On-chip terahertz coupler chip

Abstract

The invention provides an on-chip terahertz coupler chip, which is composed of an F-P resonant cavity, a bent waveguide, a tapered coupling waveguide and a substrate structure, and is characterized in that the F-P resonant cavity is composed of left and right symmetric Bragg gratings and a single-mode waveguide located in the middle, and is used for generating resonance for a signal with a specific frequency to realize a filtering effect; the bent waveguide is used for transmitting terahertz signals, and conical coupling waveguides are arranged at the two ends of the bent waveguide and serve as input and output ports of the signals; and the substrate is used for fixing the F-P resonant cavity and the bent waveguide. According to the coupler chip, terahertz efficient coupling is achieved, meanwhile, propagation of terahertz waves can be controlled, filtering of different wave bands is achieved, on-chip waveguide integration is achieved through the coupler chip structure, filtering selectivity is improved, insertion loss is reduced, out-of-band rejection is enhanced, and large-scale manufacturing is achieved.

Description

Technical Field

[0001] The present invention relates to the terahertz field, and particularly to a terahertz coupler chip. Background Art

[0002] The terahertz (THz) band generally refers to the electromagnetic wave with a frequency between 0.1 THz and 10 THz, which is between microwave and infrared. Due to the advantages of the electromagnetic wave in this band, such as penetrating non-polar substances and having no ionizing radiation, terahertz technology has received extensive attention in recent years in many fields such as communication, security inspection, medical imaging, sensing, and astronomical observation. However, with the development of terahertz communication technology, there is an urgent need to develop terahertz integrated devices to realize the miniaturization and functionalization of communication systems. The practical application of on-chip integrated terahertz devices is still restricted by many factors such as device materials, manufacturing processes, and signal processing technologies. In particular, the design and manufacture of high-efficiency and low-loss terahertz waveguides and filters still face huge challenges.

[0003] Traditional coupler chips and filter designs are mostly based on the principles of low-frequency circuit models or wave optics for design and manufacture, but there are many problems when applied in the terahertz band, such as too large volume, too high loss, and complex manufacturing. As the core device for transmitting terahertz signals, the coupler chip can effectively guide the electromagnetic wave to propagate along a specific path; the filter is used to select and tune signals within a specific frequency range to reduce interference or noise and improve the purity of the signal. In the terahertz band, the design of the coupler chip and the filter is particularly important because they directly affect the transmission efficiency and signal processing ability of the system. If the coupling and filtering functions can be realized on the same substrate, the design will be greatly simplified, and at the same time, the transmission and coupling losses between components will be reduced, realizing high-performance terahertz communication devices.

[0004] The design and manufacture of on-chip integrated terahertz devices have become a research hotspot for international scholars. In recent years, certain progress has been made in the design of optical waveguide coupler chips and filters based on silicon-based materials. For example, for the design and manufacture of filter chips for the 1550 nm communication band, one method is to combine a Bragg grating with a microring resonator, and use the stopband effect of the Bragg grating to control the on and off of the microring, and then regulate the frequency response; another method is through the Vernier effect, cascading two rings with different resonant frequencies, and using the complementary effect to achieve filtering. However, the alignment of the resonant wavelengths in these methods is relatively difficult, and sometimes additional active tuning is required, increasing the complexity of implementation. These optical devices can all be obtained based on the theory of silicon-based photonics and standard silicon-based manufacturing. However, these methods cannot be directly applied to the design and manufacture of terahertz devices. Therefore, the design and manufacture of on-chip integrated terahertz coupler chips are extremely urgent. Summary of the Invention

[0005] The object of the present invention is to provide a on-chip terahertz coupler chip.

[0006] The technical solution for achieving the object of the present invention is: a on-chip terahertz coupler chip, comprising an F-P resonator, a bent waveguide, a tapered coupling waveguide and a substrate. The F-P resonator is composed of a single-mode waveguide in the middle, symmetric Bragg gratings on the left and right, and a tapered grating connecting the single-mode waveguide and the Bragg gratings, and is used to generate resonance for signals of a specific frequency, so as to achieve the filtering effect; the Bragg gratings are composed of a periodic arrangement of wide waveguides and narrow waveguides; the bent waveguide is located below the F-P resonator and is used to transmit terahertz signals, and both ends thereof are tapered coupling waveguides, serving as signal input and output ports; the substrate is used to fix the F-P resonator and the bent waveguide.

