Terahertz filter based on bound state theory in accidental continuous spectrum

Abstract

The invention discloses a terahertz filter based on a bound state theory in an accidental continuous spectrum. According to the filter, the periodically arranged rectangular silicon column array is designed on the surface of the silicon dielectric layer, so that high-Q-value resonance mode excitation is realized. On the premise that the structural symmetry is not damaged, the frequency response of the filter can be accurately adjusted by adjusting periodic parameters, and the application requirements of different terahertz frequency bands are met. Compared with the prior art, the method does not need to depend on complex structure breaking design, the problem of unstable performance caused by manufacturing errors is avoided, the manufacturing process is simplified, and the production cost is reduced. Experimental verification shows that the narrow-band and high-Q-value frequency selective filtering can be realized in a predetermined frequency band, and the narrow-band and high-Q-value frequency selective filtering device has low insertion loss and high signal-to-noise ratio, has a relatively strong practical application prospect, and particularly has wide application potential in the fields of terahertz communication, sensing, spectrum detection and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz technology and micro-nano photonic devices, and in particular relates to a terahertz filter based on the theory of bound states in accidental continuous spectrum. Background Art

[0002] As an important frequency band connecting millimeter waves and infrared bands, the terahertz (THz) band, due to its unique spectral characteristics, shows broad application prospects in fields such as wireless communications, imaging, sensing, and biomedical testing. As the core component in THz systems, the main function of THz filters is to achieve frequency-selective filtering to ensure the effective transmission of signals in specific frequency bands, thereby improving the system's signal-to-noise ratio, transmission efficiency, and signal processing accuracy. However, due to limitations in intrinsic material losses, device processing errors, and radiation coupling mechanisms, existing THz filters generally suffer from technical bottlenecks such as low quality factor (Q value), insufficient filtering accuracy, poor dynamic control capabilities, and weak system integration, which seriously restrict the development of THz technology in high-performance application scenarios.

[0003] The existing terahertz filter technology has the following main disadvantages:

[0004] (1) Limited quality factor: Due to the cumulative effects of material absorption, radiation leakage, and process defects, traditional THz filters are difficult to achieve ultra-high Q values, resulting in a large amount of signal energy loss during transmission and processing.

[0005] (2) Insufficient coupling efficiency: In the high-Q resonance mode, the radiation channel is limited, making it difficult to effectively excite or extract external signals, reducing the input and output efficiency of the device.

[0006] (3) Limited design flexibility: Traditional structures are insufficient in frequency tuning, bandwidth control, and environmental adaptability, and are easily subject to manufacturing tolerances and environmental disturbances, resulting in performance drift.

[0007] (4) Difficulty in frequency tuning: Existing filters have a narrow tuning range and fixed response, which makes it difficult to meet the needs of broadband dynamic control.

[0008] (5) Integration and stability challenges: Some high-performance filters have complex structures, making large-scale integration and batch manufacturing difficult, and have poor stability and consistency in actual applications.

[0009] (6) High energy loss: Radiation loss and material absorption result in low overall energy transmission efficiency, limiting the application potential of the device in high energy density systems.

[0010] In recent years, the theory of bound states in the continuum (BIC) has provided a new approach to solving the above problems. BIC is a localized state whose energy is located within the continuum but does not radiate outward, which can achieve a theoretically infinite Q value. Depending on the excitation mechanism, BICs are divided into symmetry-protected BICs (SPBICs) and accidental BICs (ACBICs). Among them, SPBICs rely on structural symmetry protection and can only be excited at the center of the Brillouin zone. Usually, complex symmetry-breaking designs are required to achieve finite Q devices, which increases the manufacturing difficulty and cost.

[0011] In the prior art, Chinese patent CN114088663B discloses a terahertz sensor based on a symmetrically protected continuum bound state. The sensor consists of multiple unit structures arranged periodically. These units have the same structure, including a fused quartz substrate with microstructured columns A and B composed of N-type doped silicon disposed on its upper surface. This technical solution artificially introduces structural asymmetry, breaking the symmetry protection to achieve a high-Q resonant mode. However, this method has the following shortcomings:

[0012] (1) This technical solution adopts the symmetry-protected BIC (SPBIC) theory, which is achieved by artificially introducing asymmetry (such as slight changes in geometric structure dimensions) into a symmetric structure, breaking the symmetry of the structure and transforming the BIC mode into a quasi-BIC mode, thereby achieving a finitely high Q factor. However, this method requires additional breaking design in the structure, is more difficult to manufacture, and the adjustable range of the Q value is limited by the size of the asymmetry;

