the resonant peak wavelength versus the refractive index change. It can be seen that its change tends to be linear, and the sensitivity is extremely high, reaching 110 nm / RIU.

[0062] The above is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation, characterized in that, It includes a silica substrate and a silicon nitride thin film provided with a square hole array; The silica substrate is the bottom plate of the refractive index sensor, and an optical functional layer is formed by depositing a silicon nitride thin film on its surface; A regularly arranged square hole array is provided on the silicon nitride thin film; Each unit cell of the square hole array contains two square holes with size perturbation or position perturbation, and the BZF-BIC mode is excited through the perturbation.

2. The highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation according to claim 1, characterized in that, The cross-section of each unit cell of the square hole array is rectangular, and the long side length is twice the short side length.

3. The high-sensitivity and high-robustness BZF-BIC mode refractive index sensor with perturbation according to claim 2, characterized in that The cross-section of each unit cell in the square hole array is evenly divided into two squares along the long side, and the geometric centers of the two square holes corresponding to the unit cell are respectively located at the centers of the two squares.

4. The highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation according to claim 3, characterized in that, Each unit cell contains two square holes with cross-sections being rectangles of different sizes. The long sides of the two rectangles are parallel to the long side of the unit cell, and the long side lengths of the two rectangles are both twice the short side lengths.

5. The highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation according to claim 4, characterized in that, For the rectangle corresponding to the cross-section of each unit cell, the short side length is 100 nm to 150 nm.

6. The highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation according to claim 5, wherein For the rectangle corresponding to the cross-section of each square hole, the short side length is 15 nm to 60 nm.

7. The highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation according to claim 6, characterized in that The thickness of the silicon nitride thin film is 75 nm to 250 nm, and the depth of each square hole is the same as the film thickness.

8. The highly sensitive and highly robust BZF-BIC mode refractive index sensor with perturbation according to claim 7, characterized in that, The short side lengths of the two square holes in the unit cell of the square hole array are provided with a perturbation not exceeding 8 nm, and the two square hole centers are longitudinally provided with a perturbation not exceeding 16 nm from the initial center position.

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