[0007] Further, the resonance frequency of the F-P resonator is determined according to the formula where L c 、L pd and L t are the length of the single-mode waveguide, the penetration depth of the Bragg grating and the length of the tapered grating respectively, and n g1 、n g2 、n g3 are the group refractive indices of the single-mode waveguide, the Bragg grating and the tapered grating respectively;

[0008] The penetration depth L pd of the Bragg grating is obtained from the formula where n eff,w and n eff,n are the effective refractive indices of the wide waveguide and the narrow waveguide of the Bragg grating respectively, and λ c is the resonance wavelength;

[0009] The stop band of the Bragg grating is obtained from the formula where Δλ sb is the stop band width, that is, within this wavelength range, energy cannot pass through the grating, n eff is the equivalent refractive index of the wide waveguide and the narrow waveguide constituting the Bragg grating, P is the period of the grating, and λ B is the Bragg wavelength, which is obtained from the formula λx = 2n eff P.

[0010] Furthermore, the width of the curved waveguide is equal to that of the single-mode waveguide, and the height of the curved waveguide is equal to that of the single-mode waveguide. The thickness of the substrate is less than the height of the curved waveguide. The height of the tapered coupling waveguide is equal to the sum of the height of the curved waveguide and the thickness of the substrate. The tapered coupling waveguide is symmetric about the extension direction of the curved waveguide. The above parameters can be determined by combining the finite element method with simulation software to calculate the low-loss transmission mode of the waveguide.

[0011] Furthermore, the spectral response of the chip depends on the stopband Δλ of the Bragg grating sb and the resonance frequency FSR of the F-P resonator FP and the specific relationship is as follows:

[0012] (i) When Δλ sb < FSR FP , only one resonance mode in the stopband of the Bragg grating is excited and enhanced, and the remaining resonance modes cannot be excited because they are in the passband of the Bragg grating. There is only one resonance peak in the spectral response of the chip;

[0013] (ii) When FSR FP < Δλ sb < 2FSR FP , two resonance modes in the stopband of the Bragg grating are excited and enhanced, and the remaining resonance modes cannot be excited because they are in the passband of the Bragg grating. There are two resonance peaks in the spectral response of the chip;

[0014] (iii) When Δλ sb > 2FSR FP , three resonance modes in the stopband of the Bragg grating are excited and enhanced, and the remaining resonance modes cannot be excited because they are in the passband of the Bragg grating. There are three resonance peaks in the spectral response of the chip.

[0015] Furthermore, it is prepared by micro-nano processing, and the substrate material is selected from high-resistivity silicon, silicon dioxide, silicon carbide, gallium nitride or lithium niobate.

[0016] A preparation method for an on-chip terahertz coupler chip. First, the substrate material is thinned to the required thickness; then, photolithography and front-side deep silicon etching processes are performed on the substrate to form a single-mode waveguide, a Bragg grating, a tapered grating, a tapered coupling waveguide and a curved waveguide structure; finally, photolithography and back-side deep silicon etching processes are performed on the substrate to separate individual devices for subsequent testing.

[0017] A method for terahertz resonance control and filtering of a terahertz coupler chip on a chip. The terahertz coupler chip on a chip is encapsulated in a standard metal rectangular waveguide cavity to realize interconnection and use with a terahertz source or detector. The terahertz signal enters the bent waveguide through a tapered coupling waveguide, enters the single-mode waveguide through the coupling mode, and the terahertz wave that satisfies the resonance condition is locally concentrated at the single-mode waveguide, increasing the electric field strength at the single-mode waveguide; the terahertz signal that does not satisfy the resonance condition is directly filtered through the bent waveguide, realizing the on-chip filtering function.