[0013] (2) The structure of this technical solution is relatively complex. Its core design relies on the periodic arrangement of N-type doped silicon microstructure pillars on the substrate. By adjusting the geometric center position, shape and size of microstructure pillars A and B (for example, pillar B can be square, L-shaped, rectangular, cross-shaped, etc.), an asymmetric amount is introduced to destroy the structural symmetry. Although this method can achieve Q factor regulation, it requires precise control of small changes in the structure, which increases the manufacturing difficulty and error sensitivity, and may affect the consistency of the device.

[0014] (3) The Q factor control method of this technical solution is to adjust the size of the asymmetry, that is, as the size of the microstructure column B changes, the Q factor changes in a negative quadratic relationship. Although this method provides the ability to adjust the Q value to a certain extent, it is difficult to accurately control the change of the Q factor due to its high sensitivity to the asymmetry. When the asymmetry is small, the manufacturing error of the structure may cause performance fluctuations.

[0015] (4) The SPBIC mode of this technical solution mainly relies on structural breaking to adjust the frequency, so its tuning range is small and is limited to a certain extent by manufacturing precision. If the asymmetry is too large, the Q factor will drop rapidly, affecting the filtering performance. If the asymmetry is too small, it may be difficult to form a stable quasi-BIC mode.

[0016] (5) This technical solution is mainly used in terahertz sensing. Its main advantage lies in its strong refractive index sensing capability, which is suitable for fields such as biological detection and environmental monitoring. However, due to the need to break the symmetry, the structure of SPBIC-based sensors is usually relatively complex and the manufacturing precision requirements are high, which limits the possibility of large-scale application. Summary of the Invention

[0017] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a terahertz filter based on the theory of bound states in the accidental continuous spectrum.

[0018] The purpose of the present invention can be achieved by the following technical solutions:

[0019] On one hand, the present invention provides a terahertz filter based on the theory of bound states in a contingent continuous spectrum, comprising a silicon dielectric layer and a unit array provided on the upper and lower surfaces of the silicon dielectric layer; the unit array is composed of a plurality of symmetrically arranged high-dielectric constant microstructure units arranged periodically, each microstructure unit including a pair of dielectric structures symmetrically arranged along the z direction, the projection of the dielectric structure on the xy plane being a specific shape, wherein a coordinate system is established with the surface of the silicon dielectric layer as the xy plane and the direction perpendicular to the xy plane as the z direction.

[0020] Furthermore, the dielectric structure is a rectangular silicon column.

[0021] Furthermore, the projection of the rectangular silicon column on the xy plane is a rectangle.

[0022] Furthermore, the rectangular silicon pillars are arranged in a rotational manner at a preset angle in the xy plane.

[0023] Furthermore, the rectangular silicon column is arranged by rotating 45° along the xy plane, that is, the angle between the long side of the rectangular silicon column and the x-axis is 45°.

[0024] Furthermore, the rectangular silicon column has a long side dimension of 70 to 90 μm, a short side dimension of 45 to 65 μm, and a height of 197 to 206 μm.

[0025] Furthermore, the period length of the microstructure units in the x-direction is 120-140 μm, and the period length in the y-direction is 144-152 μm.

[0026] Furthermore, a pair of dielectric structures in each microstructure unit are arranged vertically and symmetrically along the z direction, and are mirror-symmetrical to each other in the xy plane.

[0027] Furthermore, by adjusting the period length parameters of the microstructure unit in the x and y directions, the terahertz filter is continuously switched between a high Q value bound state and a finite Q value quasi-bound state.

[0028] Furthermore, by changing the period length parameter of the microstructure unit or the size of the rectangular silicon column, the terahertz resonant frequency of the terahertz filter can be adjusted in the range of 0.2THz to 2THz.

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

[0030] (1) The present invention innovatively adopts the accidental BIC mechanism, without destroying the structural symmetry. It can achieve a high-Q resonant mode simply by placing rectangular silicon pillars symmetrically in the upper and lower parts and finely controlling the period parameters. Compared with traditional designs based on symmetry breaking, the present invention not only greatly simplifies the device structure and reduces the manufacturing difficulty and cost, but also significantly improves the structural consistency and performance stability, solving the problem of high-Q filter being difficult to manufacture on a large scale and ensuring consistency.