[0018] Compared with the prior art, the present invention has the following remarkable advantages: 1) Structures such as the F-P resonant cavity, the bent waveguide, and the tapered coupling waveguide are all on the same substrate. Compared with the discrete structures commonly used for F-P resonant cavities in other fields, the on-chip integrated design can reduce the distance error between the F-P resonant cavity and the bent waveguide and improve the coupling efficiency of the F-P resonant cavity; 2) Combining a Bragg grating with a Fabry-Perot (F-P) resonant cavity filter and adjusting the relationship between the stopband of the Bragg grating and the free spectral range (FSR) of the F-P resonant cavity, single-peak, double-peak, and triple-peak filtering effects are achieved within a frequency band of 30 GHz. Moreover, while ensuring broadband performance, this filter also has relatively loose manufacturing tolerances; 3) It is easy to encapsulate and use. Using a tapered coupling waveguide as the signal input and output ports, it can be connected to a standard terahertz rectangular waveguide, with low insertion loss. After encapsulation, it can be used as a terahertz detector with a standard interface and can be used in complex systems such as terahertz imaging or communication; 4) It improves the filtering selectivity of the terahertz coupler chip, reduces the insertion loss, enhances the out-of-band suppression, and can be mass-produced. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the structure of a terahertz coupler chip on a chip.

[0020] Figure 2 It is a schematic diagram of the size of a terahertz coupler chip on a chip.

[0021] Figure 3 It is an assembly schematic diagram of a terahertz coupler chip on a chip.

[0022] Figure 4 It is a schematic diagram of the principle of a terahertz coupler chip on a chip.

[0023] Figure 5 It is an electric field distribution diagram of a terahertz coupler chip on a chip at three frequencies.

[0024] Figure 6 It is a test result diagram of a terahertz coupler chip on a chip.

[0025] In the figure, 1 and 2 are a single-mode waveguide and a left-right symmetric Bragg grating respectively, which together form an F-P resonator. 3 is a bent waveguide, 4 is a tapered coupling waveguide, 5 is a substrate, and 6 is a standard rectangular waveguide. Detailed implementation mode

[0026] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0027] As Figure 1 shown, an on-chip terahertz coupler chip is composed of an F-P resonator, a bent waveguide 3, a tapered coupling waveguide 4, and a substrate structure 5. The F-P resonator is composed of a single-mode waveguide 1 in the middle, a left-right symmetric Bragg grating 2, and a tapered grating connecting the single-mode waveguide and the Bragg grating, and is used to generate resonance for signals of a specific frequency, so as to achieve the filtering effect; the Bragg grating 2 is composed of a periodic arrangement of wide waveguides and narrow waveguides; the bent waveguide 3 is used to transmit terahertz signals, and its two ends are tapered coupling waveguides 4, and the tapered coupling waveguide serves as the input and output ports of the signal; the substrate 5 is used to fix the F-P resonator and the bent waveguide.

[0028] High-resistivity silicon is one of the most important integrated circuit materials. The loss in the terahertz frequency band is also small, and the absorption rate at 0.4 THz is only 0.05 cm -1 , and high-resistivity silicon is selected as the substrate material in this embodiment. Deep silicon etching is a micro-nano processing technology, and functional structures with characteristic dimensions of dozens of microns or even up to hundreds of microns can be obtained by using deep silicon etching technology. This device can be prepared by deep silicon etching technology. Through photolithography and front-side deep silicon etching processes on the silicon wafer, a single-mode waveguide, a Bragg grating, a tapered grating, a tapered coupling waveguide, and a bent waveguide structure are formed. Then, photolithography and back-side deep silicon etching processes are performed on the silicon wafer to separate individual devices for subsequent testing.

[0029] The input signal enters the bent waveguide 3 from the tapered coupling waveguide 4 and is coupled into the single-mode waveguide 1 through this bent waveguide. For a bent silicon-based waveguide, the radiation loss usually has an exponential relationship with the bending radius, and the loss can be approximately expressed as: where α is the propagation loss, r is the bending radius, and r c is a critical radius related to the waveguide geometry and material. In some embodiments, r is 2000 μm.

[0030] When the energy enters the F-P resonator, the energy at the resonant frequency will resonate here, and its FSR can be obtained from:

[0031]

[0032] It is obtained that, where L c , L pd and L t are respectively the length of the single-mode waveguide, the penetration depth of the Bragg grating, and the length of the tapered grating, and n g1 , n g2 , n g3 are respectively the group refractive indices of the single-mode waveguide, the Bragg grating, and the tapered grating. L pd can be obtained from the formula

[0033]

[0034] where n eff,w and n eff,n are respectively the effective refractive indices of the wide waveguide and the narrow waveguide of the Bragg grating, and λ c is the resonant wavelength. In some embodiments, the length of L c is 100μm, 1400μm, and 3000μm, and L t is 870μm.

[0035] The stopband of the Bragg grating can be obtained from the formula where Δλ sb is the stopband width, that is, within this wavelength range, energy cannot pass through the grating, n eff is the equivalent refractive index of the wide waveguide and the narrow waveguide that make up the Bragg grating, P is the period of the grating, and λ B is the Bragg wavelength, which can be obtained from the formula λ B = 2n eff P. In some embodiments, P is 50.

[0036] The effective refractive index n eff of the curved waveguide 3 is related to the material, width, height, and thickness of the substrate of the micro-ring. In order to improve the coupling efficiency between the curved waveguide 3 and the single-mode waveguide 1, their effective refractive indices are kept the same. Therefore, the material, width, and thickness of the substrate of the waveguide are kept the same. In some embodiments, the designed width is 210μm, the height is 140μm, and the thickness of the substrate is 60μm. At this time, the effective refractive index of the waveguide is 2.58, and the transmitted fundamental mode is the TE mode.

[0037] The function of the tapered coupling waveguide 4 is the signal port. As Figure 3 shown, it is an assembly schematic diagram of a chip-on-chip terahertz coupler. Taking the tapered coupling waveguide 4 as an example, it is placed in the rectangular waveguide 6. The dimensions of the rectangular waveguide 6 can refer to the WR series waveguide specifications. The terahertz signal is coupled from the rectangular waveguide into the tapered waveguide. In order to ensure the coupling efficiency, the length of the tapered coupling waveguide needs to be more than 3 times its width. The present invention is through as Figure 3The encapsulated device shown is docked with other terahertz systems.

[0038] Figure 4 It is a schematic diagram of the principle of a on-chip terahertz coupler chip, and its spectral response mainly depends on the stopband Δλ of the Bragg grating sb and the FSR of the F-P resonator in the ideal case FP , and the stopband is defined here as the width between the zeros of the central lobe.

[0039] (i) When Δλ sb < FSR FP , only one resonant mode in the F-P resonator within the stopband of the Bragg grating is excited and enhanced, and the remaining resonant modes cannot be excited because they are in the passband of the Bragg grating. There is only one resonant peak in the spectral response of the chip.

[0040] (ii) When FSR FP < Δλ sb < 2FSR FP , two resonant modes in the F-P resonator within the stopband of the Bragg grating are excited and enhanced, and the remaining resonant modes cannot be excited because they are in the passband of the Bragg grating. There are two resonant peaks in the spectral response of the chip.

[0041] (iii) When Δλ sb > 2FSR FP , three resonant modes in the F-P resonator within the stopband of the Bragg grating are excited and enhanced, and the remaining resonant modes cannot be excited because they are in the passband of the Bragg grating. There are three resonant peaks in the spectral response of the chip.

[0042] Figure 5 It is the electric field distribution diagram of the on-chip terahertz coupler chip at three frequencies. f is the frequency at this time. When f = 500 GHz, it is within the passband range of the Bragg grating at this time, and an F-P resonator cannot be formed. This waveguide can be considered as a waveguide directional coupler chip. According to the coupled mode theory, only a very small amount of energy is coupled into the single-mode waveguide, and most of the energy is transmitted out by the curved waveguide. When f = 463 GHz, the signal is within the forbidden band range of the Bragg grating at this time, and an F-P resonator is successfully formed. At this time, this frequency is exactly the resonant frequency of the F-P resonator, so a resonance phenomenon appears, and most of the energy is concentrated in the single-mode waveguide. When f = 461 GHz, although it is within the forbidden band range of the Bragg grating at this time and an F-P resonator is formed, since the signal at this frequency cannot resonate in the F-P resonator, most of the energy still passes out through the curved waveguide.