[0031] (2) By continuously regulating the periodic parameters, the present invention moderately transforms the pure ACBIC state into a quasi-ACBIC state, precisely controlling the radiation coupling intensity. While maintaining a high quality factor, it optimizes the matching between the signal and the mode field, significantly improving the input and output coupling efficiency. Compared with the problem of traditional high-Q filters that are difficult to effectively excite and extract signals, the present invention effectively reduces insertion loss, improves the overall energy efficiency of the system, and improves the quality of the communication link.

[0032] (3) The filter structure of the present invention is based on a regular periodic array of silicon pillars. By adjusting the periodic parameters (Px, Py), the resonant frequency can be flexibly controlled, meeting the requirements of high selectivity in narrowband while also providing dynamic control capabilities across a wide frequency range. Thanks to the low material loss and structural symmetry, the present invention maintains stable filtering characteristics despite varying ambient temperatures or process fluctuations, improving the environmental adaptability and reliability of the device.

[0033] (4) The present invention adopts a modular periodic design, which can be directly fabricated on a large scale through standard micro-nanofabrication processes (such as photolithography and deep reactive ion etching (DRIE)). It can also be seamlessly integrated with terahertz antennas, detectors, modulators, and other devices, supporting the construction of multifunctional terahertz systems. Compared with the integration barriers brought about by traditional complex structures, the present invention greatly reduces the difficulty and cost of system integration, and promotes the industrial application of terahertz technology in fields such as communications, imaging, and spectral analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the high quality factor terahertz filter of the present invention;

[0035] Figure 2 is the period parameter P of the terahertz filter according to the embodiment of the present invention x and P y Schematic diagram of;

[0036] Figure 3 The terahertz filter of the embodiment of the present invention is in the variation period P x Schematic diagram of transmission situation when ;

[0037] Figure 4 The terahertz filter of the embodiment of the present invention is in the variation period P y Schematic diagram of transmission when

[0038] Figure 5 The terahertz filter of the embodiment of the present invention is subjected to a change in the length L of the rectangular silicon column. x Schematic diagram of transmission situation when ;

[0039] Figure 6 The terahertz filter of the embodiment of the present invention is subjected to a change in the length L of the rectangular silicon column. y Schematic diagram of transmission situation when ;

[0040] Figure 7 Schematic diagram of the transmission of the terahertz filter according to an embodiment of the present invention when the height h of the rectangular silicon pillar is changed;

[0041] Figure 8 Schematic diagram of experimental test results of a high-quality factor terahertz filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0043] This embodiment proposes a high-quality terahertz filter based on the theory of bound states in the continuum. By precisely designing the unit shape, size, and arrangement within a periodic structure and continuously adjusting system parameters, the invention achieves the excitation of localized ACBIC or quasi-ACBIC states, maintaining an extremely high quality factor while enabling effective coupling with external signals, achieving ideal THz filtering results.

[0044] This embodiment provides a terahertz filter based on the theory of bound states in the accidental continuous spectrum, such as Figure 1 As shown, it includes a silicon dielectric layer and a unit array arranged on the surface of the silicon dielectric layer; the unit array is composed of a number of symmetrically arranged high dielectric constant microstructure units arranged periodically, and each microstructure unit includes a pair of dielectric structures arranged symmetrically along the z direction, and the projection of the dielectric structure in the xy plane is a specific shape, wherein the surface of the silicon dielectric layer is the xy plane and the direction perpendicular to the xy plane is the z direction to establish a coordinate system. The dielectric structure is a rectangular silicon column. The projection of the rectangular silicon column in the xy plane is a rectangle. The rectangular silicon column is rotated and arranged at a preset angle in the xy plane. The rectangular silicon column is arranged by rotating 45° along the xy plane, that is, the angle between the long side of the rectangular silicon column and the x-axis is 45°. The long side size of the rectangular silicon column is 70-90μm, the short side size is 45-65μm, and the height is 197-206μm. The period length P of the microstructure unit in the x direction x The period length P in the y direction is 120-140 μm. y The pair of dielectric structures within each microstructure unit are arranged vertically symmetrically along the z-direction and mirror-symmetric in the xy plane. The rectangular silicon pillars on the upper and lower surfaces of the silicon dielectric layer are of identical size. Through precise calculations and simulations, the unit's geometric parameters (such as length, width, thickness, and arrangement period) were determined to meet the requirements for ACBIC formation within the specific terahertz frequency band.

[0045] ACBIC state excitation: In order to obtain the ACBIC state with theoretically infinite Q value and achieve effective coupling with external signals, this embodiment only continuously adjusts the system parameters in the structural design. For example, the rotation angle, length, width and thickness of the rectangular silicon column are all fixed values. Here, we can achieve a high-Q value THz filter by continuously adjusting the parameters of the microstructure unit (the period length of the microstructure unit along the x-direction and the y-direction, P x and P y ), where P x and P y like Figure 2 As shown, it is the period length of each microstructure unit along the x-direction and the y-direction, that is, the period length of the unit cell.

[0046] This paper uses the control variable method and simulation experiments to determine the range of various parameters to optimize the performance of the terahertz filter and ensure that it can achieve a high quality factor (Q value) and effective signal filtering within the required frequency band. The following is the specific process for determining the range of each parameter:

[0047] Figure 3 and Figure 4 They are respectively the terahertz filter of the embodiment of the present invention in the variation period P x and Py Schematic diagram of transmission when . The simulation shows that the period length P of the microstructure unit x When the value changes within the range of 120 to 140 μm, a higher Q value and a stable filtering effect can be achieved. x When the wavelength is 150μm, the filter shows an ideal ACBIC state near 0.606THz, with high quality factor and narrowband filtering effect. y When the period length of the filter changes between 144 and 152 μm, the performance of the filter is optimized. y When the filter is 150μm, the performance of the filter is the best, and the Q value and filtering bandwidth are the most ideal.

[0048] Figure 5 The terahertz filter of the embodiment of the present invention is configured to change the long side size L of the rectangular silicon column. x Through simulation analysis, it is found that when the long side size of the rectangular silicon column is between 70 and 90 μm, a high-quality factor resonance peak can be formed in the terahertz frequency band. The simulation results show that when L x When L is 80μm, the filter shows an ideal ACBIC state with high Q value and stable resonant frequency. x The results show that as the size increases, the filter's resonance peak gradually shifts to the high frequency band, but the Q value decreases. Therefore, the long side size range of 70 to 90 μm is selected to ensure a high Q value while meeting the required frequency band selectivity.

[0049] Figure 6 The terahertz filter of the embodiment of the present invention is configured to change the short side size L of the rectangular silicon column. y Schematic diagram of transmission when . By controlling the variable method, the short side size L is simulated. y The simulation results show that when L y When the L is 55μm, the filter shows the best filtering effect, with narrow bandwidth and high quality factor. y The value of L will reduce the Q value of the filter, while too large L y The value affects the bandwidth and frequency selectivity of the filter. Therefore, the short side size range is selected to be 45 to 65 μm to ensure high Q value and ideal filtering performance.

[0050] Figure 7The figure is a schematic diagram of the transmission of the terahertz filter of an embodiment of the present invention when the height h of the rectangular silicon column changes. When the height of the rectangular silicon column changes in the range of 197 to 206 μm, the Q value and transmission spectrum of the filter show obvious changes. Simulation shows that when the height of the rectangular silicon column is 206 μm, the resonance peak of the filter is clear, and the filter shows an ideal ACBIC state near 0.6075 THz, with the best filtering performance. As the height increases, the resonant frequency of the filter changes slightly, but the Q value does not change significantly. Therefore, the height range is selected to be 197 to 206 μm to ensure the high performance and stability of the filter.

[0051] In the above experimental process, the control variable method was adopted, that is, keeping other parameters fixed and adjusting only one parameter for simulation analysis to explore the impact of different parameters on the performance of the terahertz filter. By adjusting the long side size, short side size, structure height and period length of the rectangular silicon pillar one by one, combined with the simulation results of the transmission spectrum, the present invention finally determined the optimization range of each parameter: the long side size of the rectangular silicon pillar is 70-90μm, the short side size is 45-65μm, the height is 197-206μm, and the period length P of the microstructure unit is 100-150μm. x 120~140μm, P y It is 144~152μm.

[0052] The above simulations demonstrate that the present invention achieves a high-Q radiation mode and narrowband THz transmission without disrupting the structural symmetry required by existing SPBICs. This design can be achieved by fine-tuning the local geometry, transforming the pure ACBIC state into a quasi-ACBIC state. This quasi-ACBIC state maintains the high-Q resonance characteristics while allowing for a certain amount of radiation leakage, meeting signal input and output requirements.