[0043] To verify the effectiveness of the solution of the present invention, the on-chip terahertz coupler chip is prepared and encapsulated according to the following process, and experimental tests and simulations are carried out. The specific steps are as follows:

[0044] 1. A silicon wafer thinning process that thins the thickness of a silicon wafer to 200 μm;

[0045] 2. Use a deep silicon etching process to etch the front side of the silicon wafer by 140 μm to form a single-mode waveguide, a Bragg grating, and a bent waveguide, and then perform an overlay etching process on the back side to form a tapered coupling waveguide;

[0046] 3. Design a corresponding packaging structure according to the size of a single integrated device for testing.

[0047] In order to verify the performance of the fabricated on-chip terahertz coupler chip, the following test experiments were carried out.

[0048] Connect the packaged on-chip terahertz coupler chip to a vector network analyzer to measure the S-parameters of the device. The tapered coupling waveguide 4 serves as the signal output terminal, and the other tapered coupling waveguide serves as the signal output terminal. The S21 parameter is the insertion loss of the device. Figure 6 The S21 parameters of different devices measured using a high-frequency vector network analyzer are shown. The solid line represents the measured results, and the dashed line represents the S21 parameters calculated by simulation software. It can be observed that the insertion losses of the three types of devices are very consistent with the simulation results, all being 5 dB, indicating that after coupling through the tip structure and transmission in a 2-cm-long silicon-based waveguide, the energy loss is small, and most of the energy can still be transmitted out of the silicon-based waveguide. In terms of performance, in the single-peak case, the filtering effect of the measured results is better than that of the simulation, the lowest value of S21 is close to -40 dB, and there is only a frequency offset of 2.2 GHz compared with the simulation results; in the double-peak case, the test results are relatively consistent with the simulation results, but the lowest value of S21 of the test results can reach -25 dB, and the frequency offsets of the two resonant peaks are only 0.9 GHz and 0.8 GHz; in the triple-peak case, the effects of the three resonant peaks of the test results are better than those of the simulation results, and compared with the simulation results, there are only frequency offsets of 2.2 GHz, 2.3 GHz, and 2.1 GHz. Generally speaking, the test and simulation results in the three cases are relatively consistent in terms of loss and resonant performance, with only a small frequency offset. This is mainly because the uneven etching rate during the deep silicon etching process results in differences in the substrate thickness of the device, and the substrate thickness is closely related to the position of the resonant peak. In addition, there are also many spurious peaks in the measurement, which may be due to the influence of photoresist residues on the electromagnetic coupling between the silicon-based waveguide and the F-P resonator, or the failure to achieve the required accuracy during the etching of the tip, resulting in additional losses when the energy is coupled into the silicon-based waveguide. From Figure 6 the results, it can be seen that this design provides a new idea for the design of broadband couplers and filters, and realizes single-peak, double-peak, and triple-peak filtering effects in a 30-GHz frequency band.

[0049] In summary, the present invention adjusts the length L of the single-mode waveguide c to adjust the FSR of the F-P resonator, skillfully combines the Bragg grating with the Fabry-Perot (F-P) resonator filter, and adjusts the relationship between the stop band of the Bragg grating and the free spectral range (FSR) of the F-P resonator, achieving single-peak, double-peak, and triple-peak filtering effects within a 30 GHz frequency band. While achieving efficient terahertz coupling, this coupler chip can also control the propagation of terahertz waves to achieve filtering of different frequencies. The structure of this coupler chip realizes on-chip waveguide integration, improves filtering selectivity, reduces insertion loss, enhances out-of-band rejection, and enables large-scale manufacturing.

[0050] The embodiments of the present invention are not limited by the described examples. Any changes, simplifications, substitutions, and combinations made without departing from the essence and principle of the present invention should be included within the protection scope of the present invention.

[0051] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0052] The above-described embodiments only represent several implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An on-chip terahertz coupler chip, characterized in that: The invention comprises an FP resonant cavity, a curved waveguide, a conical coupling waveguide and a substrate. The FP resonant cavity is composed of a single-mode waveguide located in the middle, a bilaterally symmetrical Bragg grating and a conical grating connecting the single-mode waveguide and the Bragg grating, and is used to resonate a signal of a specific frequency, thereby achieving a filtering effect. The Bragg grating is composed of a wide waveguide and a narrow waveguide arranged periodically. The curved waveguide is located below the FP resonant cavity and is used to transmit a terahertz signal, and its two ends are conical coupling waveguides, which serve as input and output ports of the signal. The substrate is used to fix the FP resonant cavity and the curved waveguide.