[0053] In order to achieve proper coupling of external signals, while maintaining the excellent isolation characteristics of the ACBIC state, the ACBIC state is converted into a quasi-ACBIC state through fine-tuning of the local geometric shape, which not only ensures an extremely high Q value but also meets the needs of signal input and output.

[0054] The working principle of this embodiment is as follows:

[0055] 1. Formation of localized ACBIC mode: When the terahertz electromagnetic wave is incident on the designed periodic structure, under the conditions of meeting specific structural parameters, a localized ACBIC mode will be excited inside the filter. In the design of the present invention, the periodic arrangement of the microstructure units, the specific size and angle design of the rectangular silicon columns make the electromagnetic waves localized in the device and unable to exchange energy with the radiation mode. The existence of this localized mode can achieve a theoretically infinitely high quality factor (Q value). Specifically, in the structure of the present invention, the angle between the long side of the rectangular silicon column and the x-axis is 45°, so that the symmetrical arrangement of the microstructure units in the xy plane can effectively localize the electromagnetic field and avoid radiation leakage of energy, thereby forming a resonant peak with a high quality factor in the terahertz frequency band.

[0056] 2. Quasi-ACBIC state and coupling mechanism: By fine-tuning certain geometric parameters in the structure, such as the size and arrangement period of the rectangular silicon pillars, the present invention can convert the pure ACBIC state into a quasi-ACBIC state. The quasi-ACBIC state allows a small amount of radiation leakage, which provides conditions for the coupling between the external signal and the resonant mode field inside the filter. Specifically, the microstructure unit of the present invention ensures that when the terahertz electromagnetic wave is incident, the signal can be effectively coupled with the resonant mode of the filter by rotating the arrangement 45° along the xy plane. Through reasonable design, the quasi-ACBIC state can enable the filter to effectively input and output signals while maintaining a high Q value, meeting the high efficiency requirements in practical applications.

[0057] 3. Frequency-Selective Filtering: The filter of the present invention is designed to allow only target frequencies that meet the quasi-ACBIC excitation conditions to pass through within a specific terahertz frequency band. When the frequency of the terahertz electromagnetic wave matches the resonant frequency of the filter, the signal is effectively transmitted through the structure; when the frequencies do not match, the signal is severely attenuated. Thus, the filter of the present invention achieves the function of narrowband, highly selective filtering. In practical applications, this filter can effectively improve the system's signal-to-noise ratio, filter out noise at non-target frequencies, and ensure stable system performance.

[0058] The manufacturing process of this embodiment is as follows:

[0059] The terahertz filter of this invention utilizes advanced micro-nanofabrication technology and precise process steps to ensure the accuracy of the periodic structure, dimensional uniformity, and geometric precision of the device. The entire manufacturing process is designed to optimize the performance and stability of the device, meeting the requirements of high integration and high performance. The following is the detailed manufacturing process:

[0060] (1) Silicon wafer preparation:

[0061] First, select a piece of high resistivity ( <100> , >10kΩ·cm), double-sided polished silicon wafers, typically 4-inch diameter and (1000±5)μm thick. Before processing, the wafers are cleaned using an ultrasonic cleaning system to remove surface impurities and contaminants to ensure smooth subsequent processing.

[0062] (2) SiO2 film growth

[0063] A 500nm thick SiO2 layer is grown on both sides of the silicon wafer using a plasma-enhanced chemical vapor deposition (PECVD) process. This SiO2 layer acts as an isolation layer, providing electrical isolation and protection to prevent damage to the silicon during subsequent processing.

[0064] (3) Photolithography and patterning

[0065] Next, a positive photoresist (such as AZ4920) is spin-coated onto the SiO2 surface. The design pattern is transferred to the photoresist through exposure and development steps. After exposure, development removes the non-patterned areas, resulting in the desired photoresist pattern. This process ensures the precise arrangement of the periodic microstructure units.

[0066] (4) Oxide etching

[0067] Using an advanced oxide etching (AOE) process, the exposed SiO2 is etched to remove areas not protected by the photoresist, forming a patterned structure of the SiO2 layer. This etching process ensures precise fit between the SiO2 layer and the silicon surface, providing a foundation for subsequent silicon etching.

[0068] (5) Silicon etching

[0069] The silicon layer unprotected by photoresist is etched to a depth of 200μm using a deep reactive ion etch (DRIE) process. This process precisely etches silicon microstructure units of predetermined shapes, such as rectangular silicon pillars, to form the periodic structure required for the filter. DRIE technology ensures the verticality and accuracy of the etching process, ensuring that the size and geometry of the microstructures meet the exacting design requirements.

[0070] (6) Removal of photoresist

[0071] After the silicon layer is etched, the photoresist is removed using acetone (CH3COCH3) to remove any remaining photoresist residue. This step ensures a clean structure and prevents any remaining photoresist residue from affecting subsequent processing and performance.

[0072] (7) Repeat processing on the other side

[0073] To ensure the symmetry and precision of the filter structure, the same process steps are repeated on the other side of the silicon wafer. First, photoresist is spin-coated, exposed, and developed. AOE and DRIE etching are then performed, followed by final removal of the photoresist. This process ensures that the microstructure units on both sides of the wafer are identical, resulting in a symmetrical filter structure.

[0074] (8) Removal of SiO2 film

[0075] Finally, a buffered oxide etch (BOE) is used to remove the SiO2 film to expose the silicon surface and complete the final structure. BOE etching can effectively remove the SiO2 layer without damaging the silicon microstructure units.

[0076] The fabrication process utilizes advanced micro-nanofabrication techniques, including key steps such as PECVD, AOE, DRIE, and BOE. By precisely controlling the processing parameters at each step, the dimensional accuracy and geometric consistency of the filter's microstructure units are ensured. These processes ensure that the periodic structure designed in this invention can achieve an ideal ACBIC mode within the terahertz frequency band, thereby achieving a high quality factor and high-performance filtering.

[0077] In order to verify the design effect of the high-quality factor terahertz filter of the present invention, numerical simulation and experimental tests were carried out in this embodiment. The specific process is as follows:

[0078] The design parameters are comprehensively optimized using full-wave electromagnetic field simulation software (such as finite element method FEM, finite difference time domain method FDTD, etc.). The simulation results show that the filter can excite a quasi-ACBIC mode with a clear resonance peak within the predetermined terahertz frequency band, and its quality factor is significantly higher than that of the traditional resonant structure. The frequency response of the sample was tested using a terahertz time-domain spectroscopy (THz-TDS) system. The terahertz pulse is generated by a semiconductor photoelectric antenna under 780nm femtosecond laser excitation, and its polarization direction is along the y-axis. The diameter of the terahertz signal beam passing through the sample is 10mm. In the experiment, the time window for scanning the terahertz transmission signal is 1200ps, and the corresponding frequency resolution is 0.85GHz. All measurements are carried out at room temperature and the environment is purged with nitrogen (humidity ≤ 20%) to remove interference caused by water vapor absorption. Subsequently, the time domain signal is Fourier transformed and converted to the frequency domain to obtain the transmission spectrum. Figure 8 As shown in the figure, the test results show that the device exhibits a narrowband high resonance response in the target frequency band, while having low insertion loss and high signal-to-noise ratio, which fully verifies the superiority of this design scheme.

[0079] This embodiment incorporates the theory of ACBIC bound states in the accidental continuum (ACBIC) into terahertz filter design, achieving theoretically ultra-high-Q excitation. By innovatively transforming pure ACBIC states into quasi-ACBIC states through fine-tuning of local geometry, this overcomes the low coupling efficiency inherent in traditional high-Q designs and ensures the dual requirements of signal input and output and high quality factor.

[0080] By combining a two-dimensional periodic array with local perturbation design, the unit structure and arrangement parameters are precisely controlled, fundamentally resolving the balance between radiative coupling and localized modes. The silicon-based filter design concept opens up possibilities for system-level integration. Advanced micro-nanofabrication techniques ensure the consistency and high precision of the device structure, while low-loss materials and subsequent surface treatment techniques are utilized to reduce energy loss. The introduction of a multilayer structure allows for greater stability and repeatability in practical large-scale integration, overcoming the performance fluctuations caused by process errors in traditional processes.