2. The on-chip terahertz coupler chip according to claim 1, characterized in that: The resonant frequency of the FP resonant cavity needs to be calculated according to the formula OK, where L c , L pd and L t are the length of the single-mode waveguide, the penetration depth of the Bragg grating and the length of the tapered grating, respectively. g1 、n g2 、n g3 are the group refractive indices of single-mode waveguide, Bragg grating and tapered grating, respectively; The penetration depth L of the Bragg grating pd By formula It is concluded that n eff,w and n eff,n are the effective refractive index of the Bragg grating wide waveguide and narrow waveguide, respectively, c is the resonant wavelength; The bandgap of the Bragg grating is given by the formula It is concluded that, where Δλ sb is the bandgap width, that is, within this wavelength range, energy cannot pass through the grating, n eff is the equivalent refractive index of the wide waveguide and narrow waveguide that make up the Bragg grating, P is the period of the grating, λ B is the Bragg wavelength, according to the formula λ B =2n eff P is obtained.

3. The on-chip terahertz coupler chip according to claim 1, characterized in that: The width of the curved waveguide is equal to the width of the single-mode waveguide, the height of the curved waveguide is equal to the height of the single-mode waveguide, the thickness of the substrate is less than the height of the curved waveguide, the height of the tapered coupling waveguide is equal to the sum of the height of the curved waveguide and the thickness of the substrate, and the tapered coupling waveguide is bilaterally symmetrical in the extension direction of the curved waveguide.

4. The on-chip terahertz coupler chip according to claim 1, characterized in that: The spectral response of the chip depends on the stopband Δλ of the Bragg grating sb and the resonant frequency FSR of the FP resonant cavity FP The specific relationship is: (i) When Δλ sb <FSR FP When , only one resonance mode of the FP resonant cavity in the Bragg grating stopband is excited and enhanced, and the other resonance modes cannot be excited because they are in the passband of the Bragg grating. There is only one resonance peak in the spectrum response of the chip. (ii) When FSR FP <Δλ sb <2FSR FP When , two resonance modes of the FP resonant cavity in the Bragg grating stopband are excited and enhanced, and the remaining resonance modes cannot be excited because they are in the passband of the Bragg grating. There are two resonance peaks in the spectral response of the chip. (iii) When Δλ sb >2FSR FP When , three resonance modes of the FP resonant cavity in the Bragg grating stopband are excited and enhanced, and the remaining resonance modes cannot be excited because they are in the passband of the Bragg grating. There are three resonance peaks in the spectral response of the chip.

5. The on-chip terahertz coupler chip according to claim 1, characterized in that: It is prepared on the same substrate through micro-nano processing, and the substrate material is selected from high-resistance silicon, silicon dioxide, silicon carbide, gallium nitride or lithium niobate.

6. A method for preparing an on-chip terahertz coupler chip according to any one of claims 1 to 5, characterized in that: First, the substrate material is thinned to the required thickness; then the substrate is subjected to photolithography and front-side deep silicon etching processes to form single-mode waveguides, Bragg gratings, tapered gratings, tapered coupled waveguides and curved waveguide structures; finally, the substrate is subjected to photolithography and back-side deep silicon etching processes to separate individual devices for subsequent testing.

7. A terahertz resonance control and filtering method based on the on-chip terahertz coupler chip according to any one of claims 1 to 5, characterized in that: The on-chip terahertz coupler chip is packaged in a standard metal rectangular waveguide cavity to achieve interconnection with a terahertz source or detector. The terahertz signal enters the curved waveguide through the conical coupling waveguide, and enters the single-mode waveguide through coupling between waveguides. The terahertz waves that meet the resonance conditions are locally converged at the single-mode waveguide, increasing the electric field strength at the single-mode waveguide; the terahertz signals that do not meet the resonance conditions are directly filtered out through the curved waveguide, realizing the on-chip filtering function.

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