[0081] The advantages of the present invention are reflected in many aspects. First, in terms of theoretical innovation, compared with the existing technology based on symmetry-breaking SPBIC, the present invention adopts ACBIC (accidental bound state) theory to excite high-Q resonance modes by continuously adjusting the structural parameters without destroying the symmetry of the structure. Such innovation avoids the increased manufacturing difficulty and performance instability caused by symmetry breaking, making the design simpler and more reliable. In addition, the ACBIC theory provides a wider range of Q-factor control capabilities, which can adjust the high quality factor without sacrificing mode stability, which provides a new idea for terahertz filter design.

[0082] In terms of structural design, the present invention adopts a simple rectangular silicon column periodic structure. Compared with the complex microstructure columns (such as L-shaped, cross-shaped, etc.) used in the prior art, the structural design of the present invention has lower manufacturing precision requirements, reduces the processing difficulty and complexity, and ensures the precision and stability of the manufacturing process. By adjusting the periodic parameter (P x , P y ), the present invention can achieve tunability of high Q value modes without destroying the structural symmetry, which makes the device easier to manufacture and more stable in practical applications.

[0083] In terms of manufacturing feasibility, the present invention features a simplified structural design, allowing all processing steps to be performed using standard photolithography and deep reactive ion etching (DRIE) techniques, eliminating the need for complex micro-nanofabrication techniques. This reduces manufacturing costs and improves process repeatability. This makes the device more suitable for mass production. Compared to existing technologies, the present invention's rectangular silicon pillar design significantly reduces performance instability caused by manufacturing errors, ensuring consistency in mass production.

[0084] In addition, the present invention has a stronger frequency tuning capability. By adjusting the periodic parameter (P x , P y ) can precisely tune the resonant frequency, providing greater flexibility and enabling precise adjustments based on different application requirements, meeting a wider range of operating frequency bands. In contrast, existing structures primarily rely on symmetry breaking to adjust the Q factor and frequency. This tuning method's flexibility is limited by the structure itself, and it cannot achieve the same easy adjustment within the frequency band as the present invention.

[0085] Finally, the present invention has a wider scope of application. Besides being applicable to terahertz sensing, it can also find applications in a variety of fields, including terahertz communications, spectral detection, and narrowband filtering. Compared with existing technologies, the present invention has greater cross-domain adaptability, can meet diverse technical requirements, and expands the device's application range. It is particularly suitable for high-precision terahertz frequency band signal processing and communication technologies.

[0086] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A terahertz filter based on the theory of bound states in a continuum of chance, characterized in that: The invention comprises a silicon dielectric layer and a unit array provided on the upper and lower surfaces of the silicon dielectric layer; the unit array is composed of a plurality of symmetrically arranged high-dielectric constant microstructure units arranged periodically, each microstructure unit including a pair of dielectric structures arranged symmetrically along the z direction, and the projection of the dielectric structure on the xy plane is a specific shape, wherein a coordinate system is established with the surface of the silicon dielectric layer as the xy plane and the direction perpendicular to the xy plane as the z direction.

2. A terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 1, characterized in that: The dielectric structure is a rectangular silicon column.

3. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 2, characterized in that: The projection of the rectangular silicon column on the xy plane is a rectangle.

4. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 2, characterized in that: The rectangular silicon pillars are arranged in a rotational manner at a preset angle in the xy plane.

5. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 4, characterized in that: The rectangular silicon column is arranged along the xy plane rotated by 45 degrees, that is, the angle between the long side of the rectangular silicon column and the x-axis is 45 degrees.

6. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 4, characterized in that: The rectangular silicon column has a long side dimension of 70 to 90 μm, a short side dimension of 45 to 65 μm, and a height of 197 to 206 μm.

7. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 1, characterized in that: The period length of the microstructure unit in the x direction is 120 to 140 μm, and the period length in the y direction is 144 to 152 μm.

8. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 7, characterized in that: A pair of dielectric structures in each microstructure unit are arranged symmetrically up and down along the z direction and are mirror-symmetrical to each other in the xy plane.

9. The terahertz filter based on the theory of bound states in the accidental continuous spectrum according to claim 7, characterized in that: By adjusting the period length parameters of the microstructure unit in the x and y directions, the terahertz filter is continuously switched between a high Q value bound state and a finite Q value quasi-bound state.

10. A terahertz filter based on the theory of bound states in accidental continuous spectrum according to claim 1 or 2, characterized in that: By changing the period length parameters of the microstructure unit or the size of the rectangular silicon column, the terahertz resonant frequency of the terahertz filter can be adjusted in the range of 0.2THz to 2THz.

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